A Novel Bioelastomer Platform with Tailorable Design Parameters for Cartilage Regeneration

Abstract

Articular cartilage has a limited ability to self-repair, which often causes focal defects to progress into post-traumatic osteoarthritis. Autologous chondrocyte implantation, a process in which chondrocytes are harvested from the patient, expanded in monolayer culture, and injected into the defect, is one of the most common approaches to treating cartilage defects. However, chondrocyte dedifferentiation during this process reduces their ability to durably restore cartilage function. Chondrocyte-based cartilage tissue engineering offers alternative approaches for cartilage repair to overcome the limitations of current clinical options by developing environments that combine cues from synthetic scaffolds and biological factors to enhance chondrocyte function. However, the translation to the clinic has been limited by our incomplete understanding of how scaffold design parameters interact together to control cell function. Therefore, this dissertation focuses on designing a chondrocyte-based biomaterial platform made with a novel elastomer, poly (glycerol-dodecanedioate) (PGD), to investigate the combinatorial effects of scaffold parameters, such as surface modification and pore geometry, on chondrocyte function in vitro. First, this thesis evaluates the effects of surface modification of PGD on the shape and extracellular matrix (ECM) production of chondrocytes, both of which are crucial for robust cartilage formation. Two different strategies were investigated to generate a PGD surface with enhanced hydrophilicity: 1) coating with various concentrations of collagen type I (Col I) or hyaluronic acid (HyA) individually or in combination, or 2) altering the surface charge and roughness using various levels of alkaline hydrolysis. The results revealed the combinatorial effects of ligand composition and density on human articular chondrocyte (hAC) function. HyA-coated PGD induced a round cell shape, leading to higher ECM production, while Col I-coated PGD induced a polygonal shape. Coating with either HyA or Col I alone induced a dose-dependent response to the retention of both ligands on PGD. The combination of Col I and HyA, even with a higher HyA retention level, was not conducive to higher ECM accumulation than HyA alone. The combinatorial effects of surface charge and roughness affected hAC function in a complex manner. Increasing hydrolysis level led to higher surface charge density, however, this changed PGD’s surface morphology and roughness. Slightly rough surfaces with moderately charged resulted in round cell morphology and the highest ECM production. Lastly, this thesis describes a novel approach to generating porous PGD scaffolds with tailorable pore structures. Additionally, finite element analysis was used to determine if the local strain fields that developed inside the pores under load could be tuned to be within the range shown to have an anabolic effect on chondrocyte function. The tensile strains that develop along 31% – 71% pore surfaces inside of porous PGD scaffolds, according to varying pore size and porosity, were at levels shown to stimulate chondrocyte ECM production, indicating that the pore structural parameters could be tuned to optimize cellular strain profiles. These results suggest that porous PGD scaffolds have the potential to guide cartilage regeneration. Overall, this dissertation presents a strategy for designing an ideal platform to support hAC redifferentiation using a novel bioelastomer, PGD. This thesis provides a reasonable approach to optimize scaffold design and investigate the mechanistic regulation of scaffold parameters on chondrocyte function for tissue engineering purposes, which will be a significant push towards clinical application of chondrocytes-based cartilage defect repair using PGD or other elastomers with similar polyester properties and nonlinear elasticity.