Fractional laser technology: a compromise between efficiency and safety

Today, in the arsenal of modern dermatocosmetology, there is a fairly wide range of methods for correcting various cosmetic imperfections of the skin - chemical peels, mechanical dermabrasion, laser resurfacing, microdermabrasion, contour plastics, andother. Nevertheless, new directions and technologies in the beauty industry are constantly developing and improving.

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

Modern techniques of skin reshaping

We live in a time when more people are living to old age than ever before. And since many of them go on with their active lives, one of the most important issues in aesthetic medicine is the fight against skin aging.

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

In this case, what method should be used to influence the skin and what must be done for its true rejuvenation?

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

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

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

Chemical stimulation

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

However, to achieve the desired result, the peel must sacrifice the epidermis. Experiments with burns have misled many people, allegedly "proving" that the epidermis is a self-renewing organ that recovers quickly from damage. zoned. In this regard, peels until a certain time became more and more aggressive towards the epidermis (for example, deep phenolic peel), until finally the accumulated problems made specialists aware of the nastiness ofthis is a method which ultimately leads to thinning of the skin.

Proponents of the deep peel have ignored the emerging issues. Their essence was that due to the destruction of the papillae of the dermis and the weakening of nutrition, the epidermis becomes thinner, and the number of cells in the spinous layer is significantly reduced in comparison with what was before peeling. A decrease in the barrier function of the stratum corneum leads to a decrease in skin hydration. (Therefore, almost all patients after a deep peel for a long time experience severe dryness of the skin) At the same time, the introduction into practice of lighter peels (using trichloroacetic acids and fruits) did notlived up to their hopes of effectively firming the skin.

Mechanical stimulation

Among the methods of mechanical stimulation of involutive changes in the skin, dermabrasion using rotary devices (with a speed of v; rotation of knives 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, since the procedure requires anesthesia, postoperative treatment of the wound surface, special toilet for the eyes and mouth, as well as devices for feeding patients (due to the fact that the pronounced postoperative edema that occurs 2 to 3 days after the procedure makes it difficult to open the 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 knife penetrates through the basement membrane;
• wound surface infection;
• scarring (if the knife 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 minimally traumatic removal of the surface layer of the skin with the help of a carbon dioxide laser stimulates the synthesis of its own collagen, the amount of which increases several times after the procedure. Then it is gradually reorganized.

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

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

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 promotes the synthesis of new, oriented collagen [5]. Developed fibrosis can make the skin unusually pale. The collagen synthesized after treatment is reabsorbed after a few years, like any collagen formed on the site of the scar. As a result of the thinning of the epidermis caused by the atrophy of the papillary layer of the dermis, fine wrinkles begin to appear on the skin. Due to the weakening of the barrier function of the stratum corneum, the level of hydration of the skin decreases and it appears atrophic.

Erbium-aluminum-yttrium garnet-erbium lasers appeared a little later. The advantages of an erbium laser such as a shallower thermal penetration depth (erbium lasers penetrate to a depth of 30 μm, CO2 lasers - up to 150 μm) and (accordingly) the lower risk of tissue burns and charring, as well as the relatively low price (compared to carbon dioxide lasers), has attracted the attention of many scholars around the world.

Nevertheless, as experience of working with these two types of installations accumulates, the opinion of specialists has developed 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. In addition, it can be considered as an alternative to surgical skin tightening - of all the methods of its remodeling, only exposure to a CO2 laser can actually cause collagen contraction with visible clinical lifting effect.

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

This concept has contributed to the emergence of a 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 their action - selective photothermolysis - consists in heating and destroying structures, containing a sufficient amount of melanin or oxyhemoglobin. In the skin, these are respectively accumulations of melanocytes (lentigo, melasma) and microvessels (telangiectasia). The emitted wavelengths used in non-ablative lasers correspond to the maxima of the absorption spectra of oxyhemoglobin or melanin. The treatment procedure with non-ablative lasers and IPL is quite safe, the rehabilitation period is minimal, however, such treatment eliminates only pigmentary and vascular cosmetic defects. In this case, there is some thickening of the skin, but the effect obtained is short-lived.

Fractional skin reshaping techniques

The constant search for new highly effective and at the same time safe methods of skin rejuvenation has led to the emergence of a revolutionary technology - fractional distribution of laser radiation. The proposed skin rejuvenation method has been 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 make it possible to achieve its selective microscopic thermal damage in the form of numerous altered columns and leave areas. intact around these micro-wounds. Currently, the industry produces two types of fractional lasers: non-ablative and ablative.

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

As a result, approximately 15 to 35 skins are photocoagulated on the treated area. The chromophore of the laser 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 small volume of lesions and the short distance of migration of keratinocytes. The healing period is accompanied by moderate edema and hyperemia, followed by desquamation, appearing on the 5th to 7th day. The patient hardly loses social activity.

This technology - fractional photothermolysis (FF) - is a very effective method of non-ablative fractional skin remodeling. To achieve the desired effect, treatment of course is prescribed. Depending on the clinical situation, it is recommended to perform 3-6 procedures with an interval of 4-6 weeks. As with any other method of non-ablative skin remodeling, the final result is not visible until 4 to 8 months after the operation (cumulative effect).

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

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

Thus, during this procedure, the laser radiation, penetrating into the deep layers of the skin, destroys the upper layer of the epidermis. In terms of effectiveness, fractional ablative laser rejuvenation can be compared to plastic surgery, it's how deep the laser beam resurfaces.

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

As in the case of FF, 15 to 35% of the skin in 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 the stratum corneum remain intact. Bleeding from the skin is observed for some time immediately after the procedure, but it stops quickly (Fig. 3 a, b).

Fig. 3. Step by step skin restoration after fractional ablation procedure: see immediately after treatment (a); every other day (b); after 5 days (c); 14 days (d) after a

procedure

Numerous micro-bleeds appear in the dermis, which induce a complex cascade of changes leading to the production of new collagen. After the bleeding has stopped, it is necessary to remove the serous fluid remaining on the surface of the skin. Its release is observed within 48 hours after the procedure, until complete epithelialization of microablative areas occurs. During this period, the patient uses special external agents for wound healing. Usually begins between 3-4 days the scaling and swelling increase (Fig. 3c). On the 7th day, these phenomena gradually disappear and erythema remains the only perceptible side effect (Fig. 3d). The duration of the erythema depends on the parameters of laser exposure and the characteristics of the skin vasculature. According to the author's observations, the erythema lasts no more than 3 months.

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

To avoid scarring and the manifestation of post-inflammatory pigmentation, it is necessary to take care of the skin. Decorative cosmetics can be used from 4 to 5 days. A prerequisite for a good result is the use for at least 3 months after the procedure of sun 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 higher in patients with skin IV-V phototypes. Such hyperpigmentation is transient in nature and can last from 1 week to 3 months, which also depends on the depth of the treatment and the area of ​​the treated area. For its prevention 1 to 2 weeks before the intervention and for 2 weeks later, external agents based on hydroquinone (4%) and tretinoin (0, 1%) are prescribed. The main effects on the skin of the face after the AF procedure are: pronounced firming and reduction of excess skin, surface leveling, wrinkled skin, as well as skin affected by acne scars, reduction of discolouration, porosity.

This method has been tested by the author and his colleagues also to remove stretch marks from the skin. As clinical studies show, the method has been shown to be highly effective in removing almost all types of stretch marks, both acquired in the puberty period and postpartum. At the same time, it has been noted that the healing processes on the skin of the body are different from those on the skin of the face.

Mechanism of skin remodeling when using fractional lasers

Consider the mechanisms of skin remodeling when using fractional lasers.

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

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

It should be noted that the 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 change that is never too wild.

A completely different picture is observed after exposure to the fractional ablation laser. The trauma caused by this laser ruptures blood vessels, and blood cells, along with serum, are released into the surrounding tissues. Full skin regeneration mechanism - phase alteration begins - aseptic inflammation develops. Platelets released from damaged vessels play an important role in activating blood clotting and releasing chemotoxic factors which in turn attract other platelets, leukocytes and fibroblasts. Leukocytes, in particular neutrophils, participate in the cleansing of destroyed tissues, by removing fragments of necrotic tissue, which are partially destroyed by phagocytitis, and partially come out on the skin surface in the form of microscopic debris consisting of epidermal tissue substrates anddermal and melanin - microepidermal necrotic debris (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 inverse influence. Keratinocytes stimulate the growth of the epidermis and the release of growth factors necessary to stimulate the production of collagen by the fibroblasts. In this phase, new blood vessels are formed and the extracellular matrix is ​​formed intensively.

The last stage of restorative healing after fractional laser exposure lasts for several months.

By the 5th day after injury, the fibronectin matrix "fits" along the axis along which fibroblasts are aligned and along which collagen will be built. An important role in the formation of this matrix is ​​played by the transformation of growth factor β (TGF-β is a chemotoxic agent for fibroblasts), as well as other growth factors. The main form of collagen in the early phase of wound healing is type III collagen (this type of collagen is located in the top layer of the dermis, just below the basal layer of the epidermis). The longer the deterioration phase, the more type III collagen will be produced, but in any case, its amount increases at most 5 to 7 days after the damage. Type III collagen is gradually replaced by collagen over about a year Type I, which builds the strength of the skin. Blood circulation is gradually normalized, the skin becomes smoother and acquires a natural color.

Comparative analysis of laser skin remodeling methods

To summarize the above, here is a diagram showing the relationship between the effectiveness and safety of laser skin reshaping techniques.

Benefits of fractional pathway rejuvenation methods. The advantages of fractional methods used in clinical practice include:

• has controlled minimal skin damage. Histological studies performed 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, it 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;
• the ability to perform the procedure in 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 fractional photothermolysis, only local application 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 are ruptured in so many places that their restoration is impossible).

Main indications for fractional treatments

Indications for fractional photothermolysis:

• increase in skin density in the early stages of aging. The FF procedure is relatively straightforward 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;
• stretch marks.

Indications for fractional ablation:

• wrinkles of varying severity - fine to strongly pronounced lines (in the form of furrows);
• age-related loss of elasticity and firmness of the skin;
• excess skin in the eyelids, neck, face (as an alternative to plastic surgery);
• uneven skin texture;
• pronounced photoaging of the skin;
• acne scars;
• scar deformation of the skin after injuries, operations;
• hyperpigmentation: melasma, lentiginosis, speckled pigmentation, etc.
• vascular dyschromia;
• skin stretch marks;
• 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 have started to pay more attention to the safety of medical procedures using lasers. Technology constantly evolved. However, in many cases the safety of the method has been sacrificed in order to increase its effectiveness. Or vice versa. A compromise has been found in a new principle of delivering laser radiation to tissue. It should be noted that the types lasers remained the same: erbium, carbon dioxide, neodymium. This suggests that:

• first of all, laser skin remodeling is recognized as the most effective today;
• secondly, the scope of coverage of aesthetic and dermatological problems solved by these methods is extremely broad - from skin rejuvenation to treatment of congenital and acquired skin pathologies;
• Third, with the advent of fractional technologies, the safety and efficacy of treatment has become predictable.