# Recent Progress and Challenges Regarding Magnetic-Based Nanoparticles for Targeted Drug Delivery
## 7 Conclusions  
Original articles published over the last three years confirm high knowledge in designing systems with components enabling chemotherapeutic release in the desired areas of the tumor environment, with a limited impact on healthy cells. Despite various solutions, the synthesis products are well characterized based on many physicochemical techniques. Most of the investigated nanosystems demonstrate pH-responsiveness, and many with a disulfide bridge--redox-responsiveness. Most magnetic nanocarriers use folic acid as a targeting molecule and doxorubicin as an active agent. The primary, and frequently the sole, method for evaluating anticancer properties involves in vitro tests using cell lines. Significantly, their effectiveness is compared to the free drug and the carrier itself without adding the active components. They are used to characterize bioavailability, cytotoxicity, and cellular uptake. Conversely, in vivo studies in mice, which are less common, primarily evaluate tumor growth inhibition, the survival rate, and the impact of the drug-loaded nanocarrier on both cancer-affected and healthy organs. Numerous studies have successfully confirmed the selectivity of the drug loaded in the nanocarrier toward cancer cells, thus limiting its toxicity to healthy cells and enabling a reduction in the drug dose. Notably, many scientific papers highlight the various possibilities of using systems based on magnetite nanoparticles in cancer therapy and propose multifunctional materials, resulting in  
Figure 10: A schematic representation of achievements and challenges in research on magnetite-based nanoparticles for targeted drug delivery. a better therapeutic effect. First, a synergistic effect can be obtained by combining hyperthermia with chemotherapy. The temperature in the target area is increased by alternating magnetic field (MHT) or laser irradiation (PTT). Such systems can also perform a diagnostic function as negative contrast agents in MRI imaging. Cancer treatment often requires a combination of different therapies to increase effectiveness. Therefore, such multifunctional materials are especially in demand, and further development in this direction is required. However, their clinical applications remain elusive despite extensive knowledge and the capability to design magnetic nanocarriers for targeted cancer therapy. Presumably, the knowledge about interactions between magnetic nanocarriers and biological systems is too limited, hindering overcoming this barrier. Analyzing the recent literature reports over the past three years reveals that the predominant approach employed in most of these studies involves utilizing fluorescence microscopy to investigate those interactions. Other less frequently used techniques include magnetic resonance imaging, flow cytometry, or confocal laser scanning microscopy. Unfortunately, few recent papers use more than one method to study this issue. Each of the methods discussed above has certain limitations. Therefore, indicating one appropriate technique for a given study is difficult. Moreover, analytical methods for better interpreting interactions occurring in biological systems should be developed. According to the authors, the optimal approach would be integrating multiple methods that provide insights into the interactions between magnetic nanoparticles and cells and enable comprehension of the factors responsible for the bioseparation of active agents from nanocarriers within the specified target region. It is worthwhile to explore the application of alternative techniques that have proven successful in studying magnetic nanoparticles in different fields but have not received adequate recognition in biomedical utilizations. Adopting this strategy could offer a pathway to understanding and overcoming challenges associated with implementing potential magnetite-based systems for practical drug delivery applications. Conceptualization, J.K.; writing--original draft preparation, J.K. and B.D.