Fig. 2.

Photothermal performance of PDA-HP hydrogel. (A) Photothermal stability of PDA–HP hydrogel over six consecutive heating–cooling cycles under 808 nm laser irradiation (1 W/cm², 10 min per cycle), showing negligible attenuation of heating capacity. (B) Infrared thermal images of SCI mice treated with PDA-HP hydrogel (PDA-HP group) or without treatment (CON group) under identical ambient conditions (22 °C) and irradiation parameters (808 nm, 1 W/cm²) for 1, 3, and 5 min. The PDA-HP group exhibited a significant and localized temperature rise at the lesion site, while only minimal heating was observed in the control group. The color scale (25–45 °C) spans basal body temperature (∼36 °C) to the photothermal peak (∼42 °C). (C) Photothermal heating curves of PDA-HP hydrogels with varying PDA concentrations (1, 10, and 20 mg/mL) under NIR irradiation (808 nm, 1 W/cm²). Temperature elevation exhibited a clear concentration-dependent trend, confirming the tunable and stable photothermal behavior of the material in aqueous (in vitro) conditions. Note that these in vitro heating profiles reflect material performance in solution and may differ from intramedullary temperatures in vivo due to optical scattering, blood perfusion, and tissue heat dissipation. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)