Evaluating the physico-chemical properties of water-based and 2% lidocaine hydrochloride-based aluminum-free glass polyalkenoate cements for distal radius fixation

Abstract

Lidocaine hydrochloride is used as an anesthetic for clinical applications. This study considers the effects of the substitution of 2% lidocaine hydrochloride for deionized (DI) water on the rheological, mechanical, ion release, pH and injectable properties of two formulations of aluminum-free glass polyalkenoate cements (GPCs) using two distinct poly(acrylic) acids (PAA), E9 and E11, which have different molecular weights (Mw). The substitution of 2% lidocaine hydrochloride demonstrated increased injectability, but did not affect mechanical properties. The mechanical properties increased with time, as expected, and, in general, E9-based GPCs displayed significantly higher strengths over E11-based GPCs. With respect to ion release, which includes calcium (Ca), strontium (Sr), zinc (Zn) and silicon (Si); all ions displayed a steady and consistent increased release over time. Ca and Sr showed similar ion release patterns, whereby the GPC made with E11 PAA and lidocaine hydrochloride released significantly more ions than all other compositions likely due to similar chemical kinetics. However, Zn is also divalent in nature, but displayed only one significant difference across the GPC series at all time points, which was attributed to its higher electronegativity allowing for increased participation in the setting reaction. Finally, an analysis of the pH confirmed an increase in pH with time, suggesting that H⁺ ions were attacking the glass structure to allow for ion release. After 1 and 7 days, water-based GPCs environments achieved a higher pH than lidocaine hydrochloride-based GPCs, indicating that the lidocaine hydrochloride may be releasing additional protons upon bond formation with PAA.