Antibacterial assessment of TMPyP-incorporated p(HEMA-co-MMA)

Introduction
Light-triggered therapy to treat infectious diseases is called photodynamic antimicrobial therapy (PACT).PACT has been widely shown to have a lethal effect against bacteria, fungi, viruses, and parasites and it impacts different biofilms (Garcez et al., 2007) TMPyP (tetrakis(4-N-methylpyridyl)porphyrin) is a porphyrin frequently used in PACT, and exerts its phototoxic effect upon both gram-negative and gram-positive bacteria, via two reactions First, Type II reaction is considered the major pathway of photodynamic therapy. The second pathway, Type I reaction, involves transferring electrons/protons to a substrate and releasing a radical that can react with oxygen to produce reactive oxygen species (ROS) (Brady et al., 2007). This study aims to develop a novel surface loading with TMPyP capable of reducing the adherence of bacteria.

Materials and methods
TMPyP (tetrakis(4-N-methylpyridyl)porphyrin) IS the photosensitizer loaded into p(HEMA-co-MMA)hydrogel. S. aureus ATCC 29213 and E. coli ATCC 700928 which are required for the microbiological assessments. The LED light array activates TMPyP-incorporated p(HEMA-co-MMA). TMPyP was incorporated onto the surface of the p(HEMA-co-MMA) copolymer by swell-encapsulation shrink(SES) technique. Samples were prepared by loading them in different TMPyP soaking solutions for 2min. First, a TMPyP stock solution was prepared (2.18 mg/ml). Next, further dilutions to the appropriate concentration were made using PBS (at pH 7.4). S. aureus ATCC 29213 and E. coli ATCC 700928 represent gram-positive and gram-negative bacteria and are used for assessing adherence percentages.

Results
The percentage adherence (%) compared to dark control of S. aureus and E. coli when TMPyP-incorporated and unincorporated p(HEMA-co-MMA) were illuminated for 120 min using a whiteLED source providing a power of 5.33 mW/cm2, integrated between 450–700 nm, or in dark condition has been presented in Figure 1.

Discussion
TMPyP incorporated copolymers (7.33x10-4 M and7.33x10-5 M) significantly reduced the percentage adherence of S. aureus and E. coli compared to dark control illustrating that these materials are less likely to colonize. This antimicrobial behaviour for hydrogels loaded with 7.33x10-4 M of TMPyP shows significant promise for the development of biomaterials to prevent the colonization of gram-positive and gram-negative bacteria and prevent biofilm formation.

Conclusion
Overall, the attachment of TMPyP into the surface of p(HEMA-co-MMA) copolymers resulted in a material with antimicrobial behaviour.