Poly(hydroxyethyl methacrylate-co-methacrylated-beta-cyclodextrin) hydrogels: synthesis, cytocompatibility, mechanical properties and drug loading/release properties

Copolymerization of hydroxyethyl methacrylate (HEMA) with a methacrylated-derivative of β-cyclodextrin (β-CD) was evaluated as a way to obtain hydrogels with tunable mechanical and drug loading and release properties, particularly for preparing medicated soft contact lenses. A fully methacrylated β-CD monomer was synthesized and added to the HEMA and cross-linker solution at concentrations ranging from 0.042 to 0.333 g ml⁻¹ (i.e. 0.23–1.82 mol.%). Thermal polymerization led to transparent hydrogels with a degree of conversion above 74%, which showed a high cytocompatibility and did not induce macrophage response. The greater the content in methacrylated β-CD was, the higher the glass transition temperature, the lower the degree of swelling and free water proportion, and the greater the storage and loss moduli of the swollen disks. These findings are directly related to the increase in the degree of cross-linking caused by the methacrylated β-CD. Loading studies were carried out with hydrocortisone and acetazolamide, both able to form complexes with CDs in water and in lacrimal fluid. Hydrocortisone loading progressively decreased as the content in methacrylated β-CD rose due to a decrease in the volume of aqueous phase of the hydrogel. Acetazolamide loading showed a maximum for an intermediate content in β-CD (0.125–0.167 g ml⁻¹) owing to a balance between complexation with β-CD and hydrogel mesh size. The hydrogels sustained drug delivery for several days, the acetazolamide release rate being dependent on the β-CD content. An adequate selection of the content in β-CD enables pHEMA-co-β-CD hydrogels suitable for specific biomedical applications to be obtained.