Improvement of compressive strength of Mg-Fe-Ca alloy by heat treatment as biodegradable implant

Abstract

Bone metal implants are currently made from stainless steel or titanium alloy. A stainless steel and titanium alloy implants lead to stress shielding effect as a result of the stiffness and density gap between human bone and the implant. Stress shielding causes a reduction in bone density or osteopenia. It commonly occurs on femur bone attached with stainless steel or titanium implant because the materials have much higher density and elastic modulus compare to human bone. Biodegradable magnesium alloy becomes a new candidate for bone implant material. Biodegradable magnesium alloy based implant is expected to replace stainless steel and titanium alloy implant, due to its advantages in degradation and absorption by the human body along with the new bone growth. The application of biodegradable magnesium alloy based implants can reduce or even avoid the stress shielding effect. Although magnesium has a similar density with human bone, the compressive strength of magnesium is lower than human bone, the human bone compressive strength is 130-180 MPa while magnesium is only 60-100 MPa. Compressive strength is an important mechanical property for bone implant application because almost all of the human bone has a compressive load. In this research, to improve mechanical properties especially the compressive strength, iron and calcium were added to make Mg-Fe-Ca alloy. The composition of the alloy is 99%wt Mg-0.2%wt Fe-0.8%wt Ca. The alloy was melted in a tubular furnace at a temperature of 900°C for 7 hours under a 99%wt Ar protective gas atmosphere. After that, the heat treatment was carried out at a temperature of 500°C for 2, 3, and 4 hours holding time then followed by rapid cooling using water quench. Compressive strength for the Mg-0,2Fe-0,8Ca alloy as cast is 165.6MPa, the compressive strength is increased along with the increase of holding time. The highest compressive strength achieved from the heat treatment process is 209.7MPa.Bone metal implants are currently made from stainless steel or titanium alloy. A stainless steel and titanium alloy implants lead to stress shielding effect as a result of the stiffness and density gap between human bone and the implant. Stress shielding causes a reduction in bone density or osteopenia. It commonly occurs on femur bone attached with stainless steel or titanium implant because the materials have much higher density and elastic modulus compare to human bone. Biodegradable magnesium alloy becomes a new candidate for bone implant material. Biodegradable magnesium alloy based implant is expected to replace stainless steel and titanium alloy implant, due to its advantages in degradation and absorption by the human body along with the new bone growth. The application of biodegradable magnesium alloy based implants can reduce or even avoid the stress shielding effect. Although magnesium has a similar density with human bone, the compressive strength of magnesium is lower than human bone, the huma...