Photografting of 2-methacryloyloxyethyl phosphorylcholine from polydimethylsiloxane: Tunable protein repellency and lubrication property

The phosphorylcholine group functional methacrylate monomer, 2-methacryloyloxyethyl phosphorylcholine (MPC), was graft polymerized from the polydimethylsiloxane (PDMS) substrate using ultraviolet irradiation and using benzophenone as a photoinitiator. The varying monomer concentrations and irradiation times were investigated in order to verify the relationships between graft density and protein resistance under specific biological conditions. The ellipsometry analysis revealed that the layer thickness of the grafted polymer depended on the monomer concentrations after the irradiation for 1 min, however, it stabilized thereafter in all the specified conditions. The curve fitting of the C1s spectrum obtained by X-ray photoelectron spectroscopy analysis showed that the amount of grafted polymer increased with an increase in both monomer concentration and irradiation time. Atomic force microscopic images revealed that the terminations among the graft chains became dominant due to magnified chain mobility followed by growth of their length. In vitro albumin and fibrinogen adsorption results indicated that the resistance to protein adsorption was easily tuned by the specified conditions due to the controlled graft density. Lubrication was dramatically enhanced by the grafting and it was further promoted by an increase in the graft density in good solvents, indicating that the interactions between the graft chains and the solvents resulted in the lubrication system. These basic findings regarding the grafted PDMS surface are important for versatile applications, including its use as a biomaterial and microfluidic device.