Experimental investigation and empirical modeling for corrosion rate prediction of biodegradable zinc based composite considering the effect of constituent materials

Biodegradable zinc (Zn) has shown great potential in the area of biomedical applications. Though, the mechanical properties are decisive for the use of Zn for orthopedic and cardiovascular applications. Consequently, one needs to focus on improving the mechanical properties of Zn for its suitability in biomedical applications. Alloying of essential elements of the human body resulted in enhancement of Zn’s mechanical properties in recent years. The corrosion rate of pure Zn is ideal; however, the addition of other elements has resulted in a loss of its ideal corrosion rate. The inclusion of hydroxyapatite (HA) and iron (Fe) in Zn has also been reported in improving the mechanical properties. Hence, a need is raised for the development of a model which can predict the corrosion rate after adding HA along with Fe in Zn. In this research work, empirical based modeling is proposed to predict the corrosion rate, which incorporates the outcome of addition of Fe and HA in Zn. The Zn based materials were fabricated with the help of microwave sintering for developing the empirical model. The corrosion properties of the materials were assessed through a potentiodynamic polarization test in a simulated body fluid solution. The enhanced corrosion rate was attained with the rise in HA (wt%) and Fe (wt%) in Zn. An empirical correlation was established between the influencing controlling parameters (i.e., corrosion current, equivalent weight, and material density) of corrosion rate. Confirmation experiments were conducted to validate the developed model, and the highest error of 6.12% was obtained between the experimental and predicted values exhibiting the efficaciousness of the proposed model.

Hydrothermal assisted conventional sol-gel method for synthesis of bioactive glass 70S30Cы

Bioactive glasses (Bioglasses) are widely synthesized by the conventional sol-gel method consisting of two main steps for sol and gel formation. However, the conversion from sol to gel requires a long time (5–7 days). In this study, the hydrothermal system was used to quickly synthesize the bioactive glass by reducing the conversion time from sol to gel. The hydrothermal assisted conventional sol-gel method was applied for synthesis of the bioactive glass 70SiO2–30CaO (mol%) (noted as 70S30C). The synthetic glass was investigated by the physical-chemical techniques. The ‘‘in vitro’’ experiments in SBF (Simulated Body Fluid) solution was also performed to evaluate the bioactivity of synthetic material. The obtained results show that the bioactive glass 70S30C was successfully elaborated by using the hydrothermal assisted conventional sol-gelmethod. The consuming time was reduced compared to the conventional method. The physical-chemical characterization confirmed that the synthetic glass is amorphous material with mesoporous structure consisting of interconnected particles.The specific surface area, pore volume and average pore diameter of synthetic glass were 142.8 m2/g, 0.52 cm3/g, and 19.1 nm, respectively. Furthermore, synthetic bioactive glass exhibited interesting bioactivity when immersed in simulated body fluid (SBF) solution for 1 days and good biocompatibility when cultured in cellular media.

A study on corrosion resistance of ISO 5832-1 austenitic stainless steel used as orthopedic implant

The ISO 5832-1 austenitic stainless steel used as biomaterial is largely applied in the area of orthopedics, especially in the manufacture of implants, such as temporary or permanent replacement of bone structures. The objective of this study was to evaluate the localized corrosion resistance of the ISO 5832-1 stainless steel used in orthopedic implants by electrochemical tests in two different solutions. The results of this study are of great interest to evaluate the corrosion of metallic implants that can result in the release of corrosion products into bodily fluids causing possible adverse biological reactions. The determination of the chemical elements in the composition of the ISO 5832-1 stainless steel was performed by neutron activation analysis (NAA). The samples for electrochemical tests were grinded with silicon carbide paper up to #4000 finishing, followed by mechanical polishing with diamond paste. The open circuit potential measurements and anodic polarization curves were obtained in solution of 0.90 wt. % of NaCl and of simulated body fluid (SBF). The results indicated that the ISO 5832-1 stainless steel presented a high resistance to crevice corrosion in simulated body fluid solution but high susceptibility to this form of corrosion in the chloride solution.

Synthesis and Modification of Hydroxyapatite Nanofiber for Poly(Lactic Acid) Composites with Enhanced Mechanical Strength and Bioactivity

To enhance the bioactivity of poly(lactic acid) (PLA), a potential bone repair material, without the lowering of mechanical strength, hydroxyapatite (HA) was introduced in the form of nanofibers as the filler for application in spinal implant materials. HA nanofibers (HANF) with aspect ratio as high as ~100 were synthesized by controlling the starting pH of the reaction. While the tensile and flexural strength of PLA/HANF composites were enhanced compared with those of PLA resin, and were higher for the composites with HANF of higher aspect ratio. To further strengthen the composites, HANF was grafted with PLA chain to form HANF-g-PLA, which could improve the interface between the HANF and matrix PLA. PLA/HANF-g-PLA composites showed even higher tensile and flexural strength than PLA/HANF composites, apparently due to the better dispersion and interfacial adhesion. The composite containing 10 wt% HANF-g-PLA showed the flexural strength of 124 MPa, which was 25% higher than that of PLA resin. In the bioactivity test using a simulated body fluid solution, the rate and uniformity of the apatite growth were observed to be higher for the composites with HANF, and were even higher for those with HANF-g-PLA. This study suggested the possibility of using the PLA/HANF-g-PLA composite in the field of spinal implant materials.