Nanosolder For Safer Surgery

When surgeons operate on the gastrointestinal tract, they have to carefully close up all their incisions to prevent the spread of gut bacteria that can cause life-threatening infections. To provide a safer alternative to stitches and staples for the bowel, researchers have developed nanocomposite materials that act like surgical solder. When hit with laser light, the materials help weld together pieces of tissue (ACS Nano, DOI: 10.1021/nn303202k).

For some operations such as eye surgery, doctors already use laser light to join up pieces of tissue. The light rapidly heats up the tissue, causing proteins on each piece to denature and fuse. But surgeons are reluctant to use this technique in colorectal operations for patients with cancer or inflammatory bowel disease, says Kaushal Rege, a bioengineer at Arizona State University, Tempe. That’s because the consequences of an improper seal in this part of the body are quite dire. The seal not only has to be strong and tight, like in metal welding, but also it must match the elasticity of the surrounding tissues, Rege says.

To improve these seals, Rege wanted to create a material that acted like the solder plumbers use when connecting metal pipes. “The problem has been having the right materials to absorb heat and fuse with the tissue, without causing any thermal damage,” he says. Other research groups have developed organic dyes to act as tissue solders, but, Rege says, these don’t convert light into heat very efficiently.

Rege’s solder is made up of gold nanorods mixed with peptides. The nanorods have optical properties that help convert light from a near-infrared laser into heat. The protein fragments denature when heated up, providing extra material to help seal up a surgical site.

Other research teams have worked on surgical solders based on gold and proteins. The Arizona researchers focused on finding a peptide that was better at forming seals. The peptides they chose are extremely thermally sensitive, so they denature rapidly when the gold nanorods heat up.

The researchers make this nanosolder by mixing a solution of the peptides with a solution of gold nanorods. They put the mixture in a mold at 4 °C, and heat it to 37 °C. This creates a sticky film Rege likens to a bandage.

The Arizona researchers tested the nanosolder on dissected pig intestines in their lab. They measured the tensile strength of the intestines, then cut the tissue and tested the strength again. Next the scientists covered the incision with a bit of nanosolder. After shining laser light on the material, the researchers measured the tissue’s mechanical properties. Tissue sealed with nanosolder recovered about 50% of its tensile strength.

To see if the seal helped hold in bacteria, the researchers filled the intestine with a broth containing Escherichia coli. When they submerged the sealed intestine into a water bath, they couldn’t observe bacteria seeping through the incision.

Rutledge Ellis-Behnke, director of the Nanomedicine Translational Think Tank at Heidelberg University, in Germany, says the nanosolder shows promise and “could completely change how surgery is done.” But he cautions that the material needs many more tests to demonstrate its safety and efficacy. In particular, Ellis-Behnke worries about gold’s tendency to bond with the sulfur found in proteins. This property helps the nanocomposite itself stick together but also could cause the healing tissue to stick to other tissue, causing surgical complications. Of course, he says, this could be overcome by experimenting with other materials besides gold.