Photodynamic therapy effects on hydrogel viscoelastic properties

Implant infections pose a serious health risk to patients, both immediately after surgery and even years later. Hard materials provide the opportunity for more potent infection clearing, but soft materials like hydrogels are more delicate and may be more susceptible to the formation of sturdy bacterial biofilms. Photodynamic therapy (PDT) is a proven technique for infectious load reduction, biofilm penetration, and sensitization to antibiotic therapies. However, evaluation is lacking in efficacy of PDT in proximity to hydrogels, based on the risks of oxidative degradation. This preliminary study assesses the effects of PDT on HEMA-DMAEMA hydrogel viscoelastic properties. PDT is applied by soaking of hydrogels in PBS containing 10 mu M methylene blue and subsequent 660 nm light exposure at 9.20 mW/cm(2) for 30 minutes. PDT and all component controls cause reduction in values of storage modulus, loss modulus, and loss factor, but only differences in storage modulus are statistically significant as compared to baseline controls. Additionally, PDT component controls are comparable to the PDT test group, implying that photosensitizer integration and light degradation of hydrogels may be the primary source of interference. Overall, the changes noted in viscoelasticity are moderate and encourage further exploration with larger PDT doses, greater sample numbers, and testing of commercially available implant materials.