The Curie temperature: a key playmaker in self-regulated temperature hyperthermia

The Curie temperature is an important thermo-characteristic of magnetic materials, which causes a phase transition from ferromagnetic to paramagnetic by changing the spontaneous re-arrangement of their spins (intrinsic magnetic mechanism) due to an increase in temperature. The self-control-temperature (SCT) leads to the conversion of ferro/ferrimagnetic materials to paramagnetic materials, which can extend the temperature-based applications of these materials from industrial nanotechnology to the biomedical field. In this case, magnetic induction hyperthermia (MIH) with self-control-temperature has been proposed as a physical thermo-therapeutic method for killing cancer tumors in a biologically safe environment. Specifically, the thermal source of MIH is magnetic nanoparticles (MNPs), and thus their biocompatibility and Curie temperature are two important properties, where the former is required for their clinical application, while the latter acts as a switch to automatically control the temperature of MIH. In this review, we focus on the Curie temperature of magnetic materials and provide a complete overview beginning with basic magnetism and its inevitable relation with Curie's law, theoretical prediction and experimental measurement of the Curie temperature. Furthermore, we discuss the significance, evolution from different types of alloys to ferrites and impact of the shape, size, and concentration of particles on the Curie temperature considering the proposed SCT-based MIH together with their biocompatibility. Also, we highlight the thermal efficiency of MNPs in destroying tumor cells and the significance of a low Curie temperature. Finally, the challenges, concluding remarks, and future perspectives in promoting self-control-temperature based MIH to clinical application are discussed.

Folic acid-conjugated dextran-coated Zn0.6Mn0.4Fe2O4 nanoparticles as systemically delivered nano heaters with self-regulating temperature for magnetic hyperthermia therapy of liver tumors

Successful cancer treatment using magnetic hyperthermia therapy (MHT) strongly depends on biocompatible magnetic nanoparticles (NPs). They can effectively accumulate in tumor tissues after systemic injection and generate heat in the therapeutic temperature range (42-48 °C) by exposure to an AC magnetic field (AMF). For this purpose, folic acid-conjugated dextran-coated Zn0.6Mn0.4Fe2O4 (FA-Dex-ZMF) NPs were synthesized as smart nano heaters with self-regulating temperatures for MHT of liver tumors. Animal studies on BALB/c mice showed that the prepared NPs did not cause acute toxicity upon administration up to 100 mg kg-1. Likewise, no significant changes in hematological and biochemical factors were observed. FA-Dex-ZMF NPs were studied by exposing them to different safe AC magnetic fields (f = 150 kHz, H = 6, 8, and 10 kA m-1). Calorimetric experiments revealed that the NPs reached the desired temperature range (42-48 °C), which was suitable for MHT. Moreover, the efficacy of FA-Dex-ZMF NPs in MHT of liver tumors was investigated in vivo in liver-tumor-bearing mice. The obtained results revealed that the average volume of tumors in the control group increased 2.2 times during the study period. In contrast, the tumor volume remained almost constant during treatment in the MHT group. The results indicated that folic acid-conjugated dextran-coated Zn0.6Mn0.4Fe2O4 NPs with self-regulating temperature could be a promising tool for systemically delivered MHT.

Multifunctional effects in magnetic nanoparticles for precision medicine: combining magnetic particle thermometry and hyperthermia

An effective combination of magnetic hyperthermia and thermometry is shown to be implementable by using magnetic nanoparticles which behave either as a heat sources or as temperature sensors when excited at two different frequencies. Noninteracting magnetite nanoparticles are modeled as double-well systems and their magnetization is obtained by solving rate equations. Two temperature sensitive properties derived from the cyclic magnetization and exhibiting a linear dependence on temperature are studied and compared for monodisperse and polydisperse nanoparticles. The multifunctional effects enabling the combination of magnetic hyperthermia and thermometry are shown to depend on the interplay among nanoparticle size, intrinsic magnetic properties and driving-field frequency. Magnetic hyperthermia and thermometry can be effectively combined by properly tailoring the magnetic properties of nanoparticles and the driving-field frequencies.

Synthesis, physical properties, and biomedical applications of magnetic nanoparticles: a review

Recent innovations in nanotechnology have opened the applicability of multifunctional nanoparticles (NPs) in biomedical diagnosis and treatment. The examples of NPs which have attracted considerable attention in recent years are metals (e.g., Au, Ag, Mg), alloys (e.g., Fe-Co, Fe-Pd, Fe-Pt, Co-Pt), iron oxides (e.g., Fe₂O₃ and Fe₃O₄), substituted ferrites (e.g., MnFe₂O₄ and CoFe₂O₄), manganites (e.g., [Formula: see text]), etc. Special attention has been paid to magnetic NPs (MNPs), as they are the potential candidates for several biomedical appliances, such as hyperthermia applications, magnetic resonance imaging, contrast imaging, and drug delivery. To achieve effective MNPs, a thorough investigation on the synthesis, and characteristic properties, including size, magnetic properties, and toxicity, is required. Furthermore, the surfaces of the NPs must be tailored to improve the biocompatibility properties and reduce agglomeration. The present review focuses on different mechanisms to develop biocompatible MNPs. The utility of these MNPs in various biomedical applications, especially in treating and diagnosing human diseases, such as targeted drug delivery, hyperthermia treatment for cancer, and other biomedical diagnoses, is thoroughly discussed in this article. Different synthetic processes and important physical properties of these MNPs and their biocomposites are presented.

Magnetic Nanoparticles for Biomedical Applications: From the Soul of the Earth to the Deep History of Ourselves

Precisely engineered magnetic nanoparticles (MNPs) have been widely explored for applications including theragnostic platforms, drug delivery systems, biomaterial/device coatings, tissue engineering scaffolds, performance-enhanced therapeutic alternatives, and even in SARS-CoV-2 detection strips. Such popularity is due to their unique, challenging, and tailorable physicochemical/magnetic properties. Given the wide biomedical-related potential applications of MNPs, significant achievements have been reached and published (exponentially) in the last five years, both in synthesis and application tailoring. Within this review, and in addition to essential works in this field, we have focused on the latest representative reports regarding the biomedical use of MNPs including characteristics related to their oriented synthesis, tailored geometry, and designed multibiofunctionality. Further, actual trends, needs, and limitations of magnetic-based nanostructures for biomedical applications will also be discussed.

In vivo magnetic nanoparticle hyperthermia: a review on preclinical studies, low-field nano-heaters, noninvasive thermometry and computer simulations for treatment planning

Magnetic nanoparticle hyperthermia (MNH) is a promising nanotechnology-based cancer thermal therapy that has been approved for clinical use, together with radiation therapy, for treating brain tumors. Almost ten years after approval, few new clinical applications had appeared, perhaps because it cannot benefit from the gold standard noninvasive MRI thermometry technique, since static magnetic fields inhibit heat generation. This might limit its clinical use, in particular as a single therapeutic modality. In this article, we review the in vivo MNH preclinical studies, discussing results of the last two decades with emphasis on safety as a clinical criteria, the need for low-field nano-heaters and noninvasive thermal dosimetry, and the state of the art of computational modeling for treatment planning using MNH. Limitations to more effective clinical use are discussed, together with suggestions for future directions, such as the development of ultrasound-based, computed tomography-based or magnetic nanoparticle-based thermometry to achieve greater impact on clinical translation of MNH.

One-pot preparation of hyaluronic acid-coated iron oxide nanoparticles for magnetic hyperthermia therapy and targeting CD44-overexpressing cancer cells

In the present study, a facile one-pot hydrothermal method is introduced for preparation of hyaluronic acid-coated Fe₃O₄ nanoparticles (Fe₃O₄@HA NPs) for theranostic applications. In the proposed method, hyaluronic acid acts simultaneously as a biocompatible coating layer and as a targeting ligand for CD44 receptor overexpressed on the surface of breast cancer cells. The obtained product with narrow hydrodynamic size distribution exhibited a high colloidal stability at physiological pH for more than three months. Cytotoxicity measurements indicated a negligible toxicity of the prepared sample against L929 normal cells. Preferential targeting of Fe₃O₄@HA NPs to CD44-overexpressing cancer cells was studied by comparing the uptake of the prepared nanoparticles by MDA-MB-231 cancer cells (positive CD44 expression) and L929 normal cells (negative CD44 expression). Uptake of the Fe₃O₄@HA NPs by MDA-MB-231 cells was found to be 4-fold higher than the normal cells. Also, the in vitro analysis showed that, the uptake of Fe₃O₄@HA NPs by MDA-MB-231 breast cancer cells is significantly enhanced as compared to non-targeted dextran-coated Fe₃O₄ NPs. Moreover, the heat generation capability of the Fe₃O₄@HA NPs for magnetic hyperthermia application was studied by exposing the prepared nanoparticles to different safe alternating magnetic fields (f = 120 kHz, H = 8, 10, and 12 kA/m). The intrinsic loss power obtained for Fe₃O₄@HA NPs was about 3.5 nHm²/kg, which is about 25-fold larger than that of obtained for commercial available Fe₃O₄ nanoparticles for biomedical applications. Good colloidal stability, biocompatibility, high heating efficacy, and targeting specificity to CD44 receptor-overexpressing cancer cells could make the Fe₃O₄@HA NPs as a promising multifunctional platform for diagnosis and therapeutic applications.

Effects of multiple injections on the efficacy and cytotoxicity of folate-targeted magnetite nanoparticles as theranostic agents for MRI detection and magnetic hyperthermia therapy of tumor cells

Folate-targeted iron oxide nanoparticles (FA@Fe3O4 NPs) were prepared by a one-pot hydrothermal method and then used as cancer theranostic agents by combining magnetic resonance imaging (MRI) and magnetic hyperthermia therapy (MHT). Crystal structure, morphology, magnetic properties, surface functional group, and heating efficacy of the synthesized nanoparticles were characterized by XRD, TEM, VSM, FTIR, and hyperthermia analyses. The results indicated that the crystal structure, magnetic properties, and heating efficacy of the magnetite nanoparticles were improved by hydrothermal treatment. Toxicity of the prepared NPs was assessed in vitro and in vivo on the mammary cells and BALB/c mice, respectively. The results of the in vitro toxicity analysis showed that the FA@Fe3O4 NPs are relatively safe even at high concentrations of the NPs up to 1000 µg mL-1. Also, the targetability of the FA@Fe3O4 NPs for the detection of folate over-expressed cancer cells was evaluated in an animal model of breast tumor using MRI analysis. It was observed that T2-weighted magnetic resonance signal intensity was decreased with the three-time injection of the FA@Fe3O4 NPs with 24 h interval at a safe dose (50 mg kg-1), indicating the accumulation and retention of the NPs within the tumor tissues. Moreover, the therapeutic efficacy of the MHT using the FA@Fe3O4 NPs was evaluated in vivo in breast tumor-bearing mice. Hyperthermia treatment was carried out under a safe alternating magnetic field permissible for magnetic hyperthermia treatment (f = 150 kHz, H = 12.5 mT). The therapeutic effects of the MHT were evaluated by monitoring the tumor volume during the treatment period. The results showed that the mice in the control group experienced an almost 3.5-fold increase in the tumor volume during 15 days, while, the mice in the MHT group had a mild increase in the tumor volume (1.8-fold) within the same period (P < 0.05). These outcomes give promise that FA@Fe3O4 NPs can be used as theranostic agents for the MRI and MHT applications.

Recent advancements in manganite perovskites and spinel ferrite-based magnetic nanoparticles for biomedical theranostic applications

Recently, magnetic nanoparticles (MNPs) based on manganite perovskites (La_1-xSr_xMnO₃ or LSMO) and/or spinel ferrites (i.e. SPFs with the formula MFe₂O₄; M=Co, Mg, Mn, Ni and Zn and mixed SPFs (e.g. Co-Zn, Mg-Mn, Mn-Zn and/or Ni-Zn)) have garnered great interest in magnetic hyperthermia therapy (MHT) as heat-inducing agents due to their tuneable magnetic properties including Curie temperature (T _c) to generate controllable therapeutic temperatures (i.e. 42 °C-45 °C)-under the application of an alternating magnetic field (AMF)-for the treatment of cancer. In addition, these nanoparticles are also utilized in magnetic resonance imaging (MRI) as contrast-enhancing agents. However, the employment of the LSMO/SPF-based MNPs in these MHT/MRI applications is majorly influenced by their inherent properties, which are mainly tuned by the synthesis factors. Therefore, in this review article, we have systematically discussed the significant chemical methods used to synthesize the LSMO/SPF-based MNPs and their corresponding intrinsic physicochemical properties (size/shape/crystallinity/dispersibility) and/or magnetic properties (including saturation magnetization (M _s)/T _c). Then, we have analyzed the usage of these MNPs for the effective imaging of cancerous tumors via MRI. Finally, we have reviewed in detail the heating capability (in terms of specific absorption rate) of the LSMO/SPF-based MNPs under calorimetric/biological conditions for efficient cancer treatment via MHT. Herein, we have mainly considered the significant parameters-such as size, surface coating (nature and amount), stoichiometry, concentration and the applied AMFs (including amplitude (H) and frequency (f))-that influence the heat induction ability of these MNPs.

Biofunctional magnetic hybrid nanomaterials for theranostic applications

Cancer is a major disease that seriously threatens human health and is a leading cause of human death. At present, the commonly used cancer treatment methods are surgical therapy, chemical drug therapy and radiation therapy (RT). However, these treatments all have their own shortcomings and cannot perfectly meet the needs of clinical diagnosis and treatment. It is of great significance to improve the diagnosis and treatment level, so that the curative effect and quality of life of tumor patients can be improved. The rapid development of nanotechnology has brought hope to the diagnosis and treatment of cancer and the appearance of biofunctional magnetic hybrid nanomaterials (MHNs) has provided a new possibilities for the integration of cancer diagnosis and treatment. As a promising research direction, the multifunctional nanoplatform integrates imaging diagnosis, drug therapy and drug delivery. Better treatment effects and fewer side effects can be achieved by optimizing materials to build stable, efficient, and safe MHNs with combined functions of multimodal imaging and various treatments. This review focuses on not only the research progress of MHNs but also their applications and development trend in the integration of cancer diagnosis and treatment. A description of the applications of MHN structure optimization for both magnetic resonance imaging-based multimodal diagnosis and cancer therapy is given. Furthermore, RT is introduced and the development of MHNs for diagnosis and treatment system is investigated.

Magnetic carbon nanotubes for self-regulating temperature hyperthermia

Magnetic hyperthermia can enhance the anti-tumor effects of chemotherapy. As carbon nanotubes are ideal drug carriers for chemotherapy, their combination with magnetic nanoparticles provides a novel chance for multi-modal thermo-chemotherapy. Most related work focuses on attaching Fe₃O₄ nanoparticles on carbon nanotubes, however the hyperthermia temperature for this combination can not be self-regulated due to the high Curie temperature of Fe₃O₄. In this work, magnetic Zn_0.54Co_0.46Cr_0.6Fe_1.4O₄ nanoparticles with low Curie temperature were attached onto carbon nanotubes to obtain the magnetic carbon nanotubes. The morphology, formation mechanism, magnetic properties, heat generation ability and cytotoxicity of the magnetic carbon nanotubes were investigated. These magnetic carbon nanotubes show a Curie temperature of 43 °C and a self-regulating temperature at 42.7 °C under clinically applied magnetic field conditions (frequency: 100 kHz, intensity: 200 Oe). The evaluation of in vitro cytotoxicity suggests no obvious toxicity effects under the concentrations of 6.25 μg ml⁻¹ to 100 μg ml⁻¹. This study proposed a methodology for the bespoke synthesis of magnetic carbon nanotubes with a low Curie temperature for self-regulating magnetic hyperthermia, which may be used for further research on loading drugs for multi-modal cancer therapy.

Magnetic carbon nanotubes with low Curie temperature are synthesized for self-regulating temperature in hyperthermia.