Title: Preconditioning Methods in Cartilage Tissue Engineering
Description: Cartilage has limited intrinsic healing potential, due to the low cell density and the lack of blood supply. Current treatments for cartilage repair rarely restore full structure and function to the native state. Tissue engineering holds promise to create cartilage grafts capable to withstand the stresses present in joints. More than 90% of articular cartilage tissue is composed of extracellular matrix and is located in the loading environment under low oxygen tension in knee joints. To form engineered constructs with mechanical properties compatible to native tissue, scaffolds should provide structural support, maintain cell phenotype and subsequently promote tissue development. The focus of this dissertation is on utilizing the physiological conditions found in joints to regulate biological behavior of cells. The first factor that was studied was the extracellular matrix. Two formats of silk fibroin-hydrogel and porous scaffolds - were examined for their potential as a supporting material for creating cartilage tissue constructs.

The composite silk made from nano-fibers and hydrogel - a structure resembling the collagen network and proteoglycan in native cartilage - improved equilibrium and dynamic modulus of engineered tissue by 50% and 60%, respectively, in comparison to silk hydrogel without fibers. The second factor studied was the modulation of oxygen level, which is a major regulator during native cartilage development. Chondrogenic differentiation was induced in human embryonic stem cells under hypoxic conditions, in conjunction with biochemical cues from bovine chondrocytes. As a result, SOX9, a key transcription factor of cartilaginous lineage, was upregulated in the induced cells. Subsequent cultivation under normoxic conditions resulted in robust formation of cartilage tissue. Taken together, studies conducted in my thesis work address two major challenges in cartilage tissue engineering: i) providing cells with structural and mechanical properties similar to native ECM for generating in vitro cartilaginous tissue and ii) preconditioning cells with physiological environment for directing chondrogenic differentiation.