Network Formation Conditions Control Water Drop Adhesion for VK100 and a Model Pt-Cured Silicone

Abstract

Unexpected wetting behavior is reported for silicone elastomers platinum cured at 37 °C in water or saline. These conditions were prompted as a way to mimic cure under physiologically relevant conditions for VK100, a Pt-cured silicone used for vertebral augmentation. Water contact angles (CAs) were determined by the drop addition/withdrawal method. Network formation in air, water, or saline gave high advancing CAs (θ_A). However, compared to 74° for air cure, network formation in water (56°) or saline (46°) gave low receding CAs (θ_R). Thus, water drop adhesion to VK100 and a model Pt-cured silicone depends on whether network formation is carried out in water or saline (“sticky”) or in air (“slippery”). For cure in water or saline, autoxidation (Si-H ➔ Si-OH) and near-surface entrapment of cross-linking chains containing –Si-OH are proposed to account for low receding CAs. The origin of the low θ_R and high contact angle hysteresis (54–72°) is correlated with the theory of Johnson and Dettre by which a small area fraction of polar groups impedes retraction of a receding water drop. These results are of interest given the importance of polar interactions at interfaces that favor adhesion to bone and influence on biofouling, adhesion of proteins, and interactions with human cells.