Hydrophilic acrylic biomaterials derived from vitamin E with antioxidant properties

Hydrogels based on polymeric derivatives of vitamin E for biomedical purpos es have been prepared by copolymerization reaction of the alpha-tocopheryl methacrylate (V) with 2-hydroxyethyl methacrylate (H) in a range of composi tion between 5-20 wt % of V. The swelling behavior of the hydrogels in wate r, alkaline, and acidic media showed a slight decrease in the equilibrium w ater content with the content of V in the copolymer although in all cases i t 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) cm(2)/s. The states of water in the hydrogels were de termined by DSC. A decrease in the content of freezing water was obtained w ith the V content for all media, and for all compositions lower values of f reezing 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 an d the average fraction of the monomers in the copolymer. The polar contribu tion dropped with the introduction of a small content (4 wt %) of the vitam in E-containing monomer, and it reached a value similar to that of poly-V f or a composition of 49 wt % of V in the copolymer. This behavior is account ed for by the segregation of the macromolecular chains of both kinds of mon omers, 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 pol y-H, giving rise to a residue of 18 wt %. The V-containing copolymers also showed an improved stability (antioxidant behavior), indicating the possibi lity of the V unit's interfering with the oxidative process, based on free- radical species, and, therefore, with the aging process at the cellular lev el. (C) 1999 John Wiley & Sons, Inc.