Influence of gamma and electron beam sterilization on the stability of a premixed injectable calcium phosphate cement for trauma indications

Premixed calcium phosphate cements (CPC's) are becoming the material of choice for injectable cements as a result of their effective delivery to the target implantation site. For orthopaedic use, it is of vital importance that the attributes of these CPC's are not compromised by irradiation sterilization. Therefore, the aim of this study is to determine the influence of irradiation sterilization on a range of premixed CPC's, with an emphasis on improving product shelf life through the use of optimal packaging configurations and annealing steps. Electron spin resonance (ESR) confirmed the presence of free radicals in the inorganic phase of the CPC paste following irradiation. The inclusion of a 24-h annealing step was the only successful method in reducing the degree of free radical formation. Based on the results of injectability force testing, it was revealed that an annealing step greater than 24-h significantly altered the viscosity, however; at 24-h the key attributes of the CPC paste were minimally effected. Overall, it was established that vacuum packing the CPC paste, placing the contents into a foil pouch, gamma irradiating at the minimal dose required and using an annealing step of ≤ 24-h, has the potential to extend the shelf life of the cement.