Comparative Physicochemical Characterization of Two Commercial Hydroxyapatite‐Based Collagen Biostimulators

Hydroxyapatite (HA)‐based bioceramics are widely used as collagen biostimulators and dermal fillers. This study provides a direct comparative characterization of two commercially available HA‐based injectable products, identified in this work as Product 1 (Revita Absorbable Implant) and Product 2 (Radiesse Duo). A multimodal analytical framework was employed to assess chemical composition, microstructure, rheology, pH, and osmolality. Methods included Fourier‐transform infrared spectroscopy (FTIR) with ATR, thermogravimetric analysis (TGA), X‐ray diffraction (XRD), scanning electron microscopy (SEM), complemented by particle‐size analysis, rheological measurements, and standard pH and osmolality assays. FTIR and TGA indicate a HA‐dominated composition with auxiliary constituents (water, Na‐CMC, and glycerol) consistent with the reported formulations. XRD patterns are consistent with hydroxyapatite as the predominant crystalline phase, with no detectable secondary phases under the adopted experimental conditions in either product. SEM and laser‐diffraction analyses show spherical HA microstructures with average diameters near 30 µm (33.9 µm for Revita and 35.2 µm for Radiesse). Rheological measurements reveal closely similar complex viscosities, and the measured pH values under the adopted dilution conditions are 7.66 (Revita) and 7.76 (Radiesse), that is, near the physiological range. Osmolality values are elevated relative to isotonic targets: ∼1250 mOsm/kg for Revita and ∼1300 mOsm/kg for Radiesse. Overall, the two products show highly similar chemical composition, predominant crystalline phase, and particle microstructure, with differences primarily arising from the gel matrix, possibly related to differences in Na‐CMC molecular characteristics, which may contribute to differences in rheology and tonicity. The results indicate substantial physicochemical similarity between the two products.