Enhanced Accumulation and Penetration of Magnetic Nanoclusters in Tumors Using an 8-Magnet Halbach Array Leads to Improved Cancer Treatment.

Nanoparticles have gained attention as drug delivery vehicles for cancer treatment, but often struggle with poor tumor accumulation and penetration. Single external magnets can enhance magnetic nanoparticle delivery but are limited to superficial tumors due to the rapid decline in the magnetic field strength with distance. We previously showed that a 2-magnet device could extend targeting to greater tissue depths. Here, we improve on this approach by constructing an 8-magnet device arranged in an annular Halbach array, which facilitates radial outward movement of magnetic nanoparticles from the bore's center. Using chlorin e6-coated magnetic nanoclusters (Ce6 clusters) with densely packed cobalt-doped superparamagnetic iron oxide nanoparticles, we demonstrated nearly a 7-fold improvement in nanoparticle movement through a porous matrix compared to the 2-magnet approach. This resulted in enhanced magnetic resonance contrast, accumulation, and penetration of Ce6 clusters into 4T1 triple-negative breast tumors in mice, leading to improved photodynamic therapy and highlighting the potential therapeutic application of the 8-magnet device.