Hybrid Stents Based on Magnetic Hydrogels for Biomedical Applications

Hydrogels are typical gels with cross-linked three-dimensional hydrophilic polymeric networks characterized by high water content. They are promising biomaterials owing to their remarkable physical and mechanical properties and good biocompatibility. Moreover, hydrogel properties can be modified by adjusting the polymer type and molecular weight or altering the cross-linking extends and fabrication methods. Hydrogels can be synthesized by using either natural or synthetic polymers.

Magnetic hydrogels, typically hydrogel incorporated with magnetic nanoparticles (MNPs), have drawn research attention for potential biomedical applications. Their properties largely depend on the hydrogel type and the features of the MNPs. Magnetic hydrogels have two main advantages: (1) easy response to externally induced magnetic fields, and (2) are an effective platform for local treatment owing to their ability to prevent leakage of MNPs – an inherent challenge for MNP-based magnetic fluid usually used in magnetic particle hyperthermia. As such, magnetic hydrogels are promising candidates for anticancer treatments through hyperthermia mechanism.

Local treatment is effective in minimizing the possibility of toxic effects. Previous findings revealed the possibility of achieving local treatment using metallic stents to inhibit muscle cell proliferation or treat esophageal cancer in malignant areas. However, the big problem with this approach is that the sources of energy used to heat the stents induce high voltages and high electromagnetic radiation that result in burns and tissue perforation. It has been speculated that creating the hybrid stent using magnetic hydrogels instead of metallic stents could overcome these challenges. However, there are still limited experimental findings to validate these assertions.

Herein, Dr. Eirini Myrovali from Aristotle University of Thessaloniki reported the fabrication, characterization and evaluation of a new magnetic hydrogel-based hybrid stent prototype for magnetic hyperthermia treatment. The magnetic and structural features of MNPs prepared by coprecipitation were first evaluated. The magnetic hydrogels used in this experimental work were produced by dissolving sodium alginate with MNPs in a bath of calcium chloride with varying composition (5- 15 mg mL^-1) to achieve complete polymerization, external gelation and optimized heating rate. Sodium alginate was used as a natural polymer to synthesize the magnetic hydrogel owing to its low immunogenicity and high biocompatibility. The work is currently published in the research journal, ACS Applied Bio Materials.

The authors showed that the lowest calcium chloride content of 5 mg mL^-1 achieved the optimum heating rate. By keeping the calcium chloride concentration constant, the concentration of MNPs was varied from 1 to 8 mg mL^-1 to improve their efficiency while examining the leakage of iron oxide nanoparticles after 0, 5 and 15 days. A near-zero leakage of iron oxide nanoparticles (<0.08 mg L^-1) was reported after 15 days. The results confirmed that magnetic hydrogel-based hybrid stents are generally safe for biomedical applications.

The heat efficiency performance of the magnetic hybrid stents during the magnetic hyperthermia was evaluated in agarose phantom mode and ex vivo tissues sample. The samples were all measured in a magnetic hyperthermia device at an applied field of 30 mT and frequency of 765 kHz. For both cases, excellent heat distribution was observed in the magnetic hybrid stent surroundings than in the sample with no magnetic hybrid stent. Facile temperature control was also achieved by tuning the concentration of the MNPs.

In summary, Dr. Eirini Myrovali investigated the potential biomedical applications of hybrid stents based on magnetic hydrogels. The combination of the remarkable thermal properties of magnetic hyperthermia and the high biocompatibility of magnetic hydrogel enabled the fabrication of magnetic hybrid stents in a robust and simple way. In addition, the hybrid stents are eco-friendly and potential replacement for conventional magnetic fluid hyperthermia for local hyperthermia treatment. In a statement to Medicine Innovates, Dr. Myrovali explained her research findings would open new pathways for improved local hyperthermia treatment and therapeutic cancer treatment in hollow organs.