Immobilization of an oxalate-degrading enzyme on silicone elastomer

Urinary biomaterials are compromised by device-related urinary tract infections, bacterial biofilm formation, and biomineral encrustation. In the absence of urinary infection, calcium oxalate is the prevalent encrustation mineral formed. Considering this, a novel approach was taken in the study reported here, in that an oxalate-degrading enzyme, oxalate oxidase (OXO), was immobilized on the surface of silicone elastomer (PDMS), a common urological biomaterial. It was hypothesized that the enzymatic action of OXO could lower urinary oxalate levels near the device surface, thereby preventing calcium oxalate crystal formation. The PDMS surface was functionalized with the use of radio-frequency plasma discharge (RFPD) in the presence of water vapor, then coated with 3-aminopropyltriethoxysilane (AMEO). The resulting aminated surface was covalently coupled with OXO via glutaraldehyde bioconjugation. The ability of the OXO-coated PDMS to prevent calcium oxalate encrustation was evaluated with the use of a modified Robbins device (MRD) encrustation model. RFPD performed on PDMS resulted in an increase in the hydrophilicity of treated surfaces, as measured by contact angle. X-ray photoelectron spectroscopy studies showed increases in elemental oxygen, after water-vapor plasma, and in nitrogen after AMEO derivatization. The immobilized enzyme was shown to retain 47.5% of its specific enzymatic activity as compared to free enzyme. In vitro experiments for 6 days, with the use of a MRD, showed 53% less encrustation deposits on discs coated with OXO than control discs. The results from the current study suggest that PDMS-immobilized oxalate-degrading enzymes are active against calcium oxalate encrustation.