A novel animal model for hyaluronic acid filler longevity

Introduction: Tissue filler injections are among the most commonly performed procedures in Facial Plastic Surgery. No single animal model has emerged as an accepted standard to evaluate tissue filler longevity. To validate a rat model three hyaluronic acid fillers with different known residence times in humans were tested. Experimental Design: In vivo animal study to compare residence time of three hyaluronic acid fillers to published residence times in humans. Methods: Two hundred microliters of Restylane (n=20), Captique (n=19), and Juvederm (n=19) were injected into the dermis of Sprague-Dawley rats. The three-dimensions of the blebs were measured at Day 0, Day 1, and a weekly basis for 7 weeks. Volume, volume ratio, and filler thickness were analyzed. Histological and statistical analyses were also performed. Results: Histology demonstrated injections in the thin rat dermis with migration into the subcutaneous space. Captique's average residence time was 2 weeks, while Restylane and Juvederm had measurable volumes through 6 weeks. Both Restylane and Juvederm maintained significantly greater volumes and volume ratios than Captique through the duration of the study. Conclusion: Captique's residence time was significantly shorter than that of Restylane and Juvederm, which had comparable residence times. While the longevities of the three fillers were not of the same duration in the rat as human residence times, the relative duration of the fillers was comparable therefore establishing the rat as a valid animal model to compare various tissue filler materials. The shorter residence time in the rat dermis/subcutaneous space allows for accurate rapid preclinical testing of tissue filler materials.