Abstract
Hyaluronic acid (HA) is a high-molecular-weight glycosaminoglycan whose cross-linked hydrogels are widely used as injectable fillers; their controlled degradation is clinically important but, in practice, achievable only enzymatically with hyaluronidase. Here we compared the enzymatic, ultrasonic and photothermal degradation of a single cross-linked HA macromolecular network and characterised the resulting structural, thermal and chromatographic changes. A cross-linked HA hydrogel (Regenyal Idea, 25 mg/mL) was embedded in an ex vivo porcine skin matrix and treated in six groups: untreated control; hyaluronidase; microfocused ultrasound (7 MHz, 3 mm focal depth); and irradiation with 1064 nm Nd:YAG, diode or alexandrite lasers. Degradation was characterised by FT-IR spectroscopy, thermogravimetric analysis (TGA) and high-performance liquid chromatography (HPLC). FT-IR showed retention of the HA backbone with partial loss of the cross-linked network, while TGA revealed treatment-dependent decreases in thermal stability. By HPLC, hyaluronidase released the most soluble HA (58.2 ± 2.9% at day 1; ~88% plateau by day 2). Among the energy-based methods, only the 1064 nm Nd:YAG laser produced comparable degradation (57.3 ± 5.2%), whereas microfocused ultrasound, the diode and the alexandrite lasers released little soluble HA (3.2–5.3%). The wavelength dependence is consistent with a water-mediated photothermal scission of the HA chains. These findings identify long-pulsed 1064 nm irradiation as an effective non-enzymatic route to degrade the cross-linked hyaluronic acid macromolecule, with hyaluronidase remaining the reference standard.