Calcium and zinc ion release from polyalkenoate cements formed from zinc oxide/apatite mixtures

Abstract

Calcium and zinc ion release from hydroxyapatite-zinc oxide-poly(acrylic acid) (HAZnO-PAA) composite cements into deionised water was investigated as a function of HA content, PAA concentration, PAA molecular weight and maturation time. At any given maturation time, zinc ion release was constant until the HA content was at the maximum loading (60 wt%) resulting in the cement matrix breaking up, allowing exacerbated ion release. The calcium ion release increased with increased HA content in the composite until the maximum loading where the release drops off. Up to this point, the release of both ionic species was proportional to square root time for the initial 24 hour period, indicating that the release is diffusion controlled. In agreement with related data from conventional Glass Polyalkenoate Cements (GPCs), it is the concentration of the PAA, not the molecular weight, that influences ion release from these materials. However, unlike GPCs, the release of the active ions results in a pH rise in the deionised water, more conventionally seen with Bioglass and related bioactive glasses. It is this pH rise, caused by the ion exchange of Zn(2+) and Ca(2+) for H(+) from the water, leaving an excess of OH(-), that should result in a favourable bioactive response both in vitro and in-vivo.

The role of poly(acrylic acid) in conventional glass polyalkenoate cements

“…PAA or copolymers of acrylic and itaconic or maleic acid have been the most commonly used polymers in the preparation of GPCs. Towler et al [151] showed that increasing the concentration of PAA minimizes ion release from GPCs. They also showed that agitation (sample rotation at 1000 rounds per minute) or aging samples at higher temperature (70°C) significantly increases the ion release of Zn 2+ ions from the cement matrix into the medium, when compared to those aged at 37°C in static conditions.…”

Development of a novel aluminum-free glass ionomer cement based on magnesium/strontium-silicate glasses

“…An increased amount of zinc enhanced the mechanical properties of GICs based on CaO-ZnO-SiO 2 glass system [20,21]. Aluminum-free GICs based on zinc silicate glasses have been developed as an alternative for orthopedic applications [22,23].…”

Calcium sulfate‐containing glass polyalkenoate cement for revision total knee arthroplasty fixation

“…The incorporation of CaSO 4 was found to decrease the wt% of the Zn in the 1 wt% CaSO 4 addition which may explain the longer working time compared to other mGPC specimens. Zn acts as an intermediary in a glass structure (network modifier [ZnO 6 ] or network former [ZnO 4 ]) and increases the strength of the glass network (Alhalawani & Towler, 2016; Towler et al, 2006). Therefore, decreasing the amount of Zn could lead to an increase in working time.…”