Date of Award

Summer 7-16-2014

Document Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

First Advisor

Stephanie J. Bryant

Second Advisor

Joel L. Kaar

Third Advisor

Kristi Anseth

Abstract

Cartilage tissue engineering using biodegradable scaffolds as carriers for cartilage cells (chondrocytes) presents a promising strategy to regenerate cartilage damaged by age, injury, or disease. State-of-the-art clinical therapies implement chondrocytes harvested from the patient, however these treatments suffer from patient-to-patient variability and ineffectiveness due to aging. Photopolymerizable poly(ethylene glycol) (PEG) hydrogel scaffolds that can be modified to permit tunable degradation present an opportunity to tailor scaffolds to the patient's cells. Scaffold degradation is crucial to encourage cartilaginous matrix deposition by entrapped chondrocytes, however the rate of degradation must be matched to matrix deposition, which is a significant design challenge further complicated by the effects of age.

The goal of this thesis was to characterize degradable PEG hydrogels towards developing a suitable cartilage tissue engineering platform that can be applied to a wide range of patients regardless of age. Initial work focused on bulk hydrolytically degradable scaffolds with poly(lactic acid) in the PEG crosslinks. Chondrocytes were isolated from skeletally mature and immature (adult and juvenile) bovine cartilage, and encapsulated in hydrolytically degradable scaffolds, revealing lower anabolic and higher catabolic activity of adult cells, further motivating the need to tailor scaffolds to donor age. Bulk degrading scaffolds swelled with time, increasing the network mesh size and permitting diffusive matrix loss. To improve matrix production and retention, degradable scaffolds were bioactively modified by entrapping a native matrix molecule involved in tissue assembly, and matching the culture medium to physiological osmolarity. Both strategies stimulated matrix deposition short-term but could not overcome long-term matrix loss due to bulk degradation. A new cartilage-specific enzymatically degradable hydrogel was created to encourage cell-localized degradation, by incorporating a peptide sequence into the PEG crosslinks that is degraded by chondrocyte-secreted enzymes. Enzymatically degradable scaffolds encouraged cartilaginous matrix deposition and interconnectivity. Experimental control over diffusion- and reaction dominated degradation (bulk vs. localized), both possible in enzymatically degradable hydrogels, was demonstrated using a model system where enzyme-laden microparticles simulated enzyme secretion from cells. This thesis demonstrated that enzymatically degradable hydrogels and bioactive modification are valuable tools to create a tunable degradable platform to promote tissue regeneration using cells from any patient.

Share

COinS