This randomized, split-face, double-blind clinical trial was conducted in accordance with the principles of the Declaration of Helsinki. The study protocol was approved by the Institutional Review Board (Si 195/2024). Written informed consent and consent for image publication were obtained from all participants. This trial was registered with the Thai Clinical Trials Registry (TCTR20250803007). All data were de-identified and entered into standardized case report forms using coded identifiers.

Eligible participants were healthy adults aged 18–45 years with Fitzpatrick skin types (FST) III–V and moderate to severe AAS, defined according to the Goodman and Baron’s Quantitative Global Acne Scarring Grading System (GBQGASGS) [18]. Only individuals with bilaterally symmetrical scarring were included to allow within-subject comparison. Participants agreed to abstain from other cosmetic facial procedures during the study period, adhere to post-treatment instructions, and attend all scheduled follow-up visits.

Exclusion criteria included active acne; a history of keloid or hypertrophic scar formation; isotretinoin use within the past 6 months; pregnancy or lactation; and any systemic or dermatologic disorder that could impair wound healing or confound outcome assessment. Individuals with known hypersensitivity to PLLA or topical anesthetics, or those who had undergone resurfacing procedures (laser, chemical peel, or microneedling) within 6 months, were also excluded.

Topical anesthesia (lidocaine–prilocaine cream, EMLA®; AstraZeneca) was applied under occlusion for 60 min before treatment. A single dermatologist performed all procedures using a microneedle monopolar radiofrequency device (EXION™; BTL Industries) at a needle depth of 2.5 mm and energy 80–100%, with extended mode disabled.

Each participant underwent two treatment sessions, spaced 1 month apart. Immediately following FMRF session, 2.5 mL of PLLA suspension (Sculptra®; Galderma, reconstituted with 10 mL of sterile water) was applied evenly to one facial half to facilitate transdermal delivery through the microchannels created by microneedle insertion. The contralateral side received an equivalent volume of sterile water using the same procedure. Randomization was performed using a computer-generated block randomization sequence (www.randomization.com). Product preparation was conducted by the research team, who were aware of allocation, while participants remained blinded to treatment side.

Post-treatment care included avoiding water exposure for 24 h, followed by gentle cleansing with tap water and patting dry. Participants were instructed to apply petrolatum jelly to the treated areas four times daily for 1 week. Excessive sun exposure was to be avoided, and broad-spectrum sunscreen with a sun protection factor of 50 was required throughout the study period after micro-crusting had completely healed.

At baseline, standardized digital photographs were obtained using the Omnia® and Visia® systems from five facial angles (− 90°, − 45°, 0°, 45°, 90°) under uniform lighting and camera settings. Skin texture and scar volume were quantified using the Antera® 3D imaging system (Miravex Limited, Dublin, Ireland) on a non-identifiable 5-cm2 facial region. Bioengineering measurements of melanin and erythema indices were performed bilaterally with the Mexameter® MX 18 (Courage-Khazaka, Cologne, Germany). AAS was graded using the GBQGASGS [18].

Follow-up assessments were conducted at 1, 3, and 6 months after the second treatment session.

Primary outcomes were changes in skin texture and scar volume measured using Antera® 3D, and changes in AAS severity as assessed by GBQGASGS. Secondary outcomes included melanin and erythema indices (Mexameter® MX 18); blinded photographic evaluations by two independent dermatologists using a quartile improvement scale (QIS; 0, no improvement; 1, 1–25%; 2, 26–50%; 3, 51–75%; 4, ≥ 75% improvement); and patient self-assessments using the same scale.

Safety and tolerability were evaluated at each visit by documenting adverse events, including erythema, bruising, pigmentary alteration, infection, or scarring. Procedural pain was recorded immediately post-treatment for each side using a 10-point visual analogue scale (VAS; 0, no pain; 10, worst pain).

Data were analyzed using SPSS software, version 18.0 (IBM Corp., Armonk, NY). Continuous variables were summarized as mean ± standard deviation and categorical variables as frequency and percentage. Repeated-measures analysis of variance (ANOVA) was used for normally distributed data, the Friedman test to non-normally distributed data, and Cochran’s Q test to binary outcomes. A two-sided p value < 0.05 was considered statistically significant.