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Faber J, Hinrichsen J, Greiner A, Reiter N, Budday S. Tissue-Scale Biomechanical Testing of Brain Tissue for the Calibration of Nonlinear Material Models. Curr Protoc 2022; 2:e381. [PMID: 35384412 DOI: 10.1002/cpz1.381] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2021] [Revised: 01/14/2022] [Indexed: 06/14/2023]
Abstract
Brain tissue is one of the most complex and softest tissues in the human body. Due to its ultrasoft and biphasic nature, it is difficult to control the deformation state during biomechanical testing and to quantify the highly nonlinear, time-dependent tissue response. In numerous experimental studies that have investigated the mechanical properties of brain tissue over the last decades, stiffness values have varied significantly. One reason for the observed discrepancies is the lack of standardized testing protocols and corresponding data analyses. The tissue properties have been tested on different length and time scales depending on the testing technique, and the corresponding data have been analyzed based on simplifying assumptions. In this review, we highlight the advantage of using nonlinear continuum mechanics based modeling and finite element simulations to carefully design experimental setups and protocols as well as to comprehensively analyze the corresponding experimental data. We review testing techniques and protocols that have been used to calibrate material model parameters and discuss artifacts that might falsify the measured properties. The aim of this work is to provide standardized procedures to reliably quantify the mechanical properties of brain tissue and to more accurately calibrate appropriate constitutive models for computational simulations of brain development, injury and disease. Computational models can not only be used to predictively understand brain tissue behavior, but can also serve as valuable tools to assist diagnosis and treatment of diseases or to plan neurosurgical procedures. © 2022 The Authors. Current Protocols published by Wiley Periodicals LLC.
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Affiliation(s)
- Jessica Faber
- Friedrich-Alexander-Universität Erlangen-Nürnberg, Institute of Applied Mechanics, Egerlandstraße 5, 91058 Erlangen, Germany
| | - Jan Hinrichsen
- Friedrich-Alexander-Universität Erlangen-Nürnberg, Institute of Applied Mechanics, Egerlandstraße 5, 91058 Erlangen, Germany
| | - Alexander Greiner
- Friedrich-Alexander-Universität Erlangen-Nürnberg, Institute of Applied Mechanics, Egerlandstraße 5, 91058 Erlangen, Germany
| | - Nina Reiter
- Friedrich-Alexander-Universität Erlangen-Nürnberg, Institute of Applied Mechanics, Egerlandstraße 5, 91058 Erlangen, Germany
| | - Silvia Budday
- Friedrich-Alexander-Universität Erlangen-Nürnberg, Institute of Applied Mechanics, Egerlandstraße 5, 91058 Erlangen, Germany
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2
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Rohanifar M, Johnston BB, Davis AL, Guang Y, Nommensen K, Fitzpatrick JA, Pham CN, Setton LA. Hydraulic permeability and compressive properties of porcine and human synovium. Biophys J 2022; 121:575-581. [PMID: 35032457 PMCID: PMC8874024 DOI: 10.1016/j.bpj.2022.01.008] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2021] [Revised: 12/21/2021] [Accepted: 01/11/2022] [Indexed: 11/02/2022] Open
Abstract
The synovium is a multilayer connective tissue separating the intra-articular spaces of the diarthrodial joint from the extra-synovial vascular and lymphatic supply. Synovium regulates drug transport into and out of the joint, yet its material properties remain poorly characterized. Here, we measured the compressive properties (aggregate modulus, Young's modulus, and Poisson's ratio) and hydraulic permeability of synovium with a combined experimental-computational approach. A compressive aggregate modulus and Young's modulus for the solid phase of synovium were quantified from linear regression of the equilibrium confined and unconfined compressive stress upon strain, respectively (HA = 4.3 ± 2.0 kPa, Es = 2.1 ± 0.75, porcine; HA = 3.1 ± 2.0 kPa, Es = 2.8 ± 1.7, human). Poisson's ratio was estimated to be 0.39 and 0.40 for porcine and human tissue, respectively, from moduli values in a Monte Carlo simulation. To calculate hydraulic permeability, a biphasic finite element model's predictions were numerically matched to experimental data for the time-varying ramp and hold phase of a single increment of applied strain (k = 7.4 ± 4.1 × 10-15 m4/N.s, porcine; k = 7.4 ± 4.3 × 10-15 m4/N.s, human). We can use these newly measured properties to predict fluid flow gradients across the tissue in response to previously reported intra-articular pressures. These values for material constants are to our knowledge the first available measurements in synovium that are necessary to better understand drug transport in both healthy and pathological joints.
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Affiliation(s)
- Milad Rohanifar
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, Missouri
| | - Benjamin B. Johnston
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, Missouri
| | - Alexandra L. Davis
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, Missouri
| | - Young Guang
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, Missouri
| | - Kayla Nommensen
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, Missouri
| | - James A.J. Fitzpatrick
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, Missouri,Department of Neuroscience and Cell Biology & Physiology, Washington University School of Medicine, St. Louis, Missouri
| | - Christine N. Pham
- Department of Medicine, Division of Rheumatology, Washington University School of Medicine, St. Louis, Missouri
| | - Lori A. Setton
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, Missouri,Department of Orthopedic Surgery, Washington University School of Medicine, St. Louis, Missouri,Corresponding author
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Tiwari S, Kazemi-Moridani A, Zheng Y, Barney CW, McLeod KR, Dougan CE, Crosby AJ, Tew GN, Peyton SR, Cai S, Lee JH. Seeded laser-induced cavitation for studying high-strain-rate irreversible deformation of soft materials. SOFT MATTER 2020; 16:9006-9013. [PMID: 33021618 DOI: 10.1039/d0sm00710b] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Characterizing the high-strain-rate and high-strain mechanics of soft materials is critical to understanding the complex behavior of polymers and various dynamic injury mechanisms, including traumatic brain injury. However, their dynamic mechanical deformation under extreme conditions is technically difficult to quantify and often includes irreversible damage. To address such challenges, we investigate an experimental method, which allows quantification of the extreme mechanical properties of soft materials using ultrafast stroboscopic imaging of highly reproducible laser-induced cavitation events. As a reference material, we characterize variably cross-linked polydimethylsiloxane specimens using this method. The consistency of the laser-induced cavitation is achieved through the introduction of laser absorbing seed microspheres. Based on a simplified viscoelastic model, representative high-strain-rate shear moduli and viscosities of the soft specimens are quantified across different degrees of crosslinking. The quantified rheological parameters align well with the time-temperature superposition prediction of dynamic mechanical analysis. The presented method offers significant advantages with regard to quantifying high-strain rate, irreversible mechanical properties of soft materials and tissues, compared to other methods that rely upon the cyclic dynamics of cavitation. These advances are anticipated to aid in the understanding of how damage and injury develop in soft materials and tissues.
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Affiliation(s)
- Sacchita Tiwari
- Department of Mechanical and Industrial Engineering, University of Massachusetts, Amherst, MA 01003, USA.
| | - Amir Kazemi-Moridani
- Department of Mechanical and Industrial Engineering, University of Massachusetts, Amherst, MA 01003, USA.
| | - Yue Zheng
- Department of Mechanical and Aerospace Engineering, University of California at San Diego, La Jolla, CA 9209, USA
| | - Christopher W Barney
- Polymer Science and Engineering Department, University of Massachusetts, Amherst, MA 01003, USA
| | - Kelly R McLeod
- Polymer Science and Engineering Department, University of Massachusetts, Amherst, MA 01003, USA
| | - Carey E Dougan
- Department of Chemical Engineering, University of Massachusetts, Amherst, MA 01003, USA
| | - Alfred J Crosby
- Polymer Science and Engineering Department, University of Massachusetts, Amherst, MA 01003, USA
| | - Gregory N Tew
- Polymer Science and Engineering Department, University of Massachusetts, Amherst, MA 01003, USA
| | - Shelly R Peyton
- Department of Chemical Engineering, University of Massachusetts, Amherst, MA 01003, USA
| | - Shengqiang Cai
- Department of Mechanical and Aerospace Engineering, University of California at San Diego, La Jolla, CA 9209, USA
| | - Jae-Hwang Lee
- Department of Mechanical and Industrial Engineering, University of Massachusetts, Amherst, MA 01003, USA.
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Rubiano A, Galitz C, Simmons CS. Mechanical Characterization by Mesoscale Indentation: Advantages and Pitfalls for Tissue and Scaffolds. Tissue Eng Part C Methods 2019; 25:619-629. [PMID: 30848168 DOI: 10.1089/ten.tec.2018.0372] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
Regenerative medicine and tissue engineering are hindered by the lack of consistent measurements and standards for the mechanical characterization of tissue and scaffolds. Indentation methods for soft matter are favored because of their compatibility with small, arbitrarily shaped samples, but contact mechanics models required to interpret data are often inappropriate for soft, viscous materials. In this study, we demonstrate indentation experiments on a variety of human biopsies, animal tissue, and engineered scaffolds, and we explore the complexities of fitting analytical models to these data. Although objections exist to using Hertz contact models for soft, viscoelastic biological materials since soft matter violates their original assumptions, we demonstrate the experimental conditions that enable consistency and comparability (regardless of arguable misappropriation). Appropriate experimental conditions involving sample hydration, the indentation depth, and the ratio of the probe size to sample thickness enable repeatable metrics that are valuable when comparing synthetic scaffolds and host tissue, and bounds on these parameters are carefully described and discussed. We have also identified a reliable quasistatic parameter that can be derived from indentation data to help researchers compare results across materials and experiments. Although Hertz contact mechanics and linear viscoelastic models may constitute oversimplification for biological materials, the reporting of such simple metrics alongside more complex models is expected to support researchers in tissue engineering and regenerative medicine by providing consistency across efforts to characterize soft matter. Impact Statement To engineer replacement tissue requires a deep understanding of its biomechanical properties. Mesoscale indentation (between micron and millimeter length scales) is well-suited to characterize tissue and engineered replacements as it accommodates small, oddly shaped samples. However, it is easy to run afoul of the assumptions for common contact models when working with biological materials. In this study, we describe experimental procedures and modeling approaches that allow researchers to take advantage of indentation for biomechanical characterization while minimizing its weaknesses.
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Affiliation(s)
- Andrés Rubiano
- Department of Mechanical and Aerospace Engineering, Herbert Wertheim College of Engineering, Gainesville, Florida
| | - Carly Galitz
- Department of Mathematics, College of Liberal Arts and Sciences, Gainesville, Florida
| | - Chelsey S Simmons
- Department of Mechanical and Aerospace Engineering, Herbert Wertheim College of Engineering, Gainesville, Florida.,J. Crayton Pruitt Family Department of Biomedical Engineering Herbert Wertheim College of Engineering, Gainesville, Florida.,Division of Cardiovascular Medicine, College of Medicine, University of Florida, Gainesville, Florida
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Kang W, Raphael M. Acceleration-induced pressure gradients and cavitation in soft biomaterials. Sci Rep 2018; 8:15840. [PMID: 30367099 PMCID: PMC6203720 DOI: 10.1038/s41598-018-34085-4] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2018] [Accepted: 10/02/2018] [Indexed: 12/23/2022] Open
Abstract
The transient, dynamic response of soft materials to mechanical impact has become increasingly relevant due to the emergence of numerous biomedical applications, e.g., accurate assessment of blunt injuries to the human body. Despite these important implications, acceleration-induced pressure gradients in soft materials during impact and the corresponding material response, from small deformations to sudden bubble bursts, are not fully understood. Both through experiments and theoretical analyses, we empirically show, using collagen and agarose model systems, that the local pressure in a soft sample is proportional to the square of the sample depth in the impact direction. The critical acceleration that corresponds to bubble bursts increases with increasing gel stiffness. Bubble bursts are also highly sensitive to the initial bubble size, e.g., bubble bursts can occur only when the initial bubble diameter is smaller than a critical size (≈10 μm). Our study gives fundamental insight into the physics of injury mechanisms, from blunt trauma to cavitation-induced brain injury.
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Affiliation(s)
| | - Marc Raphael
- Naval Research Laboratory, Washington, DC, 20375, USA
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Yun S, Shin TH, Lee JH, Cho MH, Kim IS, Kim JW, Jung K, Lee IS, Cheon J, Park KI. Design of Magnetically Labeled Cells (Mag-Cells) for in Vivo Control of Stem Cell Migration and Differentiation. NANO LETTERS 2018; 18:838-845. [PMID: 29393650 DOI: 10.1021/acs.nanolett.7b04089] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Cell-based therapies are attractive for treating various degenerative disorders and cancer but delivering functional cells to the region of interest in vivo remains difficult. The problem is exacerbated in dense biological matrices such as solid tissues because these environments impose significant steric hindrances for cell movement. Here, we show that neural stem cells transfected with zinc-doped ferrite magnetic nanoparticles (ZnMNPs) can be pulled by an external magnet to migrate to the desired location in the brain. These magnetically labeled cells (Mag-Cells) can migrate because ZnMNPs generate sufficiently strong mechanical forces to overcome steric hindrances in the brain tissues. Once at the site of lesion, Mag-Cells show enhanced neuronal differentiation and greater secretion of neurotrophic factors than unlabeled control stem cells. Our study shows that ZnMNPs activate zinc-mediated Wnt signaling to facilitate neuronal differentiation. When implemented in a rodent brain stroke model, Mag-Cells led to significant recovery of locomotor performance in the impaired limbs of the animals. Our findings provide a simple magnetic method for controlling migration of stem cells with high therapeutic functions, offering a valuable tool for other cell-based therapies.
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Affiliation(s)
- Seokhwan Yun
- Brain Korea 21 Plus Project for Medical Science, Yonsei University College of Medicine , Seoul 03722, Korea
| | - Tae-Hyun Shin
- Center for NanoMedicine, Institute for Basic Science (IBS) , Seoul 03722, Korea
- Yonsei-IBS Institute, Yonsei University , Seoul 03722, Korea
- Department of Chemistry, Yonsei University , Seoul 03722, Korea
| | - Jae-Hyun Lee
- Center for NanoMedicine, Institute for Basic Science (IBS) , Seoul 03722, Korea
- Yonsei-IBS Institute, Yonsei University , Seoul 03722, Korea
- Department of Chemistry, Yonsei University , Seoul 03722, Korea
| | - Mi Hyeon Cho
- Center for NanoMedicine, Institute for Basic Science (IBS) , Seoul 03722, Korea
- Yonsei-IBS Institute, Yonsei University , Seoul 03722, Korea
- Department of Chemistry, Yonsei University , Seoul 03722, Korea
| | - Il-Sun Kim
- Department of Pediatrics, Severance Children's Hospital, Yonsei University College of Medicine , Seoul 03722, Korea
| | - Ji-Wook Kim
- Center for NanoMedicine, Institute for Basic Science (IBS) , Seoul 03722, Korea
- Yonsei-IBS Institute, Yonsei University , Seoul 03722, Korea
- Department of Chemistry, Yonsei University , Seoul 03722, Korea
| | - Kwangsoo Jung
- Department of Pediatrics, Severance Children's Hospital, Yonsei University College of Medicine , Seoul 03722, Korea
| | - Il-Shin Lee
- Department of Pediatrics, Severance Children's Hospital, Yonsei University College of Medicine , Seoul 03722, Korea
| | - Jinwoo Cheon
- Center for NanoMedicine, Institute for Basic Science (IBS) , Seoul 03722, Korea
- Yonsei-IBS Institute, Yonsei University , Seoul 03722, Korea
- Department of Chemistry, Yonsei University , Seoul 03722, Korea
| | - Kook In Park
- Brain Korea 21 Plus Project for Medical Science, Yonsei University College of Medicine , Seoul 03722, Korea
- Department of Pediatrics, Severance Children's Hospital, Yonsei University College of Medicine , Seoul 03722, Korea
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7
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Kang W, Adnan A, O'Shaughnessy T, Bagchi A. Cavitation nucleation in gelatin: Experiment and mechanism. Acta Biomater 2018; 67:295-306. [PMID: 29191509 DOI: 10.1016/j.actbio.2017.11.030] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2017] [Revised: 11/16/2017] [Accepted: 11/21/2017] [Indexed: 02/04/2023]
Abstract
Dynamic cavitation in soft materials is becoming increasingly relevant due to emerging medical implications such as the potential of cavitation-induced brain injury or cavitation created by therapeutic medical devices. However, the current understanding of dynamic cavitation in soft materials is still very limited, mainly due to lack of robust experimental techniques. To experimentally characterize cavitation nucleation under dynamic loading, we utilize a recently developed experimental instrument, the integrated drop tower system. This technique allows quantitative measurements of the critical acceleration (acr) that corresponds to cavitation nucleation while concurrently visualizing time evolution of cavitation. Our experimental results reveal that acr increases with increasing concentration of gelatin in pure water. Interestingly, we have observed the distinctive transition from a sharp increase (pure water to 1% gelatin) to a much slower rate of increase (∼10× slower) between 1% and 7.5% gelatin. Theoretical cavitation criterion predicts the general trend of increasing acr, but fails to explain the transition rates. As a likely mechanism, we consider concentration-dependent material properties and non-spherical cavitation nucleation sites, represented by pre-existing bubbles in gels, due to possible interplay between gelatin molecules and nucleation sites. This analysis shows that cavitation nucleation is very sensitive to the initial configuration of a bubble, i.e., a non-spherical bubble can significantly increase acr. This conclusion matches well with the experimentally observed liquid-to-gel transition in the critical acceleration for cavitation nucleation. STATEMENT OF SIGNIFICANCE From a medical standpoint, understanding dynamic cavitation within soft materials, i.e., tissues, is important as there are both potential injury implications (blast-induced cavitation within the brain) as well as treatments utilizing the phenomena (lithotripsy). In this regard, the main results of the present work are (1) quantitative characterization of cavitation nucleation in gelatin samples as a function of gel concentration utilizing well-controlled mechanical impacts and (2) mechanistic understanding of complex coupling between cavitation and liquid-/solid-like material properties of gel. The new capabilities of testing soft gels, which can be tuned to mimic material properties of target organs, at high loading rate conditions and accurately predicting their cavitation behavior are an important step towards developing reliable cavitation criteria in the scope of their biomedical applications.
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Affiliation(s)
- Wonmo Kang
- Leidos, Inc., Arlington, VA 22203, United States.
| | - Ashfaq Adnan
- University of Texas, Arlington, TX 76019, United States
| | | | - Amit Bagchi
- Naval Research Laboratory, Washington, DC 20375, United States
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Stewart DC, Rubiano A, Dyson K, Simmons CS. Mechanical characterization of human brain tumors from patients and comparison to potential surgical phantoms. PLoS One 2017; 12:e0177561. [PMID: 28582392 PMCID: PMC5459328 DOI: 10.1371/journal.pone.0177561] [Citation(s) in RCA: 64] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2017] [Accepted: 04/28/2017] [Indexed: 11/30/2022] Open
Abstract
While mechanical properties of the brain have been investigated thoroughly, the mechanical properties of human brain tumors rarely have been directly quantified due to the complexities of acquiring human tissue. Quantifying the mechanical properties of brain tumors is a necessary prerequisite, though, to identify appropriate materials for surgical tool testing and to define target parameters for cell biology and tissue engineering applications. Since characterization methods vary widely for soft biological and synthetic materials, here, we have developed a characterization method compatible with abnormally shaped human brain tumors, mouse tumors, animal tissue and common hydrogels, which enables direct comparison among samples. Samples were tested using a custom-built millimeter-scale indenter, and resulting force-displacement data is analyzed to quantify the steady-state modulus of each sample. We have directly quantified the quasi-static mechanical properties of human brain tumors with effective moduli ranging from 0.17–16.06 kPa for various pathologies. Of the readily available and inexpensive animal tissues tested, chicken liver (steady-state modulus 0.44 ± 0.13 kPa) has similar mechanical properties to normal human brain tissue while chicken crassus gizzard muscle (steady-state modulus 3.00 ± 0.65 kPa) has similar mechanical properties to human brain tumors. Other materials frequently used to mimic brain tissue in mechanical tests, like ballistic gel and chicken breast, were found to be significantly stiffer than both normal and diseased brain tissue. We have directly compared quasi-static properties of brain tissue, brain tumors, and common mechanical surrogates, though additional tests would be required to determine more complex constitutive models.
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Affiliation(s)
- Daniel C. Stewart
- J. Crayton Pruitt Family Department of Biomedical Engineering, University of Florida, Gainesville, Florida, United States of America
| | - Andrés Rubiano
- Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, Florida, United States of America
| | - Kyle Dyson
- Lillian S. Wells Department of Neurosurgery, University of Florida, Gainesville, Florida, United States of America
| | - Chelsey S. Simmons
- J. Crayton Pruitt Family Department of Biomedical Engineering, University of Florida, Gainesville, Florida, United States of America
- Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, Florida, United States of America
- Division of Cardiovascular Medicine, University of Florida, Gainesville, Florida, United States of America
- * E-mail:
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9
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Optical coherence tomography-based contact indentation for diaphragm mechanics in a mouse model of transforming growth factor alpha induced lung disease. Sci Rep 2017; 7:1517. [PMID: 28473708 PMCID: PMC5431417 DOI: 10.1038/s41598-017-01431-x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2016] [Accepted: 03/30/2017] [Indexed: 01/25/2023] Open
Abstract
This study tested the utility of optical coherence tomography (OCT)-based indentation to assess mechanical properties of respiratory tissues in disease. Using OCT-based indentation, the elastic modulus of mouse diaphragm was measured from changes in diaphragm thickness in response to an applied force provided by an indenter. We used a transgenic mouse model of chronic lung disease induced by the overexpression of transforming growth factor-alpha (TGF-α), established by the presence of pleural and peribronchial fibrosis and impaired lung mechanics determined by the forced oscillation technique and plethysmography. Diaphragm elastic modulus assessed by OCT-based indentation was reduced by TGF-α at both left and right lateral locations (p < 0.05). Diaphragm elastic modulus at left and right lateral locations were correlated within mice (r = 0.67, p < 0.01) suggesting that measurements were representative of tissue beyond the indenter field. Co-localised images of diaphragm after TGF-α overexpression revealed a layered fibrotic appearance. Maximum diaphragm force in conventional organ bath studies was also reduced by TGF-α overexpression (p < 0.01). Results show that OCT-based indentation provided clear delineation of diseased diaphragm, and together with organ bath assessment, provides new evidence suggesting that TGF-α overexpression produces impairment in diaphragm function and, therefore, an increase in the work of breathing in chronic lung disease.
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10
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Simulated blast overpressure induces specific astrocyte injury in an ex vivo brain slice model. PLoS One 2017; 12:e0175396. [PMID: 28403239 PMCID: PMC5389806 DOI: 10.1371/journal.pone.0175396] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2016] [Accepted: 03/25/2017] [Indexed: 12/14/2022] Open
Abstract
Exposure to explosive blasts can produce functional debilitation in the absence of brain pathology detectable at the scale of current diagnostic imaging. Transient (ms) overpressure components of the primary blast wave are considered to be potentially damaging to the brain. Astrocytes participate in neuronal metabolic maintenance, blood–brain barrier, regulation of homeostatic environment, and tissue remodeling. Damage to astrocytes via direct physical forces has the potential to disrupt local and global functioning of neuronal tissue. Using an ex vivo brain slice model, we tested the hypothesis that viable astrocytes within the slice could be injured simply by transit of a single blast wave consisting of overpressure alone. A polymer split Hopkinson pressure bar (PSHPB) system was adapted to impart a single positive pressure transient with a comparable magnitude to those that might be present inside the head. A custom built test chamber housing the brain tissue slice incorporated revised design elements to reduce fluid space and promote transit of a uniform planar waveform. Confocal microscopy, stereology, and morphometry of glial fibrillary acidic protein (GFAP) immunoreactivity revealed that two distinct astrocyte injury profiles were identified across a 4 hr post-test survival interval: (a) presumed conventional astrogliosis characterized by enhanced GFAP immunofluorescence intensity without significant change in tissue area fraction and (b) a process comparable to clasmatodendrosis, an autophagic degradation of distal processes that has not been previously associated with blast induced neurotrauma. Analysis of astrocyte branching revealed early, sustained, and progressive differences distinct from the effects of slice incubation absent overpressure testing. Astrocyte vulnerability to overpressure transients indicates a potential for significant involvement in brain blast pathology and emergent dysfunction. The testing platform can isolate overpressure injury phenomena to provide novel insight on physical and biological mechanisms.
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11
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Evaluation of the friction coefficient, the radial stress, and the damage work during needle insertions into agarose gels. J Mech Behav Biomed Mater 2016; 56:98-105. [DOI: 10.1016/j.jmbbm.2015.11.024] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2015] [Revised: 11/17/2015] [Accepted: 11/25/2015] [Indexed: 12/28/2022]
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12
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Lee D, Rahman MM, Zhou Y, Ryu S. Three-Dimensional Confocal Microscopy Indentation Method for Hydrogel Elasticity Measurement. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2015; 31:9684-9693. [PMID: 26270154 DOI: 10.1021/acs.langmuir.5b01267] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
The stiffness of the extracellular matrix (ECM) plays an important role in controlling cell functions. As an alternative to the ECM, hydrogels of tunable elasticity are widely used for in vitro cell mechanobiology studies. Therefore, characterizing the Young's modulus of the hydrogel substrate is crucial. In this paper, we propose a confocal microscopy indentation method for measuring the elasticity of polyacrylamide gel as a model hydrogel. Our new indentation method is based on three-dimensional imaging of the indented gel using confocal microscopy and automated image processing to measure indentation depth from the three-dimensional image stack. We tested and validated our method by indenting polyacrylamide gels of different rigidities with various sphere indentors and by comparing it with the rheometric method. Our measurements show consistent results regardless of the type of the indentors and agree with rheometric measurements. Therefore, the proposed confocal microscopy indentation method can accurately measure the stiffness of hydrogels.
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Affiliation(s)
- Donghee Lee
- Department of Mechanical & Materials Engineering and ‡Center for Biotechnology, University of Nebraska-Lincoln , Lincoln, Nebraska 68588, United States
| | - Md Mahmudur Rahman
- Department of Mechanical & Materials Engineering and ‡Center for Biotechnology, University of Nebraska-Lincoln , Lincoln, Nebraska 68588, United States
| | - You Zhou
- Department of Mechanical & Materials Engineering and ‡Center for Biotechnology, University of Nebraska-Lincoln , Lincoln, Nebraska 68588, United States
| | - Sangjin Ryu
- Department of Mechanical & Materials Engineering and ‡Center for Biotechnology, University of Nebraska-Lincoln , Lincoln, Nebraska 68588, United States
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13
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Filas BA, Xu G, Taber LA. Probing regional mechanical properties of embryonic tissue using microindentation and optical coherence tomography. Methods Mol Biol 2015; 1189:3-16. [PMID: 25245683 DOI: 10.1007/978-1-4939-1164-6_1] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Physical forces regulate morphogenetic movements and the mechanical properties of embryonic tissues during development. Such quantities are closely interrelated, as increases in material stiffness can limit force-induced deformations and vice versa. Here we present a minimally invasive method to quantify spatiotemporal changes in mechanical properties during morphogenesis. Regional stiffness is measured using microindentation, while displacement and strain distributions near the indenter are computed from the motion of tissue labels tracked from 3-D optical coherence tomography (OCT) images. Applied forces, displacements, and strain distributions are then used in conjunction with finite-element models to estimate regional material properties. This method is applicable to a wide variety of experimental systems and can be used to better understand the dynamic interrelation between tissue deformations and material properties that occur during time-lapse studies of embryogenesis. Such information is important to improve our understanding of the etiology of congenital disease where dynamic changes in mechanical properties are likely involved, such as situs inversus in the heart, hydrocephalus in the brain, and microphthalmia in the eye.
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Affiliation(s)
- Benjamen A Filas
- Department of Ophthalmology & Visual Sciences, Washington University School of Medicine, St. Louis, MO, 63110, USA
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In vivo evaluation of needle force and friction stress during insertion at varying insertion speed into the brain. J Neurosci Methods 2014; 237:79-89. [PMID: 25151066 DOI: 10.1016/j.jneumeth.2014.08.012] [Citation(s) in RCA: 53] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2014] [Revised: 07/31/2014] [Accepted: 08/12/2014] [Indexed: 01/06/2023]
Abstract
BACKGROUND Convection enhanced delivery (CED) infuses drugs directly into brain tissue. Needle insertion is required and results in tissue damage which can promote flowback along the needle track and improper targeting. The goal of this study was to evaluate friction stress (calculated from needle insertion force) as a measure of tissue contact and damage during needle insertion for varying insertion speeds. NEW METHOD Forces and surface dimpling during needle insertion were measured in rat brain in vivo. Needle retraction forces were used to calculate friction stresses. These measures were compared to track damage from a previous study. Differences between brain tissues and soft hydrogels were evaluated for varying insertion speeds: 0.2, 2, and 10mm/s. RESULTS In brain tissue, average insertion force and surface dimpling increased with increasing insertion speed. Average friction stress along the needle-tissue interface decreased with insertion speed (from 0.58 ± 0.27 to 0.16 ± 0.08 kPa). Friction stress varied between brain regions: cortex (0.227 ± 0.27 kPa), external capsule (0.222 ± 0.19 kPa), and CPu (0.383 ± 0.30 kPa). Hydrogels exhibited opposite trends for dimpling and friction stress with insertion speed. COMPARISON WITH EXISTING METHODS Previously, increasing needle damage with insertion speed has been measured with histological methods. Friction stress appears to decrease with increasing tissue damage and decreasing tissue contact, providing the potential for in vivo and real time evaluation along the needle track. CONCLUSION Force derived friction stress decreased with increasing insertion speed and was smaller within white matter regions. Hydrogels exhibited opposite trends to brain tissue.
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15
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Casanova F, Carney PR, Sarntinoranont M. Effect of needle insertion speed on tissue injury, stress, and backflow distribution for convection-enhanced delivery in the rat brain. PLoS One 2014; 9:e94919. [PMID: 24776986 PMCID: PMC4002424 DOI: 10.1371/journal.pone.0094919] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2013] [Accepted: 03/21/2014] [Indexed: 12/23/2022] Open
Abstract
Flow back along a needle track (backflow) can be a problem during direct infusion, e.g. convection-enhanced delivery (CED), of drugs into soft tissues such as brain. In this study, the effect of needle insertion speed on local tissue injury and backflow was evaluated in vivo in the rat brain. Needles were introduced at three insertion speeds (0.2, 2, and 10 mm/s) followed by CED of Evans blue albumin (EBA) tracer. Holes left in tissue slices were used to reconstruct penetration damage. These measurements were also input into a hyperelastic model to estimate radial stress at the needle-tissue interface (pre-stress) before infusion. Fast insertion speeds were found to produce more tissue bleeding and disruption; average hole area at 10 mm/s was 1.87-fold the area at 0.2 mm/s. Hole measurements also differed at two fixation time points after needle retraction, 10 and 25 min, indicating that pre-stresses are influenced by time-dependent tissue swelling. Calculated pre-stresses were compressive (0 to 485 Pa) and varied along the length of the needle with smaller average values within white matter (116 Pa) than gray matter (301 Pa) regions. Average pre-stress at 0.2 mm/s (351.7 Pa) was calculated to be 1.46-fold the value at 10 mm/s. For CED backflow experiments (0.5, 1, and 2 µL/min), measured EBA backflow increased as much as 2.46-fold between 10 and 0.2 mm/s insertion speeds. Thus, insertion rate-dependent damage and changes in pre-stress were found to directly contribute to the extent of backflow, with slower insertion resulting in less damage and improved targeting.
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Affiliation(s)
- Fernando Casanova
- Department of Mechanical & Aerospace Engineering, University of Florida, Gainesville, Florida, United States of America
- Escuela de Ingeniería Mecánica, Universidad del Valle, Cali, Colombia
| | - Paul R. Carney
- Department of Pediatrics, Neurology, Neuroscience, and J. Crayton Pruitt Family Department of Biomedical Engineering, Wilder Center of Excellence for Epilepsy Research, Gainesville, Florida, United States of America
| | - Malisa Sarntinoranont
- Department of Mechanical & Aerospace Engineering, University of Florida, Gainesville, Florida, United States of America
- * E-mail:
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Kantorovich S, Astary GW, King MA, Mareci TH, Sarntinoranont M, Carney PR. Influence of neuropathology on convection-enhanced delivery in the rat hippocampus. PLoS One 2013; 8:e80606. [PMID: 24260433 PMCID: PMC3832660 DOI: 10.1371/journal.pone.0080606] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2013] [Accepted: 10/03/2013] [Indexed: 01/08/2023] Open
Abstract
Local drug delivery techniques, such as convention-enhanced delivery (CED), are promising novel strategies for delivering therapeutic agents otherwise limited by systemic toxicity and blood-brain-barrier restrictions. CED uses positive pressure to deliver infusate homogeneously into interstitial space, but its distribution is dependent upon appropriate tissue targeting and underlying neuroarchitecture. To investigate effects of local tissue pathology and associated edema on infusate distribution, CED was applied to the hippocampi of rats that underwent electrically-induced, self-sustaining status epilepticus (SE), a prolonged seizure. Infusion occurred 24 hours post-SE, using a macromolecular tracer, the magnetic resonance (MR) contrast agent gadolinium chelated with diethylene triamine penta-acetic acid and covalently attached to albumin (Gd-albumin). High-resolution T1- and T2-relaxation-weighted MR images were acquired at 11.1 Tesla in vivo prior to infusion to generate baseline contrast enhancement images and visualize morphological changes, respectively. T1-weighted imaging was repeated post-infusion to visualize final contrast-agent distribution profiles. Histological analysis was performed following imaging to characterize injury. Infusions of Gd-albumin into injured hippocampi resulted in larger distribution volumes that correlated with increased injury severity, as measured by hyperintense regions seen in T2-weighted images and corresponding histological assessments of neuronal degeneration, myelin degradation, astrocytosis, and microglial activation. Edematous regions included the CA3 hippocampal subfield, ventral subiculum, piriform and entorhinal cortex, amygdalar nuclei, middle and laterodorsal/lateroposterior thalamic nuclei. This study demonstrates MR-visualized injury processes are reflective of cellular alterations that influence local distribution volume, and provides a quantitative basis for the planning of local therapeutic delivery strategies in pathological brain regions.
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Affiliation(s)
- Svetlana Kantorovich
- Department of Neuroscience, University of Florida, Gainesville, Florida, United States of America
- Wilder Center of Excellence for Epilepsy Research, University of Florida, Gainesville, Florida, United States of America
- Department of Pediatrics, Division of Pediatric Neurology, University of Florida, Gainesville, Florida, United States of America
| | - Garrett W. Astary
- J. Crayton Pruitt Family Department of Biomedical Engineering, University of Florida, Gainesville, Florida, United States of America
| | - Michael A. King
- Department of Pharmacology and Therapeutics, University of Florida, Gainesville, Florida, United States of America
- Malcom Randall Veterans Affairs Medical Center, Gainesville, University of Florida, Gainesville, Florida, United States of America
| | - Thomas H. Mareci
- Department of Biochemistry and Molecular Biology, University of Florida, Gainesville, Florida, United States of America
| | - Malisa Sarntinoranont
- Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, Florida, United States of America
| | - Paul R. Carney
- Department of Neuroscience, University of Florida, Gainesville, Florida, United States of America
- Wilder Center of Excellence for Epilepsy Research, University of Florida, Gainesville, Florida, United States of America
- Department of Pediatrics, Division of Pediatric Neurology, University of Florida, Gainesville, Florida, United States of America
- J. Crayton Pruitt Family Department of Biomedical Engineering, University of Florida, Gainesville, Florida, United States of America
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Lee SJ, King MA, Sun J, Xie HK, Subhash G, Sarntinoranont M. Measurement of viscoelastic properties in multiple anatomical regions of acute rat brain tissue slices. J Mech Behav Biomed Mater 2013; 29:213-24. [PMID: 24099950 DOI: 10.1016/j.jmbbm.2013.08.026] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2013] [Revised: 08/25/2013] [Accepted: 08/27/2013] [Indexed: 12/19/2022]
Abstract
Mechanical property data for brain tissue are needed to understand the biomechanics of neurological disorders and response of the brain to different mechanical and surgical forces. Most studies have characterized mechanical behavior of brain tissues over large regions or classified tissue properties for either gray or white matter regions only. In this study, spatially heterogeneous viscoelastic properties of ex vivo rat brain tissue slices were measured in different anatomical regions including the cerebral cortex, caudate/putamen, and hippocampus using an optical coherence tomography (OCT) indentation system. Cell viability was also tested to observe neuronal degeneration and morphological changes in tissue slices and provide a proper timeline for mechanical tests. Shear modulus was estimated by fitting normalized deformation data (D/ti), which was defined as the ratio of deformation depth (D) to initial thickness of the tissue slice (ti), to a viscoelastic finite element model. The estimated shear modulus decayed nonlinearly over 10min in each anatomical region, and the range of instantaneous to equilibrium shear modulus was 3.8-0.54kPa in the cerebral cortex, 1.4-0.27kPa in the hippocampus and 1.0-0.17kPa in the caudate/putamen. Although these regions are all gray matter structures, their measured mechanical properties were significantly different. Accurate measurement of inter-regional variations in mechanical properties will contribute to improved understanding organ-level structural parameters and regional differential susceptibility to deformation injury within CNS tissues.
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Affiliation(s)
- S J Lee
- Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, Florida
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Abstract
Biological cells are well known to respond to a multitude of chemical signals. In the nervous system, chemical signaling has been shown to be crucially involved in development, normal functioning, and disorders of neurons and glial cells. However, there are an increasing number of studies showing that these cells also respond to mechanical cues. Here, we summarize current knowledge about the mechanical properties of nervous tissue and its building blocks, review recent progress in methodology and understanding of cellular mechanosensitivity in the nervous system, and provide an outlook on the implications of neuromechanics for future developments in biomedical engineering to aid overcoming some of the most devastating and currently incurable CNS pathologies such as spinal cord injuries and multiple sclerosis.
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Affiliation(s)
- Kristian Franze
- Department of Physiology, Development and Neuroscience, University of Cambridge, Cambridge CB2 3DY, UK.
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Casanova F, Carney PR, Sarntinoranont M. Influence of needle insertion speed on backflow for convection-enhanced delivery. J Biomech Eng 2012; 134:041006. [PMID: 22667681 DOI: 10.1115/1.4006404] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Fluid flow back along the outer surface of a needle (backflow) can be a significant problem during the direct infusion of drugs into brain tissues for procedures such as convection-enhanced delivery (CED). This study evaluates the effects of needle insertion speed (0.2 and 1.8 mm/s) as well as needle diameter and flow rate on the extent of backflow and local damage to surrounding tissues. Infusion experiments were conducted on a transparent tissue phantom, 0.6% (w/v) agarose hydrogel, to visualize backflow. Needle insertion experiments were also performed to evaluate local damage at the needle tip and to back out the prestress in the surrounding media for speed conditions where localized damage was not excessive. Prestress values were then used in an analytical model of backflow. At the higher insertion speed (1.8 mm/s), local insertion damage was found to be reduced and backflow was decreased. The compressive prestress at the needle-tissue interface was estimated to be approximately constant (0.812 kPa), and backflow distances were similar regardless of needle gauge (22, 26, and 32 gauge). The analytical model underestimated backflow distances at low infusion flow rates and overestimated backflow at higher flow rates. At the lower insertion speed (0.2 mm/s), significant backflow was measured. This corresponded to an observed accumulation of material at the needle tip which produced a gap between the needle and the surrounding media. Local tissue damage was also evaluated in excised rat brain tissues, and insertion tests show similar rate-dependent accumulation of tissue at the needle tip at the lower insertion speed. These results indicate that local tissue damage and backflow may be avoided by using an appropriate insertion speed.
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Affiliation(s)
- Fernando Casanova
- Escuela de Ingenieria Mecanica, Universidad del Valle, Carrera 13 No. 100-00, Cali, Colombia.
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Sun J, Lee SJ, Wu L, Sarntinoranont M, Xie H. Refractive index measurement of acute rat brain tissue slices using optical coherence tomography. OPTICS EXPRESS 2012; 20:1084-95. [PMID: 22274454 PMCID: PMC3501791 DOI: 10.1364/oe.20.001084] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/03/2011] [Revised: 11/11/2011] [Accepted: 11/14/2011] [Indexed: 05/20/2023]
Abstract
An optical coherence tomography (OCT) system employing a microelectromechanical system (MEMS) mirror was used to measure the refractive index (RI) of anatomically different regions in acute brain tissue slices, in which viability was maintained. RI was measured in white-matter and grey-matter regions, including the cerebral cortex, putamen, hippocampus, thalamus and corpus callosum. The RI in the corpus callosum was found to be ~4% higher than the RIs in other regions. Changes in RI with tissue deformation were also measured in the cerebral cortex and corpus callosum under uniform compression (20-80% strain). For 80% strain, measured RIs increased nonlinearly by up to 70% and 90% in the cerebral cortex and corpus callosum respectively. Knowledge of RI in heterogeneous tissues can be used to correct distorted optical images caused by RI variations between different regions. Also deformation-dependent changes in RI can be applied to OCT elastography or to mechanical tests based on optical imaging such as indentation tests.
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Affiliation(s)
- Jingjing Sun
- Department of Electrical and Computer Engineering, University of Florida, Gainesville, FL 32611, USA.
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Sarntinoranont M, Lee SJ, Hong Y, King MA, Subhash G, Kwon J, Moore DF. High-strain-rate brain injury model using submerged acute rat brain tissue slices. J Neurotrauma 2011; 29:418-29. [PMID: 21970544 DOI: 10.1089/neu.2011.1772] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Blast-induced traumatic brain injury (bTBI) has received increasing attention in recent years due to ongoing military operations in Iraq and Afghanistan. Sudden impacts or explosive blasts generate stress and pressure waves that propagate at high velocities and affect sensitive neurological tissues. The immediate soft tissue response to these stress waves is difficult to assess using current in vivo imaging technologies. However, these stress waves and resultant stretching and shearing of tissue within the nano- to microsecond time scale of blast and impact are likely to cause initial injury. To visualize the effects of stress wave loading, we have developed a new ex vivo model in which living tissue slices from rat brain, attached to a ballistic gelatin substrate, were subjected to high-strain-rate loads using a polymer split Hopkinson pressure bar (PSHPB) with real-time high-speed imaging. In this study, average peak fluid pressure within the test chamber reached a value of 1584±63.3 psi. Cavitation due to a trailing underpressure wave was also observed. Time-resolved images of tissue deformation were collected and large maximum eigenstrains (0.03-0.42), minimum eigenstrains (-0.33 to -0.03), maximum shear strains (0.09-0.45), and strain rates (8.4×10³/sec) were estimated using digital image correlation (DIC). Injury at 4 and 6 h was quantified using Fluoro-Jade C. Neuronal injury due to PSHPB testing was found to be significantly greater than injury associated with the tissue slice paradigm alone. While large pressures and strains were encountered for these tests, this system provides a controllable test environment to study injury to submerged brain slices over a range of strain rate, pressure, and strain loads.
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Affiliation(s)
- Malisa Sarntinoranont
- Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, Florida, USA
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