Hydrophilic acrylic biomaterials derived from vitamin E with antioxidant properties

Hydrogels based on polymeric derivatives of vitamin E for biomedical purposes have been prepared by copolymerization reaction of the alpha-tocopheryl methacrylate (V) with 2-hydroxyethyl methacrylate (H) in a range of composition between 5-20 wt % of V. The swelling behavior of the hydrogels in water, alkaline, and acidic media showed a slight decrease in the equilibrium water content with the content of V in the copolymer although in all cases it was superior to an EWC > 20%. The diffusion mechanism followed a Fickian behavior in all media. The values of the diffusion coefficients were in the range 2.5-1.6 10(-7) cm2/s. The states of water in the hydrogels were determined by DSC. A decrease in the content of freezing water was obtained with the V content for all media, and for all compositions lower values of freezing water were obtained in acidic or basic pHs than in distilled water. The copolymeric xerogels, analyzed by contact angle measurements, deviated from those expected taking into consideration those of the homopolymers and the average fraction of the monomers in the copolymer. The polar contribution dropped with the introduction of a small content (4 wt %) of the vitamin E-containing monomer, and it reached a value similar to that of poly-V for a composition of 49 wt % of V in the copolymer. This behavior is accounted for by the segregation of the macromolecular chains of both kinds of monomers, due mainly to differences in their polarity, molecular weights, and the reactivity of both monomers. Finally, thermogravimetric analysis showed a higher thermal (antioxidant) stability of the poly-V with respect to poly-H, giving rise to a residue of 18 wt %. The V-containing copolymers also showed an improved stability (antioxidant behavior), indicating the possibility of the V unit's interfering with the oxidative process, based on free-radical species, and, therefore, with the aging process at the cellular level.