Thermal Accumulation and Collagen Remodeling in Porcine Models: Parameter‐Dependent Efficacy of Micro‐Focused Ultrasound for Human Facial Skin Tightening

BACKGROUND: Skin laxity, driven by collagen/elastin degradation and aging, is targeted by micro-focused ultrasound (MFU) through depth-specific thermal coagulation to induce collagen remodeling, yet parameter-dependent thermal kinetics and safety thresholds remain underexplored, limiting protocol optimization. AIMS: To validate the dose-effect relationship of MFU using in vitro porcine skin tissues and evaluate its safety and efficacy for human facial skin tightening. METHODS: Porcine skin tissues containing intact skin, fat, and muscle layers were treated with 8D-DL 3.0, 8D-DL 4.5, Vmax-DL 3.0, and Vmax-DL 4.5 handpieces. Subcutaneous temperatures at depths of 2.0 mm, 3.0 mm, 4.5 mm, and 6.0 mm were recorded under varying parameters (energy levels and exposure durations). Twenty patients undergoing single-session MFU facial treatment between June and August 2024 were enrolled. Skin tightening outcomes were assessed at 30- and 90-days post-treatment. RESULTS: For 8D-DL 3.0 and Vmax-DL 3.0 handpieces, peak temperatures occurred at 3.0 mm depth across all energy levels and exposure durations. For 8D-DL 4.5 and Vmax-DL 4.5 handpieces, peak temperatures localized at 4.5 mm. Focal depth temperatures increased significantly with higher energy levels and prolonged exposure. At 30- and 90-days post-treatment, upward displacement and volume reduction in bilateral cheek and jawline regions were observed. Mild procedural pain was reported, with no adverse events. CONCLUSION: MFU-induced thermal peaks align with preset focal depths, demonstrating parameter-dependent thermal accumulation. The procedure safely achieves clinically significant facial skin tightening.