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Illustration of a hydrogel implant containing photo-responsive cells.

An international team has developed and tested a prototype of an optically-enabled hydrogel patch system that could someday enable disease monitoring and therapy via implants under the skin.

Polymer hydrogels are well-known for their promising biochemical and biophysical properties in medical applications. In their paper, Myunghwan Choi of Harvard Medical School (U.S.A.) and colleagues developed a polymer hydrogel waveguide patch lit by a 491-nm blue light delivered through an optical fiber (Nature Photon. doi:10.1038/nphoton.2013.278). The team implanted the hydrogel patch under the skin of free-to-move diabetic mice for up to eight days.

The hydrogel contained genetically engineered cells that secrete an antidiabetic protein called glucagon-like peptide-1 upon absorption of the light, which enables control of dosage and timing of drug delivery. The experiment allowed successful measurement and stabilization of glucose blood levels in the mice. The hydrogel also contained other genetically engineered cells that produce a fluorescent protein in response to toxicity, which enabled the team to monitor for cadmium poisoning.

“Light is one of the most promising tools to interface with biological systems,” says Choi. However, the penetration of visible and near-infrared light in biological tissue is limited to a few millimeters as it is quickly scattered and absorbed. “Introducing the light-guiding hydrogel implant enables efficient optical communication with cells inside the body.” 

The hydrogel waveguide system demonstrated a low optical loss of less than 1 dB per cm in vivo, and was biocompatible and mechanically flexible. The experiment also showed that the hydrogel could remain transparent and viable for long-term cell encapsulation. Such a platform may someday be adaptable for diverse applications in diagnosis and therapy in humans.