Biodegradable PBAT@CoFe ₂ O ₄ foils as magnetically active photothermal materials for smart surface heating

Our study is devoted to the development, physicochemical characterization, and NIR energy conversion to heat of biodegradable PBAT@CoFe₂O₄ composite foil fabricated <i>via</i> the solvent evaporation casting technique. Superparamagnetic CoFe₂O₄ nanoparticles (6.3 nm) were synthesized through thermal decomposition and incorporated into a PBAT matrix, as confirmed by shifting vibration modes, suggesting strong interfacial interactions. TGA/DTA and DSC analyses showed a significant change in the composite foil degradation and thermal properties induced by the presence of cobalt nanoferrite due to its catalytic activity. Magnetic characterization confirmed the superparamagnetic behavior of the stock CoFe₂O₄ and ferrite-doped PBAT composite foil. We observed that under NIR₈₀₈ laser irradiation, the composite exhibited rapid heating, whereas foil heating under an AMF was ineffective due to the immobilization of particles within the polymer matrix. The highest recorded temperature was 115 °C with a specific absorption rate (SAR) of 97.5 W g^-1 (the maximum allowed laser power due to the risk of polymer matrix melting). Heating ability was further evaluated using a pork skin <i>ex vivo</i> model to simulate soft tissue interaction, revealing skin discoloration and surface changes caused by protein coagulation under heat generation. Cytotoxicity tests of a reference and the composite foil were carried out using the NIH/3T3 fibroblast cell line according to ISO standards, showing that these foils can be considered safe and non-toxic. The results confirm the potential of NIR-responsive PBAT@CoFe₂O₄ composites as smart energy-converting materials used for various practical applications. Even though the AMF cannot be applied for heating foils integrated with magnetic particles, it can be used for the fast separation of polymeric composites from a waste mixture using magnets to achieve their segregation in recycling facilities. This feature may be of particular interest upon product end-of-life.