Schematic overview of the coating method; examples of NIR images of the dip-coated steel wires and catheter tubes and spin-coated thin films.
Schematic overview of the coating method; examples of NIR images of the dip-coated steel wires and catheter tubes and spin-coated thin films.
(Left) NIR-fluorescence depth measurements of NICE-coated steel wires in porcine liver tissue. (Right) Four corners of a lesion inside the stomach were endoscopically marked by coated surgical sutures and visualized (from the exterior gastric surface) using an NIR laparoscopic system. White light and NIR imaging were performed at the same time.
(Left) NIR-fluorescence depth measurements of NICE-coated steel wires in porcine liver tissue. (Right) Four corners of a lesion inside the stomach were endoscopically marked by coated surgical sutures and visualized (from the exterior gastric surface) using an NIR laparoscopic system. White light and NIR imaging were performed at the same time.

Positioning surgical markers, catheters, implants, stents or sutures in precisely the right position in the body using medical imaging or image-guided surgery is tricky, but could become much easier thanks to a new fluorescent coating devised by a team of chemists led by Andrey Klymchenko at the University of Strasbourg/CNRS in collaboration with surgeons at IRCAD in France [Ashoka et al., Biomaterials 261 (2020) 120306, https://doi.org/10.1016/

j.biomaterials.2020.120306].

Fluorescence-guided surgery enables surgeons to visualize where medical devices are in the body or identify markers distinguishing healthy and diseased tissue. The near-infrared (NIR) region is ideal because biological cells and tissues are poorly fluorescent and more transparent in this range. Tumor tattooing, for example, involves injecting a fluorescent dye into the site of a tumor or lesion to mark it for removal. But currently used dyes tend to leak, leading a high degree of inaccuracy, and other fluorescent coatings based on indocyanine green (ICG) have a number of downsides.

“We developed a near-infrared fluorescent coating material for equipment (or NICE), suitable for coating variety of medical devices,” explain first author of the study Anila Hoskere Ashoka and Klymchenko. “We address a number of limitations of currently used NIR fluorescent materials based on ICG [such as] poor brightness, stability, dye leakage into tissue, biocompatibility, and toxicity.”

The combination of organic cyanine dyes with bulky hydrophobic counterions and a biocompatible polymer, poly (methyl methacrylate) (PMMA) is 15-20-fold brighter and more photostable than conventional fluorescent coatings. The large counterions prevent aggregation of the dye molecules, which can lead to quenching of the fluorescence, while the polymer provides a stable biocompatible scaffold. The coating is easy to deposit on a range of materials from steel and gold to silicone and PVC using a simple dip and dry procedure.

“Our coating is unique in terms of its properties: superior brightness, which allows [objects] to be seen as deep as 0.5 cm into tissue, optical compatibility with well-established laparoscopic systems, and the ability to coat various surfaces,” say Ashoka and Klymchenko. “Moreover, NICE coatings are biocompatible, non-toxic… and stable in biological media without showing any dye-leakage.”

With the surgical team led by Michele Diana, the researchers demonstrated various applications of NICE in image-guided surgery, including identifying critical structures and tumor tattooing. The organic dye and polymer scaffold, which is already approved for some medical applications, caused no sign of cytotoxicity during the tests. The coating is also compatible with standard clinical sterilization procedures.

“We do not see any obvious limitations of our coatings,” say Ashoka and Klymchenko, “[and] we anticipate taking them from the lab to market for real-time surgical applications.

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