Fractional laser technology: a trade-off between efficiency and safety

Today in the arsenal of modern dermatocosmetology there is a wide range of methods for correcting various aesthetic imperfections of the skin - chemical peels, mechanical dermabrasion, laser reflection, microdermabrasion, contour plastics and more. However, new trends and technologies in the beauty industry are constantly evolving and improving.

This trend is particularly typical of hardware methods, especially laser medicine. The use of lasers, first in dermatology and then in cosmetology, has had an impressive period. More than 25 years have passed since the appearance of one of the newest methods for laser treatment - selective photothermolysis. 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 aesthetic skin imperfections as capillary hemangiomas. 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. And given that many of them continue to live an active life, one of the most important problems in aesthetic medicine is the fight against aging skin.

Plastic surgery is able to rejuvenate the shape of the face by removing excess skin. At the same time, the skin still remains altered by time (age-related aging) or external factors (photo aging). It is also important that most patients want 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 real 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, provoking fibrosis, which further leads to its tension and thickening.

Dermatocosmetology currently uses three main types of remodeling effects on the skin, including:

• chemical stimulation - chemical peeling with acids (trichloroacetic, glycolic, etc. );
• mechanical stimulation - mechanical dermabrasion, microdermabrasion, mesotherapy, fillers, needle trimming;
• thermal stimulation - laser ablation, thermolifting with the help of laser and broadband light sources, radiofrequency lifting, fractional methods.

Chemical stimulation

Historically, acid exfoliant (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 production of collagen in the skin.

However, in order to achieve the desired result, the peeling must sacrifice the epidermis. Burning experiments have deceived many, claiming that they "prove" that the epidermis is a self-renewing organ that recovers quickly over the damaged area. In this regard, peeling for some time becomes more aggressive to the epidermis (for example, deep phenolic peeling), until finally the accumulated problems made experts realize the viciousness of this method, which ultimately leads to thinning of the skin.

Proponents of deep peels have ignored the 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 prickly layer is significantly reduced compared to what it was before peeling. The reduction of the barrier function of the stratum corneum leads to a decrease in skin hydration. (Therefore, almost all patients experience severe dryness of the skin for a long time after deep peeling). >

Mechanical stimulation

Of the methods for mechanically stimulating involutional changes in the skin, dermabrasion with the use of rotating devices (with speed v; rotation of incisors 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, as the procedure requires anesthesia, postoperative treatment of the wound surface, a special toilet for the eyes and mouth, and feeding devices for patients (due to the fact that the pronounced postoperative edema, which isappears 2-3 days after the procedure, makes it difficult to open the eyes and mouth).

The method is very effective, but unfortunately in 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 incisor penetrates the interstitial membrane;
• wound surface infection;
• scars (if the incisor is too deep in the skin)

All of the above has 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) layer by layer (4) [4]. Careful, low-trauma removal of the surface layer of the skin with the help of a carbon dioxide laser stimulates the synthesis of its own collagen in it, ie the amount of which increases several times after the procedure. It is then 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 by the effect of skin tightening. The method is called "laser dermabrasion" or "laser development" and in terms of effectiveness it could not be opposed to any other method of skin rejuvenation existing at that time (Fig. 1).

FIG. 1. Scheme of traditional laser skin respiration (laser dermabrasion)

However, the CO2 laser also causes a number of complications. In addition, further research shows 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, normally oriented collagen [5]. Developed fibrosis can make the skin look unnaturally pale. Collagen synthesized after treatment is absorbed after a few years, like 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, fine wrinkles begin to appear on the skin. Due to the weakening of the barrier function of the stratum corneum, the level of skin hydration decreases and appears atrophic.

Erbium-aluminum-yttrium garnet-erbium lasers appeared a little later. Such advantages of the erbium laser as a smaller depth of thermal penetration (erbium lasers penetrate to a depth of 30 μm, CO2 lasers - up to 150 μm) and (as a result) a lower risk of burns and tissue carbonization, as well as the relativecheapness (compared to carbon dioxide lasers) has attracted the attention of many professionals around the world.

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

The problem with all the methods described above is that they often "sacrifice", ie significantly damage the epidermis. To rejuvenate your skin and really look young, you need a perfect epidermis with natural papillae of the dermis, 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 protection against the effects 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 non-ablative skin reshaping devices 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 destruction of structures, ie containing a sufficient amount of melanin or oxyhemoglobin. In the skin, these are, respectively, accumulations of melanocytes (lentigo, melasma) and microvesules (telangiectasias). The emitted wavelengths used in non-ablative lasers correspond to the maxima 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, but such treatment eliminates only pigment and vascular defects. In this case, there is some thickening of the skin, but the effect is short-lived.

Techniques for partial skin remodeling

The constant search for new highly effective and at the same time safe methods for skin rejuvenation has led to the emergence of a revolutionary technology - partial 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 multiple altered columns and leave unaffected areas around these microwounds. Currently, the industry produces two types of fractional lasers: non-ablative ablative.

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

As a result, about 15-35 skin is photocoagulated on the treated area. The chromophore for the laser is water, the coagulation takes place 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 keratinocytes. The treatment period is accompanied by moderate edema and hyperemia, followed by desquamation, which appears on the 5th-7th day. The patient practically does not lose social activity.

This technology - fractional photothermolysis (FF) - is a highly effective method for 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 required - to correct 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 fractional principle of laser radiation supply. Unlike traditional CO2 lasers, which remove the entire layer of skin layer by layer, FA devices form a huge number of microablative zones (MAL) up to 300 µm in diameter at an evaporation 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 efficiency, ablative fractional laser rejuvenation can be compared to plastic surgery, ie how deep the laser beam appears.

FIG. 2. The principle of operation of the ablative fractional laser: the formation of microablative zones - MAZ (a); dependence of the depth of MAZ formation 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 actually exposed (in some cases up to 70%). Recovery after the FA procedure is faster than after ablation from layer to layer. This is due to the fact that a significant part of the epidermis and stratum corneum remains intact. Cutaneous bleeding was observed for some time immediately after the procedure, but soon stopped (Fig. 3 a, b).

FIG. 3. Gradual recovery of the skin after the fractional ablation procedure: examination immediately after treatment (a); every other day (b); after 5 days (s); 14 days (d) after one procedure

Numerous microblots appear in the dermis, causing 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 left on the surface of the skin. Its release is observed within 48 hours after the procedure, until complete epithelialization of the microablative areas occurs. During this period, the patient uses special means to heal wounds. It usually starts from 3-4 days of peeling and the swelling increases (Fig. 3 c). By the 7th day, these phenomena gradually subside and erythema remains the only noticeable side effect (Fig. 3d). The duration of erythema depends on the parameters of laser exposure features of vascularization of the skin. According to the author's observations, erythema lasts no more than 3 months.

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

Careful skin care is needed to prevent scarring and post-inflammatory pigmentation. Decorative cosmetics can be used for 4-5 days. A prerequisite for a good result is the use of strain 3 months after the procedure of sunscreen 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 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 prophylaxis 1-2 weeks before the procedure and for another 2 weeks after it, external means based on hydroquinone (4%) and tretinoin (0. 1%) are prescribed. The main effects on facial skin after the FA procedure are the following: strong tightening and reduction of excess skin, smoothing of the surface wrinkled skin, as well as skin affected by acne scars, reduction of dyschromia, porosity.

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

Skin remodeling mechanism using fractional lasers

Let's look at the mechanisms of skin remodeling 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 the inflammatory reaction, which actually stimulates the post-traumatic release of growth factors and infiltration of damaged tissues by fibroblasts. The approaching reaction is automatically accompanied by a breakdown 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 failure;
• 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 harmful effect of the laser is moderately aggressive, resulting in a cascade of inflammation. The change is never too wild.

After exposure to the fractional ablation laser, a completely different picture is observed. The trauma caused by this laser destroys blood vessels, and blood cells, along with serum, are released into the surrounding tissue. The full mechanism of skin regeneration - a phase change 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, especially neutrophils, are involved in cleansing the destroyed tissue, removing fragments of necrotic tissue that are partially destroyed by phagocytes, and partially emerge on the surface of the skin in the form of microscopic fragments consisting of epidermal and dermal tissue substrates and melanin. microepidermal necrotic debris (MENO).

The proliferative phase begins after 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 be under the opposite influence. Keratinocyte stimulates the growth of the epidermis and the release of growth factors needed to stimulate collagen production by fibroblasts. In this phase, new blood vessels are formed and the extracellular matrix is ​​intensively formed.

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

By the 5th day after injury, the fibronectin matrix "fits" along the axis along which the fibroblasts are arranged and along which the collagen will be built. An important role in the formation of this matrix is ​​played by the transforming 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 early phase of wound healing is collagen type III (this type of collagen is located in the upper layer of the dermis, just below the basal layer of the epidermis). The longer the phase of change, the more type III collagen will be produced, but in any case its amount increases to a maximum of 5 to 7 days after injury. Type III collagen is gradually replaced by collagen within about a year Type I, which enhances skin strength. 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 the methods for partial rejuvenation of the tracks. The advantages of fractional methods used in clinical practice include:

• controls minimal skin damage. Histological examinations performed after the procedure showed an increase in the number of papillae in the dermis, which characterized the changes in the skin as 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 in patients with thin skin;
• the ability to have a healing effect on any part of the body;
• the possibility to use light types of anesthesia: in fractional photothermolysis only local anesthesia is used, for fractional ablation a combination of conductive and infiltration anesthesia is required;
• disappearance of telangiectasias (due to the fact that there is a rupture of blood vessels in so many places that their recovery is impossible).

Basic indications for partial treatment

Indications for fractional photothermolysis:

• increase in skin density in the early stages of aging. The FF procedure is relatively easy and can be applied 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.

Fractional ablation readings:

• wrinkles of varying severity - from fine lines to pronounced (in the form of furrows);
• 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;
• scarring of the skin after injuries, operations;
• hyperpigmentation: melasma, lentiginosis, spots with pigmentation, etc.
• vascular dyschromia;
• stretch marks on the skin;
• actinic keratosis.

In conclusion, a few words about the prospects for the use of laser technology in aesthetic medicine. We must pay tribute to the manufacturers that they have begun to pay more attention to the safety of medical procedures with the help of lasers. Technology was constantly evolving. However, quite often the safety of a method is sacrificed to increase its effectiveness. Or vice versa. A compromise was found in a new principle for delivering laser radiation to tissues. It should be noted that the types of lasers remained the same: erbium, carbon dioxide, neodymium. This assumes that:

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