On-demand pain relief, triggered by light

Seeking more effective pain management, researchers have designed injectable liposomes—cell-like sacs made of phospholipids—that can repeatedly release small bursts of local anesthetic when zapped for just one minute with near-infrared light (Nano Lett. 2017, DOI: 10.1021/acs.nanolett.6b03588). The on-demand system could one day offer physicians or patients better control in delivering a local anesthetic than current approaches. Daniel S. Kohane of Harvard Medical School and his colleagues filled liposomes with the nerve blocker tetrodotoxin and decorated the outer surface of the lipid membrane with gold nanorods. The nanorods absorb near-infrared light and generate heat, causing the membrane to expand and leak some of its payload. The team also included a phosphocholine derivative in the liposome’s membrane that can break free when heated by the nanorods, creating additional pores for tetrodotoxin to escape. As the membrane cools, it tightens again and the cycle can be repeated. Rats injected in the foot with the loaded liposomes experienced no pain when poked for the first two hours. The effect wore off completely after six hours. The researchers also used the liposomes to repeatedly block the sciatic nerve in one leg of test animals, which caused them to lose sensation in that leg during the treatment.