Which statement correctly identifies the cross-linking agent used in early hydrogel lenses?

Which statement correctly identifies the cross-linking agent used in early hydrogel lenses?

• A. EDMA
• B. HEMA
• C. Silicone
• D. Water

Answer: (A)

Cross-linking agents create a three-dimensional network among polymer chains, giving the hydrogel both stability and the ability to swell with water. In early soft lenses, the base monomer is HEMA, which polymerizes into polyHEMA. To form a solid, interconnected network rather than a loose, soluble polymer, a bifunctional cross-linker is added. Ethylene dimethacrylate (EDMA) has two reactive methacrylate groups, so it links two growing polymer chains during polymerization, producing the cross-linked hydrogel structure that holds shape while absorbing water. HEMA is the monomer itself and would not by itself create a network; silicone refers to a different lens class, and water is just a solvent. Therefore, EDMA is the appropriate cross-linking agent used in early hydrogel lenses.

Cross-linking agents create a three-dimensional network among polymer chains, giving the hydrogel both stability and the ability to swell with water. In early soft lenses, the base monomer is HEMA, which polymerizes into polyHEMA. To form a solid, interconnected network rather than a loose, soluble polymer, a bifunctional cross-linker is added. Ethylene dimethacrylate (EDMA) has two reactive methacrylate groups, so it links two growing polymer chains during polymerization, producing the cross-linked hydrogel structure that holds shape while absorbing water. HEMA is the monomer itself and would not by itself create a network; silicone refers to a different lens class, and water is just a solvent. Therefore, EDMA is the appropriate cross-linking agent used in early hydrogel lenses.