Salt effects on the hydration behavior of zwitterionic poly(sulfobetaine methacrylate) aqueous solutions

• The water hydrated states of pSBMA in salt were identified by DSC.
• In low NaCl concentration, salt ions bind to the charged groups of pSBMA.
• The binding of salt ions promotes the incorporation of water into polymer chains.
• In high NaCl concentration, excess salt ions bind with free water.
• Osmotic pressure generated by ion-water interaction causes the shrinkage of pSBMA.

Hydration behavior of a biomaterial is thought to be closely related to its bio/blood compatibility and subsequent biological responses. Poly(sulfobetaine methacrylate) (pSBMA) is one of the biomimetic materials that exhibits excellent biocompatibility. It has been reported that the zwitterionic pSBMA exhibits “antipolyelectrolyte” behavior, which changes polymer conformations and antifouling properties, in solutions containing salt ions. In this study, we identified water hydrated states of pSBMA by thermal analysis of DSC in various salt concentrations. With the addition of miniscule salts, ions are attracted to the zwitterionic groups and the hydrated states are significantly changed. The attracted ions promote the incorporation of water molecules into polymer chains and enhance the solubility of pSBMA. Nevertheless, when large amounts of salts are added into the system, the excess ions tend to bind with free water molecules, which may impose an osmotic pressure on the hydrated pSBMA molecules and causes the shrinkage of the molecules. The present results demonstrated that salt has a significant effect on pSBMA–water interactions, which may affect the biocompatibility of the material.