The effect of Mg2+ incorporation into the glass phase of zinc-based glass polyalkenoate cements

Abstract

The suitability of glass polyalkenoate cements (GPCs) as injectable adhesives in orthopedics has been compromised by the presence of aluminum (Al), a component in the glass phase of all commercial GPCs. There has been considerable work on the development of Al-free GPCs which can be formulated based on calcium (Ca) zinc (Zn) silicate (Si) glasses. These materials, in terms of biocompatibility and mechanical properties, have potential for orthopedics. However, many of these experimental Al-free GPCs have setting times shorter than 60 s, restricting clinical applications. Here, the authors incorporate Magnesium (Mg) into the glass phase of Al-free GPCs in an attempt to extend their handling properties without deleteriously influencing strength. Three Mg-Ca-Zn-Si glasses with increasing amounts of Mg (up to 12 mol%) substituting for Ca were synthesized and GPCs were subsequently produced by mixing each glass with aqueous polyacrylic acid (PAA). The results show that Mg substituted for Ca in the glasses did significantly affect the chemical structure of the glasses by increasing the bridging oxygen to non-bridging oxygen (BO:NBO) ratio. The resultant GPCs exhibited extended working times, in line with Mg content in the glass, combined with significant increases in both compressive and biaxial flexural strength with both cement maturation and molecular weight of the PAA phase. Mg-based GPCs recorded working times of up to 145 s, setting times of up to 191 s, and compressive strengths in excess of 58 MPa after 30 days maturation. Thus, we have shown that Mg incorporation into Al-free ionomer glasses can result in GPCs formulated from them that have handling and mechanical properties suitable for orthopedic applications.