| BackgroundHypertrophic scars represent an aberration in the fundamental processes of wound healing.It is one of the most common pathological phenomenon after wound healing of trauma, especially in deep burned patients. The body will start a series of post-traumatic repair process after being hurt. Scar healing is a repair process that involves a variety of cells and cytokines, among which the most important one is fibroblast. After the abnormal proliferation of fibroblasts, the excessive deposit of extracellular matrix which is mainly composed of collagen type I and type III, and the vast accumulation of disordered mucopolysaccharide, a scar is finally formed. Therefore, the biological behavior of fibroblasts is considered to be the decisive factor of wound healing and scar formation. During 1960s and 1970s, Mancini defined such incontrollable scar tissue in this way that hypertrophic scar is above the skin surface but limited to the scope of the original injury. While Muir put forward another opinion that the hypertrophic scar, though limited to the scope of the original injury, does not disappear automatically and will easily relapse after resection.Pathological scars include hypertrophic scars and keloids. As the hypertrophic scars are above skin surface, it will cause various symptoms like itching, tingling, pigmentation and contracture, which will exert serious influence on the appearance and function of patients and will bring severe damage to patients both physically and psychologically. Thus its prevention and treatment has always been a urgent and difficult problem in the medical field. Certain achievements have been made in scar prevention and treatment through continuous efforts. The main treatments against it include surgery, hormone injections, compression therapy, radiation therapy, cryotherapy, the use of silica sheet and other drug therapies. At present, among the clinical non-surgical treatments of scars, steroid hormones, particularly triamcinolone acetonide is recognized as a drug with curative effect, that can be commonly used in local injection of scars. Steroid hormones can inhibit the synthesis of scar collagen, improve the collagenase activity and promote collagen breakdown. However, there are some following deficiencies:①. It hurts;②. There is uneven spread of drugs after local injection;③. At present, the drug dosage and usage is hard to control; and the systemic side effects are significant after long-term use of hormones.④. Scar injection is only applicable to small scope, and the expansion of injection scope is limited by single injection dose Therefore, among the non-surgical treatments of hypertrophic scar, a painless local drug membrane should be an ideal method. Nowadays, although there are a lot of researches on the pathogenesis of hypertrophic scars and treatment, there is still no ideal result. For these reasons, finding a convenient and effective scar treatment has always been the goal of endeavoring medical workers.In recent years, biological material applied in hypertrophic scar treatment has aroused widespread attention in the medical profession, in which bacterial cellulose is the focus. Bacterial cellulose is the finest natural fiber and nano-fiber, whose size is only 1/10 of that of synthetic fiber. In terms of chemical composition, plant cellulose and bacterial cellulose are both polymer compounds composed by glucose linked via p-1,4-glycosidic bonds. There are greater differences between bacterial cellulose and plant cellulose in structure, physicochemical properties and biochemical characteristics. Because BC is characterized with unique bio-compatibility, compatibility, and adaptability; it is degradable and won't cause any allergic reaction; it has high water holding capacity and crystallinity, with good nano-fiber network, high tension and intensity, and especially good mechanical toughness. With these excellent features, bacterial cellulose has a wide range of commercial uses; it can be used in many products such as speaker diaphragm, food additives, pervaporation membrane, paper reinforcing agents, wound care dressings and so on. So this material is expected to become an excellent wound dressing. According to literature reports, the wound of rabbit would gradually evolve from epithelium to hyperplasia, which would last for some time and then gradually disappear. From this process, it can be seen that there is similar occurrence and development process between rabbit ear wound healing and human wound healing. It is reported that both domestic and foreign scholars have done experimental researches on the effect of bacterial cellulose in promoting skin wound healing. However, there is still no study about whether BC has curative effect on the HS. Based on this, this experiment is designed and implemented.The experiment consists of two parts:1. The establishment of animal experimental model of rabbit ear hypertrophic scar. The animal scar model is the one of most useful tools in the scar studies. In previous studies, the vitro culture system of fibroblasts is generally used in doing scar research, including monolayer and three-dimensional culture system; or clinical observation is carried out to sum up experience in prevention and treatment of scars. But these methods have some shortcomings:the vitro culture system of fibroblasts is unable to simulate the vivo environment and conditions exactly; clinical observations can not study the occurrence, development and outcome of scars in detail. These shortcomings are insurmountable obstacles to more in-depth scar study. Therefore, the establishment of an effective animal model has been the working direction of domestic and foreign medical workers. In 1997, it is reported that Morris successfully established the hypertrophic scars model of rabbit ear. And it is confirmed that the hypertrophic scar caused by this model is similar to human hypertrophic scar, which can quantify the evaluation of the drug effects on scar.2. Experimental study on the effect of bacterial cellulose used in hypertrophic scar of rabbit ears. By using different application approaches of bacterial cellulose on hypertrophic scars, one can respectively observe the gross morphology and histological changes of hypertrophic scars and detect a-SMA their hydroxyproline(Hpr) content on the very 0,14,21,28,42,56 day. Such kind of BC experimental researches provide theoretical basis for clinical application. Objective1.To understand whether rabbit ears after wound healing can produce similar hypertrophic scar as human's or not.2.To investigate the effects of bacterial cellulose on reducing rabbit ear hypertrophic scar.MethodsExperiment 1:The establishment of animal experimental model of rabbit ear hypertrophic scar.After 30 adult New Zealand white rabbits are given intravenous anesthesia of pentobarbital sodium (30 mg/kg),5 circles with 1.5 cm diameter were engraved on the skin surface of each rabbit ear by means of compasses.2 circles were carved respectively in both two sides of outer ear, and 1 circle on ear base. The interval between each circle is about 1.0 cm, avoiding blood vessels. Then we would excise the skin and perichondrium inside each circle, while retaining cartilage. Every rabbit with two ears has 10 wounds, thus 30 rabbits have 300 wounds in their ears.Experiment 2:Experimental study on the effect of bacterial cellulose used in hypertrophic scar of rabbit ears.On the 21th day after the operation, there are obvious epithelization and hypertrophic scars on the wound surface of rabbits. According to the 5 different scar surface of each rabbit ear, different treatment approaches were designed and randomly divided into group A, B, C, D, E. In group A,1:5 bacterial cellulose is applied to scars; in group B,1:6 bacterial is applied to scars; in group C,1:8 bacterial is applied to scars; in group D, silicone scar sheet is applied to scars with positive control; in group E, nothing is applied to scars, leaving the scars growing naturally with negative control. Moreover, according to the general observation or collection time,30 rabbits are divided into 6 groups, each group with 5 rabbits. By taking different treatment of scar surface, one can respectively observe the hypertrophic scars of each group with 5 rabbits on the very 0,14,21,28,42,56 day, taking note of the gross morphology in the scars thickness,histological changes of hypertrophic scars in fibroblasts quantity and collagen fiber structure and alpha SMA express quantity,detecting their hydroxyproline(Hpr) content.Results1.Gross morphology observation:After the treatment of rabbit ear scars, on the 14th day, by comparing group A,B,C with group D, it can be found that the scars of group A,B,C have become larger and thicker, with deeper red color and harder texture. On the 21st day, by comparing group A,B,C with group E, it can be found that the scars of group A,B,C have the maximum thickness. And after the peak of maximum thickness, the scars of group A,B,C have gradually become softer, smaller, and thinner; but the color lightening extent of group A,B,C are lower than group D but higher than group E. The thickness variance analysis of the scars of group A,B,C,D, E at various observation time shows that their differences are of statistical significance(F=21.871, P<0.001); while the differences of group A,B,C, between every two groups are of no statistical significance (P>0.05); by comparing group A,B,C with group D, every two groups'differences between group A,B and D are of statistical significance (P<0.001); but the differences between group C and D are of no statistical significance (P>0.05); the differences between group A,B C and E are of statistical significance (P<0.05); so are the differences between group D and E (P<0.001).2.Histological observation:At the early stage after the wound healing of rabbit ear, the scars of each group would become a bump out of the surrounding regular skin, with obvious dermal tissue hyperplasia and massive connective tissue hyperplasia under epidermis. In the hypertrophic dermal tissue, massive fibroblasts, enlarged capillary and extracellular matrix can be observed. After different treatment, on the 14th day, the dermis of group A,B,C become thinner, with the concentration of collagen fibers with disordered arrangement at superficial layer; at deep layer, collagen fibers have parallel arrangement as cartilage, with partial obliteration of capillary and the number of fibroblasts reaching the peak, which is much fewer than that of group E but more than that of group D. On the 21st day after treatment, in group A,B,C medium increase of fibroblasts can be observed, as well as medium neatly arranged collagen fibers; in each group, there is inflammatory cell infiltration of different degree and much more epithelial cells and capillary can be observed. Meanwhile, in group E there is massive increase of fibroblasts and massive irregular thickening collagen fibers with swirling or nodular arrangement, the number of fibroblasts reaching the peak. On the 28th, 42th,56th day after treatment, the number of fibroblasts of each group becomes fewer than before, and by comparing the fibroblasts number of group A,B,C the result is A>B>C (P<0.05); the differences of collagen fibers'structures among group A,B,C are of no statistical significance(P>0.05); the collagen fiber arrangement of group A,B,C is more ordered than group E, but still inferior to group D. The determination ofα-SMA expression:After different treatment of each group, on that very day of treatment, generally theα-SMA expression is positive. With time prolonging, theα-SMA expression of each group is likely to increase. On the 14th day theα-SMA expression of group A,B,C,D reaches the peak. Theα-SMA expression of group E continues to be positive until the 21st day. On the peak period, theα-SMA expression of group E is strong-positive, while that of group A,B,C positive, and group D weak-positive. With time further prolonging, after the peak time, theα-SMA expression of each group gradually decreases with the minimum decrease of group E and larger decrease of group A,B,C,D. Thus, theα-SMA positive expression of each group is D<C<B<A<E; such expression differences are of statistical significance (P≤0.05).3. Hpr contents of Hypertrophic scars:After different treatments, the Hpr contents in each group all gradually increases and then decreases. On the 14th day after treatment, the Hpr content of group A,B,C,D reaches the peak, and that of group E reaches the peak on the 21 st day. The Hpr contents variance analysis of the scars of group A,B,C,D, E at various observation time shows that their differences are of statistical significance(F=50.666, P<0.001); while the differences of group A,B,C, between every two groups are of no statistical significance (P>0.05); by comparing every two groups between group A,B,C and D, every two groups'differences between group A,B and D are of statistical significance (P<0.05); but the differences between group C and D are of no statistical significance (P>0.05); the differences between group A,B C and E are of statistical significance (P<0.001); so are the differences between group D and E (P<0.001).Conclusions1. Through this experiment, it can be concluded after the full-thickness skin loss on ventral side of rabbit ear heals, hypertrophic scars will appear, which has similar histological structure and duration as human hypertrophic scar. Thus in this way, the hypertrophic scar animal model is further proved.2. It has been proved that external bacterial cellulose dressings can effectively inhibit the hypertrophic scar formation of rabbit ears after the wound healing, with relatively obvious effect.3. The relief effect of external bacterial cellulose dressings is not so obvious as that of scar patch.4. The bacterial cellulose with hygroscopicity ratio of 1:8 is the most suitable dressing to inhibit the hypertrophic scars of rabbit ears.5. The bacterial cellulose dressings are expected to be a new type of medical dressings to relieve hypertrophic scars. |
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