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In this paper, biodegradable low elastic Mg-Zn-Mn-Si-HA alloys have been synthesized by element-alloying assisted spark plasma sintering (SPS) process. The main concern of the current investigation is to study the influence of the key SPS-process variables, such as, alloying element, milling/alloying time, sintering temperature, and pressure on the porosity and elastic modulus of the fabricated alloys. Following an L27 OA-based on Taguchi method and accompanying the input parameters, a series of SPS experiments were carried out. Results indicated that sintering temperature and pressure were found to have a significant effect. The SEM observations showed that highest degree of porosity was observed at the lowest level of the parameters and the full dense compact was obtained at the highest level of the parameters. The alloying of HA and Si refined the grain structure and improved the brittleness of the composite. The SPS fabricated alloys exhibited an elastic modulus in the range between 16 and 38 GPa, that is proximate to bone and viably avoid stress-shielding. Moreover, various biocompatible phases, that is, CaMg, Mg-Si, Mn-CaO, Ca-Mn-O, and CaMgSi were observed in the alloy, which are expected to enhance its bioactivity and corrosion resistance. As-synthesized alloy would be considered potential biodegradable material for orthopedic applications. Refereed/Peer-reviewed

Electric discharge machining (EDM) is widely used to cut and shape the biomedical device substrates, following often a separate coating process to deposit another barrier layer to improve the corrosion performance. This paper presents an innovative single in-situ surface modification technique to deposit nano-hydroxyapatite (nHA) coating on biodegradable Mg-Zn-Mn alloy while shaping the device substrate via electric discharge machining (EDM). The key benefit of the technique is to carry out the whole process in a single setup, hence saving time and cost. The aim of the coating is to control implant's degradation rate and to improve in-vitro bioactivity with human cells. Morphology, elemental, and chemical composition of the nHA coated Mg-Zn-Mn surface were characterized by FE-SEM, EDS, and XRD, respectively, while microhardness is measured by a Vickers hardness tester. Corrosion tests were performed via potentiodynamic polarization measurements in a SBF (simulated body fluid) to evaluate the degradation kinetics. In-vitro cell culture study was carried out to evaluate biocompatibility and cell attachment onto the modified surface. Surface characterization results revealed that a biomimetic nHA containing interconnected nano-porosities of size 5-10 μm had been yielded on the substrate surface, which is beneficial for the apatite growth and osseo-integration. The deposited coating layer has comprised of Mg, Zn, Mn, O, Ca and P elements and formed intermetallic oxide phases, such as CaMg, Mg-Zn, Mn-CaO, Mn-P, and Ca-Mn-O, which improved the in-vitro corrosion performance. The degradation rate of Mg-Zn-Mn alloy was reduced by 90.85% from 0.82 mm/year to 0.07 mm/year by the deposition of nHA-coating layer. The microhardness of the modified surface was measured as 234 HV, which was 1.5 fold higher than the untreated surface. The corroded surface analysis showed that the dense intermetallic phases of nHA coating acted as a stable barrier layer, thus prohibiting the surface from degradation, and hence, improving the corrosion resistance. The in-vitro bioactivity analysis revealed that the nHA containing layer exhibited the superior bioactivity and promotes adhesion, growth, and proliferation of human osteoblastic MG-63 cells.

In this chapter, low elastic modulus porous Mg-Zn-Mn-(Si, HA) alloy was fabricated by mechanical alloying and spark plasma sintering technique. The microstructure, topography, elemental, and chemical composition of the as-sintered bio-composite were characterized by optical microscope, FE-SEM, EDS, and XRD technique. The mechanical properties such as hardness and elastic modulus were determined by nanoindentation technique. The as-sintered bio-composites show low ductility due to the presence of Si, Ca, and Zn elements. The presence of Mg matrix was observed as primary grain and the presence of coarse Mg2Si, Zn, and CaMg as a secondary grain boundary. EDS spectrum and XRD pattern confirms the formation of intermetallic biocompatible phases in the sintered compact, which is beneficial to form apatite and improved the bioactivity of the alloy for osseointegration. The lowest elastic modulus of 28 GPa was measured. Moreover, the as-sintered bio-composites has high corrosion resistance and corrosion rate of the Mg was decreased by the addition of HA and Si element.