Comparative Rheology of Modern HA Fillers: G′, Cohesivity, and Tissue Integration

Background: Crosslinked hyaluronic acid (HA) fillers differ substantially in their viscoelastic behavior, yet clinical selection often relies on manufacturer marketing rather than measured rheologic properties. Objective: To characterize and compare the rheologic and cohesive behavior of 14 commercially available HA fillers and correlate these properties with in-vivo tissue integration and clinical placement zones. Methods: Bench testing measured elastic modulus (G′), viscous modulus (G″), tan δ, and cohesivity using standardized oscillatory and compression protocols at 37°C. In-vivo assessment was performed in a paired forearm model (n=48) with ultrasound imaging of product spread and integration at 30 and 90 days. Blinded injectors rated ease of injection and moldability. Results: G′ values ranged from 24 to 587 Pa, with high-G′ products (>300 Pa) demonstrating superior projection but reduced lateral spread on ultrasound. Cohesivity was independent of G′ and correlated more strongly with tissue integration patterns. Products with intermediate G′ and high cohesivity produced the most uniform dermal distribution and were preferred for midface and lip placement. High-G′, low-cohesivity products performed best in deep supraperiosteal chin and jaw augmentation. Conclusions: Rheologic profiling meaningfully predicts clinical behavior and should inform product selection by anatomic zone. G′ alone is an insufficient descriptor; cohesivity should be considered as an independent selection criterion.