Introduction: Despite of its wide use in various clinical applications, the titanium-based materials still face some challenges, such as poor hemocompatibility and long healing time. In this work, we developed a novel surface modification strategy aiming to improve both biocompatibility and hemocompatibility. Monomers with two different kinds of functional group were chosen to synthesize our copolymer, namely acryloyloxyhexanoic acid (AHA) with carboxylic acid functionality and 11-acryloyloxy undecyl phosphonic acid (AcrUPA) or 6-acryloyloxy hexyl phosphonic acid (AcrHPA) with phosphonic acid terminal end. While phosphonic acid group can serve as an anchor group for metal surface, the carboxylic acid end would be considered to be biocompatible and cell-adhesive. These copolymers, synthesized by free radical copolymerization, were coated onto the electropolished titanium to form uniform surface, by spin-coating method, and then heated for the formation of a covalent-bound surface layer. To impart a better hemocompatibility, various ratios of AHA were mixed with phosphonic acid monomer for copolymerization. Two phosphonic acid monomer, AcrUPA and AcrHPA were designed to discuss the difference of carbon chain.
Materials and Methods:
Synthesis copolymer of poly (AcrHPA-AHA) and poly (AcrUPA-AHA): The synthesis scheme for copolymers was shown in Scheme 1. The phosphonic acid monomer (AcrHPA or AcrUPA) and AHA were dissolved in 0.2M degasified methanol with designated molar ratio.
Preparation of polymer layer on Ti substrate: A 3wt% polymeric methanol solution was spun-coated onto the electropolished titanium foil at 400 rpm for 30s. The samples were then heated at 145˚C for 24 h.
Surface characterization and platelet adhesion studies: The polymer modified layers were characterized by contact angle, SEM, and ESCA. The in vitro platelet adhesion experiment was performed as similar to that performed earlier [1].
Results and Discussion: By Kelen and Tüdös method, it was noted that AHA-co-AcrUPA copolymer tends to be as block copolymer while AHA-co-AcrHPA one likely to be between random and alternating one.
No significant variation in water contact angle among all samples tested and all showed relatively high contact angle values.
The Ti substrates modified by the A3H7 copolymer in both systems exhibited statistically higher amount, but less activation, in platelet adhesion testing (Fig. 1). This might be resulted from the higher amount of carboxyl functionalities within the copolymers.
Conclusion: According to the result of platelet adhesion experiment, we speculated the carboxyl group could take roles in reducing the platelet activation while increasing platelets adhered.
References:
[1] Shen CH, Lin JC. Langmuir 2011;27:7091-8