Three dimensional printing (3DP) offers precise control over macroscopic geometry and spatial distribution of multiple materials according to computerized 3D models. 3DP can also affect local composition and microstructure, and offer many new possibilities for the fabrication of biomedical devices. The ability to control microstructure is critical for drug delivery devices and tissue engineering matrices. The precise control of microstructure, however, requires a better understanding of the relationship between the material properties and processing variables. The proposed work focuses on identifying the critical parameters for controlling microstructure in 3DP polymeric parts. The ability to produce dense microstructure is critical in the fabrication of polymeric drug delivery devices. Preliminary results suggest that the ability to obtain dense microstructure is dependent on the powder material used, which is highly dependent on the purpose of drug delivery device. Oral dosage forms can be fabricated with pharmaceutical grade excipient powder and latex. The powder-binder interaction for this material combination is similar to that observed in conventional 3DP of ceramic (and stainless steel) parts, where loose ceramic particles are coated and gelled together by a polymer colloidal binder. The density of the typical pre-fired 3DP ceramic part is only on the order of 45-55o. Many of the post-processing techniques for industrial parts are inappropriate for the biomedical materials. Dense polymeric structures must, therefore, be obtained during printing. No previous work has been done on creating highly dense green parts directly by printing binder into porous powder bed. Implantable devices are designed to deliver drugs for months to years, and are typically constructed with bioerodable polymer powder and organic solvents. The powder-binder interaction for this material combination is unlike any other observed phenomena in 3DP. The neighboring polymeric particles are dissolved and joined together by the binder droplets. Oral and implantable devices with simple shapes will be fabricated with different combinations of 3DP processing variables, powder, and binder compositions. The devices will be sectioned and analyzed for density, and the results will be compared for various processing conditions. Physical models will be proposed to describe the critical phenomena which are responsible for the formation of dense structures for various materials systems. Real devices for oral delivery and implantation will be designed and constructed with 3DP, and device performance will be assessed by drug release profiles. Computer models will be proposed to model the release characteristics of the real devices. The second objective is to fabricate polymeric tissue engineering devices with controlled porosity. Tissue engineering devices are porous structures which act as scaffolds for guided tissue regeneration. The ability to preferentially promote cell adhesion and migration is accomplished by directing nutrient delivery in a complex, porous cell seeding structure. Experiments will be conducted to investigate various 3DP strategies to control channel dimensions (width and length), surface microporosity, and distribution of cell-matrix adhesion modifiers. The goal of the investigation is to determine the effects of these parameters on cell adhesion. The fundamental understanding of the relationship between material properties, 3DP variables, microstructure, and device performance will have real implications for device design and fabrication strategy of all future 3DP polymeric medical devices.
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