MRF shows a promised benefit for controlling active acne. The improvement of acne might be due to the reduction in some sebaceous glands and reduction in perifolliculitis.

Improvement of a sign of photodamage, skin laxity, texture, fine lines, and wrinkles are observed in multiple studies across different skin types and ethnicity. MRF can be used for facial rejuvenation, as well as neck laxity. MRF treatment might provide a nonsurgical option for the treatment of facial skin laxity in patients.

MRF is also beneficial in other difficult to treat skin condition such as primary axillary hyperhidrosis, rosacea, and striae distensae.

Adverse events of MRF are limited to mild pain, transient erythema or edema, and rarely epidermal atrophy after the procedure. Fewer patients demonstrate postinflammatory hyperpigmentation compared to ablative and non-ablative laser resurfacing. Skin depressions have been reported. It can be avoided by optimal contact of the hand piece to the skin and using the appropriate energy.

7.1 Radiofrequency (RF)

Radiofrequency (RF) is the term given to any alternating electrical current that, if applied to an antenna, creates an electromagnetic field, which propagates through space and time in the surrounding area. The radiofrequency spectrum can be divided into bands ranging from very low frequency (3–30 kHz) to extremely high frequency (30–300 GHz). Energy generated can be transmitted and applied directly to tissues, which absorb and even retransmit the current. Because RF radiation has a short wavelength, it interacts with polar molecules such as water, amino acids, and nucleic acids, producing a molecular vibration that is converted to thermal energy. This energy transmission changes according to the resistance of the tissue. Therefore, RF delivers heat energy to tissues nonspecifically. This process is unlike lasers, which depend on chromophores that absorb optical energy converting it to heat. ¹ RF does not affect skin color and so it can be used safely on various skin types.

7.2 Microneedling

Microneedling is a minimally invasive procedure using fine needles to puncture the epidermis. Needling alone has proved beneficial to the skin, improving blood flow and wound healing in an animal flap model. ² Fernandes developed the dermaroller mounted with tiny needles to create the microwounds in the skin. ³ Microneedling devices can be used to treat various skin conditions including acne and other scars, facial rejuvenation, dyspigmentation, alopecia, and hyperhidrosis.

7.3 Microneedling RF (MRF)

A pilot study by Hantash and colleagues was the first clinical application of Microneedling RF (MRF). Histologic analyses of treated skin excised from subsequent abdominoplasty or facelift procedures showed a fractional pattern of injury, wound healing, and dermal remodeling, while sparing the epidermis and key adnexal structures. There were zones of denatured collagen, separated by zones of spared dermis. They also discovered an increase in transforming growth factor β (TGF-β), matrix metalloproteinases-1 and 13, and heat shock proteins 47 and 72, tropoelastin, fibrillin, as well as procollagen 1 and 3. These molecules further induced neocollagenesis and neoelastogenesis. ⁴ Subsequently, alternative ablative technology called “sublative radiofrequency” was introduced for skin resurfacing. This technology creates a low-density fractional epidermal and superficial dermal coagulation under the conductive pins and delivers RF traveling through the reticular dermis combining a low-density ablative effect in the epidermis with subnecrotic heating in deeper layers of the skin. ⁵

This chapter reviews the clinical application of microneedling RF. These devices may be classified according to their type of thermal delivery pattern through the skin: sublative fractional RF, Microneedling RF with insulated needles, and Microneedling RF with non-insulated needles.

7.4 Devices and Specification

7.4.1 Sublative Fractional RF (Bipolar Fractional RF)

This type of RF uses microneedles or electrode pairs to deliver the radiofrequency energy to the skin, while the high heat at contact points creates ablation of the epidermis. Sublative RF is capable of improving superficial irregularities with minimal downtime ( ▶ Table 7.1).

7.4.2 Microneedle RF with Insulated Needles

The first generation of MRF systems covered most of the needle length and left only a small part of the tip non-insulated to protect the superficial epidermis, thus resulting in a small sphere-like shape coagulation zone in dermis. Multiple passes with different depths are required to cover entire dermal layers ( ▶ Table 7.2). The newer models have a temperature control sensor. The software is programmed to emit energy until preselected target temperatures are reached to maintain temperature for the desired duration for optimal collagen denaturation ( ▶ Table 7.3).

7.4.3 Microneedling RF with Non-Insulated Needles

Non-insulated needles have the ability to eliminate microbleeding during treatment due to effective coagulation and a broad electric field through the papillary and reticular dermis along the full length of the needles. Harth et al studied the histologic effect of the non-insulated microneedle RF on animal skin. Histologic examination showed clear mechanical disruption of the epidermis related to needle penetration with minimal thermal damage. The mechanical disruption closes rapidly and is nonexistent 4 days’ post-therapy, a finding implying that there is less significant epidermal damage ( ▶ Table 7.4). ¹⁰

7.5 Acne and Acne Scar

Acne pathophysiology is complex and arises from a dysregulation of multiple processes, including imbalance in inflammatory mediators and the microbiome with overpopulation of Propionibacterium acnes, dystrophic hyperkeratosis of the hair follicle, and excessive sebum production. These factors lead to rupture of the follicular wall with release of hair, lipids, keratin, and P. acnes into the dermis causing inflammation and activation of the classic and alternative complement pathways. Disorganized and destroyed collagen and elastic fibers from fibroblastic dysregulation around the inflamed follicle leads to the appearance of acne scar. There are three types of atrophic acne scar: ice pick, rolling scar (superficial and deep soft scar), and boxcar scar (depressed fibrotic scar). Each subtype has a varying degree of response to different treatment options. Depressed scars may reach up to 0.7 mm depth. Therefore, effective treatment will have to reach beyond this point to mechanically disrupt the dystrophic tissue. ¹¹

There is no standard of care for the treatment of acne scars due to the difference in type and degree of scars on every patient. Options for the reduction of acne scars include punch excision, punch grafting, surgical excision, subcision, dermabrasion, chemical peelings, injection of fillers, and a variety of laser skin resurfacing procedures such as ablative, non-ablative, and fractional laser technologies alone or best, in combination.

Ong and Bashi reviewed the use of the fractional photothermolysis (FP) for acne scar treatments including 13 ablative and 13 non-ablative FP devices. For ablative FP, the improvement ranged from 26 to 83% with facial erythema lasting 3 to 14 days and PIH in up to 92.3% of patients, whereas for non-ablative FP, efficacy varied from 26 to 50% with facial erythema for 1 to 3 days and PIH in up to 13% of patients. ¹² Even though ablative FP showed superior efficacy, the incidence of PIH limits its use in darker skinned patients.

7.5.1 MRF for Acne Treatment

In 2005, Prieto et al reported 32 patients with moderate acne who were treated twice-weekly for 4 weeks with a combination of pulsed light and RF energy. The result revealed 47% reduction in mean lesion count (p < 0.05). The percentage of follicles with perifolliculitis decreased from 58 to 33%, and sebaceous gland areas decreased from 0.092 to 0.07 mm². The improvement of acne might be due to reduction in some sebaceous glands and/or a reduction in perifolliculitis. ¹³

Since the overproduction of sebaceous gland activity is a main pathophysiological factor in acne, Kobayashi used a 1.50-mm-long needle with a 0.45 mm base insulation inserted into pores in the forehead and cheeks, and a high-frequency electrical current was applied for 0.25 to 0.50 seconds with an output of 40 W. The mean reduction rate of skin surface lipids was 31.5% by sebumeter measurement (p < 0.01) at 6-month follow-up. Histology showed fewer sebaceous glands and the development of fibrosis. ¹⁴ Lee et al discovered a favorable effect of MRF Scartlet (Viol Co., Korea) on moderate to severe pustular acne. ^{11 After two treatments monthly, using intensity 7 at 3 mm depth for two passes, there was a significant improvement in acne lesion count and severity. Another study confirmed the sebosuppressive effect of MRF. Twenty Korean subjects with moderate to severe acne received a single treatment of INFINI (Lutronic, Inc., Burlington, MA) to the full face at energy level 5, exposure time of 50 to 100 ms at 1.0 to 1.5 mm depth. CSL (casual sebum level) and SER (sebum excretion rate) showed 30 to 60% and 70 to 80% reduction, respectively, at week 2 (p < 0.01), and remained below the baseline level until week 8. Acne lesion count revealed clinical improvement with maximum efficacy at week 2 but returning to baseline in most patients by week 8. The findings imply there is long-term effect of MRF on sebaceous gland, but short-term effect for acne control after a single treatment of MRF. 15}

Kim et al ¹⁶evaluated the efficacy of MRF using INTRAcel (Jeisys Medical, Seoul, South Korea) in 25 patients with moderate to severe acne. The treatment was done three times monthly with exposure time of 80 ms, power level 3, and 1.5 mm depth. The result showed statistically significant reductions in acne lesions at 4, 8, and 12 weeks after treatment compared with baseline with inflammatory lesions responding better than noninflammatory lesions. The mean decrease in sebum secretion at 1 month after the third treatment was 42.18%. Sebum secretion increased slowly subsequently but remained lower than baseline until 3 months after treatment. With multiple treatments, a more prolonged control of active acne lesions was demonstrated.

Shin et al performed a comparative split-face study to evaluate the efficacy and safety of Fractional CO₂ laser (10,600 nm) versus MRF (Scarlet) for active acne treatment. Fractional CO₂ was done at 80 mJ and 100 spots/cm² for two passes. MRF treatment setting was at intensity level 8, density of 25 MTZ/cm2 at 1.5 to 2.5 mm depth. Both showed improvement in acne with no significant differences in physician-measured parameters, patient ratings, or intraoperative pain. Downtime was significantly longer for the fractional CO₂-treated side (11.75 vs. 2.35 days). Most patients refused to do another CO₂ treatment due to the extended period of erythema. Two cases of PIH occurred only on the CO₂-treated side. ¹⁷ MRF proved to be more convenient and tolerable to most of the patients.

Postinflammatory erythema (PIE) is very common following inflammatory acne and is cosmetically unacceptable to patients. Min et al conducted a retrospective review of 25 patients treated with two sessions of INFINI. There was a significant difference in the degree of erythema from investigator grading, photometric measurement, and imaging analysis by software between MRF group and control group. Furthermore, histologic studies revealed reduced inflammation, microvessels, interleukin 8 (IL-8), Nuclear Factor kappa-light-chain-enhancer of activated B cells (NF-kB), and vascular endothelial growth factor (VEGF) after treatment. MRF may be an effective treatment for PIE due to anti-inflammatory and antiangiogenetic properties. ¹⁸

7.5.2 MRF for Acne Scar Treatment

A review of six studies comprised of 121 patients compared the treatment efficacy of bipolar RF, unipolar RF, and fractional RF and demonstrated that out of all RF modalities, microneedle bipolar and fractional bipolar RF offer the best result for acne scarring. 25–75% improvement is usually achieved in 3 months posttreatment. ¹⁹

Kaminaka et al first studied the histology from punch biopsies of acne scar patients who underwent sublative fractional RF. The results showed that sublative fractional RF with two passes caused deep thermal injury depth with denaturation of sebaceous glands and hair follicles in the dermis. The results indicated that sublative fractional RF can lead to remodeling in the deep dermal structure. ²⁰ The same authors consequently performed a clinical study of five treatment sessions of eMatrix (Syneron, Yokneam Illit, Israel) on patients with acne and atrophic scar. The treatment parameter was 64 pins, peak energy was 62 mJ/pin, and coverage was 10%. They noted marked improvement in scar volume among the patients with mild scars. At least moderate improvement was achieved in 57.5% of the treated areas. The treated areas exhibited significantly fewer lesions compared with baseline at each time point (p < 0.05). Patient’s quality of life also improved considerably. Furthermore, significant reductions in the patients’ sebum levels, skin roughness, and scar depth were observed. However, 10% of subjects experienced a flare-up of acneiform lesions at the end of the study. ²¹

A new generation of eMatrix was developed to maximize the ability to deliver energy up to 100 mJ/pin. In a Chinese study, patients received four monthly high-energy (85–95 mJ/pin) treatments with this RF device. Evaluation of global improvement and satisfaction increased at the 12 week assessment visit compared with baseline. ²² Phothong et al performed a split-face, double-blinded, randomized control trial using a high-energy setting of 100 mJ/pin versus a moderate setting of 60 mJ/pin in order to treat acne scar. The side of the face receiving higher energy demonstrated statistically significant improvement versus the moderate energy side (p = 0.03). Pain score and the duration of erythema after treatment were significantly higher on the high energy side as well. Also, post-inflammatory hyperpigmentation (PIH) developed 17.5% on high energy side compared to 13.3% on moderate energy side. ²³

Hellman reported a retrospective review of patients who underwent Fractora (Invasix, Israel) treatment. Eight patients received four treatment sessions with the initial doses of 20 to 40 mJ/pin; the doses increased each visit, based on patient tolerance. Histology specimens were collected from two patients pre- and posttreatment. All participants had a significant improvement assessed by photography. Biopsy after treatment demonstrated that scar thickness diminished in depth from 1.5 to 0.8 mm with newly formed collagen fibers, adnexal structure, and elastic tissue. ²⁴ A subsequent follow-up study with four out of eight patients demonstrated the improvement increased over time during a follow-up period ranging from 4 months to 2 years. ²⁵ Another prospective trial using Intensif (EndyMed Medical, Caesarea, Israel) for acne scar treatment revealed a global aesthetic improvement scale of excellent in 25% of patients, good in 50%, and minimal in 20%. ¹⁰

MRF for Acne Scar Treatment in Darker Skin Type

Cho et al revealed the grade of acne scars improved in 73.3% of Korean patients after two treatment of INTRAcel using 1.5-mm-needle depth. Interestingly, enlarged pores also improved in 70% of participants which were confirmed by image analysis with the area of facial pores decreasing by 58.7% (p < 0.001). The side effects were mild including pain, erythema, and folliculitis. No PIH was observed. ²⁶ INTRAcel also showed a favorable effect in Thai subjects. Twenty-six patients underwent three monthly treatment sessions using energy level 3, 30 W, exposure time 80 ms for two passes. In a group with mean scar age of 7 years (range: 0.5–15 years), all subjects (100%) rated at least 25 to 50% overall satisfaction, whereas physician graded 82% of the subject having at least 25 to 50% improvement. The risk of PIH was 3.85%. An objective evaluation using Visioscan demonstrated statistically significant improvement of skin roughness (p = 0.012) and scar volume (p = 0.03) at 1-month follow-up, but no further significant change at 3 and 6 months. ²⁷

In Indian subjects, Chandrashekar et al performed a retrospective photograph analysis in 31 patients of skin types III to IV with acne scar. The INFINI system, with energy of 25 to 40 W and needle depth of 1.5 to 3.5 mm, demonstrated efficacy for treatment of acne scar evaluated by Goodman and Baron’s Global Acne scarring system. Of patients with grades 3 and 4 acne scars, 80.64% showed improvement by 2 grades and 19.35% showed improvement by 1 grade. Five patients reported PIH and two had track marks of the device probe. ²⁸ Pudukadan further evaluated the effects of MRF for treating acne scars in darker skin type patients. Nineteen patients received three treatments with Intensif. The treatment parameters were 15 to 25 W, exposure time of 110 to 140 ms, and needle depth of 2.0 to 3.0 mm. Improvement of at least 1 acne scar grade was noted in 11 of 19 patients (57.9%) after 1 month and 9 of 9 patients (100%) after 3 months. The investigators also observed dyschromia improvement in 9 patients (47.4%) and hypothesized that this effect resulted from destruction of “dropped” dermal melanosome. ²⁹

Comparative Study for Acne Scar Treatment

INFINI was more effective for ice pick and boxcar scar compared to bipolar RF Polaris WRA (Syneron Medical INC., Yokneam, Israel) in a 12-week prospective single-blind, randomized clinical trial. The MRF was applied at levels 2 to 3 for 50 to 70 ms. The bipolar RF delivered fluence of 100 mJ/cm² at 100 Hz. Both modalities were done with slight overlapping in three passes. Specimens obtained for this study demonstrated increased expression of TGF-β and collagen I and decreased expression of NF-κB, IL-8 on the MRF-treated side. ³⁰ A randomized split-face clinical study in Thai patients revealed that both fractional erbium-doped glass 1,550-nm laser Fraxel re:store DUAL 1550/1927 (Solta Medical, Hayward, CA) and fractional bipolar RF eMatrix (Syneron-Candela, Irvine, CA) significantly improved acne scar and skin texture, with no statistical difference between the two devices. The eMatrix parameter was Program C using 53 to 59 mJ/pin for two passes. Fraxel re:store treatment setting was 30 to 50 mJ/MTZ with treatment levels 4 to 5, 10 to 14% coverage for eight passes. The pain score was higher and one patient (5%) had prolonged erythema and PIH in fractional erbium-doped glass 1,550-nm-treated side. However, the duration of scab shedding was shorter after the fractional erbium-doped glass treatment. ³¹

Another randomized comparative study between 1,550-nm Er:Glass fractional laser and MRF was conducted in Korea. Forty patients randomly received either 1,550-nm Er:Glass fractional laser or MRF treatment. Scar severity scores (ECCA grading scale) improved by a mean of 25.0 and 18.6% for the devices, respectively, but no significant difference occurred between the group. Boxcar and rolling scar responded significantly after treatment, whereas ice pick scar did not. Again in this study, two patients developed PIH and acneiform eruption in the fractional laser group. Overall, the MRF group had significantly less pain, shorter downtime, and fewer side effects, leading to higher patient satisfaction. ³²

7.5.3 Combining MRF with Other Modalities for Acne Scar Treatment

Fractional bipolar RF combined with diode laser/bipolar radiofrequency (DLRF) has proven effective and safe for the treatment of acne scar. DLRF was designed to create focal coagulation and necrosis of the reticular dermis at 1.5 mm skin depth as a means of stimulating neocollagenesis, while addition of the fractional bipolar RF then produces ablation of the epidermis and papillary dermis. Diode laser bipolar radiofrequency (DLRF) setting range from 60 to 70J/cm² with RF at 80 to 100 J/cm. ³ Then, fractional bipolar RF follows with energy 19 and 25 J (Program C, 5% coverage). With this protocol, Peterson revealed that acne scar scores statistically significantly decreased by 72.3% (p < 0.001), skin texture enhanced by 66.7% (p < 0.001) and acne scar pigmentation improved by 13.3% (p = 0.05) after five monthly sessions. No subjects displayed PIH. ³³ Taub and Garretson found similar results. The median scar assessment scores significantly improved after three treatments out of five and persisted throughout the study. Skin type did not affect the outcome, and PIH occurred in a single patient with skin type IV but resolved without intervention. ³⁴

MRF has also improved a variety of acne scars while sublative RF has been shown to induce upper epidermal ablation with a column of dermal remodeling. Combining two different modalities demonstrates good results. Twenty Asian subjects with skin types III to IV received three treatments of dual mode INFINI monthly. MRF treatment parameter was: level 7, 50 ms, at 1.5 mm depth. Next, sublative RF was applied with treatment level 16 to 17 and 70 to 80 ms exposure time. Blinded physician assessors rated all subjects as having grade 2 or more clinical improvement; 4 (20%) had grade 4, 10 (50%) had grade 3, and 6 (30%) had grade 2 improvement. Furthermore, there was significant improvement in all three types of scar (p < 0.05). However, with a combination of two treatment modalities, two patients developed transient PIH, two flushing, and one worsening active acne. ³⁵

Subcision is a conventional method used to mechanically disrupt the fibrotic tissue in the dermis that tethers down scars. Faghihi et al conducted a randomized split-face study to evaluate the treatment efficacy of MRF (INFINI) with and without subcision. Combined treatment with subcision had a significantly better improvement graded by the two blinded dermatologists and by patient rating using a visual analog scale. ³⁶ From our experiences, combining MRF with subcision showed beneficial results with minimal risk of downtime and adverse effects ( ▶ Fig. 7.1).

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