A spatiotemporal “bulk erosion” mode in selective laser melted magnesium alloys and the resulting adverse cell & tissue responses

Selective laser melting (SLM) has attracted great attention in the fabrication of magnesium-based biodegradable implants. However, current SLMed magnesium alloys are generally suffered from rapid corrosion, which is deadly detrimental to their use. Herein, we thoroughly revealed why they are so vulnerable to corrosion through a typical SLMed AZ91D material model. An abnormally spatiotemporal “bulk erosion” mechanism was found, not the well-known “surface corrosion” mode of traditionally plastic-deformed alloys. The unique microstructure derived from SLM possesses high chemical reactivity, which is favorable for interactional attacks of fast fluid penetration, severe local corrosion and intensive micro-galvanic corrosion. Thus, it brings two orders of magnitude in corrosion rates compared with its plastic-deformed counterparts. In vitro, such fast-corrosion induced apparent cytotoxicity, cell damage, and further apoptosis to rat and mouse derived mesenchymal stem cells. In vivo, the material disintegrates into small pieces in a short period, and results in unexpected bone destruction and long-lasting foreign body reactions in Sprague Dawley rats. Close attention should be paid to this issue before SLMed Mg-based implants being applied in patients.