Fabrication and Characterization of Surface Texture for Bone Ingrowth by Sequential Laser Peening Biodegradable Orthopedic Magnesium-Calcium Implants

Abstract

Biodegradable magnesium-calcium (Mg–Ca) implants have the ability to gradually dissolve and absorb into the human body after implantation. The similar mechanical properties to bone indicate that Mg–Ca is an ideal implant material to minimize the negative effects of stress shielding. Furthermore, using a biodegradable Mg–Ca implant prevents the need for a secondary removal surgery that commonly occurs with permanent metallic implants. The critical issue that hinders the application of Mg–Ca implants is the poor corrosion resistance to human body fluids. The corrosion process adversely affects bone ingrowth that is critical for recovery. Therefore, sequential laser shock peening (LSP) of a biodegradable Mg–Ca alloy was initiated to create a superior surface topography for improving implant performance. LSP is an innovative treatment to fabricate functional patterns on the surface of an implant. A patterned surface promotes bone ingrowth by providing a rough surface texture. Also, LSP imparts deep compressive residual stresses below the surface, which could potentially slow corrosion rates. Unique surface topographies were fabricated by changing the laser power and peening overlap ratio. The resultant effects on surface topography were investigated. Sequential peening at higher overlap ratios (75%) was found to reduce the tensile pileup region by over 40% as well as compress the overall surface by as much as 35 μm.