# Thermoresponsive Magnetic Hydrogel for Local Thermal Ablation Treatment of Rectal Cancer

## TL;DR

A magnetic hydrogel was developed to noninvasively heat and shrink rectal tumors using an external magnetic field, showing promising results in reducing tumor size in mice.

## Contribution

A noninvasive magnetic hydrogel for localized thermal ablation of rectal cancer is introduced, enabling preoperative tumor downsizing.

## Key findings

- The magnetic hydrogel reached temperatures above 50°C within 3 minutes under an alternating magnetic field.
- Ex vivo studies showed a 30% reduction in tumor volume after 15 minutes of treatment.
- In vivo experiments demonstrated a 69% decrease in tumor volume 2 days after a 20-minute treatment.

## Abstract

Thermal ablation treats cancer by raising local tumor
temperature
above ∼50 °C to induce coagulative necrosis. However,
current approaches are invasive, as they typically require needle-like
applicators to deliver thermal energy directly into the tumor. In
this study, a magnetic hydrogel was developed as a noninvasive strategy
for localized rectal cancer ablation aimed at preoperative tumor downsizing.
The formulation comprises superparamagnetic iron oxide nanoparticles
(SPIONs: Mn0.6Zn0.4Fe2O4) dispersed in Pluronic F127 (PF127). PF127 confers thermoresponsive
sol–gel behavior at physiological temperature: upon contact
with tissue, the formulation rapidly gels and becomes immobilized
at the application site, minimizing spread to adjacent healthy tissue.
After gel placement, an alternating magnetic field (AMF) is applied
externally to activate the SPIONs to generate heat in situ, inducing local thermal ablation at the disease site. The gel can
be administered either by syringe injection or by topical application,
depending on tumor geometry. Adding SPIONs to the PF127 matrix did
not alter the critical gelation temperature (CGT, 27.7 °C) but
increased gel hardness and adhesiveness. When exposed to a 14 mT
AMF at 596.2 kHz, the magnetic hydrogel exhibited excellent
heating performance, reaching temperatures above the thermal ablation
threshold (50 °C) within 3 min. The thermal ablation efficacy
of the magnetic hydrogel was evaluated both ex vivo and in vivo using colorectal cancer xenograft mouse
models. Ex vivo studies showed that a 15 min thermal
ablation treatment resulted in an immediate 30% reduction in tumor
volume. In vivo, a more pronounced effect was observed,
with tumor volume decreased 69% 2 days after a single 20 min treatment.
The finding highlighted the potential of the magnetic hydrogel as
an alternative treatment for localized rectal cancer, either for preoperative
tumor down-sizing or in cases where standard therapies such as surgery
or chemo-radiotherapy are not feasible.