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 aesthetic imperfections of the skin - chemical peeling, mechanical dermabrasion, laser cutting, microdermabrasion, contour plastics, etc. Nevertheless, new directions and technologies in the beauty industry are constantly evolving and improving.

This trend is particularly characteristic of hardware methods, primarily laser medicine. The application of lasers, first in dermatology and then in cosmetology, has an impressive period. More than 25 years have passed since the appearance of one of the newest methods of laser treatment - selective photothermolysis. The pioneers of this field, the Americans RR Anderson and JA Parrish, predetermined the fate of fractional lasers in medicine, making them necessary in the treatment of such aesthetic skin imperfections as capillary hemangiomas. Onion spots, hypertrichosis, tattoos, rosacea, pigmentation disorders, aging, wrinkles, etc.

Modern skin rejuvenation techniques

We live in a time when more people are living to old age than ever before. And since many of them continue to live an active life, one of the most important problems of aesthetic medicine is the fight against skin aging.

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

What methods should be used to affect the skin and what should happen in it for its actual rejuvenation?

All methods that can be applied 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 tightening and compression.

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, needle trimming;
• thermal stimulation - laser ablation, thermal lifting with lasers and broadband light sources, radio frequency lifting, fractional methods.

Chemical stimulation

Historically, acid peels were 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 the fibroblasts and structures of the dermis. This damage activates the inflammatory reaction (the more powerful, the greater the volume of destruction itself), which leads to additional production of collagen in the skin.

However, in order to achieve the desired result, the peeling must sacrifice the epidermis. Experiments with burns have misled many, allegedly "proving" that the epidermis is a self-healing organ that recovers quickly from damaged areas. In this regard, peeling until it becomes more aggressive towards the epidermis for a while (for example, deep phenolic peeling), until finally accumulated problems make experts understand the evil of this method, which eventually leads to thinning of the skin.

Proponents of deep peels have ignored the problems. Their essence was that, thanks to the destruction of the papilla of the dermis and the weakening of nutrition, the epidermis becomes thinner, and the number of cells in the occipital layer is significantly reduced in relation to what was before the peeling. Decreasing the function of the stratum corneum barrier leads to a decrease in skin hydration. (Therefore, almost all patients experience severe dryness of the skin for a long time after deep peeling). At the same time, the introduction of lighter peels (using trichloroacetic and fruit acid) did not fulfill the hopes placed on them for effective skin tightening.

Mechanical stimulation

Of the methods of mechanical stimulation of involutional changes on the skin, special attention deserves dermabrasion using rotary devices (with speed v; cutter rotation up to 100, 000 rpm). Modern Schumann-Schreus devices (Germany)

are currently used

The method can be used only in a surgical hospital, because the procedure requires anesthetic help, postoperative treatment of the wound surface, special toilet for eyes and mouth, as well as feeding devices for patients (due to the fact that pronounced postoperative edema occurs 2-3 days afterthe 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;
• appearance of areas of depigmentation due to destruction of melanocytes when the incisor penetrates the basement membrane;
• superficial wound infection;
• scars (if the cutter is deep in the skin)

All of the above has established a limited application of this method in clinical practice.

Thermal stimulation

Relative remodeling <strong <

Since the late 1980s, laser has been used to rejuvenate the skin by removing (ablating) layer by layer [4]. Careful, slightly 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 reorganized.

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

Sl. 1. Scheme of traditional laser skin rejuvenation (laser dermabrasion)

However, the CO2 laser also causes a number of complications. In addition, further research has 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-oriented collagen [5]. Developed fibrosis can make the skin look unnaturally pale. Collagen synthesized after treatment is resorbed after a few years, as is any collagen formed at the site of the scar. As a result of thinning of the epidermis caused by atrophy of the papillary layer of the dermis, small wrinkles begin to appear on the skin. Due to the weakening of the barrier function of the corneal stratum, the level of skin hydration decreases and it looks atrophic.

Erbium-aluminum-yttrium-garnet-erbium lasers appeared somewhat later. Such advantages of erbium lasers as shallow depths of thermal penetration (erbium lasers penetrate to a depth of 30 µm, CO2 lasers - up to 150 µm) and (as a consequence) lower risk of burns and tissue carbonization, as well as relative cheapness compared to carbon dioxide lasers), have attracted the attention of many experts around the world.

However, as the experience of working with these two types of installations gathers, the opinion has developed among experts that CO2 lasers are more efficient [6]. Despite the negative effects of laser carbon dioxide dermabrasion described above, this method remains indispensable for correcting acne scars. In addition, it can be considered an alternative to surgical skin tightening - of all the methods of its remodeling, only exposure to CO2 laser can actually cause a pronounced contraction of collagen with a visible clinical lifting effect.

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

This concept has 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 their action - selective photothermolysis - consists in heating and destroying buildings, which contain a sufficient amount of melanin or oxyhemoglobin. Namely, in the skin, these are clusters of melanocytes (lentigo, melasma) and microhangers (telangiectasias). The emitted wavelengths used in non-ablative lasers correspond to the maxima of the absorption spectra of oxyhemoglobin or melanin. The procedure of treatment with non-ablative lasers and IPL is quite safe, the rehabilitation period is minimal, however, such treatment eliminates only pigment and vascular cosmetic defects. In this case, there is a certain thickening of the skin, but the effect obtained is short-lived.

Partial skin remodeling 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 delivery of laser radiation. The proposed method of skin rejuvenation is 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 certain depth, fractional methods allow it to achieve its selective microscopic thermal damage in the form of numerous modified pillars and leave undeveloped areas around these micro-wound. 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. Fractionated laser forms in the skin thousands and tens of thousands of microdamases in the form of pillars - microthermal treatment zone (MLZ) - diameter 70-150mk depth up to 1359 mcm

As a result, about 15-35 skin photocoagulates in the treated area. The chromophore for a 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. Recovery of the epidermis is rapid due to the small volume of the lesion and the short path of keratinocyte migration. The healing period was accompanied by moderate edema and hyperemia, followed by desquamation, and appeared 5-7. days. The patient practically does not lose social activity.

This technology - fractional photothermolysis (FF) - is a very effective method of non-ablative fractional skin remodeling. To achieve the desired effect, a course of treatment is prescribed. Depending on the clinical situation, it is recommended to perform 3 to 6 procedures with an interval of 4-6 weeks. As with any other method of non-ablative skin remodeling, 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 - to remove scars, remove deep wrinkles and excess skin, the method of fractional ablation (FA or fractional deep dermal ablation -FDDA) is used.

The fractional ablation method combines the advantages of CO2 laser and the principle of laser fraction. Unlike traditional CO2 lasers, which remove the entire surface layer of the skin, FA units make up a huge number of microablative zones (MAL) with a diameter of up to 300 µm at an evaporation depth of 350 to 1800 µm (Fig. 2).

Therefore, during this procedure, laser radiation, penetrating into 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, here is how a deep laser beam is lifted.

Sl. 2. Principle of operation of ablation fractional laser: formation of microablature zones - MAZ (a); the dependence of the depth of MAZ formation 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 FA procedure is faster than after layer-by-layer ablation. This is due to the fact that the epidermis and stratum corneum remain intact. Bleeding on the skin is noticed for some time immediately after the procedure, but soon stops (Fig. 3 a, b).

Sl. 3. Step-by-step skin regeneration after fractional ablation procedure: examination immediately after treatment (a); every other day (b); after 5 days (c); 14 days (d) after one procedure

Numerous microblems appear in the dermis that induce a complex cascade of changes leading to the production of new collagen. Once the bleeding has stopped, it is necessary to remove the serous fluid that remains on the surface of the skin. Release was observed within 48 hours after the procedure, until complete epithelialization of the microablative zones occurred. During this period, the patient uses special external means for wound healing. It usually starts with 3-4 days of peeling and the swelling increases (Fig. 3 c). By day 7, these phenomena gradually decrease, and erythema remains the only noticeable side effect (Fig. 3d). The duration of erythema depends on the parameters of laser exposure and the characteristics of skin vascularization. According to the authors, erythema lasts no more than 3 months.

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

To prevent scarring and the manifestation of post-inflammatory pigmentation, it is necessary to carefully caress the skin. Decorative cosmetics can be used from 4-5 days. A prerequisite for a good result is the use of at least 3 months after the procedure of sunscreen 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 treatment and the area of ​​the treated area. For its prevention 1-2 weeks before the procedure and for another two weeks after it, external agents based on hydroquinone (4%) and tretinoin (0. 1%) are prescribed. The main effects on facial skin after the FA procedure are as follows: pronounced tightening and reduction of excess skin, smoothing of the surface of wrinkled skin, as well as skin affected by acne scars, reduction of dyschromia, porosity.

This method has been tested by both the author and his colleagues to remove stretch marks on the skin. As clinical studies show, the method has shown high efficiency in removing almost all types of stretch marks, both obtained during puberty and after childbirth. It has been noticed that the healing processes on the skin of the body are different than 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 formed micro-wounds. The more aggressive the exposure, the more pronounced the inflammatory response, which, in fact, stimulates the post-traumatic release of growth factors and the infiltration of damaged tissues by fibroblasts. The incoming reaction is automatically accompanied by a torrent of cellular activity, which inevitably leads to the fact that fibroblasts begin to produce more collagen and elastin. The skin remodeling process involves three classic phases of regeneration:

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

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

A completely different picture was observed after fractional ablation laser exposure. The trauma caused by this laser destroys the blood vessels, and the blood cells are released into the surrounding tissue together with the serum. A full-fledged mechanism of skin regeneration - the change of phases begins - aseptic inflammation develops. Platelets released from damaged blood vessels play an important role in activating blood clotting and releasing chemotoxic factors which, in turn, attract other platelets, leukocytes and fibroblasts. Leukocytes, especially neutrophils, participate in the cleansing of destroyed tissue, removing fragments of necrotic tissue, which are partially destroyed by phagocytitis, and partially rise to the skin surface in the form of microscopic fragments consisting of substrates of epidermal and dermal tissue and melanin - microepieronal.

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. Keratinocyte stimulates the growth of the epidermis and the release of growth factors necessary to stimulate collagen production by fibroblasts. In this phase, new blood vessels are formed and the extracellular matrix is ​​intensively formed.

The last, reconstructive phase of healing after fractional exposure to lasers lasts several months.

By day 5 after injury, the fibronectin matrix “fits” along the axis along which the fibroblasts are positioned and along which collagen will build. An important role in creating this matrix is ​​played by the transformation of growth factor β (TGF-β is a potent 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 upper layer of the dermis, just below the basal layer of the epidermis). The longer the exchange 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 damage. Type III collagen is gradually replaced by type I collagen in about a year, which strengthens the skin. Blood circulation gradually normalizes, the skin becomes smoother and takes on a natural color.

Comparative analysis of laser skin rejuvenation methods

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

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

• controlled minimal skin damage. Histological examinations performed after the procedure show an increase in the number of papillae in the dermis, which characterizes the changes in the skin as a productive regeneration;
• its effective rejuvenation: the skin becomes thicker, significantly (more than 400% (! )) increases the production of collagen and elastin;
• short healing time: average 3 days after FF and 7-14 days after PA;
• minimal risk of hyperpigmentation;
• the ability to perform the procedure on patients with thin skin;
• ability to heal on any part of the body;
• possibility of using light types of anesthesia: with fractional photothermolysis only local application anesthesia is used; fractional ablation requires a combination of conduction and infiltration anesthesia;
• disappearance of telangiectasia (due to the fact that there is a rupture of blood vessels 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 simple and can be applied without fear. The therapeutic effect can be shown on the neck, décolleté, arms, abdomen, thighs, mammary glands;
• skin aging;
• hyperpigmentation, melasma;
• hypertrophic scars;
• stretch marks.

Indications for fractional ablation:

• wrinkles of different weights - from fine lines to strongly pronounced (in the form of furrows);
• loss of elasticity and firmness of the skin associated with age;
• excess skin on eyelids, neck, face (as an alternative to plastic surgery);
• uneven skin texture;
• pronounced photoaging of the skin;
• acne scars;
• cicatricial skin deformity after injury, surgery;
• hyperpigmentation: melasma, lentiginosis, spicy pigmentation, etc.
• vascular dichromia;
• stretch marks on the skin;
• actinic keratosis.

In conclusion, a few words about the prospects for the use of laser technologies in aesthetic medicine. We must pay tribute to the manufacturers that they have begun to pay more attention to the safety of medical procedures using lasers. Technology is constantly evolving. However, very often the safety of the method has been sacrificed in order to increase its efficiency. Or vice versa. A compromise was found in the new principle of delivery of laser radiation to tissue. It should be noted that the typovilasers remained the same: erbium, carbon dioxide, neodymium. This suggests that:

• first, laser skin remodeling is recognized as the most effective today;
• secondly, the breadth of coverage of aesthetic and dermatological problems that solve these methods is extremely large - from skin rejuvenation to the treatment of congenital and acquired skin pathologies;
• third, with the advent of fractional technologies, the safety and efficacy of treatment have become predictable.