Simple surface treatment using amphiphilic phospholipid polymers to obtain wetting and lubricity on polydimethylsiloxane-based substrates

Simple surface treatment of polydimethylsiloxane (PDMS) substrates was performed using an aqueous-ethanolic solution of amphiphilic phospholipid polymers to reduce the hydrophobic and high friction characteristics of PDMS. The phospholipid polymers, poly(2-methacryloyloxyethyl phosphorylcholine (MPC)-co-2-ethylhexyl methacrylate (EHMA)-co-2-(N,N-dimethylamino)ethyl methacrylate) (PMED) and poly(MPC-co-EHMA) (PMEH) were synthesized, and the effects of the electric charge of the polymer chain on the stability of the attachment to the PDMS surface was investigated. The polymers were dissolved in a mixed solvent of ethanol and water, and the PDMS samples were treated by a simple dipping method using the polymer solution. Pure ethanol as the solvent was ineffective for the attachment of the polymers to the PDMS surface. It was considered that the hydrophobic interactions and electrostatic attraction forces between the polymer chains and the PDMS surface were too weak for efficient interaction in this solvent. On the other hand, the surface wettability and lubricity of PDMS could be improved by treatment with an aqueous-ethanolic solution of PMED. The static contact angle was decreased from 90° to 20° by this treatment, and the dynamic friction coefficient against a Co-Cr ball was decreased by nearly 80% compared with that of the untreated PDMS. The hydrophobic interactions and electrostatic attraction forces generated by PMED were both essential for the stable adsorption of the polymer layer on PDMS. Furthermore, the solubilized state of the polymers affected the adsorption of the polymer. We concluded that the surface of PDMS could be stably modified using aqueous-ethanolic solutions of PMED without the need for pretreatments.