In vivo performance of a rare earth free Mg-Zn-Ca alloy manufactured using twin roll casting for potential applications in the cranial and maxillofacial fixation devices

A magnesium alloy containing essential,non-toxic,biodegradable elements such as Ca and Zn has been fabricated using a novel twin-roll casting process(TRC).Microstructure,mechanical properties,in vivo corrosion and biocompatibility have been assessed and compared to the properties of the rare earth(RE)element containing WE43 alloy.TRC Mg-0.5 wt% Zn-0.5 wt% Ca exhibited fine grains with an average grain size ranging from 70 to 150μm.Mechanical properties of a TRC Mg-0.5Zn-0.5Ca alloy showed an ultimate tensile strength of 220 MPa and ductility of 9.3%.The TRC Mg-0.5Zn-0.5Ca alloy showed a degradation rate of 0.51±0.07 mm/y similar to that of the WE43 alloy(0.47±0.09 mm/y)in the rat model after 1 week of implantation.By week 4 the biodegradation rates of both alloys studied were lowered and stabilized with fewer gas pockets around the implant.The histological analysis shows that both WE43 and TRC Mg-0.5Zn-0.5Ca alloy triggered comparable tissue healing responses at respective times of implantation.The presence of more organized scarring tissue around the TRC Mg-0.5Zn-0.5Ca alloys suggests that the biodegradation of the RE-free alloy may be more conducive to the tissue proliferation and remodelling process.

Microstructure refinement in biodegradable Zn-Cu-Ca alloy for enhanced mechanical properties,degradation homogeneity,and strength retention in simulated physiological condition

Zn-1.0Cu-0.5Ca(TA15)alloy has shown promising characteristics of enhanced mechanical properties and biodegradability for absorbable cardiovascular stents,endovascular devices,and wound closure devices applications.In this study,the TA15 alloy for bioabsorbable biomedical applications is investigated.In the conventionally cast TA15(TA15-C)alloy,CaZn_(13) phase are present as a large dendritic network with an average size of 73.25±112.84μm,Hot rolling of the TA15-C alloy has broken the long and dendritic network of the CaZn_(13) phases,however,the refined phases are observed as segregations and the distribution is non-uniform.These segregated CaZn_(13) suffered heavy localised corrosion which lead to poor mechanical properties in the as-fabricated condition and after biodegradation.Ultrasonic treatment(UST)during casting is identified as an effective technique for the refinement and redistribution of CaZn_(13) particles in TA15 alloy,which successfully reduce the size of the CaZn_(13) phase to 10.91±4.65μm in the as-solidified condition.After hot rolling,the UST processed TA15(TA15-UST)shows improved mechanical properties due to grain refinement and the reduction in microstructural defects,i.e.the broken CaZn_(13) phase.Results of 8-week immersion corrosion tests showed that both alloys possess very similar corrosion rate.However,TA15-UST has markedly improved corrosion homogeneity compared to TA15-N which favours the retention of mechanical properties even after prolonged exposure to physiological fluids.