Hydrogels as potential probes for investigating the mechanism of lenticular presbyopia

Purpose. To synthesize and characterize hydrogels with viscoelastic properties comparable to those of the natural lens. Methods. Hydrogels were synthesized in water by free-radical polymerization of the monomer poly(ethyleneglycol)-monomethacrylate. Three different molecular weights of poly(ethyleneglycol)-dimethacrylates were used as crosslinkers. For each crosslinker used, five different monomer-to-crosslinker weight ratios were utilized while the total mass of the reactants was kept constant. In another series, the concentration of the reactants was varied while the weight ratio of monomer to crosslinker was kept constant at 95:5. The percent optical transmission, equilibrium water content, moduli (elastic, shear, storage, and loss), and retardation time constant of the hydrogels were determined. In addition, endo-capsular polymerization was performed in the capsular bag of porcine eyes. Results. The hydrogels examined exhibited the following ranges for viscoelastic properties: elastic modulus, 1.33-2.37 × 10⁴ Pa; shear modulus, 3.35-6.72 × 10³ Pa; storage modulus, 1.65-6.24×10⁴Pa. For any given hydrogel, raising its crosslinker's weight ratio increased its moduli and decreased its equilibrium water content and optical transmission. For any given monomer-to-crosslinker weight ratio, increasing the molecular weight of the crosslinker reversed these trends. Reactant concentrations increased the elastic modulus and decreased the equilibrium water content. The hydrogels formedex vivo (in the evacuated capsular bag of porcine eyes) allowed for the clear and undistorted viewing of objects. Conclusions. Hydrogels that exhibit physical and mechanical properties comparable to those of the natural lens were successfully identified, synthesized, and characterized, and the feasibility of endocapsular polymerization was demonstrated.