This study aims to evaluate the safety and effectiveness of Juläine™ (poly-L-lactic acid) injections for the treatment of buttock skin laxity.

Participants will be randomized to an immediate-treatment group or a delayed-treatment group. The immediate-treatment group will receive 2 to 3 treatment sessions over up to 2 months and will be compared with the delayed-treatment group during the control period; the delayed-treatment group will receive the same treatment after the delay.

The primary objective is to assess clinical improvement in buttock skin elasticity 6 months after the last treatment, defined as an increase in skin elasticity measured by a cutometer. Total study participation is up to 16 months, including follow-up.

This multicenter trial will be conducted in Brazil.

This is an pivotal, open-label, two-arm, randomized, parallel-group, prospective clinical investigation conducted in Brazil to evaluate the safety and effectiveness of Juläine™ (poly-L-lactic acid) administered as intradermal injections for the treatment skin laxity in the buttock (gluteal) region in adults.

A total of 100 participants will be randomized to either an immediate-treatment group or a delayed-treatment group (delayed-start control). Participants in the immediate-treatment group will receive Juläine™ intradermal injections in up to three sessions at Day 0, Day 30, and Day 60. During this initial control period, outcomes in the immediate-treatment group will be compared with those in the delayed-treatment group, which will not receive treatment. After the control period, participants in the delayed-treatment group will receive the same Juläine™ regimen at Day 240, Day 270, and Day 300. Each participant will remain in the study for up to 16 months, including screening, treatment sessions, and follow-up assessments.

The primary efficacy endpoint is improvement in buttock skin elasticity 6 months after the enrolment defined as an increase in global skin elasticity measured by a cutometer, with assessments at screening/baseline and at the primary post-treatment timepoint. The mean change in global skin elasticity measured by cutometer and Global Aesthetic Improvement Scale (GAIS) will also be evaluated, comparing groups during the control period.

Safety will be monitored through the collection of adverse events (AEs) through 240 days after screening, with comparisons between groups during the control period. Adverse events will also be evaluated through extended follow-up, including up to 180 days in the overall study population and up to 480 days in the immediate-treatment group.

Inclusion Criteria:

• Adults aged 18 to 55 years;
• Body Mass Index (BMI) between 18.5 and 24.95 kg/m².
• Skin laxity of the gluteal region defined as sagging and reduced tightness of the skin.
• Women of childbearing potential must be willing to abide by the contraceptive requirements
• Ability to understand the study and provide informed consent, attend follow-up visits, and follow post-injection instructions.

Exclusion Criteria:

• Pregnancy or breastfeeding, or planned pregnancy/lack of adequate contraception (through 8 weeks post-study);
• Is planning to donate/bank or retrieve eggs (ova, oocytes) or donate sperm during the study or within 8-weeks of the end of participation of the clinical investigation.
• Active infection, inflammation or lesions at or near the treatment site.
• Acute infection at screening;
• History of autoimmune disease;
• Immune deficiencies;
• History of hypertrophic scarring or keloid formation;
• Previous surgical procedures involving the buttocks
• Aesthetic procedure on the buttocks (including fillers, elevation wires, radiofrequency, ultrasound, cryotherapy, fat injection, neurotoxin, laser or light treatment, or chemical peel) within 6 months prior to randomization.
• Hemorrhagic disease or ongoing use of antiplatelets/anticoagulant therapy.
• Treatment with chemotherapy, immunosuppressive agents, systemic corticosteroids within 3 months before treatment (inhaled or ophthalmic corticosteroids are allowed).
• Use of hormonal replacement therapy (HRT) unless the participant has been on a stable dose for at least 3 months prior to screening and does not plan to make any changes to the HRT regimen during the study period.
• Use of topical corticosteroids, topical prescription retinoids in the treatment area within 1 month of the Baseline visit or systemic retinoid treatment within 6 months of the baseline visit, or plan to receive such treatment.
• Use of other agents that inhibit collagen production.
• Known allergy or hypersensitivity to any component of the investigational product.
• History of herpes simplex rashes, malignant skin diseases, or any other serious dermatologic or systemic disease.
• Presence of any condition that may impair wound healing (e.g., connective tissue disorders, severe malnutrition).
• Planned or ongoing cosmetic procedures involving the buttocks or surrounding area during the period of clinical investigation.
• Extensive tattoos covering >50% of the total gluteal area.
• Participants actively taking GLP-1 medications with the intention of achieving additional weight loss (expected >10% during study) will be excluded. Participants on a stable GLP-1 regimen (≥3 months) for diabetes management or weight maintenance, with documented weight stability (±10% in past 6 months) and no planned or expected weight change >10%, may be included.
• Any other medical or psychological condition that, in the opinion of the investigator, may interfere with participation in clinical research or evaluation of results.