Enzymatic release of drug from polymer matrices: Diffusion and activity of lysozyme within ophtalmic hydrogels

Diffusional behaviour of lysozyme into a high-hydrated hydrogel, used as precursor of contact lenses, is reported. The gel is a swollen statistical copolymer of methyl methacrylate and N-vinyl-2-pyrrolidone (≁ 70% water), and the penetration of the enzyme, labeled with 8-anilinonaphthalene-1-sulfonate, was followed by fluorescence microscopy. Mathematical analysis of the profiles led to the diffusion parameters (D ≁ (2–6) · 10⁻⁸ cm² · s⁻¹). It is shown that the enzymatic activity persists when the lysozyme and the cleavable substrate are trapped in the matrix.