Dissertation Defense: Stephanie Frahs

Title: Biomaterials and Biomimetic Models for Musculoskeletal Tissue Repair

Program: Biomolecular Sciences PhD

Committee Chair: Julia Oxford

Committee: Julia Oxford, Ken Cornell, Daniel Fologea

Abstract: Musculoskeletal tissue repair represents a major therapeutic challenge due to the complex structural, biochemical and mechanical heterogeneity of musculoskeletal tissues including ligament, tendon, cartilage, and bone. To elucidate the mechanisms governing ECM assembly and tissue repair, this research evaluated three biomimetic models targeting distinct musculoskeletal tissues: fibroblast-collagen hydrogels for ligament and tendon scar formation, three-dimensional (3D) graphene foam (GF) as a scaffold for cartilage regeneration, and freeze-dried decellularized cancellous bone allografts for osteogenic repair.

For ligament repair, culturing fibroblast-collagen hydrogels under stress-free, biaxial, and uniaxial conditions over three weeks demonstrated that stress-free loading induced time-dependent gene expression of early scar markers (Col3a1, TnC), whereas biaxial stress optimized matrix protein accumulation (type III collagen, decorin). Thus, initial culturing under biaxial stress best replicates native mechanical boundary constraints during early scar modeling.

For cartilage tissue engineering studies, functionalizing 3D GF scaffolds with fibronectin (FN) altered cellular responses in prechondrocytes. Molecular dynamics simulations identified non-covalent bonding via arginine side chains as the primary FN-graphene interface stabilizer. While FN functionalization increased scaffold elastic strength and promoted actin stress fiber formation, quantitative RT-PCR across a 34-gene panel revealed that unfunctionalized 3D GF provided a superior microenvironment for early chondrogenesis, underscoring the critical interplay between substrate mechanics and surface chemistry.

For osseous defect repair, comparative proteomic and spatial surface accessibility analyses of two freeze-dried demineralized human cancellous bone protocols revealed that differences in manufacturing processes directly shape ECM protein presentation and growth factor bioavailability to progenitor cells differentiating into mature osteoblasts.

Collectively, these findings demonstrate that successful musculoskeletal biomimetic models and bioscaffolds depend on a multi-facet approach that include biomechanical loading, surface microarchitecture, and proteomic bioavailability. Harnessing these combined insights allows for the better understanding of the design of next-generation biomimetic platforms and engineered scaffolds that allows for the study and understanding of the biological processes that can restore functional tissue integrity across soft and hard musculoskeletal tissues.