Analysis of the shelf life of a two-solution bone cement

Two-solution bone cement consists of methyl methacrylate monomer and poly(methyl methacrylate) polymer dissolved together to yield a viscous solution. Two solutions are used such that the initiator, benzoyl peroxide (BPO), is placed in one solution and the activator, N,N, dimethyl-para- toluidine, is placed in the other. This approach to bone cement provides for a simplified use during surgery and eliminates some of the sources of porosity formation. However, the BPO-containing solution cement will spontaneously polymerize over time and will limit the useful shelf life of this component of the system. The activator-containing component is much more stable and is not as susceptible to spontaneous polymerization. In making two-solution cements, it is envisioned that antibiotics may be incorporated and that the polymer may be sterilized using γ(gamma)-irradiation. Therefore, this study investigated the shelf life of the initiator-containing solution bone cement and studied the effects of initiator concentration, γ-irradiation, gentamicin addition, and the role of storage temperature. Isothermal differential scanning calorimetry (Iso-DSC) techniques were used to monitor the polymerization of BPO-containing solutions. It was found that the shelf life was highly temperature dependent and followed an Arrhenius expression where refrigeration storage (4°C) yielded approximately a 12-month storage time, while 70°C storage results in setting in about 5-7 min. γ-irradiation and gentamicin addition did not significantly affect the shelf life. Initiator concentration affected storage time with higher levels resulting in shorter shelf life.