Efficient light-triggered anti-infective ocular biomaterials

Bacterial adherence to implanted intraocular lenses is a known contributor to the development of postoperative infectious endophthalmitis. As yet, no effective preventative strategy has been found. Recently, we described a novel series of porphyrin-incorporated hydrogels for anti-infective ocular applications using tetrakis(4-N-methylpyridyl)porphyrin (TMPyP). Photoactivation of TMPyP causes generation of highly reactive singlet oxygen (1O2), which can indiscriminately initiate further oxidative reactions with bacterial cell components, and reduce surface adherence, but due to the short effective distance of 1O2, damage to host tissue is obviated. TMPyP penetration of 180μm was achieved1, however improved surface localisation is required.
In this work, we report methods for surface localization to improve optical transparency and efficiency of action. Modification of polymer composition, altering either methyl methacrylate (MMA) or methacrylic acid (MAA) content at the expense of hydroxyethylmethacrylate (HEMA), to produce varying ratios of MMA:MAA:HEMA, represents a rational strategy to optimize this. Materials were impregnated with TMPyP, characterised physiochemically, and challenged with Staphylococcus aureus and Pseudomonas aeruginosa.
Increasing the MMA content allowed a greater TMPyP uptake in a thinner layer at the material surface, in contrast to the MAA series of materials. Reduction in the thickness of the porphyrin surface layer by up to 89.87±1.21% relative to 20:80/MAA:HEMA, resulted in a depth of penetration of 18.24±2.18µm.

Overall, the MMA series of materials displayed more favourable porphyrin loading, surface localisation, mechanical properties, and reduction in bacterial adherence on light exposure (2-3 log cycle reductions relative to controls). This therefore demonstrates a simple method of obtaining a high, localised concentration of photosensitiser at the surface of polymeric materials for photo-triggered anti-infective purposes.