Calcification is one of the major issues in the field of implantable medical devices which reduces their function and lifetime. The calcification process on the surface of the devices is largely divided into two stages. The initial stage is the formation of calcium complexes due to various biological and artificial factors, and the final stage is the non specific adsorption of the resulting calcium complexes onto the surface Several methods have been studied to interfere with the crystallization phase of calcium. However, due to the diverse mechanisms by which crystals are formed, calcium deposition cannot be completely prevented. Therefore, there is a need for a method that results in minimal calcium deposits on the surface. The surface treatment strategy to prevent this adsorption mainly uses the anti-fouling properties.
It has been reported that hydrated surfaces using various kinds of hydrophilic materials exhibited anti-fouling properties. Many studies suggested that zwitterionic molecules have high anti-fouling properties due to their strong electrostatically induced hydration effect. In this study, various strategies were used to confirm the anti-calcification ability by surface modification of zwitterionic polymers. We synthesized phenol-conjugated zwitterionic poly (sulfobetaine methacrylate-co-tyramine) (pSBTA) and PEG type polymers with different end group charges. The polymers were characterized by 1H NMR and UV-Vis spectroscopy to confirm the conjugation of TA groups. Then the polymers were grafted onto surfaces via tyrosinase (Tyr)-catalyzed reaction which can be used to modify phenolic moieties in mild environments with fast reaction rates and on regardless of the type of substrates. Optimized grafting conditions for each type were set (pSBTA : 2.5 wt%, 0.4 kU/mL) (PEG types : 2.5 wt%, 0.8 kU/mL). The immobilization of pSBTA was confirmed by measuring static water contact angle and X ray p hotoelectron s pectroscopy (XPS). In PU-pSBTA, contact angle degree was decreased compared with bare-PU and XPS revealed new picks were confirmed at 167 eV in the S 2p region and 401 eV in the N 1s region compared to the Bare PU. The in vitro (7 days) and in vivo (4 weeks) anti-calcification effects of bare-PU and PU-pSBTA were analyzed by ICP. The amounts of calcium measured in vitro were decreased from 10.6 to 4.2 μg/cm2 compared to bare-PU. In vivo, it decreased from 75.6 to 45.6 μg/cm2. These developed functional surfaces with anti-calcification property could be expected as promising materials for various biomaterial implants.
