1
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S. A. F, K. S. C, L. D, M. G, S. P, R. L. L, C. A. H. Engineering Vascularized Islet Macroencapsulation Devices: An in vitro Platform to Study Oxygen Transport in Perfused Immobilized Pancreatic Beta Cell Cultures. Front Bioeng Biotechnol 2022; 10:884071. [PMID: 35519615 PMCID: PMC9061948 DOI: 10.3389/fbioe.2022.884071] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2022] [Accepted: 04/01/2022] [Indexed: 02/01/2023] Open
Abstract
Islet encapsulation devices serve to deliver pancreatic beta cells to type 1 diabetic patients without the need for chronic immunosuppression. However, clinical translation is hampered by mass transport limitations causing graft hypoxia. This is exacerbated in devices relying only on passive diffusion for oxygenation. Here, we describe the application of a cylindrical in vitro perfusion system to study oxygen effects on islet-like clusters immobilized in alginate hydrogel. Mouse insulinoma 6 islet-like clusters were generated using microwell plates and characterized with respect to size distribution, viability, and oxygen consumption rate to determine an appropriate seeding density for perfusion studies. Immobilized clusters were perfused through a central channel at different oxygen tensions. Analysis of histological staining indicated the distribution of viable clusters was severely limited to near the perfusion channel at low oxygen tensions, while the distribution was broadest at normoxia. The results agreed with a 3D computational model designed to simulate the oxygen distribution within the perfusion device. Further simulations were generated to predict device performance with human islets under in vitro and in vivo conditions. The combination of experimental and computational findings suggest that a multichannel perfusion strategy could support in vivo viability and function of a therapeutic islet dose.
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Affiliation(s)
- Fernandez S. A.
- Department of Chemical Engineering, McGill University, Montréal, QC, Canada
| | - Champion K. S.
- Department of Chemical Engineering, McGill University, Montréal, QC, Canada
| | - Danielczak L.
- Department of Chemical Engineering, McGill University, Montréal, QC, Canada
| | - Gasparrini M.
- Human Islet Transplant Laboratory, McGill University Health Centre, Montréal, QC, Canada
| | - Paraskevas S.
- Human Islet Transplant Laboratory, McGill University Health Centre, Montréal, QC, Canada
- Department of Surgery, McGill University Health Centre, Montréal, QC, Canada
| | - Leask R. L.
- Department of Chemical Engineering, McGill University, Montréal, QC, Canada
- Department of Biomedical Engineering, McGill University, Montréal, QC, Canada
| | - Hoesli C. A.
- Department of Chemical Engineering, McGill University, Montréal, QC, Canada
- Department of Biomedical Engineering, McGill University, Montréal, QC, Canada
- *Correspondence: Hoesli C. A.,
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2
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Shim JJ, Ateshian GA. A Hybrid Reactive Multiphasic Mixture With a Compressible Fluid Solvent. J Biomech Eng 2022; 144:011013. [PMID: 34318318 PMCID: PMC8547015 DOI: 10.1115/1.4051926] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2021] [Revised: 07/26/2021] [Indexed: 01/03/2023]
Abstract
Mixture theory is a general framework that has been used to model mixtures of solid, fluid, and solute constituents, leading to significant advances in modeling the mechanics of biological tissues and cells. Though versatile and applicable to a wide range of problems in biomechanics and biophysics, standard multiphasic mixture frameworks incorporate neither dynamics of viscous fluids nor fluid compressibility, both of which facilitate the finite element implementation of computational fluid dynamics solvers. This study formulates governing equations for reactive multiphasic mixtures where the interstitial fluid has a solvent which is viscous and compressible. This hybrid reactive multiphasic framework uses state variables that include the deformation gradient of the porous solid matrix, the volumetric strain and rate of deformation of the solvent, the solute concentrations, and the relative velocities between the various constituents. Unlike standard formulations which employ a Lagrange multiplier to model fluid pressure, this framework requires the formulation of a function of state for the pressure, which depends on solvent volumetric strain and solute concentrations. Under isothermal conditions the formulation shows that the solvent volumetric strain remains continuous across interfaces between hybrid multiphasic domains. Apart from the Lagrange multiplier-state function distinction for the fluid pressure, and the ability to accommodate viscous fluid dynamics, this hybrid multiphasic framework remains fully consistent with standard multiphasic formulations previously employed in biomechanics. With these additional features, the hybrid multiphasic mixture theory makes it possible to address a wider range of problems that are important in biomechanics and mechanobiology.
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Affiliation(s)
- Jay J Shim
- Department of Mechanical Engineering, Columbia University, New York, NY 10027
| | - Gerard A Ateshian
- Department of Mechanical Engineering, Columbia University, New York, NY 10027
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3
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Warner RM, Shuttleworth R, Benson JD, Eroglu A, Higgins AZ. General tissue mass transfer model for cryopreservation applications. Biophys J 2021; 120:4980-4991. [PMID: 34662558 PMCID: PMC8633834 DOI: 10.1016/j.bpj.2021.10.014] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2021] [Revised: 09/15/2021] [Accepted: 10/13/2021] [Indexed: 10/20/2022] Open
Abstract
Successful cryopreservation of complex specimens, such as tissues and organs, would greatly benefit both the medical and scientific research fields. Vitrification is one of the most promising techniques for complex specimen cryopreservation, but toxicity remains a major challenge because of the high concentration of cryoprotectants (CPAs) needed to vitrify. Our group has approached this problem using mathematical optimization to design less toxic CPA equilibration methods for cells. To extend this approach to tissues, an appropriate mass transfer model is required. Fick's law is commonly used, but this simple modeling framework does not account for the complexity of mass transfer in tissues, such as the effects of fixed charges, tissue size changes, and the interplay between cell membrane transport and transport through the extracellular fluid. Here, we propose a general model for mass transfer in tissues that accounts for all of these phenomena. To create this model, we augmented a previously published acellular model of mass transfer in articular cartilage to account for the effects of cells. We show that the model can accurately predict changes in CPA concentration and tissue size for both articular cartilage and pancreatic islets, tissue types with vastly different properties.
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Affiliation(s)
- Ross M Warner
- School of Chemical, Biological and Environmental Engineering, Oregon State University, Corvallis, Oregon
| | - Robyn Shuttleworth
- Department of Biology, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
| | - James D Benson
- Department of Biology, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
| | - Ali Eroglu
- Department of Neuroscience and Regenerative Medicine, Medical College of Georgia - Augusta University, Augusta, Georgia
| | - Adam Z Higgins
- School of Chemical, Biological and Environmental Engineering, Oregon State University, Corvallis, Oregon.
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4
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Yang T, Peng J, Fang C, Li S, Gao D. Numerical Modeling of Temperature-Dependent Cell Membrane Permeability to Water Based on a Microfluidic System with Dynamic Temperature Control. SLAS Technol 2021; 26:477-487. [PMID: 34041975 DOI: 10.1177/24726303211015199] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
In order to describe temperature-dependent cell osmotic behaviors in a more reliable method, a novel mathematical mass transfer model coupled with dynamic temperature change has been established based on the combination of a time domain to temperature domain transformation equation and a constant temperature mass transfer model. This novel model is numerically simulated under multiple temperature changing rates and extracellular osmolarities. A microfluidic system that can achieve single-cell osmotic behavior observation and provide dynamic and swift on-chip temperature control was built and tested in this paper. Utilizing the temperature control system, the on-chip heating processes are recorded and then described as polynomial time-temperature relationships. These dynamic temperature changing profiles were performed by obtaining cell membrane properties by parameter fitting only one set of testing experimental data to the mathematical model with a constant temperature changing rate. The numerical modeling results show that predicting the osmotic cell volume change using selected dynamic temperature profiles is more suitable for studies concerning cell membrane permeability determination and cryopreservation process than tests using constant temperature changing rates.
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Affiliation(s)
- Tianhang Yang
- Department of Fluid Control and Automation, Harbin Institute of Technology, Harbin, Heilongjiang, People's Republic of China
| | - Ji Peng
- Mechanical Engineering, University of Washington, Seattle, WA, USA
| | | | - Songjing Li
- Department of Fluid Control and Automation, Harbin Institute of Technology, Harbin, Heilongjiang, People's Republic of China
| | - Dayong Gao
- Mechanical Engineering, University of Washington, Seattle, WA, USA
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5
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Jacobsen T, Hernandez P, Chahine N. Inhibition of toll-like receptor 4 protects against inflammation-induced mechanobiological alterations to intervertebral disc cells. Eur Cell Mater 2021; 41:576-591. [PMID: 34013512 PMCID: PMC8329983 DOI: 10.22203/ecm.v041a37] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
Intervertebral disc (IVD) degeneration is associated with elevated levels of inflammatory cytokines implicated in disease aetiology and matrix degradation. Toll-like receptor-4 (TLR4) has been shown to participate in the inflammatory responses of the nucleus pulposus (NP) and its levels are upregulated in disc degeneration. Activation of TLR4 in NP cells leads to significant, persistent changes in cell biophysical properties, including hydraulic permeability and osmotically active water content, as well as alterations to the actin cytoskeleton. The study hypothesis was that inflammation-induced changes to cellular biomechanical properties and actin cytoskeleton of NP cells could be prevented by inhibiting TLR4 signalling. Isolated NP cells from bovine discs were treated with lipopolysaccharide (LPS), the best studied TLR4 agonist, with or without treatment with the TLR4 inhibitor TAK-242. Cellular volume regulation responses to step osmotic loading were measured and the transient volume-response was captured by time-lapse microscopy. Volume-responses were analysed using mixture theory framework to investigate hydraulic permeability and osmotically active intracellular water content. Hydraulic permeability and cell radius were significantly increased with LPS treatment and these changes were blocked in cells treated with TAK-242. LPS-induced remodelling of cortical actin and IL-6 upregulation were also mitigated by TAK-242 treatment. These findings indicated that TLR4 signalling participated in NP cell biophysical regulation and may be an important target for mitigating altered cell responses observed in IVD inflammation and degeneration.
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Affiliation(s)
- T.D. Jacobsen
- Department of Biomedical Engineering, Columbia University,
New York, NY
| | - P.A. Hernandez
- Department of Orthopaedic Surgery, University of Texas
Southwestern Medical Centre, Dallas, TX
| | - N.O. Chahine
- Department of Biomedical Engineering, Columbia University,
New York, NY,Department of Orthopaedic Surgery, Columbia University, New
York, NY,Address for correspondence: Nadeen
Chahine, 650 W 168th St, William Black Building, 14th
Floor Room 14-1408E, New York, NY 10032, USA. Telephone number: +1 2123051515,
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6
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Hernandez PA, Jacobsen TD, Chahine NO. Actomyosin contractility confers mechanoprotection against TNFα-induced disruption of the intervertebral disc. SCIENCE ADVANCES 2020; 6:eaba2368. [PMID: 32875103 PMCID: PMC7438088 DOI: 10.1126/sciadv.aba2368] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/25/2019] [Accepted: 07/08/2020] [Indexed: 06/11/2023]
Abstract
Inflammation triggers degradation of intervertebral disc extracellular matrix (ECM), a hallmark of disc degeneration that contributes to back pain. Mechanosensitive nucleus pulposus cells are responsible for ECM production, yet the impact of a proinflammatory microenvironment on cell mechanobiology is unknown. Using gain- and loss-of-function approaches, we show that tumor necrosis factor-α (TNFα)-induced inflammation alters cell morphology and biophysical properties (circularity, contractility, cell stiffness, and hydraulic permeability) in a mechanism dependent on actomyosin contractility in a three-dimensional (3D) culture. We found that RhoA activation rescued cells from TNFα-induced mechanobiological disruption. Using a novel explant-in-hydrogel culture system, we demonstrate that nuclear factor kappa-B nuclear translocation and transcription are mechanosensitive, and its downstream effects on ECM degradation are regulated by actomyosin contractility. Results define a scaling relationship between circularity, contractility, and hydraulic permeability that is conserved from healthy to inflammatory microenvironments and is indicative of cell mechanobiological control across scales in 3D.
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Affiliation(s)
- Paula A. Hernandez
- Department of Orthopaedic Surgery, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Timothy D. Jacobsen
- Department of Biomedical Engineering, Columbia University, New York, NY, USA
| | - Nadeen O. Chahine
- Department of Biomedical Engineering, Columbia University, New York, NY, USA
- Department of Orthopedic Surgery, Columbia University, New York, NY, USA
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7
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Nuclei deformation reveals pressure distributions in 3D cell clusters. PLoS One 2019; 14:e0221753. [PMID: 31513673 PMCID: PMC6771309 DOI: 10.1371/journal.pone.0221753] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2018] [Accepted: 08/14/2019] [Indexed: 12/16/2022] Open
Abstract
Measuring pressures within complex multi-cellular environments is critical for
studying mechanobiology as these forces trigger diverse biological responses,
however, these studies are difficult as a deeply embedded yet well-calibrated
probe is required. In this manuscript, we use endogenous cell nuclei as pressure
sensors by introducing a fluorescent protein localized to the nucleus and
confocal microscopy to measure the individual nuclear volumes in 3D
multi-cellular aggregates. We calibrate this measurement of nuclear volume to
pressure by quantifying the nuclear volume change as a function of osmotic
pressure in isolated 2D culture. Using this technique, we find that in
multicellular structures, the nuclear compressive mechanical stresses are on the
order of MPa, increase with cell number in the cluster, and that the
distribution of stresses is homogenous in spherical cell clusters, but highly
asymmetric in oblong clusters. This approach may facilitate quantitative
mechanical measurements in complex and extended biological structures both
in vitro and in vivo.
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8
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Verheyen CA, Morales L, Sussman J, Paunovska K, Manzoli V, Ziebarth NM, Tomei AA. Characterization of Polyethylene Glycol-Reinforced Alginate Microcapsules for Mechanically Stable Cell Immunoisolation. MACROMOLECULAR MATERIALS AND ENGINEERING 2019; 304:1800679. [PMID: 31929732 PMCID: PMC6953757 DOI: 10.1002/mame.201800679] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/05/2018] [Indexed: 06/02/2023]
Abstract
Islet transplantation within mechanically stable microcapsules offers the promise of long-term diabetes reversal without chronic immunosuppression. Reinforcing the ionically gelled network of alginate (ALG) hydrogels with covalently linked polyethylene glycol (PEG) may create hybrid structures with desirable mechanical properties. This report describes the fabrication of hybrid PEG-ALG interpenetrating polymer networks and the investigation of microcapsule swelling, surface modulus, rheology, compression, and permeability. It is demonstrated that hybrid networks are more resistant to bulk swelling and compressive deformation and display improved shape recovery and long-term resilience. Interestingly, it is shown that PEG-ALG networks behave like ALG during microscale surface deformation and small amplitude shear while exhibiting similar permeability properties. The results from this report's in vitro characterization are interpreted according to viscoelastic polymer theory and provide new insight into hybrid hydrogel mechanical behavior. This new understanding of PEG-ALG mechanical performance is then linked to previous work that demonstrated the success of hybrid polymer immunoisolation devices in vivo.
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Affiliation(s)
- Connor A Verheyen
- Diabetes Research Institute, 1450 NW 10th Avenue, Miami, FL 33136, USA
| | - Laura Morales
- Diabetes Research Institute, 1450 NW 10th Avenue, Miami, FL 33136, USA
| | - Joshua Sussman
- Diabetes Research Institute, 1450 NW 10th Avenue, Miami, FL 33136, USA
| | - Kalina Paunovska
- Diabetes Research Institute, 1450 NW 10th Avenue, Miami, FL 33136, USA
| | - Vita Manzoli
- Diabetes Research Institute, 1450 NW 10th Avenue, Miami, FL 33136, USA
| | - Noel M Ziebarth
- Department of Biomedical Engineering, University of Miami, 1251 Memorial Drive, Coral Gables, FL-33146, USA
| | - Alice A Tomei
- Diabetes Research Institute, 1450 NW 10th Avenue, Miami, FL 33136, USA
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9
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Hou JC, Maas SA, Weiss JA, Ateshian GA. Finite Element Formulation of Multiphasic Shell Elements for Cell Mechanics Analyses in FEBio. J Biomech Eng 2018; 140:2696682. [PMID: 30098156 PMCID: PMC10577663 DOI: 10.1115/1.4041043] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2018] [Revised: 07/17/2018] [Indexed: 10/18/2023]
Abstract
With the recent implementation of multiphasic materials in the open-source finite element (FE) software FEBio (febio.org), 3D models of cells embedded within the tissue may now be analyzed, accounting for porous solid matrix deformation, transport of interstitial fluid and solutes, membrane potential, and reactions. The cell membrane is a critical component in cell models, which selectively regulates the transport of fluid and solutes in the presence of large concentration and electric potential gradients, while also facilitating the transport of various proteins. The cell membrane is much thinner than the cell; therefore, in an FE environment, shell elements formulated as 2D surfaces in 3D space would be preferred for modeling the cell membrane, for the convenience of mesh generation from image-based data, especially for convoluted membranes. However, multiphasic shell elements are yet to be developed in the FE literature and commercial FE software. This study presents a novel formulation of multiphasic shell elements and its implementation in FEBio. The shell model includes front- and back-face nodal degrees of freedom for the solid displacement, effective fluid pressure and effective solute concentrations, and a linear interpolation of these variables across the shell thickness. This formulation was verified against classical models of cell physiology and validated against reported experimental measurements in chondrocytes. This implementation of passive transport of fluid and solutes across multiphasic membranes makes it possible to model the biomechanics of isolated cells or cells embedded in their extracellular matrix, accounting for solvent and solute transport.
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Affiliation(s)
- Jay C Hou
- Department of Mechanical Engineering, Columbia University, New York, NY 10027
| | - Steve A Maas
- Department of Bioengineering, University of Utah, Salt Lake City, UT 84112
| | - Jeffrey A Weiss
- Department of Bioengineering, University of Utah, Salt Lake City, UT 84112
| | - Gerard A Ateshian
- Department of Mechanical Engineering, Columbia University, New York, NY 10027
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10
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Lai VK, Nedrelow DS, Lake SP, Kim B, Weiss EM, Tranquillo RT, Barocas VH. Swelling of Collagen-Hyaluronic Acid Co-Gels: An In Vitro Residual Stress Model. Ann Biomed Eng 2016; 44:2984-2993. [PMID: 27150674 PMCID: PMC5045778 DOI: 10.1007/s10439-016-1636-0] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2016] [Accepted: 04/30/2016] [Indexed: 02/02/2023]
Abstract
Tissue-equivalents (TEs), simple model tissues with tunable properties, have been used to explore many features of biological soft tissues. Absent in most formulations however, is the residual stress that arises due to interactions among components with different unloaded levels of stress, which has an important functional role in many biological tissues. To create a pre-stressed model system, co-gels were fabricated from a combination of hyaluronic acid (HA) and reconstituted Type-I collagen (Col). When placed in solutions of varying osmolarity, HA-Col co-gels swell as the HA imbibes water, which in turn stretches (and stresses) the collagen network. In this way, co-gels with residual stress (i.e., collagen fibers in tension and HA in compression) were fabricated. When the three gel types tested here were immersed in hypotonic solutions, pure HA gels swelled the most, followed by HA-Col co-gels; no swelling was observed in pure collagen gels. The greatest swelling rates and swelling ratios occurred in the lowest salt concentration solutions. Tension on the collagen component of HA-Col co-gels was calculated from a stress balance and increased nonlinearly as swelling increased. The swelling experiment results were in good agreement with the stress predicted by a fibril network + non-fibrillar interstitial matrix computational model.
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Affiliation(s)
- Victor K Lai
- Department of Chemical Engineering, University of Minnesota, Duluth, MN, USA
| | - David S Nedrelow
- Department of Biomedical Engineering, University of Minnesota - Twin Cities, 7-105 Nils Hasselmo Hall, 312 Church St. SE, Minneapolis, MN, 55455, USA
| | - Spencer P Lake
- Department of Mechanical Engineering & Materials Science, Washington University in St. Louis, St. Louis, MO, USA
| | - Bumjun Kim
- Department of Biomedical Engineering, University of Minnesota - Twin Cities, 7-105 Nils Hasselmo Hall, 312 Church St. SE, Minneapolis, MN, 55455, USA
| | - Emily M Weiss
- Department of Biomedical Engineering, University of Minnesota - Twin Cities, 7-105 Nils Hasselmo Hall, 312 Church St. SE, Minneapolis, MN, 55455, USA
| | - Robert T Tranquillo
- Department of Biomedical Engineering, University of Minnesota - Twin Cities, 7-105 Nils Hasselmo Hall, 312 Church St. SE, Minneapolis, MN, 55455, USA
- Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN, USA
| | - Victor H Barocas
- Department of Biomedical Engineering, University of Minnesota - Twin Cities, 7-105 Nils Hasselmo Hall, 312 Church St. SE, Minneapolis, MN, 55455, USA.
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11
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Moshtagh PR, Pouran B, van Tiel J, Rauker J, Zuiddam MR, Arbabi V, Korthagen NM, Weinans H, Zadpoor AA. Micro- and nano-mechanics of osteoarthritic cartilage: The effects of tonicity and disease severity. J Mech Behav Biomed Mater 2016; 59:561-571. [PMID: 27043052 DOI: 10.1016/j.jmbbm.2016.03.009] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2015] [Revised: 02/23/2016] [Accepted: 03/09/2016] [Indexed: 10/22/2022]
Abstract
The present study aims to discover the contribution of glycosaminoglycans (GAGs) and collagen fibers to the mechanical properties of the osteoarthritic (OA) cartilage tissue. We used nanoindentation experiments to understand the mechanical behavior of mild and severe osteoarthritic cartilage at micro- and nano-scale at different swelling conditions. Contrast enhanced micro-computed tomography (EPIC-μCT) was used to confirm that mild OA specimens had significantly higher GAGs content compared to severe OA specimens. In micro-scale, the semi-equilibrium modulus of mild OA specimens significantly dropped after immersion in a hypertonic solution and at nano-scale, the histograms of the measured elastic modulus revealed three to four components. Comparing the peaks with those observed for healthy cartilage in a previous study indicated that the first and third peaks represent the mechanical properties of GAGs and the collagen network. The third peak shows considerably stiffer elastic modulus for mild OA samples as compared to the severe OA samples in isotonic conditions. Furthermore, this peak clearly dropped when the tonicity increased, indicating the loss of collagen (pre-) stress in the shrunk specimen. Our observations support the association of the third peak with the collagen network. However, our results did not provide any direct evidence to support the association of the first peak with GAGs. For severe OA specimens, the peak associated with the collagen network did not drop when the tonicity increased, indicating a change in the response of OA cartilage to hypertonicity, likely collagen damage, as the disease progresses to its latest stages.
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Affiliation(s)
- P R Moshtagh
- Faculty of Mechanical, Maritime, and Materials Engineering, Delft University of Technology (TU Delft), Mekelweg 2, 2628 CD, Delft, The Netherlands; Department of Orthopaedics, University Medical Center Utrecht, Q.03.2.103-1, Heidelberglaan 100, 3584 CX, Utrecht, The Netherlands.
| | - B Pouran
- Faculty of Mechanical, Maritime, and Materials Engineering, Delft University of Technology (TU Delft), Mekelweg 2, 2628 CD, Delft, The Netherlands; Department of Orthopaedics, University Medical Center Utrecht, Q.03.2.103-1, Heidelberglaan 100, 3584 CX, Utrecht, The Netherlands.
| | - J van Tiel
- Department of Orthopaedics and Radiology, Erasmus Medical Centre, Rotterdam, The Netherlands.
| | - J Rauker
- Faculty of Mechanical, Maritime, and Materials Engineering, Delft University of Technology (TU Delft), Mekelweg 2, 2628 CD, Delft, The Netherlands.
| | - M R Zuiddam
- Kavli Institute of Nanoscience, Delft University of Technology, Lorentzweg 1, 2628 CJ, Delft, The Netherlands.
| | - V Arbabi
- Faculty of Mechanical, Maritime, and Materials Engineering, Delft University of Technology (TU Delft), Mekelweg 2, 2628 CD, Delft, The Netherlands.
| | - N M Korthagen
- Department of Orthopaedics, University Medical Center Utrecht, Q.03.2.103-1, Heidelberglaan 100, 3584 CX, Utrecht, The Netherlands; Department of Equine Sciences, Faculty of Veterinary Medicine, Utrecht University, Utrecht, The Netherlands.
| | - H Weinans
- Faculty of Mechanical, Maritime, and Materials Engineering, Delft University of Technology (TU Delft), Mekelweg 2, 2628 CD, Delft, The Netherlands; Department of Orthopaedics, University Medical Center Utrecht, Q.03.2.103-1, Heidelberglaan 100, 3584 CX, Utrecht, The Netherlands; Department of Rheumatology, University Medical Center Utrecht, Utrecht, The Netherlands.
| | - A A Zadpoor
- Faculty of Mechanical, Maritime, and Materials Engineering, Delft University of Technology (TU Delft), Mekelweg 2, 2628 CD, Delft, The Netherlands.
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12
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Ribeiro FO, Gómez-Benito MJ, Folgado J, Fernandes PR, García-Aznar JM. In silico Mechano-Chemical Model of Bone Healing for the Regeneration of Critical Defects: The Effect of BMP-2. PLoS One 2015; 10:e0127722. [PMID: 26043112 PMCID: PMC4456173 DOI: 10.1371/journal.pone.0127722] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2014] [Accepted: 04/18/2015] [Indexed: 01/08/2023] Open
Abstract
The healing of bone defects is a challenge for both tissue engineering and modern orthopaedics. This problem has been addressed through the study of scaffold constructs combined with mechanoregulatory theories, disregarding the influence of chemical factors and their respective delivery devices. Of the chemical factors involved in the bone healing process, bone morphogenetic protein-2 (BMP-2) has been identified as one of the most powerful osteoinductive proteins. The aim of this work is to develop and validate a mechano-chemical regulatory model to study the effect of BMP-2 on the healing of large bone defects in silico. We first collected a range of quantitative experimental data from the literature concerning the effects of BMP-2 on cellular activity, specifically proliferation, migration, differentiation, maturation and extracellular matrix production. These data were then used to define a model governed by mechano-chemical stimuli to simulate the healing of large bone defects under the following conditions: natural healing, an empty hydrogel implanted in the defect and a hydrogel soaked with BMP-2 implanted in the defect. For the latter condition, successful defect healing was predicted, in agreement with previous in vivo experiments. Further in vivo comparisons showed the potential of the model, which accurately predicted bone tissue formation during healing, bone tissue distribution across the defect and the quantity of bone inside the defect. The proposed mechano-chemical model also estimated the effect of BMP-2 on cells and the evolution of healing in large bone defects. This novel in silico tool provides valuable insight for bone tissue regeneration strategies.
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Affiliation(s)
| | - María José Gómez-Benito
- Multiscale in Mechanical and Biological Engineering (M2BE), Aragón Institute of Engineering Research (I3A), University of Zaragoza, Zaragoza, Spain
| | - João Folgado
- IDMEC, Instituto Superior Técnico, Universidade de Lisboa, Lisbon, Portugal
| | - Paulo R. Fernandes
- IDMEC, Instituto Superior Técnico, Universidade de Lisboa, Lisbon, Portugal
| | - José Manuel García-Aznar
- Multiscale in Mechanical and Biological Engineering (M2BE), Aragón Institute of Engineering Research (I3A), University of Zaragoza, Zaragoza, Spain
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13
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Maidhof R, Jacobsen T, Papatheodorou A, Chahine NO. Inflammation induces irreversible biophysical changes in isolated nucleus pulposus cells. PLoS One 2014; 9:e99621. [PMID: 24936787 PMCID: PMC4061011 DOI: 10.1371/journal.pone.0099621] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2013] [Accepted: 05/16/2014] [Indexed: 11/20/2022] Open
Abstract
Intervertebral disc degeneration is accompanied by elevated levels of inflammatory cytokines that have been implicated in disease etiology and matrix degradation. While the effects of inflammatory stimulation on disc cell metabolism have been well-studied, their effects on cell biophysical properties have not been investigated. The hypothesis of this study is that inflammatory stimulation alters the biomechanical properties of isolated disc cells and volume responses to step osmotic loading. Cells from the nucleus pulposus (NP) of bovine discs were isolated and treated with either lipopolysaccharide (LPS), an inflammatory ligand, or with the recombinant cytokine TNF-α for 24 hours. We measured cellular volume regulation responses to osmotic loading either immediately after stimulation or after a 1 week recovery period from the inflammatory stimuli. Cells from each group were tested under step osmotic loading and the transient volume-response was captured via time-lapse microscopy. Volume-responses were analyzed using mixture theory framework to investigate two biomechanical properties of the cell, the intracellular water content and the hydraulic permeability. Intracellular water content did not vary between treatment groups, but hydraulic permeability increased significantly with inflammatory treatment. In the 1 week recovery group, hydraulic permeability remained elevated relative to the untreated recovery control. Cell radius was also significantly increased both after 24 hours of treatment and after 1 week recovery. A significant linear correlation was observed between hydraulic permeability and cell radius in untreated cells at 24 hours and at 1-week recovery, though not in the inflammatory stimulated groups at either time point. This loss of correlation between cell size and hydraulic permeability suggests that regulation of volume change is disrupted irreversibly due to inflammatory stimulation. Inflammatory treated cells exhibited altered F-actin cytoskeleton expression relative to untreated cells. We also found a significant decrease in the expression of aquaporin-1, the predominant water channel in disc NP cells, with inflammatory stimulation. To our knowledge, this is the first study providing evidence that inflammatory stimulation directly alters the mechanobiology of NP cells. The cellular biophysical changes observed in this study are coincident with documented changes in the extracellular matrix induced by inflammation, and may be important in disease etiology.
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Affiliation(s)
- Robert Maidhof
- Center for Autoimmune and Musculoskeletal Diseases, The Feinstein Institute for Medical Research, North Shore-LIJ Health System, Manhasset, New York, United States of America
| | - Timothy Jacobsen
- Center for Autoimmune and Musculoskeletal Diseases, The Feinstein Institute for Medical Research, North Shore-LIJ Health System, Manhasset, New York, United States of America
| | - Angelos Papatheodorou
- Center for Autoimmune and Musculoskeletal Diseases, The Feinstein Institute for Medical Research, North Shore-LIJ Health System, Manhasset, New York, United States of America
| | - Nadeen O. Chahine
- Center for Autoimmune and Musculoskeletal Diseases, The Feinstein Institute for Medical Research, North Shore-LIJ Health System, Manhasset, New York, United States of America
- Hofstra-North Shore LIJ School of Medicine, Hempstead, New York, United States of America
- * E-mail:
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14
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Ateshian GA, Maas S, Weiss JA. Multiphasic finite element framework for modeling hydrated mixtures with multiple neutral and charged solutes. J Biomech Eng 2014; 135:111001. [PMID: 23775399 DOI: 10.1115/1.4024823] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2012] [Accepted: 06/17/2013] [Indexed: 11/08/2022]
Abstract
Computational tools are often needed to model the complex behavior of biological tissues and cells when they are represented as mixtures of multiple neutral or charged constituents. This study presents the formulation of a finite element modeling framework for describing multiphasic materials in the open-source finite element software febio.1 Multiphasic materials may consist of a charged porous solid matrix, a solvent, and any number of neutral or charged solutes. This formulation proposes novel approaches for addressing several challenges posed by the finite element analysis of such complex materials: The exclusion of solutes from a fraction of the pore space due to steric volume and short-range electrostatic effects is modeled by a solubility factor, whose dependence on solid matrix deformation and solute concentrations may be described by user-defined constitutive relations. These solute exclusion mechanisms combine with long-range electrostatic interactions into a partition coefficient for each solute whose value is dependent upon the evaluation of the electric potential from the electroneutrality condition. It is shown that this electroneutrality condition reduces to a polynomial equation with only one valid root for the electric potential, regardless of the number and valence of charged solutes in the mixture. The equation of charge conservation is enforced as a constraint within the equation of mass balance for each solute, producing a natural boundary condition for solute fluxes that facilitates the prescription of electric current density on a boundary. It is also shown that electrical grounding is necessary to produce numerical stability in analyses where all the boundaries of a multiphasic material are impermeable to ions. Several verification problems are presented that demonstrate the ability of the code to reproduce known or newly derived solutions: (1) the Kedem-Katchalsky model for osmotic loading of a cell; (2) Donnan osmotic swelling of a charged hydrated tissue; and (3) current flow in an electrolyte. Furthermore, the code is used to generate novel theoretical predictions of known experimental findings in biological tissues: (1) current-generated stress in articular cartilage and (2) the influence of salt cation charge number on the cartilage creep response. This generalized finite element framework for multiphasic materials makes it possible to model the mechanoelectrochemical behavior of biological tissues and cells and sets the stage for the future analysis of reactive mixtures to account for growth and remodeling.
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15
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Ateshian GA, Morrison B, Holmes JW, Hung CT. Mechanics of Cell Growth. MECHANICS RESEARCH COMMUNICATIONS 2012; 42:118-125. [PMID: 22904576 PMCID: PMC3418607 DOI: 10.1016/j.mechrescom.2012.01.010] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
Cell growth describes an essential feature of biological tissues. This growth process may be modeled by using a set of relatively simple governing equations based on the axioms of mass and momentum balance, and using a continuum framework that describes cells and tissues as mixtures of a solid matrix, a solvent and multiple solutes. In this model the mechanics of cell growth is driven by osmotic effects, regulated by the cells' active uptake of solutes and passive uptake of solvent. By accounting for the anisotropy of the cells' cytoskeletal structures or extracellular matrix, as well as external constraints, a wide variety of growing shapes may be produced as illustrated in various examples.
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Affiliation(s)
- Gerard A. Ateshian
- Columbia University, Department of Mechanical Engineering, 500 W 120th St, MC4703, New York, NY 10027 USA
- Columbia University, Department of Biomedical Engineering, 1210 Amsterdam Ave, MC8904, New York, NY 10027 USA
- Corresponding author (Gerard A. Ateshian)
| | - Barclay Morrison
- Columbia University, Department of Biomedical Engineering, 1210 Amsterdam Ave, MC8904, New York, NY 10027 USA
| | - Jeffrey W. Holmes
- University of Virginia, Departments of Biomedical Engineering and Medicine and Robert M. Berne Cardiovascular Research Center, Box 800759, Health System, Charlottesville, VA 22908
| | - Clark T. Hung
- Columbia University, Department of Biomedical Engineering, 1210 Amsterdam Ave, MC8904, New York, NY 10027 USA
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16
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Ateshian GA, Albro MB, Maas S, Weiss JA. Finite element implementation of mechanochemical phenomena in neutral deformable porous media under finite deformation. J Biomech Eng 2012; 133:081005. [PMID: 21950898 DOI: 10.1115/1.4004810] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Biological soft tissues and cells may be subjected to mechanical as well as chemical (osmotic) loading under their natural physiological environment or various experimental conditions. The interaction of mechanical and chemical effects may be very significant under some of these conditions, yet the highly nonlinear nature of the set of governing equations describing these mechanisms poses a challenge for the modeling of such phenomena. This study formulated and implemented a finite element algorithm for analyzing mechanochemical events in neutral deformable porous media under finite deformation. The algorithm employed the framework of mixture theory to model the porous permeable solid matrix and interstitial fluid, where the fluid consists of a mixture of solvent and solute. A special emphasis was placed on solute-solid matrix interactions, such as solute exclusion from a fraction of the matrix pore space (solubility) and frictional momentum exchange that produces solute hindrance and pumping under certain dynamic loading conditions. The finite element formulation implemented full coupling of mechanical and chemical effects, providing a framework where material properties and response functions may depend on solid matrix strain as well as solute concentration. The implementation was validated using selected canonical problems for which analytical or alternative numerical solutions exist. This finite element code includes a number of unique features that enhance the modeling of mechanochemical phenomena in biological tissues. The code is available in the public domain, open source finite element program FEBio (http:∕∕mrl.sci.utah.edu∕software).
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Affiliation(s)
- Gerard A Ateshian
- Department of Mechanical Engineering, Columbia University, New York, NY 10027, USA
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17
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Oswald ES, Ahmed HS, Kramer SP, Bulinski JC, Ateshian GA, Hung CT. Effects of hypertonic (NaCl) two-dimensional and three-dimensional culture conditions on the properties of cartilage tissue engineered from an expanded mature bovine chondrocyte source. Tissue Eng Part C Methods 2011; 17:1041-9. [PMID: 21797756 DOI: 10.1089/ten.tec.2011.0212] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Clinically relevant mature cartilage cells (chondrocytes) present challenges for use in cartilage tissue engineering applications, given their low capacity for cell division and tissue production. Since the in situ environment of chondrocytes is hypertonic relative to standard culture medium conditions, in this study we tested the hypothesis that using culture medium of a hypertonic, more physiologic osmolarity during both two-dimensional (2D) expansion of mature bovine chondrocytes (MBCs) and their subsequent encapsulation culture in three-dimensional (3D) agarose hydrogel constructs produces improved engineered tissue construct mechanical and biochemical properties. Results demonstrate that 2D expansion of MBCs in hypertonic (NaCl) medium before encapsulation yielded improved construct mechanical properties. However, 3D encapsulation culture of cells in hypertonic (NaCl) medium yielded poorer construct mechanical properties. Osmolarity-related differences in construct biochemical content and organization may have contributed to differences in mechanical properties, as construct glycosaminoglycan content correlated moderately with construct mechanical properties, and construct collagen distribution varied between 3D osmotic culture groups. Results of this study suggest that application of hypertonic (NaCl) medium during 2D mature chondrocyte expansion, but not 3D encapsulated chondrocyte culture, may serve as a convenient and inexpensive method for improving mechanical properties of expanded cell-seeded constructs.
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Affiliation(s)
- Elizabeth S Oswald
- Department of Biomedical Engineering, Columbia University, New York, New York, USA
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18
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Finan JD, Guilak F. The effects of osmotic stress on the structure and function of the cell nucleus. J Cell Biochem 2010; 109:460-7. [PMID: 20024954 PMCID: PMC3616882 DOI: 10.1002/jcb.22437] [Citation(s) in RCA: 84] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Osmotic stress is a potent regulator of the normal function of cells that are exposed to osmotically active environments under physiologic or pathologic conditions. The ability of cells to alter gene expression and metabolic activity in response to changes in the osmotic environment provides an additional regulatory mechanism for a diverse array of tissues and organs in the human body. In addition to the activation of various osmotically- or volume-activated ion channels, osmotic stress may also act on the genome via a direct biophysical pathway. Changes in extracellular osmolality alter cell volume, and therefore, the concentration of intracellular macromolecules. In turn, intracellular macromolecule concentration is a key physical parameter affecting the spatial organization and pressurization of the nucleus. Hyper-osmotic stress shrinks the nucleus and causes it to assume a convoluted shape, whereas hypo-osmotic stress swells the nucleus to a size that is limited by stretch of the nuclear lamina and induces a smooth, round shape of the nucleus. These behaviors are consistent with a model of the nucleus as a charged core/shell structure pressurized by uneven partition of macromolecules between the nucleoplasm and the cytoplasm. These osmotically-induced alterations in the internal structure and arrangement of chromatin, as well as potential changes in the nuclear membrane and pores are hypothesized to influence gene transcription and/or nucleocytoplasmic transport. A further understanding of the biophysical and biochemical mechanisms involved in these processes would have important ramifications for a range of fields including differentiation, migration, mechanotransduction, DNA repair, and tumorigenesis.
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Affiliation(s)
- John D Finan
- Department of Surgery, Duke University Medical Center, Durham, North Carolina 27710, USA
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19
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Elkin BS, Shaik MA, Morrison B. Fixed negative charge and the Donnan effect: a description of the driving forces associated with brain tissue swelling and oedema. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2010; 368:585-603. [PMID: 20047940 PMCID: PMC2944388 DOI: 10.1098/rsta.2009.0223] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Cerebral oedema or brain tissue swelling is a significant complication following traumatic brain injury or stroke that can increase the intracranial pressure (ICP) and impair blood flow. Here, we have identified a potential driver of oedema: the negatively charged molecules fixed within cells. This fixed charge density (FCD), once exposed, could increase ICP through the Donnan effect. We have shown that metabolic processes and membrane integrity are required for concealing this FCD as slices of rat cortex swelled immediately (within 30 min) following dissection if treated with 2 deoxyglucose + cyanide (2DG+CN) or Triton X-100. Slices given ample oxygen and glucose, however, did not swell significantly. We also found that dead brain tissue swells and shrinks in response to changes in ionic strength of the bathing medium, which suggests that the Donnan effect is capable of pressurizing and swelling brain tissue. As predicted, a non-ionic osmolyte, 1,2 propanediol, elicited no volume change at 2000 x 10(-3) osmoles l(-1) (Osm). Swelling data were well described by triphasic mixture theory with the calculated reference state FCD similar to that measured with a 1,9 dimethylmethylene blue assay. Taken together, these data suggest that intracellular fixed charges may contribute to the driving forces responsible for brain swelling.
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20
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Influence of the partitioning of osmolytes by the cytoplasm on the passive response of cells to osmotic loading. Biophys J 2010; 97:2886-93. [PMID: 19948117 DOI: 10.1016/j.bpj.2009.09.011] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2009] [Revised: 08/15/2009] [Accepted: 09/03/2009] [Indexed: 12/14/2022] Open
Abstract
Due to the dense organization of organelles, cytoskeletal elements, and protein complexes that make up the intracellular environment, it is likely that membrane-permeant solutes may be excluded from a fraction of the interstitial space of the cytoplasm via steric restrictions, electrostatic interactions, and other long-range intermolecular forces. This study investigates the hypothesis that the intracellular partitioning of membrane-permeant solutes manifests itself as a partial volume recovery in response to hyperosmotic loading, based on prior theoretical and biomimetic experimental studies. Osmotic loading experiments are performed on immature bovine chondrocytes using culture conditions where regulatory volume responses are shown to be insignificant. Osmotic loading with membrane-permeant glycerol (92 Da) and urea (60 Da) are observed to produce partial volume recoveries consistent with the proposed hypothesis, whereas loading with 1,2-propanediol (76 Da) produces complete volume recovery. Combining these experimental results with the previous theoretical framework produces a measure for the intracellular partition coefficient of each of these solutes. At 1000 mOsm, 1,2-propanediol is the only osmolyte to yield a partition coefficient not statistically different from unity, kappa(p)(i) = 1.00 +/- 0.02. For glycerol, the partition coefficient increases with osmolarity from kappa(p)(i) = 0.48 +/- 0.19 at 200 mOsm to kappa(p)(i) = 0.80 +/- 0.07 at 1000 mOsm; urea exhibits no such dependence, with an average value of kappa(p)(i) = 0.87 +/- 0.07 for all osmolarities from 200 to 1000 mOsm. The finding that intracellular partitioning of membrane-permeant solutes manifests itself as a partial volume recovery under osmotic loading offers a simple method for characterizing the partition coefficient. These measurements suggest that significant partitioning may occur even for small membrane-permeant osmolytes. Furthermore, a positive correlation is observed, suggesting that a solute's cytoplasmic partition coefficient increases with increasing hydrophobicity.
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21
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Ateshian GA, Costa KD, Azeloglu EU, Morrison B, Hung CT. Continuum modeling of biological tissue growth by cell division, and alteration of intracellular osmolytes and extracellular fixed charge density. J Biomech Eng 2010; 131:101001. [PMID: 19831471 DOI: 10.1115/1.3192138] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
A framework is formulated within the theory of mixtures for continuum modeling of biological tissue growth that explicitly addresses cell division, using a homogenized representation of cells and their extracellular matrix (ECM). The model relies on the description of the cell as containing a solution of water and osmolytes, and having a porous solid matrix. The division of a cell into two nearly identical daughter cells is modeled as the doubling of the cell solid matrix and osmolyte content, producing an increase in water uptake via osmotic effects. This framework is also generalized to account for the growth of ECM-bound molecular species that impart a fixed charge density (FCD) to the tissue, such as proteoglycans. This FCD similarly induces osmotic effects, resulting in extracellular water uptake and osmotic pressurization of the ECM interstitial fluid, with concomitant swelling of its solid matrix. Applications of this growth model are illustrated in several examples.
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Affiliation(s)
- Gerard A Ateshian
- Department of Mechanical Engineering, Columbia University, New York, NY 10027, USA.
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22
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Albro MB, Rajan V, Li R, Hung CT, Ateshian GA. Characterization of the Concentration-Dependence of Solute Diffusivity and Partitioning in a Model Dextran-Agarose Transport System. Cell Mol Bioeng 2009; 2:295-305. [PMID: 21152414 DOI: 10.1007/s12195-009-0076-4] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
This study reports experimental measurements of solute diffusivity and partition coefficient for various solute concentrations and gel porosities, and proposes novel constitutive relations to describe these observed values. The longer-term aim is to explore the theoretical ramifications of accommodating variations in diffusivity and partition coefficient with solute concentration and tissue porosity, and investigate whether they might suggest novel mechanisms not previously recognized in the field of solute transport in deformable porous media. The study implements a model transport system of agarose hydrogels to investigate the effect of solute concentration and hydrogel porosity on the transport of dextran polysaccharides. The proposed phenomenological constitutive relations are shown to provide better fits of experimental results than prior models proposed in the literature based on the microstructure of the gel. While these constitutive models were developed for the transport of dextran in agarose hydrogels, it is expected that they may also be applied to the transport of similar molecular weight solutes in other porous media. This quantification can assist in the application of biophysical models that describe biological transport in deformable tissues, as well as the cell cytoplasm.
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Affiliation(s)
- Michael B Albro
- Department of Biomedical Engineering, Columbia University, New York
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23
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Moffat KL, Kwei ASP, Spalazzi JP, Doty SB, Levine WN, Lu HH. Novel nanofiber-based scaffold for rotator cuff repair and augmentation. Tissue Eng Part A 2009; 15:115-26. [PMID: 18788982 DOI: 10.1089/ten.tea.2008.0014] [Citation(s) in RCA: 237] [Impact Index Per Article: 15.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The debilitating effects of rotator cuff tears and the high incidence of failure associated with current grafts underscore the clinical demand for functional solutions for tendon repair and augmentation. To address this challenge, we have designed a poly(lactide-co-glycolide) (PLGA) nanofiber-based scaffold for rotator cuff tendon tissue engineering. In addition to scaffold design and characterization, the objective of this study was to evaluate the attachment, alignment, gene expression, and matrix elaboration of human rotator cuff fibroblasts on aligned and unaligned PLGA nanofiber scaffolds. Additionally, the effects of in vitro culture on scaffold mechanical properties were determined over time. It has been hypothesized that nanofiber organization regulates cellular response and scaffold properties. It was observed that rotator cuff fibroblasts cultured on the aligned scaffolds attached along the nanofiber long axis, whereas the cells on the unaligned scaffold were polygonal and randomly oriented. Moreover, distinct integrin expression profiles on these two substrates were observed. Quantitative analysis revealed that cell alignment, distribution, and matrix deposition conformed to nanofiber organization and that the observed differences were maintained over time. Mechanical properties of the aligned nanofiber scaffolds were significantly higher than those of the unaligned, and although the scaffolds degraded in vitro, physiologically relevant mechanical properties were maintained. These observations demonstrate the potential of the PLGA nanofiber-based scaffold system for functional rotator cuff repair. Moreover, nanofiber organization has a profound effect on cellular response and matrix properties, and it is a critical parameter for scaffold design.
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Affiliation(s)
- Kristen L Moffat
- Biomaterials and Interface Tissue Engineering Laboratory, Department of Biomedical Engineering, Columbia University, New York, New York, USA
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24
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Finan JD, Chalut KJ, Wax A, Guilak F. Nonlinear osmotic properties of the cell nucleus. Ann Biomed Eng 2008; 37:477-91. [PMID: 19107599 DOI: 10.1007/s10439-008-9618-5] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2008] [Accepted: 12/03/2008] [Indexed: 12/20/2022]
Abstract
In the absence of active volume regulation processes, cell volume is inversely proportional to osmolarity, as predicted by the Boyle Van't Hoff relation. In this study, we tested the hypothesis that nuclear volume has a similar relationship with extracellular osmolarity in articular chondrocytes, cells that are exposed to changes in the osmotic environment in vivo. Furthermore, we explored the mechanism of the relationships between osmolarity and nuclear size and shape. Nuclear size was quantified using two independent techniques, confocal laser scanning microscopy and angle-resolved low coherence interferometry. Nuclear volume was osmotically sensitive but this relationship was not linear, showing a decline in the osmotic sensitivity in the hypo-osmotic range. Nuclear shape was also influenced by extracellular osmolarity, becoming smoother as the osmolarity decreased. The osmotically induced changes in nuclear size paralleled the changes in nuclear shape, suggesting that shape and volume are interdependent. The osmotic sensitivity of shape and volume persisted after disruption of the actin cytoskeleton. Isolated nuclei contracted in response to physiologic changes in macromolecule concentration but not in response to physiologic changes in ion concentration, suggesting solute size has an important influence on the osmotic pressurization of the nucleus. This finding in turn implies that the diffusion barrier that causes osmotic effects is not a semi-permeable membrane, but rather due to size constraints that prevent large solute molecules from entering small spaces in the nucleus. As nuclear morphology has been associated previously with cell phenotype, these findings may provide new insight into the role of mechanical and osmotic signals in regulating cell physiology.
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Affiliation(s)
- John D Finan
- Department of Surgery, Duke University Medical Center, 375 MSRB, Box 3093, Durham, NC 27710, USA
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