Controlled temperature photothermal tissue welding

Autofluorescence guided welding of heart tissue by laser pulse bursts at 1550 nm

Wound healing and other surgical technologies traditionally solved by suturing and stapling have recently been enhanced by the application of laser tissue welding. The usage of high energy laser radiation to anastomose tissues eliminates a foreign body reaction, reduces scar formation, and allows for the creation of watertight closure. In the current work, we show that an ultrafast pulsed fibre laser beam with 183 µJ·cm^-2 energy fluence at 1550 nm provides successful welding of dissected chicken heart walls with the tensile strength of 1.03±0.12 kg·cm^-2 equal to that of native tissue. The welding process was monitored employing fluorescence spectroscopy that detects the biochemical composition of tissues. We believe that fluorescence spectroscopy guided laser tissue welding is a promising approach for decreasing wound healing times and the avoiding risks of postoperative complications.

Strength and Persistence of Energy-Based Vessel Seals Rely on Tissue Water and Glycosaminoglycan Content

Vessel ligation using energy-based surgical devices is steadily replacing conventional closure methods during minimally invasive and open procedures. In exploring the molecular nature of thermally-induced tissue bonds, novel applications for surgical resection and repair may be revealed. This work presents an analysis of the influence of unbound water and hydrophilic glycosaminoglycans on the formation and resilience of vascular seals via: (a) changes in pre-fusion tissue hydration, (b) the enzymatic digestion of glycosaminoglycans (GAGs) prior to fusion and (c) the rehydration of vascular seals following fusion. An 11% increase in pre-fusion unbound water led to an 84% rise in vascular seal strength. The digestion of GAGs prior to fusion led to increases of up to 82% in seal strength, while the rehydration of native and GAG-digested vascular seals decreased strengths by 41 and 44%, respectively. The effects of increased unbound water content prior to fusion combined with the effects of seal rehydration after fusion suggest that the heat-induced displacement of tissue water is a major contributor to tissue adhesion during energy-based vessel sealing. The effects of pre-fusion GAG-digestion on seal integrity indicate that GAGs are inhibitory to the bond formation process during thermal ligation. GAG digestion may allow for increased water transport and protein interaction during the fusion process, leading to the formation of stronger bonds. These findings provide insight into the physiochemical nature of the fusion bond, its potential for optimization in vascular closure and its application to novel strategies for vascular resection and repair.

Enhanced tumor treatment using biofunctional indocyanine green-containing nanostructure by intratumoral or intravenous injection

Indocyanine green (ICG) is a conventional dye that can be used in clinical near-infrared (NIR) imaging, and it is also an effective light absorber for laser-mediated photothermal therapy. However, applications of ICG were limited due to its fast degradation in aqueous media and quick clearance from the body. Herein, an ICG-containing nanostructure, ICG-PL-PEG, was developed for photothermal therapy, which was self-assembled by ICG and phospholipid-polyethylene glycol (PL-PEG). Our in vitro and in vivo experiments demonstrated that ICG-PL-PEG suspension was more efficient in producing a NIR-dependent temperature increase than ICG alone, due to the increase of ICG monomers from the addition of PL-PEG to match the central wavelength of the 808 nm laser. When conjugated with integrin α(v)β(3) monoclonal antibody (mAb), ICG-PL-PEG could be selectively internalized and retained in target tumor cells. Irradiation of an 808 nm laser after intravenous administration of ICG-PL-PEG-mAb resulted in tumor suppression in mice, while ICG alone had only limited effect. This is the first time an ICG-containing nanostructure has been used through systemic administration to achieve an efficient in vivo photothermal effect for cancer treatment. Therefore, ICG-PL-PEG could be used as a fluorescent marker as well as a light-absorber for imaging-guided photothermal therapy. All the components of ICG-PL-PEG have been approved for human use. Therefore, this unique ICG-containing nanostructure has great potential in clinical applications.

Microvascular anastomosis using a photochemical tissue bonding technique

BACKGROUND AND OBJECTIVES

Photochemical tissue bonding (PTB) combines photoactive dyes with visible light to create fluid-tight seals between tissue surfaces without causing collateral thermal damage. The potential of PTB to improve outcomes over standard of care microsurgical reanastomoses of blood vessels in ex vivo and in vivo models was evaluated.

STUDY DESIGN

The mechanical strength and integrity of PTB and standard microsurgical suture repairs in ex vivo porcine brachial arteries (n = 10) were compared using hydrostatic testing of leak point pressure (LPP). Femoral artery repair in vivo was measured in Sprague-Dawley rats using either standard microvascular sutures (n = 20) or PTB (n = 20). Patency was evaluated at 6 hours (n = 10) and 8 weeks post-repair (n = 10) for each group.

RESULTS

PTB produced significantly higher LPPs (1,100+/- 150 mmHg) than suture repair (350+/-40 mmHg, P<0.001) in an ex vivo study. In an in vivo study all femoral arteries in both suture and PTB repair groups were patent at 6 hours post-repair. At 8 weeks post-repair the patency rate was 80% for both groups. No evidence of aneurysm formation was seen in either group and bleeding was absent from the repair site in the PTB-treated vessels, in contrast to the suture repair group.

CONCLUSION

PTB is a feasible microvascular repair technique that results in an immediate, mechanically robust bond with short- and long-term patency rates equal to those for standard suture repair.

Thermal-feedback-controlled coagulation of egg white by the CO2 laser

Temperature feedback control during laser-assisted tissue coagulation was investigated and demonstrated with the egg-white model. We observed the dynamics of photothermal denaturation during CO2 laser irradiation by simultaneously controlling surface temperature and monitoring He-Ne laser transmission of egg-white samples. Once a quasi-constant surface temperature was established, transmission of egg white tended to decrease linearly with time. Analysis of experimental data strongly suggested a first-order rate process. Since transmission was primarily affected by heat-induced increase in the scattering coefficient and depth of coagulation, we speculated that changes in transmission were reliable indicators of accumulating photothermal damage. Our experiments demonstrated that thermal feedback can effectively control or limit photothermal damage.