Radiation-absorbing hydrogel/melanin blends for ocular devices

Hydrophilic polymers and copolymers of 2-hydroxyethyl methacrylate, with low or high crosslinking density, were synthesized and then treated in aqueous medium with epinephrine (adrenaline) at neutral or acid pH, at room temperature, and in the presence of oxygen and light. During this treatment, a melanin is formed and uniformly dispersed in polymers. The resulting slightly colored hydrogels display radiation-absorbing properties in the ultraviolet and visible regions of the natural spectrum. This enhances significantly their value as materials for ocular devices (contact lenses, intraocular lenses) that should protect the retina of the patients without their natural lens from potential damage induced by ultraviolet and visible (violet and blue) radiation. The incorporation of common ultraviolet absorbers led to transmittances similar to that of the natural human lens, i.e., 30% or less at 450 nm, 40% or less at 500 nm, and no more than 50% at 700 nm. The two-phase morphology of the melanized hydrogels, as investigated by TEM, revealed a very fine structure comprising melanin domains of 1 to 2 nm in size. Although no proof for a network interpenetration could be provided, it is believed that the novel blends are true sequential interpenetrating polymer networks.