## 4 Biomedical Applications
Magnetic nanoparticles are also applied in biomedical applications using different stimuli, and each living system responds to stimuli, regardless of the type of stimuli, even if it is temperature, pH, or light. Applying several stimuli to the body, we obtain an answer, and this response is vital for the proper operation of the whole system [108]. These features have been an inspiration for scientists to develop \"smart\" materials designed to react to various stimuli such as temperature, pH, or magnetic field; as they are sensitive to a magnetic field, they can incorporate magnetic nanoparticles and lead to smart materials with good magnetic guidance and (magnetic) stimuli release. To transform energy into heat, magnetic particles were used as heat generators. The above phenomenon is important in cancer therapy because hyperthermia can be used in killing cancer cells, but also in targeted delivery, and increasing temperature will increase diffusion, therefore increasing the drug delivery [139]. Many studies have confirmed that nano-magnetic and microparticles have great applicability in magnetic storage media, biosensing and biomedical applications, as contrast agents in MRI--using them in tumor tissue under the action of magnetic fields--and also in new applications that aim to deliver and control the release of chemicals [35; 131; 140]. Another good example of a multifunctional magnetic nanocomposite is Fe\({}_{3}\)O\({}_{4}\)@SiO\({}_{2}\), with biomedical applications related to the production of hyperthermia, which is an effective method to fight cancer. Hyperthermia is also combined with radiotherapy and chemotherapy, and is used to adjust the delivery rate of the chemotherapeutic drugs. The review describes the most important applications, and some of them are presented in this section. An important biomedical application worth mentioning is the use of magnetic nanomaterials in applications such as hyperthermia and controlled drug delivery [4; 53; 54]. As the term implies, hyperthermia means using heat in cancer therapy. Magnetic nanoparticle-based hyperthermia has proven to generate local heat that releases drugs at a specific site [5; 32; 68; 117; 140; 141; 142]. In medical hyperthermia, magnetic nanoparticles are used as a generator to raise tissue temperatures to 41 (mild)-43 \({}^{\circ}\)C (curative hyperthermia) in tumour cells, tissues, or organs. Coated magnetic nanoparticles can be functionalized/loaded with different molecules, such as drugs or antibodies, for use in targeted tumours from specific tissues/organs [35; 143]. A new material synthesized by a solvothermal method with promising applications in drug delivery is monodisperse superparamagnetic single-crystal magnetite nanoparticles (MSSMN). Tests were conducted and the most important result stated that MSSMN is efficient in drug delivery applications. Doxorubicin (Dox) has been used as an anticancer drug, and the results have shown that these materials have a perfect loading capacity and favourable delivery profile for Dox [4; 5; 34]. Figure 4 is a graphical representation of the MSSMN synthesis as well as its use in biomedical applications. Researchers are trying to develop certain modalities to control the transport of drugs and the rate of release, in a targeted way, on the specific tumour site. Through nano-engineering, an efficient drug delivery carrier was developed that can precisely localize the targeted tissue and release the perfect amount of medication that annihilates cancer without harming those in good health, which is the most desired challenge [5; 105; 107]. After many studies, breast tumours are classified by histopathological degree, type, and stage; the classification was determined to find the best treatment, such as chemotherapy or immunotherapy [33; 101]. Tumours were classified according to the epidermal growth of the factor receptor family in HER1, HER2, HER3, and HER4.