Investigation of Crosslinking Parameters and Characterization of Hyaluronic Acid Dermal Fillers: From Design to Product Performances

Abstract

Despite process similarities, distinctive manufacturing technologies offer hyaluronic acid dermal fillers with different in vitro physicochemical and rheological properties due to peculiar crosslinked hydrogel networks. A better understanding of dermal filler properties could provide specific clinical indications and expectations with more accurate performance correlations. In this study, with an emphasis on the degree of modification, hyaluronic acid concentration and molecular weight, these process parameters were able to modulate dermal filler properties, especially rheology. Moreover, an extensive characterization of commercial hyaluronic acid injectables of the Hyal System line was described to present product properties and help to elucidate related clinical effects. Standardized methodologies were applied to correlate in vitro parameters with feasible clinical indications. In view of an optimized dermal filler design, the results of the extrudability measurements allowed the quantification of the effect of hydrogel composition, rheological properties and needle size on injectability. Composition, dynamic viscosity and needle size showed an impactful influence on hydrogel extrudability. Finally, the positive influence of 200 KDa hyaluronic acid in comparison to fragments of ether-crosslinked hyaluronic acid on fibroblast recognition were shown with a migration assay.

Keywords: crosslinking; dermal fillers; hyaluronic acid.

Figure 1

Elastic modulus (light blue dots), viscous modulus (red squares) and degree of modification (green triangles) of HA hydrogels with theoretical crosslinking degree from 5 to 20% mol/mol vs. HA repeat unit (A) and HA reaction concentration from 65 to 300 mg/mL (B). Elastic modulus and cohesivity (C), and particle size and soluble fraction (D) of HA hydrogels with starting molecular weights (200, 700 and 1800 KDa). Mean ± DS; n = 2.

Figure 2

Properties of Hyal System dermal fillers (1.8%, ACP, DUO, LIP, VOL): Elastic modulus, viscous modulus and dynamic viscosity (A). Cohesivity and elastic modulus (B), HA conc. x elasticity (values above the dashed line: WSRS score > 1) (C). elasticity and tanδ, (D), and soluble fraction and swelling factor (E) (values to the left of the dashed line: linear HA, to the right: cross-linked HAs). Mean ± DS; n = 3.

Figure 3

Schematic representation of the correlation between in vitro parameters and clinical aspects of Hyal System dermal fillers (1.8%, ACP, DUO, LIP, VOL).

Figure 4

Average extrusion force and dynamic viscosity of Hyal System dermal fillers (1.8%, ACP, DUO, LIP, VOL) with needle reference. Mean ± DS; n = 3.

Figure 5

Extrusion values of ether-crosslinked hydrogels with linear HA (200, 700, 1200, 1800 KDa) or ACP at different concentrations (A). Extrusion values of ether-crosslinked hydrogels with different dynamic viscosity values (0.6–102.3 P·s at 1 Hz) (B) and needle sizes (30 G and 27 G) (C). Mean ± DS; n = 3; **** p < 0.0001.

Figure 6

Murine fibroblast migration plot after treatments with HA 200 KDa, 700 KDa and depolymerized BDDE-crosslinked HA after 6 h. Mean ± DS; n = 3; * p < 0.05 and *** p < 0.001.