Magnesium Alloys as Promising Degradable Implant Materials in Orthopaedic Research

Abstract

Magnesium alloys as degradable implant materials in orthopaedic research received a lot of interest in recent years (Witte et al., 2007a; Xu et al., 2008; Zhang et al., 2010). The application of resorbable implant material avoids an implant removal surgery and therewith helps to diminish the costs and the burden for the patient. In comparison to other degradable implant materials like polymers, magnesium alloys excel in higher tensile and compressive strength and the young’s modulus is near to cortical bone (Hofmann, 1995; Staiger et al., 2006; Kaese, 2002). Another advantage that leads to the choice of magnesium alloys as implant material is the fact, that magnesium is a natural component of the body and furthermore has many important functions within the body (Hartwig, 2001). Magnesium is tested as non-allergenic (Witte et al., 2007a) and due to several studies it is assumed, that it stimulates new bone formation in vitro and in vivo (Revell et al., 2004; Zreitqat et al., 2002; Witte et al., 2007b). For the application as orthopedic implant material in weight bearing bones, only magnesium alloys with a slow corrosion rate are useful. A high corrosion rate results in gas formation, a too fast loss of mechanical stability and a considerably higher bone remodelling activity (Thomann et al., 2009; Krause et al., 2010). Beside to different coating facilities (Witte et al., 2009; Zhang et al., 2010) and surface treatments (von der Hoh et al., 2006; Hanzi et al., 2008), in particular the alloying of aluminium, lithium, rare earth metals or calcium decrease the corrosion rate in vitro and in vivo (Kaese, 2002; Staiger, 2006; Hanzi et al., 2008; Krause et al., 2010; Thomann et al., 2009). However, in vivo and in vitro corrosion rates can be quite different (Witte et al., 2006; Zhang et al., 2010), which makes it more difficult to develop and adapt magnesium alloys for biomedical use. In order to investigate if the chosen magnesium-alloys are suitable for the use in orthopedic applications, in vivo-studies in rabbit tibiae were conducted. Therefor the selected and in vitro examined magnesium alloys LAE442, WE43, MgCa0.8, AX30, ZEK100 were implanted into the rabbit tibia and examined with regard to the mechanical stability, the in vivo corrosion rate and the biocompatibility. For the in vivo investigation of the implant materials, the rabbit was used as established animal model for orthopaedic applications (Pearce, 2007). All animal experiments were conducted under an ethic committee approved protocol in accordance with German federal welfare legislation. Five rabbits were used for each group. Extruded pins with 2.5 mm in