Objectives: Over the past decade, the use of topical skin adhesives (TSA) for wound closure has increased. Among TSA characteristics, strength and flexibility are most important. Prior studies have compared the wound bursting strengths (WBSs) of the cyanoacrylates immediately after wound closure. In this study the authors compared the WBS and flexibility of multiple TSAs immediately and up to 2 days after closure.
Methods: This was a controlled animal experiment. Two-centimeter incisions were created on both sides of 210 Sprague-Dawley rats and randomly closed with one of five commercially available TSAs (Dermabond [D], Indermil [I], Histoacryl [H], Liquiband [L], or GluStitch [G]). WBS and TSA flexibility were measured using the BTC-2000 device immediately after closure and at 1 and 2 days after closure. WBS and TSA flexibility were compared across groups with analysis of variance (ANOVA).
Results: Wound bursting strengths were higher (p < 0.05) at 0, 1, and 2 days for D (274, 388, 232 mm Hg) than for all other TSAs (I 182, 225, and 107; H 189, 214, and 69; L 146, 118, and 75; or G 161, 150, and 73). TSA flexibility was also greater (p < 0.05) at 0, 1, and 2 days for D (36, 27, and 29 mm Hg/mm) than for all other TSAs (I 18, 14, and 12; H 18, 13, and 15; L 19, 14, and 12; G 26, 23, and 18).
Conclusions: The octyl-cyanoacrylate–based adhesive is significantly stronger and more flexible than all the butyl-cyanoacrylate–based adhesives at 0, 1 and 2 days after closure.
The cyanoacrylate topical skin adhesives (TSAs) were first introduced for clinical use in wound closure nearly 50 years ago.1 Since then, multiple, randomized clinical trials have demonstrated that the cyanoacrylates are faster to apply than sutures and result in comparable rates of infection, dehiscence, and optimal scarring after repair of traumatic lacerations and surgical incisions.2 The TSAs offer many potential advantages over sutures, including the fact that they are simple to use, rapid, noninvasive, and painless and do not require removal since they slough off spontaneously within 5 to 10 days.3 By creating an occlusive dressing over the wound, they also function as a microbial barrier4 and create a moist wound environment that has been shown to optimize wound healing.5,6 Currently there are several commercially available TSAs, including an octyl-cyanoacrylate– and several butyl-cyanoacrylate–based TSAs.
From a clinical standpoint, we believe that the two most important characteristics of a TSA are its strength and flexibility, which are required to maintain a secure wound closure and an intact microbial barrier. Furthermore, to prevent wound dehiscence and reduce bacterial contamination, the wound bursting strength (WBS) and flexibility of the adhesives must be maintained for several days as the wound heals. Several prior studies have compared the WBS of octyl-cyanoacrylate and butyl-cyanoacrylate in animal models.7,8 However, these studies only measured the WBS immediately after closure and did not evaluate the flexibility of the TSA. In addition, several new TSAs have been introduced over the past few years.
The goal of this study was to compare the WBSs and flexibility of five different TSAs immediately after wound closure and curing of the adhesives, as well as 1 and 2 days after closure.
A prospective, randomized, animal experiment was conducted to compare the WBS and flexibility of five commercially available TSAs. The study was conducted in an accredited animal research facility in compliance with the U. S. Food and Drug Administration (FDA) Good Laboratories Practice Regulations. The study was approved by our institutional animal care committee.
A total of 210 male Sprague-Dawley rats weighing 250–300 g were used in this experiment. The animals were acclimatized 7 days prior to experimentation and given a standard rodent diet (Teklad 22/5 rodent diet [W] 8640 [Harlan Teklad Inc, Madison, WI]) and water ad libitum.
One day prior to experimentation the animals were anesthetized with intramuscular injection of a combination of ketamine-HCl (80 mg/kg) and xylazine (15 mg/kg). Supplemental isoflurane 0.5%–2.0% in oxygen was used to maintain anesthesia as necessary. The animals’ hair was clipped with a hair clipper, the remaining stubble was removed with a depilatory cream (Nair, Carter Products, New York, NY), and the animals were recovered from anesthesia.
One day later, the animals were similarly anesthetized, placed on a surgical table with a water-heating pad, and prepped with Betadine surgical skin prep and 70% alcohol solution to remove any residual iodine that may interfere with the adherence of the TSA. To control for incision length and location, a template and surgical skin-marking pen were used to mark one symmetric 2-cm linear incision over the left and one over the right dorsolateral flank area, creating two linear incisions per animal. Using a No. 15 blade scalpel, incisions were made along the skin markings. All incisions were made by the same operator and extended through the dermis (full thickness), subcutaneous tissue, and panniculus carnosus. Hemostasis was achieved by applying pressure with gauze. The wound margins were then manually approximated and closed with one of the adhesives, the order of which was randomized using a computerized random numbers table. The following TSAs were used in the experiment: Dermabond (D; Ethicon Inc., Somerville, NJ), Indermil (I; Tyco Healthcare, Norwalk, CT), Histoacryl (H; Aesculap, Inc., Center Valley, PA), Liquiband (L; MedLogic, Plympton, UK), and GluStitch (G; GluStitch Inc., Delta, Canada). While D is an octyl-cyanoacrylate based adhesive, all others are based on butyl-cyanoacrylate. Application of the adhesives was according to the respective manufacturers instructions in the package inserts. For the octyl-cyanoacrylate, the adhesive was applied in two layers, while for the butyl-cyanoacrylates, only one layer was used, as recommended. All applications were by a single operator to ensure uniformity in application. G is marketed as a wound dressing and not as a wound closure device. We chose to include this product in the study because some practitioners have questioned whether the cyanoacrylate wound dressings can also be used for skin closure.
Measures and Outcomes
Wound bursting strength and TSA flexibility were measured by an investigator masked to treatment assignment using a previously validated device (BTC-2000, Surgical Research Laboratories, Franklin, TN; Figure 1).9 Measurements were made immediately after wound closure and drying of the adhesive and at 1 and 2 days after closure. At each time point, 14 wounds from each adhesive group were tested for in vivo WBS, and another 14 from each group were tested for tissue adhesive compliance. For in vivo wound strength measurements, a disposable acrylic ring (internal diameter of 2.5 cm) was placed around the wound and secured to the skin using medical-grade cyanoacrylate adhesive (Adhesive Systems, Inc., Frankfort, IL). A small amount of perfluorinated grease was applied to the top of the ring interface to assure a tight vacuum seal with the bursting strength device. The BTC-2000 test chamber was integrated with the test ring until the chamber and ring were securely interconnected. The test chamber was held by hand comfortably to assure that no positive force was being exerted on the wound. The BTC-2000 test-start button was triggered. A constant negative pressure was applied to the wound at a rate of 10 mm Hg/second, producing a multiaxial stress on the wound. A displacement laser captured displacement of the wound margins. The maximum amount of pressure (mm Hg) required to induce wound failure was then recorded.
For in vivo tissue adhesive compliance (or flexibility) measurements, a disposable adhesive collar was attached to the bottom of the BTC test chamber (internal diameter of 2.0 cm). The chamber handpiece unit was positioned vertically against the skin. The BTC-2000 test-start button was triggered. A linear negative pressure (ramp) at a rate of 10 mm Hg per second (up to 50 mm Hg maximum pressure) was applied to the skin, while an infrared target laser measured the vertical deformation of the skin wound closure in micrometers (μm). The BTC-2000 automatically calculated the biomechanical property for energy absorption (mm Hg × mm). Energy absorption (mm Hg × mm) reflects the entire deformation response and thus depicts the tissue or material overall flexibility. The higher the energy the more compliant the tissue or material. The inverse, lower energy response, demonstrates tissue or material firmness. All animals were euthanized upon completion of biomechanical testing.
Continuous data are presented as means with 95% confidence intervals (CIs). The overall significance level of trend and between-group comparisons was determined using repeated-measures analysis of variance (ANOVA). To determine whether there was any increase in WBS over the first day within each group, a paired comparison of Day 0 vs. Day 1 was performed with an upper tail t-test. To have an overall significance level for these comparisons, a Bonferroni adjustment was used so that p = 0.01 was the level of significance used for each of these tests. Our sample size had 80% power to detect a 100 mm Hg difference between the highest and lowest WBSs.
We conducted 210 measurements of WBS on 210 incisions (14 wounds per time point [0, 1, and 2 days] per adhesive) and 210 measurements of adhesive compliance on 210 incisions (14 wounds per time point per adhesive). The in vivo WBSs of the five adhesives at 0, 1, and 2 days after wound closure are presented in Figure 2. Repeated-measures ANOVA indicated that there were differences among the groups, a nonconstant time profile within group, and the group–profile interaction (i.e., tests if the time profiles were different across groups) were all statistically significant at p < 0.001. After a Bonferroni correction, the only adhesive with a significant increase in WBS 1 day after wound closure was the octyl-cyanoacrylate–based D (p = 0.01).
At all time points the WBS was significantly higher for wounds closed with the octyl-cyanoacrylate–based D. For three of the adhesives (D, H, and I), the WBS increased after 1 day and then later decreased after 2 days. For the other two adhesives (L and G) the WBS decreased both after 1 and 2 days.
TSA flexibility could not be measured in all wounds because the adhesive was inflexible and had fractured in some cases (Figure 3). While none of the adhesives in the D group fractured, the number of adhesives that fractured in the other four groups ranged from 36% to 86% at 1 and 2 days (Figure 4).
At all time points, the flexibility of the adhesive was highest for the octyl-cyanoacrylate–based D group (Figure 5). In all groups tissue adhesive flexibility dropped over the course of the experiment (Figure 5).
The cyanoacrylate TSAs are formed from condensation of cyanoacetate and formaldehyde.10 On contact with the wound, the cyanoacrylate monomers polymerize, forming long, strong chains that bond to the skin’s surface, holding the apposed wound edges together while the wound heals. While the basic structure of the various cyanoacrylates is similar, the length of the side chains and the presence of plasticizers and stabilizers differ among the TSAs, accounting for major differences in their mechanical characteristics.3
Prior studies have demonstrated that the octyl-cyanoacrylate–based adhesives are stronger than the butyl-cyanoacrylate–based adhesives.7,8 A study comparing the bursting strength of incisional rat wounds closed with D and H found that the octyl-cyanoacrylate–based adhesive (D) was roughly three times stronger than the butyl-cyanoacrylate–based adhesive (H).7 A similar study found that the WBS of D was significantly greater than that of the butyl-cyanoacrylate I (difference 98 mm Hg [95% CI = 32 to 165]).8 However, both of these studies measured WBS only immediately after wound closure. To maximize their effectiveness, the adhesives must maintain a high bursting strength for several days until they slough off.
The results of our study clearly demonstrate that of all adhesives tested, the octyl-cyanoacrylate–based D is the strongest and most flexible. Furthermore, unlike some, but not all adhesives, the WBS of D actually increased over the first day, probably as the octyl-cyanoacrylate continued to cure over time.
While all adhesives are designed to perform as a secure wound closure device and as a microbial barrier, our results confirm that there are significant differences between the commercially available TSAs that must be taken into consideration when choosing the optimal adhesive to use in clinical practice. One of the prerequisites to maintaining a secure wound closure and a microbial barrier is the ability of the adhesive to remain strong and intact over time. Obviously, when an adhesive fractures, this diminishes its strength and damages its barrier function. Thus, flexibility plays an important role in the function of a TSA. The current study shows that of all the tested adhesives, only the octyl-cyanoacrylate–based D was flexible enough that it did not fracture during the entire course of the study. This is in agreement with a prior study demonstrating that D maintained a thick uniform covering over the wound while the butyl-cyanoacrylate–based adhesive I did not.10 Furthermore, the flexibility of D was significantly higher than the butyl-cyanoacrylate–based adhesives at all measured time points.
Our finding that the WBS of octyl-cyanoacrylate–based D is the highest and remains above 200 mm Hg throughout the experiment should be put into clinical context. A prior study measured the intraabdominal pressures generated during normal daily activities in a group of human volunteers. The maximal intraabdominal pressures associated with the following activities were standing (13 mm Hg), pain (44 mm Hg), pressing (59 mm Hg), vomiting (110 mm Hg), cough (150 mm Hg), and jumping (252 mm Hg).11,12 Of all tested adhesives, only D had WBS above the range of these common activities. While most TSAs may be strong enough for simple, low-tension wounds,13 there is evidence that only D is strong enough for more challenging14,15 and longer wounds.16 Unfortunately, there are no prior studies that evaluated the amount of tension on repaired lacerations and incisions during various activities.
We only measured WBS up to 2 days after closure. Thus, we cannot comment on the WBS of the tested adhesives at later time points. We tested five commercially available skin adhesives and our results cannot generalize to other TSAs. Our study was conducted in rats, which may not reflect the performance of the adhesives in humans. We did not assess other TSA characteristics that are also important to clinicians, such as cost, ease of use, infection rate, patient satisfaction, and cosmetic wound appearance, which were all beyond the scope of the current study. The clinical relevance of the actual WBSs in topical skin closure is unclear, despite the data presented on maximal intraabdominal pressures during various activities. Finally, we used alcohol to remove the iodine solution prior to TSA application to minimize any potential interference of the iodine solution on TSA adhesiveness. We cannot exclude the possibility that a different method of skin preparation might have altered the WBS and flexibility measurements.
Our results demonstrate that the octyl-cyanoacrylate–based D was significantly stronger, and more flexible, in comparison to the butyl-cyanoacrylate–based I, H, L, and G both immediately after wound closure and 1 and 2 days after closure. This information should be taken into consideration when selecting an appropriate TSA for wound closure in the clinical setting.