The objectives of this work are the development of the processes, materials, and tooling to directly "3-D print" living, pre-seeded, patient-specific implants of spatially heterogeneous compositions. The research presented herein attempts to overcome some of the challenges to scaffolding, such as the difficulty of producing spatially heterogeneous implants that require varied seeding densities and/or cell-type distributions. In the proposed approach, living implants are fabricated by the layer-wise deposition of pre-cell-seeded alginate hydrogel. Although alginate hydrogels have been previously used to mold living implants, the properties of the alginate formulations used for molding were not suitable for 3-D printing. In addition to changing the formulation to make the alginate hydrogels "printable," we developed a robotic hydrogel deposition system and supporting CAD software to deposit the gel in arbitrary geometries. We demonstrated this technology's capabilities by printing alginate gel implants of multiple materials with various spatial heterogeneities, including, implants with completely embedded material clusters. The process was determined to be both viable (94±5% n=15) and sterile (less than one bacterium per 0.9 μL after 8 days of incubation). Additionally, we demonstrated the printing of a meniscus cartilage-shaped gel generated directly from a CT Scan. The proposed approach may hold advantages over other tissue printing efforts. This technology has the potential to overcome challenges to scaffolding and could enable the efficient fabrication of spatially heterogeneous, patient-specific, living implants.
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