Magnetically responsive hydrogels with high and reproducible hyperthermic performance Karina Nigoghossian 1 , Krutika Singh 1 , Danielle Winning 1 , Jacek Wychowaniec 1 , Shane Clerkin 2 , Ivan Krupa 2 , John Crean 2 , Dermot F. Brougham 1 1 School of Chemistry, University College Dublin, Ireland, 2 School of Biomolecular and Biomedical Science, University College Dublin, Ireland The development of magnetically responsive nanocomposite hydrogels (mag-gels) is increasingly demanded for designing extracellular scaffolds for hyperthermia and drug delivery applications [1] . The main challenge is achieving controlled and homogeneous heat distribution to avoid overheating and provide the required thermal dose [2] . The design of optimal mag-gels requires the structural control of the material from the nano- to the macroscale. Firstly, the control over properties of magnetic nanoparticles (such as size, shape and surface) is crucial for achieving high heating performance and ensure homogeneous dispersion in the hydrogel network. Secondly, the nanocomposite preparation must achieve the maximum crosslinking of hydrogel to allow the design of 3D-patterned structures stable against temperature variations. Among several polymers used for developing printable nanocomposite hydrogels, gelatin offers excellent biocompatibility and suitable biodegradability for several biomedical applications, such as drug delivery and tissue engineering [3,4] . In this work, we report mag- gel formulations containing highly efficient heating PEGylated iron oxide nanoflowers (PNFs) able to induce fast temperature increments under external AC-magnetic field stimulus. The optimization of mag-gel formulations aimed at: (i) cross-likability to ensure the shape fidelity; (ii) homogeneous iron distribution; (iii) reproducible hyperthermia performance (SAR); and (iv) spatiotemporally controlled AC-field heating. The MNFs were homogeneously loaded (variation ≤ 3%) over a broad range of concentration (10 – 119 mM Fe) as demonstrated by a systematic study of iron quantification from different parts of the mag-gel. The heating ability was measured in a quasi-adiabatic AC-field exposure system by varying the positioning of the temperature probe, which showed reproducibility of the hyperthermic responses (variation ≤ 5%). The initial heating rate increased linearly with MNF concentration, suggesting that this formulation parameter can be varied to achieve suitable temperature increases for the intended application. The mag-gels presented hyperthermic performance independent of the Fe concentration with full SAR retention of 100% from the starting aqueous colloidal suspension (312 ± 10 W g -1 , Fe). To further investigate the heating properties in conditions susceptible to heat loss, thermal imaging of the mag- gels was conducted in an open coil system, which showed temperature jumps of 2 to 15 °C in 90 seconds across the available concentration range. A swelling study performed in water at 37 °C demonstrated the physical stability of mag-gels, absence of PNF leaching and the increase in water absorption with Fe content. The presentation will discuss the design strategies and outputs in details. Taken together, the mag-gel proposed here offers homogeneous and tuneable heat generation and suitable properties for a further development of extracellular scaffolds for hyperthermia applications. References
1. Ganguly, S. and Margel, S., 2021. Polymers , 13(23), 4259. 2. Gavilán, H. et al. 2021. Chem. Soc. Rev. , 50(20), 11614. 3. Lai, J. et al., 2021. Appl. Phys. Rev. , 8(2), 021322. 4. Lewis, P.L. et al., 2018. Acta Biomater. , 69, 63.
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