Implantable Fiber Diagnoses, Treats, Biodegrades in Place

　　Light is used in medical applications to image, diagnose, and even treat maladies. But externally applied lasers can penetrate no more than centimeters and sometimes just microns into the body, depending on the wavelength of the light and the turbidity (opacity) of the targeted tissue. Implanting traditional optical fibers allows therapeutic light to reach the targeted tissue, but the fibers must be surgically removed after use, damaging the surrounding tissue and posing a danger if they break during removal.

　　Now an electrical engineer and a biomaterials engineer at The Pennsylvania State University have found a way to shine any wavelength of light at any depth into the body with what they say is the first citrate-based flexible biodegradable polymeric step-index optical fiber.

　　Deciphering all those adjectives reveals that the optical fiber is made from a citric-acid-based organic polymer that is biodegradable (meaning the fiber can safely be left in place after a procedure) and can be fabricated with a conductive core and opaque cladding to deliver any wavelength of light, anywhere in the body, with pinpoint accuracy.

　　“Light is an enabling tool for many medical applications. For example, our citrate-based biodegradable fibers can potentially be used to deliver laser light into the body to remove tumors. The fiber can enable deep tissue imaging for disease diagnosis and for monitoring clinical treatment outcomes. Another example is that light can be delivered into the body to activate drugs for cancer treatment — photodynamic [light activated] therapy,” Jian Yang, a professor of biomedical engineering at Penn State, told EE Times.

　　The citrate fiber can be used to perform the required therapeutic function repeatedly and then left in place to biodegrade safely at the end of its service lifetime. It can be engineered to be low-loss and flexible, with a variable index of refraction, to confine the light so that it shines only on a specific area for destroying tumors or stimulating neurons. It can be co-engineered with multiple cores for sensing fluorescence, imaging tissues, delivering liquid drugs, or precisely placing nanoparticles containing time-released medications.

　　“Our fibers are made of citrate-based polymers, of which there are many functional groups that can be used for drug conjugation [bonding a molecule to a toxin to render it harmless]. Drugs can be encapsulated in the cladding layer of the step-index fibers. We can also fabricate hollow channels that are juxtaposed with the solid fiber [so that] drug solutions can be delivered through the channels from outside the body to the implantation sites,” Yang said.

　　It’s still early days for the technology. Having proved the fibers in the lab, the researchers will work on optimizing the materials and improving the fabrication procedure to yield longer and lower-loss fibers as well as fibers with special functionalities. “We will also start to investigate biological and biomedical applications,” said Zhiwen Liu, an electrical engineer professor at Penn State.

　　Yang and Liu co-authored a “paper on the work along with former graduate student Surge Kalaba and current doctoral candidate Gloria Kim, both from Yang’s group, and postdoctoral researcher Nikhil Mehta from Liu’s group. The National Institutes of Health funded the project.