Bioengineering controlled release from contact lens hydrogels

The controlled release of agents from contact lens materials has applications in, for example, ophthalmic drug delivery, development of corneal reconstructive on-lays, enhancing bio-integration of corneal inlays and improving end-of-day comfort for contact lens wearers. Small molecules are readily absorbed into modern hydrogel matrix of modern contact lenses from, for example, contact lens packing solutions, and may be retained through a range of hydrophilic, lipophilic and ionic interactions depending on the nature of hydrogel material and the specific nature of the small molecule. Larger molecules may be adsorbed to the surface of the lens material and retained through multi-point ionic electrostatic or van der Waals interactions.

The specific release of molecules from contact lens materials within the ocular environment will depend on a range of factors including the concentration of free-ions, solubilising agents and molecular ‘sinks’ within the tear film and the molecular solubility and diffusivity of the agent in the hydrogel. Release from such materials will usually be biphasic with initial rapid ‘burst’ release followed by a slower sustained release profile. However this is undesirable in the context of delivering agents from contact lenses over a sustained period.

Although extensive research has been undertaken into the controlled release of hydrophobic/lipophilic molecules through simple absorption into phase separated regions of silicone hydrogels as yet there have been no systems developed which provide zero order release of hydrophilic and/or amphiphilic agents from contact lens materials which significantly broadens the pool of potential active agents which could be incorporated into lens materials.

Our work on use of hydrogels as chemoembolization systems has also highlighted the importance of intramolecular interactions of ab(d)sorbed molecules in changing the physiochemical properties of the hydrogels and the release characteristics of such materials. Such materials can be engineered to reduce the burst phase and ‘tune’ the release profile to provide a sustained period of effective of zero order release. The incorporation of nanogels or nanoparticles into contact lens materials may also offer additional ways of bioengineering zero order controlled release of active agents from the hydrogel matrix by providing diffusion and/or dissolution barriers. Using thermo-responsive or opto-responsive systems it may also be possible to trigger release on eye.

This programme therefore seeks to investigate the ways in which zero-order controlled release of hydrophilic/amphiphilic low molecular weight molecules may be achieved from contact lens materials.