Release kinetics of oleyl alcohol from a self-lubricating silicone biomaterial

Due to their excellent versatility and biocompatibility, silicone elastomers have gained widespread acceptance in clinical applications as medical or drug delivery devices. However, in common with all current biomaterials, silicone is prone to surface formation of a resistant microbial film and, in the case of urinary catheters, to encrustation with complex inorganic salts. In addition, although catheters manufactured from or coated with silicone have a relatively low coefficient of friction compared to other biomaterials, they are still difficult to insert without the use of a lubricating gel. More importantly for a long-term indwelling silicone catheter, the device is difficult to remove, typically resulting in epithelial damage. Recently, silicone elastomers have been reported with inherently low coefficients of friction that may overcome the lack of lubricity associated with conventional silicone elastomers. The development of self-lubricating silicone elastomeric biomaterials, prepared using the novel crosslinking agent tetra(oleyloxy)silane and having very low coefficients of friction, has recently been reported. In this study, the in vitro release characteristics of lubricious oleyl alcohol produced during the silicone curing reaction have been quantitatively evaluated for a range of tetra(propoxy)silane /tetra(oleyloxy)silane crosslinker compositions using a novel evaporative light scattering detection method in combination with high performance liquid chromatography. The mechanism of oleyl alcohol release was seen to deviate from a simple, matrix-controlled diffusion process and instead obeyed an anomalous transport mechanism. An explanation for the observed release behaviour has been proposed based on competitive reaction kinetics between the tetra(oleyloxy)silane and tetra(propoxy)silane substituents of the silicone crosslinking agents.