POLYMERIZED LYOTROPIC LIQUID-CRYSTALS AS CONTACT-LENS MATERIALS

When an aqueous solution of a hydrophilic monomer such as 2-hydroxyethylmethacrylate (HEMA) is mixed with a surfactant at the correct proportions, the components self-assemble into a lyotropic liquid crystal comprising a highly ordered periodic microstructure, and polymerization of the monomer and removal of the surfactant results in a macroporous hydrogel of potential importance as a material for contact lenses and other prostheses. The two most important properties of these structured polymers as contact lens material are: (1) unlike simple hydrogels which have irregular pores with a highly polydispersed size distribution, these new materials have an extremely well-characterized - in fact, triply periodic - network of pores of identical size, which can be preselected so as to allow for the transport of proteins, mucins, and other components of the pre-ocular tear film; and (2) this pore size can be selected independently of the polymer concentration and crosslink density, unlike simple hydrogels where large pores can only be obtained by reducing the crosslink density and along with it the shear modulus. The pore diameter can be selected in the range 20-400 angstrom and possibly higher. A wide variety of surfactant systems that have been shown to yield materials of this degree of precision and versatility is reviewed.