Experimental investigations on hardness of the biomedical implants prepared by hybrid investment casting

In this paper for total hip replacement, a systematic procedure for development of primary (1°) implants of stainless steel has been outlined with fused deposition modeling (FDM) assisted hybrid investment casting process. As the suitability of the implant is mainly assessed by in vitro analysis, the change in microstructure and surface hardness is one of the important parameter/criterion for estimating the functional ability of 1° implants. In order to achieve the increased hardness and improved microstructure of the implants, process parameters of FDM and investment casting process have been identified and optimized in this research work. The analysis of variance has been used to find the percentage contribution of each factor. It has been observed that mold thickness and volume to surface area ratio of the casting plays a significant role in deciding the microstructure and hardness of the castings. Therefore, by controlling these parameters the required microstructure and hardness can be achieved for 1° implants. This study may be used as a yardstick for deciding the levels of coating as secondary (2°) implants (if required) for in vitro and in vivo analysis.