Direct Freeform Fabrication of Seeded Hydrogels in Arbitrary Geometries

TLDR

A major challenge in tissue engineering is generating cell‑seeded implants that mimic native tissue in both anatomic geometry and intratissue cell distribution. By combining injection molding tissue engineering with solid freeform fabrication, the authors fabricated 3‑D pre‑seeded implants without custom tooling, enabling efficient production of patient‑specific implants. The authors used a custom‑built robotic SFF platform with gel deposition tools to print alginate hydrogel seeded with cells, crosslinked by calcium sulfate, producing pre‑seeded implants of arbitrary geometries. The method produced sterile, viable implants (94 ± 5 %) with GAG and hydroxyproline production comparable to other shaping methods, enabled geometrically complex, multiple‑material constructs with spatially heterogeneous properties, and achieved high geometric fidelity with an RMS surface roughness of 0.16 ± 0.02 mm.

Abstract

A major challenge in tissue engineering is the generation of cell-seeded implants with structures that mimic native tissue, both in anatomic geometries and intratissue cell distributions. By combining the strengths of injection molding tissue engineering with those of solid freeform fabrication (SFF), three-dimensional (3-D) pre-seeded implants were fabricated without custom-tooling, enabling efficient production of patient-specific implants. The incorporation of SFF technology also enabled the fabrication of geometrically complex, multiple-material implants with spatially heterogeneous properties that would otherwise be challenging to produce. Utilizing a custom-built robotic SFF platform and gel deposition tools, alginate hydrogel was used with calcium sulfate as a crosslinking agent to produce pre-seeded living implants of arbitrary geometries. The process was determined to be sterile and viable at 94 ± 5%. The GAG and hydroxyproline production was found to be similar to that of other implants fabricated using the same materials with different shaping methods. The geometric fidelity of the process was quantified by using the printing platform as a computerized measurement machine (CMM); the RMS surface roughness of printed samples in the z-dimension was found to be 0.16 ± 0.02 mm.