Effects of hydration water on bioresponsiveness of polymer interfaces revealed by analysis of linear and cyclic polymer-grafted substrates

Given that the hydration water of polymer matrices may differ from that of outermost polymer surfaces, processes at biomaterial-biofluid interfaces and role of hydration water therein cannot be adequately examined using most conventional characterization methods. To bridge this gap, a gold substrate was herein modified with linear and cyclic poly(2-methoxyethyl acrylate) to prepare gl-PMEA and gc-PMEA surfaces, respectively, as models for the outermost surfaces of blood-contacting medical devices. Both surfaces suppressed the adhesion of human platelets but differed in the adhesion behaviors of normal and tumor cells despite having the same areal density of fixed-end units. The surfaces were analyzed using quartz crystal microbalance (QCM), frequency modulation atomic force microscopy (FM-AFM), and X-ray emission spectroscopy (XES) measurements under wet conditions to clarify the relationship between bioresponsivity and hydration water. QCM measurements provided evidence that both grafted-PMEA were hydrated. FM-AFM observations revealed that the swelling layer was thicker for gc-PMEA. To rationalize the differences in the surface hydration states, we performed XES measurements under conditions enabling control over the number of hydration water molecules. In the low-water-content region, hydrogen bonds or interactions between water molecules developed in the vicinity of gl-PMEA but not gc-PMEA. Thus, the initial hydration behavior of the gc-PMEA surface, which promoted intermediate water formation, was different from that of the gl-PMEA surface. The results suggested that the adjustment and optimization of the hydration state of outermost biomaterial surfaces enable the control of bioresponsivity, including the selective isolation of tumor cells.