Laser tissue soldering in urinary tract reconstruction: first human experience

Corneal cut closure using temperature-controlled CO2 laser soldering system

We aimed to evaluate the effectiveness of temperature-controlled laser soldering for repair of large perforated corneas in a porcine model. Eight Yorkshire pigs aged 6 months underwent 6-mm-deep 180° crescent-shaped trephination of the central corneas. Right corneal injuries were repaired by placement of 47 % bovine albumin along the cut followed by CO2 laser soldering (power density 16 W/cm(2)) to a target temperature of 65(°). Left corneal injuries were repaired with 10/0 nylon sutures. The groups were compared for operative time, leakage, and histopathological findings. Mean tissue temperature was 63 ± 4 °C. Mean operative time was 31.57 ± 2.8 min in laser-soldered eyes and 41.38 ± 2.3 min in controls (p < 0.0001, unpaired Student's t test). Compared to controls, the soldered corneas had less neovascularization, complete re-epithelization, and mild stromal inflammation. There was no leakage in either group. Combined CO2 laser and radiometer is effective for the in vivo repair of corneal cuts. These results have important implications for modern corneal surgery. Further studies are needed in the clinical setting.

CO₂ laser welding of corneal cuts with albumin solder using radiometric temperature control

PURPOSE

To examine the efficacy and reproducibility of CO₂ laser soldering of corneal cuts using real-time infrared fiber-optic radiometric control of tissue temperature in bovine eyes (in vitro) and to evaluate the duration of this procedure in rabbit eyes (in vivo).

METHODS

In vitro experiment: a 6-mm central perforating cut was induced in 40 fresh bovine eyes and sealed with a CO₂ laser, with or without albumin soldering, following placement of a single approximating nylon suture. A fiber-optic radiometric temperature control system for the CO₂ laser was used. Leaking pressure and histological findings were analyzed and compared between groups. In vivo experiment: following creation of a central perforation, 6 rabbit eyes were treated with a CO₂ laser with albumin solder and 6 rabbit eyes were treated with 10-0 nylon sutures. The amount of time needed for completion of the procedures was compared.

RESULTS

In vitro experiment: effective sealing was achieved by CO₂ laser soldering. Mean (± SD) leaking pressure was 109 ± 30 mm Hg in the bovine corneas treated by the laser with albumin solder compared to 51 ± 7 mm Hg in the sutured control eyes (n = 10 each; p < 0.001). Mean leaking pressures were much lower in the corneal cuts sealed only with the laser without albumin solder (48 ± 12 mm Hg) and in the cuts sealed only with albumin without laser welding (6.3 ± 4 mm Hg) than in the cuts treated with laser welding and albumin solder. In vivo experiment: mean surgical time was 140 ± 17 s in the laser-treated rabbits compared to 330 ± 30 s in the sutured controls (n = 6; p < 0.001). A histopathological study of the rabbit corneas 1 day after laser soldering revealed sealed corneal edges with a small gap bridged by coagulated albumin. The inflammatory reaction was minimal in contrast to the sutured controls. No thermal damage was detected at the wound edges.

CONCLUSIONS

CO₂ laser soldering combined with the fiber-optic radiometer is an effective, reliable, and rapid tool for the closure of corneal wounds, and holds advantages over conventional suturing in terms of leaking pressure and surgical time.

Laser welding of ruptured intestinal tissue using plasmonic polypeptide nanocomposite solders

Approximately 1.5 million people suffer from colorectal cancer and inflammatory bowel disease in the United States. Occurrence of leakage following standard surgical anastomosis in intestinal and colorectal surgery is common and can cause infection leading to life-threatening consequences. In this report, we demonstrate that plasmonic nanocomposites, generated from elastin-like polypeptides (ELPs) cross-linked with gold nanorods, can be used to weld ruptured intestinal tissue upon exposure to near-infrared (NIR) laser irradiation. Mechanical properties of these nanocomposites can be modulated based on the concentration of gold nanorods embedded within the ELP matrix. We employed photostable, NIR-absorbing cellularized and noncellularized GNR-ELP nanocomposites for ex vivo laser welding of ruptured porcine small intestines. Laser welding using the nanocomposites significantly enhanced the tensile strength, leakage pressure, and bursting pressure of ruptured intestinal tissue. This, in turn, provided a liquid-tight seal against leakage of luminal liquid from the intestine and resulting bacterial infection. This study demonstrates the utility of laser tissue welding using plasmonic polypeptide nanocomposites and indicates the translational potential of these materials in intestinal and colorectal repair.

Evaluation of a polysaccharide gel for laser-assisted skull base repair

BACKGROUND

Endoscopic reconstruction of skull base defects remains a challenge. Laser tissue welding (LTW) is a technique in which a laser-activated solder is used to create instantaneous repairs of skull base defects with burst strengths far exceeding intracranial pressure (ICP). This study was designed to define the thermal and inflammatory profile of a novel polysaccharide soldering gel, to assess the burst strength of the repair, and to determine the time required for solder resorption.

METHODS

A prospective study was performed in rabbit and mouse models. Ten dorsal rabbit maxillary sinusotomies were laser welded and burst pressure thresholds were compared with control wounds on postoperative days (PODs) 0 and 5. All welds were examined histologically on PODs 0, 5, and 45 for thermal injury, inflammation, and degree of solder resorption. In mice, dura was exposed and laser welding was performed (n = 2). Results were compared histologically with dura exposed to laser energy alone (n = 2) on POD 7.

RESULTS

The burst pressures of the rabbit LTW group were significantly higher than control on PODs 0 (135.0 mmHg and SD = 5.8 versus 8.0 mmHg and SD = 0.5; n = 4) and 5 (155.4 mmHg and SD = 2.9 versus 41.7 mmHg and SD = 7.3; n = 4; p < 0.05). No significant thermal or inflammatory effect was found in any of the rabbit or mouse welds. Complete solder resorption was noted by POD 45.

CONCLUSION

LTW using a polysaccharide gel is capable of creating mucosal repairs capable of withstanding over four times normal ICP without additional grafting materials. These repairs increase in strength over time, have no thermal or inflammatory sequelae, and establish complete solder resorption within 45 days.

Experimental evaluation of a new system for laser tissue welding applied on damaged lungs

OBJECTIVES

Alveolar air leaks represent a challenging problem in thoracic surgery, leading to increased patient morbidity and prolonged hospitalization. Several methods have been used, but no ideal technique exists yet. We investigated the lung-sealing capacity of an experimental kit for laser tissue welding.

METHODS

The kit is composed of a semiconductor laser system applied on a protein substrate associated with a chromophore that increases absorption. In vitro tests on porcine lung tissue were done to define ideal laser parameters (power 100 Å, frequency 50 Hz, pulse duration 400 µs) and protein substrate dilution (50%). For in vivo tests, through a left thoracotomy, 14 pigs received two different lung damages: a linear incision and a circular incision. Protein substrate applied on damaged areas was treated with laser to obtain a layer that reconstituted the integrity of the visceral pleura. Air leaks were intraoperatively evaluated by water submersion test with an airway pressure of 20 cmH2O. Animals were sacrificed at postoperative days 0 and 7 to study early and late pathological features.

RESULTS

After applying laser treatment, no air leaks were seen in all proofs except in 2 cases in which a second application was required. At time 0, pathological damage mostly consisted of superficial alveolar necrotic tissue covered by protein membrane. At time 7, a complete recovery of lung lesions by fibrous scar with slight inflammatory reaction of adjacent lung tissue was seen.

CONCLUSIONS

This experimental study demonstrated the effectiveness of laser tissue welding applied to seal air leaks after lung surgery. Further studies are needed to verify acceptability for human application.

New laser soldering-based closures: a promising method in natural orifice transluminal endoscopic surgery

BACKGROUND

Complete closure of gastrotomy is the linchpin of safe natural orifice transgastric endoscopic surgery.

OBJECTIVE

To evaluate feasibility and efficacy of a new method of gastrotomy closure by using a sutureless laser tissue-soldering (LTS) technique in an ex vivo porcine stomach.

DESIGN

In vitro experiment.

SETTING

Experimental laboratory.

INTERVENTIONS

Histological analysis and internal and external liquid pressure with and without hydrochloric acid exposure were determined comparing gastrotomy closure with LTS and with hand-sewn surgical sutures.

MAIN OUTCOME MEASUREMENTS

Comparison of LTS and hand-sewn surgical gastrotomy closure. The primary outcome parameter was the internal leak pressure. Secondary parameters were the difference between internal and external leak pressures, the impact of an acid environment on the device, histological changes, and feasibility of endoscopic placement.

RESULTS

The internal liquid leak pressure after LTS was almost twice as high as after hand-sewn surgical closure (416 ± 53 mm Hg vs 229 ± 99 mm Hg; P = .01). The internal leak pressure (416 ± 53 mm Hg) after LTS was higher than the external leak pressure (154 ± 46 mm Hg; P < .0001). An acidic environment did not affect leak pressure after LTS. Endoscopic LTS closure was feasible in all experiments. Histopathology revealed only slight alterations beneath the soldering plug.

LIMITATIONS

In vitro experiments.

CONCLUSIONS

Leak pressure after LTS closure of gastrotomy is higher than after hand-sewn surgical closure. LTS is a promising technique for closure of gastrotomies and iatrogenic perforations. Further experiments, in particular survival studies, are mandatory.

The evolution of lasers in urology

The world's first laser was developed by Theodore Maiman in 1960. Over the course of the past five decades, this technology has evolved into a highly specialized entity, also finding a niche market in the field of urology. Lasers obtained from various lasing mediums producing amplified light of different wavelengths have been tested for urological applications. Today, these lasers are most commonly used in the surgical management of benign prostatic hyperplasia and as intracorporeal lithotripters. Other uses include ablation of various urologic tumors and incising strictures of the upper- and lower urinary tract. A continuous process of evolution of this technology is taking place, resulting in surgical lasers becoming ever safer, more effective, and more affordable.

Endonasal laser tissue welding: first human experience

BACKGROUND

Adequate repair of cerebrospinal fluid leak remains a significant challenge in endoscopic skull base surgery. Laser tissue welding (LTW) is a method of creating an instant watertight wound closure using a chromophore doped biological solder, which may be used for cranial base reconstruction. The objective of this study is to assess the safety and technical feasibility of endoscopic LTW in human sinonasal mucosa.

METHODS

A prospective, Institutional Review Board-approved study was performed of 10 patients undergoing endoscopic LTW using an albumin and hyaluronic acid-based solder for repair of mucosal injuries. Data were collected on patient demographics, total lasing time, and volume of solder used. Wounds were prospectively followed by endoscopic exam and scored on a scale of zero to two by three blinded observers (B.S.B., J.N.P., and A.G.C.) for inflammation, thermal injury, and edema. Results were compared with control wounds using the Mann-Whitney U test.

RESULTS

Ten patients (seven men and three women; average age 50 years; range, 33-71 years) underwent endoscopic LTW. Total lasing time was 11 +/- 11 minutes requiring 0.96 +/- 0.83 mL of solder per patient. Patients were followed for an average of 72 days (range, 12-138 days) and no complications were noted. Solder persisted for up to 26 days and there was no significant difference between the lased and control wounds with regard to inflammation (0.87 +/- 0.72 versus 1.31 +/- 0.87), thermal injury (0.06 +/- 0.25 versus 0.12 +/- 0.34), or edema scores (1.13 +/- 0.81 versus 1.44 +/- 0.73).

CONCLUSION

Endoscopic LTW is a technically feasible and rapid method of wound closure in sinonasal mucosa that does not result in any significant thermal or inflammatory sequelae.

Evolving materials and techniques for endoscopic sinus surgery

Functional endoscopic sinus surgery was initially introduced as a minimally invasive procedure to treat chronic rhinosinusitis (CRS) in patients for whom medical management failed. Sinus surgery has been deemed an extremely effective part of the overall management of chronic sinus disease with symptomatic improvement in the vast majority of patients. At the forefront, technologic advances have been critical in advancing endoscopic sinus surgical procedures. With the introduction of improved optics and lighting, advanced instrumentation, and image-guided surgical navigation, the limitations of endoscopic procedures have been significantly reduced. Endoscopic techniques have evolved to include the management of both malignant and benign neoplasms of the sinuses and anterior skull base. This article highlights some of the newest advances in technology, materials, and medical/surgical techniques used in endoscopic sinus and skull base procedures and illustrates how they advance overall patient care to help minimize morbidity and complications.

Cranial-base repair using endoscopic laser welding

As the scope of transnasal cranial-base surgery expands, reconstruction of the complex residual defects remains a challenge. Laser welding is a novel technology that can be performed endoscopically and offers the potential of producing instantaneous, watertight repairs using a chromophore-doped biologic solder.

In vivo laser tissue welding in the rabbit maxillary sinus

BACKGROUND

One of the challenges in the current expansion of endoscopic sinonasal surgery is the ability to adequately reconstruct the skull base. Laser tissue welding (LTW) uses laser energy coupled to a biological solder to produce tissue bonds with burst thresholds exceeding human intracranial pressure. This technology could be used to reduce the rate of postoperative cerebrospinal fluid (CSF) leak. We performed this study to determine whether LTW can create durable tissue bonds in sinonasal mucosa that support normal wound healing and produce minimal collateral thermal injury.

METHODS

Bilateral maxillary sinus mucosal incisions were made in 20 New Zealand white rabbits and one side was repaired using LTW. Burst pressure thresholds were measured on postoperative days 0, 5, and 15 and were compared with control using a two- way ANOVA and a post hoc Tukey test. Welds were examined histologically for thermal injury, inflammation, and fibroplasia and graded on a 4-point scale by three blinded observers.

RESULTS

The burst pressures of the LTW group were significantly higher than control on postoperative day 0 (120.85 mm Hg, N = 4, SD = 47.84 versus 7.85 mm Hg, N = 4, SD = 0.78), and day 5 (132.56 mm Hg, N = 8, SD = 24.02 versus 41.7 mm Hg, N = 8, SD = 7.2; p < 0.05). By postoperative day 15 there was no significant difference between LTW (169.64 mm Hg, N = 8, SD = 18.49) and control (160.84 mm Hg, N = 8, SD = 14.16) burst thresholds. There was no evidence of thermal injury to the surrounding tissue in any group as well as no difference between experimental group and control with respect to inflammation or fibroplasia.

CONCLUSION

This is the first in vivo study showing that LTW is capable of producing tissue bonds exceeding human intracranial pressure with negligible thermal injury in sinonasal tissue. Welding can be performed endoscopically using a fiberoptic cable and may be useful in CSF leak and skull base repair.

Laser-welded endoscopic endoluminal repair of iatrogenic esophageal perforation: an animal model

OBJECTIVE

To test the feasibility of laser tissue welding (LTW) in creating an endoscopic transluminal repair of esophageal perforation.

STUDY DESIGN

Animal model.

SUBJECTS AND METHODS

A diode laser was used to create an endoluminal rabbit esophageal perforation repair. Burst pressures were compared with open incision, external suture, and external laser-augmented suture closure. Comparisons were performed five times and analyzed with Kruskal-Wallis analysis of variance and a post hoc Dunn method.

RESULTS

The burst threshold of the endoluminal weld (54.78 +/- 5.84 mm Hg) was significantly higher than that of the open incision (6.5 +/- 1.94 mm Hg) and not significantly different than that of the external suture (37.18 +/- 1.97 mm Hg) or the laser-augmented suture group (71.60 +/- 7.58 mm Hg).

CONCLUSION

Laser welding is a feasible method of creating endoluminal repairs with burst strengths comparable with external suture repair, which may allow a subset of patients to avoid traditional open approaches. This is the first reported animal model of LTW for endoscopic closure of iatrogenic esophageal perforation.

Laser-assisted cerebrospinal fluid leak repair: an animal model to test feasibility

OBJECTIVES

To test the feasibility of laser tissue welding as a method of creating an endonasal tissue bond for the purpose of cerebrospinal fluid leak repair.

STUDY DESIGN AND SETTING

An 808 nm diode laser was used with a 42% albumin solder to create laser welds in sheep nasal septal mucosa, periosteum, and in situ rabbit maxillary sinus mucosa. Each condition was tested five times. Groups were compared with Kruskal-Wallis nonparametric analysis of variance (ANOVA) and post-hoc multiple-comparisons testing with the Bonferroni test.

RESULTS

The burst pressures of sheep septal mucosa (34.88 +/- 3.49 mmHg) and periosteum (30.02 +/- 2.23 mmHg) were significantly higher than suture repair. A burst pressure of 69.58 +/- 2.85 mmHg was achieved in rabbit in situ maxillary sinus mucosa.

CONCLUSION

Laser welding is capable of producing tissue bonds whose burst strength exceeds that of human intracranial pressure.

SIGNIFICANCE

This is the first study to examine the feasibility of laser tissue welding in endonasal tissues. The ability to produce instant transnasal tissue bonds with burst pressures that exceed human intracranial pressure make this technology ideal for cerebrospinal fluid leak repair.

Underlay Tympanoplasty with Laser Tissue Welding

We investigated the feasibility of using laser tissue welding techniques to perform transcanal underlay tympanoplasty. We used 10 temporal bones obtained from human cadavers. After creating a subtotal tympanic membrane perforation, we introduced harvested periosteum through the perforation and used laser tissue welding to secure the periosteum graft in place in an underlay fashion. The procedure was performed via a transcanal approach and did not require middle ear packing. Immediately after the graft had been placed, we qualitatively tested its integrity with a blunt probe. The graft was as strong as the native cadaver tympanic membrane in all 10 cases. We conclude that laser transcanal underlay tympanoplasty is a feasible and effective method of repairing a tympanic membrane. The ultimate goal is to develop a technique that will allow physicians to routinely perform underlay tympanoplasty on moderately sized perforations in an office setting.

Near infrared laser-tissue welding using nanoshells as an exogenous absorber

BACKGROUND AND OBJECTIVE

Gold nanoshells are a new class of nanoparticles that can be designed to strongly absorb light in the near infrared (NIR). These particles provide much larger absorption cross-sections and efficiency than can be achieved with currently used chemical chromophores without photobleaching. In these studies, we have investigated the use of gold nanoshells as exogenous NIR absorbers to facilitate NIR laser-tissue welding.

STUDY DESIGN/MATERIALS AND METHODS

Gold nanoshells with peak extinction matching the NIR wavelength of the laser being used were manufactured and suspended in an albumin solder. Optimization work was performed on ex vivo muscle samples and then translated into testing in an in vivo rat skin wound-healing model. Mechanical testing of the muscle samples was immediately performed and compared to intact tissue mechanical properties. In the in vivo study, full thickness incisions in the dorsal skin of rats were welded, and samples of skin were excised at 0, 5, 10, 21, and 32 days for analysis of strength and wound healing response.

RESULTS

Mechanical testing of nanoshell-solder welds in muscle revealed successful fusion of tissues with tensile strengths of the weld site equal to the uncut tissue. No welding was accomplished with this light source when using solder formulations without nanoshells. Mechanical testing of the skin wounds showed sufficient strength for closure and strength increased over time. Histological examination showed good wound-healing response in the soldered skin.

CONCLUSIONS

The use of nanoshells as an exogenous absorber allows the usage of light sources that are minimally absorbed by tissue components, thereby, minimizing damage to surrounding tissue and allowing welding of thicker tissues.

NIR laser tissue welding of in vitro porcine cornea and sclera tissue

BACKGROUND AND OBJECTIVE

The objective of this study was to test the hypothesis that an near infrared (NIR) laser system (1,455 nm) in combination with a motorized translational stage to control the position and speed of the laser beam and a shutter to control the laser exposure to the tissue being welded could be used to successfully weld ocular tissues.

STUDY DESIGN/MATERIALS AND METHODS

Seventy-five porcine corneas and 23 porcine scleral tissues were welded in vitro in this study. The welded tissues were examined using histopathology and tensile strength analysis. Eight different welding conditions were analyzed for porcine cornea and one for sclera tissues. The tensile strength of the welded groups was compared to a sutured cornea control group.

RESULTS

The NIR laser welding system provides strong, full thickness welds and does not require the use of extrinsic dyes, chromophores, or solders. Mean weld strengths of 0.15-0.45 kg/cm(2) were obtained for the cornea and 1.01 kg/cm(2) for sclera welds. The native H(2)O in the ocular tissue serves as an absorber of the 1,455 nm radiation and helps to induce the welds.

CONCLUSIONS

We conclude that an NIR laser system using an optimal laser radiation wavelength of 1,455 nm can effectively weld cornea and sclera tissue and that this laser tissue welding (LTW) methodology typically causes minimal disruption of tissue, and thus, avoids opacities and irregularities in the tissue which may result in decreased visual acuity. The optimization of a laser welding system that leads to a strong full thickness tissue bond without tissue destruction, an instant seal that promotes wound healing, and the absence of a continued presence of a foreign substance like a suture, is of considerable importance to the ophthalmology medical community. This need is especially apparent with respect to corneal transplantation and fixing the position of corneal flaps in Laser-Assisted In Situ Keratomileusis (LASIK), a laser procedure used to permanently change the shape of the cornea.

Optimal Dye Concentration and Irradiance for Laser-Assisted Vascular Anastomosis

OBJECTIVE

This investigation was done in order to find optimal indocyanine green (ICG) concentration and energy irradiance in laser vascular welding.

BACKGROUND DATA

Many studies have shown that laser tissue welding with albumin solder/ICG may be an effective technique in surgical reconstruction. However, there are few reports regarding optimal laser settings and concentrations of ICG within the albumin solder in laser-assisted vascular anastomosis.

MATERIALS AND METHODS

Porcine carotid artery strips (n = 120) were welded in end-to-end by diode laser with 50% albumin solder of 0.01, 0.1, and 1.0 mM ICG at irradiance of 27.7, 56.7, and 76.9 W/cm(2), respectively. Temperature was measured by inserting thermocouples outside and inside the vessel. Tensile strength and histology were studied.

RESULTS

Temperature and strength of the anastomosis significantly decreased (all p < 0.05) with increasing ICG concentration at 56.7 W/cm(2). Histological study showed minimal thermal injury limited to adventitia and no appreciable difference between all groups.

CONCLUSIONS

ICG concentration within solder is the most important factor affecting both vascular temperature and tensile strength. The optimal balance between strength and minimal thermal injury may be achieved primarily at 56.7 W/cm(2) and 0.01 mM ICG.

Sutureless laparoscopic heminephrectomy using laser tissue soldering

BACKGROUND AND PURPOSE

Widespread application of laparoscopic partial nephrectomy has been limited by the lack of a reliable means of attaining hemostasis. We describe laser tissue welding using human albumin as a solder to control bleeding and seal the collecting system during laparoscopic heminephrectomy in a porcine model.

MATERIALS AND METHODS

Laparoscopic left lower-pole heminephrectomy was performed in five female domestic pigs after occluding the hilar vessels. Using an 810-nm pulsed diode laser (20 W), a 50% liquid albumin-indocyanine green solder was welded to the cut edge of the renal parenchyma to seal the collecting system and achieve hemostasis. Two weeks later, an identical procedure was performed on the right kidney, after which, the animals were sacrificed and both kidneys were harvested for ex vivo retrograde pyelograms and histopathologic analysis.

RESULTS

All 10 heminephrectomies were performed without complication. The mean operative time was 82 minutes, with an average blood loss of 43.5 mL per procedure. The mean warm ischemia time was 11.7 minutes. For each heminephrectomy, a mean of 4.2 mL of solder was welded to the cut parenchymal surface. In three of the five acute kidneys and all five 2-week kidneys, ex vivo retrograde pyelograms demonstrated no extravasation. In addition, no animal had clinical evidence of urinoma or delayed hemorrhage. Histopathologic analysis showed preservation of the renal parenchyma immediately beneath the solder.

DISCUSSION

Laser tissue welding provided reliable hemostasis and closure of the collecting system while protecting the underlying parenchyma from the deleterious effect of the laser during porcine laparoscopic heminephrectomy.

Laser tissue soldering: applications in the genitourinary system

Within the past 25 years, lasers have transitioned from merely destructive or ablative tools to those with reconstructive uses. It has been shown that the application of laser thermal energy to tissue will result in welding of the approximated areas. Furthermore, the addition of protein solder and chromophores (tissue soldering) has increased wound tensile strength while decreasing peripheral tissue damage. Laboratory studies have demonstrated application of laser tissue soldering to virtually all components of the genitourinary system. Increasing human experience in recent years has reinforced the success of this technique.

Potential use of diode laser soldering in middle ear reconstruction

BACKGROUND AND OBJECTIVES

To assess the potential use of diode laser soldering to improve mechanical stability of middle ear reconstruction. The diode laser with a biological solder may offer benefits over traditional methods. We evaluated the strength of soldered bonds and a means to apply such a technique in the human middle ear.

STUDY DESIGN/MATERIALS AND METHODS

The strength of soldered junctions using fascia, cartilage, bone, and hydroxyappatite was evaluated in vitro. A diode laser (810-nm wavelength) and 50% albumin with 0.1% indocyanine green dye was used. Soldered bonds were compared to those obtained with adhesive alone. A fiberoptic delivery system was evaluated. Ten hydroxyappatite prostheses were soldered to the stapes in human cadaver temporal bones, and the force required to disrupt the bonds were measured.

RESULTS

Statistically significant greater strength was obtained with soldering. Ossicular prostheses can be effectively secured to the stapes in a cadaver model.

CONCLUSIONS

Soldering techniques show promise in middle ear reconstruction.

Intraluminal albumin stent assisted laser welding for ureteral anastomosis

BACKGROUND AND OBJECTIVES

The success of laser tissue welding or soldering depends on optimal laser settings, solder material, and tissue type and geometry. To develop a practical laser welding technique for ureteral repair, an intraluminal albumin stent was designed to enhance the welding effects on ureteral end to end anastomosis.

STUDY DESIGN/MATERIALS AND METHODS

In vitro porcine ureters were anastomosed using an albumin stent alone, the albumin stent plus a solder, and the solder alone. All welding was performed with an 810-nm diode laser with either a continuous wave (1 W, CW) or two pulse modes (2 W, 3.3 Hz; 1 W, 5 Hz). Laser parameters, tensile strength (TS) and burst pressure (BP) of the ureteral anastomosis, and tissue thermal injury were measured.

RESULTS

In the 2-W pulse mode, BP in the albumin stent plus solder group (mean 185 mmHg) and the stent only group (mean 133 mmHg) were significantly higher than the solder only group (mean 77 mmHg, P < 0.05). Laser ureteral anastomosis with the stent plus solder group at 1-W CW and 2-W pulse laser modes yielded the highest TS (mean 97, 82 g) and BP (mean 183, 185 mmHg). Among the three modes, the 1 W pulse delivered the lowest energy and yielded the lowest TS and BP in ureteral anastomosis. There was no significant difference in the thermal damage to the tissue among the modes and groups.

CONCLUSIONS

Using the albumin stent increased the reliability of ureter end-to-end laser anastomosis. Further studies will be warranted in vivo and other tubular organs as well.

Optimal solder and power density for diode laser tissue soldering (LTS)

BACKGROUND AND OBJECTIVE

Laser tissue soldering (LTS) using albumin and indocyanine green dye (ICG) is an effective technique utilized in various reconstructive surgical procedures. The purpose of this study was to describe in vivo and in vitro temperature profiles of an albumin-based solder while varying ICG concentration and laser power density (PD), and to describe immediate and short-term tensile strength measurements and histology of tissue with variable ICG concentrations and PD.

STUDY DESIGN/MATERIALS AND METHODS

ICG ranged from 0.31 to 20 mg/mL while PD ranged from 3.2 to 63.7 W/cm(2). Direct solder temperature measurements were obtained at 5-second intervals during laser activation. Differential temperature measurements were determined within the dermis of rat skin and the overlying solder. Eighteen rats were subjected to 2.0-cm incisions (n = 113) created on the dorsal skin followed by closure with LTS at varying PD and ICG concentrations. ICG concentrations included 0.31, 2.5, and 20 mg/mL, while PD ranged from 8.0 to 63.7 W/cm(2). Tensile strength (TS) profiles were measured immediately and 10 days post-operatively. Histological examination was performed at the time of sacrifice.

RESULTS

Temperature profiles of the ICG/albumin solder differed significantly only at the highest concentration of ICG (20 mg/mL), but showed statistically significant variability at different laser PD. Using solder color changes as an endpoint of LTS, average peak solder temperature ranged from 69 degrees C at a PD of 8.0 W/cm(2), 105 degrees -120 degrees C at PD 15.9-31.8 W/cm(2), and > 200 degrees C at PD > or = 47.7 W/cm(2). Peak intradermal temperatures remained below 50 degrees C at all PDs. Varying ICG concentration only had an effect on the immediate TS of wounds at the lowest power densities. Increasing PD resulted in statistically significant increases in immediate TS up to a PD of 23.9 W/cm(2) at an ICG concentrations of 0.31 and up to a PD of 15.9 W/cm(2) at a concentration of 2.5 mg/mL. Statistically insignificant decreases in 10-day would strength resulted from higher PD. Power densities > or = 23.9 W/cm(2) showed significant thermal injury upon histologic examination.

CONCLUSIONS

Power density, not ICG concentration, is the primary determinant of solder and tissue temperature during LTS. Effective and reproducible laser tissue soldering may be achieved primarily by power density control when using diode laser and ICG-based albumin solder. Alterations in PD show the most direct and predictable effects on the healing properties of skin closed by LTS. Optimal laser wound closure occurs with an ICG of 2.5 mg/mL and at a PD between 15.9 and 23.9 W/cm(2).

Surgical adhesives for laser-assisted wound closure

Solid protein solder-doped polymer membranes were developed for laser-assisted tissue repair. Biodegradable polymer membranes of controlled porosity were fabricated with poly(L-lactic-co-glycolic acid) (PLGA), poly(ethylene glycol) (PEG), and salt particles, using a solvent-casting and particulate-leaching technique. The membranes provided a porous scaffold that readily absorbed the traditional protein solder composed of serum albumin, indocyanine green dye, and de-ionized water. In vitro investigations were conducted to assess the influence of various processing parameters on the strength of tissue repairs formed using the new membranes. These parameters included PLGA copolymer and PLGA/PEG blend ratios, membrane pore size, initial albumin weight fraction, and laser irradiance used to denature the solder. Altering the PLGA copolymer ratio had little effect on repair strength, however such variations are known to influence the degradation rate of the membranes. The repair strength increased with increased membrane pore size and bovine serum albumin concentration. The addition of PEG during the membrane casting stage increased the flexibility of the membranes but not necessarily the repair strength. Typically, the repair strength increased with increasing irradiance from 12 to 18 W/cm(2). The new solder-doped polymer membranes provided all of the benefits associated with solid protein solders including high repair strength and improved edge coaptation. In addition, the flexible, moldable nature of the new membranes offers the capability of tailoring the membranes to a wide range of clinically relevant geometries.

Impact of solubility on laser tissue-welding with albumin solid solders

BACKGROUND AND OBJECTIVE

The correlation between the solubility of solid albumin solders and their laser weld strength was investigated.

STUDY DESIGN/MATERIALS AND METHODS

Sections of dog intestine were laser welded with soluble or insoluble solid strips of solder. Two different treatments were followed for tissue soldering: "wet weld" and "dry weld." These treatments were chosen to assess the impact of solubility on the repair strength. The laser power and radiation dose were 0.14 W and 14 J/mg, respectively. Calorimetric measures of solders were also performed.

RESULTS

The moisture on the tissue partially dissolved the soluble strips at the tissue interface. Hence, the repair strength of the soluble solder was significantly stronger than the repair strength of the insoluble solder (0.22 N and 0.06 N, P < 0.0001). Temperature (approximately 70 degrees C) and enthalpy variation (approximately 1.4 J/g) for denaturing the soluble and insoluble solders were not significantly different (P > 0.05).

CONCLUSION

The soluble solid solder behaved like dense liquid solder at the tissue interface. Hence, the interface strength of these two forms of solder should be similar. This correlation made it possible to identify an intrinsic limit for the weld strength of albumin solders.

Laser tissue soldering for hypospadias repair: results of a controlled prospective clinical trial

PURPOSE

Laser tissue soldering has been shown to provide safe and effective tissue closure by creating an immediate leak-free anastomosis with minimal scar formation. We compared the results of laser tissue soldering and conventional suturing for hypospadias repair.

MATERIALS AND METHODS

A consecutive group of 138 boys 4 months to 8 years old (mean age 15 months) was divided into a standard suturing (84) and a sutureless laser (54) hypospadias repair group. Urethral repair was defined as simple (Thiersch-Duplay or Snodgrass) and complex (onlay island flap or tube) in 101 and 37 cases, respectively. Laser tissue soldering was performed with 50% human albumin solder doped with 2.5 mg./ml. indocyanine green dye using an 808 nm. diode laser at 0.5 W. In the laser group sutures were used for tissue alignment only. At surgery neourethral and penile length, operative time for neourethral construction and the number of sutures or throws were measured. Postoperatively patients were examined for complications of wound healing, stricture or fistula.

RESULTS

Mean patient age, urethral defect severity, type of repair, neourethral length and stenting time plus or minus standard error of mean were not significantly different in the 2 groups. Mean operative time was a fifth as long for laser tissue soldering in simple and complex hypospadias repair compared to controls (1.5 +/- 0.1 and 5.1 +/- 0.3 versus 8.5 +/- 0.8 and 26.7 +/- 1.7 minutes, respectively, p <0.001). The mean number of sutures used for tissue alignment in the laser group for simple and complex repair was significantly less than in controls (3.0 +/- 0.2 and 8.2 +/- 0.6 versus 8.5 +/- 0.8 and 23.2 +/- 1.5, respectively, p <0.001). All patients were followed a mean of 12 months (minimum 6, maximum 22). The complication rate was 4.7% in the laser group and 10.7% in controls with fistula in 2 of 54 cases, and fistula and meatal stenosis in 7 and 2 of 84, respectively.

CONCLUSIONS

These preliminary results indicate that laser tissue soldering for hypospadias repair may be performed in almost sutureless fashion and more rapidly than conventional suturing. The ease of the laser technique and the lower complication rate in the laser group indicate that laser tissue soldering is an acceptable means of tissue closure in hypospadias repair.

Improved vascular tissue fusion using new light-activated surgical adhesive on a canine model

Newly developed light-activated surgical adhesives have been investigated as a substitute to traditional protein solders for vascular tissue fusion without the need for sutures. Canine femoral arteries (n = 14), femoral veins (n = 14), and carotid arteries (n = 10) were exposed, and a 0.3-0.6 cm longitudinal incision was made in the vessel walls. The surgical adhesive, composed of a poly(L-lactic-co-glycolic acid) scaffold doped with the traditional protein solder mix of bovine serum albumin and indocyanine green dye, was used to close the incisions in conjunction with an 805 nm diode laser. Blood flow was restored to the vessels immediately after the procedure and the incision sites were checked for patency. The new adhesives were flexible enough to be wrapped around the vessels while their solid nature avoided the problems associated with "runaway" of the less viscous liquid protein solders widely used by researchers. Assessment parameters included measurement of the ex vivo intraluminal bursting pressure 1-2 h after surgery, as well as histology. The acute intraluminal bursting pressures were significantly higher in the laser-solder group (>300 mmHg) compared to the suture control group (<150 mmHg) where four evenly spaced sutures were used to repair the vessel (n = 4). Histological analysis showed negligible evidence of collateral thermal damage to the underlying tissue in the laser-solder repair group. These initial results indicated that laser-assisted vascular repair using the new adhesives is safe, easy to perform, and contrary to conventional suturing, provides an immediate leak-free closure. In addition, the flexible and moldable nature of the new adhesives should allow them to be tailored to a wide range of tissue geometries, thus greatly improving the clinical applicability of laser-assisted tissue repair.

Novel solid protein solder designs for laser-assisted tissue repair

BACKGROUND AND OBJECTIVES

Previous studies have shown that the application of chromophore-enhanced albumin protein solders to augment laser tissue repairs significantly improves repair strength, enhances edge co-optation, and reduces thermal tissue injury. These investigations are furthered with this in vitro study conducted to assess a new range of specially designed chromophore-enhanced solid protein solders manufactured and tested for application during laser-assisted tissue repair.

STUDY DESIGN/MATERIALS AND METHODS

The experimental study was divided into three parts. In the first part of the study, the creation of a chromophore concentration gradient across the thickness of the solid protein solder was investigated as a means to improve control of the heat source gradient through the solder during laser irradiation. In the second part of the study, predenaturation of the solid protein solder was investigated as a means for enhancing the stability of the solder in physiological fluids before irradiation. Finally, in the third part of the study, the feasibility of using synthetic polymers as a scaffold for traditional albumin protein solder mixes was investigated as a means of improving the flexibility of the solder.

RESULTS

Uniform denaturation across the thickness of the solder was achieved by controlling the chromophore concentration gradient, thus ensuring stable solder-tissue fusion when the specimen was submerged in a hydrated environment. Predenaturation of the solid protein solder significantly reduced the solubility of the solder, and consequently, improved the handling characteristics of the solder. The solder-doped polymer membranes were flexible enough to be wrapped around tissue, whereas their solid nature avoided problems associated with "runaway" of the less viscous liquid solders currently used by researchers. In addition, the solder-doped polymer membranes could be easily tailored to a wide range of geometries suitable to many clinical applications.

CONCLUSION

The novel solid protein solder designs presented here add a new dimension to tissue repair as their flexible, moldable, and absorption controllable nature, greatly improves the clinical applicability of laser-assisted tissue repair.

Effects of endogenous absorption in human albumin solder for acute laser wound closure

BACKGROUND AND OBJECTIVE

Human albumin is currently being used as a biological solder in laser tissue welding. Experiments were performed to characterize the effects of differing albumin concentrations on wound closure when a 1.32 microm Nd:YAG laser is used to repair skin incisions.

MATERIALS AND METHODS

In vivo comparison of acute tensile strength was made in full thickness porcine skin wounds using different solder concentrations. Histology of the repairs was also completed to evaluate the thermal denaturation of the tissue and solder. Transmission measurements were completed for nondenatured and denatured albumin solders. Finally, the real time denaturation pattern of different solder concentrations during laser irradiation was investigated.

RESULTS

A tissue solder consisting of 50% albumin provides the greatest tensile strength for acute in vivo skin closure. The transmission measurements verify that the primary absorber of 1.32-microm laser light was the solder solvent (water). A significant decrease in power transmission occurs when the 25% albumin solder was denatured. The real time denaturation profiles demonstrate that 1.32-microm laser light denatures 25% albumin solder from the outer surface, while in 50% albumin solder, denaturation occurs from within the solder bulk. Wound histology corroborates the pattern of denaturation seen in vitro.

CONCLUSION

The combination of 1.32-microm laser light and 50% human albumin solder can be used to create a deep tissue weld resulting in higher acute repair tensile strength. This permits a deep to superficial closure of wounds, which may result in an optimal method of acute closure for full-thickness wounds.

Solubility study of albumin solders for laser tissue-welding

BACKGROUND/OBJECTIVE

Current albumin solders for tissue-welding are soluble in physiological fluids, prior to laser irradiation. These solders are therefore subjected to mechanical alterations, which can weaken the solder-tissue repair. In this study, an albumin solder (laser activated) was developed with low solubility and with the ability to retain (partially) its mechanical characteristics in saline solution.

STUDY DESIGN/MATERIALS AND METHODS

Gauged protein samples of solder were immersed into 0.5 ml saline solution for fixed intervals of time. The solder samples contained four bovine serum albumin (BSA) concentrations: 56%, 66%, 70%, and 75% (by weight). A Bradford protein assay measured the BSA solubility of the solders. The 70% and 75% BSA solders were also used to weld in vitro Wistar rat intestine sections with a diode laser (lambda = 810 nm, power = 270 mW).

RESULTS

The solubility of the 75% BSA solder was significantly decreased with respect to the other solders (Anova, P < 0.05). This solder also showed comparable weld strength (13 gm) to the 70% BSA solder.

CONCLUSION

The 75% BSA solder strongly reduced the albumin solubility in saline solution, without affecting its tissue-welding properties.

Laser assisted soldering: microdroplet accumulation with a microjet device

BACKGROUND AND OBJECTIVE

We investigated the feasibility of a microjet to dispense protein solder for laser assisted soldering.

STUDY DESIGN

Successive micro solder droplets were deposited on rat dermis and bovine intima specimens. Fixed laser exposure was synchronized with the jetting of each droplet. After photocoagulation, each specimen was cut into two halves at the center of solder coagulum. One half was fixed immediately, while the other half was soaked in phosphate-buffered saline for a designated hydration period before fixation (1 hour, 1, 2, and 7 days). After each hydration period, all tissue specimens were prepared for scanning electron microscopy (SEM).

RESULTS

Stable solder coagulum was created by successive photocoagulation of microdroplets even after the soldered tissue exposed to 1 week of hydration.

CONCLUSIONS

This preliminary study suggested that tissue soldering with successive microdroplets is feasible even with fixed laser parameters without active feedback control.

Optimal parameters for laser tissue soldering. Part I: tensile strength and scanning electron microscopy analysis

BACKGROUND AND OBJECTIVES

The use of liquid and solid albumin protein solders to enhance laser tissue repairs has been shown to significantly improve postoperative results. The published results of laser-solder tissue repair studies have, however, indicated inconsistent success rates. This can be attributed to variations in laser irradiance, exposure time, solder composition, chromophore type, and concentration. An in vitro study was performed using indocyanine green-doped albumin protein solders in conjunction with an 808 nm diode laser to determine optimal laser and solder parameters for tissue repair in terms of tensile strength and stability during hydration.

STUDY DESIGN/MATERIALS AND METHODS

Twenty-five different combinations of laser irradiance (6.4, 12.7, 19.1, 25.5, 31.8 W/cm2) and exposure time (20, 30, 40, 50, 100 or 40, 60, 80, 100, 200 seconds) were used. The effect of changing bovine serum albumin (BSA) concentration (25% and 60%) and indocyanine green (ICG) dye concentration (2.5 mg/ml and 0.25 mg/ml) of the protein solder on the tensile strength of the resulting bonds was investigated. The effect of hydration on bond stability was also investigated using both tensile strength and scanning electron microscopy analysis.

RESULTS

Tensile strength was observed to decrease significantly with increasing irradiance. An optimum exposure time was found to exist where further irradiation did not improve the tensile strength of the bond. Tensile strength was found to be greatly improved by increasing the BSA concentration. Finally, the lower ICG dye concentration increased the penetration depth of the laser light in the protein solder leading to higher tensile strengths. The strongest repairs were formed by using 6.4 W/cm2 irradiation for 50 seconds with a protein solder composed of 60% BSA and 0.25mg/ml ICG. In addition, the solid protein solder provided more stable adhesion to the tissue than did the liquid protein solder when the tissue was submerged in a hydrated environment.

CONCLUSIONS

This study greatly enhances the current understanding of the various factors affecting the soldering process. It provides a strong basis for optimization of the laser light delivery parameters and the solder constituents to achieve strong and reliable laser tissue repairs.

Comparison of dermal and epithelial approaches to laser tissue soldering for skin flap closure

BACKGROUND AND OBJECTIVE

Prior studies of laser tissue soldering (LTS) of epithelial skin have shown poor wound strength in the short-term; however, we hypothesize that greater tensile strength and healing properties will result from directing laser energy to the dermal aspect of the skin. The current study compares wound strength and histology in a rat skin flap model of epithelial and dermally applied LTS.

STUDY DESIGN/MATERIALS AND METHODS

Skin flaps (2.5 x 4 cm) were raised and bisected on the dorsum of Sprague-Dawley rats. The center line of bisection was closed from a dermal approach by LTS (LTS-D, diode laser 15.9 W/cm2 + Columbia solder), the upper incision by epithelial LTS (LTS-E), and the lower incision by suturing (7-0 Vicryl). Wound skin strips (1-2 mm x 10 mm) were studied immediately (N = 14) and at 3 (N = 57), 7 (N = 31), and 10 (N = 28) days postoperatively and were subjected to tensiometric analysis. Histologic staining with hematoxylin and eosin and Mallory's trichrome methods were used to define wound architecture.

RESULTS

No wound dehiscences were noted in any group. Greater immediate tensile strength was noted in wounds closed by LTS-D (521 +/- 61 g/cm2) versus LTS-E (342 +/- 65 g/cm2); however, this difference was not statistically significant (P = .08). By 3 days, both LTS-D (476 +/- 55 g/cm2) and LTS-E (205 +/- 37 g/cm2) maintained their initial strength; however, LTS-D and sutured (436 +/- 49 g/cm2) wounds were stronger (P < .05) than LTS-E. At 7 and 10 days, LTS-D (2,433 +/- 346 g/cm2 and 3,100 +/- 390 g/cm2) showed superior tensile strength (P < .05) compared to both LTS-E (1,542 +/- 128 g/cm2 and 2,081 +/- 219 g/cm2) and suturing (1,342 +/- 119 g/cm2 and 1,661 +/- 115 g/cm2). Histologic analysis of LTS-D wounds at 3 days showed full-thickness tissue apposition, complete epithelialization, and minimal inflammation or thermal injury. At 7 days, solder was present in the wounds. In contrast, LTS-E wounds at 3 days displayed lack of epithelialization secondary to thermal injury and partial-thickness tissue apposition. However by 7 days, epithelialization was complete with moderate scarring, and no solder was seen. Sutured samples appeared similar to LTS-D, except for poorer tissue apposition at the hypodermis.

CONCLUSION

Our results show that skin flap wound healing after dermal LTS is superior to epithelial LTS and emphasizes the importance of site specificity in the utilization of this operative technique in reconstructive surgery.

Laser nerve repair by solid protein band technique. I: identification of optimal laser dose, power, and solder surface area

Thirty-four tibial nerves in 17 adult male wistar rats were repaired by applying protein bands longitudinally across the nerve join. The bands were then irradiated with a fibre-coupled diode laser (lambda = 810 nm). The relations among the laser weld breaking force, the power, and the solder surface area were investigated, while maintaining a consistent ratio between the total mass of protein solder in a band and total laser energy delivered (the laser energy dose). When this laser energy dose was held constant, the average breaking force of the laser welds irradiated by 72 mW laser output power was weaker than that reached after 90 mW laser radiation. There is a linear relation between the solder breaking force and the solder surface area when band thickness, laser power, and laser dose are unvaried.

Optimal parameters for laser tissue soldering: II. Premixed versus separate dye-solder techniques

BACKGROUND AND OBJECTIVE

Laser tissue soldering by using an indocyanine green (ICG)-doped protein solder applied topically to the tissue surface and denatured with a diode laser was investigated in Part I of this study. The depth of light absorption was predominantly determined by the concentration of the ICG dye added to the solder. This study builds on that work with an in vitro investigation of the effects of limiting the zone of heat generation to the solder-tissue interface to determine whether more stable solder-tissue fusion can be achieved.

STUDY DESIGN/MATERIALS AND METHODS

An alternative laser tissue soldering technique was investigated, which increased light absorption at the vital solder-tissue interface. A thin layer of ICG dye was smeared over the surface to be treated, the protein solder was then placed directly on top of the dye, and the solder was denatured with an 808-nm diode laser. Because laser light at approximately 800 nm is absorbed primarily by the ICG dye, this thin layer of ICG solution restricted the heat source to the space between the solder and the tissue surfaces. A tensile strength analysis was conducted to compare the separate dye-solder technique with conventional techniques of laser tissue soldering for which a premixed dye-solder is applied directly to the tissue surface. The effect of hydration on bond stability of repairs formed by using both techniques was also investigated using tensile strength and scanning electron microscopy analysis.

RESULTS

Equivalent results in terms of tensile strength were obtained for the premixed dye-solder technique using protein solders containing 0.25 mg/ml ICG (liquid solder, 220 +/- 35 N/cm(2); solid solder, 602 +/- 32 N/cm(2)) and for the separate dye-solder technique (liquid solder, 228 +/- 41 N/cm(2); solid solder, 578 +/- 29 N/cm(2)). The tensile strength of native bovine thoracic aorta was 596 +/- 31 N/cm(2). Repairs created by using the separate dye-solder technique were more stable during hydration than their premixed dye-solder counterparts. The conventional premixed dye-solder was simpler and approximately twice as fast to apply. The separate dye-solder technique, however, increased the shelf-life of the solder, because the dye was mixed at the time of the experiment, thus conserving its spectral absorbency properties.

CONCLUSION

Two laser-assisted tissue soldering techniques have been evaluated for repairing aorta incisions in vitro. The advantages and disadvantages of each of these techniques are discussed.

Optical and thermal characterization of albumin protein solders

The effect of temperature on the optical and thermal properties of pure and indocyanine green-doped albumin protein solders as a function of wavelength has been studied between 25 degrees C and 100 degrees C. An increase in the group refractive index by up to 4% and a decrease in absorption coefficient (approximately 800 nm) by up to 8%, after denaturing the solder specimens in a constant-temperature water bath at temperatures of 60-100 degrees C, were not significant. The reduced scattering coefficient, however, increased rapidly with temperature as the solder changed from being a highly nonscattering medium at room temperature to a highly scattering medium at temperatures close to 70 degrees C. The thermal conductivity, thermal diffusivity, and heat capacity increased by up to 30%, 15%, and 10%, respectively. Finally, the frequency factor and activation energy were measured to be 3.17 x 10(56) s(-1) and 3.79 x 10(5) J mol(-1), respectively, for liquid protein solders (25% bovine serum albumin) and 3.50 x 10(57) s(-1) and 3.85 x 10(5) J mol(-1), respectively, for solid protein solders (60% bovine serum albumin). Incorporation of dynamic optical and thermal properties into modeling studies of laser tissue interactions could have a significant influence on the determination of the expected zone of damage.

Two-layer film as a laser soldering biomaterial

BACKGROUND AND OBJECTIVES

A two-layer solder was developed to weld at low laser intensity and to provide a new method of measuring solder-tissue temperature.

STUDY DESIGN/MATERIALS AND METHODS

A film solder consisted of a white layer (bovine serum albumin (BSA) and distilled water) and a black layer (BSA, carbon black (CB), and distilled water). This two-layer solder was used with a diode laser to weld sections of dog small intestine (lambda = 810 nm, power = 200 +/- 20 mW, radiation dose = 18 +/- 1 J/mg). Sections of intestine were welded only with one-layer black solders as control group. The temperature difference between the external solder surface and the tissue-solder interface was evaluated during welding.

RESULTS

The two-layer solder performed welds as strong as the one-layer solder ( approximately 0.12 N) but with less laser intensity on the black layer. The temperature difference between the external surface of the solder and the solder-tissue interface was significantly less for the two-layer solder than for the one-layer solder ( approximately 6 degrees C and approximately 15 degrees C, respectively; P < 0.05).

CONCLUSIONS

The two-layer solder appeared to be more efficient at soldering biomaterials than the one-layer solder. Furthermore, the heat diffusion from the black midplane of the two-layer solder decreased the difference in temperature recorded on the solder external surface and on the solder-tissue interface.

Photothermal effects of laser tissue soldering

Low-strength anastomoses and thermal damage of tissue are major concerns in laser tissue welding techniques where laser energy is used to induce thermal changes in the molecular structure of the tissues being joined, hence allowing them to bond together. Laser tissue soldering, on the other hand, is a bonding technique in which a protein solder is applied to the tissue surfaces to be joined, and laser energy is used to bond the solder to the tissue surfaces. The addition of protein solders to augment tissue repair procedures significantly reduces the problems of low strength and thermal damage associated with laser tissue welding techniques. Investigations were conducted to determine optimal solder and laser parameters for tissue repair in terms of tensile strength, temperature rise and damage and the microscopic nature of the bonds formed. An in vitro study was performed using an 808 nm diode laser in conjunction with indocyanine green (ICG)-doped albumin protein solders to repair bovine aorta specimens. Liquid and solid protein solders prepared from 25% and 60% bovine serum albumin (BSA), respectively, were compared. The efficacy of temperature feedback control in enhancing the soldering process was also investigated. Increasing the BSA concentration from 25% to 60% greatly increased the tensile strength of the repairs. A reduction in dye concentration from 2.5 mg ml(-1) to 0.25 mg ml(-1) was also found to result in an increase in tensile strength. Increasing the laser irradiance and thus surface temperature resulted in an increased severity of histological injury. Thermal denaturation of tissue collagen and necrosis of the intimal layer smooth muscle cells increased laterally and in depth with higher temperatures. The strongest repairs were produced with an irradiance of 6.4 W cm(-2) using a solid protein solder composed of 60% BSA and 0.25 mg ml(-1) ICG. Using this combination of laser and solder parameters, surface temperatures were observed to reach 85+/-5 degrees C with a maximum temperature difference through the 150 microm thick solder strips of about 15 degrees C. Histological examination of the repairs formed using these parameters showed negligible evidence of collateral thermal damage to the underlying tissue. Scanning electron microscopy suggested albumin intertwining within the tissue collagen matrix and subsequent fusion with the collagen as the mechanism for laser tissue soldering. The laser tissue soldering technique is shown to be an effective method for producing repairs with improved tensile strength and minimal collateral thermal damage over conventional laser tissue welding techniques.

The application of laser techniques to vasectomy reversal surgery

OBJECTIVE

A review of the application of laser technology to vasectomy reversal surgery.

SUMMARY BACKGROUND

Modern methods of vasectomy reversal that employ microsurgical techniques have resulted in a high reported success rate. However, the procedure is tedious and time consuming. Laser technology offers the possibility of simplifying the procedure and reducing operative time, with possibly even better results.

CONCLUSIONS

Application of lasers in vasovasostomy for vasectomy reversal is still in its early development. Several animal and human studies have been conducted with mixed results. Contained clinical trials will be necessary to prove the benefit of the laser in this surgical setting.

Skin flap closure by dermal laser soldering: a wound healing model for sutureless hypospadias repair

OBJECTIVES

Laser tissue soldering (LTS) with the diode laser and human albumin-hyaluronate-indocyanine green solder is a safe and effective method of providing an immediate leak-free closure during hypospadias repair. In this report, we compare the physiology, histology, and immunohistochemistry of wound healing following LTS and suturing in a rat skin flap model.

METHODS

A 4 x 5-cm skin flap was raised and bisected (4 cm) on the dorsum of 48 Sprague-Dawley rats. The central wound was either closed from a dermal approach by suturing or LTS or left open, and studied at 0, 3, 5, 7, 10, 14, and 21 days postoperatively. An intraoperative comparison was made between suturing and LTS with respect to operative time. Postoperatively, flaps were excised for tensiometric analysis, and sections were stained with hematoxylin-eosin to define wound architecture. Resting skin temperature, laser exposed temperature without solder, and maximum temperature with solder (one drop) were measured at the level of the deep dermis, superficial striated muscle layer, and within the solder. Mean peak temperatures were recorded during a 1-minute laser activation time.

RESULTS

Mean continuous suturing time (4.9 +/- 1.1 minutes) was significantly (P < 0.001) faster than either LTS (7.7 +/- 0.77 minutes) or discontinuous suturing (8.2 +/- 0.62 minutes). Two seromas (sutured) and two instances of partial wound dehiscence (1 sutured, 1 LTS) were noted. Tensile strength was increased significantly (P < 0.001) for up to 5 days in the LTS group, but was equal to suturing at 7 and 10 days. Immediate tensile strength after LTS was equivalent to a 7-day healed wound. At 14 days, wounds initially left open and those closed by LTS were stronger than sutured wounds (P < 0.05). There was no evidence of thermal injury or foreign body reaction in the LTS group. Solder was incorporated within the dermis in all wounds at 21 days. Laser activation of solder resulted in significant increases in temperature at all three tissue levels: 65.0 +/- 5.2 and 69.9 +/- 6.8 degrees C in the deep and superficial skin (no significant difference between the two), and 101 +/- 15.6 degrees C within the solder (P < 0.001 versus superficial and deep skin).

CONCLUSIONS

Our results indicate that sutureless dermal LTS of skin flaps provides increased tensile strength for up to 7 days, with relatively greater tensile strength provided within the first 3 days. Our laser technique does not appear to alter the normal wound healing process. Rather, solder-tissue interaction initially, and extracellular matrix infiltration of solder later, provide the basis for improved wound strength. For hypospadias repair using skin flaps, these wound attributes may permit sutureless surgery.