(5dr) Studies in Cell Mechanobiology toward Tissue Engineering

The study of cellular responses to mechanical forces and the modification of these responses by growth factors allows for exploration of the underlying principles of tissue physiology and disease. Chondrocytes (cartilage cells) were utilized as a model for cell mechanotransduction with the goal of pinpointing stimuli that could be used for the formulation of future cartilage tissue repair and replacement strategies, as well as etiopathogenesis and treatments for the disease osteoarthritis. Initial work established unconfined compression as a method for creep testing single adherent chondrocytes and continuum mechanics models were developed to obtain viscoelastic material properties. Concurrently, techniques were developed to isolate specific single chondrocytes and assay their gene expression with real-time RT-PCR. The development of these techniques allowed gene expression to be assayed after static compression in single cells. Static compression was shown to elicit a catabolic response that could be partially rescued with exposure to soluble growth factors. Further studies suggested that transcription was modified directly by nuclear strains through force-mediated changes of the chromatin. This work provided the first evidence of mechanical forces modifying gene expression and provides a starting point for future studies where precise thresholds of mechanical stimulation required to elicit desired metabolic changes in single cells can be determined.

Postdoctoral work (under the supervision of Molly Shoichet, University of Toronto):

Recent findings have demonstrated that adult tissues harbor cells that have the potential to differentiate into multiple cell types. These cells have been termed adult or somatic stem cells. Adult stem cells may offer treatments for previously untreatable diseases or traumatic injuries. To apply these cells toward the functional regeneration of tissues, we must first decipher the microenvironment that guides these cells towards tissue specific differentiation, proliferation and matrix synthesis. In response to this need, a novel photo-crosslinkable methacrylamide-chitosan (MAC) scaffold has been developed to enable precise control of the cell microenvironment. This MAC system facilitates the study of cell responses to substrate stiffness in both 2D and 3D. Additionally, bioactive proteins and chemicals can be covalently attached to MAC to further modify cell responses. MAC has been utilized to study the influence of substrate stiffness, ECM proteins, soluble and immobilized cytokines on the differentiation of adult brain-derived neural stem cells (BNSCs). This scaffold has guided BNSC differentiation, has helped to improve our understanding of the stem cell niche and has revealed the influence of substrate stiffness during stem cell differentiation and maturation. Such information is vital for successful future tissue engineering endeavors as well as the study of tissue homeostasis and disease.