The contribution of pore size and porosity of 3D printed porous titanium scaffolds to osteogenesis

Porous titanium implants were popularly fabricated to promote bone formation. A desirable porous scaffold was recommended to be with porosity of >60% or/and pore size of >300 pm for better osteointegration. However, whether the pore size and porosity could be randomly selected within the recommended values? And what is the correlation between pore size and porosity for accelerating osteointegration? In this study, porous titanium with cubic cell structure was produced by selective laser melting. The designed porosities of scaffolds with 700-pm pore size were 40%, 70% and 90%; and the pore sizes of scaffolds with 70% porosity were 400, 700 and 900 pm. The in vitro osteogenic potential and in vivo bone formation were investigated. Results showed that porosity and pore size could be tuned by altering strut size, which was further directly responsible for mechanical properties. Besides, pore size and porosity synergistically contributed to osteogenic activity in vitro and new bone formation in vivo. In regard to pore sizes herein, the optimized one for better osteogenic response and bone forming ability was -600-700 pm (p70). Too smaller or too larger pore size might more or less hinder cellular behaviors and bone regeneration, even if both pore size (300-900 pm) and porosity (70%) were within the recommended value range. At a constant pore size (-600-700 pm), p70 and p90 with higher porosity was more conductive to biological effects, compared with p40. As a result, pore-size variation revealed more significant influence on osteogenesis, compared with variation of porosity within recommended values. However, the applicable porosity within recommended values should be designed with the consideration of specific load-bearing conditions. This study helps to provide guidance for designing porous scaffolds with appropriate mechanical strengths and effective bone-forming ability, so as to develop better custom-made bone substitutes.

Automated summary

This study investigated the effects of pore size and porosity on bone formation using porous titanium implants. The results showed that the pore size and porosity could be controlled by altering the strut size, which had a direct impact on mechanical properties. In vitro and in vivo experiments demonstrated that both pore size and porosity played a synergistic role in promoting osteogenic activity and bone formation. The optimal pore size for better osteogenic response and bone forming ability was found to be around 600-700 pm. Additionally, variations in pore size had a more significant influence on osteogenesis compared to variations in porosity within the recommended values. Therefore, the design of porous scaffolds should consider specific load-bearing conditions.