Efficacy and safety of bipolar fractional radiofrequency vs. 2940‐nm Er:YAG ablative fractional laser in striae distensae treatment: A split abdomen study

Striae distensae (SD) is a challenging cosmetic condition. Ablative fractional laser (AFL) is an effective method for treating SD. Recently, fractional radiofrequency (FRF) has been shown to be a promising treatment for SD; however, few studies have shown the differences between FRF and AFL in the treatment of SD.


| INTRODUC TI ON
Striae distensae (SD; stretch marks) represent a common and cosmetically undesirable problem that affects people of all sexes, ages, and ethnicities.SD usually occurs owing to rapid changes in weight, height, or muscle mass.Additionally, SD can be caused by the longterm systemic or topical use of glucocorticoids.SD commonly manifests during pregnancy, affecting numerous expectant mothers. 1 The manifestation of SD is characterized by the appearance of red to purplish lines called striae rubra (SR).Gradually, as the initial inflammation and vasodilatation subside, these lines evolve into striae alba (SA), exhibiting characteristics of an atrophic scar.Histopathological examination of the skin from the SA region has revealed epidermal thinning and flattening of the ridges as well as a decrease in dermal thickness and collagen bundle thinning.Moreover, a decrease in the amount and breakage of elastin has been observed. 2Various therapeutic approaches, such as topical drugs (olive oil, topical tretinoin, and moisturizing creams), microdermabrasion, and skin needling, have been proposed to improve SD with unsatisfactory outcomes. 3Based on the success of photoelectric treatments for scarring and rhytides, photoelectric treatments have been applied to SD to achieve a similar level of effectiveness. 3 Fractional treatments, such as fractional radiofrequency (FRF) and ablative fractional laser (AFL), performed better in remodeling the dermis. 4,5Recently, nonablative fractional laser (NAFL) and AFL (2940-nm Er:YAG laser, ablative 10 600 nm carbon dioxide fractional laser) have been shown to be effective in improving SD. 5,6 In 2018, our research team found a significant clinical benefit in utilizing a combination of 2940-nm Er:YAG AFL with LED-RL and rb-bFGF for treating SA. 7 However, few studies have been conducted on FRF for the treatment of SD. 8,9 Building on prior research, the present study aimed to assess the effectiveness and safety of bipolar FRF and 2940-nm Er:YAG AFL for the treatment of SD.

| Patients
This investigation was conducted in a randomized, prospective, controlled manner, with participants recruited from the Department of Dermatology at Huadong Hospital, Fudan University, Shanghai, China.The study recruited a cohort of 20 Chinese individuals, aged between 23 and 45 years, who possessed Fitzpatrick skin types III-IV, and had both SR and SA.They had not received any associated treatment for 6 months prior to the selection.Exclusion criteria included a history of keloids, any skin infections, light-sensitive conditions, pregnancy or breastfeeding, a medical history of systemic lupus erythematosus, a pacemaker or other metallic implants, and a prior occurrence of skin cancer, including squamous cell carcinoma, basal cell carcinoma, or melanoma.
The ethics committee of Huadong Hospital, Fudan University, Shanghai, China approved the clinical study protocol.Prior to participation, all participants were provided with information regarding the therapeutic purpose of the study as well as the potential benefits and risks.Written informed consent was obtained from all participants.

| The procedure for treatment
Each patient received treatment using the available equipment.
Initially, a thin layer of an anesthetic cream composed of prilocaine and lidocaine sourced from Qinghua Ziguang in Beijing, China, was administered to the treatment area and subsequently covered with a plastic film and left in place for 1 h.After removing the anesthetic cream, the area was carefully disinfected using a 75% alcohol-soaked cotton pad.The patient donned an eye mask, while the operator wore protective goggles.The abdomen was divided into two halves and randomly assigned to two treatment groups according to the principle of randomization.One side was treated with a 2940-nm Er:YAG AFL (Lovelly II platform, Alma Laser, Israel), utilizing a laser handle comprising 49 laser beams (7 × 7 points) and a treatment window measuring 11 × 11 mm.This method required operational parameters that involved a prolonged pulse set at a frequency of 2 Hz and an output energy ranging from 1200 to 1400 mJ per pulse, which varied based on the patient's skin type.The treatment was repeated six times per area and concluded with a single sweep of the entire treatment area.Following the procedure, it was recommended to apply a cold compress and schedule three sessions at 4-week intervals.The other side was treated with bipolar FRF (American Syneron Medical Co. Ltd.Bipolar Fractional, Sublative Treatment Head).The treatment head comprised rows of 64 electrode needles, transmitting bipolar FRF energy in the form of a dot matrix.The skin was thoroughly cleaned and dried before the treatment.Subsequently, the treatment head was launched vertically against the skin surface, and finally, a postoperative cold compress was applied for three sessions at 4-week intervals.The specific treatment parameters of bipolar FRF were as follows: energy 70-85 mJ/needle, the ablation depth ranged from 390 to 420 μm and the coagulation depth ranged from 700 to 950 μm, administered one to two times, with a 50% overlap of the treatment area permitted.The treatment parameters were adjusted according to skin type, lesion distribution, anatomical location, pain tolerance, and immediate skin response.
Mild erythema and edema were the treatment endpoints.In case of no adverse reactions, subsequent treatment was maintained or the energy consumption was increased by 20% (Figure 1).

| Clinical efficacy evaluations
Photographs were taken at baseline prior to treatment initiation, and additional photographs were captured 3 months after the final treatment session.The enhancement of the SD appearance, including the area and color of the SD, was evaluated by two independent dermatologists using a percentage category scale ranging from no improvement (0%) to excellent improvement (76%-100%).The scale also included categories of mild improvement (1%-25%), fair improvement (26%-50%), and good improvement (51%-75%). 10

| The self-assessment of patients and their tolerance towards treatment
Discomfort and pain were assessed using a 0-10 visual analog scale (VAS), with 0 representing no pain and 10 representing unbearable pain.
Furthermore, the degree of satisfaction among participants regarding alterations in lesional texture, size, and overall improvement was assessed using a five-point rating system as follows:1 = very dissatisfied, 2 = not very satisfied, 3 = slightly satisfied, 4 = satisfied, and 5 = very satisfied.

| Histopathologic assessment
Two patients were selected randomly using a computer.Each patient underwent one biopsy taken from the most representative SD lesion on the abdomen before treatment.Additionally, 3 months after the final treatment session, biopsies were taken from representative lesions on each side of the abdomen, totaling three sites.To prevent scar tissue acquisition from prior biopsies, the biopsy sites were adequately spaced apart.Subsequently, the specimens were stained with hematoxylin and eosin (H&E) and special stains, including Masson's trichrome for collagen fibers and Weigert's for elastic fibers.

| Adverse effects
The current investigation assessed immediate and short-term responses, including erythema, purpura, and edema, within a 30min timeframe of treatment using a four-point scale (1 = mild, 2 = moderate, 3 = significant, 4 = severe).The term "downtime" was operationally defined as the duration following the procedure in which the patient reported discomfort resulting from the manifestation of edema and/or erythema.Moreover, the investigation documented the duration of resolution, therapeutic interventions, and resultant effects of any unfavorable responses, such as pruritus, blistering, peeling, epidermal detachment, scarring, prolonged erythema, and post-inflammatory hyperpigmentation.

| Clinical improvement in SD
After treatment, the patient's clinical photographs were evaluated, and all 18 patients exhibited bilateral improvement at the 3-month follow-up.Notably, 16.7% (3/18) of the 2940-nm Er:YAG AFL-treated sides and 22.2% (4/18) of the bipolar FRF-treated sides were rated as having achieved "excellent" improvement.For the 2940-nm Er:YAG AFL-treated sides, 33.3% (6/18) achieved "good" improvement, while 38.9% (7/18) achieved the same for the bipolar FRF-treated sides.In terms of "fair" improvement, 33.3% (6/18) of the 2940-nm Er:YAG AFL-treated sides and 27.8% (5/18) of the bipolar FRF-treated sides received this rating.Lastly, 16.7% (3/18) of the 2940-nm Er:YAG AFL-treated sides and 11.1% (2/18) of the bipolar FRF-treated sides were rated as having achieved "mild" improvement.Overall, the statistical analysis indicated no statistically significant difference in effectiveness between the two modalities (p = 0.766) (Table 2).There was no statistically significant difference observed in the therapeutic efficacy between the two treatment modalities for striae rubra (SR) (p = 0.856) and striae alba (SA) (p = 0.784).Clinical photographs of two representative patients before and after treatment showed diverse levels of amelioration (Figure 2).

| Patients' self-evaluation and treatment tolerance
In the assessment of patient satisfaction, 50% (9/18) of the participants indicated high levels of satisfaction, including both "satisfied" and "very satisfied" with the 2940-nm Er:YAG AFL treatment, whereas 55.6% (10/18) reported "satisfied" and "very satisfied" with the bipolar FRF treatment.This is consistent with the evaluators' assessments.No statistically significant difference was observed between the two groups (p = 0.8).None of the participants perceived their SD appearance to be worse after either treatment.All patients tolerated the treatment.Despite the application of a topical anesthetic cream, the patients' reported mean pain score was 2.5 ± 1.3 (mean ± SD) on the 2940-nm Er:YAG AFL-treated side and 3.0 ± 1.1 (mean ± SD) on the bipolar FRF-treated side.No statistically significant difference was noted between the two modalities (Table 2).

| Histopathological analysis
H&E-, trichrome-, and Weigert-stained pretreatment biopsy specimens revealed broken collagen and reduced dermal density.Thin, straight, and clumped collagen fibers were horizontally arranged in the dermal papillae, in contrast to the random arrangement of collagen fibers in the normal skin dermis. 11H&E-and trichrome-stained post-treatment biopsy specimens showed increased collagen density in the dermis (Figures 3 and 4).Weigert-stained biopsy specimens showed fine elastic fiber proliferation in both treatment groups, with more elastic proliferation in the dermal reticular layer in the bipolar FRF treatment group (Figure 5).

| Side effects
Both treatments were well-tolerated and did not result in any substantial adverse effects.The treatment time of the bipolar FRFtreated side was considerably longer than that of the 2940-nm Er:YAG AFL-treated side owing to the scanning pattern.After the two treatments, the degree of edema and erythema differed bilaterally, resembling urticaria on the side treated with bipolar FRF.
Epidermal peeling on the 2940-nm Er:YAG AFL-treated side (mean, 7 ± 3 days) showed faster regression than on the bipolar FRF-treated side (mean, 10 ± 3 days).During the treatment period, some patients developed different levels of PIH and the PIH faded faster on the side treated with 2940-nm Er:YAG AFL (mean, 6 ± 2 weeks) compared to those on the side treated with bipolar FRF (mean, 8 ± 2 weeks).PIH was transient in all patients, and none of the patients exhibited PIH at the 3-month follow-up (Table 2).

| DISCUSS ION
Numerous efforts have been made to enhance the efficacy of SD treatment.However, no single therapeutic approach has demonstrated marked or consistent superiority over alternative treatments.At present, fractional-mode photoelectric devices, such as AFL and FRF, may be more effective than other treatments in promoting dermal remodeling. 12,13The fractional mode of photoelectric TA B L E 1 Summary of demographic and baseline characteristics.therapy produces microscopic thermal injuries in groups of small beams at particular depths, targeting only a small portion of the skin called microscopic treatment zones.The preservation of intact adjacent tissues serves the dual purpose of providing a supportive framework and a source of nutrients for the synthesis of collagen and elastin.Given that the absorption spectrum of 2940-nm Er:YAG is proximal to the peak absorption wavelength of water (3000 nm), it can provide more precise heat delivery and mitigate undue thermal harm to adjacent tissues. 14With the increasing popularity of radiofrequency therapy for stimulating dermal growth, 15 it is important to understand the difference between FRF devices and AFL.

Enrolled subjects 20
Bipolar FRF generates heat by causing polar water molecules to rotate rapidly and frictionally interact in an electromagnetic field.Both treatments work on water molecules, which is an important target chromophore in skin collagen.Two treatments have no effect on the target chromophores of melanocytes and hemoglobin.So there was no statistically significant difference observed in the therapeutic efficacy between the two treatment modalities for SR and SA.
In this study, two non-study-blinded dermatologists provided positive clinical evaluations of both sides of the abdomen in 18 patients.The bipolar FRF treatment side garnered marginally more "good" or "excellent" ratings on average.Nevertheless, the difference in the clinical ratings between the two treatments was not statistically significant.
Histopathologically, post-treatment biopsy specimens showed improvements in epidermal and dermal thickness and collagen and elastin density in all patients.Although the improvements between the two treatments were not statistically significant, the bipolar   in the epidermis and less energy in the dermis. 16Conversely, bipolar FRF is referred to as droplet FRF because of its energy distribution pattern, which generates pyramid-shaped fractionated thermal zones in the skin.Specifically, the energy impact is narrower on the surface of the epidermis and wider and deeper within the dermis.
This results in alterations in the connective tissue, primarily characterized by heating-coagulation in the dermis and minimal exfoliation in the epidermis. 17,18 expected, both treatments were well tolerated, with transient PIH being the most common side effect and no significant longterm adverse events in any patient.Interestingly, the average PIH duration was shorter on the 2940-nm Er:YAG AFL-treated side than on the bipolar FRF-treated side.This may be related to the energy parameters.Although radiofrequency treatment only targets water molecules and not melanocytes, 19,20 increasing the energy parameters can generate more heat to stimulate dermal collagen remodeling more effectively.However, excessive heat can also elevate the risk of hyperpigmentation.

3 | RE SULTS 3 . 1 |
Statistical analyses were conducted using SPSS version 19.0, developed by SPSS Inc., Chicago, Illinois, USA.Categorical variables are presented as the number of valid cases and corresponding percentages for each category.Continuous variables are represented as mean values along with their corresponding standard deviations.Chi-square tests were used to compare the frequencies of categorical variables across study groups.Statistical significance was determined using p-values less than 0.05.Participant demographics A total of 20 female volunteers diagnosed with abdominal SD were enrolled in our department.It was observed that all 20 participants experienced SD as a result of pregnancy.Eighteen patients successfully completed the entire treatment protocol and subsequent follow-up, while the remaining two patients discontinued their participation in the study due to their pregnancies.These 18 participants with an average age of 30 ± 5.5 years demonstrated a diverse range of Fitzpatrick skin types, encompassing type II to type V, with type IV being the most prevalent.The duration of the disease varied from 1 to 15 years, with an average duration of 3.8 ± 2.4 years.Furthermore, the participants were further classified into two subtypes, namely SR (n = 7) and SA (n = 11) (Table1).

F I G U R E 1
The flow map of study.| 2025HEN et al.

FRF-treated side
showed thicker collagen and deeper elastin hyperplasia in the pathological images than those observed on the 2940nm Er:YAG AFL-treated side.This may have been because the two treatments used different heating patterns.The 2940-nm Er:YAG AFL delivers energy that generates columnar or conical fractionated thermal zones in the skin, resulting in greater absorption of energy TA B L E 2 Distribution of the studied patients based on the extent of clinical improvement and their reported satisfaction with side effects during the follow-up period.

F I G U R E 3 F I G U R E 5
Hematoxylin and eosin staining (A-C).(A) Before treatment, the dermis of the SD was loose and floccular.(B) 3 months after the final 2940-nm Er:YAG AFL treatment, the collagen density of the dermis increased; (C) 3 months after the last bipolar FRF treatment, the collagen density of the dermis increased.Scale bar = 300 μm.F I G U R E 4 Masson's trichrome staining of collagen fibers (A-C).(A)Prior to treatment, the epidermal rete ridges underwent flattening, while the collagen bundles in the dermis exhibited thinness and straightness, with a dense packing arrangement that was parallel and horizontal to the skin surface; (B) 3 months after the last 2940-nm Er:YAG AFL treatment, collagen density in the dermis increased and collagen fibers were arranged randomly; (C) 3 months after the last bipolar FRF treatment, regularlyarranged, continuous, thicker collagen fibers were observed.Scale bar = 300 μm.Weigert staining of elastic fibers (A-C).(A) Prior to treatment, the elastic fibers that were damaged (as depicted in black) displayed a finely fragmented state within the reticular layer; (B) 3 months after the final 2940nm Er:YAG AFL treatment, there was observed a notable augmentation in the quantity of fine elastic fibers exhibiting thickening within the reticular layer; (C) 3 months after the last bipolar FRF treatment, increased elastic fibers were more abundant in the dermal reticular layer.Scale bar = 200 μm.