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ETH Zurich and Empa close wounds with laser soldering

18 Jan 2024

iSoldering technique uses nanoparticles in solder material to improve tissue sealing.

Sutures and staples are established tools for reconnecting tissues during surgery or to treat wounds where necessary, but they are inherently invasive and can encourage subsequent infections or leakage.

A project at Switzerland's Empa and ETH Zurich research centers has now developed an alternative method of resectioning tissues based on laser soldering, and published the findings in Small Methods.

Laser soldering as a possible wound closing method has been investigated for some time, according to the ETH team, as a way to accelerate healing and lower the risk of infection. But challenges relating to temperature monitoring and control have been difficult to solve.

"The fact that this thermal reaction must remain within narrow limits for biological materials, while at the same time the temperature is difficult to measure in a non-invasive way, has been a problem for the application of soldering processes in medicine," commented the project.

Previous work in this area has included a 2018 project at Arizona State University which incorporated gold nanoparticles into a solder material to influence the thermal effects and minimize inflammation.

The solution devised by the Particles-Biology Interactions Lab at Empa and the Nanoparticle Systems Engineering Laboratory at ETH Zurich involves using a bonding agent containing both metallic and ceramic nanoparticles, and the use of nanothermometry to control the temperature. The method has been named iSoldering.

Two types of nanoparticles are incorporated in the bonding protein-gelatin paste used for the new soldering process, titanium nitride and bismuth vanadate. When irradiated by a light source at wavelengths only weakly absorbed by surrounding tissues, the titanium nitride turns the light into heat, while the bismuth vanadate acts as nano-thermometer by re-emitting at wavelengths that vary with the temperature being experienced.

Clinical translation via medical IR lamps

This combination of nanoparticles is intended to make the method particularly suitable for use in minimally invasive surgery, said the researchers, as the bonding solder does not require stirring and determines temperature differences with extremely fine spatial resolution in both superficial and deep wounds.

After mathematical modelling of the proposed technique, the project worked alongside surgeons from the University Hospital Zurich, the Cleveland Clinic in the USA and Charles University in Prague to start assessing iSoldering for potential clinical use.

"The team achieved fast, stable and biocompatible bonding of wounds on organs such as the pancreas or liver in laboratory tests with various tissue samples," commented Empa. "Equally successful and gentle was the sealing of particularly challenging pieces of tissue, such as the urethra, fallopian tube or intestine, using iSoldering."

An iSoldering approach might be particular valuable in robotic and laparoscopic surgeries, noted the team in its paper, when issues of incorrect suture positioning can be particularly prevalent.

Although the initial conception of iSoldering envisaged direct laser irradiation, the project will now investigate whether gentler, less intense near-IR illumination can be used in the same way. If so, this would simplify clinical transfer for the process, since medically approved IR lamps are already available and in use in hospitals.

"If medically approved IR lamps were applied, the innovative soldering technology could be used in conventional operating rooms without additional laser protection measures," commented Empa's Inge Herrmann.

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