Biocompatibility of Hydroxyapatite and Stainless Steel Alloys

The biomaterial used for medical implantable devices, such as artificial joints, tooth implants, and screws and plates for fracture repair, must sufficiently integrate within the biological system and be compatible with surrounding tissue. Stainless steel is commonly used due to its mechanical properties, its ease of fabrication, and its cost effectiveness. Hydroxyapatite (HA), a bioactive material that is a major and essential component of normal bone and teeth, is often used for coating metal implants to initiate infiltration. However, its bioactivity leads to high biodegradation when implanted alone, which can result in clinical implant failure. Our focus is on the biocompatibility of an alloy mixture of stainless steel and hydroxyapatite that can be used for implantable devices fabricated with a three-dimensional printer. Stainless steel alloy and hydroxyapatite components were distinguishable under scanning electron microscopy. The biocompatibility of the alloy is currently being tested in vivo. Alloy pieces (two mm thick) containing mixture ratios of hydroxyapatite and stainless steel are aseptically inserted between the skin and the outer surface of the skulls of anesthetized rats. At intervals between one week and one month, the rats were euthanized and the metal pieces were removed and observed under scanning electron microscopy to determine the degree of infiltration by bone and other connective tissue such as blood vessels. The surrounding connective tissue was examined for inflammation and other tissue damage. We expect the incorporation of hydroxyapatite into stainless steel will allow tissue infiltration, which will improve mechanical endurance and biocompatibility