Tissue Soldering Research Articles

Novel Laser-Activated Solder for Sealing Corneal Wounds

To compare the effectiveness of a laser-activated biological tissue solder with that of standard sutures for sealing corneal incisions. Two keratome knives measuring either 3.0 mm or 2.85 mm were used to create a non-self-sealing peripheral oblique corneal wound (POCW) or a central perpendicular corneal wound (CPCW) in fresh rabbit cadaver eyes. Wounds were sealed with a solder strip (POCW; n = 5), a solder patch (CPCW; n = 5), or three interrupted nylon 10-0 sutures (n = 5). After the solder was placed on the wound, a diode laser was used to activate the solder, resulting in cross-linking to tissue. Wound stability was tested by a stepwise infusion of saline, and pressure changes were monitored with a digital manometer. Leaking pressure was recorded. The pressurized mean baseline IOP in the intact globe was 131.13 mm Hg (SD, 4.66). Mean IOP after CPCW was 1.7 mm Hg (SD, 0.13); for POCW it was 3.62 mm Hg (SD, 3.09). For the CPCW group, the mean leaking pressure in the sutured eyes was 82.76 mm Hg (SD, 6.55), whereas in the solder patch it was 101.42 mm Hg (SD, 29.92; P = 0.2222). For the POCW group, the mean leaking pressure in the sutured eyes was 33.44 mm Hg (SD, 9.38), and the mean IOP achieved in the solder repaired eyes was 125.16 mm Hg (SD, 9.85; P = 0.0079). The tested laser-activated solder was as effective as sutures when used as a patch and superior to sutures for clear corneal incisions in this animal ex vivo model.

Healing of rabbits’ cornea following laser welding: effect of solid and semisolid formulations containing indocyanine green

Laser-assisted tissue welding using chromophores and/or biomaterials as solders may offer several advantages over conventional methods (sutures and staples) such as reduced inflammation and foreign body response, faster healing, and simplicity. This technique makes it possible to perform sutureless surgery and repair wounds that are difficult or impossible to repair using standard surgical techniques. This in turn may be particularly important in ophthalmology, where conventional sutures may cause inflammation, tissue injury, scarring, and stenosis. The objective of this research was the preparation and technological and biological characterization of new solid (S) and semisolid (SS) formulations containing indocyanine green (ICG), which is a chromophore commonly used in laser welding or tissue soldering. The formulations were aimed at improving the cromophore-assisted laser welding process while ensuring the chemical stability of ICG. Polyvinyl alcohol (PVA), sodium hyaluronate (HYAL), sodium alginate (ALG), 5-methylpyrrolidinone chitosan (MPCh), and tamarind seed polysaccharide (TSP) were chosen as vehicles for the ocular application of ICG. The wetting and hydrophilicity characteristics of the solid formulations (film) were evaluated by contact angle and swelling measurements and correlated with the in vitro release of ICG. The biological efficacy of the formulations was evaluated on a corneal cut in a rabbit model by monitoring the healing process after laser welding and comparing it to the healing process of a conventional suture. The best results were obtained with a solid formulation based on TSP that showed high wettability, good chemical stability, and slow release of ICG. Its use resulted in a rapid and safe healing process.

Effect of laser soldering irradiation on covalent bonds of pure collagen

Laser tissue welding and soldering is being increasingly used in the clinical setting for defined surgical procedures. The exact induced changes responsible for tensile strength are not yet fully investigated. To further improve the strength of the bonding, a better understanding of the laser impact at the subcellular level is necessary. The goal of this study was to analyze whether the effect of laser irradiation on covalent bonding in pure collagen using irradiances typically applied for tissue soldering. Pure rabbit and equine type I collagen were subjected to laser irradiation. In the first part of the study, rabbit and equine collagen were compared using identical laser and irradiation settings. In the second part of the study, equine collagen was irradiated at increasing laser powers. Changes in covalent bonding were studied indirectly using the sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS-PAGE) technique. Tensile strengths of soldered membranes were measured with a calibrated tensile force gauge. In the first experiment, no differences between the species-specific collagen bands were noted, and no changes in banding were found on SDS-PAGE after laser irradiation. In the second experiment, increasing laser irradiation power showed no effect on collagen banding in SDS-PAGE. Finally, the laser tissue soldering of pure collagen membranes showed virtually no determinable tensile strength. Laser irradiation of pure collagen at typical power settings and exposure times generally used in laser tissue soldering does not induce covalent bonding between collagen molecules. This is true for both rabbit and equine collagen proveniences. Furthermore, soldering of pure collagen membranes without additional cellular components does not achieve the typical tensile strength reported in native, cell-rich tissues. This study is a first step in a better understanding of laser impact at the molecular level and might prove useful in engineering of combined collagen-soldering matrix membranes for special laser soldering applications.

APPLICATION OF NOVEL HEMOSTATIC AGENT DURING LAPAROSCOPIC PARTIAL NEPHRECTOMY

We determined if QuikClot, a novel hemostatic agent made of a granulated mineral substance, could be used to control renal parenchymal bleeding and collecting system leakage during open and laparoscopic partial nephrectomy. After obtaining renal hilar vascular control 2 domestic female pigs underwent bilateral open and 4 underwent unilateral laparoscopic partial nephrectomy. After excision of the lower pole without cautery the hemostatic agent was applied to the cut surface of the kidney and hilar vascular control was released. Additional QuikClot was added until complete hemostasis was achieved. One week postoperatively the animals were sacrificed and the operated kidneys were harvested for ex vivo retrograde pyelograms and histopathological analysis. All partial nephrectomies were performed without complication. Mean operative and warm ischemia times were 62 and 16 minutes, respectively. An average of 23% of renal mass by weight was resected with a mean blood loss of 73 ml per procedure. No cautery, additional hemostatic agents or techniques were used. No animal had clinical or radiographic evidence of urinoma or delayed hemorrhage. Histopathological analysis showed preservation of the renal parenchyma immediately beneath the QuikClot layer. In the porcine model QuikClot allowed the resection of large renal segments, while providing reliable hemostasis and closure of the renal collecting system. No deleterious effect on underlying renal parenchyma or surrounding tissues was observed.

Preliminary Assessment of Postoperative Adhesion Formation After Laser-Assisted Mesh Fixation to the Peritoneal Surface

This study evaluated the incidence and persistence of adhesions following intraperitoneal onlay mesh fixation with tissue soldering in an experimental model. Anesthetized New Zealand white rabbits (n = 21), weighing 2.8-3.2 kg, underwent laparotomy. Controls (group 1 [n = 3]) had 2 x 2 cm Mersilene (Ethicon, Somerville, New Jersey) polyester mesh segments fixed to the peritoneum with staples (USSC, Norwalk, Connecticut). Group 2 (n = 7) rabbits had Mersilene mesh affixed by melting 55% collagen solder using a prototype laser (1.43 micro, 2.5 W CW, 4 mm spot size, 60 degrees C set temperature) over mesh. Group 3 (n = 6) rabbits had Vicryl (Ethicon, Somerville, New Jersey) polyglactin mesh embedded in 60% collagen solder placed onto the peritoneum and fixed with identical laser parameters as group 2. Group 4 (n = 5) rabbits had 55% collagen solder placed and Mersilene pressed into it after melting. Four segments were placed in each experimental animal. Animals were euthanized at 2, 4, or 6 weeks. Adhesions were graded (0 = none; I = filmy adhesions; II = omental; III = bowel adhesions gently lysed; IV = dense adhesions requiring sharp dissection). Grade III adhesions were observed in both control and group 4 animals at 2 weeks, persisting in group 4 animals at 6 weeks, but having lysed in controls at 6 weeks. No adhesions were present in group 3 specimens at any interval. Grade I adhesions were present in group 2 at 2 weeks at exposed mesh areas, and declined in frequency at 6 weeks. Evidence of reabsorption of the polyglactin mesh-solder composite was apparent in the group 3 specimens at 4 weeks, and complete resorption had occurred by 6 weeks postoperatively. Laser-assisted solder fixation caused minimal adhesion formation when mesh was covered by solder. Adhesions were observed if Mersilene mesh material was exposed to the abdominal contents. Vicryl mesh-solder composites reabsorbed without inflammation, scarring, or adhesions at the sites of mesh fixation. Further development of this technology is warranted.

Histologic assessment of mesh fixation following laser-assisted tissue soldering in a lapine model

Wound histology and mesh bioincorporation following intraperitoneal fixation using laser-assisted soldering was evaluated. 2.8-3.2 kg NZW rabbits underwent laparotomy. Controls had 2x2 cm segments of Mersilene stapled to peritoneum. Group 2 segments were affixed with 55% collagen solder onlay by fiber-coupled diode laser (1.43 +/- 10 micro, 2.5 W CW, 4 mm spot, 60 degrees C set temperature). Group 4 had Mersilene inlaid into melted solder. Group 3 had solder-embedded Vicryl mesh affixed. Animals were euthanized at 0, 2, 4, 6 weeks. Fixed sections were assessed for integrity, inflammation, and fibrosis using H & E, Masson's Trichrome and Evans Van Gieson staining. Histology demonstrated cell types, local mesh reaction, and progressive evidence of solder reabsorption mimicking normal healing and bioincorporation. Mersilene groups demonstrated normal arrangement of collagen-rich layers around mesh. Collagen-based tissue soldering permits normal wound healing and may mitigate use of staples. Further development of this strategy is warranted.

Albumin-genipin solder for laser tissue repair.

Laser tissue soldering (LTS) is an alternative technique to suturing for tissue repair that avoids foreign body reaction and provides immediate sealing of the wound. One of the major drawbacks of LTS, however, is the weak tensile strength of the solder welds when compared to sutures. In this study, a crosslinking agent of low cytotoxicity was investigated for its ability to enhance the bond strength of albumin solders with sheep intestine. Solder strips were welded onto rectangular sections of sheep small intestine using a diode laser. The laser delivered in continuous mode a power of 170 +/- 10 mW at lambda = 808 nm, through a multimode optical fiber (core size = 200 microm) to achieve a dose of 10.8 +/- 0.5 J/mg. The solder thickness and surface area were kept constant throughout the experiment (thickness = 0.15 +/- 0.01 mm, area = 12 +/- 1.2 mm2). The solder was composed of 62% bovine serum albumin (BSA), 0.38% genipin, 0.25% indocyanin green dye (IG), and water. Tissue welding was also performed with a BSA solder without genipin, as a control group. The repaired tissue was tested for tensile strength by a calibrated tensiometer. Murine fibroblasts were also cultured in extracted media from heat-denatured genipin solder to assess cell growth inhibition in a 48 hours period. The tensile strength of the genipin solder was doubled that of the BSA solder (0.21 +/- 0.04 N and 0.11 +/- 0.04 N, respectively; P = 10(-15) unpaired t-test, N = 30). Media extracted from crosslinked genipin solder showed negligible toxicity to fibroblast cells under the culture conditions examined here. Addition of a chemical crosslinking agent, such as genipin, significantly increased the tensile strength of adhesive-tissue bonds. A proposed mechanism for this enhanced bond strength is the synergistic action of mechanical adhesion with chemical crosslinking by genipin.

ULTRAFAST RADIATION HEAT TRANSFER IN LASER TISSUE WELDING AND SOLDERING

Laser tissue welding and soldering with use of short laser pulses are proposed. The transient radiation heat transfer in the picosecond time scale is numerically investigated for the first time using the discrete ordinate method for cylindrical geometries. The numerical method developed incorporates the propagation of radiation with the speed of light. The temporal radiation fields of tissue cylinders under the irradiation of short laser pulses are obtained. The use of short laser pulses for tissue welding and soldering is found to have reduced thermal damage to the healthy tissue and improves the uniformity of heating in the tissue closure region in both the depth and radial directions. The addition of absorbing solders in tissue soldering results in a well-confined radiation energy deposition field in the proximity of the solder-stained region and lessens the outgoing radiative heat flux at the laser incident surface. Comparisons of radiation heat transfer are made between the spatially square-variance and Gaussian-variance laser inputs and between the temporally Gaussian-profile and skewed-profile pulses, respectively.

A preliminary study of laser tissue soldering as arterial wall reinforcement in an acute experimental aneurysm model.

Aneurysm formation results from destruction of structural arterial wall connective tissue, leading to wall weakening and rupture. The purpose of this study was to demonstrate that reinforcement of the arterial wall using laser tissue soldering contributes to arterial wall stabilization and rupture prevention in an acute experimental model. Elastase (10 U/mg protein, Sigma-Aldrich Co., St. Louis, MO) was applied with a fine paint brush on femoral artery segments to cause fusiform aneurysm formation. After aneurysms formed (approximately 45 minutes after treatment), elastase was rinsed out and indocyanine green (ICG) and albumin soldering mixture (2.5 mg/ml ICG in 50% albumin) was delivered to the arterial segment, followed by laser irradiation at 830 nm, (15mW output for 20 minutes). In situ pressure burst measurements were then performed. In situ burst pressures were > 503 mmHg for normal arteries and 181 +/- 26.0 mmHg, for Elastase treated segments. (P < 0.0001) Treatment of experimental aneurysms laser tissue soldering returned burst strengths to > 503 mmHg. These results indicate laser tissue soldering reinforcement of weak arterial walls, is possible and may reduce the likelihood of acute rupture. Further development of this technique for aneurysm management is warranted.

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.

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

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. 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. 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. 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).

LASER TISSUE SOLDERING FOR HYPOSPADIAS REPAIR:: RESULTS OF A CONTROLLED PROSPECTIVE CLINICAL TRIAL

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. 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. 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. 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.

LESSONS LEARNED FROM LASER TISSUE SOLDERING AND FIBRIN GLUE PYELOPLASTY IN AN IN VIVO PORCINE MODEL

LESSONS LEARNED FROM LASER TISSUE SOLDERING AND FIBRIN GLUE PYELOPLASTY IN AN IN VIVO PORCINE MODEL

Differential scanning calorimetry of albumin solders: interspecies differences and fatty acid binding effects on protein denaturation.

Understanding albumin solder denaturation is important for laser tissue soldering. Human (HSA), bovine (BSA), porcine (PSA), and canine (CSA) albumin both fatty acid containing (FAC) and fatty acid free (FAF) were evaluated by using differential scanning calorimetry (DSC). DSC was used to measure difference thermograms to determine the irreversible thermal denaturation profile for 50% albumin solutions. The denaturation transition's onset, end and peak temperatures, and enthalpy were measured. All FAC species, except BSA, exhibited twin peaked endotherms. Single endotherms were observed for all FAF species and BSA-FAC. Onset and end temperatures were significantly [P < 0.001] lower for all FAF species (except BSA's end temperature). There was a 30% decrease in the denaturation enthalpy between FAF and FAC groups. FAF albumin solders were found to denature at significantly lower temperatures, while also having a 30% reduction in enthalpy when compared with their FAC counterparts.

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

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

BLADDER WELDING IN RATS USING CONTROLLED TEMPERATURE CO 2 LASER SYSTEM

Laser tissue welding has potential advantages over conventional suture closure of surgical wounds. It is a noncontact technique that introduces no foreign body and limits the possibility of infections and complications. The closure could be immediately watertight and the procedure may be less traumatic, faster and easier. In spite of these positives laser welding has not yet been approved for wide use. The problem in the clinical implementation of this technique arises from the difficulty in defining the conditions under which a highly reliable weld is formed. We have assumed that the successful welding of tissues depends on the ability to monitor and control the surface temperature during the procedure, thereby avoiding underheating or overheating. The purpose of this work was to develop a laser system for reliable welding of urinary tract tissues under good temperature control. We have developed a "smart" laser system that is capable of a dual role: transmitting CO2 laser power for tissue heating, and noncontact (radiometric) temperature monitoring and control. Bladder opening (cystotomy) was performed in 38 rats. Thirty-three animals underwent laser welding. In 5 rats (control group) the bladder wound was closed with one layer of continuous 6-0 dexon sutures. Reliable welding was obtained when the surface temperature was kept at 71 + 5C. Quality of weld was controlled immediately after operation. The rats were sacrificed on days 2, 10 and 30 for histological study. Bladder closure using the laser welding system was successful in 31/33 (94%) animals. Histological examination revealed an excellent welding and healing of the tissue. Efficiency of laser welding of urinary bladder in rats was confirmed by high survival rate and quality of scar that was demonstrated by clinical and histological examinations. In the future, optimal laser welding conditions will be studied in larger animals, using CO2 lasers and other lasers, with deeper radiation penetration into tissues.

Current trends in hypospadias repair

There is no single, universally applicable technique for hypospadias repair. Command of a technically straightforward repair with few complications and proven success and versatility in a reasonable range of hypospadias defects are desired goals. Several well-established techniques exist for the repair of all hypospadias defects. The Snodgrass tubularized incised plate urethroplasty, a recent contribution with exemplary early results, has become a popular technique for primary and preoperative repair of middle and anterior hypospadias. Other innovative modifications, and technical advances, such as the use of laser and tissue solder, continue to emerge. With time, these may herald improvements to even the most basic of sound principles involved in all hypospadias repair.

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 to 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 using a solid protein solder composed of 60% BSA and ICG. Using this combination of laser and solder parameters, surface temperatures were observed to reach C with a maximum temperature difference through the thick solder strips of about 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.

Dynamic optical-thermal modeling of laser tissue soldering with a scanning source

A transient two-dimensional optical-thermal model that accounts for dynamic changes in optical and thermal properties with temperature was developed to investigate the mechanisms leading to thermal damage during laser tissue soldering. The model was implemented using the electrical circuit simulator simulation program with integrated circuit emphasis (SPICE). Electrical analogies for the optical and thermal behavior of the solder and tissue mere established. With these analogies, light was propagated using a flux representation of the light and the electrical simulator mas used to calculate heat transfer with an algorithm based on the finite difference technique. Thermal damage was calculated using the Arrhenius rate process relation. Temperature-dependent absorption and scattering coefficients, thermal conductivity and thermal diffusivity, mere incorporated in the SPice optical-thermal simulation (SPOTS), as well as the time domain behavior of a scanning laser source. Experimental results from an in vitro study performed using an 808-nm diode laser in conjunction with indocyanine green-doped albumin protein solders to repair bovine aorta specimens compared favorably with numerical results obtained from SPOTS using dynamic optical and thermal properties. The maximum surface temperature was over-estimated by almost 10% when dynamic properties were not taken into account. This difference corresponds to over two orders of magnitude difference in terms of the Arrhenius tissue damage integral. The incorporation of dynamic changes in optical and thermal properties of tissue during laser-induced heating represents a significant advance in computer modeling of laser tissue interactions.

Laser assisted soldering: microdroplet accumulation with a microjet device.

We investigated the feasibility of a microjet to dispense protein solder for laser assisted soldering. 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). Stable solder coagulum was created by successive photocoagulation of microdroplets even after the soldered tissue exposed to 1 week of hydration. This preliminary study suggested that tissue soldering with successive microdroplets is feasible even with fixed laser parameters without active feedback control.