²H-NMR and ¹³C-NMR study of the hydration behavior of poly(2-methoxyethyl acrylate), poly(2-hydroxyethyl methacrylate) and poly(tetrahydrofurfuryl acrylate) in relation to their blood compatibility as biomaterials

We recorded ²H-NMR spectra of (deuterated) water in the presence of poly(2-methoxyethyl acrylate) (PMEA), poly(2-hydroxyethyl methacrylate) (PHMEA) and poly(tetrahydrofurfuryl acrylate) (PTHFA). The observed ²H-NMR peak intensities varied substantially with water content and temperature, depending upon either strong binding to polymer surface or suppressed peaks due to freezing. Indeed, ²H-NMR signals in the presence of PHEMA were strongly dependent upon its water content, while those of hydrated PMEA and PTHFA remained unchanged even at -30°C and -20°C. The latter were considerably broadened at -50°C and -30°C, respectively, due to freezing water from the super-cooled state. As a result, the states of the water molecules in PMEA and PTHFA can be classified into three types; free, freezing bound and non-freezing water molecules. The states of the water in PHEMA depend on the water content, and the water can be classified into two types, free and non-freezing water, which exhibit rapid fluctuation and restricted mobility because of the presence of macromolecules, respectively. A kind of freezing bound water, however, should exist in PHEMA. This is also consistent with the substantially decreased ²H spin-lattice relaxation times of hydrated PHEMA as compared with those of PMEA or PTHFA. It is also interesting to note that the flexibility of bound water or polymer (PMEA > PTHFA > PHEMA) is related to a characteristic parameter for biocompatibility such as the production of TAT (thrombin-antithrombin III complex) as a marker of activation of the coagulation system. Therefore, it is naturally recognized that such differential polymer dynamics might be responsible for concomitant changes in structure and dynamics of surrounding water molecules in the vicinity of constituent polymer network.