Tuning the Surface Properties and Biofouling Resistance of Fluorinated Siloxane Copolymers

This study explores the suitability of fluorinated polysiloxanes in medical applications through biofouling studies with Escherichia coli MG1655 (E. coli) and Pseudomonas aeruginosa PAO1 (P. aeruginosa). Commercially available fluorinated poly(dimethylsiloxane) poly(trifluoropropyl methylsiloxane) (PTFPMS) exhibits a significantly higher resistance to biofouling compared to traditional poly(dimethylsiloxanes) (PDMS), such as Sylgard 184. The enhanced resistance is likely due to the reduction in surface energy and friction coefficients due to the incorporation of fluorine groups. Varying the fluorination content from 0 to 35 mol % trifluoropropylmethylsiloxane (TFPMS) in cross-linked PDMS exhibits consistent patterns in tribological and surface data: increased fluorination decreases friction and surface energy while increasing roughness. Profilometry reveals the formation of circular domains as fluorine groups are introduced, which increase in size with higher fluorine content. Corresponding roughness measurements show a significant rise in three dimensional (3D) root-mean-square roughness (S_q) from 0.07 ± 0.06 μm for PDMS to 1.89 ± 0.02 μm for 22.7 mol % TFPMS. Tribological data mirror the roughness trend: the friction coefficients decrease as roughness increases. Contact angle measurements for water increase from 100° to a plateau of 110°, while those for diiodomethane increase from 65° to a plateau of 90°. Contact angle hysteresis indicates that the minimum fluorination needed to impact hydrophobicity is 22.7 mol %. Lap shear tests confirm bulk adhesion of 35 mol % TFPMS to glass (0.45 ± 0.23 MPa) and to PDMS (0.10 ± 0.04 MPa). 35 mol % TFPMS exhibits 2.7 (rough) to 10 (smooth) times lower cell adhesion for E. coli and 1.7 (smooth) to 43 (rough) times lower cell adhesion for P. aeruginosa compared to PDMS. These findings highlight how a mechanistic understanding of how polymer structure and chemistry influence fouling resistance, with implications extending beyond the medical field to many industries requiring antifouling surfaces.