Date of Award

2019

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Graduate Group

Bioengineering

First Advisor

Jason A. Burdick

Abstract

Articular cartilage injury and progressive degeneration, combined with the clinical needs that result from an aging population and increasing rates of diagnosed osteoarthritis, have created a burgeoning demand for therapies aimed at cartilage repair. One approach that has gained traction is the delivery of clinically relevant cell types such as mesenchymal stromal cells to the injury site using hydrogels, which are water-swollen polymer networks that can be engineered to suit a wide variety of applications. Previous insights have led us to identify the roles of parameters such as cellular density, matrix degradation, mechanical loading, and even cell-cell communication in engineered cartilage formation and maturation. These hydrogels often employ biomaterials such as hyaluronic acid that are native to the body and intended to influence cell behavior. However, hydrogel-based therapies to date have predominantly focused on permitting or facilitating the eventual maturation of cartilage tissue by enabling matrix remodeling and distribution; meanwhile, the need for materials with controlled and timely presentation of cues that are essential for correct initial lineage commitment and early differentiation by cells has often been overlooked.

This dissertation describes the design and characterization of hyaluronic acid hydrogels that incorporate developmentally relevant and tunable cell-matrix and cell-cell cues that are critical in the early lineage commitment and differentiation of mesenchymal stromal cells. In particular, emphasis is given to the presentation of such cues over time at the cell-hydrogel interface, where cells encapsulated in these hydrogels actively interact with and even contribute to their microenvironments.

First, we examine tunable cell-matrix interactions in hydrogels by demonstrating that the biological activity of cell-laden hydrogels formed using crosslinkable modified hyaluronic acid, which provides cell-matrix cues relevant to cartilage development, may be altered as a function of the extent, type, and location of macromer modification. In both early gene expression and long-term in vitro culture, we show that this can alter mesenchymal stromal cell differentiation and subsequent construct maturation. Building on this, we explore a hyaluronic acid-based hydrogel with additional tunable cell-cell interaction mimicry via N-Cadherin mimetic peptides. We demonstrate the ability of this cue to also enhance both early differentiation and long-term neotissue formation by cells in a dose- and timing-dependent manner, where higher concentrations further promote the maturation of the engineered construct as long as the signal is stably presented to influence cell behavior during early timepoints. Finally, we examine the spatial deposition of pericellular matrix at the cell-hydrogel interface using live-cell metabolic labeling to determine when, and for how long, the cues that are engineered into hydrogels may in fact be presented to cells. We show that cells may physically displace the hydrogel from their microenvironment as they begin to synthesize and deposit pericellular matrix, and that this can occur as soon as 3 days after encapsulation, with important implications for hydrogel design towards cartilage tissue engineering applications.

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