In-vitro corrosion and biocompatibility of additively manufactured biodegradable molybdenum

Abstract

Recently, molybdenum (Mo) has been recognized a promising biodegradable metal, however, it is difficult to be processed through traditional deformation or machining due to its high strength & hardness. Additive manufacturing is a good way to get rid of this dilemma. Here, Mo components were directly fabricated with fine Mo powder through selective laser melting (SLM). Microstructure, in-vitro corrosion behaviors and biocompatibility of the as-obtained Mo were thoroughly investigated. Compared to Mo fabricated through rotary swaging (RS), ineluctable hot cracks were found in SLMed bulk Mo, and those defects accelerated the initial ion release rate (1.31 μg·mL^-1·d^-1 during the first week, one order of magnitude higher than that of RSed Mo). The unique SLMed microstructure resulted in different surface chemical components, constituent phases and corrosion layer structures, thus leading to a different corrosion mode and corrosion evolution along with time. SLMed Mo exhibited good hemocompatibility, and mouse/rat-derived mesenchymal stem cells have certain tolerance to soluble Mo in the sample extracts. However, the deteriorative surface condition on SLMed Mo impaired its biocompatibility to directly attached cells. Cells could adhere onto SLMed Mo, however their proliferation and spreading were impaired along with further corrosion. Additive manufacturing is a powerful tool to fabricate Mo based structural parts, however, the issue of microstructural defects should be well resolved. Close attention should be paid to the hot-cracks and accompanied fast & non-uniform corrosion. STATEMENT OF SIGNIFICANCE: Additive manufacturing is a good way to fabricate implants based on refractory and un-processable biodegradable metals. Here, Mo components were directly fabricated with Mo powder through selective laser melting (SLM). Microstructure, in-vitro corrosion behaviors and biocompatibility of the as-obtained Mo were thoroughly investigated. Compared to Mo fabricated through traditional rotary swaging (RS), the unique SLMed microstructure resulted in different corrosion mode and corrosion evolution along with time. Localized corrosion appeared at the micro-cracks in SLMed samples, thus leading to a 10-fold ion release at week 1. Cells could adhere onto SLMed Mo, however their proliferation and spreading were impaired along with further corrosion. Close attention should be paid to the hot-cracks and accompanied fast & non-uniform corrosion.

Keywords: Biocompatibility; Biodegradable molybdenum; Corrosion; Micro-crack; Selective laser melting.