Extracellular Matrix-Enhanced Biomimetic Scaffolds for Tissue-Specific Orthopaedic Tissue Engineering

The work contained herein sought to combine soluble extracellular matrices (ECMs) derived from decellularized musculoskeletal tissues with biomimetic scaffolds for the purpose of orthopaedic tissue engineering. More broadly, tissue engineering combines cells, scaffolds, and biomolecules (e.g., growth factors and cytokines) to restore or replace biological tissues. Scaffolds derived from decellularized tissues provide cells with the biophysical and biochemical motifs that constitute the ECM of the native tissue, in turn promoting homologous (i.e., tissue-specific) cell phenotypes. However, decellularized whole tissues are limited in clinical use due to poor cell infiltration and constrained geometries. On the other hand, decellularized tissues can be pulverized or solubilized to theoretically provide a tissue-specific supplement that, in combination with biomimetic scaffolds, promotes homologous neotissue formation in a tissue defect regardless of shape or size. Nevertheless, the retention of tissue-specific bioactivity following solubilization of ECMs remains uncertain. In particular, few studies have explored the tissue-specific bioactivity of soluble ECM derived from decellularized musculoskeletal tissues.\ud \ud In this thesis, tendon, hyaline cartilage, and knee menisci were decellularized and solubilized through one of two methods – (1) urea extraction or (2) pepsin digestion. When added as medium supplements to in vitro cultures of human mesenchymal stem cells (MSCs) grown on two-dimensional (2D) plastic or as 3D MSC pellets, only urea-extracted ECM fractions promoted tissue-specific differentiation. Urea-extracted fractions of ECM derived from the inner and outer halves of the meniscus exerted region-specific effects, in agreement with the regional variations in ultrastructure, biochemical composition, and cell phenotype seen in native menisci. The soluble ECMs further enhanced tissue-specific differentiation when combined with biomimetic scaffolds, including aligned electrospun nanofibers to mimic tendon and photocrosslinkable hydrogels to mimic hyaline cartilage and inner meniscus. Additionally, soluble ECMs interacted synergistically with transforming growth factor beta (TGF-β) when provided as an exogenous supplement. Taken together, the work contained herein begins to elucidate the mechanisms by which soluble ECMs promote tissue specific effects and provides support for their use in orthopaedic tissue engineering