Gold nanorods-based thermosensitive hydrogel produces selective long-lasting regional anesthesia triggered by photothermal activation of Transient Receptor Potential Vanilloid Type-1 channels.

Long-lasting regional anesthesia and selective sensory block are useful in post-operative analgesia and treatment of pathological pain. Previous studies have demonstrated that activation of TRPV1 (Transient Receptor Potential Vanilloid Type-1) channels facilitated the potency of QX-314 for selective long-lasting regional anesthesia in vivo. Hydrogel is a solid jelly-like material covering a wide range of properties from soft and weak to hard and tough. Gold nanorods are nanoparticles, which can be used for hyperthermia by exposure to near-infrared radiation. We fabricated a gold nanorods and QX-314 containing hydrogel. The molecular weight of hydrogel was adjusted to achieve a targeted phase transition temperature. Gold nanorods with a desired photothermal conversion efficacy and QX-314 were mixed with hydrogel to produce a gold nanorods-QX-314/hydrogel nanocomposite. A rat model of sciatic nerve block was applied to evaluate the regional anesthetic effect of the gold nanorods-QX-314/hydrogel nanocomposite. Upon exposure to near-infrared irradiation, the gold nanorods-QX-314/hydrogel nanocomposite activated TRPV1 channels through photothermal conversion and release of QX-314 at the same time. The gold nanorods and QX-314 loaded hydrogel exhibited a long-lasting regional anesthetic effect with selective sensory function block. Sensory block duration of the nanocomposite was significantly longer than of 1% lidocaine (90.0 ± 12.2 vs. 37.5 ± 12.5 min, P < 0.01). Motor block by the nanocomposite was observed for only 40% of rats with significantly shorter duration than its sensory block (42.5 ± 17.1 vs. 90.0 ± 12.2 min, P < 0.01). The gold nanorods-QX-314/hydrogel nanocomposite can produce a selective long-lasing regional anesthetic effect in a rat model of sciatic nerve block.