Investigation Of Nanoparticle-Assisted Laser Tissue Soldering By Terahertz Radiation

Summary form only given. Laser tissue soldering is an attractive approach for surgical repair. The principle is to use laser light in combination with a solder solution, such as albumin, to `stitch' wound openings together. The soldering process can be enhanced by combining albumin with plasmonic nanoparticles, which act as localized absorbers that effectively transfer the impinging light into heat localized within the wound area. Advantages of laser tissue soldering over conventional sutures are a less inflammatory response of the tissue, a reduced chance of infection post-surgery, and no allergic reactions to foreign materials being introduced by traditional stitches [1]. Yet, laser tissue soldering has not been widely used for clinical applications. The underlying reason is that elevated temperatures reached due to laser light absorption and concomitant heat generation can cause significant photothermal tissue damage. Therefore, a rigorous monitoring of the heated solder solution and underlying tissue is necessary to minimize tissue damage and optimize the soldering process. Due to its high sensitivity to the hydration level in biological tissues, terahertz (THz) radiation was employed in this study to investigate the laser skin-tissue soldering of an incision made in porcine skin samples. The experimental setup is shown in Fig.(a). As a solder solution, we used albumin dissolved in an aqueous gold nanorod dispersion (size:10 x 41 nm and Optical Density: 50). This protein-nanoparticle composite was applied evenly to the incision edges and surrounding skin. Afterwards, the incision was soldered by laser irradiation at the wavelength of 786 nm and with an optical power density of 320 mW/mm 2 . The sample was raster-scanned with a step of 0.5 mm using a typical THz time-domain spectroscopy system in reflection configuration. The recorded THz waveform for each pixel was processed with a deconvolution method. THz in-plane image of the sample is shown in Fig.(b) with the contrast based on the peak amplitude. The line-shaped incision with lower contrast is clearly observed. In order to investigate the subsurface condition, THz cross-section image (i.e., in depth) along the Y = 12 mm position is illustrated in Fig.(c). The underlying tissue with thermal damage is identified due to its low water content, which leads to deeper THz penetration. Our results demonstrate the potential of THz imaging in providing three-dimensional information of different stages of photothermal wound healing, in turn paving the way for THz imaging to assist the course of clinical laser tissue soldering procedures.