UCLA

Three-dimensional printing (3DP) uses inkjet printheads to selectively deposit liquid binder to adjoin powder particles in a layer-by-layer fashion to create a computer-modeled 3D object. Two general approaches for 3DP have been described for biomedical applications-- direct and indirect 3DP. The two approaches offer competing advantages, and both are limited by print resolution. This study describes materials processing strategies to enhance both indirect and direct 3DP resolution by shrinking.

For indirect 3DP, 3DP resolution was improved by controlled shrinking of net-shape scaffolds. Briefly, porogen preforms are printed and infused with the desired monomer or polymer solution. After solidification or polymerization, the porogen is leached and the polymer is allowed to shrink by controlled drying. Heat treatment is performed to retain the dimensions against swelling forces. The main objectives are to determine the effects of polymer content and post-processing on dimension, microstructure, and thermomechanical properties of the scaffold. For polyethylene glycol diacrylate, reducing polymer content corresponded with greater shrinkage, with maximum shrinkage of ~80 vol% at polymer content of 20%. The secondary heat treatment retains the microarchitecture and new dimensions of the scaffolds, even when the scaffolds are immersed into water. This material processing strategy provides an alternative method to enhance the resolution of 3D scaffolds, for a wide range of polymers, without optimizing the binder-powder interaction physics for each material combination.

For direct 3DP, a novel fabrication method was developed to create prints without organic solvent in the binder and shrinking was induced by a solvent plasticizer. PLGA was first made into microparticles and then mixed with sucrose particles to create the printing powder. A water-based binder was deposited onto the powder layers to create a print and then the polymer microparticles fused together with solvent vapor fusion. The sucrose was then removed by leaching and PLGA scaffolds permanently shrunken ~80% volumetrically in a solution of methanol to a final resolution of ~400 μm. The methanol was acting as a plasticizer by decreasing the Tg below room temperature to allow for the polymer network to collapse upon itself. This approach to increasing the resolution allows for material flexibility of 3DP by increasing the range of materials used in this process since polymer microparticles are fused after printing and polymer-binder printing conditions do not need to be optimized.

This thesis presents novel materials processing strategies to improve the resolution of indirect and direct 3DP resolution for biomaterials.