Specificity and biological activity of the protein deposited on the hydrogel surface. Relationship of polymer structure to biofilm formation.

The in-situ lens-bound protein layer (LBPL) was characterized on hydrogels of varying water content and ionic-binding capacity. The LBPL proved to be critically dependent on the ionic binding capacity of a given hydrogel. On nonionic polymers the LBPL invariably was thin and largely insoluble. Histochemical staining allowed the detection of all major types of tear proteins. Amino acid analysis revealed a variable composition. Extractable protein proved devoid of active lysozyme. Electrophoresis of pooled samples revealed a variable mixture of acidic, neutral, and basic bands. To what extent variability is dependent on tear film composition and lens structure awaits use of more sensitive analytic procedures. On anionic hydroxyethylmethacrylate copolymer lenses, the LBPL proved radically different. Here the LBPL invariably was much thicker and composed primarily of loosely bound protein. Electrophoresis and enzymatic analysis revealed a homogenous layer consisting primarily of lysozyme much of which retains enzymatic activity. The amino acid analysis of the insoluble protein suggests a similar composition. Specificity of deposition can be attributed to ionic affinity. Conformational integrity can be attributed partly to the unique stability of lysozyme. Electrophoresis of a pooled anionic lens extract revealed an unknown, highly mobile, basic protein. This presumably represents the selective accumulation of a highly basic trace or transient constituent of the tear film. The specificity and biological activity of the LBPL on the anionic lens may modify hydrogel biocompatibility affecting risk of spoilage, microbial colonization, and propensity to trigger an inflammatory and immune response.