UC Santa Barbara

The last decade has seen tremendous advances in the use of stem cell-based therapies to treat injury and disease, yet there are many hurdles still to overcome. Tissue or organ-specific strategies have begun to emerge as our knowledge of stem cell biology and transplant biology increases. This thesis presents results aimed at understanding and improving cell based therapies for soft tissue repair. Defects in soft-tissue can occur by many means, including traumatic injury, tumor resection, and congenital causes. Current approaches to the treatment of these deficiencies include autologous fat transplantation, which falls short of optimal. There are numerous negative outcomes associated with this procedure, the most common of which is loss of transplanted volume; which occurs in 92% of cases.

This thesis describes efforts to improve autologous treatments by utilizing the stem cell population present in transplanted tissue, adipose-derived stem cells (ASCs), and encapsulating them in an environment that supports survival, improving treatment options. The following chapters provide an in-depth overview of the development of a synthetic scaffolding system that supports the survival and differentiation of ASCs in vitro. By utilizing poly(ethylene) glycol (PEG) we were able to model a biomimetic environment and demonstrate that functionalization of inert PEG with different Arg-Gly-Asp (RGD)-containing peptides resulted in different levels of adhesion.

After the development of the scaffolding system we sought to further engineer capabilities of the system to provide the possibility for numerous applications using the same basic chemistry. Capitalizing on what is known about the remodeling of natural extracellular matrix (ECM) we were able to incorporate peptides that permit the degradation of the scaffolding after the stem cells differentiate. Selecting a cleavage sequence that is sensitive to proteinases that are secreted by mature adipocyte and not by undifferentiated ASCs we succeeded in creating a hydrogel that mimics a natural environment and is degradable upon the differentiation of ASCs to the desired cell types. We have further demonstrated that ASCs encapsulated in this system are viable for 12 weeks, both in vitro and in vivo. Although we examined just adipogenic differentiation in this work, due to the simple nature of the system it should be possible to systematically alter the incorporated components for applications of other cell types. This affords extensive possible targets for tissue regeneration utilizing a basic scaffolding system. Collectively, the work described here advances the understanding and application of stem cell based therapies for soft tissue repair and regeneration.