The experiments indicated that the fatty acid-based bioink is very suited to regenerative medicine as it enables rapid and simple 3D printing of biocompatible and bone-forming implants.
In the current in vivo mouse study, Ossiform’s nonpolymeric thermoplastic bioink composed of fatty acids and β-tricalcium phosphate was used to 3D print the skull implants. The bone implants were 3D printed as nets that were subsequently cut into circular implants with nine pores. Some of the implants were sintered to yield pure β-tricalcium phosphate implants while others were nonsintered to retain the fatty acid, all were sterilized, and some were seeded with stem cells. The results of the study’s two experiments introduced below demonstrated that both the sintered tricalcium phosphate implants and nonsintered fatty acid/tricalcium phosphate implants were highly biocompatible. However, only the sintered implants promoted defect healing, with osseointegration with adjacent bone and the formation of new bone and bone marrow tissue in the implant pores. Stem cells seeded onto these implants engraft and proliferate on the implants after implantation and contribute to bone formation. Meanwhile, the nonsintered implants formed vascularized and cell-rich tissues but no bone. Finally, the implant resorption rate appeared to depend strongly on the fatty acid tail length, confirming in vivo our previous in vitro observations (Jensen et al., 2018).
The purpose of the first experiment was to compare the performance of nonsintered lauric acid/tricalcium phosphate implants with sintered implants of pure tricalcium phosphate. The implants were 3D printed using the same technique and implanted in a mouse calvarial defect with and without stem cells. In addtion to the nonsintered and sintered implants with and without cells, the experimental groups included a hydroxyapatite-coated collagen sponge with cells which was used as positive control, and a negative control with an untreated empty void.
CT scans along with confirmatory histological images showed that the sintered implants supported bone formation and osseointegration at the implant/skull interface both with and without stem cells (see CT imaging below).