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Rossi T, Querzoli G, Angelini G, Malvasi C, Rossi A, Morini M, Esposito G, Micera A, di Luca NM, Ripandelli G. Hydraulic Resistance of Vitreous Cutters: The Impact of Blade Design and Cut Rate. Transl Vis Sci Technol 2016; 5:1. [PMID: 27441099 PMCID: PMC4942252 DOI: 10.1167/tvst.5.4.1] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2015] [Accepted: 03/26/2016] [Indexed: 11/24/2022] Open
Abstract
Purpose To measure the hydraulic resistance (HR) of vitreous cutters equipped with a Regular guillotine Blade (RB) or double edge blade (DEB) at cut rates comprised between 0 and 12,000 cuts per minute (CPM) and compare it with vitreous fragment size. This was an in vitro experimental study; in vivo HR measure and vitreous sampling. Methods HR, defined as aspiration pressure/flow rate, was measured in balanced salt solution (BSS; Alcon, Fort Worth, TX) (in vitro) and during pars plana vitrectomy of 20 consecutive patients aged 18 to 65, undergoing macular surgery. HR was recorded at increasing cut rates (500–6000 CPM for the RB and 500–12,000 CPM for the DEB; 5 mL/min flow). Vitreous samples were withdrawn and analyzed with Western and collagen type II and IX immunostaining to evaluate protein size. The main outcome measures were hydraulic resistance (mm Hg/ml/min [±SD]) and optic density for Western blot and immunostaining. Results RB and DEB showed identical HR in BSS between 0 and 3000 CPM. Above 3000 CPM, RB HR steadily increased, and was significantly higher than DEB HR. Vitreous HR was also similar for the two blades between 0 and 1500 CPM. Above 1500 CPM, RB offered a significantly higher resistance. Western blot and immunostaining of vitreous samples did not yield a significant difference in size, regardless of blade type and cut rate. Conclusions DEB is more efficient, offering a lower HR than RB over 1500 CPM in human vitreous. There is no viscosity reduction as a function of cut-rate between 1500 and 12,000 CPM, as HR does not vary. Translational Relevance Future vitreous cutters will benefit of a DEB; optimal cut rate needs to be defined, and the simple increase of cut rate does not provide benefits after a certain limit to be assessed.
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Affiliation(s)
- Tommaso Rossi
- IRCCS Azienda Ospedaliera Universitaria San Martino, IST Istituto Nazionale per la Ricerca sul Cancro, Genoa, Italy
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Yesin KB, Vollmers K, Nelson BJ. Modeling and Control of Untethered Biomicrorobots in a Fluidic Environment Using Electromagnetic Fields. Int J Rob Res 2016. [DOI: 10.1177/0278364906065389] [Citation(s) in RCA: 366] [Impact Index Per Article: 45.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
This paper investigates fundamental design, modeling, and control issues related to untethered biomedical microrobots guided inside the human body through external magnetic fields. Proposed areas of application for these microrobots include sensing, diagnosis, and surgical procedures in intraocular, cardiovascular, and inner-ear environments. A prototype microrobot and steering system are introduced. Fluid drag experiments performed on the prototype robot show that the 950 × 400 μ m elliptical shape has a spherical equivalent diameter of 477 μ m. Drag forces combined with saturation magnetization (5 × 10 5 A/m) of the prototype indicate that the required magnetic field gradients for application inside the vitreous humor and blood vessels are on the order of 0.7T/m.
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Affiliation(s)
- K. Berk Yesin
- Institute of Robotics and Intelligent Systems, ETH Zürich, 8092 Zürich, Switzerland,
| | - Karl Vollmers
- Institute of Robotics and Intelligent Systems, ETH Zürich, 8092 Zürich, Switzerland,
| | - Bradley J. Nelson
- Institute of Robotics and Intelligent Systems, ETH Zürich, 8092 Zürich, Switzerland,
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Karimi A, Razaghi R, Navidbakhsh M, Sera T, Kudo S. Computing the stresses and deformations of the human eye components due to a high explosive detonation using fluid-structure interaction model. Injury 2016; 47:1042-50. [PMID: 26861803 DOI: 10.1016/j.injury.2016.01.030] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/01/2015] [Revised: 01/12/2016] [Accepted: 01/23/2016] [Indexed: 02/02/2023]
Abstract
INTRODUCTION In spite the fact that a very small human body surface area is comprised by the eye, its wounds due to detonation have recently been dramatically amplified. Although many efforts have been devoted to measure injury of the globe, there is still a lack of knowledge on the injury mechanism due to Primary Blast Wave (PBW). The goal of this study was to determine the stresses and deformations of the human eye components, including the cornea, aqueous, iris, ciliary body, lens, vitreous, retina, sclera, optic nerve, and muscles, attributed to PBW induced by trinitrotoluene (TNT) explosion via a Lagrangian-Eulerian computational coupling model. MATERIALS AND METHODS Magnetic Resonance Imaging (MRI) was employed to establish a Finite Element (FE) model of the human eye according to a normal human eye. The solid components of the eye were modelled as Lagrangian mesh, while an explosive TNT, air domain, and aqueous were modelled using Arbitrary Lagrangian-Eulerian (ALE) mesh. Nonlinear dynamic FE simulations were accomplished using the explicit FE code, namely LS-DYNA. In order to simulate the blast wave generation, propagation, and interaction with the eye, the ALE formulation with Jones-Wilkins-Lee (JWL) equation defining the explosive material were employed. RESULTS The results revealed a peak stress of 135.70kPa brought about by detonation upsurge on the cornea at the distance of 25cm. The highest von Mises stresses were observed on the sclera (267.3kPa), whereas the lowest one was seen on the vitreous body (0.002kPa). The results also showed a relatively high resultant displacement for the macula as well as a high variation for the radius of curvature for the cornea and lens, which can result in both macular holes, optic nerve damage and, consequently, vision loss. CONCLUSION These results may have implications not only for understanding the value of stresses and strains in the human eye components but also giving an outlook about the process of PBW triggers damage to the eye.
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Affiliation(s)
- Alireza Karimi
- Department of Mechanical Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan.
| | - Reza Razaghi
- Tissue Engineering and Biological Systems Laboratory, Department of Biomechanics, School of Mechanical Engineering, Iran University of Science and Technology, Tehran 16887, Iran
| | - Mahdi Navidbakhsh
- Tissue Engineering and Biological Systems Laboratory, Department of Biomechanics, School of Mechanical Engineering, Iran University of Science and Technology, Tehran 16887, Iran
| | - Toshihiro Sera
- Department of Mechanical Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan
| | - Susumu Kudo
- Department of Mechanical Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan
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Quantifying the injury of the human eye components due to tennis ball impact using a computational fluid–structure interaction model. SPORTS ENGINEERING 2015. [DOI: 10.1007/s12283-015-0192-4] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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Pokki J, Parmar J, Ergeneman O, Torun H, Guerrero M, Pellicer E, Sort J, Pané S, Nelson BJ. Mobility-Enhancing Coatings for Vitreoretinal Surgical Devices: Hydrophilic and Enzymatic Coatings Investigated by Microrheology. ACS APPLIED MATERIALS & INTERFACES 2015; 7:22018-22028. [PMID: 26359763 DOI: 10.1021/acsami.5b06937] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Ophthalmic wireless microrobots are proposed for minimally invasive vitreoretinal surgery. Devices in the vitreous experience nonlinear mobility as a result of the complex mechanical properties of the vitreous and its interaction with the devices. A microdevice that will minimize its interaction with the macromolecules of the vitreous (i.e., mainly hyaluronan (HA) and collagen) can be utilized for ophthalmic surgeries. Although a few studies on the interactions between the vitreous and microdevices exist, there is no literature on the influence of coatings on these interactions. This paper presents how coatings on devices affect mobility in the vitreous. Surgical catheters in the vasculature use hydrophilic polymer coatings that reduce biomolecular absorption and enhance mobility. In this work such polymers, polyvinylpyrrolidone (PVP), polyethylene glycol (PEG), and HA coatings were utilized, and their effects on mobility in the vitreous were characterized. Hydrophilic titanium dioxide (TiO2) coating was also developed and characterized. Collagenase and hyaluronidase enzymes were coated on probes' surfaces with a view to enhancing their mobility by enzymatic digestion of the collagen and HA of the vitreous, respectively. To model the human vitreous, ex vivo porcine vitreous and collagen were used. For studying the effects of hyaluronidase, the vitreous and HA were used. The hydrophilic and enzymatic coatings were characterized by oscillatory magnetic microrheology. The statistical significance of the mean relative displacements (i.e., mobility) of the coated probes with respect to control probes was assessed. All studied hydrophilic coatings improve mobility, except for HA which decreases mobility potentially due to bonding with vitreal macromolecules. TiO2 coating improves mobility in collagen by 28.3% and in the vitreous by 15.4%. PEG and PVP coatings improve mobility in collagen by 19.4 and by 39.6%, respectively, but their improvement in the vitreous is insignificant at a 95% confidence level (CL). HA coating affects mobility by reducing it in collagen by 35.6% (statistically significant) and in the vitreous by 16.8% (insignificant change at 95% CL). The coatings cause similar effects in collagen and in the vitreous. However, the effects are lower in the vitreous, which can be due to a lower concentration of collagen in the vitreous than in the prepared collagen samples. The coatings based on enzymatic activity increase mobility (i.e., >40% after 15 min experiments in the vitreous models) more than the hydrophilic coatings based on physicochemical interactions. However, the enzymes have time-dependent effects, and they dissolve from the probe surface with time. The presented results are useful for researchers and companies developing ophthalmic devices. They also pave the way to understanding how to adjust mobility of a microdevice in a complex fluid by choice of an appropriate coating.
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Affiliation(s)
- Juho Pokki
- Institute of Robotics and Intelligent Systems, ETH Zurich , Zurich, Switzerland
| | - Jemish Parmar
- Institute of Robotics and Intelligent Systems, ETH Zurich , Zurich, Switzerland
| | - Olgaç Ergeneman
- Institute of Robotics and Intelligent Systems, ETH Zurich , Zurich, Switzerland
| | - Hamdi Torun
- Department of Electrical and Electronics Engineering, Boğaziçi University , Istanbul, Turkey
- Center for Life Sciences and Technologies, Boğaziçi University , Istanbul, Turkey
| | - Miguel Guerrero
- Departament de Física, Universitat Autònoma de Barcelona , Bellaterra, Spain
| | - Eva Pellicer
- Departament de Física, Universitat Autònoma de Barcelona , Bellaterra, Spain
| | - Jordi Sort
- Departament de Física, Universitat Autònoma de Barcelona , Bellaterra, Spain
- Institució Catalana de Recerca i Estudis Avançats (ICREA) , Barcelona, Spain
| | - Salvador Pané
- Institute of Robotics and Intelligent Systems, ETH Zurich , Zurich, Switzerland
| | - Bradley J Nelson
- Institute of Robotics and Intelligent Systems, ETH Zurich , Zurich, Switzerland
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Pokki J, Ergeneman O, Sevim S, Enzmann V, Torun H, Nelson BJ. Measuring localized viscoelasticity of the vitreous body using intraocular microprobes. Biomed Microdevices 2015; 17:85. [DOI: 10.1007/s10544-015-9988-z] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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Bonfiglio A, Lagazzo A, Repetto R, Stocchino A. An experimental model of vitreous motion induced by eye rotations. EYE AND VISION (LONDON, ENGLAND) 2015; 2:10. [PMID: 26613091 PMCID: PMC4660830 DOI: 10.1186/s40662-015-0020-8] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/10/2014] [Accepted: 04/30/2015] [Indexed: 11/10/2022]
Abstract
BACKGROUND During eye rotations the vitreous humour moves with respect to the eye globe. This relative motion has been suggested to possibly have an important role in inducing degradation of the gel structure, which might lead to vitreous liquefaction and/or posterior vitreous detachment. Aim of the present work is to study the characteristics of vitreous motion induced by eye rotations. METHODS We use an experimental setup, consisting of a Perspex model of the vitreous chamber that, for simplicity, is taken to have a spherical shape. The model is filled with an artificial vitreous humour, prepared as a solution of agar powder and hyaluronic acid sodium salt in deionised water, which has viscoelastic mechanical properties similar to those of the real vitreous. The model rotates about an axis passing through the centre of the sphere and velocity measurements are taken on the equatorial plane orthogonal to the axis of rotation, using an optical technique. RESULTS The results show that fluid viscoelasticity has a strong influence on flow characteristics. In particular, at certain frequencies of oscillation of the eye model, fluid motion can be resonantly excited. This means that fluid velocity within the domain can be significantly larger than that of the wall. CONCLUSIONS The frequencies for which resonant excitation occurs are within the range of possible eye rotations frequencies. Therefore, the present results suggest that resonant excitation of vitreous motion is likely to occur in practice. This, in turn, implies that eye rotations produce large stresses on the retina and within the vitreous that may contribute to the disruption of the vitreous gel structure. The present results also have implications for the choice of the ideal properties for vitreous substitute fluids.
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Affiliation(s)
- Andrea Bonfiglio
- Department of Civil, Chemical and Environmental Engineering, University of Genoa, Italy, Via Montallegro 1, Genoa, 16145 Italy
| | - Alberto Lagazzo
- Department of Civil, Chemical and Environmental Engineering, University of Genoa, Italy, Via Montallegro 1, Genoa, 16145 Italy
| | - Rodolfo Repetto
- Department of Civil, Chemical and Environmental Engineering, University of Genoa, Italy, Via Montallegro 1, Genoa, 16145 Italy
| | - Alessandro Stocchino
- Department of Civil, Chemical and Environmental Engineering, University of Genoa, Italy, Via Montallegro 1, Genoa, 16145 Italy
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Spaide RF. Visualization of the posterior vitreous with dynamic focusing and windowed averaging swept source optical coherence tomography. Am J Ophthalmol 2014; 158:1267-74. [PMID: 25174895 DOI: 10.1016/j.ajo.2014.08.035] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2014] [Revised: 08/26/2014] [Accepted: 08/26/2014] [Indexed: 10/24/2022]
Abstract
PURPOSE To survey the anatomic structures seen in the posterior vitreous using a newly developed technique, dynamic focusing and windowed averaging swept source optical coherence tomography. DESIGN A cross-sectional study of subjects without a history of eye disease or posterior vitreous detachment. METHODS A focused illumination beam was swept through the scan depth during 96 successive B-scans and the corresponding most highly resolved portion of each scan was used to make an averaged composite image. The main outcome measures were the frequency and interconnectedness of anatomic features visualized. RESULTS There were 44 eyes of 25 subjects, who ranged in age from 23 to 62. An optically empty space was seen above the macula in all eyes, and corresponded to the premacular bursa. Above the optic nerve head was a conical space corresponding to the area of Martegiani. The 2 areas were interconnected in 25 cases (56.8%). Anterior to the premacular bursa was another lacuna, named the supramacular bursa, that was separate from the premacular bursa in horizontal scans centered on the fovea and was found in 38 eyes (86.4%). Both the supramacular and premacular bursae coursed anteriorly and in 21 of the 38 eyes (55.3%) were seen to interconnect. CONCLUSIONS The anatomic arrangement of the vitreous is consistent in living eyes with no posterior vitreous detachment, and does not correspond precisely to that described from dissection studies of autopsy specimens. The constancy of the specific findings suggests there may be some beneficial effect from the architectural structure of the vitreous that enhances evolutionary fitness.
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Yamazaki J, Yoshida M, Mizunuma H. Experimental analyses of the retinal and subretinal haemorrhages accompanied by shaken baby syndrome/abusive head trauma using a dummy doll. Injury 2014; 45:1196-206. [PMID: 24810668 DOI: 10.1016/j.injury.2014.04.014] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/10/2014] [Revised: 03/11/2014] [Accepted: 04/05/2014] [Indexed: 02/02/2023]
Abstract
INTRODUCTION We explored several modes of violent shaking using a dummy doll with an eyeball model to reproduce abusive events that lead to retinal haemorrhages (RH) seen in shaken baby syndrome or abusive head trauma (SBS/AHT). MATERIALS AND METHODS A dummy doll equipped with an eyeball model was prepared. The eyeball model was filled with a model of vitreous body, i.e. agar gel or water, and was with a pressure sensor to measure normal stress. RESULTS The modes of shaking were classified into three patterns, i.e. fast shaking with the fore arms, fast shaking with the whole arms and synchronized shaking with the whole arms. The frequency of the cyclic acceleration-deceleration history experienced by the head of the dummy doll was 5.0, 4.0 and 2.2 Hz, respectively, with the maximum acceleration of 20, 20 and 60 m/s(2), respectively. We considered the last of these three modes of shaking as possibly corresponding to the worst case of violent shaking. This mode of shaking could be instructed to volunteers who acted as imitate perpetrators, and resulted in both increased peak intensities of the acceleration experienced by the head of the dummy doll and increased stresses on the retina at the posterior pole of the eyeball model. DISCUSSION The time integral of the stress through a single cycle of shaking was 107 Pa·s, much larger than that of a single event of fall, which resulted in 60-73 Pa·s. Taking into account that abusive shaking is likely to include multiple cycles, the time integral of the stress due to abusive shaking can be even larger. This clear difference may explain why RH in SBS/AHT is frequent, while RH in accidental falls is rare.
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Affiliation(s)
- Junpei Yamazaki
- Department of Mechanical Engineering, Tokyo Metropolitan University, 1-1 Minami-Osawa, Hachioji, Tokyo 192-0397, Japan.
| | - Makoto Yoshida
- Department of Mechanical Engineering, Tokyo Metropolitan University, 1-1 Minami-Osawa, Hachioji, Tokyo 192-0397, Japan.
| | - Hiroshi Mizunuma
- Department of Mechanical Engineering, Tokyo Metropolitan University, 1-1 Minami-Osawa, Hachioji, Tokyo 192-0397, Japan.
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Yang W, Yuan Y, Zong Y, Huang Z, Mai S, Li Y, Qian X, Liu Y, Gao Q. Preliminary study on retinal vascular and oxygen-related changes after long-term silicone oil and foldable capsular vitreous body tamponade. Sci Rep 2014; 4:5272. [PMID: 24920425 PMCID: PMC4053724 DOI: 10.1038/srep05272] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2014] [Accepted: 05/23/2014] [Indexed: 12/27/2022] Open
Abstract
Silicone oil has been the only long-term vitreous substitute used in the treatment of retinal detachment since 1962 by Cibis. Nevertheless, its effects on retinal vascular morphology and oxygen supply to the retina are ambiguous in current research. We previously invented a foldable capsular vitreous body (FCVB) to use as a new vitreous substitute in the treatment of severe retinal detachment, but its effects on the retinal vessel were unknown. Therefore, in this study, a standard three-port pars plana vitrectomy (PPV) was performed on the right eye of each rabbit and then silicone oil and FCVB were injected into the vitreous cavity as vitreous substitutes. After 180 days of retention, the retinal vascular morphology did not display any distinct abnormalities, and hypoxia-induced factor-1alpha (HIF-1α) and vascular endothelial growth factor (VEGF) did not vary markedly during the observation period in silicone oil tamponade- and FCVB-implanted eyes. This study may suggest that silicone oil and FCVB tamponade in rabbit eyes did not cause retinal vascular pathologic changes or retinal hypoxia for 180 days.
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Affiliation(s)
- Wei Yang
- State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou 510060, China
| | - Yongguang Yuan
- State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou 510060, China
| | - Yao Zong
- State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou 510060, China
| | - Zhen Huang
- State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou 510060, China
| | - Shuyi Mai
- State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou 510060, China
| | - Yujie Li
- State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou 510060, China
| | - Xiaobing Qian
- State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou 510060, China
| | - Yaqin Liu
- State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou 510060, China
| | - Qianying Gao
- State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou 510060, China
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Liu X, Wang L, Wang C, Fan J, Liu S, Fan Y. Prediction of globe rupture caused by primary blast: a finite element analysis. Comput Methods Biomech Biomed Engin 2014; 18:1024-1029. [DOI: 10.1080/10255842.2013.869317] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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Filas BA, Zhang Q, Okamoto RJ, Shui YB, Beebe DC. Enzymatic degradation identifies components responsible for the structural properties of the vitreous body. Invest Ophthalmol Vis Sci 2014; 55:55-63. [PMID: 24222300 DOI: 10.1167/iovs.13-13026] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
PURPOSE Vitreous degeneration contributes to several age-related eye diseases, including retinal detachment, macular hole, macular traction syndrome, and nuclear cataracts. Remarkably little is understood about the molecular interactions responsible for maintaining vitreous structure. The purpose of this study was to measure the structural properties of the vitreous body after enzymatic degradation of selected macromolecules. METHODS Mechanical properties of plugs of bovine and porcine vitreous were analyzed using a rheometer. Oscillatory and extensional tests measured vitreous stiffness and adhesivity, respectively. Major structural components of the vitreous were degraded by incubation overnight in collagenase, trypsin, or hyaluronidase, singly or in combination. Vitreous bodies were also incubated in hyper- or hypotonic saline. Effects of these treatments on the mechanical properties of the vitreous were measured by rheometry. RESULTS Enzymatic digestion of each class of macromolecules decreased the stiffness of bovine vitreous by approximately half (P < 0.05). Differential effects were observed on the damping capacity of the vitreous (P < 0.05), which was shown to correlate with material behavior in extension (P < 0.01). Digestion of hyaluronan significantly decreased the damping capacity of the vitreous and increased adhesivity. Collagen degradation resulted in the opposite effect, whereas digestion of proteins and proteoglycans with trypsin did not alter behavior relative to controls. Osmotic perturbations and double-enzyme treatments further implicated hyaluronan and hyaluronan-associated water as a primary regulator of adhesivity and material behavior in extension. CONCLUSIONS Collagen, hyaluronan, and proteoglycans act synergistically to maintain vitreous stiffness. Hyaluronan is a key mediator of vitreous adhesivity, and mechanical damping is an important factor influencing dynamic vitreous behavior.
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Affiliation(s)
- Benjamen A Filas
- Department of Ophthalmology & Visual Sciences, Washington University School of Medicine, St. Louis, Missouri
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Evaluation and correction for optical scattering variations in laser speckle rheology of biological fluids. PLoS One 2013; 8:e65014. [PMID: 23705028 PMCID: PMC3660338 DOI: 10.1371/journal.pone.0065014] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2012] [Accepted: 04/22/2013] [Indexed: 11/19/2022] Open
Abstract
Biological fluids fulfill key functionalities such as hydrating, protecting, and nourishing cells and tissues in various organ systems. They are capable of these versatile tasks owing to their distinct structural and viscoelastic properties. Characterizing the viscoelastic properties of bio-fluids is of pivotal importance for monitoring the development of certain pathologies as well as engineering synthetic replacements. Laser Speckle Rheology (LSR) is a novel optical technology that enables mechanical evaluation of tissue. In LSR, a coherent laser beam illuminates the tissue and temporal speckle intensity fluctuations are analyzed to evaluate mechanical properties. The rate of temporal speckle fluctuations is, however, influenced by both optical and mechanical properties of tissue. Therefore, in this paper, we develop and validate an approach to estimate and compensate for the contributions of light scattering to speckle dynamics and demonstrate the capability of LSR for the accurate extraction of viscoelastic moduli in phantom samples and biological fluids of varying optical and mechanical properties.
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Diller E, Giltinan J, Sitti M. Independent control of multiple magnetic microrobots in three dimensions. Int J Rob Res 2013. [DOI: 10.1177/0278364913483183] [Citation(s) in RCA: 172] [Impact Index Per Article: 15.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
A major challenge for untethered microscale mobile robotics is the control of many agents in the same workspace for distributed operation. In this work, we present a new method to independently control multiple sub-mm microrobots in three dimensions (3D) using magnetic gradient pulling as the 3D motion generation method. Motion differentiation is accomplished through the use of geometrically or magnetically distinct microrobots which assume different magnetization directions in a rotating or oscillating magnetic field. This allows for different magnetic forces to be exerted on each, enabling independent motion control and path following of multiple microrobots along arbitrary 3D trajectories. Path following in 3D with less than 310 μ m mean error is shown for a set of two microrobots of size 350 μ m and 1500 μ m, and independent motions are shown with three microrobots. It is also shown that control of more microrobots could be possible using improved magnetic coil hardware. Microrobot diversity is analyzed with regards to the effect on independent control. The proposed addressability method could be used for the 3D control of a team of microrobots inside microfluidic channels or in the human body for localized therapy or diagnostics.
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Affiliation(s)
- Eric Diller
- Department of Mechanical Engineering, Carnegie Mellon University, USA
| | - Joshua Giltinan
- Department of Mechanical Engineering, Carnegie Mellon University, USA
| | - Metin Sitti
- Department of Mechanical Engineering, Carnegie Mellon University, USA
- Robotics Institute, Carnegie Mellon University, USA
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Liu X, Wang L, Wang C, Sun G, Liu S, Fan Y. Mechanism of traumatic retinal detachment in blunt impact: A finite element study. J Biomech 2013; 46:1321-7. [DOI: 10.1016/j.jbiomech.2013.02.006] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2012] [Revised: 01/31/2013] [Accepted: 02/05/2013] [Indexed: 10/27/2022]
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Simpson ARH, Petrarca R, Jackson TL. Vitreomacular adhesion and neovascular age-related macular degeneration. Surv Ophthalmol 2013; 57:498-509. [PMID: 23068973 DOI: 10.1016/j.survophthal.2012.01.011] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2011] [Revised: 01/30/2012] [Accepted: 01/31/2012] [Indexed: 02/05/2023]
Abstract
We explore the hypothesis that vitreomacular adhesion (VMA) and vitreomacular traction (VMT) play a role in the pathogenesis and clinical course of neovascular ("wet") age-related macular degeneration (AMD). Several biological theories are offered to explain this possible association, including direct tractional force, altered vitreous oxygenation, altered diffusion coefficients of intravitreal molecules, and alterations in the pharmacokinetics of intravitreal drugs. Release of VMT may improve the clinical course of neovascular AMD, and a few case series suggest that vitrectomy can lead to both a functional and anatomic improvement. A large, randomized, controlled clinical trial is underway, investigating pharmacologic release of VMA in eyes with neovascular AMD.
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Affiliation(s)
- Andrew R H Simpson
- King's College London and King's College Hospital, London, United Kingdom
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68
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Bonfiglio A, Repetto R, Siggers JH, Stocchino A. Investigation of the motion of a viscous fluid in the vitreous cavity induced by eye rotations and implications for drug delivery. Phys Med Biol 2013; 58:1969-82. [DOI: 10.1088/0031-9155/58/6/1969] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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69
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Wang Z, Pokki J, Ergeneman O, Nelson BJ, Hirai S. Viscoelastic interaction between intraocular microrobots and vitreous humor: a finite element approach. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2013; 2013:4937-4940. [PMID: 24110842 DOI: 10.1109/embc.2013.6610655] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Vitreous humor exhibits complex biomechanical properties and determination of these properties is essential for designing ophthalmic biomedical microdevices. In this paper, the viscoelastic properties of porcine vitreous humor were studied based on ex vivo creep experiments, in which a microrobot was magnetically actuated inside the vitreous. A three-dimensional (3D) finite element (FE) model was proposed to simulate the viscoelastic interaction between the microrobot and porcine vitreous humor. An optimization-based method was employed to estimate the viscoelastic parameters of the vitreous humor. The proposed model successfully validated the experimental measurements. The estimated parameters were compared with published data in literature. The model was then used to study the shape-dependent interaction of the microrobot with the vitreous humor. The methods presented in this paper can be used for the optimization of ophthalmic microrobots and microsurgical tools.
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Smith CA, Newson TA, Hutnik CML, Hill KA. Identification of anomalous features of intravitreal injections using micro-computed tomography. Curr Eye Res 2012; 38:375-80. [PMID: 23249301 DOI: 10.3109/02713683.2012.744059] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
PURPOSE To identify anomalous features that impact drug delivery in the eye as a result of intravitreal injections using micro-computed tomography imaging. METHODS Three-dimensional micro-computed tomography images were acquired following an intravitreal injection of 0.03 mL of contrast agent into ex vivo porcine eyes (n = 24). A baseline scan was acquired prior to injection to detect any abnormalities in the eyes. Acquisition continued at various time intervals up to 230 min post-injection. RESULTS Air bubbles were clearly visible within the vitreous of 21 eyes following injections. There was a total of 36 air bubbles in the 21 eyes and the volume of the air bubbles ranged from 0.01 µL to 1.50 µL. It was found the size of the air bubbles decreased over the scanning period. Furthermore, many of the injected boli in the eye specimens did not have the commonly assumed spherical shape; rather, a variety of other shapes resulted. CONCLUSION The presence of air bubbles and inconsistent bolus shapes have indicated that intravitreal injections have high variability. It is only through the realization of these anomalous features that the efficacy of intravitreal drug delivery will be improved through a consistent and accurate injection technique.
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Affiliation(s)
- Corey A Smith
- Biomedical Engineering Graduate Program, The University of Western Ontario, London, Ontario, Canada
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71
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Abouali O, Modareszadeh A, Ghaffariyeh A, Tu J. Numerical simulation of the fluid dynamics in vitreous cavity due to saccadic eye movement. Med Eng Phys 2012; 34:681-92. [DOI: 10.1016/j.medengphy.2011.09.011] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2011] [Revised: 09/11/2011] [Accepted: 09/15/2011] [Indexed: 10/16/2022]
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72
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Rossi T, Querzoli G, Pasqualitto G, Iossa M, Placentino L, Repetto R, Stocchino A, Ripandelli G. Ultrasound imaging velocimetry of the human vitreous. Exp Eye Res 2012; 99:98-104. [DOI: 10.1016/j.exer.2012.03.014] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2012] [Revised: 03/24/2012] [Accepted: 03/27/2012] [Indexed: 11/30/2022]
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73
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Preservative-free triamcinolone acetonide injectable suspension versus "traditional" triamcinolone preparations: impact of aggregate size on retinal biocompatibility. Retina 2012; 31:2050-7. [PMID: 21747324 DOI: 10.1097/iae.0b013e318214d076] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
PURPOSE To evaluate the biocompatibility of the three currently most commonly used triamcinolone acetonide (TA) preparations on retinal cells. METHODS Preservative containing KL (Kenalog-40; Bristol-Myers Squibb, Princeton, NJ), compounded preservative-free triamcinolone acetonide (PFTA; compounded from Volon A; Dermapharm, Vienna, Austria), and preservative-free triamcinolone acetonide injectable suspension (TRIESENCE; Alcon, Inc, Fort Worth, TX) (0.01-1 mg/mL) were either added directly on top or separated by a Boyden chamber filter or by a layer of vitreous to confluent cell cultures of retinal pigment epithelial cells (ARPE19) or retinal ganglion cells (RGC5). The distribution pattern of the TA crystals was assessed microscopically. Cell viability was assessed using MTT-ELISA and Live/Dead-Assay. RESULTS Sedimentation of triamcinolone acetonide injectable suspension, KL, or PFTA caused a pronounced decrease in cell viability. Cytotoxicity was most pronounced when triamcinolone acetonide injectable suspension and PFTA were used. Without direct sedimentation of TA crystals on top of the cells, none of the three formulations were cytotoxic. Triamcinolone acetonide injectable suspension showed the largest and most dense TA crystal aggregates on top of the cells. CONCLUSION Retinal cytotoxicity of TA seems only to occur when there is intimate contact of TA crystals with the cellular membrane. Cytotoxicity depends on the number and size of TA crystal aggregates-with larger conglomerates being more harmful. Of the TA formulations tested, triamcinolone acetonide injectable suspension had the strongest tendency to form large TA crystal conglomerates and to gravitate downward.
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Piccirelli M, Bergamin O, Landau K, Boesiger P, Luechinger R. Vitreous deformation during eye movement. NMR IN BIOMEDICINE 2012; 25:59-66. [PMID: 21567512 DOI: 10.1002/nbm.1713] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/23/2010] [Revised: 01/19/2011] [Accepted: 02/15/2011] [Indexed: 05/30/2023]
Abstract
Retinal detachment results in visual loss and requires surgical treatment. The risk of retinal detachment depends, among other factors, on the vitreous rheology, which varies with age. To date, the viscoelasticity of the vitreous body has only been measured in cadaver eyes. However, the ex vivo and in vivo viscoelasticity may differ as a result of the effect of intravitreal membranes. Therefore, an MRI method and appropriate postprocessing tools were developed to determine the vitreous deformation and viscoelastic properties in the eyes of living humans. Nineteen subjects (eight women and 11 men; mean age, 33 years; age range, 14-62 years) gazed at a horizontal sinusoidal moving target during the segmented acquisition of complementary spatial modulation of magnetization images. The center of the lens and the scleral insertion of the optic nerve defined the imaging plane. The vitreous deformation was tracked with a dedicated algorithm and fitted with the commonly used viscoelastic model to determine the model parameters: the modified Womersley number a and the phase angle b. The vitreous deformation was successfully quantified in all 17 volunteers having a monophasic vitreous. The mean and standard deviation of the model parameters were determined to be 5.5 ± 1.3 for a and -2.3 ± 0.2 for b. The correlation coefficient (-0.76) between a and b was significant. At the eye movement frequency used, the mean storage and loss moduli of the vitreous were around 3 ± 1 hPa. For two subjects, the vitreous deformation was clearly polyphasic: some compartments of the vitreous were gel-like and others were liquefied. The borders of these compartments corresponded to reported intravitreal membrane patterns. Thus, the deformation of the vitreous can now be determined in situ, leaving the structure of the intravitreal membranes intact. Their effect on vitreous dynamics challenges actual vitreous viscoelastic models. The determination of the vitreous deformation will aid in the quantification of local vitreous stresses and their correlation with retinal detachment.
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Affiliation(s)
- Marco Piccirelli
- Branco-Weiss Laboratory for Social and Neural Systems Research, Empirical Research in Economics, University of Zurich, Zurich, Switzerland.
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Balachandran RK, Roychowdhury J, Dorfman KD, Barocas VH. Telescopic time-scale bridging for modeling dispersion in rapidly oscillating flows. AIChE J 2011. [DOI: 10.1002/aic.12721] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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76
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Baino F. Towards an ideal biomaterial for vitreous replacement: Historical overview and future trends. Acta Biomater 2011; 7:921-35. [PMID: 21050899 DOI: 10.1016/j.actbio.2010.10.030] [Citation(s) in RCA: 77] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2010] [Revised: 10/22/2010] [Accepted: 10/27/2010] [Indexed: 02/03/2023]
Abstract
Removal of the natural vitreous body from the eye and its substitution with a tamponade agent may be necessary in cases of complicated retinal detachment. Many materials have been variously proposed and tested over the years in an attempt to find an ideal vitreous substitute. This review highlights the evolution of research in the field of vitreous replacement and chronicles the main advances that have been made in such a context. The suitability and limitations of vitreous tamponade agents and substitutes in current clinical use are examined, and the future promise of experimentally tested biomaterials are described and discussed. Future trends in research are also considered and, specifically, the great potential of polymeric hydrogels is emphasized, as they seem to be very effective in closely mimicking the features of the natural vitreous and they could successfully act as long-term vitreous substitutes without inducing clinical complications in the patient's eye.
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Affiliation(s)
- Francesco Baino
- Materials Science and Chemical Engineering Department, Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Torino, Italy.
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77
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Rheology of the vitreous gel: Effects of macromolecule organization on the viscoelastic properties. J Biomech 2011; 44:419-23. [DOI: 10.1016/j.jbiomech.2010.10.002] [Citation(s) in RCA: 73] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2010] [Revised: 10/02/2010] [Accepted: 10/06/2010] [Indexed: 11/23/2022]
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78
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Contribution of saccadic motion to intravitreal drug transport: theoretical analysis. Pharm Res 2011; 28:1049-64. [PMID: 21258958 DOI: 10.1007/s11095-010-0356-7] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2010] [Accepted: 12/15/2010] [Indexed: 10/18/2022]
Abstract
PURPOSE The vitreous humor liquefies with age and readily sloshes during eye motion. The objective was to develop a computational model to determine the effect of sloshing on intravitreal drug transport for transscleral and intra-vitreal drug sources at various locations METHODS A finite element model based on a telescopic implicit envelope tracking scheme was developed to model drug dispersion. Flow velocities due to saccadic oscillations were solved for and were used to simulate drug dispersion. RESULTS Saccades induced a three-dimensional flow field that indicates intense drug dispersion in the vitreous. Model results showed that the time scale for transport decreased for the sloshing vitreous when compared to static vitreous. Macular concentrations for the sloshing vitreous were found be much higher than that for the static vitreous. For low viscosities the position of the intravitreal source did not have a big impact on drug distribution. CONCLUSION Model results show that care should be taken when extrapolating animal data, which are mostly done on intact vitreous, to old patients whose vitreous might be a liquid. The decrease in drug transport time scales and changes in localized concentrations should be considered when deciding on treatment modalities and dosing strategies.
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79
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Juan T, Hubschman JP, Eldredge JD. A Computational Study of the Flow Through a Vitreous Cutter. J Biomech Eng 2010; 132:121005. [DOI: 10.1115/1.4002796] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Vitrectomy is an ophthalmic microsurgical procedure that removes part or all of the vitreous humor from the eye. The procedure uses a vitreous cutter consisting of a narrow shaft with a small orifice at the end through which the humor is aspirated by an applied suction. An internal guillotine oscillates back and forth across the orifice to alter the local shear response of the humor. In this work, a computational study of the flow in a vitreous cutter is conducted in order to gain better understanding of the vitreous behavior and provide guidelines for a new vitreous cutter design. The flow of a Newtonian surrogate of vitreous in a two-dimensional analog geometry is investigated using a finite difference-based immersed boundary method with an algebraically formulated fractional-step method. A series of numerical experiments is performed to evaluate the impact of cutting rate, aspiration pressure, and opening/closing transition on the vitreous cutter flow rate and transorifice pressure variation during vitrectomy. The mean flow rate is observed to increase approximately linearly with aspiration pressure and also increase nearly linearly with duty cycle. A study of time-varying flow rate, velocity field, and vorticity illuminates the flow behavior during each phase of the cutting cycle and shows that the opening/closing transition plays a key role in improving the vitreous cutter’s efficacy and minimizing the potential damage to surrounding tissue. The numerical results show similar trend in flow rate as previous in vitro experiments using water and balanced saline solution and also demonstrate that high duty cycle and slow opening/closing phases lead to high flow rate and minor disturbance to the eye during vitrectomy, which are the design requirements of an ideal vitreous cutter.
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Affiliation(s)
- Tingting Juan
- Department of Mechanical and Aerospace Engineering, University of California, Los Angeles, CA 90095
| | - Jean-Pierre Hubschman
- Jules Stein Eye Institute, Department of Ophthalmology, University of California, Los Angeles, CA 90025
| | - Jeff D. Eldredge
- Department of Mechanical and Aerospace Engineering, University of California, Los Angeles, CA 90095
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Repetto R, Tatone A, Testa A, Colangeli E. Traction on the retina induced by saccadic eye movements in the presence of posterior vitreous detachment. Biomech Model Mechanobiol 2010; 10:191-202. [DOI: 10.1007/s10237-010-0226-6] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2009] [Accepted: 05/12/2010] [Indexed: 01/12/2023]
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81
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Stocchino A, Repetto R, Siggers JH. Mixing processes in the vitreous chamber induced by eye rotations. Phys Med Biol 2009; 55:453-67. [DOI: 10.1088/0031-9155/55/2/008] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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82
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Gisladottir S, Loftsson T, Stefansson E. Diffusion characteristics of vitreous humour and saline solution follow the Stokes Einstein equation. Graefes Arch Clin Exp Ophthalmol 2009; 247:1677-84. [PMID: 19639333 DOI: 10.1007/s00417-009-1141-3] [Citation(s) in RCA: 70] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2008] [Accepted: 06/27/2009] [Indexed: 11/25/2022] Open
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Repetto R, Siggers JH, Stocchino A. Mathematical model of flow in the vitreous humor induced by saccadic eye rotations: effect of geometry. Biomech Model Mechanobiol 2009; 9:65-76. [PMID: 19471979 DOI: 10.1007/s10237-009-0159-0] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2008] [Accepted: 04/27/2009] [Indexed: 10/20/2022]
Abstract
Saccadic eye rotations induce a flow in the vitreous humor of the eye. Any such flow is likely to have a significant influence on the dispersion of drugs injected into the vitreous chamber. The shape of this chamber deviates from a perfect sphere by up to 10-20% of the radius, which is predominantly due to an indentation caused by the lens. In this paper we investigate theoretically the effect of the domain shape upon the flow field generated by saccades by considering an idealized model. The posterior chamber geometry is assumed to be a sphere with a small indentation, undergoing prescribed small-amplitude sinusoidal torsional oscillations, and, as an initial step towards understanding the problem, we treat the vitreous humor as a Newtonian fluid filling the chamber. The latter assumption applies best in the case of a liquefied vitreous or a tamponade fluid introduced in the vitreous chamber after vitrectomy. We find the flow field in terms of vector spherical harmonics, focusing on the deviation from the flow that would be obtained in a perfect sphere. The flow induced by the departure of the domain geometry from the spherical shape has an oscillating component at leading order and a smaller-amplitude steady streaming flow. The oscillating component includes a circulation cell formed every half-period, which migrates from the indentation towards the center of the domain where it disappears. The steady component has two counter-rotating circulations in the anterior part of the domain. These findings are in good qualitative agreement with the experimental results of Stocchino et al. (Phys Med Biol 52:2021-2034, 2007). Our results predict a significant reduction in the expected time for drug dispersal across the eye compared with the situation in which there is no fluid flow present.
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Affiliation(s)
- R Repetto
- Department of Engineering of Structures, Water and Soil, University of L'Aquila, L'Aquila, Italy.
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84
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Hans SA, Bawab SY, Woodhouse ML. A finite element infant eye model to investigate retinal forces in shaken baby syndrome. Graefes Arch Clin Exp Ophthalmol 2008; 247:561-71. [PMID: 19052768 DOI: 10.1007/s00417-008-0994-1] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2008] [Revised: 10/10/2008] [Accepted: 10/29/2008] [Indexed: 10/21/2022] Open
Abstract
BACKGROUND Shaken baby syndrome (SBS) is a form of abuse in which an infant, typically 6 months or less, is held and submitted to repeated acceleration-deceleration forces. One of the indicators of abuse is bilateral retinal hemorrhaging. A computational model of an infant eye, using the finite element method, is built in order to assess forces at the posterior retina for a shaking and an impact motions. METHOD The eye model is based on histological studies, diagrams, and materials from previous literature. Motions are applied to the model to simulate a four-cycle shaking motion in 1 second with maximum extension/flexion of the neck. The retinal forces of the shaking motion, at the posterior eye, are compared to an impact pulse (60G) simulating a fall for a total duration of 100 ms. RESULTS The shaking motion, for the first cycle, shows retinal force means at the posterior eye to be around 0.08 N sustained from the time range of 50 to 200 ms, into the shake, with a peak in excess of 0.2 N. The impulse, area under the curve, is 15 N-ms for 250 msec for the first cycle. The impact simulation reveals a mean retinal force around 0.025 N for a time range of 0 to 26 ms, with a peak force around 0.11 N. Moreover, the impulse for the impact simulation is 13 times lower than the shaking motion. CONCLUSION The results suggest that shaking alone may be enough to cause retinal hemorrhaging, as there are more sustained and higher forces in the posterior retina, compared to an impact due to a fall. This is in part due to the optic nerve causing more localized stresses in a shaking motion than an impact.
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Affiliation(s)
- Steven Alex Hans
- Department of Mechanical Engineering, Old Dominion University, Norfolk, VA 23529-0247, USA.
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85
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In situformation of hydrogels as vitreous substitutes: Viscoelastic comparison to porcine vitreous. J Biomed Mater Res A 2008; 87:656-65. [DOI: 10.1002/jbm.a.31769] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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86
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Physiology of vitreous surgery. Graefes Arch Clin Exp Ophthalmol 2008; 247:147-63. [PMID: 19034481 DOI: 10.1007/s00417-008-0980-7] [Citation(s) in RCA: 185] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2008] [Accepted: 10/06/2008] [Indexed: 12/11/2022] Open
Abstract
Vitreous surgery has various physiological and clinical consequences, both beneficial and harmful. Vitrectomy reduces the risk of retinal neovascularization, while increasing the risk of iris neovascularization, reduces macular edema and stimulates cataract formation. These clinical consequences may be understood with the help of classical laws of physics and physiology. The laws of Fick, Stokes-Einstein and Hagen-Poiseuille state that molecular transport by diffusion or convection is inversely related to the viscosity of the medium. When the vitreous gel is replaced with less viscous saline, the transport of all molecules, including oxygen and cytokines, is facilitated. Oxygen transport to ischemic retinal areas is improved, as is clearance of VEGF and other cytokines from these areas, thus reducing edema and neovascularization. At the same time, oxygen is transported faster down a concentration gradient from the anterior to the posterior segment, while VEGF moves in the opposite direction, making the anterior segment less oxygenated and with more VEGF, stimulating iris neovascularization. Silicone oil is the exception that proves the rule: it is more viscous than vitreous humour, re-establishes the transport barrier to oxygen and VEGF, and reduces the risk for iris neovascularization in the vitrectomized-lentectomized eye. Modern vitreous surgery involves a variety of treatment options in addition to vitrectomy itself, such as photocoagulation, anti-VEGF drugs, intravitreal steroids and release of vitreoretinal traction. A full understanding of these treatment modalities allows sensible combination of treatment options. Retinal photocoagulation has repeatedly been shown to improve retinal oxygenation, as does vitrectomy. Oxygen naturally reduces VEGF production and improves retinal hemodynamics. The VEGF-lowering effect of photocoagulation and vitrectomy can be augmented with anti-VEGF drugs and the permeability effect of VEGF reduced with corticosteroids. Starling's law explains vasogenic edema, which is controlled by osmotic and hydrostatic gradients between vessel and tissue. It explains the effect of VEGF-induced vascular permeability changes on plasma protein leakage and the osmotic gradient between vessel and tissue. At the same time, it takes into account hemodynamic changes that affect the hydrostatic gradient. This includes the influence of arterial blood pressure, and the effect oxygen (laser treatment) has in constricting retinal arterioles, increasing their resistance, and thus reducing the hydrostatic pressure in the microcirculation. Reduced capillary hydrostatic pressure and increased osmotic gradient reduce water fluxes from vessel to tissue and reduce edema. Finally, Newton's third law explains that vitreoretinal traction decreases hydrostatic tissue pressure in the retina, increases the pressure gradient between vessel and tissue, and stimulates water fluxes from vessel into tissue, leading to edema.
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Giblin FJ, Quiram PA, Leverenz VR, Baker RM, Dang L, Trese MT. Enzyme-induced posterior vitreous detachment in the rat produces increased lens nuclear pO2 levels. Exp Eye Res 2008; 88:286-92. [PMID: 18835558 DOI: 10.1016/j.exer.2008.09.003] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2008] [Revised: 08/26/2008] [Accepted: 09/04/2008] [Indexed: 11/28/2022]
Abstract
It has been proposed that disruption of normal vitreous humor may permit O(2) to travel more easily from the retina to the center of the lens where it may cause nuclear cataract (Barbazetto, I.A., Liang, J., Chang, S., Zheng, L., Spector, A., Dillon, J.P., 2004. Oxygen tension in the rabbit lens and vitreous before and after vitrectomy. Exp. Eye Res. 78, 917-924; Harocopos, G.J., Shui, Y.B., McKinnon, M., Holekamp, N.M., Gordon, M.O., Beebe, D.C., 2004. Importance of vitreous liquefaction in age-related cataract. Invest. Ophthalmol. Vis. Sci. 45, 77-85). In the present study, we injected enzymes intravitreally into guinea pigs (which possess an avascular retina) and rats (which possess a vascular retina) to produce either vitreous humor liquefaction plus a posterior vitreous detachment (PVD) (with use of microplasmin) or vitreous humor liquefaction only (with use of hyaluronidase), and 1-2 weeks later measured lens nuclear pO(2) levels in vivo using a platinum-based fluorophore O(2) sensor (Oxford-Optronix, Ltd.). Experiments were also conducted in which the animals were allowed to breathe 100% O(2) following intravitreal injection with either microplasmin or hyaluronidase in order to investigate possible effects on O(2) exchange within the eye. Injection of guinea pigs with either of the two enzymes produced no significant differences in lens pO(2) levels 1-2 weeks later, compared to controls. However, for the rat, injection of microplasmin produced a 68% increase in O(2) level in the center of the lens, compared to the controls (5.6mm Hg increasing to 9.4mm Hg, p<0.05), with no corresponding effect observed following similar use of hyaluronidase. Treatment of guinea pigs with microplasmin dramatically accelerated movement of O(2) across the vitreal space when the animals were later allowed to breathe 100% O(2) (for example, O(2) traveled to a location directly behind the lens 5x faster than control; p<0.01); however, the effect following treatment with hyaluronidase was significantly less. When microplasmin-injected rats breathed 100% O(2), the time required for O(2) to reach the center of the lens was 3x faster than control (0.4 min compared to 1.4 min, p<0.01). The results have implication with regard to the occurrence of age-related PVD in the human, and a possible acceleration of maturity-onset nuclear cataract. In addition, enzymatic creation of a PVD to increase the rate of O(2) exchange within the vitreal space may have potential application for treatment of retinal ischemic disease.
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Affiliation(s)
- F J Giblin
- Eye Research Institute, Oakland University, Rochester, MI 48309-4480, USA.
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Barar J, Javadzadeh AR, Omidi Y. Ocular novel drug delivery: impacts of membranes and barriers. Expert Opin Drug Deliv 2008; 5:567-81. [PMID: 18491982 DOI: 10.1517/17425247.5.5.567] [Citation(s) in RCA: 176] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
BACKGROUND Ocular drug delivery is an extremely challenging area due to its restrictive barrier functionalities. OBJECTIVE Drug transport via corneal/non-corneal routes involves several intricate biological processes such as drug penetration across the ocular barriers and transfer to the anterior or posterior chambers, thus the influence of these processes on the pharmacotherapy of the eye should be fully addressed. METHODS To pursue the impacts of such impediments in novel drug therapy, recent publications were reviewed regarding advanced strategies such as nanomedicines. CONCLUSION The ocular barriers are highly specialized and selectively control the inward/outward traverse of compounds, hence a better understanding of these biological obstacles would provide a platform to advance ophthalmic drug therapy towards specified delivery/targeting with minimal adverse consequences.
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Affiliation(s)
- Jaleh Barar
- Cellular & Molecular Pharmaceutics, Tabriz University of Medical Sciences, Research Centre for Pharmaceutical Nanotechnology, Faculty of Pharmacy, Tabriz, Iran
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89
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Nickerson CS, Park J, Kornfield JA, Karageozian H. Rheological properties of the vitreous and the role of hyaluronic acid. J Biomech 2008; 41:1840-6. [DOI: 10.1016/j.jbiomech.2008.04.015] [Citation(s) in RCA: 100] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2006] [Revised: 03/24/2008] [Accepted: 04/08/2008] [Indexed: 11/29/2022]
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90
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Kummer MP, Abbott JJ, Dinser S, Nelson BJ. Artificial Vitreous Humor for In Vitro Experiments. ACTA ACUST UNITED AC 2007; 2007:6407-10. [DOI: 10.1109/iembs.2007.4353822] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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91
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Stocchino A, Repetto R, Cafferata C. Eye rotation induced dynamics of a Newtonian fluid within the vitreous cavity: the effect of the chamber shape. Phys Med Biol 2007; 52:2021-34. [PMID: 17374925 DOI: 10.1088/0031-9155/52/7/016] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The dynamics of the vitreous body induced by eye rotations is studied experimentally. In particular, we consider the case in which the vitreous cavity is filled by a Newtonian fluid, either because the vitreous is liquefied or because it has been replaced, after vitrectomy, by a viscous fluid. We employ a rigid Perspex container which models, in a magnified scale, the vitreous cavity of the human eye. The shape of the cavity closely resembles that of the real vitreous chamber; in particular, the anterior part of the container is concave in order to model the presence of the eye lens. The container is filled with glycerol and is mounted on the shaft of a computer-controlled motor which rotates according to a periodic time law. PIV (particle image velocimetry) measurements are taken on the equatorial plane orthogonal to the axis of rotation. The experimental measurements show that the velocity field is strongly influenced by the deformed geometry of the domain. In particular, the formation of a vortex in the vicinity of the lens, which migrates in time towards the core of the domain, is invariably observed. The vortex path is tracked in time by means of a vortex identification technique and it is found that it is significantly influenced by the Womersley number of the flow. Particle trajectories are computed from the PIV measurements. Particles initially located at different positions on the equatorial horizontal plane (perpendicular to the axis of rotation) tend to concentrate in narrow regions adjacent to the lens, thus suggesting the existence, in such regions, of a vertical fluid ejection. Such a strong flow three-dimensionality, which is essentially induced by the irregular shape of the domain, may play a significant role in the mixing processes taking place inside the eye globe. The tangential stresses acting on the rigid boundary of the domain are also computed from the experimental measurements showing that regions subject to particularly intense stresses exist along the boundary close to the lens.
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92
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Barton KA, Shui YB, Petrash JM, Beebe DC. Comment on: the Stokes-Einstein equation and the physiological effects of vitreous surgery. ACTA ACUST UNITED AC 2007; 85:339-40. [PMID: 17362364 PMCID: PMC2585384 DOI: 10.1111/j.1600-0420.2007.00902.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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93
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Stefánsson E, Loftsson T. The Stokes-Einstein equation and the physiological effects of vitreous surgery. ACTA ACUST UNITED AC 2007; 84:718-9. [PMID: 17083526 DOI: 10.1111/j.1600-0420.2006.00778.x] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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94
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Schurz J. Rheology of Synovial Fluids and Substitute Polymers. JOURNAL OF MACROMOLECULAR SCIENCE PART A-PURE AND APPLIED CHEMISTRY 2006. [DOI: 10.1080/10601329608010919] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Affiliation(s)
- Josef Schurz
- a Institut for Physical Chemistry Karl-Franzens-University Graz , Heinrichstrasse 28, A-8010 , Graz , Austria
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95
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Cirovic S, Bhola RM, Hose DR, Howard IC, Lawford PV, Marr JE, Parsons MA. Computer modelling study of the mechanism of optic nerve injury in blunt trauma. Br J Ophthalmol 2006; 90:778-83. [PMID: 16421184 PMCID: PMC1860230 DOI: 10.1136/bjo.2005.086538] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 01/03/2006] [Indexed: 11/04/2022]
Abstract
AIM The potential causes of the optic nerve injury as a result of blunt object trauma, were investigated using a computer model. METHODS A finite element model of the eye, the optic nerve, and the orbit with its content was constructed to simulate blunt object trauma. We used a model of the first phalanx of the index finger to represent the blunt body. The trauma was simulated by impacting the blunt body at the surface between the globe and the orbital wall at velocities between 2-5 m/s, and allowing it to penetrate 4-10 mm below the orbital rim. RESULTS The impact caused rotations of the globe of up to 5000 degrees /s, lateral velocities of up to 1 m/s, and intraocular pressures (IOP) of over 300 mm Hg. The main stress concentration was observed at the insertion of the nerve into the sclera, at the side opposite to the impact. CONCLUSIONS The results suggest that the most likely mechanisms of injury are rapid rotation and lateral translation of the globe, as well as a dramatic rise in the IOP. The strains calculated in the study should be sufficiently high to cause axonal damage and even the avulsion of the nerve. Finite element computer modelling has therefore provided important insights into a clinical scenario that cannot be replicated in human or animal experiments.
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Affiliation(s)
- S Cirovic
- Ophthalmic Sciences Unit, Academic Unit of Ophthalmology and Orthoptics, Royal Hallamshire Hospital, Sheffield S10 2JF, UK.
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96
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Ter-Oganessian N, Quinn B, Pink DA, Boulbitch A. Active microrheology of networks composed of semiflexible polymers: computer simulation of magnetic tweezers. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2005; 72:041510. [PMID: 16383388 DOI: 10.1103/physreve.72.041510] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/23/2005] [Indexed: 05/05/2023]
Abstract
We have simulated the motion of a bead subjected to a constant force while embedded in a network of semiflexible polymers which can represent actin filaments. We find that the bead displacement obeys the power law x approximately t(alpha). After the initial stage characterized by the exponent alpha1 approximately 0.75, we find a different regime with alpha2 approximately 0.5. The response in this regime is linear in force and scales with the polymer concentration as c(-1.4). We find that the polymers pile up ahead of the moving bead, while behind it the polymer density is reduced. We show that the force resisting the bead motion is due to steric repulsion exerted by the polymers on the front hemisphere of the bead.
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Affiliation(s)
- Nikita Ter-Oganessian
- Department for Biophysics E22, Technical University Munich, James-Franck-Strasse 1, D-85747 Garching, Germany
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97
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Repetto R, Stocchino A, Cafferata C. Experimental investigation of vitreous humour motion within a human eye model. Phys Med Biol 2005; 50:4729-43. [PMID: 16177501 DOI: 10.1088/0031-9155/50/19/021] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
We present an experimental study of the vitreous motion induced by saccadic eye movements. A magnified model of the vitreous chamber has been employed, consisting of a spherical cavity carved in a perspex cylindrical container, which is able to rotate with a prescribed time law. Care has been taken to correctly reproduce real saccadic eye movements. The spherical cavity is filled with glycerol and the flow field is measured on the equatorial plane orthogonal to the axis of rotation, through the PIV technique. Visualizations of the fully three-dimensional flow suggest that it essentially occurs on planes perpendicular to the axis of rotation, the motion orthogonal to such planes being smaller by three to four orders of magnitude. Theoretical results, based on a simplified solution, are in very good agreement with the experimental findings. The maximum value of the shear stress at the wall, which is thought to play a possibly important role in the pathogenesis of retinal detachment, does not significantly depend on the amplitude of saccadic movements. This suggests that relatively small eye rotations, being much more frequent than large movements, are mainly responsible for vitreous stresses on the retina. Results also illustrate the dependence of the maximum shear stress at the wall from the vitreous viscosity.
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Affiliation(s)
- Rodolfo Repetto
- Dipartimento di Ingegneria delle Strutture, delle Acque e del Terreno, University of L'Aquila, Italy.
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98
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Zamir EA, Taber LA. Material Properties and Residual Stress in the Stage 12 Chick Heart During Cardiac Looping. J Biomech Eng 2005; 126:823-30. [PMID: 15796341 DOI: 10.1115/1.1824129] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
During the morphogenetic process of cardiac looping, the initially straight cardiac tube bends and twists into a curved tube. The biophysical mechanisms that drive looping remain unknown, but the process clearly involves mechanical forces. Hence, it is important to determine mechanical properties of the early heart, which is a muscle-wrapped tube consisting primarily of a thin outer layer of myocardium surrounding a thick extracellular matrix compartment known as cardiac jelly. In this work, we used microindentation experiments and finite element modeling, combined with an inverse computational method, to determine constitutive relations for the myocardium and cardiac jelly at the outer curvature of stage 12 chick hearts. Material coefficients for exponential strain-energy density functions were found by fitting force-displacement and surface displacement data near the indenter. Residual stress in the myocardium also was estimated. These results should be useful for computational models of the looping heart.
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Affiliation(s)
- Evan A Zamir
- Department of Biomedical Engineering, Washington University, St. Louis, MO 63130, USA
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99
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Abstract
Mechanical and chemical models of vasculogenesis are critically reviewed with an emphasis on their ability to predict experimentally measured quantities. Final remarks suggest a possibility to merge the capabilities of different models into a unified approach.
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Affiliation(s)
- D. Ambrosi
- Department of Mathematics, Politecnico di Torino, Corso Duca degli Abruzzi, 24 10129, Torino, Italy
| | - F. Bussolino
- Division of Molecular Angiogenesis, Institute for Cancer Research and Treatment, 10060 Candiolo, Torino, Italy
| | - L. Preziosi
- Department of Mathematics, Politecnico di Torino, Corso Duca degli Abruzzi, 24 10129, Torino, Italy
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100
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Yesin KB, Exner P, Vollmers K, Nelson BJ. Design and control of in-vivo magnetic microrobots. MEDICAL IMAGE COMPUTING AND COMPUTER-ASSISTED INTERVENTION : MICCAI ... INTERNATIONAL CONFERENCE ON MEDICAL IMAGE COMPUTING AND COMPUTER-ASSISTED INTERVENTION 2005; 8:819-26. [PMID: 16685922 DOI: 10.1007/11566465_101] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
This paper investigates fundamental design, modeling and control issues related to untethered biomedical microrobots guided inside the human body through external magnetic fields. Immediate application areas for these microrobots include cardiovascular, intraocular and inner-ear diagnosis and surgery. A prototype microrobot and steering system are introduced. Experimental results on fluid drag and magnetization properties of the robots are presented along with an analysis of required magnetic fields for application inside blood vessels and vitreous humor.
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Affiliation(s)
- K Berk Yesin
- Institute of Robotics and Intelligent Systems, Swiss Federal Institute of Technology (ETH) Zurich, Switzerland.
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