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A predominant challenge in tissue engineering is the need of a robust technique for producing structures with precise three-dimensional control of mechanical properties. In an effort to understand how to control the mechanical and chemical properties of materials patterned using stereolithography, this study focuses on the development of a model that allows for orthogonally programmable elastic modulus and geometry in a 3D hydrogel structure. In this study, we use pediatric physeal tissue engineering as a model application. Pediatric physeal injuries can be detrimental to children because damaged cartilage within the physis can lead to assymetric growth arrest. A challenge related to physeal tissue regeneration is the presence of three distinct zones within the physis or growth plate, where cells evolve differently and are known to be sensitive to the mechanical environment. We use a poly(ethylene glycol) diacrylate based photopolymerization chain-growth reaction with a modulus that can range from 600KPa to 39 MPa to spatially control the mechanical properties in our 3D parts and match the growth plate tissue environment. We apply Fourier transform infrared spectroscopy (FTIR) to quantify the degree of monomer conversion over time and intensity, while comparing it with a mechanical model that relates conversion to modulus. To evaluate the spatially controlled mechanical properties in printed structures, nanoindentation is performed to extract the modulus in each biomimetic zone. In this work we present the implementation of both a gradual change in mechanical properties, as well as a step function in 3D scaffolds on the order of 100 microns. This work enables predictive models of structural properties that can be translated into tissue engineering microstructures that match the native biomechanical environment of any tissue.
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