Development of the porous bone scaffold utilizing 3-dimensional CAD and solid freeform fabrication method

Abstract

The number of bone-graft surgery is rising rapidly with the growth of the interest in the quality of life and the population recently. The grafting bone should have proper pores and mechanical strength with a shape adjusting to the bone defect area.At present, commercially available porous bone substitutes are manufactured by a sacrificial template method, a direct foaming method and a polymer replication method (PRM). But current manufacturing methods provide the simplest form of the bone scaffold and also limited in that it cannot easily control pore size. However, in recent years with the development of medical imaging technology, computer-aided design (CAD) and the solid freeform fabrication (SFF), it is possible to accurately produce the synthetic porous bone scaffolds to fit the bone defect shape. Therefore, this study aimed to propose a new approach to the bone scaffold with various kinds of external and internal structure, which could existing bone growth factor as the optimal bone scaffold.For the suggestion of the optimal structure with internal pores, an engineering review of the various design by 3D CAD and a comparison between their structural characteristics by finite element analysis (FEA) were conducted. SFF scaffolds were fabricated using the suggested model and the one produced by commercialized method was prepared for the biomechanical stability comparison. And for the cell-compatibility assessment and the biological safety evaluation, in vitro and in vivo test on the SFF scaffold were proceeded. The efficacy was confirmed from the aspect of bone histomorphometry and the interfacial strength. The suggested 3D model has interconnected cubic pores of 500 ㎛ and its calculated porosity is 25%. Whereas HA scaffolds fabricated by SFF showed connective macropores, that by PRM formed closed pores. Average compressive strength of scaffold fabricated by SFF was 14.6 ㎫, and that of scaffold fabricated by polymer replication was 3.56 ㎫. It was confirmed that SFF fabrication could have relatively higher mechanical property than that by PRM at the same porosity.Biocompatibility safety was confirmed by tests of cytotoxicity, hemolysis, irritation, sensitization and implantation. There was no abnormal response and potential hazard in the tests. And the histological analysis and interfacial strength evaluation on the scaffolds fabricated by SFF and PRM were carried out for the assessment of efficacy. The histological results on osteoconductivity showed no significant difference. An average of maximum load of SFF type (169 N) is higher than that of PRM type (153 N) without any statistical significance. It means that implantation of SFF type would have the effective results to the level of the conventional scaffolds in terms of the osteoconduction. In summary, this study was to implement the porous bone scaffolds freely controlling pore shape and size, and to verify safety and efficacy on the scaffolds by biomechanical, biological and implantation tests. Therefore, this research could promote the feasibility of bone substitute with following feature: regeneration of bone tissue suitable to biological environment like bone grafts, no need of extra surgery like synthesis material, no limit to the amount or shape, and endurance of physiological load occurring in operating area.