Hybrid carriers with the mineral CaCO3/Fe3O4 core and the protein–tannin shell are attractive for drug delivery applications due to reliable coupling of anticancer drugs with protein–tannin complex and the possibility of remote control over drug localization and delivery by the external magnetic field. This study aims to elucidate the mechanisms of drug release via enzymatic degradation of a protein–tannin carrier shell triggered by proteolytic hydrolases trypsin and pepsin under physiological conditions. To do this, the carriers were incubated with the enzyme solutions in special buffers to maintain the enzyme activity. The time-lapse spectrophotometric and electron microscopy measurements were carried out to evaluate the degradation of the carriers. It was established that the protein–tannin complex demonstrates the different degradation behavior depending on the enzyme type and buffer medium. The incubation in trypsin solution mostly resulted in the protein shell degradation. The incubation in pepsin solution did not affect the protein component; however, the citric buffer stimulates the degradation of the mineral core. The presented results allow for predicting the degradation pathways of the carriers including the release profile of the loaded cargo under physiological conditions. The viability of 4T1 breast cancer cells with mineral magnetic carriers with protein–tannin shells was investigated, and their movement in the fields of action of the permanent magnet was shown.

Cell spheroids (CSs) are three-dimensional models in vitro that have a microenvironment similar to tissues. Such three-dimensional cellular structures are of great interest in the field of nano biomedical research, as they can simulate information about the characteristics of nanoparticles (NPs) by avoiding the use of laboratory animals. Due to the development of areas such as bioethics and tissue engineering, it is expected that the use of such 3D cell structures will become an even more valuable tool in the hands of researchers. We present an overview of carbon nanotubes (CNTs) research on CSs in order to determine the mechanism of their incorporation into CSs, drug delivery, and photothermal therapy. We will look at such areas as the application of CNTs for medical purposes, the advantages of spheroids over classical 2D cell culture, the ways in which CNTs pass into the intercellular space, and the ways in which they are absorbed by cells in a three-dimensional environment, the use of the spheroid model for such studies as drug delivery and photothermal therapy. Thus, CSs are suitable models for obtaining additional information on the required properties of CNTs in their application in nanobiomedicine.

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