Preparation Of A Novel Phospholipid Polymer And Application For Modifying Titanium-based Material Surface

Titanium (Ti) alloys have many desirable properties such as a relatively low Young’s modulus, good fatigue strength, formability, machinability, and corrosion resistance. Accordingly, they have been widely used in biomedical devices and components since the late1970s, especially in cardiac and cardiovascular applications (e.g., prosthetic heart valves, protective cases in pacemakers, implantable blood pumps, cardiovascular stents, and circulatory devices). However, Ti substrates induce severe biological responses such as thrombus formation and tissue reaction. As a result, anticoagulant therapy is necessary to minimize the risk of thromboembolic complications. Therefore, surface modification of Ti substrates is indispensable for improving its thrombogenicity and tissue compatibility.A promising and effective way to attain biocompatibility is to prepare an artificial cell membrane surface on the substrates using2-methacryloyloxyethyl phosphorylcholine (MPC) polymers. They have excellent thrombogenicity and tissue compatibility. At present, MPC polymers are widely used for the surface modification of implantable medical devices and artificial organs.There are many reports of surface immobilization of MPC polymers on Ti substrates. However, these methods have many limitations for widespread practical use. Layer-by-layer assembly (LBL) involves complex multistep procedures, the self-assembled monolayer (SAMs) technique requires surface-specific interaction, and surface-initiated atom transfer radical polymerization (ATRP) needs unstable polymerization conditions. Thus, for practical applications, it is desirable to use a more simple, convenient, and versatile method to immobilize MPC on Ti substrate surface.In this paper, the surface of a titanium (Ti) alloy substrate was modified by a simple and quick process using a water-soluble polymer, and the effects of catechol groups in the polymer side chain on the modification process were examined. The polymers (PMDP) composed of both2-methacryloyloxyethyl phosphorylcholine (MPC) unit and3,4-dihydroxyphenyl methacrylate unit were synthesized for surface anchoring. The Ti substrate was coated with PMDP using an aqueous solution of the polymer. A PMDP layer with a thickness of20nm was formed on the Ti substrate simply by dip coating for10s without drying. Even when the Ti substrate with PMDP coating was immersed in the aqueous medium for1month, no change in the thickness was observed, i.e., the PMDP layer was bound to the surface very stably. Oxidation of the catechol groups reduced the stability of the polymer layer significantly. Thus, the catechol groups play a significant role in achieving stable binding. Protein was adsorbed on the Ti substrate; however, this was not observed for the PMDP-coated Ti substrate. In conclusion, we confirmed the effects of catechol groups in PMDP on the stability of the coating on the Ti substrate. Moreover, we found that surface treatment using PMDP was simple, quick, and reliable, and thus, it has great potential for improving biocompatibility of Ti substrates used in medical devices.