Comparative study of suture and cyanoacrylates in skin closure of rats 1 Estudo comparativo entre sutura e cianoacrilatos no fechamento de pele de ratos

Purpose: To compare the biocompatibility of ethyl-cyanoacrylate (ECA) and octylcyanoacrylate (OCA) wound closures to sutures in rat skin. Methods: Twenty-four male Wistar rats were subjected to three incisions which were closed using ECA, OCA or sutures . Rats were divided into four groups which received biopsies on the 3rd, 7th, 14th or 21st postoperative days. Necrosis, inflammation, dermatitis, infection, dehiscence, cicatricial enlargement and costs were examined; the histopathology evaluated was epithelialization, deep openings, foreign substance reaction, residues of synthesis material, fibrosis, inflammation, dehiscence and necrosis. Results: The tissue adhesives presented the largest dehiscence levels, and ECA the lowest cost while the other measures were similar. Regarding histopathology, deep openings were more common with OCA and granulomas were most frequently obtained with ECA. The two tissue adhesives produces less inflammation than the inicial suture from post-operative day 7, while ECA and OCA cause similar inflammatory reactions. ECA did not differ significantly from OCA and sutures on other measures. Conclusion: ECA was well tolerated in this study and did not induce necrosis, allergic reactions or infections, presenting several advantages in relation to OCA and sutures, including lower costs and fewer complications.


Introduction
Tissue adhesives are substances that self-polymerize to join the edges of an injury and aid its cicatrisation.They constitute an alternative to automatic synthetic methods such as suturing.Beyond this, they do not promote tissue trauma and they eliminate the need to remove stitches.The ideal adhesive must provide adequate tensile strength against biological fluids and keep tissues joined until the proper cicatrisation occurs, but it should not alter immune system function in the wound.Furthermore, it should be biodegradable, nontoxic, readily available and quick drying 2,3 .Since the end of the 1950's, synthetic adhesives have been used in medical applications 4 .One type of such adhesive is the cyanoacrilates (CA) which are currently the most commonly used adhesives for cutaneous closings, especially the 2-butyl-cyanoacrilate (BCA) and 2-octilcyanoacrilate (OCA) forms.In a spontaneous exothermic reaction, these substances self-polymerize by ester cyanoacrilic monomerous CH2=C(CN)COOR spreading.The resulting pellicle joins the adhesives like a bridge.The most important chemical characteristic of CAs is the capacity to form a quick, strong bond that progressively increases in intensity over the following 48 h 5,6 .The advantages of CA in cutaneous synthesis are widely described in the literature 7 , however, these products have been underutilized in Brazil due to high costs 6 .Moreover, the most accessible CA form is 2-ethyl cyanoacrilate 4 (ECA), which has been not widely studied in terms of tolerance, histological reactions in different cicatrisation phases and capacity to avoid dehiscence 6,8- 11 .Low income patients, who constitute a large portion of the population attending public hospitals, have been deprived of CAs' benefits due to the high costs of the CA form approved for human use.One type of CA that has been considered a relatively good solution for wound closure in relation to other CAs and sutures 6,8,10 is ECA.It has been used satisfactorily in clinical procedures involving odontology, abdominal surgery, gynecology, gastrology, neurological surgery, maxillary surgery, orthopedics, plastic surgery, urology, vascular surgery, cardiac surgery, thoracic surgery, and legal medicine 4, 12- 15 .Furthermore, ECA is not carcinogenic 11 , while another CA type metil cyanoacrilat monomerous (MCA, Eastman monomerous) in large doses caused sarcoma development in rats 16 .The present study compares the biocompatibility of ECAs and OCAs to that of sutures in an experimental model.

Methods
Twenty four male Wistar rats (250-300 g) were acclimated in individuals cages with for 14 days with a 12 / 12 light / dark cycle and received food and water ad libitum.Rats were anesthetized with ketamine hydrochloride (100 mg/Kg, i.p.) and tyaside hydrochloride (20 mg/Kg, i.p.).They were put in a ventral decubitus with legs secured to a surgical plate.A rectangular area of 9 cm x 7 cm in the dorsal central region of the back was trichotomised manually.Antiasepsis was achieved with 2% iodine alcohol solution followed by placement of discarded sterile fields.Three longitudinal incisions (two on the left and one on the right) were made 1 to 1.5 cm from the mid-line in the trichotomised area and were guided by a standard model; left cuts were separated by 4 cm.A scalpel with blade 15 was used to entirely penetrate the skin.Hemostasia was achieved by manual compression with gauze for about 2 minutes.Each of the 3 cuts received one kind of closure, either suture, ECA or OCA.The methods were distributed equally amongst the cut positions.Sutures were made with three simple nylon 5-0 stitches; deep relaxing sutures were used.Two successive drops of adhesive were put on the respective incisions to form two thin superimposed films; one minute was allotted to polymerize each pellicle.The products were not permitted escape onto the rat to prevent damage.Digital photographs were taken for macroscopic comparison.Next, the animals were randomly distributed into four groups according to the post-operative day on which biopsies were performed, either 3, 7, 14 or 21 d after surgery.On the 7 th day the stitches were removed (Figure 1).Post-operative monitoring entailed noting the development of: 1) necrosis -darkening and cutaneous scab of an ulcer; 2) inflammation -edema or erythema continuous with the incision edges; 3) contact dermatitis -spots, plates or erythemathosus papule, phlyctena or erythema formation in non-continuous or distant edges of the incision; 4) infection -presence of purulent secretion or abscess; 5) dehiscence -distance > 1 mm from the skin edges; and 6) fibrosis -widening of the scar by >1 mm over at least half of its length.For biopsy, animals were euthanized by carbon dioxide inhalation and a 2.5 cm x 1.0 cm rectangle that contained the incisions was resected.Samples were kept in 10% formaldehyde and coded for pathological screening before blocking in paraffin.Sections were cut (6 cm) on a microtome, including the scar middle and stained with picrosirius and hematoxylin-eosin (HE).Quarantine fields were visualized in each cut and they were evaluated with optics microscopy for epithelization, inflammation (acute, chronic and granulomathose), fibrosis, dehiscence, deep opening, residues of materials and necrosis.Observations were done blind by the same pathologist on three separate occasions.Data were analyzed using descriptive statistics.

Clinical evaluation
Two rats died (83%) within the first 24 h after the surgery; necropsies were performed but the causa mortis could not be identified in either case.In wounds with ECA closing, 5 showed dehiscence, two on the 3 rd POD and three on the 7 th POD; these could not be visualized in the following periods.Two of the OCA closings presented dehiscence, both on the 3 rd POD.No evidence of infection, necrosis, allergies/inflammation, scar widening or fibrosis was apparent.

Histopathological evaluation
The following histopathological descriptions are made in order beginning with the elements that presented most frequently.The 3 rd and 7 th POD's were considered to be within the initial period and the 14 th and 21 st POD's the end period.

Epithelization
Epithelization rate on the 3 rd POD was 20% lower than the other PODs.Complete closing of the epidermis was infrequent and a wide empty space was observed between the incision edges.On the 7 th POD, epithelization increased considerably by 83, 50 and 67% for the ECA, OCA, and suture closings, respectively.All wounds developed epithelization by the 14 th POD (Figure 2).

Deep openings
As shown in Figure 2, the deep opening profile was triangular with the apex turned up in contact with the epidermis; the triangle was filled in the initial periods by an empty space while in the end it was filled by fibrous tissues.On first examination, deep openings were frequent especially with OCA (80%) and suture (60%) closings, while ECA was 40%.Generally higher levels were seen on the 7 th POD with all of the OCA closings having deep openings; those for ECA (87%) and suture (50%) were lower.Deep opening frequency decreased on the 14 th and 21 st POD's (ECA -40% and 17%, OCA -20% and 87% and suture 20% and 17%), except the dehiscence peak on the 21 st POD for the OCA closings (87%).In all, the worst result periods were presented by the adhesives, especially OCA.

Reactions to foreign substances in the wound
Formations achieved with ECA on the 3 rd POD, OCA on the 7 th POD and suture on the 14 th POD presented the highest percentages of reactions to foreign substances (100, 67 and 100%, respectively).On the 3 rd POD the reactions were less frequent in the OCA closings (20%) and absent in the suture condition.Adhesives caused more reactions than sutures in all periods examined, apart from 14 th POD on which all sutures had reactions; at this time ECA was 60% and OCA was 40%; Figure 3).

Material residues
Generally, ECA closings presented high amounts of material inside the formation of abnormal multi-nucleus somatic cells: 60, 67, 60 and 50% for PODs 3, 7, 14 and 21, respectively.Comparatively, less material residues were seen in suture closings at each POD except for 14 which was 100%; the OCA presented intermediate results (20,  67, 20 and 34% for ascending PODs; Figure 4).

Inflammation
Acute and chronic inflammatory reactions were present only in the initial periods, especially on the 3 rd POD.At this time, acute inflammation was higher in all groups than the other PODs but was larger in the ECA and OCA closings than with sutures (80, 100, and XX%, respectively).However, after the 3 rd POD, inflammation, whether acute or chronic, was absent from the adhesive groups.On the 7 th POD, inflammation was verified only in suture closings.Chronic inflammation was observed in closings with ECA on the 3 rd POD (33%) and sutures at PODs 3 and 7 (20 and 17%, respectively), but not OCA (Figure 7).

Fibrosis
As shown in Figures 5 and 6, fibrosis was not seen on the 3 rd POD and was only seen on 7 th POD in the ECA closings (17%).All closing methods showed similarly high incidences of fibrosis in the final periods, especially sutures in which 100% presented on PODs 14 and 21 compared to ECA with 100 and 67%, and OCA with 40 and 100%, respectively.

Dehiscence and necrosis
Wound opening was observed in the initial periods in all groups, but on the 3 rd POD, the OCA presented high dehiscence values for all groups were: ECA -20 and 17%; OCA -40 and 17%; suture -2 and 17%, for PODs 3 and 7, respectively.In the final periods, dehiscence was not observed with any of the closure methods (Figures 8 and  9).Necrosis did not occur at any time point in any of the closings, regardless of the method used.

Discussion
Studies comparing the biocompatibility of ECA to BCA, MCA or gelatin adhesives on skin, using silk or nylon sutures as controls yielded promising results 6,8,10 .Thus, we based the present experiments on their methodologies with some modifications to more directly evaluate our objectives.Our adjustments included (1) the use of rats as an experimental model since they afforded ease of use, due to their small size, and care as well as suiting the NUPE-UFBA's experience in their care, (2) the use of OCA instead of BCA because it is more widely used in our area, (3) more clinical and histological features related to cicatrisation were examined, (4) the incisions were dorsal to avoid closing precocious removal materials by the rodent, (5) three cuts were made in the same animal to reduce the quantity of sacrificed animals and to allow within animal comparisons and eliminate between animal variability, (6) the incisions were put distant enough to the cicatrisation so that they did not interfere with each other, (7) to eliminate the effect of the position of the cut the closure type was evenly distributed throughout positions, (8) the observation periods were chosen according to initial phases (3 and 7 days) and the final period (14 and 21), which is most critical to cicatrisation complications, (9) the incisions were removed in monoblocks which provide a sufficient quantity of tissue for microscopic analyses, (10) histological examination was performed in the incision center, where most phenomenon occurred, and (11) HE staining enabled global microscopic evaluation while the picrocirius specifically visualized fibrosis.Acute and chronic inflammation 5 , seroma, necrosis and bony graft extrusion 11 , cytotoxity in vitro 12,17 , skin necrosis 18 , leuconiquia 19 , contact dermatitis 20 and aneurism in anomalous cerebral artery 21 have been problems that the literature attributes to ECA use.These problems have made difficult to accept for wide use.In spite of the possible complications, many authors have considered ECA a safe bio-adhesive for use in vivo due to the qualities it shares with the other CAs such as its resistance to exuded actions, the ability to support up to a traction of 500g, fast polymerization, provisory toxicity and related effects, bactericide and hemostatic effects when applied to the wound 2,6,12 .Furthermore, many studies have suggested a more widespread use of ECA over other CAs due to its low cost, fast degradation and ample disposability 4,8,14,15 .These suggestions have prompted many professionals to use the derivative short chain as ECA in their clinical practice, in spite of the disposability of other products supposing that they are less toxic 11 .This study showed that the CA's substantially facilitated wound closure.Once polymerized, the CAs formed a flexible, strong and fluid-resistant covering on the wound which eliminated the need to use stitches and needles.This eradicated puncture accidents, reduced the amount of care monitoring and the use of anesthetics in animals, resulting in lower costs.The adhesives spontaneously lost skin adherence in 7 or 14 days, and they were relatively easy to apply therefore eliminating the demand for expert surgeons.These characteristics have been confirmed by the literature and the use of these substances as a method of wound closing was satisfactory for doctors and patients 7,9 .On the other hand, this study also showed that using CA on the skin had unfavorable effects restricted to local complications especially dehiscence and inflammation.These effects were probably due to specific surgeries and not attributable to properties of the adhesives 3,7,22 .The registered deaths were probably due to anesthetic complications that occurred after the surgery, which was quick (10 min) consisting of a small superficial incision.Necropsies did not show evidence of traumatic wounds or systemic toxicity.The economical differences among the closing methods were remarkable.Each OCA recipient was thoroughly investigated due to its high cost.Although the ECA (3 ml) tube allowed it to be applied in a volume 6 times that of OCA, they were used identically to permit comparisons and minimize infection risks.For sutured incisions, threads were used in large quantities from each purchased unit.The total costs were about $572 for OCA, $81 for sutures and $20 for ECA.Thus, ECA cost about 4 and 29 times less than OCA and sutures, respectively.According to our results, epithelization was similar with each wound closure method suggesting that the CAs and sutures affect the epidermis similarly without disrupting its regeneration.Experimental researchers have noticed that in the first 24 h after surgery epithelization was more complete with sutures than with ECA but they were equivalent by the 72 h period 9 .The fast polymerization of CAs enables tissues to join early and allows a faster surgical time providing fast keratinized epithelization 7 .Significant levels of dehiscence occurred in the initial cicatrisation periods.We observed that dehiscence appeared early and it was reduced by the natural process of cicatricial retraction so that in the final periods the opening could not be observed; thus, the final product was identical in the three groups.Other reports state that early dehiscence is the second main disadvantage of CA use especially on the extremity of the localized wounds without deep relaxing sutures which oscillate between 0.3 and 26% 7,26 .According to our experiments, differences in the occurrence of dehiscence at the macroscopic and microscopic levels were attributed to large amounts of histopathological detection.The animal's constant movement, the presence of stitches, scabs, and adhesive pellicles on the wound and the difficulty of measuring openings with the naked eye, was not favorable for the clinical detection of dehiscence.References to deep openings were not found in the literature.This effect was seen as partial dehiscence; the epidermis surface remained humid and formed a bridge on the deep section which, in initial periods, was far, partial (until the dermis), or total (reached the flesh panniculus).In the final periods, the epidermis tended to regress, probably due to fibrosis retraction, but not a result of frank dehiscence or cicatricial widening.The presence of deep openings in all the groups was attributed to the absence of deep relaxing sutures, since studies show that when those are present, dehiscence does not occur 26 .The worst results presented by adhesives were the absence of support in the deepest parts of the incisions, so the cyanoacrilate pellicle was located only on the cutaneous surface.We postulate that in a large series this would not result in cicatricial widening.The highest deep opening occurrence in the OCA closings on the 21st POD was attributed to technical mistakes in the closing or to the small sample size.Positive results concerning reactions to the closing materials were the most irregular and were more prevalent with adhesives than sutures; ECA and OCA produced similar results in this regard.Microscopic analysis showed that in spite of care in application, the CAs penetrated the wound, but did not polymerize inside it.Moreover, the CAs initiated phagocytosis by multinucleus giant cells which completely disappeared one year after surgery 11 .We confirmed that acute inflammatory reactions related to ECA occur primarily on the 5 th or 7 th PODs and are present in the area adjacent to the adhesives; this reaction is gradually reduced as the acrylate is incorporated into cells 6,11 .In the present research, the highest incidence of acute inflammation was observed with suture usage which was followed by ECA and OCA.The fast contact permanency with CA tissues can explain the inflammation triggered by adhesives compared to sutures from the 7 th POD.These initial observations contradicted the findings in the literature that showed important differences in toxicity between ECA and OCA; but the exact toxic effect of ECA was not established.In one study, rats submitted to myocardial repair, and lung and aorta repair using polytetrafluoroethylene patch cuttings which were joined with ECA showed similar necrosis, granulomathosis and inflammatory reactions 15 .In rats, inflammation, tissue granulation, reactions to foreign substances and fibrosis were worse in ECA closings compared to BCA and sutures, although ECA was just as efficient in the final cicatrisation 8 .Other authors demonstrated that when ECA was used to close rats' skin, inferior histological behavior at the suture end was observed after 2, 5 and 10 days.This effect was similar to the 21 st day, but the histological standard was better compared to glue with gelatin as a basis 10 .Another study demonstrated that ECA produced more inflammation than BCA with the latter showing persistent reactions to foreign substances, exacerbated fibrosis, seroma and cartilaginous graft rejection applied to rabbits' ears 11 .Compared to MCA, ECA caused less infiltration of neutrophils and did not produce necrosis, however the ECA fragments stayed longer than MCA 6 .A clear relationship between ECA concentration and toxicity was observed, with cell number reducing proportionally as the concentration increased; however, this cytotoxicity was smaller with ECA than MCA 12,17 .The presence of granulation tissue and fibrosis were similar to what was expected in the normal cicatrisation process with predominant use of ECA.The former were more abundant in the initial periods and then substituted with fibrosis in the final periods.This suggests that fiber collagen deposition was less significant in the final interference when synthetic methods were used.This mechanism can be the main cause of the favorable cosmetic results seen with the scars in the present research which were mostly observed in later periods of cicatrisation.Other studies revealed large formations of granulation tissues in ECA compared to sutures 8 .The fibrotic tissues seem to substitute the degraded polimeric 11 .Several authors have shown that the main disadvantage of ECA and the other CAs is their cytotoxicity.The CAs have been shown to lyse cells in vitro and to cause acute or chronic inflammation in vivo 6,11,12 .The toxicity was primarily attributed to release of toxic metabolites, with small chain derivatives more toxic than the big chain because they are degraded faster.The inflammation intensity triggered by CAs seems to affect the ECAs' tensile strength 2,6 .The toxic effect due to CA use is more noticeable in deep and vascular tissues and has been recommended for use topically on the skin not on vessels surfaces 1,3,11 .In spite of recent advances, the problem persists since the use of any CA is not exempt from risks 4,11,17,18,[21][22][23] .The most favorable result obtained in this study was that necrosis did not occur in any of the animals.The lack of this complication could be due to the correct technical performance of the operation, use of the CAs externally, short contact period with the skin surface, and presence of small quantities of adhesives inside the wound.The toxicity question appeared in doctor's environment with the initial CA application in adhering nerves, tendon, bones, lungs, blood vessels and skin.Other data suggests that necrosis is induced by CAs however these reports were restricted only to the MCA formulation 6 and cutaneous necrosis is rare.There is one account of skin necrosis in a patient who used commercial ECA without a doctor 's recommendation to treat a dried cut in his thumb 18 .Impressively, our results show that complications related to cicatrisation, including infection, necrosis, allergic reactions or scar hypertrophy, were completely absent and, after 21 d, scars formed that did not widen and were acceptable cosmetically.Clinical studies concur that using CAs on skin produced scars with aesthetic aspects similar to intradermic sutures 7 .Consistent with previous studies, the present results strongly suggest that ECA is suitable for use on skin.The low infection indexes of the CAs have been attributed to reduced foreign substances inside the wound.Sutures had increased infection rates due to more contaminated wounds and smaller quantities of contamination necessary to produce infection 24 ; allergic reactions were extremely rare 20 .

Conclusion
Ethyl-cyanoacrylate was well tolerated in this study and did not induce necrosis, allergic reactions or infections, presenting several advantages in relation to octylcyanoacrylat and sutures, including lower costs and fewer complications.

FIGURE 3 -
FIGURE 3 -Summary of epithelization histopathological results, deep opening and reactions to foreign substances.