Rheological Properties and In Vivo Performance Characteristics of Soft Tissue Fillers.

Physicochemical properties and performance in nonclinical animal models can provide insights into soft tissue filler performance.To evaluate the in vivo performance of fillers with different compositions and physicochemical properties.Physicochemical properties were measured in vitro. Rat models were developed and used to compare lift capacity, resistance to deformation, and tissue integration. Four homogeneous hyaluronic acid (HA) fillers, 2 nonanimal stabilized HA (NASHA) fillers, and 1 calcium hydroxylapatite/carboxymethyl cellulose (CaHA/CMC) filler were evaluated.Filler lift capacity correlated better with filler composition/type (homogeneous > NASHA > CaHA/CMC) than with specific rheological properties. The CaHA/CMC filler had high initial resistance to deformation relative to other groups; all HA fillers exhibited lower initial resistance to deformation, which increased over time. Homogeneous HA fillers were integrated with surrounding tissue, whereas integration within particle-based fillers (NASHA and CaHA/CMC) was variable, with some areas void of tissue.The animal models provide a platform to make comparative evaluations among fillers. The results indicated that biological interaction plays an important role in how the filler performs. Rheology alone was not sufficient to understand filler performance but was most useful when comparing within fillers of similar composition.