Effects of gamma-irradiation on physical and biologic properties of crosslinked hyaluronan tissue engineering scaffolds

Hydrogels containing divinyl sulfone (DVS)-crosslinked hyaluronan (HA) (hylans) are potentially useful implant biomaterials because of their non-cytotoxicity and -antigenicity. However, to successfully fulfill their intended role in vivo, their properties (e. g., mechanics, pore size, surface topography, hydrophilicity, swelling) must be modulated to match the demands of the target application. This study explored whether controlled irradiation with gamma (c) can strengthen hylans and modulate their physical and biologic properties, as has previously been shown to be possible with other natural and synthetic polymers. Hydrated hylans containing two different amounts of DVS were irradiated in vacuum to increasing doses of gamma (0-13.5 kGy). The properties of the irradiated gels were compared with those of non-irradiated controls. Changes to bulk structure were evaluated using swelling tests, surface topography and pore structure were evaluated using scanning electron microscopy, mechanics were evaluated using unconfined compression tests, and surface hydrophilicity was evaluated by measuring contact angle changes. Irradiated gels exhibited lower swelling capacity, structural weakening, increase in elasticity, surface texturing, increased pore size, and decreased surface hydrophilicity in direct correlation with received dose. Cells adhered and proliferated readily on the irradiated gel surfaces but not on control gels. The irradiated gels, however, deteriorated during long-term (< 60 days) storage. Irradiation of hylans in a lyophilized state instead resulted in gels that were more compact, swelled less, and exhibited smaller pores than their hydrated counterparts. The results show that c-irradiation, although useful to modulate hylan gel properties, presents challenges of degradation that may be associated with its generation of free-radicals, HA chain fragmentation, and disruption of DVS crosslinks, particularly when the gels are irradiated in their native hydrated state (> 98% water content). Future studies will optimize parameters for c-mediated modulation of hylan properties through irradiation under water-free conditions.