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Vernerey FJ, Lalitha Sridhar S, Muralidharan A, Bryant SJ. Mechanics of 3D Cell-Hydrogel Interactions: Experiments, Models, and Mechanisms. Chem Rev 2021; 121:11085-11148. [PMID: 34473466 DOI: 10.1021/acs.chemrev.1c00046] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Hydrogels are highly water-swollen molecular networks that are ideal platforms to create tissue mimetics owing to their vast and tunable properties. As such, hydrogels are promising cell-delivery vehicles for applications in tissue engineering and have also emerged as an important base for ex vivo models to study healthy and pathophysiological events in a carefully controlled three-dimensional environment. Cells are readily encapsulated in hydrogels resulting in a plethora of biochemical and mechanical communication mechanisms, which recapitulates the natural cell and extracellular matrix interaction in tissues. These interactions are complex, with multiple events that are invariably coupled and spanning multiple length and time scales. To study and identify the underlying mechanisms involved, an integrated experimental and computational approach is ideally needed. This review discusses the state of our knowledge on cell-hydrogel interactions, with a focus on mechanics and transport, and in this context, highlights recent advancements in experiments, mathematical and computational modeling. The review begins with a background on the thermodynamics and physics fundamentals that govern hydrogel mechanics and transport. The review focuses on two main classes of hydrogels, described as semiflexible polymer networks that represent physically cross-linked fibrous hydrogels and flexible polymer networks representing the chemically cross-linked synthetic and natural hydrogels. In this review, we highlight five main cell-hydrogel interactions that involve key cellular functions related to communication, mechanosensing, migration, growth, and tissue deposition and elaboration. For each of these cellular functions, recent experiments and the most up to date modeling strategies are discussed and then followed by a summary of how to tune hydrogel properties to achieve a desired functional cellular outcome. We conclude with a summary linking these advancements and make the case for the need to integrate experiments and modeling to advance our fundamental understanding of cell-matrix interactions that will ultimately help identify new therapeutic approaches and enable successful tissue engineering.
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Affiliation(s)
- Franck J Vernerey
- Department of Mechanical Engineering, University of Colorado at Boulder, 1111 Engineering Drive, Boulder, Colorado 80309-0428, United States.,Materials Science and Engineering Program, University of Colorado at Boulder, 4001 Discovery Drive, Boulder, Colorado 80309-613, United States
| | - Shankar Lalitha Sridhar
- Department of Mechanical Engineering, University of Colorado at Boulder, 1111 Engineering Drive, Boulder, Colorado 80309-0428, United States
| | - Archish Muralidharan
- Materials Science and Engineering Program, University of Colorado at Boulder, 4001 Discovery Drive, Boulder, Colorado 80309-613, United States
| | - Stephanie J Bryant
- Materials Science and Engineering Program, University of Colorado at Boulder, 4001 Discovery Drive, Boulder, Colorado 80309-613, United States.,Department of Chemical and Biological Engineering, University of Colorado at Boulder, 3415 Colorado Avenue, Boulder, Colorado 80309-0596, United States.,BioFrontiers Institute, University of Colorado at Boulder, 3415 Colorado Avenue, Boulder, Colorado 80309-0596, United States
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McEvoy E, Shishvan SS, Deshpande VS, McGarry JP. Thermodynamic Modeling of the Statistics of Cell Spreading on Ligand-Coated Elastic Substrates. Biophys J 2018; 115:2451-2460. [PMID: 30527450 DOI: 10.1016/j.bpj.2018.11.007] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2018] [Revised: 10/18/2018] [Accepted: 11/06/2018] [Indexed: 01/15/2023] Open
Abstract
Biological spread cells exist in a perpetually fluctuating state and therefore cannot be described in terms of a unique deterministic system. For modeling approaches to provide novel insight and uncover new mechanisms that drive cell behavior, a framework is required that progresses from traditional deterministic methods (whereby simulation of an experiment predicts a single outcome). In this study, we implement a new, to our knowledge, modeling approach for the analysis of cell spreading on ligand-coated substrates, extending the framework for nonequilibrium thermodynamics of cells developed by Shishvan et al. to include active focal adhesion assembly. We demonstrate that the model correctly predicts the coupled influence of surface collagen density and substrate stiffness on cell spreading, as reported experimentally by Engler et al. Low surface collagen densities are shown to result in a high probability that cells will be restricted to low spread areas. Furthermore, elastic free energy induced by substrate deformation lowers the probability of observing a highly spread cell, and, consequentially, lower cell tractions affect the assembly of focal adhesions. Experimentally measurable observables such as cell spread area and aspect ratio can be directly postprocessed from the computed homeostatic ensemble of (several million) spread states. This allows for the prediction of mean and SDs of such experimental observables. This class of cell mechanics modeling presents a significant advance on conventional deterministic approaches.
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Affiliation(s)
- Eoin McEvoy
- College of Engineering and Informatics, National University of Ireland Galway, Galway, Republic of Ireland
| | - Siamak S Shishvan
- Department of Structural Engineering, University of Tabriz, Tabriz, East Azarbayjan, Iran; Department of Engineering, University of Cambridge, Cambridge, United Kingdom
| | - Vikram S Deshpande
- Department of Engineering, University of Cambridge, Cambridge, United Kingdom
| | - J Patrick McGarry
- College of Engineering and Informatics, National University of Ireland Galway, Galway, Republic of Ireland.
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Lalitha Sridhar S, Vernerey FJ. The Chain Distribution Tensor: Linking Nonlinear Rheology and Chain Anisotropy in Transient Polymers. Polymers (Basel) 2018; 10:E848. [PMID: 30960773 PMCID: PMC6403683 DOI: 10.3390/polym10080848] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2018] [Revised: 07/27/2018] [Accepted: 07/30/2018] [Indexed: 01/14/2023] Open
Abstract
Transient polymer networks are ubiquitous in natural and engineered materials and contain cross-links that can reversibly break and re-form. The dynamic nature of these bonds allows for interesting mechanical behavior, some of which include nonlinear rheological phenomena such as shear thickening and shear thinning. Specifically, physically cross-linked networks with reversible bonds are typically observed to have viscosities that depend nonlinearly on shear rate and can be characterized by three flow regimes. In slow shear, they behave like Newtonian fluids with a constant viscosity. With further increase in shear rate, the viscosity increases nonlinearly to subsequently reach a maximum value at the critical shear rate. At this point, network fracture occurs followed by a reduction in viscosity (shear-thinning) with a further increase in shear rate. The underlying mechanism of shear thickening in this process is still unclear with debates between a conversion of intra-chain to inter-chain cross-linking and nonlinear chain stretch under high tension. In this paper, we provide a new framework to describe the nonlinear rheology of transient polymer networks with the so-called chain distribution tensor using recent advances from the transient network theory. This tensor contains quantitatively and statistical information of the chain alignment and possible anisotropy that affect network behavior and mechanics. We investigate shear thickening as a primary result of non-Gaussian chain behavior and derive a relationship for the nonlinear viscosity in terms of the non-dimensional Weissenberg number. We further address the criterion for network fracture at the critical shear rate by introducing a critical chain force when bond dissociation is suddenly accelerated. Finally, we discuss the role of cross-linker density on viscosity using a "sticky" reptation mechanism in the context of previous studies on metallo-supramolecular networks with reversible cross-linkers.
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Affiliation(s)
- Shankar Lalitha Sridhar
- Department of Mechanical Engineering, University of Colorado Boulder, Boulder, CO 80309, USA.
| | - Franck J Vernerey
- Department of Mechanical Engineering, University of Colorado Boulder, Boulder, CO 80309, USA.
- Materials Science and Engineering Program, University of Colorado Boulder, Boulder, CO 80309, USA.
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Genin GM, Shenoy VB, Peng G, Buehler MJ. Integrated Multiscale Biomaterials Experiment and Modeling. ACS Biomater Sci Eng 2017; 3:2628-2632. [PMID: 31157296 PMCID: PMC6544164 DOI: 10.1021/acsbiomaterials.7b00821] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
The integration of modeling and experimentation is an integral component of all engineering design. Developing the technologies to achieve this represents a critical challenge in biomaterials because of the hierarchical structures that comprise them and the spectra of timescales upon which they operate. Progress in integrating modeling and experiment in biomaterials represents progress towards harnessing them for engineering application. We present here a summary of the state of the art, and outlooks for the field as a whole.
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Affiliation(s)
- Guy M Genin
- Department of Mechanical Engineering and Materials Science, 1 Brookings Drive, Washington University in St. Louis, St. Louis, MO 63130 United States
- NSF Science and Technology Center for Engineering Mechanobiology, 1 Brookings Drive, Washington University in St. Louis, St. Louis, MO 63130 United States
| | - Vivek B Shenoy
- Department of Materials Science and Engineering, University of Pennsylvania, 220 South 33rd Street, Philadelphia, PA 19104-6391 United States
- NSF Science and Technology Center for Engineering Mechanobiology, University of Pennsylvania, 220 South 33rd Street, Philadelphia, PA 19104-6391 United States
| | - Grace Peng
- National Institute of Biomedical Imaging and Bioengineering, 6707 Democracy Boulevard, Suite 202, Bethesda, MD 20892-5469 United States
| | - Markus J Buehler
- Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States
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Sridhar SL, Schneider MC, Chu S, de Roucy G, Bryant SJ, Vernerey FJ. Heterogeneity is key to hydrogel-based cartilage tissue regeneration. SOFT MATTER 2017; 13:4841-4855. [PMID: 28613313 PMCID: PMC5552053 DOI: 10.1039/c7sm00423k] [Citation(s) in RCA: 31] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
Degradable hydrogels have been developed to provide initial mechanical support to encapsulated cells while facilitating the growth of neo-tissues. When cells are encapsulated within degradable hydrogels, the process of neo-tissue growth is complicated by the coupled phenomena of transport of large extracellular matrix macromolecules and the rate of hydrogel degradation. If hydrogel degradation is too slow, neo-tissue growth is hindered, whereas if it is too fast, complete loss of mechanical integrity can occur. Therefore, there is a need for effective modelling techniques to predict hydrogel designs based on the growth parameters of the neo-tissue. In this article, hydrolytically degradable hydrogels are investigated due to their promise in tissue engineering. A key output of the model focuses on the ability of the construct to maintain overall structural integrity as the construct transitions from a pure hydrogel to engineered neo-tissue. We show that heterogeneity in cross-link density and cell distribution is the key to this successful transition and ultimately to achieve tissue growth. Specifically, we find that optimally large regions of weak cross-linking around cells in the hydrogel and well-connected and dense cell clusters create the optimum conditions needed for neo-tissue growth while maintaining structural integrity. Experimental observations using cartilage cells encapsulated in a hydrolytically degradable hydrogel are compared with model predictions to show the potential of the proposed model.
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Affiliation(s)
| | - Margaret C. Schneider
- Department of Chemical and Biological Engineering, University of Colorado Boulder, USA
| | - Stanley Chu
- Department of Chemical and Biological Engineering, University of Colorado Boulder, USA
| | - Gaspard de Roucy
- Department of Mechanical Engineering, University of Colorado Boulder, USA
| | - Stephanie J. Bryant
- Department of Chemical and Biological Engineering, University of Colorado Boulder, USA
- Material Science and Engineering Program, University of Colorado Boulder, USA
- BioFrontiers Institute, University of Colorado Boulder, USA
| | - Franck J. Vernerey
- Department of Mechanical Engineering, University of Colorado Boulder, USA
- Material Science and Engineering Program, University of Colorado Boulder, USA
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