Controlled fabrication of three-dimensional structures using photopolymerization

Controlled fabrication of three-dimensional structures at the molecular-, nano-, and micro-scale allows the manipulation of properties integral to biomedical applications, membranes, 3D printing, and other applications. This research examines methods of fabricating polymers with controlled, three-dimensional structure using photopolymerization and the effect of structured polymers on material properties. Structure can be modified on the molecular-scale by modifying the molecular weight and number of functional groups on a degradable poly(caprolactone) (PCL) prepolymer, the nano-scale by using lyotropic liquid crystals (LLCs) as polymer templates, and the micro-scale through stereolithography (SL) 3D printing. PCL is a degradable polyester used in a number of biomedical applications. Incorporating acrylate groups onto PCL allows cross-linked PCL polymer networks to be formed through photopolymerization. Modifying the molecular weight and number of functional groups on the PCL prepolymers enables control of polymer network structure and the resulting polymer properties. Controlled polymer structure enables reaction kinetics, mechanical properties, degradation rates, and 3D printed resolution to be successfully tailored without affecting in vitro and in vivo biocompatibility. Such control over polymer properties enables further use of cross-linked PCL in biomedical applications. LLCs are formed by the self-assembly of surfactant molecules in a solvent and form mesophases with structure on the nanometer-scale. Monomers can be incorporated into these structures and used to template ordered nanostructure in polymer materials when photopolymerized. In this work, a dicarboxylate gemini surfactant is used to template a hydrophobic monomer in the gyroid mesophase. The nanoporous nature of these materials remains after surfactant removal and leads to enhanced water swelling. The exquisite level of control over polymer network porosity provided by templating within the gyroid phases furnishes a promising new route toward nanostructured hydrophobic polymers. SL is an additive manufacturing technique that uses photopolymerization to build objects layer by layer. As such, it is a valuable technology for rapid prototyping, customization, and manufacturing of intricate structures. The layered nature of SL leads to significant anisotropic microstructure and properties that persist through UV post-cure. When a thermal initiator is incorporated into the 3D printed formulation, the degree of observed anisotropy decreases but is not completely eliminated. Furthermore, a reversible addition-fragmentation chain transfer (RAFT) agent can be incorporated into the formulation to modify anisotropic properties through living radical polymerization. The addition of a RAFT agent likely delays the polymer gel-point and improves 3D printing of micro-scale features by hindering polymer formation outside of illuminated areas. Further understanding the role of microstructure in 3D printed objects may lead to expanded applications of high-resolution, high-fidelity SL.