Influence of laser parameters on the microstructures and surface properties in laser surface modification of biomedical magnesium alloys

Biodegradable implants from magnesium (Mg) alloys have emerged in the biomedical field especially in the orthopedic and cardiovascular stent applications owing to their low density, high specific strength, excellent machinability, good biocompatibility, and biodegradability. The primary shortcoming of Mg-based implants is their low corrosion resistance in the physiological environment, which results in premature mechanical integrity loss before adequate healing and the production of excessive hydrogen gas, which is harmful to the body tissues and negatively affects the biocompatibility of the implant. Laser surface modification has recently received attention because it can improve the surface properties such as surface chemistry, roughness, topography, corrosion resistance, wear resistance, hydrophilicity, and thus cell response to the surface of the material. The composition and microstructures including textures and phases of laser-treated surfaces depend largely on the laser processing parameters (input laser power, laser scan velocity, frequency, pulse duration, pressure, gas circulation, working time, spot size, beam focal position, and laser track overlap) and the thermophysical properties of the substrate (solubility, melting point, and boiling point). This review investigates the impacts of various laser surface modification techniques including laser surface melting, laser surface alloying, laser cladding, laser surface texturing, and laser shock peening, and highlights their significance in improving the surface properties of biodegradable Mg alloys for implant applications. Additionally, we explore how different laser process parameters affect its composition, microstructure, and surface properties in each laser surface modification technique.