Fractional laser technology: a compromise between efficiency and safety

Today, in the arsenal of modern dermatocosmetology, there is a very wide range of methods to correct various aesthetic imperfections of the skin - chemical peels, mechanical dermabrasion, laser resurfacing, microdermabrasion, contour plastic and others. However, new directions and technologies in the beauty industry are constantly developing and improving.

This trend is especially typical for hardware methods, especially for laser medicine. The use of lasers, first in dermatology and then in cosmetology, has an impressive period. Even since the appearance of one of the newest laser treatment methods - selective photothermolysis - more than 25 years have passed. The pioneers of this direction, Americans RR Anderson and JA Parrish, predetermined the fate of fractional lasers in medicine, making them indispensable in the treatment of this aesthetic. skin imperfections like capillary hemangiomas. Port wine stains, hypertrichosis, tattoos, rosacea, pigmentation disorders, photoaging, wrinkles, etc.

Modern skin remodeling techniques

We live in a time when more people are living to old age than ever before. And as many of them remain active, one of the most important problems in aesthetic medicine is combating skin aging.

Plastic surgery is able to rejuvenate the shape of the face by removing excess skin. However, at the same time, the skin still remains altered by time (age-related aging) or external factors (photoaging). It is also important that most patients want to look younger without surgery.

In that case, what method should be used to influence the skin and what should happen in it for its real rejuvenation?

All the methods that can be used to improve the appearance of the skin are joined by a principle - they use a traumatic effect on the skin, causing fibrosis, which further leads to its tension and compactness.

Currently, dermatocosmetology uses three main types of skin remodeling effects, including:

• chemical stimulation - chemical peels with acids (trichloroacetic, glycolic, etc. );
• mechanical stimulation - mechanical dermabrasion, microdermabrasion, mesotherapy, fillers, subcision with needles;
• thermal stimulation - laser ablation, termolifting using lasers and broadband light sources, radiofrequency survey, fractional methods.

Chemical stimulation

Historically, acid exfoliation (peeling) was the first method of skin rejuvenation. The principle of peeling is partial (as in superficial peeling) or almost complete (as in medium and deep peeling) destruction of the epidermis, damaging fibroblasts and structures of the dermis. This damage activates an inflammatory reaction (the more powerful, the greater the volume of destruction itself), which leads to additional collagen production in the skin.

However, to achieve the desired result, the peel has to sacrifice the epidermis. Burn experiments have deceived many, allegedly "proving" that the epidermis is an organ that self-renews and quickly recovers over the area. In this sense, peels to a certain extent became increasingly aggressive to the epidermis (for example, deep phenolic peeling), until finally the accumulated problems made the specialists realize the evil of it. a method that ends up leading to thinning of the skin.

Proponents of deep peeling ignored emerging problems. Its essence was that, due to the destruction of the dermal papillae and the weakening of nutrition, the epidermis became thinner and the number of cells in the spinous layer was significantly reduced compared to what was before the peel. A decrease in the barrier function of the stratum corneum leads to a decrease in skin hydration. (Therefore, almost all patients after deep peeling for a long time experience severe skin dryness) At the same time, the introduction in practiceLighter peels (using trichloroacetic acid and fruit) did not live up to their hopes of effectively tightening the skin.

Mechanical stimulation

Of the methods of mechanical stimulation of involutional changes in the skin, dermabrasion with the use of rotating devices (with speed of v; rotation of the cutters up to 100, 000 rpm) deserves special attention. Currently, modern Schumann-Schreus devices are used (Germany)

The method can only be used in a surgical hospital, as the procedure requires anesthesia, post-operative treatment of the wound surface, a special bathroom for eyes and mouth, in addition to devices for feeding patients (due to the fact that the edema after- pronounced operation that occurs 2-3 days after the procedure makes it difficult to open your eyes and mouth).

The method is very effective, but unfortunately, with mechanical dermabrasion, there is a high risk of complications such as:

• persistent postoperative hyperemia;
• the appearance of areas of depigmentation due to the destruction of melanocytes when the cutter penetrates through the basement membrane;
• infection of the wound surface;
• scar (if the cutter is too deeply immersed in the skin)

All of the above determined the limited application of this method in clinical practice.

Thermal stimulation

Ablative remodeling

Since the late 1980s, a laser has been used to rejuvenate the skin by removing tissue layer by layer (ablation) [4]. Careful and non-traumatic removal of the surface layer of the skin using a carbon dioxide laser stimulates the synthesis of its own collagen in it, the amount of which increases several times after the procedure. Then, it is gradually rearranged.

The most effective was the use of the CO2 laser, when exposed to a profound thermal effect on all layers of the dermis, manifested externally by the skin tightening effect. The method is called "laser dermabrasion" or "laserresurfacing", and in terms of effectiveness, it could not be countered by any other skin rejuvenation method that existed at the time (fig. 1).

Fig. 1. Traditional laser skin resurfacing scheme (laser dermabrasion)

However, the CO2 laser also causes a large number of complications. In addition, other studies have shown that such a profound effect on the dermis stimulates the formation of fibrous tissue to a greater extent than it contributes to the synthesis of new normal tissue. oriented collagen [5]. The developed fibrosis can make the skin abnormally pale. The collagen synthesized after treatment is reabsorbed after a few years, like any collagen formed at the scar site. As a result of thinning the epidermis caused by atrophy of the papillary layer of the dermis, fine wrinkles begin to appear on the skin. Due to the weakening of the stratum corneum barrier function, the skin's hydration level decreases and appears atrophic.

Erbium-aluminum-yttrium-garnet-erbium lasers appeared a little later. These advantages of an erbium laser as a shallower thermal penetration depth (erbium lasers penetrate to a depth of 30 μm, CO2 lasers - up to 150 μm) and (as a consequence) the lower risk of burns and carbonization of tissues, as well as the relatively low cost (compared to carbon dioxide lasers), has attracted the attention of many experts worldwide.

However, as experience of working with these two types of installations accumulates, experts believe that CO2 lasers are more efficient [6]. Despite the negative effects of carbon dioxide laser dermabrasion described above, this method remains indispensable for the correction of acne scars. Furthermore, it can be considered as an alternative to surgical hardening of the skin - of all its remodeling methods, only exposure to a CO2 laser can really cause a sharp increase in collagen contraction with a visible clinical lifting effect.

The problem with all the methods described above is that they often "sacrifice", that is, significantly damage the epidermis. To rejuvenate your skin and really look young, you need a perfect epidermis with dermis hair, good hydration, normal skin tone and elasticity. The epidermis is a highly specialized and very complex organ, up to 200 microns thick, which is our only defense against the effects of negative environmental factors. So, whatever we do to rejuvenate the skin, we need to make sure that its normal underlying architecture is never damaged.

This concept contributed to the emergence of non-ablative skin remodeling technology.

Non-ablative remodeling

The most common devices for non-ablative skin remodeling are neodymium (Nd-YAG) and diode lasers, as well as broadband light sources (IPL). The principle of its action - selective photothermolysis - consists of heating and destroying structures, containing a sufficient amount of melanin or oxyhemoglobin. In the skin, they are, respectively, accumulations of melanocytes (lentigo, melasma) and microvessels (telangiectasia). The emitted wavelengths used in non-ablative lasers correspond to the maximums of the absorption spectra of oxyhemoglobin or melanin. The procedure for treatment with non-ablative lasers and IPL is quite safe, the rehabilitation period is minimal, however, such treatment eliminates only pigmentation and vascular cosmetic defects. In this case, there is a certain thickening of the skin, but the effect obtained is of short duration.

Fractional skin remodeling techniques

The constant search for new highly effective and safe methods of skin rejuvenation has led to the emergence of a revolutionary technology - the fractional distribution of laser radiation. The proposed skin rejuvenation method was specially designed to overcome some of the above difficulties. Unlike "conventional" ablative and non-ablative laser methods, which are designed to achieve uniform thermal damage to the skin at a specific depth, fractional methods allow you to achieve your selective microscopic thermal damage in the form of numerous altered columns and leave unaffected areasaround these micro-wounds. Currently, the industry produces two types of fractionated lasers: non-ablative and ablative.

The first uses an erbium-doped optical fiber that generates radiation at a wavelength of 1550 nm. The fractional laser forms thousands and tens of thousands of micro-damages in the form of columns - microthermal treatment zones (MLZ) - with a diameter of 70-150 mk depth up to 1359 mcm

As a result, about 15-35 skin is photocoagulated in the treated area. The laser chromophore is water. Coagulation occurs mainly in the lower layers of the epidermis and dermis. The stratum corneum remains intact because it contains a relatively small amount of water, which significantly reduces the risk of infection. Epidermal recovery is rapid due to the low volume of the lesion and the short migration distance from keratinocytes. The healing period is accompanied by moderate edema and hyperemia, followed by desquamation, appearing on the 5-7th day. The patient practically does not lose social activity.

This technology - fractional photothermolysis (FF) - is a highly effective method of fractional remodeling of non-ablative skin. To achieve the desired effect, regular treatment is prescribed. Depending on the clinical situation, it is recommended to perform 3 to 6 procedures with an interval of 4 to 6 weeks. As with any other non-ablative skin remodeling method, the final result can be seen only 4-8 months after the procedure (cumulative effect).

In cases where a more aggressive effect on the skin is needed - for scar correction, removal of deep wrinkles and excess skin, the fractional ablation method (AF or fractional deep dermal ablation -FDDA) is used.

The fractional ablation method combines the advantages of a CO2 laser and the fractional principle of applying laser radiation. In contrast to traditional CO2 lasers, which remove the entire surface of the skin layer by layer, the AF units form a large number of microablative zones (MAL) up to 300 µm in diameter at a vaporization depth of 350 to 1800 µm (Fig. 2).

Thus, during this procedure, laser radiation, penetrating the deep layers of the skin, destroys the upper layer of the epidermis. In terms of efficiency, ablative fractional laser rejuvenation can be compared to plastic surgery, it is the depth of the resurgence of the laser beam.

Fig. 2. The principle of operation of the ablative fractional laser: the formation of microablative zones - MAZ (a); dependence of the MAZ formation depth on the laser radiation power (b)

As in the case of FF, 15 to 35% of the skin of the treated area is actually exposed (in some cases, up to 70%). Recovery after the AF procedure is faster than after layer-by-layer ablation. This is due to the fact that part of the epidermis and stratum corneum remain intact. Cutaneous bleeding is observed for some time immediately after the procedure, but soon stops (Fig. 3 a, b).

Fig. 3. Skin restoration step by step after the fractional ablation procedure: seen immediately after treatment (a); every other day (b); after 5 days (c); 14 days (d) after an

procedure

Numerous micro-hemorrhages appear in the dermis, which induce a complex cascade of changes that lead to the production of new collagen. After the bleeding stops, it is necessary to remove the serous fluid that remains on the skin surface. Its release is observed within 48 hours after the procedure, until complete epithelialization of the microablative zones occurs. During this period, the patient uses special external agents for wound healing. It usually starts in 3-4 days the peeling and the swelling increases (Fig. 3c). On the seventh day, these phenomena gradually subside and erythema remains the only noticeable side effect (Fig. 3d). The duration of erythema depends on the parameters of exposure to lasers and characteristics of vascularization of the skin. According to the author's observations, the erythema does not last more than 3 months.

The patient's loss of social activity after the PA procedure lasts from 5 to 10 days.

To prevent scarring and post-inflammatory pigmentation, it is necessary to take care of the skin carefully. Decorative cosmetics can be used for 4-5 days. A prerequisite for a good result is the use of deposit at least 3 months after the procedure of sun protection cosmetics with a high degree of protection (SPF at least 50). The risk of post-inflammatory pigmentation occurs in 20% of patients and is generally greater in patients with skinPhototypes IV-V. This hyperpigmentation is transient in nature and can last from 1 week to 3 months, which also depends on the depth of treatment and the area of ​​the treated area. For its prevention 1-2 weeks before the procedure and for another 2 weeks afterwards, external agents based on hydroquinone (4%) and tretinoin (0. 1%) are prescribed. The main effects on facial skin after the AF procedure are as follows: pronounced tightening and reduction of excess skin, leveling of the wrinkled skin surface, as well as skin affected by acne scars, reduction of dyschromia, porosity.

This method has been tested by the author and his colleagues as well to remove stretch marks from the skin. As shown by clinical studies, the method has demonstrated high efficiency in eliminating almost all types of stretch marks, both acquired at puberty. period and postpartum. It was noted that the healing processes in the skin of the body are different from those of the skin of the face.

Skin remodeling mechanism when using fractional lasers

Let's consider the mechanisms of skin remodeling when using fractional lasers.

After exposure to the laser, aseptic inflammation develops in the area of ​​the formed micro-wounds. The more aggressive the laser exposure, the more pronounced is the inflammatory response, which, in fact, stimulates post-traumatic release growth factors and infiltration of tissues damaged by fibroblasts. The next reaction is automatically accompanied by an explosion of cellular activity, which inevitably leads to the fact that fibroblasts begin to produce more collagen and elastin. The skin remodeling process includes three classic phases of regeneration:

• phase I - alteration (tissue inflammation). Starts immediately after damage;
• phase II - proliferation (tissue formation). It starts 3-5 days after the injury and lasts about 8 weeks;
• phase III - tissue remodeling. Lasts from 8 weeks to 12 months.

It should be noted that all three phases of skin remodeling are observed both after fractional photothermolysis and after fractional ablation. But in the first case, the damaging effect of the laser is moderately aggressive, resulting in a cascade of inflammatory reactions. Change is never too wild.

A completely different image is seen after exposure to fractional ablation laser. The trauma caused by this laser breaks the blood vessels and blood cells, along with the serum, are released into the surrounding tissue. The complete skin regeneration mechanism - pha change begins - aseptic inflammation develops. Platelets released from damaged vessels play an important role in activating blood clotting and in releasing chemotoxic factors that, in turn, other platelets, leukocytes and fibroblasts are attracted. Leukocytes, in particular neutrophils, participate in cleaning the destroyed tissue, removing fragments of necrotic tissue, which are partially destroyed by phagocytitis, and partially to the surface of the skin in the form of microscopic debris consisting of epidermal and dermal tissue substrates and melanin- microepidermal necrotic fragments (MENO).

The proliferative phase begins in about 5 days. During this period, neutrophils are replaced by monocytes. Monocytes, keratinocytes and fibroblasts continue to influence growth factors and, at the same time, are under their reverse influence. Keratinocytes stimulate the growth of the epidermis and the release of growth factors necessary to stimulate the production of collagen by fibroblasts. At this stage, new blood vessels are formed, and the extracellular matrix is ​​intensely formed.

The last phase of reconstructive healing after fractional laser exposure lasts several months.

On the 5th day after the injury, the fibronectin matrix “fits” along the axis along which the fibroblasts are aligned and along which the collagen will be formed. An important role in the formation of this matrix is ​​played by the transformation of the growth factor β (TGF-β is a strong chemotoxic agent for fibroblasts), as well as other growth factors. The main form of collagen in the initial phase of wound healing is type III collagen (this type of collagen is located in the upper layer of the dermis, just below the basal layer of the epidermis). The longer the alteration phase, the more type III collagen will be produced, but in any case, its amount increases to a maximum of 5 to 7 days after the damage. Type III collagen is gradually replaced by collagen over about one year, Type I, which strengthens the skin's resistance. The blood circulation gradually normalizes, the skin becomes smoother and acquires a natural color.

Comparative analysis of laser skin remodeling methods

Summarizing the above, here is a diagram showing the relationship between the effectiveness and safety of laser skin remodeling techniques.

Advantages of fractional strip rejuvenation methods. The advantages of fractional methods used in clinical practice include:

• controlled minimal damage to the skin. Histological studies carried out after the procedure show an increase in the number of papillae in the dermis, which characterizes changes in the skin as productive regeneration;
• its effective rejuvenation: the skin becomes thicker, significantly increases (more than 400% (! )) the production of collagen and elastin;
• short healing time: on average 3 days after FF and 7-14 days after PA;
• minimal risk of hyperpigmentation;
• possibility of performing the procedure on patients with thin skin;
• the ability to have a healing effect on any part of the body;
• the possibility of using light types of anesthesia: with fractionated photothermolysis, only locally applied anesthesia is used; for fractional ablation, a combination of conduction and infiltration anesthesia is required;
• disappearance of telangiectasias (due to the fact that blood vessels rupture in so many places that their restoration is impossible).

Main indications for fractional treatments

Indications for fractional photothermolysis:

• increased skin density in the early stages of aging. The FF procedure is relatively easy and can be administered without fear. The therapeutic effect can be exerted on the neck, décolleté, arms, abdomen, thighs, mammary glands;
• photoaging of the skin;
• hyperpigmentation, melasma;
• hypertrophic scars;
• streaks.

Indications for Fractional Ablation:

• wrinkles of varying severity - from fine to strongly pronounced lines (in the form of grooves);
• age-related loss of elasticity and firmness of the skin;
• excess skin on the eyelids, neck, face (as an alternative to plastic surgery);
• uneven skin texture;
• pronounced photoaging of the skin;
• acne scars;
• scar deformity of the skin after injuries, operations;
• hyperpigmentation: melasma, lentiginosis, speckled pigmentation, etc.
• vascular dyschromia;
• streaks of the skin;
• actinic keratosis.

In conclusion, a few words about the prospects for using laser technologies in aesthetic medicine. We must pay tribute to the manufacturers who started to pay more attention to the safety of medical procedures with lasers. Technology has constantly evolved. However, the safety of the method has often been sacrificed to increase its effectiveness. Or vice versa. A compromise has been found in a new principle of distributing laser radiation to the tissue. It should be noted that the types of lasers have remained the same: erbium, carbon dioxide, neodymium. This suggests that:

• Firstly, laser skin reshaping is recognized as the most effective today;
• secondly, the breadth of coverage of aesthetic and dermatological problems resolved by these methods is extremely large - from skin rejuvenation to the treatment of congenital and acquired skin pathologies;
• Thirdly, with the advent of fractional technologies, the safety and effectiveness of treatment have become predictable.