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 peels, mechanical dermabrasion, laser resurfacing, microdermabrasion, contour plastics and others. However, 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 and then in cosmetology, has an impressive period. Even after the emergence of one of the newest laser treatment methods - selective photothermolysis - more than 25 years have passed. The pioneers of this direction, the Americans RR Anderson and JA Parrish, predetermined the fate of fractionated lasers in medicine, making them indispensable in the treatment of such aesthetic skin imperfections such as capillary hemangiomas. Port wine stains, hypertrichosis, tattoos, rosacea, pigmentation disorders, photoaging, wrinkles, etc.

Modern skin remodeling techniques

We live in an age where more people are living to old age than ever. And given that many of them continue active lives, one of the most important problems of aesthetic medicine is the fight against 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 by external factors (photoaging). It is also important that most patients wish to look younger without surgery.

In this case, what method should be used to affect the skin and what should happen in it 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 reshaping effects on the skin, including:

• chemical stimulation - chemical peels with acids (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, 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 triggers an inflammatory reaction (the more powerful, the greater the volume of the destruction itself), which leads to further production of collagen in the skin.

However, to achieve the desired result, the peel must sacrifice the epidermis. Experiments with burns have misled many, presumably "proving" that the epidermis is a self-renewing organ that quickly recovers on the damaged area. In this regard, peelings until some time became more and more aggressive towards the epidermis (for example, deep phenolic peeling), until finally the accumulated problems made the specialists understand the nastiness of this method that ultimately leadsthinning of the skin.

Advocates of deep peeling have ignored emerging problems. 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 deep peeling for a long time experience severe dryness of the skin) At the same time, the introduction into the practice of lighter peels (using trichloroacetics and fruit acids) did not live up to their hopes ofeffectively firm the skin.

Mechanical stimulation

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

are currently used

The method can only be used in a surgical hospital, since the procedure requires anesthesia, postoperative treatment of the wound surface, a special toilet for the eyes and mouth, as well as devices for nursing patients (due to the factthat pronounced postoperative edema occurring 2-3 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 cutter penetrates through the basement membrane;
• wound surface infection;
• scars (if the cutter is too immersed in the skin)

All of the above has resulted in 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 the tissue layer by layer (ablation) [4]. The careful and low-traumatic removal of the superficial layer of the skin using a carbon dioxide laser stimulates the synthesis of its own collagen in it, the quantity of which increases several times after the procedure. Then it is gradually rearranged.

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

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

However, the CO2 laser also causes a large number of complications. Furthermore, further 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 a new, normal oriented collagen [5]. Developed fibrosis can make the skin look unnaturally pale. Collagen synthesized after treatment is reabsorbed after a few years, like any collagen formed at the scar site. As a result of the thinning of 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 barrier function of the stratum corneum, the level of hydration of the skin decreases and appears atrophic.

Erbium-aluminum-yttrium garnet-erbium lasers appeared a little later. Such advantages of an erbium laser as a lower thermal penetration depth (erbium lasers penetrate to a depth of 30 μm, CO2 lasers - up to 150 μm) and (consequently) the lower risk of burnsand carbonization of tissues, as well as their relative cheapness (compared to carbon dioxide lasers), have attracted the attention of many specialists around the world.

However, as experience of working with these two types of installations accumulates, the opinion has developed among specialists 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 an alternative to surgical skin tightening: of all the methods of its reshaping, only exposure to a CO2 laser can actually cause pronounced contraction of collagen with a visible clinical lifting effect.

The problem with all the methods described above is that they often "sacrifice", that is, they significantly damage the epidermis. To rejuvenate your skin and look really young, you need perfect epidermis with natural dermal 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 effects of negative environmental factors. Therefore, whatever we do to rejuvenate the skin, we must ensure that its normal underlying 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 lasers (Nd-YAG) and diodes, as well as broadband light sources (IPL). The principle of their action - selective photothermolysis - consists in the heating and destruction of structures, containing a sufficient amount of melanin or oxyhemoglobin. In the skin, these are, respectively, accumulations of melanocytes (lentigo, melasma) and microvessels (telangiectasias). The wavelengths emitted used in non-ablative lasers correspond to the maxima of the absorption spectra of oxyhemoglobin or melanin. The procedure for non-ablative laser and IPL treatment is quite safe, the rehabilitation period is minimal, however, such treatment eliminates only pigmentary and vascular aesthetic defects. In this case, there is some thickening of the skin, but the effect obtained is short-lived.

Fractional skin remodeling techniques

The constant search for new methods of highly effective and at the same time safe skin rejuvenation has led to the emergence of a revolutionary technology: the fractional delivery of laser radiation. The proposed skin rejuvenation method 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 on the skin at a specific depth, fractional methods allow to obtain its selective microscopic thermal damage in the form of numerous altered columns and leave unaltered areas aroundthese micro wounds. Currently, the industry produces two types of fractional lasers: non-ablative and ablative.

The former 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 microdamages 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 15-35 skin is photocoagulated in 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 and this significantly reduces the risk of infection. Epidermal recovery is rapid due to the low volume of the lesion and the short migration distance of the keratinocytes. The healing period is accompanied by moderate edema and hyperemia, followed by peeling, which appear on the 5-7th day. The patient practically does not lose social activity.

This technology, fractional photothermolysis (FF), is a highly effective method of non-ablative fractional skin remodeling. To achieve the desired effect, a course 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 non-ablative skin remodeling method, the final result can only be seen 4-8 months after the procedure (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 is used (AF, or fractional deep dermal ablation -FDDA).

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

Therefore, during this procedure, the 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, this is how deeply the laser beam resurfaces.

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

As in the case of FF, 15 to 35% of the skin in the treated area is effectively 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 significantpart of the epidermis and stratum corneum remain intact. Skin bleeding is observed for some time immediately after the procedure, but soon stops (Fig. 3 a, b).

Fig. 3. Gradual skin restoration after fractional ablation procedure: visualization 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 that induce a complex cascade of changes that lead to the production of new collagen. After the bleeding has stopped, it is necessary to remove the remaining serous fluid on the surface of the skin. Its release is observed within 48 hours of the procedure, until complete epithelialization of the microablative zones occurs. During this period, the patient uses special external agents for wound healing. Usually it starts from 3-4 days, peeling and swelling increase (Fig. 3 c). By the 7th day, these phenomena gradually subside and erythema remains the only noticeable side effect (Fig. 3d). The duration of the erythema depends on the parameters of exposure to the lasere characteristics of the cutaneous vascularization. According to the author's observations, the erythema lasts no more than 3 months.

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

To prevent scar formation and the manifestation of post-inflammatory pigmentation, it is necessary to take care of the skin with care. Decorative cosmetics can be used for 4-5 days. A prerequisite for a good result is the use of 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 types 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 more than 2 weeks after, external agents based on hydroquinone (4%) and tretinoin (0. 1%) are prescribed. The main effects on the facial skin after the AF procedure are the following: strong firming and reduction of excess skin, leveling of the surface of wrinkled skin, as well as skin affected by acne scars, reduction of discoloration, porosity.

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

Skin remodeling mechanism when using fractional lasers

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

After exposure to the laser, 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 tissues damaged by fibroblasts. The approaching reaction is automatically accompanied by an explosion of cellular activity, which inevitably leads to the fact that the fibroblasts begin to produce more collagen and elastin. The skin remodeling process involves three classic regeneration phases:

• phase I - alteration (inflammation of the tissues). 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. It 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, as a result of which a cascade of inflammationschange is never too wild.

A completely different image is observed after exposure to the fractional ablation laser. The trauma caused by this laser breaks the blood vessels and the blood cells, along with the serum, are released into the surrounding tissue. The actual skin regeneration mechanism - phase alteration begins - aseptic inflammation develops. Platelets released from damaged vessels play an important role in activating blood clotting and in the release of chemotoxic factors which, 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 emerge on the surface of the skin in the form of microscopic debris consisting of substrates of epidermal and dermal tissue and melanin -microepidermal necrotic debris (LESS).

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. Keratinocytistimulate 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 ​​intensively formed.

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

By the 5th day after injury, the fibronectin matrix "adapts" along the axis along which the fibroblasts are aligned and along which the 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 strong chemotoxic reagent for fibroblasts), as well as other growth factors. The main form of collagen in the initial stage of wound healing is type III collagen (this type of collagen is found in the upper layer of the dermis, just below the basal layer of the epidermis). The longer the alteration phase, the greater the production of type III collagen, but in any case its quantity increases at most 5 to 7 days after the injury. Type III collagen is gradually replaced by collagen over about a year. Type I, which strengthens the skin's strength. Blood circulation is gradually normalized, 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 efficacy and safety of laser skin remodeling techniques.

Advantages of Fractional Trace Rejuvenation Methods. The advantages of fractional methods used in clinical practice include:

• controlled for 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, 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 types of light anesthesia: with fractional photothermolysis, only anesthesia for local application is used; a combination of conduction and infiltration anesthesia is required for fractional ablation;
• disappearance of telangiectasias (due to the fact that there is a rupture of the blood vessels 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 simple 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 - from fine to very 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);
• irregular skin structure;
• pronounced photoaging of the skin;
• acne scars;
• scarring deformity of the skin after injuries, operations;
• hyperpigmentation: melasma, lentiginous, spotted pigmentation, etc.
• vascular dyschromia;
• skin stretch marks;
• 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 who have begun to pay more attention to the safety of medical procedures that use lasers. Technology in continuous evolution. However, very often the safety of the method has been sacrificed to increase its effectiveness. Or viceversa. A compromise has been found in a new principle of delivering laser radiation to tissues. It should be noted that the types of lasers remained the same: erbium, carbon dioxide, neodymium. This suggests that:

• First, laser skin remodeling is recognized as the most effective today;
• secondly, the extent of the coverage of aesthetic and dermatological problems solved with these methods is extremely wide: from skin rejuvenation to the treatment of congenital and acquired skin diseases;
• Third, with the advent of fractional technologies, the safety and efficacy of treatment have become predictable.