Rheological and Physicochemical Properties of Hyaluronic Acid Fillers for Body Contouring: Clinical Implications and Anatomical Considerations

INTRODUCTION: The use of hyaluronic acid (HA) fillers is rising globally. Traditionally, the rheology of HA fillers has been subject to investigations for their use in facial soft tissues. Hitherto, there has been a significant gap in understanding their rheologic properties in body applications. The requirements for body fillers are different from facial fillers as they are applied for larger volume deficits, and experience greater mechanical stress. This study aims to fill this gap by analyzing the physicochemical and rheological properties of HA body fillers to guide clinical practice. MATERIALS AND METHODS: Four commercially available HA-based body fillers were analyzed under standardized laboratory conditions. The physicochemical properties, including pH, osmolality, ion concentrations, clarity, and swelling factor, were assessed. Rheological properties, including storage modulus (G'), loss modulus (G″), complex modulus (G*), and tan delta (tan δ), were assessed between 0.1 and 1 Hz. RESULTS: The physicochemical analysis revealed no significant differences among the fillers, indicating uniform chemical stability. However, rheological analysis showed significant variations. Infini B Body exhibited the lowest G', G″, and G* values. In contrast, HYAcorp MLF1 and MLF2 displayed higher G' and G* values, indicating greater elasticity and stiffness. Consistent rankings between 0.1 and 1 Hz suggest stable mechanical performance under dynamic and sustained loading, supporting their suitability for high-load applications such as gluteal augmentation. CONCLUSION: Selecting HA body fillers based on their rheological properties is crucial for optimizing outcomes, particularly in body contouring procedures where mechanical demands differ from those of facial applications. Clinicians should tailor filler selection to the specific requirements of each body area. Further research is required to validate these findings in long-term clinical settings.