Designing Hydrogels that Recapitulate Physiological Cell-Matrix Adhesions

PROJECT SUMMARY Better model systems are needed to improve our understanding of how tissues develop, function, and regenerate in order to design more effective biomedical therapies. Synthetic hydrogel matrices have been widely used in these applications and have significant advantages as fully defined systems that can be tailored

to specific biomedical applications through the inclusion bioactive ligands within matrices having tunable viscoelasticity. However, the extracellular matrix (ECM) that surrounds cells in tissues contains numerous proteins and biopolymers that are dynamically modified by cells, and which aspects of cell-ECM interactions

are most important for recapitulating physiological adhesions is an area of active research. All adherent cell types use both syndecans and integrins to mediate cell attachment to the ECM and measure the local viscoelastic properties. However, most hydrogel systems are often functionalized with a single integrin-binding

RGD ligand covalently attached to the polymer network, which does not bind syndecans and cannot be re- arranged by cells. We propose to develop a platform technology that can be used to better mimic cell-ECM interactions found in tissues. This will be done by including dynamic ligands for both integrins and syndecans

within a hydrogel having tunable viscoelastic properties. We have developed a platform that utilizes interpenetrating networks of covalent and multiplexed non-covalent polymers to enables us to independently tune the mobility of multiple adhesion ligands in addition to both the stiffness and stress relaxation of the

hydrogel. We hypothesize that including dynamic ligands for syndecans will lead to cell-matrix adhesions that better recapitulate those found in tissues, and this will increase osteogenic differentiation of human mesenchymal stem cells within viscoelastic matrices. We will test this hypothesis in two aims. The First Aim

utilizes a multiplexed system containing multiple discrete self-assembling peptide nanofiber networks, each which can be functionalized with ligands for either integrins or syndecans having tunable mobility. Different ligand combinations and mobilities will be tested the number and size of focal adhesions will be quantified, in

addition to the extent of actin network formation. The Second Aim will utilize covalent and non-covalent networks to tune the viscoelastic properties of the hydrogel to understand how syndecans and integrins combine to transduce mechanical signals that drive cell behavior. We will culture hMSCs in gels having

different viscoelastic properties and ligand compositions to understand and quantify how dynamic syndecan ligands increase osteogenic differentiation of hMSCs. The PI has significant experience designing dynamic, viscoelastic hydrogel matrices to target specific cell-matrix interactions. This proposal will both help develop a

highly modular engineering platform that can be applied to a range of tissue systems, while also uncover design rules for recapitulate physiologically relevant cell-matrix interactions within synthetic systems.