Microneedling: a review

1 Universidade de Ribeirão Preto, Pós-Graduação Fisioterapia Dermatofuncional, Ribeirão Preto, SP, Brazil. Conflicts of interest: none. Introduction: Microneedling, also called percutaneous collagen induction therapy (PCIT), is a technique applied with an equipment called roller. It is suitable for rejuvenation, alopecia, all types of scars, acne, photo rejuvenation, stretch marks, skin flaccidity, melasma, expression wrinkles, and improvement of the general aspect of the skin. Objective: Perform a literature review to identify the major clinical applications of microneedling. Methods: The research was done from 2009 to 2018, in electronic databases PubMed and Scielo. The studies recovered were described and analyzed. Results: We selected 12 articles and two books for their relevant content. Conclusion: Microneedling is a simple technique, an innovative treatment that has been used for different dermatological pathologies. This method acts by naturally stimulating collagen by responding to the inflammatory process and also by activating the transdermal ingredient access system (TIAS), known as Drug Delivery. ■ ABSTRACT


DISCUSSION
Microneedling is a technique that uses a device called a roller, it consists of a polyethylene roller embedded in sterile stainless steel or titanium needles, its number varies from 190 to 450 needles whose length ranges from 0.5mm to 2.5mm 2,7 .
The 0.25mm and 0.5mm needles are used to deliver drugs in fine wrinkles and to improve the shine and texture of the skin; those of 1.0mm and 1.5mm are used for sagging skin, medium wrinkles and global rejuvenation; those of 2.0mm and 2.5mm are used for distensible depressed scars, stretch marks, wavy and retractable scars 3 .
Regarding the use of anesthetics, sizes from 0.2mm to 0.3mm do not require the use of anesthesia, while sizes from 0.5 to 2.0mm need topical anesthetic and needles from 2.0mm to 2.5mm need general anesthesia 3,8 .
The technique works in two ways: the first one by stimulating the natural production of collagen (NPC) by responding to the inflammatory process and the second by facilitating the Transdermal Ingredient Access System (TIAS), known as "drug delivery," that is, increased permeation of actives 2 .
The stimulus to collagen production begins with the loss of the integrity of the skin barrier, targeting the dissociation of keratinocytes, which results in the release of cytokines such as interleukin, resulting in dermal vasodilation and migration of keratinocytes to restore damage epidermal 1 .
The healing process occurs in three phases: In the first, injury, there is the release of platelets and neutrophils responsible for growth factors with action on keratinocytes and fibroblasts. In the second, neutrophils are replaced by monocytes, and angiogenesis, epithelialization, and proliferation of fibroblasts occur, followed by the production of type III collagen, elastin, glycosaminoglycans and proteoglycans. In the third, maturation, type III collagen, which is predominant in the initial phase of the healing process and which is slowly being replaced by type I collagen, which is more durable, persisting for a period ranging from five to seven years. 7 The mechanism of action of drug delivery is as follows: when rolling the equipment over the skin, microchannels are created, and in this way, the applied cosmetics or formulations permeate the skin much more effectively and quickly. In the literature, there are a range of studies that report the effectiveness of the technique in increasing the permeation of the actives, this can vary from 80% to 500%. Thus, the active ingredients present in the treatment products can reach the deeper parts of the skin with more efficiency than if they were applied only topically 2 .

INTRODUCTION
Microneedling, also called percutaneous collagen induction therapy (PCIT), is a technique applied with a device called roller 1 . The first roller was developed in 1993, in France, by a South African surgeon named Dr. Desmond Fernandes 1 , who is considered the father of microneedling.
This equipment consists of a polyethylene roll that has embedded sterile stainless steel or titanium needles, whose number varies between 190 and 450 needles, according to the manufacturer 2,3 . In the literature, we find some nomenclatures used, being the most appropriate: microneedling, percutaneous collagen induction, CIT (collagen induction therapy or collagen therapy), roller technique, or just roller.
The technique is indicated for rejuvenation, alopecia 4 , all types of scars, acne, photo rejuvenation, stretch marks, sagging skin, melasma, wrinkles, expression lines, and to improve the overall appearance of the skin 1,2,3,5,6 .
Therefore, the objective of this study is to support the clinical applicability of microneedling in the literature.

METHODS
To carry out this study, we have searched the PubMed and Scielo electronic databases, using as keywords: "microagulhamento", "drug delivery" and "microneedlings." The inclusion criteria were: clinical studies on the use of microneedling to treat aesthetic disorders, in Portuguese, English and also textbooks with relevant content, in the period from 2009 to 2018. The exclusion criteria were: experimental work, study of bibliographic review and those that were not related to the topic.
After selecting the studies, the data were organized in a table that considers the following items: identification of the author, year and title of the work, material, treatment location, treatment technique, number of sessions, use of assets after microneedling, anesthetic use, associated resources and complications, evaluation methods, results and conclusions.

RESULTS
The research consisted of 12 articles; five of them were selected and placed in a table for a better understanding of the studies, the other seven were not included in the table because they were experimental, review, master's thesis and course completion papers, however, because present relevant content, were used for the study, in the same way as two more books ( one with movements in four directions: horizontal, diagonal, vertical to the right and left, ten times each 13 ; and an article with repetitions of 10 times in each direction, following the shape of the wind rose 12 . Another proposal recommends that the movements be performed in the same directions, being applied first horizontally in the direction of the lymphatic path, then vertically and finally in one of the diagonals (except for the center of the frontal region and nose, for which it is suggested to use the two diagonal lines) 17 .
The application of the roller should be per quadrant, working in small regions, around twice the width of the roller for facial and capillary areas, and four times for the body. When applying it in four directions (vertical, horizontal, diagonal right, and left), you must pass ten times over each direction, with five reciprocating movements in each one 2 .
Studies have shown the use of various active substances or drugs such as hyaluronic acid and vitamin E 14 , growth factor 8,13 , skin regenerator, hydroquinone 7 , retinoic acid, vitamin C 8 and minoxidil. 4 The results vary according to the therapeutic proposal and the definition of needle sizes ranging from 0.25mm to 2.5mm 3 . In the treatment for alopecia 4 , there was a partial and satisfactory response, applying one treatment only with microneedling and the other together with minoxidil. In the stretch mark study 13, it was shown that the technique is effective in reducing its size in millimeters, the growth factors used helped in the process of collagen formation.
The application in the treatment of wrinkles and acne scars 11 can produce improvement in the quality of the skin, attenuating wrinkles and correcting depressed acne scars. The addition of 88% phenol applied with gauze until substantial bleaching is achieved, followed immediately by microneedling enhances the results for acne scar treatments. 7 Although considered a simple technique with a specialized tool, it can have an "immediate effect" on the improvement of wrinkles, showing after two sessions that they were highly reduced and that the overall aesthetic improvement was also important 11 .
In another article, it shows a slight improvement in atrophic acne scars, in which the increase in hemoglobin is related to the initial tissue injury, providing neocolagenesis. Ice-pick scars did not improve with the procedure 12 .
Concerning the rejuvenation treatment 14 , the author says that the technique is safe and established. Still, to obtain results for advanced global rejuvenation, the action of specific actives for skin rejuvenation in drug delivery is necessary, promoting significant The created microchannels show a retraction after 5 minutes, but their complete closure occurs after 24 hours 9 . And the absence of retraction after 15 minutes has also been reported 10 .
Its use is individual and comes sterilized a t t h e f a c t o r y a n d r e g i s t e r e d i n A N V I S A (Agência Nacional de Vigilância Sanitária). The treatment can be done by several professionals such as physiotherapists, doctors, biomedical, and other professionals in the aesthetic and health area.
The microneedling technique has been used in several aesthetic procedures. The present study consists of 5 articles, namely, an article on the treatment of alopecia4, one on periorbital wrinkles 11 , one on acne scars 12 , one on skin rejuvenation of the anterior chest 13 and one on flaccidity treatment, wrinkles and acne scars on the face 7 .
The microneedling interspersed with 5% retinoic acid peeling at 21-day intervals between sessions was also useful in the treatment of melasma and aging associated with growth factors. It was possible to observe a significant improvement in the two dysfunctions. 8 It also presents promising results for gynoid lipodystrophy; changes in patients' lifestyle and behavioral habits contribute significantly to the success of therapy, as well as the appropriate drug and a correct technique 14 .
The method proved to be effective in the treatment of stretch marks with a reduction in size (millimeters) when they were associated with growth factors. By assisting in the process of collagen formation, it reconstructs the broken fibers, promoting skin filling. The technique does not provide a significant improvement in cases of phototype VI, although the depigmentation process is reversible, it is slow. 15 Comparing the results for the treatment of atrophic acne scars between the non-ablative fractional Erbium laser and microneedling, the degree of posttreatment improvement evaluated by the participants on a scale of 0 to 10, had an average of 7.65 in the microneedling and 7.95 in the laser group. The difference between the groups was not significant, showing that the technique is as effective as fractional technology 5 .
Concerning the correct form of application and prior care with the area to be treated, we analyzed an article that used back and forth movement 4 ; one with horizontal, vertical, diagonal movements, 15 to 20 times each 7 ; one with horizontal, diagonal, vertical movements to the right and left 11 ; one with movements in multiple directions until slight bleeding and four times in all directions until the petechiae appear 8,14 ; improvement in the overall appearance, with minimal adverse effects and high patient satisfaction index.
Regarding the study of rejuvenation and melasma, it is stated that it is essential to carry out more in-depth scientific studies to corroborate the data presented in this work and to be able to evaluate the effectiveness of the therapy 8 .
For the article on gynoid lipodystrophy, it is worth mentioning that it is a promising treatment, significantly contributing to the success of therapy 14 , the choice of an appropriate drug, a correct technique, and changes in patients' lifestyle and behavioral habits.
It can be said that the association of the technique with several actives provided the optimization of results, as well as the low cost and easy application if compared to other treatments on the market. But it is emphasized that there is a need for more research on the topic. Some care must be taken about the application of the technique: the first has to do with the choice of equipment that must be sterile and registered with ANVISA; on the other hand, the skin can be previously cleaned with, for example, alcohol 70% 13 . One article mentions that the skin was disinfected, but does not describe what was used 11 ; in another case, it is said that the procedure was performed after cleaning the face 12 , asepsis with chlorhexidine degermante solution 14 and also the degreasing of the skin with liquid soap and asepsis with chlorhexidine 7 .
Regarding the evaluation criteria used in the studies, photographic records were pointed 4,7,11,12,13 , volunteer satisfaction questionnaires 7,13 , histological analysis 12 , and silicone molds from digitalized photographs to measure the depth of wrinkles 11 . In this way, we can observe that the standardized photographic record before and after the treatment, as well as a satisfaction questionnaire concerning the results found, can be performed because it is easy to apply and low cost CONCLUSION Based on the results found in this review, we can say that microneedling is a simple, promising, and easy to apply technique. This innovative treatment has been used for different dermatological pathologies. The method works in two ways: the first by stimulating natural collagen production (NCP), by responding to the inflammatory process, and the second facilitating the Transdermal Ingredient Access System (TIAS), known as "drug delivery," that is, increasing the permeation of actives.
The technique can be painful, and this is related to the size of the needles. The use of local anesthetics may be indicated in some cases.
However, it is necessary to generate more knowledge with other studies to reach more reliable conclusions regarding the maintenance of long-term results, as well as about the repaired tissue.

COLLABORATIONS ASF
Project Administration, Writing -Review & Editing

MAM
Data Curation, Writing -Original Draft Preparation