Dermal Equivalence. History of origin and results of clinical trials

In the late 1980s, a liquid form of bovine collagen was developed at Stanford University, which transformed into a soft elastic substrate at body temperature. The drug was registered and approved for use in a number of European countries as an implantable agent called Zyderm Collagen Implantant. This drug became the first implant. Later, other means for contour plastics appeared, such as Restylane, Perlane, Pharmacrylic gel, Artecol, Biopolymer gel and others. These drugs began to be used not only for contour modeling and correction of age-related skin changes, but also for treatment, or more precisely, for smoothing out the relief of scars. All of them were injected under the bottom of the scar.

The search for more advanced methods for treating hypotrophic scars led us to the idea of using an artificially created analogue of skin for this purpose - "dermal equivalent" (DE), which also used liquid collagen. There were many options for artificial skin substitutes, but the general idea was to create a skin-like tissue from the structural components of the dermis, which would not be rejected in the event of transplants and would be a good substrate for the ingrowth of the dermis and epidermis's own components. It is known that the main structural components of the dermis are cellular, fibrous elements and interstitial substance. Fibrous elements are mainly represented by collagen and elastin fibers, the interstitial substance - glycoproteins, proteoglycans and glycosaminoglycans. The main functional cellular element of the dermis is the fibroblast, the cellular population of fibroblasts is the source of formation of almost all structural components of the dermis. Therefore, when creating a "skin substitute", most scientists use a collagen substrate mixed with fibroblasts and glycosaminoglycans. A layer of keratinocytes is applied on top in one form or another to create a full-layer skin and more rapid restoration of the viability of the transplanted skin equivalent, which is facilitated by numerous growth factors secreted by keratinocytes. One of the first versions of a "living skin equivalent" was proposed in 1983 by E. Bell et al. Skin fibroblasts were mixed with collagen, plasma and growth medium, which led to the formation of a gel, on the surface of which keratinocytes were grown. All this was cultured for 1-2 weeks in vilro, after which the dermal equivalent was considered mature and represented a viable tissue in the form of a translucent elastic mass. The authors proposed to transfer it to the wound surfaces of burn patients to recreate a full-layer skin structure. Some authors used a collagen sponge or collagen matrix covered with proteoglycans and populated with fibroblasts as a basis for the dermal equivalent, on top of which autologous keratinocytes were grown. As a result, a so-called three-dimensional model of the skin was created. For the cultivation of keratinocytes for the purpose of their subsequent transfer to wound surfaces, some authors also used an artificial matrix of collagen, glycosaminoglycans and chitosan, cadaveric skin, and pig skin as a substrate. After 7-14 days from the start of cultivation, a full-layer transplant containing the dermis and epidermis was transplanted onto the wounds of patients or animals.

Artificial skin substitute has been used not only to restore skin in burn victims, but also to test drugs for cytotoxicity and to study growth factors in vitro.

Insufficient, from our point of view, effectiveness of surgical dermabrasion of deep hypotrophic scars in combination with transplantation of MPC gave reason to try to level the skin relief by inoculating an analogue of the dermal equivalent into the depression of the hypotrophic scar. Liquid collagen obtained in the laboratory, into which a suspension of fibroblasts was introduced, became the substrate for creating the dermal equivalent. The dermal equivalent, as well as MPC, was created in a specialized laboratory certified for this type of activity and on the day and hour of the operation was delivered in a glass bottle in a container with ice to the clinic.

Operative scar polishing was performed using the standard technique after antiseptic treatment of the skin and local anesthesia with 2% lidocaine or novocaine or ultracaine. Polishing smoothed the scar surface and at the same time created conditions for the engraftment of cultured cells or cell compositions. After that, the cooled liquid collagen gel with fibroblasts inoculated into it was applied with a sterile spatula to the polished surface of hypotrophic scars (into the deepening of the scar), where it polymerized under the influence of body temperature.

As a result, after 5-10 minutes, the collagen with fibroblasts polymerized from a liquid state into a thick gel state. After the DE thickened, a bandage with a suspension or MPC on a substrate was applied on top.

A multilayer sterile dressing was fixed as in the case of MPC transplantation. Depending on the surface of the scar, the wound covering on which the keratinocytes were located and the type of grinding, the dressing was rejected within 7 to 12 days.

The method of combined treatment of hypotrophic scars using surgical dermabrasion with subsequent transplantation of the "dermal equivalent" and keratinocytes in the form of a multilayer layer grown on special wound dressings or in the form of a suspension into the scar depression allows achieving significantly better, cosmetically acceptable results with a reduction or complete disappearance of (-) tissue. The dermal equivalent forms the patient's own tissue (dermis), the scar tissue remains below the newly formed tissue. The MPC creates an epidermis of normal thickness and functional activity, due to which the general appearance of the scar tends to significantly improve over several months.

This tactic of treating hypotrophic scars can be called optimal in solving this problem today. However, the DE variant we used in the form of a collagen gel with fibroblasts inoculated into it is not very convenient to work with. DE for working with hypotrophic scars should initially be thicker so that it can be placed in the scar cavity, distributed in it, and then apply a wound covering with keratinocytes on top. Thus, we can say that this direction in working with hypotrophic scars is only outlined, but the forecasts for its further development and study are very optimistic.

The complexity and high cost of obtaining multilayered keratinocyte layers as a therapeutic material stimulated the need to search for other options for cell compositions. Of great interest to researchers is the cultivation of fibroblasts, which, when transplanted onto wound surfaces, give an effect that is in many ways similar to the results of keratinocyte transplantation, but are a much simpler and cheaper cellular material. In our studies, we treated several patients with hypotrophic scars with mesotherapeutic injection of fibroblast suspension under the scars.

A suspension of fibroblasts in a growth medium with 1.5-2 million cells per 1 ml was introduced under the scars using mesotherapeutic techniques (micropapular, infiltrative). The number of treatment sessions was from 4 to 10, depending on the age of the scar, the patient's age and the depth of the defect. The interval between sessions was 7-10 days. As a rule, the introduction of a suspension of autologous and allogenic fibroblasts was accompanied by a minor, transient vascular reaction.

As a result of clinical studies, it was revealed that under the influence of transplanted MPCs, the duration of the inflammatory reaction in the skin and scars after surgical dermabrasion is reduced and the epithelialization of wound surfaces is accelerated by an average of 3-4 days.

When working with normotrophic and hypertrophic scars, accelerating the healing of postoperative erosions is of the greatest importance, since this is where the possibility of achieving an optimal therapeutic effect lies.

Transplantation of the dermal equivalent led to filling (-) tissue of hypotrophic scars, leveling their relief, smoothing with the surrounding skin, due to which the area of scars became significantly smaller.

The introduction of a fibroblast suspension into hypotrophic scars also led to a smoothing of the skin relief and a reduction in the area of scars.

In all cases of cell transplantation, an aftereffect was observed, when over the course of several months there was an improvement in the aesthetic appearance of the scars, which tended to transform into a dermal-like structure.

All the effects we observed are related to the implementation of the biostimulating potential of the transplanted cells. It seems to us that the number of cell layers in the transplants is usually 10-30% higher. Consequently, the total cell potential per unit area is already 10-30% higher than normal. In addition, the best results in transplanting keratinocytes and fibroblasts were obtained when transplanting cell material from young healthy people. This fact, by the way, speaks in favor of using an allogeneic culture obtained from young and healthy donors. The bioenergetic and information potential of such a culture is transferred to the recipients' own cells, sometimes not very young, due to which the "quality" of the recipients' own tissues and cells improves.

Thus, the use of keratinocyte and fibroblast culture allows:

• Accelerate the epithelialization of scars after dermabrasion.
• Reduce the visibility of scars not only by leveling their surface with the surface of the surrounding skin, but also by forming a full-fledged epidermis over them.
• Improve the results of surgical dermabrasion due to the effect of cytokines of transplanted cells on the scar, which eventually tends to transform into a dermal-like structure.
• To obtain aesthetically significantly more acceptable results of treatment of patients with normotrophic, hypotrophic, hypertrophic, atrophic scars and striae.

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