Biodegradable Magnesium Implants for Medical Application

A number of biodegradable devices with various applications has been fabricated; mostly by a novel photochemical etching (PE) technique. A diverse array of biodegradable magnesium (Mg) AZ31 stents of different dimensions and textures has been fabricated by this technique. Results of stent expandability tests and stent expansion simulations led to multiple design modifications; which include elimination of end rings, reduction in stent length as well as elimination of the welding bar. These design modifications resulted in uniform expandability of the stents. The PE technique has also been employed to fabricate helical flow inducing devices; namely the Mg AZ31 helical stent; which exhibited an expansion mode different from that of the cylindrical stent. Preliminary in vivo studies with such a device in porcine models demonstrated promising characteristics of a helical flow pattern. Corrosion studies of photochemically etched cylindrical Mg AZ31 stents were performed. A flow induced shear stress (FISS) based corrosion study revealed localized corrosion of small amount under static conditions and uniform corrosion under dynamic conditions. Another corrosion study was carried out with Mg AZ31 stents with different polymer coatings; in which poly(carbonate urethane) urea i.e. PCUU-coated stents showed improved corrosion resistance as well as reduced thrombotic deposition in comparison with uncoated or poly(lactic-co-glycolic acid) i.e. PLGA-coated stents. A corrosion study on photochemically etched helical Mg AZ31 stents in three different environments (static immersion, in vitro and ex vivo) revealed a high dynamic degradation rate as well as production of intermediate corrosion products. Another helical stent made of a Mg single crystal has been fabricated; which is expected to show higher ductility and fracture toughness in comparison with polycrystalline Mg. In addition, fabrication of biodegradable Mg AZ31 staples for soft tissue application has been attempted by employing the PE method. However, the bending of the staple strip to the target shape remains a challenge; due to the required small radius of curvature of the current staple design.