Impacts of residual 3D printing metal powders on immunological response and bone regeneration: An in vivo study

Abstract

Background Residual powder is a defect in powder bed fusion-based additive manufacturing (3D printing), and it is difficult to completely remove it from as-printed materials. In addition, it is not necessary to apply 3D printed implants with residual powder in the clinic. The immunological response triggered by the residual powder is an important area of study in medical research. Methods To further understand the possible immunological reactions and hidden dangers caused by residual powders in vivo, this study compared the immunological reactions and osteolysis caused by typical powders for four implant materials: 316L stainless steel, CoCrMo, CP-Ti, and Ti-6Al-4V (particle size range of 15–45 µm), in a mouse skull model. Furthermore, the possible immunological responses and bone regeneration induced by the four 3D printed implants with residual powder in a rat femur model were compared. Results In the mouse skull model, it was found that the 316L-S, CoCrMo-S, and especially the 316L-M powders, upregulated the expression of pro-inflammatory factors, increased the ratio of RANKL/OPG, and activated more functional osteoclasts, resulting in more severe bone resorption compared with those in other groups. In the rat femur model, which is more suitable for clinical practice, there is no bone absorption in implants with residual powders, but they show good bone regeneration and integration ability because of their original roughness. The results indicate that the expressions of inflammatory cytokines in all experimental groups were the same as those in the control group, showing good biological safety. Conclusions The results answered some critical questions related to additively manufactured medical materials in vivo and indicated that as-printed implants may have great potential in future clinical applications.

Role of Triply Periodic Minimal Surface Ti6Al4V ELI alloy lattices fabricated by L-PBF method on cell behavior and inflammatory response

“…There were no major differences in the expression of pro-in ammatory cytokines between non-etching and etching groups, regardless of lattice design, but the printed lattice seemed to increase the cytokines within 24 h. In terms of in ammatory gene expression, both IDO and IFN-γ were upregulated, while in ammatory cytokines IL-1β and TNF-α were slightly increased. The low expression of in ammatory cytokines in the current investigation could be due to the biocompatibility property of titanium alloy powder itself as mentioned in the previous study 27 . It cannot, however, indicate that residual unmelted metallic powder is completely safe for human health.…”

“…These loosely attached powder particles could affect the mechanical properties of printed parts, like fatigue strength. Moreover, if the unmelted powders loosen, these can trigger an immunological response and result in chronic in ammation 14,15,27 . This was among the primary reasons behind the post-surface treatment used in this investigation, which was to remove as many unmelted powder particles as possible.…”