This is a microscopic image of a silk
optical implant treated with the
cancer fighting drug doxorubicin;
© Tufts University
The devices also lend themselves to a variety of other biomedical functions. Biodegradable and biocompatible, these tiny mirror-like devices dissolve harmlessly at predetermined rates and require no surgery to remove them.
The technology is the brainchild of a research team led by Fiorenzo Omenetto. For several years Omenetto, David L. Kaplan and their colleagues have been exploring ways to leverage silk's optical capabilities with its capacity as a resilient, biofriendly material that can stabilize materials while maintaining their biochemical functionality.
"This work showcases the potential of silk to bring together form and function. In this case an implantable optical form - the mirror - can go beyond imaging to serve multiple biomedical functions," Omenetto says.
To create the optical devices, the Tufts bioengineers poured a purified silk protein solution into molds of multiple micro-sized prism reflectors, or microprism arrays (MPAs). They pre-determined the rates at which the devices would dissolve in the body by regulating the water content of the solution during processing. The cast solution was then air dried to form solid silk films in the form of the mold. The resulting silk sheets were much like the reflective tape found on safety garments or on traffic signs.
When implanted, these MPAs reflected back photons that are ordinarily lost with reflection-based imaging technologies, thereby enhancing imaging, even in deep tissue.
The researchers tested the devices using solid and liquid "phantoms" (materials that mimic the scattering that occurs when light passes through human tissue). The tiny mirror-like devices reflected substantially stronger optical signals than implanted silk films that had not been formed as MPAs.
The Tufts researchers also demonstrated the silk mirrors' potential to administer therapeutic treatments. In one experiment, the researchers mixed gold nanoparticles in the silk protein solution before casting the MPAs. They then implanted the gold-silk mirror under the skin of mice. When illuminated with green laser light, the nanoparticles converted light to heat. Similar in-vitro experiments showed that the devices inhibited bacterial growth while maintaining optical performance.
COMPAMED.de; Source: Tufts University