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3D printing hydrogels via stereolithography is a promising system for the creation of regenerative medical implants. However, the mechanical and chemical properties of materials patterned using stereolithography-based printing techniques are largely unknown. In an effort to understand how optical propagation, polymerization, and transport dynamics result in material mechanical property distribution, this study focuses on the axial (depth) characterization of single-layer printed materials as a function of light intensity, exposure time and absorption depth. We use a poly(ethylene glycol) diacrylate based photopolymerization chain-growth reaction with an approximate bulk modulus of 39 MPa to explore this phenomenon. Fourier transform infrared spectroscopy (FTIR) is employed to quantify the degree of monomer conversion over time and intensity, while comparing it with a Beer-Lambert model that describes the effect of Tinuvin CarboProtect, the neutral absorber in our material on conversion as a function of depth. To evaluate the mechanical properties of the printed materials, compression testing is performed on each sample to extract the bulk modulus and to map conversion as a function of exposure time by fitting the force-displacement curves of each condition to the Hertz model for a quantitative comparison of material stiffness. This study aims to understand material and mechanical property distribution in a single layer, and use this understanding to create a predictive model of these properties, as well as decrease the scale of the distribution with the implementation of a novel post-cure technique. This work enables predictive models of microscopic polymer properties that can be translated into improved macroscopic structural properties to form a robust polymer network for tissue engineering microstructures.
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