Magnetic hybrid Pd/Fe-oxide nanoparticles meet the demands for ablative thermo-brachytherapy

Figures & data

Table 1. Overview of the AMF frequencies generated by the magneTherm™ Digital and the corresponding measured maximum magnetic field peak strengths including standard deviation (n = 3).

Frequency (kHz)	50	159	188	251	297	346	390	454	570	730
Magnetic field (mT)	26.36 ± 0.12	21.06 ± 0.04	18.66 ± 0.03	21.80 ± 0.04	20.74 ± 0.09	19.13 ± 0.12	16.81 ± 0.02	16.18 ± 0.12	13.20 ± 0.03	12.33 ± 0.04
Field-Frequency product (T s^−1)	1318	3349	3508	5472	6160	6619	6556	7346	7524	9013

Figure 1. Schematic drawing of the insulated polystyrene sample holder (grey) containing the plastic sample vial (blue) and two glass fiber thermometers.

Table 2. Overview of MNPs evaluated in this study and their corresponding magnetic properties [21].

MNPs	Diameter (nm)	Ms (300 K/5 K) (emu/gNP)	Hc (300 K/5 K) (Oe)	TB (K)	Batch name in Ref. [21]
Fe-oxide-comm	15	—^a	—^a	—^a	—^b
Pd/Fe-oxide-10	10	20.5/26.4	10/466	30	Exp_[surf]/[Fe] = 2
Pd/Fe-oxide-12	12	28.1/36.9	19/236	23	Exp_DPE
Pd/Fe-oxide-13	13	45.1/52.1	8/287	40	Exp_3 °C
Pd/Fe-oxide-16	16	39.9/46.5	9/56	120	Exp_ODE:DPE(1:1)
Pd/Fe-oxide-18	18	55.4/63.6	4/13	160	Exp_DBE
Pd/Fe-oxide-19	19	57.5/63.7	6/213	130	Exp_7 °C
Pd/Fe-oxide-20	20	58.7/67.9	8/20	180	Exp_standard
Pd/Fe-oxide-21	21	61.4/69.2	12/67	200	Exp_10mg

^a not determined; ^bcommercial MNPs.

Figure 2. Heating/cooling curve of HyperMag-C sample in the insulated sample holder. The solid and the dashed lines represent the core and the bottom temperatures of the sample, respectively.

Figure 3. Heating curves of an old, unstable batch of HyperMag-C MNPs obtained with two thermometers placed at the center (solid line) and the bottom (dashed line) of the sample measured immediately after (A) or a few hours after (B) rigorous stirring.

Figure 4. The SLP of all synthesized Pd/Fe-oxide-n MNPs vs their size (n) measured at 50, 346 and 730 kHz. Commercial nanoparticles (Fe-oxide-comm, HyperMag-C) with the size of 15 nm are also included for comparison.

Figure 5. Magnetization curves measured with dry Pd/Fe-oxide MNPs at 300 K (A) as described in [21] and magnification of the x-axis showing coercivities H_c at static field.

Figure 6. Blocking temperatures of the Pd/Fe-oxide-n MNPs [21] vs their SLP at 50, 346 and 730 kHz.

Figure 7. Modeled relationship between SLP and tumor radius, and the achievable temperature increase within the tumor with homogeneously distributed MNPs. The lines represent the actual SLP values of Pd/Fe-oxide-21 (A), Pd/Fe-oxide-18 (B) and Pd/Fe-oxide-20 (C) measured at the optimal field (19 mT) and frequency (345 kHz) combination.

Table 3. The Pd/Fe-oxide-n MNP batches and corresponding SLP measured at 346 kHz. For each sample the minimum tumor radius R_min that can be thermally ablated (ΔT = 15 °C) is calculated using Eq. (5)(5) $$\mathit{\text{SLP}}=\frac{\Delta T·3\lambda }{c·R^2}$$(5) , any tumor with a radius larger than R_min can be thermally ablated. The shaded samples have the highest SLP and are therefore most suitable for thermal ablation.

Sample	SLP (W/g)	Rmin (mm) c = 1 mg/mL	Rmin (mm) c = 5 mg/mL	Rmin (mm) c = 10 mg/mL
Pd/Fe-oxide-21	233	11.1	5.0	3.5
Pd/Fe-oxide-18	209	11.7	5.2	3.7
Pd/Fe-oxide-20	116	15.8	7.1	5.0
Pd/Fe-oxide-16	106	16.5	7.4	5.2
Pd/Fe-oxide-19	103	16.7	7.5	5.3
Pd/Fe-oxide-13	71	20.1	9.0	6.4

Maier A, van Oossanen R, van Rhoon GC, et al. From structure to function: understanding synthetic conditions in relation to magnetic properties of hybrid Pd/Fe-oxide nanoparticles. Nanomaterials (Basel). 2022;12(20):3649. doi: 10.3390/nano12203649.

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Data availability statement

The data underlying this work is available upon request from the corresponding author.