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Di Federico E, Bader DL, Shelton JC. 3D models of chondrocytes within biomimetic scaffolds: Effects of cell deformation from loading regimens. Clin Biomech (Bristol, Avon) 2020; 79:104972. [PMID: 32093973 DOI: 10.1016/j.clinbiomech.2020.01.022] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/04/2019] [Revised: 11/26/2019] [Accepted: 01/28/2020] [Indexed: 02/07/2023]
Abstract
BACKGROUND Mechanical conditioning has been widely used to attempt to enhance chondrocyte metabolism for the evolution of functionally competent cartilage. However, although upregulation of proteoglycans have been reported through the application of uniaxial compression, minimal collagen has been produced. The study is designed to examine whether alternative loading regimens, equivalent to physiological conditions, involving shear in addition to compression can enhance collagen production. METHODS Finite element models were developed to determine how the local chondrocyte environments within agarose constructs were influenced by a range of static and dynamic loading regimens. 3-D poro-viscoelastic models were validated against experimental data. In particular, these models were used to characterise chondrocyte deformation in compression with and without shear superimposed, with special reference to the formation of pericellular matrix around the cells. FINDINGS The models of the hydrogel constructs under stress relaxation and dynamic cyclic compression conditions were highly correlated with the experimental data. The cell deformation (y/z) in the constructs was greatest in the centre of the constructs, increasing with magnitude of compression up to 25%. The superposition of shear however did not produce significant additional changes in deformation, with the presence of PCM reducing the chondrocyte deformation. INTERPRETATION The use of FE models can prove important in the definition of appropriate, optimised mechanical conditioning regimens for the synthesis and organisation of mature extra cellular matrix by chondrocyte-seeded constructs. They will also provide insight into the mechanisms relating cell deformation to mechanotransduction pathways, thereby progressing the development of functionally competent tissue engineered cartilage.
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Affiliation(s)
- Erica Di Federico
- Institute of Bioengineering, School of Engineering and Materials Science, Queen Mary University of London, London, UK
| | - Dan L Bader
- Faculty of Health Sciences, University of Southampton, UK
| | - Julia C Shelton
- Institute of Bioengineering, School of Engineering and Materials Science, Queen Mary University of London, London, UK.
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Kleinhans KL, McMahan JB, Jackson AR. Electrical conductivity and ion diffusion in porcine meniscus: effects of strain, anisotropy, and tissue region. J Biomech 2016; 49:3041-3046. [DOI: 10.1016/j.jbiomech.2016.06.011] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2016] [Revised: 06/02/2016] [Accepted: 06/07/2016] [Indexed: 10/21/2022]
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Wright GJ, Kuo J, Shi C, Bacro TRH, Slate EH, Yao H. Effect of mechanical strain on solute diffusion in human TMJ discs: an electrical conductivity study. Ann Biomed Eng 2013; 41:2349-57. [PMID: 23771300 DOI: 10.1007/s10439-013-0840-4] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2013] [Accepted: 06/04/2013] [Indexed: 11/26/2022]
Abstract
This study investigated the effect of mechanical strain on solute diffusion in human TMJ discs (mean cadaver age 77.8) using the electrical conductivity method. The electrical conductivity, as well as small ion diffusivity, of male and female TMJ discs was determined under three compressive strains. In the male group, the average disc electrical conductivity (mean ± SD) at 0% strain was 5.14 ± 0.97 mS/cm, decreased to 4.50 ± 0.91 mS/cm (-12.3%) at 10% strain, and 3.93 ± 0.81 mS/cm (-23.5%) at 20% compressive strain. Correspondingly, the average disc relative ion diffusivity at 0% strain was 0.44 ± 0.08, decreased to 0.40 ± 0.08 (-8.9%) at 10% strain, and 0.36 ± 0.08 (-16.7%) at 20% compressive strain. In the female group, the average disc electrical conductivity at 0% strain was 5.84 ± 0.59 mS/cm, decreased to 5.01 ± 0.50 mS/cm (-14.2%) at 10% strain, and 4.33 ± 0.46 mS/cm (-25.8%) at 20% compressive strain. Correspondingly, the average disc relative ion diffusivity at 0% strain was 0.49 ± 0.05, decreased to 0.43 ± 0.04 (-11.3%) at 10% strain, and 0.39 ± 0.04 (-19.9%) at 20% compressive strain. The results indicated that mechanical strain significantly impeded solute diffusion through the disc. This mechanical strain effect was larger in the female than in the male human TMJ disc. This study may provide new insights into TMJ pathophysiology.
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Affiliation(s)
- Gregory J Wright
- Clemson-MUSC Bioengineering Program, Department of Bioengineering, Clemson University, 173 Ashley Avenue, P.O. Box 250508, Charleston, SC, 29425, USA
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A feasibility study for evaluation of mechanical properties of articular cartilage with a two-electrode electrical impedance method. J Orthop Sci 2012; 17:272-80. [PMID: 22427018 DOI: 10.1007/s00776-012-0208-x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/22/2011] [Accepted: 02/21/2012] [Indexed: 10/28/2022]
Abstract
BACKGROUND Since articular cartilage has important mechanical properties such as load-bearing, shock absorption and lubrication for activities in daily life, it is important to evaluate the mechanical properties of repaired cartilage in terms of whether those properties are the same as those of natural cartilage. The purpose of this study was to investigate the effectiveness of an electrical impedance method for quantitatively measuring the mechanical properties of cartilage. METHODS Cartilage specimens were harvested from porcine knee joint, and two kinds of enzyme-treated cartilages were prepared to investigate the correlation between mechanical and electrical properties resulting from changes in the structure of the extracellular matrix. Collagenase solution and hyaluronidase solution were used to digest the collagen fibril and proteoglycan, respectively. Electrical impedance measurement, indentation test and biochemical analysis were carried out for the enzyme-treated cartilages. RESULTS The water content increased with enzyme treatment time, and the permeability of the treated cartilages increased with decreasing glycosaminoglycan content for both types of enzyme-treated cartilages. The aggregate modulus and the electrical resistivity for both types of enzyme-treated cartilages decreased with increasing permeability after 12-h treatment. The aggregate modulus and the electrical resistivity for both types of treated cartilages decreased with increasing water content and permeability after 24-h treatment. The electrical resistivity and the aggregate modulus of articular cartilage depended not only on the water content, but also on the permeability, and the electrical resistivity for both types of enzyme-treated cartilages was found to be significantly linearly correlated with the aggregate modulus. CONCLUSIONS These results showed that the aggregate modulus of articular cartilage can be estimated by measuring its electrical impedance.
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Yuan TY, Huang CY, Yong Gu W. Novel technique for online characterization of cartilaginous tissue properties. J Biomech Eng 2012; 133:094504. [PMID: 22010750 DOI: 10.1115/1.4004920] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The goal of tissue engineering is to use substitutes to repair and restore organ function. Bioreactors are an indispensable tool for monitoring and controlling the unique environment for engineered constructs to grow. However, in order to determine the biochemical properties of engineered constructs, samples need to be destroyed. In this study, we developed a novel technique to nondestructively online-characterize the water content and fixed charge density of cartilaginous tissues. A new technique was developed to determine the tissue mechano-electrochemical properties nondestructively. Bovine knee articular cartilage and lumbar annulus fibrosus were used in this study to demonstrate that this technique could be used on different types of tissue. The results show that our newly developed method is capable of precisely predicting the water volume fraction (less than 3% disparity) and fixed charge density (less than 16.7% disparity) within cartilaginous tissues. This novel technique will help to design a new generation of bioreactors which are able to actively determine the essential properties of the engineered constructs, as well as regulate the local environment to achieve the optimal conditions for cultivating constructs.
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Affiliation(s)
- Tai-Yi Yuan
- Department of Biomedical Engineering, Tissue Biomechanics Laboratory, College of Engineering, University of Miami, Coral Gables, FL 33146, USA
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Travascio F, Jackson AR, Brown MD, Gu WY. Relationship between solute transport properties and tissue morphology in human annulus fibrosus. J Orthop Res 2009; 27:1625-30. [PMID: 19489044 PMCID: PMC2798905 DOI: 10.1002/jor.20927] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Poor nutritional supply to the intervertebral disc is believed to be an important factor leading to disc degeneration. However, little is known regarding nutritional transport in human annulus fibrosus (AF) and its relation to tissue morphology. We hypothesized that solute diffusivity in human AF is anisotropic and inhomogeneous, and that transport behaviors are associated with tissue composition and structure. To test these hypotheses, we measured the direction-dependent diffusivity of a fluorescent molecule (fluorescein, 332 Da) in three regions of AF using a fluorescence recovery after photobleaching (FRAP) technique, and associated transport results to the regional variation in water content and collagen architecture in the tissue. Diffusivity in AF was anisotropic, with higher values in the axial direction than in the radial direction for all regions investigated. The values of the diffusion coefficient ranged from 0.38 +/- 0.25 x 10(-6) cm(2)/s (radial diffusivity in outer AF) to 2.68 +/- 0.84 x 10(-6) cm(2)/s (axial diffusivity in inner AF). In both directions, diffusivity decreased moving from inner to outer AF. Tissue structure was investigated using both scanning electron microscopy and environmental scanning electron microscopy. A unique arrangement of microtubes was found in human AF. Furthermore, we also found that the density of these microtubes varied moving from inner to outer AF. A similar trend of regional variation was found for water content, with the highest value also measured in inner AF. Therefore, we concluded that a relationship exists among the anisotropic and inhomogeneous diffusion in human AF and the structure and composition of the tissue.
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Affiliation(s)
- Francesco Travascio
- Tissue Biomechanics Lab, Dept. of Biomedical Engineering, University of Miami, Coral Gables, FL
| | - Alicia R. Jackson
- Tissue Biomechanics Lab, Dept. of Biomedical Engineering, University of Miami, Coral Gables, FL
| | - Mark D. Brown
- Dept. of Orthopaedics, Miller School of Medicine, University of Miami, Miami, FL
| | - Wei Yong Gu
- Tissue Biomechanics Lab, Dept. of Biomedical Engineering, University of Miami, Coral Gables, FL,Corresponding author: WY Gu, Ph.D. Department of Biomedical Engineering College of Engineering University of Miami P.O. Box 248294 Coral Gables, Fl 33124-0621 USA Telephone: (305) 284-5434 Fax: (305)284-6494
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Yuan TY, Jackson AR, Huang CY, Gu WY. Strain-dependent oxygen diffusivity in bovine annulus fibrosus. J Biomech Eng 2009; 131:074503. [PMID: 19640139 DOI: 10.1115/1.3127254] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
The intervertebral disk (IVD) is the largest avascular structure in the human body. Transport of small molecules in IVD is mainly through diffusion from the endplates and the peripheral blood vessels surrounding IVD. Studies have investigated the structure, chemical components, and water content in IVD, but to our knowledge no study has investigated the effect of mechanical loading on oxygen transport in IVD. The objective of this study was to determine the strain-dependent behavior of oxygen diffusivity in IVD tissue. A one-dimensional steady-state diffusion experiment was designed and performed to determine the oxygen diffusivity in bovine annulus fibrosus (AF). The oxygen diffusivity was calculated using equation derived from Fick's law. A total of 20 AF specimens (d=6 mm, h approximately 0.5 mm) from bovine coccygeal IVD were used to determine oxygen diffusivity at three levels of compressive strain. The average oxygen diffusivity (mean+/-SD) of bovine AF in the axial direction was 1.43+/-0.242 x 10(-5) cm(2)/s (n=20) at 4.68+/-1.67% compressive strain level, 1.05+/-0.282 x 10(-5) cm(2)/s (n=20) at 14.2+/-1.50% strain level, and 7.71+/-1.63 x 10(-6) cm(2)/s (n=20) at 23.7+/-1.34% strain level. There was a significant decrease in oxygen diffusivity with increasing level of compressive strain (ANOVA, p<0.05). Oxygen diffusivity of bovine AF in the axial direction has been determined. The mechanical loading has a significant effect on oxygen transport in IVD tissues. This study is important in understanding nutritional transport in IVD tissues and related disk degeneration.
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Affiliation(s)
- T-Y Yuan
- Department of Biomedical Engineering, Tissue Biomechanics Laboratory, University of Miami, Coral Gables, FL 33146, USA
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Jackson AR, Yuan TY, Huang CY, Gu WY. A conductivity approach to measuring fixed charge density in intervertebral disc tissue. Ann Biomed Eng 2009; 37:2566-73. [PMID: 19757059 DOI: 10.1007/s10439-009-9792-0] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2009] [Accepted: 08/31/2009] [Indexed: 01/08/2023]
Abstract
A new method for measuring the fixed charge density (FCD) in intervertebral disc (IVD) tissues employing a two-point electrical conductivity approach was developed. In this technique, the tissue is first confined and equilibrated in a potassium chloride (KCl) solution, and the tissue conductivity is then measured. This is then repeated with a second concentration of KCl solution. The FCD can be determined from the conductivity measurements. Using this method, the FCD values of bovine annulus fibrosus (AF) and nucleus pulposus (NP) tissues were determined to be 0.060 +/- 0.027 mEq/g wet tissue and 0.19 +/- 0.039 mEq/g wet tissue, respectively. The FCD of AF was significantly lower than that of NP tissue, similar to results in the literature for human IVD tissues. In order to verify the accuracy of the new method, the glycosaminoglycan (GAG) contents of the tissues were measured and used to estimate the tissue FCD. A strong correlation (R (2) = 0.84-0.87) was found to exist between FCD values measured and those estimated from GAG contents, indicating that the conductivity approach is a reliable technique for measuring the FCD of IVD tissues.
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Affiliation(s)
- Alicia R Jackson
- Tissue Biomechanics Laboratory, Department of Biomedical Engineering, College of Engineering, University of Miami, P.O. Box 248294, Coral Gables, FL, 33124-0621, USA
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Jackson AR, Travascio F, Gu WY. Effect of mechanical loading on electrical conductivity in human intervertebral disk. J Biomech Eng 2009; 131:054505. [PMID: 19388789 DOI: 10.1115/1.3116152] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
The intervertebral disk (IVD), characterized as a charged, hydrated soft tissue, is the largest avascular structure in the body. Mechanical loading to the disk results in electromechanical transduction phenomenon as well as altered transport properties. Electrical conductivity is a material property of tissue depending on ion concentrations and diffusivities, which are in turn functions of tissue composition and structure. The aim of this study was to investigate the effect of mechanical loading on electrical behavior in human IVD tissues. We hypothesized that electrical conductivity in human IVD is strain-dependent, due to change in tissue composition caused by compression, and inhomogeneous, due to tissue structure and composition. We also hypothesized that conductivity in human annulus fibrosus (AF) is anisotropic, due to the layered structure of the tissue. Three lumbar IVDs were harvested from three human spines. From each disk, four AF specimens were prepared in each of the three principal directions (axial, circumferential, and radial), and four axial nucleus pulposus (NP) specimens were prepared. Conductivity was determined using a four-wire sense-current method and a custom-designed apparatus by measuring the resistance across the sample. Resistance measurements were taken at three levels of compression (0%, 10%, and 20%). Scanning electron microscopy (SEM) images of the human AF tissue were obtained in order to correlate tissue structure with conductivity results. Increasing compressive strain significantly decreased conductivity for all groups (p<0.05, analysis of variance (ANOVA)). Additionally, specimen orientation significantly affected electrical conductivity in the AF tissue, with conductivity in the radial direction being significantly lower than that in the axial or circumferential directions at all levels of compressive strain (p<0.05, ANOVA). Finally, conductivity in the NP tissue was significantly higher than that in the AF tissue (p<0.05, ANOVA). SEM images of the AF tissues showed evidence of microtubes orientated in the axial and circumferential directions, but not in the radial direction. This may suggest a relationship between tissue morphology and the anisotropic behavior of conductivity in the AF. The results of this investigation demonstrate that electrical conductivity in human IVD is strain-dependent and inhomogeneous, and that conductivity in the human AF tissue is anisotropic (i.e., direction-dependent). This anisotropic behavior is correlated with tissue structure shown in SEM images. This study provides important information regarding the effects of mechanical loading on solute transport and electrical behavior in IVD tissues.
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Affiliation(s)
- Alicia R Jackson
- Department of Biomedical Engineering, Tissue Biomechanics Laboratory, University of Miami, Coral Gables, FL 33146, USA
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Abstract
STUDY DESIGN Investigation of the effect of static compression and anisotropy on the apparent diffusivity of glucose in bovine annulus fibrosus (AF). OBJECTIVE. To determine the apparent glucose diffusivity in 2 directions (axial and radial) of bovine AF under 3 levels of compressive strain (0%, 10%, and 20%). SUMMARY OF BACKGROUND DATA Knowledge of diffusivity of small molecules is important for understanding nutritional supply in intervertebral discs and the mechanisms of disc degeneration. However, little is known regarding the strain-dependent and anisotropic behavior of glucose diffusivity in intervertebral discs. METHODS Apparent glucose diffusivity measurements were performed on 10 axial and 10 radial AF specimens from bovine coccygeal discs. The dependence of diffusivity on compression was determined using 3 levels of strain (0%, 10%, and 20%). RESULTS The apparent glucose diffusivity (mean +/- standard deviation) of the bovine AF in the axial direction was 1.38 +/- 0.015 x 10 cm/s (n = 10) at 0%, 1.00 +/- 0.070 x 10 cm/s (n = 10) at 10%, and 7.65 +/- 0.552 x 10 cm/s (n = 10) at 20% compression. For radial specimens, the apparent glucose diffusivity was determined to be 9.17 +/- 1.12 x 10 cm/s (n = 10), 7.29 +/- 0.863 x 10 cm/s (n = 10), and 5.43 +/- 1.16 x 10 cm/s (n = 10) for 0%, 10%, and 20% compressions, respectively. A significant decrease in diffusivity with increasing strain was found for both axial and radial specimens [analysis of variance (ANOVA), P < 0.05]. Diffusion in the radial direction was determined to be significantly less than that in the axial direction (ANOVA, P < 0.05). A significant interaction was found between the level of strain and the direction of diffusion (ANOVA, P < 0.05). CONCLUSION Diffusion of glucose in bovine AF is dependent on strain and the direction of diffusion.
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Travascio F, Gu WY. Anisotropic diffusive transport in annulus fibrosus: experimental determination of the diffusion tensor by FRAP technique. Ann Biomed Eng 2007; 35:1739-48. [PMID: 17605108 PMCID: PMC2671030 DOI: 10.1007/s10439-007-9346-2] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2006] [Accepted: 06/20/2007] [Indexed: 01/08/2023]
Abstract
The annulus fibrosus (AF) of the intervertebral disc (IVD) exhibits a fiber-organized structure which is responsible for anisotropic and inhomogeneous mechanical and transport properties. Due to its particular morphology, nutrient transport within AF is regulated by complex transport kinetics. This work investigates the diffusive transport of a small solute in the posterior and anterior regions of AF since diffusion is the major transport mechanism for low molecular weight nutrients (e.g., oxygen and glucose) in IVD. Diffusion coefficient (D) of fluorescein (332 Da) in bovine coccygeal AF was measured in the three major (axial, circumferential, and radial) directions of the IVD by means of fluorescence recovery after photobleaching (FRAP) technique. It was found that the diffusion coefficient was anisotropic and inhomogeneous. In both anterior and posterior regions, the diffusion coefficient in the radial direction was found to be the lowest. Circumferential and axial diffusion coefficients were not significantly different in both posterior and anterior regions and their values were about 130% and 150% the value of the radial diffusion coefficient, respectively. The values of diffusion coefficients in the anterior region were in general higher than those of corresponding diffusion coefficients in the posterior region. This study represents the first quantitative analysis of anisotropic diffusion transport in AF by means of FRAP technique and provides additional knowledge on understanding the pathways of nutritional supply into IVD.
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Affiliation(s)
| | - Wei Yong Gu
- Corresponding author: W.Y. Gu, Ph.D. Department of Biomedical Engineering College of Engineering University of Miami P.O. Box 248294 Coral Gables, FL 33124-0621 USA Telephone: (305)284-5434 Fax: (305)284-4720 E-mail:
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Jackson A, Yao H, Brown MD, Yong Gu W. Anisotropic ion diffusivity in intervertebral disc: an electrical conductivity approach. Spine (Phila Pa 1976) 2006; 31:2783-9. [PMID: 17108829 DOI: 10.1097/01.brs.0000245842.02717.1b] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
STUDY DESIGN Investigation of the transport behavior of ions in intervertebral disc using an electrical conductivity method. OBJECTIVES To determine the electrical conductivity and ion diffusivity of nucleus pulposus and anulus fibrosus in 3 major directions (axial, circumferential, and radial). SUMMARY OF BACKGROUND DATA Knowledge of diffusivity of small molecules is important for understanding nutrition supply in intervertebral disc and disc degeneration. However, little is known on the anisotropic behaviors of ion diffusivity and of electrical conductivity in intervertebral disc. METHODS Electrical conductivity measurement was performed on 24 axial, circumferential, and radial anulus fibrosus specimens and 24 axial nucleus pulposus specimens from bovine coccygeal discs. The diffusivity of Na and Cl were estimated by the analysis of conductivity data. RESULTS The electrical conductivity (mean +/- standard deviation; n = 24) of the bovine anulus fibrosus was 4.70 +/- 1.08 mS/cm in the axial, 2.86 +/- 0.83 mS/cm in the radial, and 4.38 +/- 1.25 mS/cm in the circumferential direction. For nucleus pulposus, the electrical conductivity (mean +/- standard deviation; n = 24) was 8.95 +/- 0.89 mS/cm. The mean value for nucleus pulposus was significantly higher than that of anulus fibrosus (t test, P < 0.05). For anulus fibrosus, the conductivity in the radial direction was significantly lower than in axial or circumferential directions. Similar trends were found for both Na and Cl diffusivities. Both electrical conductivity and ion diffusivity were highly sensitive to water content. CONCLUSIONS Electrical conductivity and ion diffusivity of anulus fibrosus are anisotropic.
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Affiliation(s)
- Alicia Jackson
- Tissue Biomechanics Lab, Department of Biomedical Engineering, University of Miami, Coral Gables, FL 33124-0621, USA
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Mossop BJ, Barr RC, Henshaw JW, Zaharoff DA, Yuan F. Electric Fields in Tumors Exposed to External Voltage Sources: Implication for Electric Field-Mediated Drug and Gene Delivery. Ann Biomed Eng 2006; 34:1564-72. [PMID: 16917743 DOI: 10.1007/s10439-006-9151-3] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2006] [Accepted: 06/05/2006] [Indexed: 10/24/2022]
Abstract
The intratumoral field, which determines the efficiency of electric field-mediated drug and gene delivery, can differ significantly from the applied field. Therefore, we investigated the distribution of the electric field in mouse tumors and tissue phantoms exposed to a large range of electric stimuli, and quantified the resistances of tumor, skin, and electrode-tissue interface. The samples used in the study included 4T1 and B16.F10 tumors, mouse skin, and tissue phantoms constructed with 1% agarose gel with or without 4T1 cells. When pulsed electric fields were applied to samples using a pair of parallel-plate electrodes, we determined the electric field and resistances in each sample as well as the resistance at the electrode-tissue interface. The electric fields in the center region of tissue phantoms and tumor slices ex vivo were macroscopically uniform and unidirectional between two parallel-plate electrodes. The field strengths in tumor tissues were significantly lower than the applied field under both ex vivo and in vivo conditions. During in vivo stimulation, the ratio of intratumoral versus applied fields was approximately either 20% or 55%, depending on the applied field. Meanwhile, the total resistance of skin and electrode-tissue interface was decreased by approximately 70% and the electric resistance at the center of both tumor models was minimally changed when the applied field was increased from 50 to 400 V/cm. These results may be useful for improving electric field-mediated drug and gene delivery in solid tumors.
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Affiliation(s)
- Brian J Mossop
- Department of Biomedical Engineering, Duke University, 136 Hudson Hall, Box 90281, Durham, NC 27708, USA
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Kruszewska D, Podgurniak P, Ljungh A, Sebastian A, Larsson L, Zajdel-Dabrowska J, Pierzynowski SG. Extremely low electrical current generated by porcine small intestine smooth muscle alters bacterial autolysin production. Exp Physiol 2005; 90:855-63. [PMID: 16118236 DOI: 10.1113/expphysiol.2005.030858] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The effect of extremely low electrical currents, identical to those generated by the gut smooth muscle, on bacterial autolysin production in vitro was tested in the present study. When stimulated with these electrical currents, the bacteria Pediococcus pentosaceus 16:1 produced groups of peptidoglycan hydrolases that differed from those produced by the unstimulated (control) bacteria. The autolysins synthesized by the P. pentosaceus 16:1 under extremely low electrical currents were effective against peptidoglycans from the cell walls of various lactic acid bacteria strains, whereas the autolysins from the control bacteria acted exclusively against P. pentosaceus 16:1 cell walls. Thus, it can be predicted that in vivo the electrical currents generated by the intestinal smooth muscles, which can be recorded as the myoelectrical migrating complexes, could regulate lactic acid bacteria strain growth in the gut.
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Affiliation(s)
- Danuta Kruszewska
- Department of Laboratory Medicine, Lund University, Sölvegatan 23, SE-223 62 Lund, Sweden
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Gu WY, Yao H, Vega AL, Flagler D. Diffusivity of ions in agarose gels and intervertebral disc: effect of porosity. Ann Biomed Eng 2005; 32:1710-7. [PMID: 15675682 DOI: 10.1007/s10439-004-7823-4] [Citation(s) in RCA: 86] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
The effect of tissue porosity on ion (sodium, potassium, and chloride) diffusivity in agarose gels and porcine intervertebral disc tissues was investigated using an electrical conductivity method. An empirical, constitutive model for diffusivity (D) of solutes in porous fibrous media was proposed: D/Do = exp[-alpha(r(s)/k(1/2))beta] where r(s) is the Stokes radius of a solute, kappa is the Darcy permeability of the porous medium, Do is the diffusivity in free solution, alpha and beta are two positive parameters whose values depend on material structure. It is found that alpha = 1.25 +/- 0.138, beta = 0.681 +/- 0.059 (95% confidence interval, R2 = 0.92, n = 72) for agarose gels and alpha = 1.29 +/- 0.171 and beta = 0.372 +/- 0.088 (95% confidence interval, R2 = 0.88, n = 86) for porcine annulus fibrosus. The functional relationship between solute diffusivity and tissue deformation was derived. Comparisons of our model prediction with experimental data on diffusion coefficients of macromolecules (proteins, dextrans, polymer beads) in agarose gels in the literature were made. Our results were also compared to the data on ion diffusivity in charged gels and in cartilaginous tissues reported in the literature. There was a good agreement between our model prediction and the data in the literature. The present study provides additional information on solute diffusivity in uncharged gels and charged tissues, and is important for understanding nutritional transport in avascular cartilaginous tissues under different mechanical loading conditions.
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Affiliation(s)
- Wei Yong Gu
- Tissue Biomechanics Laboratory, Department of Biomedical Engineering, University of Miami, Coral Gables, FL 33124-0621, USA.
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Binette JS, Garon M, Savard P, McKee MD, Buschmann MD. Tetrapolar Measurement of Electrical Conductivity and Thickness of Articular Cartilage. J Biomech Eng 2004; 126:475-84. [PMID: 15543865 DOI: 10.1115/1.1785805] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
A tetrapolar method to measure electrical conductivity of cartilage and bone, and to estimate the thickness of articular cartilage attached to bone, was developed. We determined the electrical conductivity of humeral head bovine articular cartilage and subchondral bone from a 1- to 2-year-old steer to be 1.14±0.11S/m(mean±sd,n=11) and 0.306±0.034S/m,(mean±sd,n=3), respectively. For a 4-year-old cow, articular cartilage and subchondral bone electrical conductivity were 0.88±0.08S/m(mean±sd,n=9) and 0.179±0.046S/m(mean±sd,n=3), respectively. Measurements on slices of cartilage taken from different distances from the articular surface of the steer did not reveal significant depth-dependence of electrical conductivity. We were able to estimate the thickness of articular cartilage with reasonable precision (<20% error) by injecting current from multiple electrode pairs with different inter-electrode distances. Requirements for the precision of this method to measure cartilage thickness include the presence of a distinct layer of calcified cartilage or bone with a much lower electrical conductivity than that of uncalcified articular cartilage, and the use of inter-electrode distances of the current injecting electrodes that are on the order of the cartilage thickness. These or similar methods present an attractive approach to the non-destructive determination of cartilage thickness, a parameter that is required in order to estimate functional properties of cartilage attached to bone, and evaluate the need for therapeutic interventions in arthritis.
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Affiliation(s)
- J S Binette
- Institute of Biomedical Engineering Faculty of Dentistry, and Department of Anatomy and Cell Biology, McGill University, Montréal, Québec, Canada
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