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Van Asten JGMV, Fung MT, Oomens CWJ, Bader DL, Worsley PR. A combined experimental and computational approach to evaluate microclimate control at the support surface interface. J Tissue Viability 2021; 30:395-401. [PMID: 34030943 DOI: 10.1016/j.jtv.2021.04.007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2020] [Revised: 03/23/2021] [Accepted: 04/23/2021] [Indexed: 11/28/2022]
Abstract
Temperature and humidity conditions at the interface between a support surface and the skin, termed microclimate, has been implicated in the development of pressure ulcers. Support surface technologies have been developed to control microclimate conditions, although only a few standard test methods exist to evaluate their performance. This study describes a combined experimental-computational approach to analyzing microclimate control systems. The study used a modified physical model protocol to evaluate two specific support surface systems involving a spacer fabric cover with i) no air flow and ii) an active fan. The physical model deposited moisture at a controlled rate for 25 min, and the microclimate conditions under the model and the surrounding area were monitored for 24 h. Using the experimental data as boundary conditions, a finite element model was developed using mass transport principles, which was calibrated using experimental results. Model inputs included mass density and mass diffusivity, resulting in an estimated absolute humidity change over time. The physical model tests revealed distinct differences between the support surfaces with and without active airflow, with the former having little effect on local humidity levels (RH>75% for 24hr). By contrast, there was a spatial and temporal change in microclimate with the active fan, with sensors positioned towards the source of airflow reaching ambient conditions within 24hr. The computational model was refined to produce comparable results with respect to both the spatial distribution of microclimate and the change in values over time. The combined experimental and computation approach was able to distinguish distinct difference in microclimate change between two support surface designs. The approach could enable the efficient evaluation of different mattress design principles to aid decision making for personalized support surface solutions, for the prevention of pressure ulcers.
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Affiliation(s)
- J G M V Van Asten
- Department of Biomedical Engineering, Eindhoven University of Technology, the Netherlands
| | - M-T Fung
- Department of Biomedical Engineering, Eindhoven University of Technology, the Netherlands
| | - C W J Oomens
- Department of Biomedical Engineering, Eindhoven University of Technology, the Netherlands
| | - D L Bader
- Department of Biomedical Engineering, Eindhoven University of Technology, the Netherlands; School of Health Sciences, Faculty of Environmental and Life Sciences, University of Southampton, UK
| | - P R Worsley
- School of Health Sciences, Faculty of Environmental and Life Sciences, University of Southampton, UK.
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Verberne JWR, Worsley PR, Bader DL. A 3D registration methodology to evaluate the goodness of fit at the individual-respiratory mask interface. Comput Methods Biomech Biomed Engin 2020; 24:1-12. [PMID: 33241703 DOI: 10.1080/10255842.2020.1849156] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2020] [Revised: 10/16/2020] [Accepted: 11/04/2020] [Indexed: 02/08/2023]
Abstract
Respiratory masks are used to deliver non-invasive ventilation for cardiorespiratory pathologies. Masks must minimize skin tissue compression while maintaining a seal at the interface. Ill-fitting masks or those applied too tightly are implicated in pressure ulcer formation. This study aimed to analyse respiratory mask goodness of fit in a cohort of face shapes. A number of parameters were identified and analysed with a novel registration protocol. In the majority of cases, mask indentation exceeded the thickness of the interface material and significant gapping was observed. The size range was most appropriate for males, with only one size suitable for females.
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Affiliation(s)
- J W R Verberne
- Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands
| | - P R Worsley
- School of Health Sciences, University of Southampton, Southampton, UK
| | - D L Bader
- Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands
- School of Health Sciences, University of Southampton, Southampton, UK
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Henshaw FR, Bostan LE, Worsley PR, Bader DL. Evaluating the effects of sedentary behaviour on plantar skin health in people with diabetes. J Tissue Viability 2020; 29:277-283. [PMID: 32943281 DOI: 10.1016/j.jtv.2020.09.001] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2019] [Revised: 08/31/2020] [Accepted: 09/01/2020] [Indexed: 01/13/2023]
Abstract
BACKGROUND Diabetes-Related Foot Ulcers (DRFUs) are a common and devastating consequence of Diabetes Mellitus and are associated with high morbidity, mortality, social and economic costs. Whilst peak plantar pressures during gait are implicated cited as a major contributory factor, DRFU occurrence has also been associated with increased periods of sedentary behaviour. The present study was designed aimed to assess the effects of sitting postures on plantar tissue health. METHODS After a period of acclimatisation, transcutaneous oxygen tensions (TCPO2) and inflammatory cytokines (IL-1α and IL-1RA) were measured at the dorsal and plantar aspects of the forefoot before, during and after a 20-min period of seated-weight-bearing in participants with diabetes (n = 11) and no diabetes (n = 10). Corresponding interface pressures at the plantar site were also measured. RESULTS During weight-bearing, participants with diabetes showed increases in tissue ischaemia which were linearly correlated proportional to plantar pressures (Pearson's r = 0.81; p < 0.05). Within the healthy group, no such correlation was evident (p > 0.05). There were also significant increases in post seated weight-bearing values for ratio for IL-1α and IL-1RA, normalised to total protein, post seated weight-bearing in participants with diabetes compared to healthy controls. CONCLUSION This study shows that prolonged sitting may be detrimental to plantar skin health. It highlights the need to further examine the effects of prolonged sitting in individuals, who may have a reduced tolerance to loading in the plantar skin and soft tissues.
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Affiliation(s)
- F R Henshaw
- School of Health Sciences, Western Sydney University, Sydney, Australia.
| | - L E Bostan
- Clinical Academic Facility, Faculty of Health Sciences, University of Southampton, Southampton, UK
| | - P R Worsley
- Clinical Academic Facility, Faculty of Health Sciences, University of Southampton, Southampton, UK
| | - D L Bader
- Clinical Academic Facility, Faculty of Health Sciences, University of Southampton, Southampton, UK
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Bramley JL, Worsley PR, Bostan LE, Bader DL, Dickinson AS. Establishing a measurement array to assess tissue tolerance during loading representative of prosthetic use. Med Eng Phys 2020; 78:39-47. [PMID: 32035813 DOI: 10.1016/j.medengphy.2020.01.011] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2019] [Revised: 01/17/2020] [Accepted: 01/26/2020] [Indexed: 02/07/2023]
Abstract
BACKGROUND In the early stages of rehabilitation after primary amputation, residual limb soft tissues have not been mechanically conditioned to support load and are vulnerable to damage from prosthetic use. There is limited quantitative knowledge of skin and soft tissue response to prosthetic loading. METHODS An in-vivo protocol was developed to establish suitable measures to assess tissue tolerance during loading representative of early prosthesis use. Ten participants without amputation one participant with trans-tibial amputation were recruited, and pressure applied to their calf in increments from 20 to 60 mmHg. Measurements were recorded at relevant skin sites including interface pressures, transcutaneous oxygen (TCPO2) and carbon dioxide (TCPCO2) tensions and inflammatory biomarkers. FINDINGS At the maximum cuff pressure, mean interface pressures were between 66 and 74 mmHg, associated with decreased TCPO2 values. On the release of pressure, the ischaemic response was reversed. Significant upregulation (p < 0.05) in inflammatory biomarker IL-1α and its antagonist IL-1RA were observed at all sites immediately following loading. INTERPRETATION The protocol was successful in applying representative prosthetic loads to lower limb tissues and monitoring the physiological response, both in terms of tissue ischemia and skin inflammation. Results indicated that the measurement approaches were sensitive to changes in interface conditions, offering a promising approach to monitor tissue status for people with amputation.
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Affiliation(s)
- J L Bramley
- Bioengineering Science Research Group, Faculty of Engineering and Physical Sciences, University of Southampton, Highfield Campus, University Rd, Southampton SO17 1BJ, UK
| | - P R Worsley
- Skin Health Research Group, Faculty of Environmental and Life Sciences, University of Southampton, UK
| | - L E Bostan
- Skin Health Research Group, Faculty of Environmental and Life Sciences, University of Southampton, UK
| | - D L Bader
- Skin Health Research Group, Faculty of Environmental and Life Sciences, University of Southampton, UK
| | - A S Dickinson
- Bioengineering Science Research Group, Faculty of Engineering and Physical Sciences, University of Southampton, Highfield Campus, University Rd, Southampton SO17 1BJ, UK.
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Bader DL, Worsley PR, Gefen A. Bioengineering considerations in the prevention of medical device-related pressure ulcers. Clin Biomech (Bristol, Avon) 2019; 67:70-77. [PMID: 31077978 DOI: 10.1016/j.clinbiomech.2019.04.018] [Citation(s) in RCA: 38] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/13/2019] [Accepted: 04/26/2019] [Indexed: 02/07/2023]
Abstract
BACKGROUND In recent years, it has become increasingly apparent that medical device-related pressure ulcers represent a significant burden to both patients and healthcare providers. Medical devices can cause damage in a variety of patients from neonates to community based adults. To date, devices have typically incorporated generic designs with stiff polymer materials, which impinge on vulnerable soft tissues. As a result, medical devices that interact with the skin and underlying soft tissues can cause significant deformations due to high interface pressures caused by strapping or body weight. METHODS This review provides a detailed analysis of the latest bioengineering tools to assess device related skin and soft tissue damage and future perspectives on the prevention of these chronic wounds. This includes measurement at the device-skin interface, imaging deformed tissues, and the early detection of damage through biochemical and biophysical marker detection. In addition, we assess the potential of computational modelling to provide a means for device design optimisation and material selection. INTERPRETATION Future collaboration between academics, industrialists and clinicians should provide the basis to improve medical device design and prevent the formation of these potentially life altering wounds. Ensuring clinicians report devices that cause pressure ulcers to regulatory agencies will provide the opportunity to identify and improve devices, which are not fit for purpose.
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Affiliation(s)
- D L Bader
- School of Health Sciences, University of Southampton, Southampton, UK
| | - P R Worsley
- School of Health Sciences, University of Southampton, Southampton, UK.
| | - A Gefen
- Department of Biomedical Engineering, Tel Aviv University, Israel
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Soetens JFJ, van Vijven M, Bader DL, Peters GWM, Oomens CWJ. A model of human skin under large amplitude oscillatory shear. J Mech Behav Biomed Mater 2018; 86:423-432. [PMID: 30031246 DOI: 10.1016/j.jmbbm.2018.07.008] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2018] [Revised: 07/03/2018] [Accepted: 07/04/2018] [Indexed: 10/28/2022]
Abstract
Skin mechanics is of importance in various fields of research when accurate predictions of the mechanical response of skin is essential. This study aims to develop a new constitutive model for human skin that is capable of describing the heterogeneous, nonlinear viscoelastic mechanical response of human skin under shear deformation. This complex mechanical response was determined by performing large amplitude oscillatory shear (LAOS) experiments on ex vivo human skin samples. It was combined with digital image correlation (DIC) on the cross-sectional area to assess heterogeneity. The skin is modeled as a one-dimensional layered structure, with every sublayer behaving as a nonlinear viscoelastic material. Heterogeneity is implemented by varying the stiffness with skin depth. Using an iterative parameter estimation method all model parameters were optimized simultaneously. The model accurately captures strain stiffening, shear thinning, softening effect and nonlinear viscous dissipation, as experimentally observed in the mechanical response to LAOS. The heterogeneous properties described by the model were in good agreement with the experimental DIC results. The presented mathematical description forms the basis for a future constitutive model definition that, by implementation in a finite element method, has the capability of describing the full 3D mechanical behavior of human skin.
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Affiliation(s)
- J F J Soetens
- Department of Biomedical Engineering, Eindhoven University of Technology, Den Dolech 2, Gem-Z. 4.11, P.O. Box 513, 5600 MB Eindhoven, The Netherlands.
| | - M van Vijven
- Department of Biomedical Engineering, Eindhoven University of Technology, Den Dolech 2, Gem-Z. 4.11, P.O. Box 513, 5600 MB Eindhoven, The Netherlands; Institute for Complex Molecular Systems, Eindhoven University of Technology, Eindhoven, The Netherlands
| | - D L Bader
- Department of Biomedical Engineering, Eindhoven University of Technology, Den Dolech 2, Gem-Z. 4.11, P.O. Box 513, 5600 MB Eindhoven, The Netherlands; Faculty of Health Sciences, University of Southampton, Southampton, United Kingdom
| | - G W M Peters
- Department of Mechanical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands
| | - C W J Oomens
- Department of Biomedical Engineering, Eindhoven University of Technology, Den Dolech 2, Gem-Z. 4.11, P.O. Box 513, 5600 MB Eindhoven, The Netherlands
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Worsley PR, Parsons B, Bader DL. An evaluation of fluid immersion therapy for the prevention of pressure ulcers. Clin Biomech (Bristol, Avon) 2016; 40:27-32. [PMID: 27794259 DOI: 10.1016/j.clinbiomech.2016.10.010] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/14/2016] [Revised: 10/14/2016] [Accepted: 10/17/2016] [Indexed: 02/07/2023]
Abstract
BACKGROUND Individuals with impaired mobility can spend prolonged periods on support surfaces, increasing their risk of developing pressure ulcers. Manufacturers have developed mattresses to maximise contact area. The present study evaluated both the biomechanical and physiological responses to lying postures on a Fluid Immersion Simulation mattress. METHODS Seventeen healthy participants were recruited to evaluate the mattress during three prescribed settings of immersion (high, medium and low). Parameters reflecting biomechanical and physiological responses, and the microclimate were monitored during three postures (supine, lateral and high-sitting) over a 90minute test session. Transcutaneous oxygen and carbon dioxide gas responses were categorised according to three criteria and data were compared between each condition. FINDINGS Results indicated that interface pressures remained consistent, with peak sacral values ranging from 21 to 27mmHg across all immersion settings and postures. The majority of participants (82%) exhibited minimal changes in gas tensions at the sacrum during all test conditions. By contrast, three participants exhibited decreased oxygen with increased carbon dioxide tensions for all three immersion settings. Supine and high sitting sacral microclimate values ranged between 30.1-30.6°C and 42.3-44.5% for temperature and relative humidity respectively. During lateral tilt there was a reduction of 1.7-2.5°C and 3.3-5.3% in these values. The majority of participants reported high comfort scores, although a few experienced bottoming out during the high-sitting posture at the high immersion setting. INTERPRETATION Fluid Immersion Simulation provides an intelligent approach to increase the support area. Further research is required to provide evidence based guidance on the use of personalised support surfaces.
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Affiliation(s)
- P R Worsley
- Clinical Academic Facility, Faculty of Health Sciences, University of Southampton, Southampton SO16 6QY, UK.
| | - B Parsons
- Clinical Academic Facility, Faculty of Health Sciences, University of Southampton, Southampton SO16 6QY, UK
| | - D L Bader
- Clinical Academic Facility, Faculty of Health Sciences, University of Southampton, Southampton SO16 6QY, UK
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Bader DL, Khodadadeh S, Turner A, Edmonds-Seal J, Fuller DJ. Biomechanical and Clinical Assessment of Hip Nerve Block in Unilateral Osteoarthrosis. ACTA ACUST UNITED AC 2016. [DOI: 10.1243/emed_jour_1982_011_008_02] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
This paper combines a biomechanical analysis with a clinical assessment of eighteen patients with unilateral hip osteoarthrosis. A double blind trial was established to evaluate the potential of a regional hip nerve block in relieving pain. The characteristics of the vertical ground-reaction forces were analysed using two Kistler force plates, once before the injection and at three-monthly intervals following it. At the same time pain, mobility and functional activity were assessed clinically. A significant change in some of the gait parameters for the good leg was recorded for the total patient group one month after the injection. However, no further significant differences were found. When the symmetry of gait was evaluated no significant differences at the 1 per cent level were observed at any period. These results suggest that gait symmetry is not a significant factor in assessment of patients with hip osteoarthrosis. There was a transient decrease in subjective pain level following the injection, but this rose to pre-injection levels by the fourth week. There were no other significant general improvements after the injection. It is concluded that the biomechanical/clinical assessment has demonstrated that the hip nerve block does not provide any useful long-term pain relief.
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Affiliation(s)
- D L Bader
- Oxford Orthopaedic Engineering Centre, Nuffield Orthopaedic Centre, Headington, Oxford
| | - S Khodadadeh
- Oxford Orthopaedic Engineering Centre, Nuffield Orthopaedic Centre, Headington, Oxford
| | - A Turner
- Writhington Hospital, Appley Bridge, Wigan
| | - J Edmonds-Seal
- Nuffield Department of Anaesthetics, Radcliffe Infirmary, Oxford
| | - D J Fuller
- Nuffield Orthopaedic Centre, Headington, Oxford
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Tilwani RK, Vessillier S, Pingguan-Murphy B, Lee DA, Bader DL, Chowdhury TT. Oxygen tension modulates the effects of TNFα in compressed chondrocytes. Inflamm Res 2016; 66:49-58. [PMID: 27658702 PMCID: PMC5209429 DOI: 10.1007/s00011-016-0991-5] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2016] [Revised: 09/07/2016] [Accepted: 09/13/2016] [Indexed: 11/28/2022] Open
Abstract
OBJECTIVE AND DESIGN Oxygen tension and biomechanical signals are factors that regulate inflammatory mechanisms in chondrocytes. We examined whether low oxygen tension influenced the cells response to TNFα and dynamic compression. MATERIALS AND METHODS Chondrocyte/agarose constructs were treated with varying concentrations of TNFα (0.1-100 ng/ml) and cultured at 5 and 21 % oxygen tension for 48 h. In separate experiments, constructs were subjected to dynamic compression (15 %) and treated with TNFα (10 ng/ml) and/or L-NIO (1 mM) at 5 and 21 % oxygen tension using an ex vivo bioreactor for 48 h. Markers for catabolic activity (NO, PGE2) and tissue remodelling (GAG, MMPs) were quantified by biochemical assay. ADAMTS-5 and MMP-13 expression were examined by real-time qPCR. 2-way ANOVA and a post hoc Bonferroni-corrected t test were used to analyse data. RESULTS TNFα dose-dependently increased NO, PGE2 and MMP activity (all p < 0.001) and induced MMP-13 (p < 0.05) and ADAMTS-5 gene expression (pp < 0.01) with values greater at 5 % oxygen tension than 21 %. The induction of catabolic mediators by TNFα was reduced by dynamic compression and/or L-NIO (all p < 0.001), with a greater inhibition observed at 5% than 21 %. The stimulation of GAG synthesis by dynamic compression was greater at 21 % than 5 % oxygen tension and this response was reduced with TNFα or reversed with L-NIO. CONCLUSIONS The present findings revealed that TNFα increased production of NO, PGE2 and MMP activity at 5 % oxygen tension. The effects induced by TNFα were reduced by dynamic compression and/or the NOS inhibitor, linking both types of stimuli to reparative activities. Future therapeutics should develop oxygen-sensitive antagonists which are directed to interfering with the TNFα-induced pathways.
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Affiliation(s)
- R K Tilwani
- Institute of Bioengineering, School of Engineering and Materials Science, Queen Mary University of London, Mile End Road, London, E1 4NS, UK
| | - S Vessillier
- Biotherapeutics Group, National Institute for Biological Standards and Control, South Mimms, Potters Bar, Hertfordshire, EN6 3QG, UK
| | - B Pingguan-Murphy
- Department of Biomedical Engineering, Faculty of Engineering, University of Malaya, Kuala Lumpur, 50603, Malaysia
| | - D A Lee
- Institute of Bioengineering, School of Engineering and Materials Science, Queen Mary University of London, Mile End Road, London, E1 4NS, UK
| | - D L Bader
- Faculty of Health Sciences, Southampton General Hospital, University of Southampton, Southampton, SO16 6YD, UK
| | - T T Chowdhury
- Institute of Bioengineering, School of Engineering and Materials Science, Queen Mary University of London, Mile End Road, London, E1 4NS, UK.
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Gray RJ, Worsley PR, Voegeli D, Bader DL. Monitoring contractile dermal lymphatic activity following uniaxial mechanical loading. Med Eng Phys 2016; 38:895-903. [DOI: 10.1016/j.medengphy.2016.04.020] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2015] [Revised: 02/18/2016] [Accepted: 04/23/2016] [Indexed: 11/25/2022]
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Abstract
Human tendons were tested in uniaxial tension with the use of specially designed grips and the local measurement of tendon cross-sectional area. The resulting stress-strain relationship was non-linear in form, with the modulus of elasticity initially increasing to a constant value which decreased as the tendon failed. The ultimate tensile strength (UTS) for the extensor digitorum longus and extensor hallucis longus tendons were 99.9 ± 12.2 MPa and 87.1 ± 125 MPa, respectively. Dynamic characterization of those tendon specimens was achieved by the method of forced oscillations using dedicated software on a hydraulic testing machine. Specimens were subjected to cyclic tension-tension loads at frequencies in the physiological range of 1–4 Hz. The sta*** load was set at values corresponding to prescribed levels between 10 and 80 per cent of the calculated UTS. Results suggest that both the dynamic modulus and the storage modulus were non-linearly proportional to the mean static stress level reaching a peak value at 60 per cent UTS, whereas the loss modulus was independent of the mean static stress. All three dynamic parameters were generally independent of frequency. The trends in the dynamic parameters were explained in terms of the loading/unloading response of tendons, as well as the structural organization of their collagen fibres.
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Affiliation(s)
- H Schechtman
- Interdisciplinary Research Centre in Biomedical Materials, Queen Mary and Westfield College, University of London
| | - D L Bader
- Interdisciplinary Research Centre in Biomedical Materials, Queen Mary and Westfield College, University of London
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Oomens CWJ, Broek M, Hemmes B, Bader DL. How does lateral tilting affect the internal strains in the sacral region of bed ridden patients? - A contribution to pressure ulcer prevention. Clin Biomech (Bristol, Avon) 2016; 35:7-13. [PMID: 27111878 DOI: 10.1016/j.clinbiomech.2016.03.009] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/27/2015] [Revised: 03/24/2016] [Accepted: 03/29/2016] [Indexed: 02/07/2023]
Abstract
BACKGROUND Repositioning of individuals with reduced mobility and at risk of pressure ulcers is an essential preventive step. Manual or automatic lateral tilting is a way of doing this and the international guidelines propose a 30° to 40° side lying position. The goal of the present study was to determine the internal strains in individuals lying in a supine position and during tilting. METHODS Based on magnetic resonance imaging (MRI) of the sacral area of human volunteers, subject specific finite element models were developed. By comparing calculated contours of the skin, fat and muscle with MRI measurements on a flat surface the models were validated. A parameter study was performed to assess the sensitivity of the model for changes in material properties. Simulations were performed at tilting angles of volunteers between 0° and 45°. FINDINGS Subjects in a supine position or tilted have the highest strains in the muscle and fat. Tilting does affect the strain distribution, taking away the highest peak strains. There seems to exist an optimal tilting angle between 20° and 30°, which may vary depending on factors such as BMI of the subject and is in the current paper investigated only for the sacrum. INTERPRETATION The study shows that tilting indeed has a significant, positive influence on internal strains, which is important for the prevention of deep tissue injury. Additional studies are needed to draw conclusions about the greater trochanter area and the tissues around the shoulder.
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Affiliation(s)
- C W J Oomens
- Biomedical Engineering Department, Eindhoven University of Technology, Eindhoven, The Netherlands.
| | - M Broek
- Biomedical Engineering Department, Eindhoven University of Technology, Eindhoven, The Netherlands
| | - B Hemmes
- Network Acute Care Limburg, Maastricht University Medical Center, Maastricht, The Netherlands
| | - D L Bader
- Biomedical Engineering Department, Eindhoven University of Technology, Eindhoven, The Netherlands; Faculty of Health Sciences, University of Southampton, Southampton, United Kingdom
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13
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Laszczak P, McGrath M, Tang J, Gao J, Jiang L, Bader DL, Moser D, Zahedi S. A pressure and shear sensor system for stress measurement at lower limb residuum/socket interface. Med Eng Phys 2016; 38:695-700. [PMID: 27118308 DOI: 10.1016/j.medengphy.2016.04.007] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2015] [Revised: 03/02/2016] [Accepted: 04/03/2016] [Indexed: 11/26/2022]
Abstract
A sensor system for measurement of pressure and shear at the lower limb residuum/socket interface is described. The system comprises of a flexible sensor unit and a data acquisition unit with wireless data transmission capability. Static and dynamic performance of the sensor system was characterised using a mechanical test machine. The static calibration results suggest that the developed sensor system presents high linearity (linearity error ≤ 3.8%) and resolution (0.9 kPa for pressure and 0.2 kPa for shear). Dynamic characterisation of the sensor system shows hysteresis error of approximately 15% for pressure and 8% for shear. Subsequently, a pilot amputee walking test was conducted. Three sensors were placed at the residuum/socket interface of a knee disarticulation amputee and simultaneous measurements were obtained during pilot amputee walking test. The pressure and shear peak values as well as their temporal profiles are presented and discussed. In particular, peak pressure and shear of approximately 58 kPa and 27 kPa, respectively, were recorded. Their temporal profiles also provide dynamic coupling information at this critical residuum/socket interface. These preliminary amputee test results suggest strong potential of the developed sensor system for exploitation as an assistive technology to facilitate socket design, socket fit and effective monitoring of lower limb residuum health.
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Affiliation(s)
- P Laszczak
- Faculty of Engineering and the Environment, University of Southampton, UK.
| | - M McGrath
- Faculty of Engineering and the Environment, University of Southampton, UK
| | - J Tang
- Faculty of Engineering and the Environment, University of Southampton, UK
| | - J Gao
- Faculty of Engineering and the Environment, University of Southampton, UK
| | - L Jiang
- Faculty of Engineering and the Environment, University of Southampton, UK
| | - D L Bader
- Faculty of Health Sciences, University of Southampton, UK
| | - D Moser
- Chas. A. Blatchford & Sons Ltd, Endolite Technology Centre, Kingsland Business park, Hampshire RG24 8PZ, UK
| | - S Zahedi
- Chas. A. Blatchford & Sons Ltd, Endolite Technology Centre, Kingsland Business park, Hampshire RG24 8PZ, UK
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Peake NJ, Bader DL, Vessillier S, Ramachandran M, Salter DM, Hobbs AJ, Chowdhury TT. C-type natriuretic peptide signalling drives homeostatic effects in human chondrocytes. Biochem Biophys Res Commun 2015; 465:784-9. [PMID: 26307537 DOI: 10.1016/j.bbrc.2015.08.087] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2015] [Accepted: 08/20/2015] [Indexed: 10/23/2022]
Abstract
Signals induced by mechanical loading and C-type natriuretic peptide (CNP) represent chondroprotective routes that may potentially prevent osteoarthritis (OA). We examined whether CNP will reduce hyaluronan production and export via members of the multidrug resistance protein (MRP) and diminish pro-inflammatory effects in human chondrocytes. The presence of interleukin-1β (IL-1β) increased HA production and export via MRP5 that was reduced with CNP and/or loading. Treatment with IL-1β conditioned medium increased production of catabolic mediators and the response was reduced with the hyaluronan inhibitor, Pep-1. The induction of pro-inflammatory cytokines by the conditioned medium was reduced by CNP and/or Pep-1, αCD44 or αTLR4 in a cytokine-dependent manner, suggesting that the CNP pathway is protective and should be exploited further.
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Affiliation(s)
- N J Peake
- Institute of Bioengineering, School of Engineering and Materials Science, Queen Mary University of London, Mile End Road, London E1 4NS, UK
| | - D L Bader
- Institute of Bioengineering, School of Engineering and Materials Science, Queen Mary University of London, Mile End Road, London E1 4NS, UK
| | - S Vessillier
- National Institute for Biological Standards and Control, Biotherapeutics Group, South Mimms, Potters Bar, Hertfordshire EN6 3QG, UK
| | - M Ramachandran
- Department of Orthopaedics and Trauma, The Royal London Hospital and Barts & The London School of Medicine & Dentistry, Queen Mary University of London, Whitechapel Road, London E1 1BB, UK
| | - D M Salter
- Centre for Genomics and Experimental Medicine, MRC Institute of Genetics and Molecular Medicine, University of Edinburgh, Crew Road, Edinburgh EH4 2XU, UK
| | - A J Hobbs
- William Harvey Research Institute, Barts and The London School of Medicine and Dentistry, QMUL, Charterhouse Square, London EC1M 6BQ, UK
| | - T T Chowdhury
- Institute of Bioengineering, School of Engineering and Materials Science, Queen Mary University of London, Mile End Road, London E1 4NS, UK.
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15
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Laszczak P, Jiang L, Bader DL, Moser D, Zahedi S. Development and validation of a 3D-printed interfacial stress sensor for prosthetic applications. Med Eng Phys 2014; 37:132-7. [PMID: 25455164 DOI: 10.1016/j.medengphy.2014.10.002] [Citation(s) in RCA: 80] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2013] [Revised: 09/07/2014] [Accepted: 10/01/2014] [Indexed: 11/16/2022]
Abstract
A novel capacitance-based sensor designed for monitoring mechanical stresses at the stump-socket interface of lower-limb amputees is described. It provides practical means of measuring pressure and shear stresses simultaneously. In particular, it comprises of a flexible frame (20 mm × 20 mm), with thickness of 4mm. By employing rapid prototyping technology in its fabrication, it offers a low-cost and versatile solution, with capability of adopting bespoke shapes of lower-limb residua. The sensor was first analysed using finite element analysis (FEA) and then evaluated using lab-based electromechanical tests. The results validate that the sensor is capable of monitoring both pressure and shear at stresses up to 350 kPa and 80 kPa, respectively. A post-signal processing model is developed to induce pressure and shear stresses, respectively. The effective separation of pressure and shear signals can be potentially advantageous for sensor calibration in clinical applications. The sensor also demonstrates high linearity (approx. 5-8%) and high pressure (approx. 1.3 kPa) and shear (approx. 0.6 kPa) stress resolution performance. Accordingly, the sensor offers the potential for exploitation as an assistive tool to both evaluate prosthetic socket fitting in clinical settings and alert amputees in home settings of excessive loading at the stump-socket interface, effectively preventing stump tissue breakdown at an early stage.
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Affiliation(s)
- P Laszczak
- Faculty of Engineering and the Environment, University of Southampton, UK
| | - L Jiang
- Faculty of Engineering and the Environment, University of Southampton, UK
| | - D L Bader
- Faculty of Health Sciences, University of Southampton, UK
| | - D Moser
- Chas A Blatchford & Sons Ltd., Endolite Technology Centre, Kingsland Business Park, Hampshire RG24 8PZ, UK
| | - S Zahedi
- Chas A Blatchford & Sons Ltd., Endolite Technology Centre, Kingsland Business Park, Hampshire RG24 8PZ, UK
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16
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Chowdhury B, David AL, Thrasivoulou C, Becker DL, Bader DL, Chowdhury TT. Tensile strain increased COX-2 expression and PGE2 release leading to weakening of the human amniotic membrane. Placenta 2014; 35:1057-64. [PMID: 25280972 DOI: 10.1016/j.placenta.2014.09.006] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/26/2014] [Revised: 07/14/2014] [Accepted: 09/11/2014] [Indexed: 11/25/2022]
Abstract
INTRODUCTION There is evidence that premature rupture of the fetal membrane at term/preterm is a result of stretch and tissue weakening due to enhanced prostaglandin E2 (PGE2) production. However, the effect of tensile strain on inflammatory mediators and the stretch sensitive protein connexin-43 (Cx43) has not been examined. We determined whether the inflammatory environment influenced tissue composition and response of the tissue to tensile strain. METHODS Human amniotic membranes isolated from the cervix (CAM) or placenta regions (PAM) were examined by second harmonic generation to identify collagen orientation and subjected to tensile testing to failure. In separate experiments, specimens were subjected to cyclic tensile strain (2%, 1 Hz) for 24 h. Specimens were examined for Cx43 by immunofluorescence confocal microscopy and expression of COX-2 and Cx43 by RT-qPCR. PGE2, collagen, elastin and glycosaminoglycan (GAG) levels were analysed by biochemical assay. RESULTS Values for tensile strength were significantly higher in PAM than CAM with mechanical parameters dependent on collagen orientation. Gene expression for Cx43 and COX-2 was enhanced by tensile strain leading to increased PGE2 release and GAG levels in PAM and CAM when compared to unstrained controls. In contrast, collagen and elastin content was reduced by tensile strain in PAM and CAM. DISCUSSION Fibre orientation has a significant effect on amniotic strength. Tensile strain increased Cx43/COX-2 expression and PGE2 release resulting in tissue softening mediated by enhanced GAG levels and a reduction in collagen/elastin content. CONCLUSION A combination of inflammatory and mechanical factors may disrupt amniotic membrane biomechanics and matrix composition.
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Affiliation(s)
- B Chowdhury
- Institute for Women's Health, University College London, 86-96 Chenies Mews, London WC1E 6HX, UK
| | - A L David
- Institute for Women's Health, University College London, 86-96 Chenies Mews, London WC1E 6HX, UK
| | - C Thrasivoulou
- Department of Cell and Developmental Biology, UCL, Gower Street, London WC1E 6BT, UK
| | - D L Becker
- Lee Kong Chian School of Medicine, Nanyang Technological University, 11, Mandalay Road, Singapore
| | - D L Bader
- Institute of Bioengineering, School of Engineering and Material Science, Queen Mary University of London, Mile End Road, London E1 4NS, UK; Faculty of Health Sciences, University of Southampton, Southampton General Hospital, Southampton SO16 6YD, UK
| | - T T Chowdhury
- Institute of Bioengineering, School of Engineering and Material Science, Queen Mary University of London, Mile End Road, London E1 4NS, UK.
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17
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Oomens CWJ, Zenhorst W, Broek M, Hemmes B, Poeze M, Brink PRG, Bader DL. A numerical study to analyse the risk for pressure ulcer development on a spine board. Clin Biomech (Bristol, Avon) 2013; 28:736-42. [PMID: 23953331 DOI: 10.1016/j.clinbiomech.2013.07.005] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/23/2013] [Revised: 06/28/2013] [Accepted: 07/02/2013] [Indexed: 02/07/2023]
Abstract
BACKGROUND Spine boards are used to immobilise accident victims suspected of having spinal injury. Guidelines about the maximum time patients remain on the board are often exceeded and on occasions may lead to pressure ulcers. Etiological research has shown that two processes ultimately lead to pressure ulcers:"Ischemic damage" which takes several hours to initiate and "deformation damage" at high strains. The latter process is very quick and the first signs of cell damage are already evident within minutes. Thus in order to minimise the risk of pressure ulcer development during prolonged loading, a new soft-layered long spine board has been designed. METHODS A subject specific numerical approach has been adopted to evaluate the prototype spine board in comparison to a conventional spine board, with reference to the estimated strains in the soft tissues adjacent to the sacrum in the supine position. The model geometry is derived from magnetic resonance images of three human volunteers in an unloaded situation. The loaded images are used to "tune" the material parameters of skin, fat and muscle. The prediction of the deformed contours on the soft-layered board is used to validate the model. FINDINGS Comparison of the internal strains in muscle tissue near the spine showed that internal strains on the soft-layered board are reduced and maximum strains are considerably less than the threshold at which deformation damage is possible. By contrast, on the rigid spine board this threshold is exceeded in all cases. INTERPRETATION The prototype comfort board is able to reduce the risk for deformation damage and thus reduces the risk of developing pressure ulcers.
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Affiliation(s)
- C W J Oomens
- Biomedical Engineering Department, Eindhoven University of Technology, Eindhoven, The Netherlands.
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18
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Loerakker S, Bader DL, Baaijens FP, Oomens CW. Which factors influence the ability of a computational model to predict thein vivodeformation behaviour of skeletal muscle? Comput Methods Biomech Biomed Engin 2013; 16:338-45. [DOI: 10.1080/10255842.2011.621423] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/14/2022]
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19
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Chen J, Irianto J, Inamdar S, Pravincumar P, Lee DA, Bader DL, Knight MM. Cell mechanics, structure, and function are regulated by the stiffness of the three-dimensional microenvironment. Biophys J 2013; 103:1188-97. [PMID: 22995491 DOI: 10.1016/j.bpj.2012.07.054] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2012] [Revised: 07/06/2012] [Accepted: 07/27/2012] [Indexed: 11/17/2022] Open
Abstract
This study adopts a combined computational and experimental approach to determine the mechanical, structural, and metabolic properties of isolated chondrocytes cultured within three-dimensional hydrogels. A series of linear elastic and hyperelastic finite-element models demonstrated that chondrocytes cultured for 24 h in gels for which the relaxation modulus is <5 kPa exhibit a cellular Young's modulus of ∼5 kPa. This is notably greater than that reported for isolated chondrocytes in suspension. The increase in cell modulus occurs over a 24-h period and is associated with an increase in the organization of the cortical actin cytoskeleton, which is known to regulate cell mechanics. However, there was a reduction in chromatin condensation, suggesting that changes in the nucleus mechanics may not be involved. Comparison of cells in 1% and 3% agarose showed that cells in the stiffer gels rapidly develop a higher Young's modulus of ∼20 kPa, sixfold greater than that observed in the softer gels. This was associated with higher levels of actin organization and chromatin condensation, but only after 24 h in culture. Further studies revealed that cells in stiffer gels synthesize less extracellular matrix over a 28-day culture period. Hence, this study demonstrates that the properties of the three-dimensional microenvironment regulate the mechanical, structural, and metabolic properties of living cells.
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Affiliation(s)
- J Chen
- Institute of Bioengineering, School of Engineering and Materials Science, Queen Mary University of London, London, United Kingdom
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20
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Adegun OK, Tomlins PH, Hagi-Pavli E, Bader DL, Fortune F. Quantitative optical coherence tomography of fluid-filled oral mucosal lesions. Lasers Med Sci 2012; 28:1249-55. [DOI: 10.1007/s10103-012-1208-y] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2012] [Accepted: 09/07/2012] [Indexed: 11/24/2022]
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21
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Abstract
The mechanics of adhesions at a local tissue level have not been extensively studied. This study compared microstrains and macrostrains in adhesions of immobilized and mobilized partially lacerated flexor digitorum profundus tendons in a New Zealand White rabbit model. At 2 weeks, 50 digits were randomized to either gross tensile testing or micromechanical assessment, in which the movement of fluorescently labelled cell nuclei, acting as dynamic markers, was visualized using real-time confocal microscopy. The structural stiffness and load at failure of immobilized adhesions were 140% and 160% of that of mobilized adhesions, respectively, and both differences were statistically significant. Micromechanically, different patterns of loading and failure were observed. Mobilized adhesions exhibited over a three-fold higher local strain, which was less uniformly distributed. Confocal microscopy provided an accurate measure of local strain. For the first time, it has been possible to visualize, define, and quantify local adhesion tissue mechanics. Mobilization appears to favour the formation of sites expressing increased local strain responses or those predisposed to heterogeneity and localized failure.
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Affiliation(s)
- O A Branford
- RAFT, Mount Vernon Hospital, Northwood, Middlesex, UK.
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22
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Loerakker S, Manders E, Strijkers GJ, Nicolay K, Baaijens FPT, Bader DL, Oomens CWJ. The effects of deformation, ischemia, and reperfusion on the development of muscle damage during prolonged loading. J Appl Physiol (1985) 2011; 111:1168-77. [DOI: 10.1152/japplphysiol.00389.2011] [Citation(s) in RCA: 101] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Deep tissue injury (DTI) is a severe form of pressure ulcer where tissue damage starts in deep tissues underneath intact skin. In the present study, the contributions of deformation, ischemia, and reperfusion to skeletal muscle damage development were examined in a rat model during a 6-h period. Magnetic resonance imaging (MRI) was used to study perfusion (contrast-enhanced MRI) and tissue integrity (T2-weighted MRI). The levels of tissue deformation were estimated using finite element models. Complete ischemia caused a gradual homogeneous increase in T2 (∼20% during the 6-h period). The effect of reperfusion on T2 was highly variable, depending on the anatomical location. In experiments involving deformation, inevitably associated with partial ischemia, a variable T2 increase (17–66% during the 6-h period) was observed reflecting the significant variation in deformation (with two-dimensional strain energies of 0.60–1.51 J/mm) and ischemia (50.8–99.8% of the leg) between experiments. These results imply that deformation, ischemia, and reperfusion all contribute to the damage process during prolonged loading, although their importance varies with time. The critical deformation threshold and period of ischemia that cause muscle damage will certainly vary between individuals. These variations are related to intrinsic factors, such as pathological state, which partly explain the individual susceptibility to the development of DTI and highlight the need for regular assessments of individual subjects.
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Affiliation(s)
| | - E. Manders
- Soft Tissue Biomechanics and Engineering and
| | - G. J. Strijkers
- Biomedical NMR, Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands; and
| | - K. Nicolay
- Biomedical NMR, Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands; and
| | | | - D. L. Bader
- Soft Tissue Biomechanics and Engineering and
- Faculty of Health Sciences, University of Southampton, Southampton, United Kingdom
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23
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Loerakker S, Oomens CWJ, Manders E, Schakel T, Bader DL, Baaijens FPT, Nicolay K, Strijkers GJ. Ischemia-reperfusion injury in rat skeletal muscle assessed with T2-weighted and dynamic contrast-enhanced MRI. Magn Reson Med 2011; 66:528-37. [PMID: 21360588 DOI: 10.1002/mrm.22801] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2010] [Revised: 11/15/2010] [Accepted: 12/10/2010] [Indexed: 11/07/2022]
Abstract
Pressure ulcers are localized areas of soft tissue breakdown due to mechanical loading. Susceptible individuals are subjected to pressure relief strategies to prevent long loading periods. Therefore, ischemia-reperfusion injury may play an important role in the etiology of pressure ulcers. To investigate the inter-relation between postischemic perfusion and changes in skeletal muscle integrity, the hindlimbs of Brown Norway rats were subjected to 4-h ischemia followed by 2-h reperfusion. Dynamic contrast-enhanced MRI was used to examine perfusion, and changes in skeletal muscle integrity were monitored with T2-weighted MRI. The dynamic contrast-enhanced MRI data showed a heterogeneous postischemic profile in the hindlimb, consisting of areas with increased contrast enhancement (14-76% of the hindlimb) and regions with no-reflow (5-77%). For T2, a gradual increase in the complete leg was observed during the 4-h ischemic period (from 34 to 41 msec). During the reperfusion phase, a heterogeneous distribution of T2 was observed. Areas with increased contrast enhancement were associated with a decrease in T2 (to 38 msec) toward preischemic levels, whereas no-reflow areas exhibited a further increase in T2 (to 42 msec). These results show that reperfusion after prolonged ischemia may not be complete, thereby continuing the ischemic condition and aggravating tissue damage.
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Affiliation(s)
- S Loerakker
- Soft Tissue Biomechanics and Engineering, Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands.
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24
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Chen J, Bader DL, Lee DA, Knight MM. Finite Element Modeling of Cell Deformation When Chondrocyte Seeded Agarose Is Subjected to Compression. IFMBE Proceedings 2011. [DOI: 10.1007/978-3-642-19044-5_5] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
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25
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Bader DL, Knight MM. Biomechanical analysis of structural deformation in living cells. Med Biol Eng Comput 2008; 46:951-63. [PMID: 18726630 DOI: 10.1007/s11517-008-0381-4] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2007] [Accepted: 07/21/2008] [Indexed: 10/24/2022]
Abstract
Most tissues are subject to some form of physiological mechanical loading which results in deformation of the cells triggering intracellular mechanotransduction pathways. This response to loading is generally essential for the health of the tissue, although more pronounced deformation may result in cell and tissue damage. In order to determine the biological response of cells to loading it is necessary to understand how cells and intracellular structures deform. This paper reviews the various loading systems that have been adopted for studying cell deformation both in situ within tissue explants and in isolated cell culture systems. In particular it describes loading systems which facilitate visualisation and subsequent quantification of cell deformation. The review also describes the associated microscopy and image analysis techniques. The review focuses on deformation of chondrocytes with additional information on a variety of other cell types including neurons, red blood cells, epithelial cells and skin and muscle cells.
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Affiliation(s)
- D L Bader
- School of Engineering and Materials Science, Queen Mary, University of London, Mile End Road, London, UK
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26
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Campbell JJ, Bader DL, Lee DA. Mechanical loading modulates intracellular calcium signaling in human mesenchymal stem cells. J Appl Biomater Biomech 2008; 6:9-15. [PMID: 20740441] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
Mesenchymal stem cells (MSCs) are a promising cell source for tissue-engineered connective tissue repair strategies. Additionally, increasing evidence confirms the role of the mechanical environment in maintaining tissue homeostasis, with calcium signaling implicated as a mediator in mechanotransduction pathways. Spontaneous intracellular calcium signaling was observed in a subset of MSCs embedded within 4% alginate hydrogel constructs, measured by a Ca2+ indicator fluo-4 in conjunction with confocal laser-scanning microscopy. By the use of pair-wise analysis, it was shown that distinct populations of MSCs up-regulated and down-regulated the frequency of calcium transients with the application of a 20% static uniaxial compressive strain of 20 min duration, delivered after a 20 min unstrained period. Calcium transients in control specimens were monitored throughout two unstrained 20 min periods. These values were statistically significant (p<0.05) by chi 2 test of independence. This dual-response indicator highlights the heterogeneous nature of MSC populations, which may have important implications for their successful use in cell therapies.
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Affiliation(s)
- J J Campbell
- Medical Engineering Division, School of Engineering and Materials Science, Queen Mary, University of London - UK
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27
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Chowdhury TT, Akanji OO, Salter DM, Bader DL, Lee DA. Dynamic compression influences interleukin-1beta-induced nitric oxide and prostaglandin E2 release by articular chondrocytes via alterations in iNOS and COX-2 expression. Biorheology 2008; 45:257-274. [PMID: 18836229] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
Interleukin-1beta (IL-1beta) induces the release of nitric oxide (.NO) and prostaglandin E2 (PGE2) by chondrocytes and this effect can be reversed with the application of dynamic compression. Previous studies have indicated that integrins may play a role. In addition, IL-1beta upregulates the expression of iNOS and COX-2 mRNA via upstream activation of p38 MAPK. The current study examines the involvement of these pathways in mediating .NO and PGE2 release in IL-1beta stimulated bovine chondrocytes subjected to dynamic compression. Bovine chondrocytes were seeded in agarose constructs and cultured with 0 or 10 ng.ml(-1) IL-1beta with or without the application of 15% dynamic compressive strain at 1 Hz. Selected inhibitors were used to interrogate the role of alpha5beta1 integrin signalling and p38 MAPK activation in mediating the release of .NO and PGE2 in response to both IL-1beta and dynamic compression. The relative expression levels of iNOS and COX-2 were assessed using real-time quantitative PCR. Nitrite, a stable end product of .NO, was measured using the Griess assay and PGE2 release was measured using an enzyme immunoassay. IL-1beta enhanced .NO and PGE2 release and this effect was reversed by the application of dynamic compression. Co-incubation with an integrin binding peptide (GRGDSP) abolished the compression-induced effect. Real-time quantitative PCR analysis revealed that IL-1beta enhanced iNOS and COX-2 mRNA levels, with the maximum expression at 6 or 12 hours. Dynamic compression reduced this effect via a p38 MAPK sensitive pathway. These results suggest that dynamic compression acts to abrogate of .NO and PGE2 release by directly influencing the expression levels of iNOS and COX-2.
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Affiliation(s)
- T T Chowdhury
- School of Engineering and Materials Science, Queen Mary, University of London, London, E1 4NS, UK
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28
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Ohashi T, Hagiwara M, Bader DL, Knight MM. Intracellular mechanics and mechanotransduction associated with chondrocyte deformation during pipette aspiration. Biorheology 2006; 43:201-14. [PMID: 16912394] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
The present study utilised pipette aspiration and simultaneous confocal microscopy to test the hypothesis that chondrocyte deformation is associated with distortion of intracellular organelles and activation of calcium signalling. Aspiration pressure was applied to isolated articular chondrocytes in increments of 2 cm of water every 60 seconds up to a maximum of 10 cm of water. At each pressure increment, confocal microscopy was used to visualise the mitochondria and nucleus labelled with JC-1 and Syto-16, respectively. To investigate intracellular calcium signalling, separate cells were labelled with Fluo 4, rapidly aspirated to 5 cm of water and then imaged for 5 minutes at a tare pressure of 0.1 cm of water. Partial cell aspiration was associated with distortion of the mitochondrial network, elongation of the nucleus and movement towards the pipette mouth. Treatment with cytochalasin D or nocodazole produced an increase in cell aspiration indicating that both the actin microfilaments and microtubules provide mechanical integrity to the cell. When the data was normalised to account for the increased cell deformation, both actin microfilaments and microtubules were shown to be necessary for strain transfer to the intracellular organelles. Mitochondria and nucleus deformation may both be involved in chondrocyte mechanotransduction as well as cellular and intracellular mechanics. In addition, pipette aspiration induced intracellular calcium signalling which may also form part of a mechanotransduction pathway. Alternatively calcium mobilisation may serve to modify actin polymerisation, thereby changing cell mechanics and membrane rigidity in order to facilitate localised cell deformation. These findings have important implications for our understanding of cell mechanics and mechanotransduction as well as interpretation and modelling of pipette aspiration data.
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Affiliation(s)
- T Ohashi
- Medical Engineering Division, Department of Engineering, Queen Mary University of London, London, UK
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29
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Pingguan-Murphy B, El-Azzeh M, Bader DL, Knight MM. Cyclic compression of chondrocytes modulates a purinergic calcium signalling pathway in a strain rate- and frequency-dependent manner. J Cell Physiol 2006; 209:389-97. [PMID: 16883605 DOI: 10.1002/jcp.20747] [Citation(s) in RCA: 75] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Mechanical loading modulates cartilage homeostasis through the control of matrix synthesis and catabolism. However, the mechanotransduction pathways through which chondrocytes detect different loading conditions remain unclear. The present study investigated the influence of cyclic compression on intracellular Ca2+ signalling using the well-characterised chondrocyte-agarose model. Cells labelled with Fluo4 were visualised using confocal microscopy following a period of 10 cycles of compression between 0% and 10% strain. In unstrained agarose constructs, not subjected to cyclic compression, a subpopulation of approximately 45% of chondrocytes exhibited spontaneous global Ca2+ transients with mean transient rise and fall times of 19.4 and 29.4 sec, respectively. Cyclic compression modulated global Ca2+ signalling by increasing the percentage of cells exhibiting Ca2+ transients (population modulation) and/or reducing the rise and fall times of these transients (transient shape modulation). The frequency and strain rate of compression differentially modulated these Ca2+ signalling characteristics providing a potential mechanism through which chondrocytes may distinguish between different loading conditions. Treatment with apyrase, gadolinium and the P2 receptor blockers, suramin and basilen blue, significantly reduced the percentage of cells exhibiting Ca2+ transients following cyclic compression, such that the mechanically induced upregulation of Ca2+ signalling was completely abolished. Thus cyclic compression appears to activate a purinergic pathway involving the release of ATP followed by the activation of P2 receptors causing a combination of extracellular Ca2+ influx and intracellular Ca2+ release. Knowledge of this fundamental cartilage mechanotransduction pathway may lead to improved therapeutic strategies for the treatment of cartilage damage and disease.
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Affiliation(s)
- B Pingguan-Murphy
- Biomedical Engineering Department, Faculty of Engineering, University Malaya, Kuala Lumpur, Malaysia
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30
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Stekelenburg A, Oomens CWJ, Strijkers GJ, de Graaf L, Bader DL, Nicolay K. A new MR-compatible loading device to study in vivo muscle damage development in rats due to compressive loading. Med Eng Phys 2006; 28:331-8. [PMID: 16118060 DOI: 10.1016/j.medengphy.2005.07.005] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2005] [Revised: 06/09/2005] [Accepted: 07/08/2005] [Indexed: 10/25/2022]
Abstract
To study the aetiology of pressure ulcers an MR-compatible loading device was developed. Magnetic resonance imaging provides the possibility of non-invasive evaluation of muscle tissue after compressive loading. Pressure was applied to the tibialis anterior region of rats by means of an indenter. The developed MR-compatible loading device allowed high quality consecutive MR measurements for up to 6h. Tissue was evaluated both during and after loading. Two loading protocols were used; a large indentation of 4.5mm (mean pressure 150 kPa) was applied for 2h and a small indentation of 2.9 mm (mean pressure 50 kPa) was applied for 4h. T2-weighted MR images after the large indentation showed an immediate increase in signal intensity, associated with damage, following load removal. After 20 h the signal intensity remained higher in the affected regions. Afterwards the tissue was perfusion fixated for histological examination. Histological evaluation revealed an inflammatory response and severe muscle necrosis. No signal increase was observed after small indentation. With this new set-up, the different factors that may play a role in the onset of muscle damage can be studied, what we believe will lead to a better understanding of the contributing factors to pressure ulcer development.
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Affiliation(s)
- A Stekelenburg
- Department of Materials Technology, Department of Biomedical Engineering, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands.
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31
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Enobakhare B, Bader DL, Lee DA. Concentration and M/G ratio influence the physiochemical and mechanical properties of alginate constructs for tissue engineering. J Appl Biomater Biomech 2006; 4:87-96. [PMID: 20799207] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
The diffusion and mechanical properties of calcium alginate gels were determined using constructs of different alginate concentrations and guluronic acid contents. It was found that the diffusion of small molecules such as sulphate, glucose and thymidine was not impeded by any of the alginates tested at concentrations of 1% and 3% (w/v). By contrast, the diffusion of large molecules, including insulin like growth factor-1 (IGF-1), human growth hormone and bovine serum albumin was impeded by alginate. This effect was enhanced with increasing alginate concentration, but was less evident for alginates with increased guluronic acid content. These findings have significant implications in tissue engineering where cells such as chondrocytes depend on the supply of factors such as IGF-1 to remain viable. An increase in both alginate concentration and guluronic acid content also increased the compressive properties, as determined by both tangent and equilibrium modulus, of alginate constructs. Although the 3% alginate constructs exhibited enhanced stiffness compared to some reported cartilage substitute biomaterials, such as PGA, their absolute values were still appreciably less stiff than articular cartilage.
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Affiliation(s)
- B Enobakhare
- Medical Engineering Division and IRC in Biomedical Materials, Department of Engineering, Queen Mary, University of London, London - UK
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32
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Knight MM, Bomzon Z, Kimmel E, Sharma AM, Lee DA, Bader DL. Chondrocyte deformation induces mitochondrial distortion and heterogeneous intracellular strain fields. Biomech Model Mechanobiol 2006; 5:180-91. [PMID: 16520962 DOI: 10.1007/s10237-006-0020-7] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2005] [Accepted: 08/03/2005] [Indexed: 11/26/2022]
Abstract
Chondrocyte mechanotransduction is poorly understood but may involve cell deformation and associated distortion of intracellular structures and organelles. This study quantifies the intracellular displacement and strain fields associated with chondrocyte deformation and in particular the distortion of the mitochondria network, which may have a role in mechanotransduction. Isolated articular chondrocytes were compressed in agarose constructs and simultaneously visualised using confocal microscopy. An optimised digital image correlation technique was developed to calculate the local intracellular displacement and strain fields using confocal images of fluorescently labelled mitochondria. The mitochondria formed a dynamic fibrous network or reticulum, which co-localised with microtubules and vimentin intermediate filaments. Cell deformation induced distortion of the mitochondria, which collapsed in the axis of compression with a resulting loss of volume. Compression generated heterogeneous intracellular strain fields indicating mechanical heterogeneity within the cytoplasm. The study provides evidence supporting the potential involvement of mitochondrial deformation in chondrocyte mechanotransduction, possibly involving strain-mediated release of reactive oxygen species. Furthermore the heterogeneous strain fields, which appear to be influenced by intracellular structure and organisation, may generate significant heterogeneity in mechanotransduction behaviour for cells subjected to identical levels of deformation.
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Affiliation(s)
- M M Knight
- Medical Engineering Division, Dept. of Engineering and IRC in Biomedical Materials, Queen Mary University of London, London, UK.
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33
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Sengers BG, Oomens CWJ, Nguyen TQD, Bader DL. Computational Modeling to Predict the Temporal Regulation of Chondrocyte Metabolism in Response to Various Dynamic Compression Regimens. Biomech Model Mechanobiol 2006; 5:111-22. [PMID: 16514518 DOI: 10.1007/s10237-006-0023-4] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2005] [Accepted: 09/01/2005] [Indexed: 10/25/2022]
Abstract
Based on previously published experimental work, computational models were developed to simulate the effect of different dynamic compression regimens on the activity of chondrocytes seeded in agarose constructs. In particular, the balance between proliferation and matrix synthesis can be adjusted by applying different intervals of continuous or intermittent mechanical compression. A phenomenological compartment based-modeling approach was used as first model. A more mechanistic cell cycle model was used as the second model. The compartment-based modeling approach was found to be useful in representing a balance between proliferation and proteoglycan synthesis, when the effect of a certain stimulation protocol is known. In order to predict the response to different intervals of mechanical stimulation, however, a more mechanistic cell cycle-based approach is required. The cell cycle model supports an important role of the onset of loading. In addition, an inhibitory effect of further loading is required, which is more likely to be related to cell cycle progression velocity than to a decreased probability of commitment to the cell cycle. The mechanisms behind this inhibitory effect and the computational implementation, however, require further investigation.
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Affiliation(s)
- B G Sengers
- Department of Biomedical Engineering, Eindhoven University of Technology, P.O. Box 513, 5600, MB, Eindhoven, The Netherlands
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34
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Stekelenburg A, Oomens CWJ, Strijkers GJ, Nicolay K, Bader DL. Compression-induced deep tissue injury examined with magnetic resonance imaging and histology. J Appl Physiol (1985) 2006; 100:1946-54. [PMID: 16484364 DOI: 10.1152/japplphysiol.00889.2005] [Citation(s) in RCA: 89] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The underlying mechanisms leading to deep tissue injury after sustained compressive loading are not well understood. It is hypothesized that initial damage to muscle fibers is induced mechanically by local excessive deformation. Therefore, in this study, an animal model was used to study early damage after compressive loading to elucidate on the damage mechanisms leading to deep pressure ulcers. The tibialis anterior of Brown-Norway rats was loaded for 2 h by means of an indenter. Experiments were performed in a magnetic resonance (MR)-compatible loading device. Muscle tissue was evaluated with transverse relaxation time (T2)-weighted MRI both during loading and up to 20 h after load removal. In addition, a detailed examination of the histopathology was performed at several time points (1, 4, and 20 h) after unloading. Results demonstrated that, immediately after unloading, T2-weighted MR images showed localized areas with increased signal intensity. Histological examination at 1 and 4 h after unloading showed large necrotic regions with complete disorganization of the internal structure of the muscle fibers. Hypercontraction zones were found bilateral to the necrotic zone. Twenty hours after unloading, an extensive inflammatory response was observed. The proposed relevance of large deformation was demonstrated by the location of damage indicated by T2-weighted MRI and the histological appearance of the compressed tissues. Differences in damage development distal and proximal to the indenter position suggested a contribution of perfusion status in the measured tissue changes that, however, appeared be to reversible.
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Affiliation(s)
- A Stekelenburg
- Eindhoven University of Technology, Department of Materials Technology, PO Box 513, Den Dolech 2, 5600 MB Eindhoven, The Netherlands.
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35
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Chowdhury TT, Bader DL, Lee DA. Anti-inflammatory effects of IL-4 and dynamic compression in IL-1β stimulated chondrocytes. Biochem Biophys Res Commun 2006; 339:241-7. [PMID: 16297873 DOI: 10.1016/j.bbrc.2005.11.016] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2005] [Accepted: 11/02/2005] [Indexed: 10/25/2022]
Abstract
Mechanical loading can counteract inflammatory pathways induced by IL-1beta by inhibiting *NO and PGE2, catabolic mediators known to be involved in cartilage degradation. The current study investigates the potential of dynamic compression, in combination with the anti-inflammatory cytokine, IL-4, to further abrogate the IL-1beta induced effects. The data presented demonstrate that IL-4 alone can inhibit nitrite release in the presence and absence of IL-1beta and partially reverse the IL-1beta induced PGE2 release. When provided in combination, IL-4 and dynamic compression could further abrogate the IL-1beta induced nitrite and PGE2 release. IL-1beta inhibited [3H]thymidine incorporation and this effect could be reversed by IL-4 or dynamic strain alone or both in combination. By contrast, 35SO4 incorporation was not influenced by IL-4 and/or dynamic strain in IL-1beta stimulated constructs. IL-4 and mechanical loading may therefore provide a potential protective mechanism for cartilage destruction as observed in OA.
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Affiliation(s)
- T T Chowdhury
- Department of Engineering, Queen Mary, University of London, Mile End Road, London E1 4NS, UK.
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36
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Pingguan-Murphy B, Lee DA, Bader DL, Knight MM. Activation of chondrocytes calcium signalling by dynamic compression is independent of number of cycles. Arch Biochem Biophys 2005; 444:45-51. [PMID: 16289021 DOI: 10.1016/j.abb.2005.09.015] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2005] [Revised: 09/28/2005] [Accepted: 09/29/2005] [Indexed: 01/28/2023]
Abstract
Mechanical loading is necessary for the development and maintenance of healthy articular cartilage through the control of extracellular matrix synthesis and catabolism. However, the underlying process of chondrocyte mechanotransduction remains unclear. This study examined the influence of cyclic compression on intracellular calcium (Ca(2+)) signalling within isolated articular chondrocytes cultured in agarose constructs. A validated experimental system was developed for applying controlled cyclic cell deformation. Cell-agarose constructs were subjected to 1Hz cyclic compression between 0 and 10% gross strain for 1, 10, 100 or 300 cycles. The cells were subsequently visualised for 300s in the unstrained state using confocal microscopy and the Ca(2+) indicator, Fluo-4 AM. Within unloaded control constructs, a sub-population of approximately 50% of chondrocytes exhibited characteristic spontaneous Ca(2+) transients each lasting approximately 40-60s. Cyclic compression, for only 1 cycle, significantly up-regulated the percentage of cells exhibiting Ca(2+) transients in the subsequent 5min period (p<0.05). Increasing the number of cycles to 10 or 100 had no additional effect. The up-regulated Ca(2+) signalling was maintained for up to 5min before returning to basal levels. By contrast, 300 cycles were followed by Ca(2+) signalling that was not significantly different from that in unloaded controls. However, this response was shown to be due to the increased time following the start of compression. In conclusion, this study indicates that chondrocyte Ca(2+) signalling is stimulated by dynamic compression, probably mediated by cyclic cell deformation. The overall response appears to be independent of the number of cycles or duration of cyclic compression. The sustained up-regulation of Ca(2+) signalling after 1, 10 or 100 cycles suggests the involvement of an autocrine-paracrine signalling mechanism. Furthermore, the reduced response following 300 cycles indicates a possible receptor desensitisation mechanism. Therefore, Ca(2+) signalling may be part of a mechanotransduction pathway through which chondrocyte populations can modulate their metabolic activity in response to changing mechanical stimuli.
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Affiliation(s)
- B Pingguan-Murphy
- Medical Engineering Division, Department of Engineering and IRC in Biomedical Materials, Queen Mary University of London, London, UK
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37
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Peeters EAG, Oomens CWJ, Bouten CVC, Bader DL, Baaijens FPT. Mechanical and failure properties of single attached cells under compression. J Biomech 2005; 38:1685-93. [PMID: 15958226 DOI: 10.1016/j.jbiomech.2004.07.018] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2004] [Accepted: 07/13/2004] [Indexed: 10/26/2022]
Abstract
Eukaryotic cells are continuously subjected to mechanical forces under normal physiological conditions. These forces and associated cellular deformations induce a variety of biological processes. The degree of deformation depends on the mechanical properties of the cell. As most cells are anchorage dependent for normal functioning, it is important to study the mechanical properties of cells in their attached configuration. The goal of the present study was to obtain the mechanical and failure properties of attached cells. Individual, attached C2C12 mouse myoblasts were subjected to unconfined compression experiments using a recently developed loading device. The device allows global compression of the cell until cell rupture and simultaneously measures the associated forces. Cell bursting was characterized by a typical reduction in the force, referred to as the bursting force. Mean bursting forces were calculated as 8.7+/-2.5 microN at an axial strain of 72+/-4%. Visualization of the cell using confocal microscopy revealed that cell bursting was preceded by the formation of bulges at the cell membrane, which eventually led to rupturing of the cell membrane. Finite element calculations were performed to simulate the obtained force-deformation curves. A finite element mesh was built for each cell to account for its specific geometrical features. Using an axisymmetric approximation of the cell geometry, and a Neo-Hookean constitutive model, excellent agreement between predicted and measured force-deformation curves was obtained, yielding an average Young's modulus of 1.14+/-0.32 kPa.
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Affiliation(s)
- E A G Peeters
- Department of Biomedical Engineering, Eindhoven University of Technology, Den Dolech 2, P.O. Box 513, 5600 MB Eindhoven, The Netherlands.
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38
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Hendriks FM, Brokken D, Oomens CWJ, Bader DL, Baaijens FPT. The relative contributions of different skin layers to the mechanical behavior of human skin in vivo using suction experiments. Med Eng Phys 2005; 28:259-66. [PMID: 16099191 DOI: 10.1016/j.medengphy.2005.07.001] [Citation(s) in RCA: 144] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2005] [Revised: 04/27/2005] [Accepted: 07/07/2005] [Indexed: 11/19/2022]
Abstract
Although the mechanical behavior of the top layer of the skin, the epidermis, is an important consideration in several clinical and cosmetic applications, there are few reported studies on this layer. The in vivo mechanical behavior of the upper skin layer (here defined as epidermis and papillar dermis) was characterized using a combined experimental and modeling approach. The work was based on the hypothesis that experiments with different length scales represent the mechanical behavior of different skin layers. Suction measurements with aperture diameters of 1, 2 and 6 mm were combined with ultrasound and optical coherence tomography to study the deformation of the skin layers. The experiments were simulated for small displacements with a two-layered finite element model representing the upper layer and the reticular dermis. An identification method compared the experimental and numerical results to identify the material parameters of the model. For one subject the whole parameter estimation procedure was completed, leading to a stiffness of C(10,ul) = 0.11 kPa for the top-layer and C(10,rd) = 0.16 MPa for the reticular dermis. This unexpected, extreme stiffness ratio of the material parameters let to convergence problems of the finite element software for most of the individuals.
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Affiliation(s)
- F M Hendriks
- Eindhoven University of Technology, Department of Biomedical Engineering, P.O. Box 513, 5600 MB Eindhoven, The Netherlands
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39
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Knight MM, Toyoda T, Lee DA, Bader DL. Mechanical compression and hydrostatic pressure induce reversible changes in actin cytoskeletal organisation in chondrocytes in agarose. J Biomech 2005; 39:1547-51. [PMID: 15985265 DOI: 10.1016/j.jbiomech.2005.04.006] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2004] [Accepted: 04/05/2005] [Indexed: 12/31/2022]
Abstract
In numerous cell types, the cytoskeleton has been widely implicated in mechanotransduction pathways involving stretch-activated ion channels, integrins and deformation of intracellular organelles. Studies have also demonstrated that the cytoskeleton can undergo remodelling in response to mechanical stimuli such as tensile strain or fluid flow. In articular chondrocytes, the mechanotransduction pathways are complex, inter-related and as yet, poorly understood. Furthermore, little is known of how the chondrocyte cytoskeleton responds to physiological mechanical loading. This study utilises the well-characterised chondrocyte-agarose model and an established confocal image-analysis technique to demonstrate that both static and cyclic, compressive strain and hydrostatic pressure all induce remodelling of actin microfilaments. This remodelling was characterised by a change from a uniform to a more punctate distribution of cortical actin around the cell periphery. For some loading regimes, this remodelling was reversed over a subsequent 1h unloaded period. This reversible remodelling of actin cytoskeleton may therefore represent a mechanism through which the chondrocyte alters its mechanical properties and mechanosensitivity in response to physiological mechanical loading.
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Affiliation(s)
- M M Knight
- IRC in Biomedical Materials and Medical Engineering Division, Department of Engineering, Queen Mary University of London, London, UK.
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40
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Abstract
Soft tissue breakdown can be initiated at the muscle layer associated with bony prominences, leading to the development of pressure ulcers. Both the magnitude and duration of pressure are important factors in this breakdown process. The present study utilizes a physical model, incorporating C2C12 mouse myoblasts in a homogeneous agarose gel, to examine the damaging effects of prolonged applied pressure. Identical cylindrical cores cut from the agarose/cell suspension were subjected to two separate compressive strains, of 10 and 20 per cent. The strain was applied for time periods ranging from 0.5 to 12 hours, using a specially designed loading apparatus. After each compression period, sections taken from the central horizontal plane of the individual constructs were stained using either haematoxylin and eosin or with the fluorescent probes, Calcein AM and ethidium homodimer-1, and assessed for cell damage. It was found that constructs subjected to the higher strain values demonstrated significantly higher values of non-viable cells for equivalent time points compared to the unstrained constructs. Further analysis on sections using the DNA nick-translation method suggested that this increase was primarily due to apoptosis. These findings imply a relationship between the duration of applied compression and damage to muscle cells seeded in the gel, which was particularly apparent at the strain level of 20 per cent, equivalent to a clinically relevant pressure of 32 mmHg (4.3 kPa). Such an approach might be useful in establishing damage threshold levels at a cellular level.
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41
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Abstract
The effect of design features of an internal spinal fixator on the loading of its individual components is paramount to the understanding of the interaction between the fixator and the instrumented spine. Using a corpectomy injury model, a strain gauge instrumented spinal fixation device was employed to investigate the role of clamp tightening torque and the inclusion of transverse bars on the distribution of bending and torsional moments acting on the fixator under torsional loading. The increase in clamp torque from 5 to 10 Nm caused a marked decrease (40%) in torsional moments acting on the vertical rods, an increase of 24% in torsional moments acting on the screws and an increase of 44% in bending moments acting on the rods along the sagittal plane of the fixator. The inclusion of transverse elements significantly increased (132%) the bending moment acting on the rods and decreased (92%) the bending moments acting on the screws along the sagittal plane. The change in both design parameters significantly reduced the response hysteresis and decreased the asymmetry of loading. A theoretical model, developed to elucidate the load path mechanisms underlying this response, successfully predicted the external response of the fixator. This model suggested both design parameters would affect the internal force and moment distribution across the fixator and the relative role of each load response mechanism in effecting this response. The changes in load patterns across the fixator will influence both its ability to augment the process of spinal fusion and the long-term performance of its components.
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Affiliation(s)
- R N Alkalay
- IRC in Biomedical Materials and Department of Engineering, University of London, Queen Mary, Mile End Road, London E1 4NS, UK
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42
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Goldberg AJ, Lee DA, Bader DL, Bentley G. Autologous chondrocyte implantation. Culture in a TGF-beta-containing medium enhances the re-expression of a chondrocytic phenotype in passaged human chondrocytes in pellet culture. J Bone Joint Surg Br 2005; 87:128-34. [PMID: 15686253] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 05/01/2023]
Abstract
An increasing number of patients are treated by autologous chondrocyte implantation (ACI). This study tests the hypothesis that culture within a defined chondrogenic medium containing TGF-beta enhances the re-expression of a chondrocytic phenotype and the subsequent production of cartilaginous extracellular matrix by human chondrocytes used in ACI. Chondrocytes surplus to clinical requirements for ACI from 24 patients were pelleted and cultured in either DMEM (Dulbecco's modified eagles medium)/ITS+Premix/TGF-beta1 or DMEM/10%FCS (fetal calf serum) and were subsequently analysed biochemically and morphologically. Pellets cultured in DMEM/ITS+/TGF-beta1 stained positively for type-II collagen, while those maintained in DMEM/10%FCS expressed type-I collagen. The pellets cultured in DMEM/ITS+/TGF-beta1 were larger and contained significantly greater amounts of DNA and glycosaminoglycans. This study suggests that the use of a defined medium containing TGF-beta is necessary to induce the re-expression of a differentiated chondrocytic phenotype and the subsequent stimulation of glycosaminoglycan and type-II collagen production by human monolayer expanded chondrocytes.
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Affiliation(s)
- A J Goldberg
- Interdisciplinary Research Centre, Institute of Orthopaedics, Royal Free and University College Medical School, Stanmore, Middlesex, England, UK
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43
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Abstract
An increasing number of patients are treated by autologous chondrocyte implantation (ACI). This study tests the hypothesis that culture within a defined chondrogenic medium containing TGF-β enhances the reexpression of a chondrocytic phenotype and the subsequent production of cartilaginous extracellular matrix by human chondrocytes used in ACI. Chondrocytes surplus to clinical requirements for ACI from 24 patients were pelleted and cultured in either DMEM (Dulbecco’s modified eagles medium)/ITS+Premix/TGF-β1 or DMEM/10%FCS (fetal calf serum) and were subsequently analysed biochemically and morphologically. Pellets cultured in DMEM/ITS+/TGF-β1 stained positively for type-II collagen, while those maintained in DMEM/10%FCS expressed type-I collagen. The pellets cultured in DMEM/ITS+/TGF-β1 were larger and contained significantly greater amounts of DNA and glycosaminoglycans. This study suggests that the use of a defined medium containing TGF-β is necessary to induce the re-expression of a differentiated chondrocytic phenotype and the subsequent stimulation of glycosaminoglycan and type-II collagen production by human monolayer expanded chondrocytes.
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Affiliation(s)
- A. J. Goldberg
- Interdisciplinary Research Centre, Institute of Orthopaedics, Royal Free & University College Medical School, Brockley Hill, Stanmore, Middlesex HA7 4LP, UK
| | - D. A. Lee
- Medical Engineering Division and IRC in Biomedical Materials, Department of Engineering, Queen Mary, University of London, Mile End Road, London E1 4NS, UK
| | - D. L. Bader
- Medical Engineering Division and IRC in Biomedical Materials, Department of Engineering, Queen Mary, University of London, Mile End Road, London E1 4NS, UK
| | - G. Bentley
- Interdisciplinary Research Centre, Institute of Orthopaedics, Royal Free & University College Medical School, Brockley Hill, Stanmore, Middlesex HA7 4LP, UK
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Breuls RGM, Bouten CVC, Oomens CWJ, Bader DL, Baaijens FPT. Compression induced cell damage in engineered muscle tissue: an in vitro model to study pressure ulcer aetiology. Ann Biomed Eng 2004; 31:1357-64. [PMID: 14758926 DOI: 10.1114/1.1624602] [Citation(s) in RCA: 98] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
The aetiology of pressure ulcers is poorly understood. The complexity of the problem, involving mechanical, biochemical, and physiological factors demands the need for simpler model systems that can be used to investigate the relative contribution of these factors, while controlling others. Therefore, an in vitro model system of engineered skeletal muscle tissue constructs was developed. With this model system, the relationship between compressive tissue straining and cell damage initiation was investigated under well-defined environmental conditions. Compression of the engineered muscle tissue constructs revealed that cell death occurs within 1-2 h at clinically relevant straining percentages and that higher strains led to earlier damage initiation. In addition, the uniform distribution of dead cells throughout the constructs suggested that sustained deformation of the cells was the principle cause of cell death. Therefore, it is hypothetised that sustained cell deformation is an additional mechanism that plays a role in the development of pressure ulcers.
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Affiliation(s)
- R G M Breuls
- Laboratory for Tissue Biomechanics and Engineering, Department of Biomedical Engineering, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands
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45
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Chowdhury TT, Salter DM, Bader DL, Lee DA. Integrin-mediated mechanotransduction processes in TGFbeta-stimulated monolayer-expanded chondrocytes. Biochem Biophys Res Commun 2004; 318:873-81. [PMID: 15147953 DOI: 10.1016/j.bbrc.2004.04.107] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2004] [Indexed: 11/17/2022]
Abstract
Previous studies have demonstrated that passage in monolayer detrimentally affects the response of articular chondrocytes to the application of dynamic compression. Transforming growth factor beta (TGFbeta) is known to regulate metabolic processes in articular cartilage and can enhance the re-expression of a chondrocytic phenotype following monolayer expansion. The current study tests the hypothesis that TGFbeta also modulates the response of monolayer-expanded human chondrocytes to the application of dynamic compression, via an integrin-mediated mechanotransduction process. The data presented demonstrate that TGFbeta3 enhanced 35SO4 and [3H]thymidine incorporation and inhibited nitrite release after 48 h of culture when compared to unsupplemented constructs. Dynamic compression also enhanced 35SO4 and [3H]thymidine incorporation and inhibited nitrite release in the presence of TGFbeta3. By contrast, dynamic compression did not alter these parameters in the absence of the growth factor. The addition of the peptide, GRGDSP, which acts as a competitive ligand for the alpha5beta1 integrin, reversed the compression-induced stimulation of 35SO4 incorporation, [3H]thymidine incorporation, and suppression of nitrite release. No effect was observed when the control peptide, GRADSP, was used. The current data clearly demonstrate that the dynamic compression-induced changes observed in cell metabolism for human monolayer-expanded chondrocytes were dependent on the presence of TGFbeta3 and are integrin-mediated.
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Affiliation(s)
- T T Chowdhury
- Medical Engineering Division and IRC in Biomedical Materials, Department of Engineering, Queen Mary, University of London, Mile End Road, London E1 4NS, UK.
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46
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Screen HRC, Lee DA, Bader DL, Shelton JC. An investigation into the effects of the hierarchical structure of tendon fascicles on micromechanical properties. Proc Inst Mech Eng H 2004; 218:109-19. [PMID: 15116898 DOI: 10.1243/095441104322984004] [Citation(s) in RCA: 149] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
During physiological loading, a tendon is subjected to tensile strains in the region of up to 6 per cent. These strains are reportedly transmitted to cells, potentially initiating specific mechanotransduction pathways. The present study examines the local strain fields within tendon fascicles subjected to tensile strain in order to determine the mechanisms responsible for fascicle extension. A hierarchical approach to the analysis was adopted, involving micro and macro examination. Micro examination was carried out using a custom-designed rig, to enable the analysis of local tissue strains in isolated fascicles, using the cell nuclei as strain markers. In macro examination, a video camera was used to record images of the fascicles during mechanical testing, highlighting the point of crimp straightening and macro failure. Results revealed that local tensile strains within a collagen fibre were consistently smaller than the applied strain and showed no further increase once fibres were aligned. By contrast, between-group displacements, a measure of fibre sliding, continued to increase beyond crimp straightening, reaching a mean value of 3.9 per cent of the applied displacement at 8 per cent strain. Macro analysis displayed crimp straightening at a mean load of 1 N and sample failure occurred through the slow unravelling of the collagen fibres. Fibre sliding appears to provide the major mechanism enabling tendon fascicle extension within the rat-tail tendon. This process will necessarily affect local and cellular strains and consequently mechanotransduction pathways.
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Affiliation(s)
- H R C Screen
- Medical Engineering Division, Department of Engineering, Queen Mary, University of London, UK
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Holloway I, Kayser M, Lee DA, Bader DL, Bentley G, Knight MM. Increased presence of cells with multiple elongated processes in osteoarthritic femoral head cartilage. Osteoarthritis Cartilage 2004; 12:17-24. [PMID: 14697679 DOI: 10.1016/j.joca.2003.09.001] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
OBJECTIVE This study examined the morphology of chondrocytes in articular cartilage from osteoarthritic (OA) and non-OA human femoral heads and in particular the appearance of a sub-population of cells with multiple elongated processes radiating up to 30 microm into the extracellular matrix. METHODS Cartilage explants were removed from 8 anatomical sites over the surface of OA (n=6) and non-OA (n=5) femoral heads. Cells were labeled for vimentin intermediate filaments and visualized using epi-fluorescence and confocal microscopy. The percentage of cells with elongated processes was correlated with macroscopic and histological indicators of osteoarthritis. RESULTS Cells with processes accounted for less than 10% of the total cell population in non-OA cartilage. By contrast, in the peripheral regions of the OA femoral head these cells accounted for 20-45% of the total cell population, the differences being statistically significant. These peripheral areas are habitually non-load bearing and were also the most likely to show gross fibrillation and pannus formation. A statistically significant correlation was demonstrated between the percentage of cells with processes and the histological extent of the OA degradation, quantified in terms of the Mankin score. CONCLUSIONS The extension of cell processes, which may be associated with localized breakdown of the pericellular matrix, will undoubtedly alter numerous aspects of cell function including phenotypic expression and mechanotransduction. Hence these significant changes in chondrocyte morphology are likely to have important implications for the aetiology of osteoarthritis and the development of potential treatment strategies.
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Affiliation(s)
- I Holloway
- Institute of Orthopaedics, University College London Medical School, Brockley Hill, Stanmore, UK
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Chowdhury TT, Bader DL, Lee DA. Dynamic compression counteracts IL-1 beta-induced release of nitric oxide and PGE2 by superficial zone chondrocytes cultured in agarose constructs. Osteoarthritis Cartilage 2003; 11:688-96. [PMID: 12954240 DOI: 10.1016/s1063-4584(03)00149-3] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
OBJECTIVE To examine the effect of IL-1 beta-induced *NO and PGE(2)release by stimulated superficial and deep chondrocyte/agarose constructs subjected to mechanical compression. DESIGN Chondrocyte sub-populations were seeded separately in agarose constructs and cultured unstrained, within a 24-well tissue culture plate, for 48 h in medium supplemented with IL-1 beta and/or L-N-(1-iminoethyl)-ornithine (L-NIO). In a separate experiment, superficial and deep cell containing constructs were subjected to 15% dynamic compressive strain at 1 Hz, for 48 h, in the presence or absence of IL-1 beta and/or L-NIO. Nitrite was measured using the Griess assay, PGE(2)release was determined using an EIA kit and [3H]-thymidine and 35SO(4)incorporation were assessed by TCA and alcian blue precipitation, respectively. RESULTS The current data reveal that IL-1 beta significantly enhanced *NO and PGE(2)release for superficial chondrocytes, an effect reversed with L-NIO. *NO and PGE(2)levels did not significantly change by deep cells in the presence of IL-1 beta and/or L-NIO. For both cell sub-populations, IL-1 beta inhibited cell proliferation whereas proteoglycan synthesis was not affected. Dynamic compression inhibited the release of *NO and PGE(2)in the presence and absence of IL-1 beta, for cells from both sub-populations. L-NIO reduced *NO and enhanced PGE(2)release for superficial zone chondrocytes, an effect not observed for deep cells in response to dynamic compression. The magnitude of stimulation of [3H]-thymidine incorporation was similar for both cell sub-populations and was not influenced by L-NIO, indicating an z.rad;NO-independent pathway. The dynamic compression-induced stimulation of 35SO(4)incorporation was enhanced with L-NIO for IL-1 beta-stimulated deep cells, indicating an *NO-dependent pathway. CONCLUSION The present findings suggest that dynamic compression inhibits *NO and PGE(2)release in IL-1 beta-stimulated superficial cells via distinct pathways, a significant finding that may contribute to the development of intervention strategies for the treatment of inflammatory joint disorders.
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Affiliation(s)
- T T Chowdhury
- Medical Engineering Division and IRC in Biomedical Materials, Department of Engineering, Queen Mary, University of London, Mile End Road, London, UK.
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Wiseman M, Henson F, Lee DA, Bader DL. Dynamic compressive strain inhibits nitric oxide synthesis by equine chondrocytes isolated from different areas of the cartilage surface. Equine Vet J 2003; 35:451-6. [PMID: 12875322 DOI: 10.2746/042516403775600532] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
REASONS FOR PERFORMING STUDY Chondrocytes within articular cartilage respond to the mechanical stresses associated with normal joint loading via a series of signalling pathways. Specific biomolecules, such as nitric oxide (NO), have been implicated in these mechanotransduction processes. It has been shown that the synthesis of NO can be inhibited by dynamic compressive strain of chondrocytes in vitro which, in turn, leads to an up-regulation of specific metabolic parameters. HYPOTHESIS Chondrocytes isolated from different joint locations and seeded in agarose constructs respond in a distinct manner to the application of dynamic compression. METHODS Chondrocytes were isolated separately from the equine patella groove and the femoral condyle, representing high loaded areas (HLA) and low loaded areas (LLA), respectively, of 6 specimens of different ages. The cells were seeded in agarose constructs and cultured either in an unstrained state or strained under dynamic loading at 1 Hz for 48 h. The synthesis of nitric oxide (NO), proteoglycan synthesis and chondrocyte proliferation were assessed. RESULTS Equine chondrocytes were found to synthesise significant basal levels of NO, regardless of topographical origin or age of tissue. Marked differences in both proteoglycan synthesis and cell proliferation were, however, revealed between the 2 chondrocyte subpopulations. Dynamic compression inhibited NO synthesis but significant alterations in proteoglycan synthesis and cell proliferation were apparent in a minority of cases. CONCLUSIONS AND POTENTIAL RELEVANCE The differential response of the subpopulations of chondrocytes derived from the HLA and LLA provides a potential mechanism which enables the biomechanical demands of differing joint regions to be maintained.
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Affiliation(s)
- M Wiseman
- IRC Biomedical Materials, Institute of Orthopaedics, Stanmore, London, UK
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Berry CC, Cacou C, Lee DA, Bader DL, Shelton JC. Dermal fibroblasts respond to mechanical conditioning in a strain profile dependent manner. Biorheology 2003; 40:337-45. [PMID: 12454424] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/27/2023]
Abstract
Fibroblasts within tissues are exposed to a dynamic mechanical environment, which influences the structural integrity of both healthy and healing soft tissues. Various systems have been proposed to subject such cells to mechanical stimulation in culture. However the diverse nature of the studies, in terms of the strain profiles and the cell types, makes direct comparisons almost impossible. The present study addresses this issue by examining the metabolic response of two cell types subjected to three well defined strain profiles.A young fibroblast cell population, represented by HuFFs, showed both greater cell proliferation and collagen production than adult dermal fibroblasts under unstrained conditions. The three strain profiles produced differing effects on both cell types. Uniaxial strains enhanced [(3)H]-thymidine incorporation for both cell types, whilst biaxial strains either inhibited or had no effect on its incorporation. In contrast, [(3)H]-proline incorporation was inhibited under biaxial and uniaxial strains for the adult fibroblasts, whilst the HuFF cells showed a small increase in proline incorporation under non-uniform and uniaxial strains.
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Affiliation(s)
- C C Berry
- IRC in Biomedical Materials and Medical Engineering Division, Department of Engineering, Queen Mary, University of London, UK
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