Immediate Tight Sealing of Skin Incisions Using an Innovative Temperature-controlled Laser Soldering Device

Abstract

Background:

A feedback temperature-controlled laser soldering system (TCLS) was used for bonding skin incisions on the backs of pigs. The study was aimed: 1) to characterize the optimal soldering parameters, and 2) to compare the immediate and long-term wound healing outcomes with other wound closure modalities.

Materials and Methods:

A TCLS was used to bond the approximated wound margins of skin incisions on porcine backs. The reparative outcomes were evaluated macroscopically, microscopically, and immunohistochemically.

Results:

The optimal soldering temperature was found to be 65°C and the operating time was significantly shorter than with suturing. The immediate tight sealing of the wound by the TCLS contributed to rapid, high quality wound healing in comparison to Dermabond or Histoacryl cyanoacrylate glues or standard suturing.

Conclusions:

TCLS of incisions in porcine skin has numerous advantages, including rapid procedure and high quality reparative outcomes, over the common standard wound closure procedures. Further studies with a variety of skin lesions are needed before advocating this technique for clinical use.

A temperature-controlled laser soldering system (TCLS) was used for bonding skin incisions on the backs of pigs. The bonded incisions were evaluated mechanically and histologically. The immediate tight sealing of the wound by the TCLS contributed to high-quality, rapid wound healing in comparison to cyanoacrylate glues or standard suturing. TCLS carries several advantages and should be further evaluated on humans.

The primary goals of treating wounds in general and skin incisions in particular are rapid closure with the creation of a functional and esthetic scar.¹

Acute wound healing by first intention follows a pathway that differs from chronic wound healing, in that there is less inflammatory reaction and granulation tissue formation, less wound contraction, and faster wound sealing.² This faster, acute wound healing results in less scarring.

Over the years, research on acute wound healing has resulted in the development of technologies such as staples and adhesives (eg, glues, adhesive tapes). Unfortunately, none of those techniques is able to produce optimal wound repair by first intention.

Data have accumulated showing that laser assisted tissue bonding (LTB) offers a fast and efficient method for incision closure, which diminishes scar formation and reduces the development of complications.^3–5

LTB is basically subdivided into 2 main subphases differing in their mechanism of action: 1) photochemical tissue bonding⁶ (PTB) and 2) photothermal tissue bonding. The latter can be further subdivided into 2 different systems: laser tissue welding (LTW) and laser tissue soldering (LTS).

LTW refers to the introduction of concentrated laser energy to the apposed wound margins that causes their initial liquefaction, followed by fusion of the 2 edges, whereas LTS uses an additional component known as a “solder,” which refers to a protective proteinaceous barrier (eg, semisolid/solid serum albumin) that minimizes the potential thermal damage of the tissue infrastructure caused by the laser beam, as well as enhancing the adherence of the 2 wound margins. A pioneering modification of LTS, known as temperature-controlled laser tissue soldering (TCLS), was introduced by Katzir et al^7–11 as well as by other groups in a variety of tissues and animal models and for a range of surgical procedures and disciplines such as brain and minimally invasive surgeries.^12–16

The encouraging results obtained in vivo using injured skin of small laboratory animals^9–11 have provided the stimulus to consider introducing the technology into the clinical arena, serving as a forerunner for implementation in many surgical disciplines. A crucial step toward the implementation of wound healing techniques into clinical practice should include experimentation in a porcine model, to assess their safety and efficacy. The rationale behind the use of a porcine model is based on the gross similarity between skin anatomy and physiology of pigs and humans.¹⁷ The dermal and epidermal thickness, the apocrine and sweat glands, and even hair density are similar in human and porcine skins. Nevertheless, differences do exist between human and porcine skin. The human skin contains superficial and deep fascia, eccrine sweat glands, and richer vasculature compared with porcine skin.

The purpose of the present study was to progress toward clinical trials by evaluating the efficacy, reproducibility, and safety of the TCLS procedure in juvenile and mature domestic farm pigs, comparing the results with those obtained previously in smaller animals.

MATERIALS AND METHODS

Laser Soldering System

The TCLS system has been described in detail in earlier publications;9–11,13–16 therefore, only a brief description is provided herein. A CO₂, laser with emission at λ = 10.6 μm, was used for laser bonding because its radiation is highly absorbed both by albumin and by most tissues. Two optic fibers, which are made of polycrystalline silver halides (AgCl_xBr_1-x), and are highly transparent in the mid-IR spectral range 3 to 25 μm, were also used. One fiber named a “delivery fiber” transmits the laser energy from the CO₂ laser apparatus (Synrad, Model D48-1) to a spot over the animal's skin. Typically, the CO₂ laser output at the distal optic fiber tip is roughly 500 mW. A second fiber acts as a “sensing fiber” for noncontact thermometry, by collecting the mid-IR radiation emitted from the heated spot and transmitting it to a pyroelectric IR detector, which generates a signal that is linearly proportional to the tissue surface temperature T. This signal is then used by a personal computer (PC) system to control the laser power, in a feedback manner, thus controlling the tissue surface temperature within ±2.6°C (Fig. 1). Detailed specifications are provided elsewhere.9–11,13–16

FIGURE 1. Real-time temperature-controlled laser soldering system.

Animal Models and the Laser Soldering Procedure

Animals

Eleven Large-Whitex and Landrace farm pigs (Kibbutz “Lahav”, Israel) were used. There were seven 4-week-old juvenile pigs weighing 8 to 9 kg and four 5-month-old mature pigs weighing 70 ± 2 kg. They were divided into 3 groups: group A consisted of 3 juvenile animals, group B comprised 4 mature animals, and group C comprised 4 juvenile animals. Each pig was housed in a separate standard cage with standard food and water ad libitum. All procedures were in accordance with the protocols approved by the Animal Care and Use Committee of Tel Aviv University. One operator performed all surgical procedures.

Surgical Procedures

Group A

We used this group to determine the optimal pig skin soldering temperature. Incisions were created on the backs of the pigs, and each incision was soldered using a different soldering temperature (T = 50°C, 55°C, 60°C, 65°C, 75°C, and 85°C). This was actually spot soldering, and soldering was carried out for a fixed time at each spot. Six incisions created on other areas of the back were sutured and served as controls. The animals were kept alive for 7 days and were then anesthetized. Skin samples were taken for analysis and the pigs were then killed.

Group B

Four mature female pigs served for immediate tensile strength measurements at the optimal soldering temperature, as determined by the first experiment (group A). Two commercially available cyanoacrylate glues were used as controls.

Group C

Four juvenile pigs were laser-soldered at the optimal temperature and skin samples were taken on postoperative days 3, 7, 14, and 28.

Anesthesia and Skin Preparation

Each pig was anesthetized using either intramuscular ketamine (20 mg/kg, Fort Dodge, IA) and Rompun (xylazine 4 mg/kg, Vitamed, Israel) in the juvenile pigs or halothane gas inhalation in the mature pigs. The dorsal skin of the pig was shaved. Twelve full-thickness incisions, each 22-mm long, passing through the subcutaneous tissue, were made on the pig's back from the level of the scapula to 10 cm above the tail, using a #10 scalpel blade. At the end of each experiment, the animals were killed by an overdose of pentobarbital (100 mg/kg) injection. Skin samples taken beforehand were sent for histologic and tensile strength measurements.

Laser Soldering and Control Groups

The edges of each incision were approximated using a simple approximation device (Fig. 2). Then, a drop of 47% bovine albumin (albumin, bovine, Sigma Chemical Co., St. Louis, MO) was placed and smeared on the precisely apposed wound margins, using a small spatula. The bonding technique used was spot soldering, using the temperature control system described earlier. The laser first heated a spot on the albumin to the desired temperature and then, the hot spot was moved along the soldering line, from one point to a neighboring point. The cut wounds that served as the control group were either glued with Dermabond (2-octylcyanoacrilate, Closure Medical Corp. Raleigh, NC) or Histoacryl (N-Butyl 2-cyanoacrylate, B. Braun Surgical, Melsungen, Germany) for group B, or were sutured with 5 simple interrupted stitches using 4-0 nylon thread (19-mm cutting needle, Ethicon, Edinburgh, UK) for groups A and C. The rationale behind the selection of glued incisions over sutured incisions as a control group for immediate tensile strength (group B only) is due to the fact that the immediate testing of sutured specimens provides information only about the mechanical properties of the suture thread¹⁸ and the knot security.¹⁹ To eliminate these factors and test the bonded tissue alone, one should remove the sutures; this makes it impossible to determine the immediate tensile strength of sutured incisions. However, it is well established that the breaking strength of butylcyanoacrylates is comparable to that of a 5-0 monofilament suture.²⁰ Operating time was measured in the laser-soldered incisions compared with the sutured incisions, from the moment of the holder placement, through the albumin smearing and laser heating and ending with the removal of the holder.

FIGURE 2. Wound edges approximating device.

After the operation, the wounds were covered with Hiporplast dressing (Plastod, Calderara Di Reno, Bologna, Italy) and a custom-made canvas jacket was applied. The pigs were housed separately to prevent them from licking and biting each other's wounds.

Skin Harvesting and Tensile Strength Measurements

An area of the skin with the repaired incisions (soldered or sutured) was harvested. Using a small guillotine, strips approximately 5 × 40 mm were cut, so that each strip contained a segment of the repaired incision in the middle. For mechanical testing, skin strips were clamped into small tensile jigs, and set between 2 pieces of fine sandpaper to prevent the strips from sliding in the metal jigs. The specimens were loaded into a universal testing machine (Instron, Model 4502, High Wycombe, England), using a 100-N load-cell and 5 mm/min crosshead speed, and tested to rupture. An automatic data acquisition system collected the data during testing. The thickness of the pig's skin was found to be approximately 2.5 mm. The tensile strength was calculated by dividing the maximum load at rupture (N) by the cross-sectional area of the specimen (approximately 12.5 mm²). To calculate the relative strength of the specimen compared with unwounded skin, 10 skin samples of unwounded skin were tested in the same manner.

Histology Technique and Wound Healing Grading System

Strips from each biopsy were fixed in 10% formaldehyde solution, embedded with paraffin, and stained by hematoxylin and eosin for histologic examination.

The process of first intention healing was analyzed by utilizing a wound healing grading system based on indices as described previously.^9,10 Briefly, each stage of the skin incision reparative process such as re-epithelialization, inflammation of leukocytes and macrophages, fibroplasia, and hypodermal recuperation were evaluated, graded, and compared according to the time elapsed.

The scar width and thickness (from epidermis to the superficial fascia) were measured using an eyepiece (Leitz Periplan GW 10 x M, Ernst Leitz, Wetzlar, Germany) and an objective micrometer (Ernst Leitz) with a resolution of 10 μm and an accuracy of ±10 μm at a magnification ×100. The well-established clinical cosmesis criteria, namely, the modified Hollander Wound Evaluation Scale (HWES) and the Visual Analogue Scale (VAS) are qualitative in origin.²¹ However, in cases where an excisional biopsy is an option, the use of scar width as a quantitative measurable feature that reflects the amount of scar production is perhaps preferable.

Immunohistochemical Technique

A 3-stage indirect immunoperoxidase technique^22,23 was performed on 5 μm-thick paraffin-embedded sections obtained from group C on day 7. Paraffin sections were heated for 50 minutes at 60°C and deparaffinized in toluene, followed by dehydration in graded alcohols and soaked in a 3% hydrogen peroxide solution to quench endogenous peroxidase activity.

Slides were washed in tris-buffered saline (TBS) and the sections incubated for 1 hour with a 1:750 dilution of the primary cytokeratins 10 and 14, Loricrin and Fillagrin epidermal rabbit polyclonal antibodies (Covance, Berkeley, CA, #PRB-169P, #PRB-159P, #PRB-145P, #PRB-417P). After rinsing with TBS, the slides were incubated with biotinylated IgG for 15 minutes, rinsed, and then incubated with streptavidin conjugated to horseradish peroxidase (ie, ABC complex; DAKO) for 15 minutes. Sections were rinsed and incubated with Liquid DAB Substrate-Chromogen system for 5 minutes to identify bound antibody. After a final wash in TBS and distilled water, the slides were counterstained with a 50% dilution of Gills hematoxylin for 1 minute, dehydrated in alcohol, and mounted with a coverslip using Permount.

Statistical Analysis

For groups A and C, the means and standard deviations were calculated. In addition, the P values for the differences between the behaviors of the treated groups at all the postinjury time intervals (termed “trend”) were calculated using the 2-way analysis of variance test. To bring to light differences between the groups, for the same time intervals, either the Student t test (for normally distributed variables) or the Mann-Whitney U test (for non-normally distributed variables) was used. Statistically significant differences were considered as P < 0.05.

RESULTS

Operating Time and Temperature Control Accuracy

The operating time for the sutured incisions (5 stitches) and laser soldering of 22 mm incisions were 228 ± 6 seconds and 176 ± 5 seconds, respectively, the latter being significantly faster (P = 0.04).

The system was set to maintain the temperature of an irradiated spot on the skin at 50°C to 85°C. Temperature control accuracy of 66.3°C ± 2.6°C was achieved during the laser soldering of a 22-mm-long incision in the pig skin.

Macroscopic Results

Albumin remnants were separated from the skin and adhered to the covering plaster. The soldered scars appeared cosmetically superior to the sutured scars, especially within the first 14 days postoperatively (Fig. 3).

FIGURE 3. Left: Macroscopic view of sutured and laser soldered incisions at 3 days postoperation. Sutured incisions (A and C) demonstrate thicker scars and crosshatch marks while soldered incisions (B and D) demonstrate thinner scars. Right: A macroscopic view of sutured (E) and laser soldered (F) incisions at 7 days postoperation. The soldered scar (F) is almost invisible while the sutured scar and the crosshatch marks (E) are apparent.

Group A: Laser Soldering at Differing Soldering Temperatures

No dehiscence of the laser-soldered or sutured incisions was noted prior to killing the animals. The tensile strength measurements carried out on group A indicated that strong bonding of the soldered incisions was achieved at 65°C to 70°C, as shown in Figure 4. In the lower temperature subgroup (55°C–60°C), only 3 of 10 skin samples survived the trimming process (Table 1). No statistically significant difference was noted between subgroups of medium (65°C–70°C) and high (75°C–85°C) temperatures.

FIGURE 4. Mean long-term tensile strength values (in MPa) and standard deviations 7 days postoperatively of specimens tested after soldering at different temperatures. No statistically significant differences were noted (Tukey post hoc test, P > 0.05).

TABLE 1. Dehiscence Rates of Soldered Incisions at Different Soldering Temperatures During the Trimming Process

Thermal damage and carbonaceous substance were seen over the epidermis and dermis in the high temperature soldered incisions. No significant differences were noted in the scar thickness between the different treatments (P > 0.05).

Group B: Laser-Soldered Versus Cyanoacrylate Glued Incisions (Immediate Results)

There was no statistically significant difference in the immediate tensile strength between incisions soldered at 65°C and the Dermabond or Histoacryl glued incisions (Table 2). It should be emphasized that many incisions were disqualified since they had opened during the trimming process.

TABLE 2. The Mean Immediate Tensile Strength Values and Standard Deviation (SD) in MPa and the SD of Laser-Soldered and Cyanoacrylate Glued Incisions

No thermal damage was seen in the soldered incisions immediately after laser soldering at the optimal temperature setting (Fig. 5). In the histologic sections, albumin remnants were seen adhering to the stratum corneum. The cyanoacrylate glue remnants, seen macroscopically, disappeared during the histologic processing, most likely dissolving in the formaldehyde solution used for the histologic fixation process. The incision gap that had been subjected to the laser soldering procedure exhibited complete epidermal-dermal wound sealing, with formation of an immediate matrix coagulum. On the other hand, the incision gap treated with the cyanoacrylate glues stayed open (Fig. 5). Average scar thickness for laser soldered, Dermabond, and Histoacryl glued incisions, were 4.38 ± 0.45 mm, 4.32 ± 0.79 mm, and 4.19 ± 0.14 mm, respectively (P > 0.05).

FIGURE 5. Photomicrograph of the immediate histologic appearance of bonded incisions: A, Incision glued with Dermabond. The glued incision demonstrates a gap between the wound margins. No glue remnants are present. B, Laser-soldered incision. The laser-soldered gap is filled with collagen coagulum, thus sealing the wound from the external environment. The albumin remnants adhere to the wound over the closed epidermal layer. There is no evidence of thermal damage (hematoxylin and eosin, original magnification ×100).

Group C: Laser-Soldered Incisions Versus Sutured Incisions (Long-term Results)

The tensile strength measurements in group C did not show any statistical difference between soldering at 65°C and suturing, 7, 14, and 28 days after the operation (Fig. 6). At 3 days postoperation, both sutured and soldered incisions exhibited weak bonding. In group C, no dehiscence of the 11 soldered scars was observed.

FIGURE 6. Long-term tensile strength (LTS) values measured for soldered and sutured incisions for 28 days postoperatively, as percentage of unwounded skin strength (7.45 MPa in 10 unwounded skin specimens). No statistically significant differences were noted between the different treatments.

Scar Width and Thickness

Scar width trend measured at the dermal-epidermal border was significantly lower in soldered incisions for all time periods (P = 0.03). A statistically significant difference between laser-soldered and sutured scar widths, favoring the laser-soldered scars, was observed on days 3 and 7 (P = 0.065 and P = 0.041, respectively) as seen in Figure 7. However, no changes in scar thickness were noted with the different treatments; for sutured and laser soldered incisions, the scar thicknesses were 3.78 ± 0.35 mm and 3.7 ± 0.5 mm, respectively (P > 0.05).

FIGURE 7. Twenty-eight days (long-term) follow-up period of the superficial scar width, measured at the dermal-epidermal border in laser-soldered and sutured incisions. A statistically significant difference was noted at days 3 and 7 postoperation (P = 0.065 and P = 0.041, respectively) in favor of soldered incisions. A statistically significant difference in the trend was also observed in favor of soldered incisions (P = 0.03). Note that during the scar contraction period, both scars reached their maximal contraction between days 7 and 14.

Re-epithelialization

No statistically significant difference was found between the re-epithelization rate of the laser-soldered and sutured incisions. No craters or ulcers were seen at any time in either group.

However, cytokeratins 10 and 14, Loricrin and Fillagrin markers demonstrated much faster re-epithelialization of the soldered incisions, compared with sutured incisions (Fig. 8), and faster differentiation toward expression of a late-stage cornified epidermal layer by day 7.

FIGURE 8. Immunoperoxidase staining of epidermal K10 marker of (A) sutured and (B) laser-soldered incisions and epidermal Loricrin marker of (C) sutured and (D) laser soldered incisions at 7 days postoperation. Epidermal K10 marker is expressed at the proliferation stage of the re-epithelialization while epidermal Loricrin marker is expressed at the late stage of wound healing keratinocyte differentiation. These images indicate that, while laser-soldered incisions are in the final stages of epidermal recuperation (arrow points to loricrin accumulation), sutured incisions are still in the early stages of epidermal recuperation (hematoxylin and eosin, original magnification ×200).

Dermal Inflammatory Response

There were no differences in the overall total cellular inflammatory reactions between the groups. However, there was less inflammatory reaction in laser-soldered incisions compared with the sutured incisions (P = 0.058) on day 3. During the 28-day follow-up period, the sutured incisions showed a more aggressive macrophage reaction (P = 0.04 for trend). No statistically significant difference was noted in the neutrophil reaction for both treatments. The inflammation generated by the laser soldering evoked a neutrophilic and macrophage reaction that subsided by day 14, while the inflammatory reactions of the sutured incisions persisted for up to 28 days.

The fibroblastic reaction was also less intense in the laser-soldered incisions (P = 0.005 for trend). In both treatments, a fibroblastic reaction was seen after 28 days. Foreign body reaction, including forms of granulomas and giant cells, were rarely seen in either group.

Hypodermal (Panniculus Adiposus/Superficial Fascia) Recuperation

Hypodermal recuperation in the laser-soldered incisions was better and faster over all time periods (P = 0.04 for trend). A statistically significant difference was achieved by day 14 (P = 0.031). Perfect hypodermal recuperation was seen in almost all soldered incision specimens as early as day 14, compared with sutured scars, which reached perfect union only by day 28. This reflects a faster and more satisfactory anatomic regeneration of the hypodermal layer of the soldered incisions.

DISCUSSION

The concept that surgeons can replace their scalpels and tedious suturing techniques with a simple, non–operator-dependent, safe, and rapid technique, which will result in optimal cosmetic appearance of the scar and will avoid infections¹ by immediately sealing the wounds, has inspired many investigators in both the medical and applied science disciplines to experiment on different tissues and models of laser tissue soldering (LTB).

However, only few studies of LTB have been conducted in human subjects.²⁴ This may be partially explained by the perceived problem of thermal damage created by LTB, resulting in impaired wound healing.⁴ Other investigators share the opinion that the low initial tensile strength and the weak long-term tensile strength associated with LTB preclude the use of this technique in routine clinical practice.⁵

Two decades ago, Katzir et al7,8,12,13 hypothesized that the use of IR-based optic fibers, with a noncontact temperature measuring system and using albumin as a solder, may improve tensile strength and eliminate thermal injury. Bass and McNally^4,5 pointed out that laser heating of collagen strand fibers on both sides of the wound margins will induce them to intertwine and generate an immediate wound seal (Fig. 5), followed by immediate integration of the extracellular matrix network. Moreover, that would result in faster re-epithelialization (Fig. 8) and reduced granulation tissue formation and fibroplasia, as demonstrated by scar width and macroscopic appearance (Figs. 7 and 3, respectively).

The above considerations led to the development of a noncontact temperature-controlled laser system that is able to bond skin incisions by using semisolid serum albumin together with a simple approximation device.

As have prior studies,^9–11 the present study demonstrated that there is only a small range of temperatures that can bond the skin wound margins and at the same time avoid thermal damage. It was found that TCLS at temperatures below 60°C resulted in a high dehiscence rate during trimming of the skin samples (Table 1), whereas at temperatures exceeding 70°C, excessive thermal damage occurred. Therefore, the optimal soldering temperature has to be within the range of 65°C to 70°C.

At this range of soldering temperatures, it is possible to immediately achieve adequate tensile strength and tight sealing of the wound, features that are difficult, or even impossible, to achieve by the standard gluing (Fig. 5A) or suturing procedures.

One of the main objectives of wound closure by first intention is to provide immediate tight closure of the wound to block hostile elements from the environment and provide an optimal environment for wound repair. TCLS appears to be the first experimental technology that is consistently able to achieve this essential goal.¹⁰

Another important characteristic of any wound closure device should include operating time. Laser soldering of 22-mm-long incisions was 25% faster then the corresponding tedious suturing procedure. Furthermore, since it carried out almost automatically, it is relatively not operator-dependent.

According to the trajectory theory,²⁵ improvement in the wound reparative process correlates well with the development of the wound's tensile strength. Deterioration and failure of the healing process with wound dehiscence are typically associated with low tensile strength.

In the current study, in contrast to our previous results in rabbits and rats,^9–11 no difference was noted between laser soldering and sutured incisions with respect to the long-term tensile strength. However, macroscopically, soldered incisions produced thinner and almost undetectable scars as early as 7 days postoperatively, while sutured incisions resulted in an obviously thicker scar with crosshatch suture marks (Fig. 3), even on day 14 after the operation.

These results were corroborated by microscopic examination of hematoxylin and eosin-stained sections of soldered and sutured scars. The evaluation of the healing outcomes was based on grading indices previously described.^9–11 This grading system enabled us to qualitatively compare the rapidity of wound healing between the different closure modalities (current study) and compare them with previous studies. A histologic parameter that has been found to be the best measurable variable of scar characteristics is the scar width as measured at the anatomic level of the dermal-hypodermal junction. The findings in the present study suggest that the laser-soldered incisions created less scar tissue during the initial 14 days after the operation. However, by day 28, there were no significant differences between laser-soldered and sutured incisions. Interestingly, in both treatments, the maximal scar contraction was observed between days 7 and 14 (Fig. 7), followed by relaxation on day 28. This phenomenon has been reported previously in other model systems.^9–11

Scar thickness was measured histologically and did not differ with the different treatments in all the study groups. Nevertheless, it should be emphasized that, during the routine histologic processing, a 40% increase in the thickness dimension was noted, which correlates with prior publications.²⁶ This observation was reexamined in a different experiment (not published) and noted again.

In addition, standard comparison of the 2 skin closure procedures showed that the re-epithelialization rate was similar in both.

A more precise method for distinguishing between the different re-epithelialization stages of the healed skin involves examining the expression and down-regulation of epidermal cell markers and excretion of cornified precursor proteins. Each epidermal layer represents a different phenotypic stage in the terminal differentiation program of keratinocytes. For example, the transition of keratinocytes from the basal layer to the spinous layer, termed early-stage differentiation, is accompanied by the expression of cytokeratin-10 (K10) marker and the down-regulation of basal K14, while the transition from spinous to granular layer is accompanied by the suppression of K10 and the up-regulation of transcripts for the cornified envelope precursor proteins such as Loricrin and Fillagrin. These latter changes are termed late-stage differentiation markers.²⁷

The presence of K10 cytokeratins and the Loricrin and Fillagrin proteins in the laser-soldered incisions and their absence in the sutured incisions (Fig. 8) demonstrates that, although plain histologic sections stained with hematoxylin and eosin did not detect notable differences in the rate of re-epithelialization, the more precise grading system of re-epithelialization markers was able to demonstrate that laser-soldered incisions on day 7 after the operation produced faster re-epithelialization than did sutured incisions.

Histologic changes in the dermal layer of laser-soldered and sutured incisions were analyzed by using indices that have been described previously.^9–11 The intensity of dermal inflammation, especially that of the macrophages and fibroblasts (termed fibroplasia), was significantly lower in laser-soldered than in sutured incisions at all postoperative time points studied. The healing processes in the laser-soldered scars resulted in faster fusion of the scar and diminished scar tissue formation, as demonstrated by the presence of a thinner and almost undetectable scar by day 7 postoperatively (Figs. 3, 7). Moreover, perfect hypodermal union was established as early as 14 days postoperation, indicating that anatomic regeneration was established by that time.

CONCLUSION

Conventional techniques for tissue bonding (sutures, staples, and adhesives) are highly reliable procedures that have proven themselves over the years to be good clinical practice. The temperature-controlled laser soldering procedure (TCLS) was shown in both the current and earlier studies,^9–11 carried out in different animal models, to be advantageous over the traditional tissue bonding modalities. The major advantages of the TCLS system are: 1) procedure faster and relatively nonoperator dependent compared with suturing; 2) avoids introduction of foreign body or toxic elements into the wounded tissue; 3) immediate creation of a biologic watertight seal that isolates the wound from the environment (Fig. 5) and may result with less infection rate; 4) faster and more efficient wound repair, which could shorten hospital stay and reduce postoperative complications; 5) improved near scarless cosmetic results without crosshatch marks across the suture line; 6) a needle-free alternative; 7) avoids the need for stitch removal with its discomfort; and finally 8) the technique is compatible with minimally invasive surgery.¹⁴ Further investigations should be carried out to explore these promising advantages of TCLS bonding system, as demonstrated in the initial animal studies and in different surgical settings such as endoscopy¹⁴ and brain surgery.¹⁵ Ultimately, the TCLS method may even replace the conventional bonding techniques and become the standard surgical closure procedure.

ACKNOWLEDGMENTS

The authors thank Dr. Naam Kariv, Mr. Irena Wasserman, Mr. Arie Levita, and Mr. Ezra Shaked for their contributions.