Design and evaluation of neuroregenerative properties of 4D hydrogel scaffolds

Understanding and controlling the interactions that occur between cells and engineered materials (i.e. attachment-detachment, or that influence cell development, function or fate) are central challenges towards progress in the development of biomedical devices and regenerative medicine therapies. A particularly complex system to translate in vitro is that of the dorsal root ganglion (DRG), an interesting research target due to its relevance in peripheral nerve repair, and to its connection to the non-regenerative central nervous system (CNS). Severe peripheral nerve injuries have a limited regenerative capacity, with interventions typically not leading to full functional recovery. Ways to improve functional recovery include engineering devices that connect to both injured sides, having both cell growth guiding properties and a gradient contour to control the extent of cell-scaffold interactions. Direct ink writing (DIW) is prominent among fabrication techniques relevant to tissue engineering due to its versatility in terms of the range of materials that can be used and the limitless geometries that are easily programmed. This thesis describes three different in vitro systems, representing increasing functionality towards next generation 4D scaffolds for nerve reconstruction in vitro or nerve regeneration in vivo. The first takes advantage of cell-extracellular matrix interactions and presents an extracellular matrix (ECM)-mimetic surface treatment which, combined with DIW scaffolds of a wide range of geometries and a “blank-slate” hydrogel (pHEMA), leads to a means to exert control on the degree of cell-scaffold interactions, and manipulate cell culture development in 4D. The second explores a different class of scaffolds, compressively buckled mesostructures, which can be used as high-strain cellular frameworks leading to interesting cell behavior depending on scaffold strain and geometric aspect ratio. Further, this approach allows for the incorporation of increased functionality into these mesostructures, as they can function as electronic scaffolds for stimulation and recording of action potentials from DRG cells. Finally, the third approach combines efforts of the first two projects, building upon the ink and surface chemistries explored in the first, and the geometries explored in the second, adding a bioactive inorganic composite to create selectively growth compliant scaffolds that generate a hierarchal reorganization of DRG cells in culture mimicking that of a nerve. With the possibility of extending the complexity of these scaffolds by including controlled degradation, this last approach provides important guidelines to developing effective 4D scaffolds for nerve regeneration