Because light cannot penetrate deep into tissue, doctors are limited in their use of light-based treatments to, for instance, activate drugs. An international team of researchers led by Seok Hyun Yun of Harvard Medical School and Massachusetts General Hospital has developed a polymeric waveguide that delivers light deep into tissue and can then biodegrade (Nat. Commun. 2016, DOI: 10.1038/ncomms10374). In this demonstration, the researchers used poly(l-lactic acid) to make a comb-shaped planar device with multiple waveguides, which they then used to photochemically heal a wound. The team made an incision in pigskin, applied rose bengal dye, inserted the device into the wound, and shone laser light into the device through a coupled optical fiber. Reactive species generated by the dye induced cross-linking of collagen in the tissue. Without the waveguide, the light activated the dye only near the tissue surface. With the waveguide, the dye was activated along the whole device. After illumination, the researchers clipped off the end of the bioabsorbable device, leaving the rest embedded in the tissue. Such devices could enable improvements in other light-based therapies such as photodynamic therapy and optogenetics.