Stainless Steel with Tailored Porosity Using Canister-Free Hot Isostatic Pressing for Improved Osseointegration Implants

Porous biomedical implants hold great potentials in preventing stress shielding while improving bone osseointegration and regeneration. In this paper, a novel approach is introduced to control the porosity of 316L stainless steel implants by using canister-free hot isostatic pressing (CF-HIPing). The proposed approach uses cold isostatic pressing (CIPing) to generate powder compacts with various particle size, followed by CF-HIPing. 316L stainless steel samples with controlled porosity, mechanical and biological properties were successfully achieved. The results showed a significant increase in the samples porosity with increasing the powder size. Porous structures with strength of 108-360 MPa, Vickers hardness of 25-49 HV and elastic modulus between 17-50 GPa were produced using a particle size range of 5-50 µm. The effect of samples with various porosity on in vitro response of mouse pre-osteoblastic in terms of toxicity and proliferation was studied. All samples showed that they had a minimal toxic effect on the osteoblasts. Samples with low porosity, prepared using a particle size of 5 µm, is believed to hinder the transport of nutrients and oxygen to the cells hence had lower proliferation. In addition, samples prepared using a particle size range of 16-50 µm were associated with an increased proliferation and are therefore expected to improve the rate of bone osseointegration.