Antimicrobial and anti-inflammatory thermo-reversible hydrogel for periodontal delivery

In periodontal treatment, topical adjunctive therapy with antimicrobials or anti-inflammatory agents is frequently applied. However, currently available drug carrier biomaterials often exhibit poor perfusion into small crevices, such as the deep and irregular periodontal pockets, due to relatively high viscosity. Moreover, high polymer concentrations of the polymer can potentially be cytotoxic upon confined local administration. This study aimed to formulate an antimicrobial and anti-inflammatory treatment option, by incorporating doxycycline (DOX) and/or lipoxin A₄ (LXA₄) into 0.5 wt% thermo-reversible polyisocyanopeptide (PIC). PIC can form hydrogels upon low polymer concentration, and we hypothesized that the thermo-reversible nature of the material would allow for application into the periodontal pocket. The formulations were characterized in vitro and finally tested in dogs with naturally occurring periodontitis, which were not euthanized afterward. Results showed that PIC/DOX/LXA₄ hydrogel could be easily prepared and injected into periodontal pockets. The PIC hydrogel facilitated the release of DOX or LXA₄ for around 4 days in vitro. When applied in dogs, the hydrogel exerted no local or systemic adverse effects. Gels loaded with LXA₄ and/or DOX reduced the subgingival bacterial load and pro-inflammatory interleukin-8 level. In addition, PIC-DOX and PIC-DOX+LXA₄ improved gingival clinical attachment by 0.6 mm compared with conventional periodontal treatment alone (i.e. mechanical debridement). In conclusion, the thermo-reversible PIC hydrogel is a safe and effective vehicle for periodontal drug delivery.