On September 26, Bioactive Materials formally published a paper titled "Enhancing remanent magnetization of injectable hydrogels improves realtime transluminal localization of tumor in hollow soft viscera". This achievement was carried out through the joint Electromagnetic Medical Clinical Application Research Laboratory established by the National Pulsed High Magnetic Field Science Center and Union Hospital, Tongji Medical College, Huazhong University of Science and Technology. It was completed collaboratively by researchers from Professor Li Liang's team at the Center, Professor Cai Kailin's team at Union Hospital, Professor Ouyang Jun's team from the School of Integrated Circuits, and researchers from the Naval University of Engineering, among other units. 

In gastrointestinal surgery, achieving precise localization of transluminal tumors is crucial for surgical quality and prognosis. For instance, the accuracy of intraoperative localization in rectal cancer directly determines the possibility of sphincter preservation. Traditional clinical methods face issues such as insufficient localization accuracy, limited duration of effect, or high medical costs. Electromagnetic localization, with its strong tissue penetration capability, shows great application potential. However, current magnetic markers used for localization suffer from inadequate sustained tracking efficacy and poor biocompatibility of solid materials. Furthermore, applying electromagnetic localization to soft tissue organs like the gastrointestinal tract urgently requires overcoming the challenge of dynamic registration.

Addressing the above problems, the team reported an electromagnetic localization technology based on a multi-source magnetic marker (SEML) for transluminal localization in minimally invasive gastrointestinal surgery. The team designed an injectable magnetic hydrogel (MagLabel-IH) with sustained magnetization properties for accurate and stable magnetic tracing in vivo, and proposed an intraoperative dynamic registration model that maps magnetic coordinate sites to real anatomical locations, eliminating the need for reliance on preoperative imaging for registration. This technology can conveniently achieve millimeter-level localization within the gastrointestinal tract and can be applied to diverse surgical scenarios such as multi-target co-localization and the planning and guidance of digestive tract tissue reconstruction.

Figure 1. Overview of the intraoperative electromagnetic localization technology based on MagLabel-IH.

The team developed an interpenetrating network magnetic hydrogel (MagLabel-IH) with layered arrangements of magnetic particles to address the challenge of injectable fluids struggling to maintain remanent magnetization. In in vitro experiments, remanent magnetization weakened by tissue injection could be rapidly recovered via in-situ reorientation under a weak magnetic field (~150 mT), and the remanent magnetization could be maintained for up to 5 days, facilitating sustained in vivo magnetic tracing. MagLabel-IH also exhibited good rheological properties and injectability, demonstrating typical shear-thinning behavior in shear tests; furthermore, its injection pressure did not significantly increase compared to medical sodium hyaluronate injection (0.4%) in endoscopic needle injection tests. Additionally, in a series of biosafety evaluations targeting ion release (simulated gastric fluid, intestinal fluid, etc.), cytotoxicity, systemic acute toxicity, and long-term in vivo safety, MagLabel-IH consistently demonstrated good biocompatibility.

Figure 2. Magnetic properties of MagLabel-IH.

Simultaneously, the team built an electromagnetic localization system (SEML) for surgical intraoperative localization and guidance. The system consists of a magnetic sensor array, signal processing unit, electromagnetic detection guide rod, and visual localization software. Utilizing the developed EPSO-LM localization algorithm and an AC-DC hybrid signal detection model, this system can achieve global search and local rapid tracking of targets within the human abdominal cavity area, and can be used for co-localization of multiple magnetic source signals, including AC (electromagnetic guide rod) and DC (MagLabel-IH). The system demonstrated millimeter-level localization accuracy and good stability across a series of experiments including standardized measurement platforms, artificial digestive fluid environments, simulated surgical scenarios, phantoms, and ex vivo tissues.

Figure 3. Manufacturing and technical characteristics of the electromagnetic localization system (SEML).

In further in vivo animal surgery experiments, the electromagnetic localization technology based on MagLabel-IH demonstrated localization capability significantly superior to traditional biological dye marking (P < 0.05). Using the self-developed electromagnetic system (suitable for humans and large animals) to perform in-situ reorientation magnetization of MagLabel-IH in experimental rabbits enabled sustained in vivo magnetic tracing for up to ~5 days. During laparoscopic surgery, the localization accuracy of MagLabel-IH marking was significantly better than that of India ink (3.8 ± 0.8 mm vs. 16.8 ± 8.6 mm, P < 0.05), while the localization time proportion (of the total surgery time) was less than 0.01%.

Figure 4. In vivo animal surgery evaluation of gastrointestinal transluminal localization.

Furthermore, this technology also demonstrated broad application potential in surgical margin measurement, multi-point co-localization, and planning for digestive tract reconstruction, and is expected to provide a multi-functional electromagnetic localization and guidance platform for precise and individualized surgical operations in the future.

Figure 5. Application in planning digestive tract reconstruction.

Paper link: https://doi.org/10.1016/j.bioactmat.2025.08.025