Tribological Behavior of Zwitterionic-Polyester Composite Films with Phase-Separated Structures

Enhancing the lubrication and wear resistance of biomedical devices remains challenging. The zwitterionic polymer poly(sulfobetaine methacrylate) (PSBMA) provides superlubricity through hydration but lacks mechanical strength. Poly(ε-caprolactone) (PCL) offers toughness, but its hydrophobicity compromises both lubrication and biocompatibility. The hydrophilic/hydrophobic polarity contrast in solvent-cast PCL/PSBMA composites induces macrophase separation. These microstructures critically govern surface homogeneity, interfacial characteristics, and tribological behavior. Therefore, this study investigates the tribological behavior of solvent-cast zwitterionic PCL/PSBMA composite films exhibiting macrophase separation. Films of varying PCL/PSBMA compositions (30:70, 50:50, and 70:30) were tested against different counterfaces (PTFE, Si₃N₄, GCr15 balls) under reciprocating and rotational motion modes at loads of 0.5–1.0 N in both air and water environments. Results demonstrate that the P3Z7 film achieved ultralow friction (COF reduction >50%) in water via hydration lubrication, while the P7Z3 films showed superior stability in air.