At present, most ophthalmic drugs are delivered via eye drops, but it is estimated that 95 per cent of the activity of medication delivered in this way is lost as the eye drops mix with tears and drain into the nasal canal. This can also cause side effects. Now, researchers at Singapore's Institute of Bioengineering and Nanotechnology (IBN) claim to have solved this problem by developing polymeric contact lens material that can be loaded with active compounds.
Using an in situ micro-emulsion polymerisation process, Drs Edwin Chow and Yang Yi-Yan were able to incorporate drugs within a nanostructured polymer matrix. To do this, they used a bi-continuous micro-emulsion as a medium to prepare the drug-loaded contact lens material. This material is ideal for biological and biomedical applications, as it is compatible with human skin cells and corneal epithelial cells, and is also permeable to gases, water and components of the tear fluid.
Chow, the lead scientist in the project, said: "This process involves combining oil-based monomers, water and a polymerisable surfactant."
Using the approach, the surfactant binds the monomers and water to create a clear mixture. A specific dose of drugs is added and the combined mixture is then poured into a lens mould. When this mixture is hard, the resulting lens is full of tiny nanometre-sized channels, through which the drug can slowly diffuse onto the surface of the eye.
"This cross-polymerisation of organic components in a bicontinuous micro-emulsion can be initiated readily using either heat or ultraviolet light. Using this simple process, one can easily fabricate transparent and mechanically strong contact lens material in the form of sheets or ophthalmic moulds," according to Chow.
Because the lenses are made in a one-step process, cost of manufacture is kept low, he added.
Another advantage of using these contact lenses over other ophthalmic drug delivery systems is that the drug delivery rate can be controlled and remains effective over longer periods of time.
" We can control the flow of the drugs by varying the width of the channels. This can be done by changing the constitution of the mixture that makes up the lens material," said Chow.
IBN is currently looking for partners to commercialise the lens materials and said it has already received enquiries from several contact lens companies. The technology could be used to deliver medication for a range of eye diseases, including glaucoma, a leading cause of blindness that is currently difficult to treat.
Chow noted that the technology allows different types of eye medication to be incorporated into the lens' mixture, and initial studies suggest that glaucoma medications, antibiotics and anti-inflammatory drugs would all be suitable for delivery in this way.
The material could also be modified to produce self-lubricating contact lenses to relieve the discomfort of contact lens wearers suffering from dry eyes, while other potential applications include loading wound-healing drugs in the lenses to treat corneal wounds, or as a means of modifying the lens material for use in vision correction.
The researchers are now conducting in vivo studies in laboratory animals, in order to understand the detailed pharmacokinetics of drug release with their lenses.