Magnetically Controlled Microrobots Cross Gastrointestinal Barriers to Release Nanoparticle Cancer Drugs in Stages

Delivering oral drugs precisely to gastrointestinal lesions involves more than overcoming distance. Gastric acid may destroy drugs prematurely, mucus and intestinal folds hinder contact, and peristalsis and fluid continuously push the payload away from the target. The research team therefore designed a “staged relay” system: an external magnetic field first guides microrobots into position, after which they release nanoparticles capable of adhering to cancer cells.

The microrobot, about 550 micrometers wide, contains a magnetic layer and a drug compartment whose opening is covered by a pH-sensitive polymer coating. Simulations showed that the coating remained intact in gastric fluid and began to dissolve after entering intestinal fluid; the researchers could also delay release by adjusting the drug-loading formulation. This protects the payload as it passes through the stomach and allows it to be released gradually only after reaching the higher-pH intestinal environment.

The released second-stage carriers are nanoparticles coated with platelet cell membranes and loaded with the chemotherapy drug doxorubicin. The platelet membranes retain some surface proteins that can participate in interactions with tumor cells. In cell experiments, these particles bound to the colorectal cancer cell lines SW480 and HCT116 at levels approximately 3.1 times and 2.4 times those of uncoated particles, respectively. The design seeks to connect the spatial control provided by magnetic guidance with biological recognition at the cellular scale.

The team further developed a colon-mimicking microfluidic model incorporating flow, pH changes, villus-like structures, and tumor spheroids. When two microrobots were used for delivery, the nanoparticle signal on the tumor spheroids was approximately 3.4 times that observed with direct nanoparticle administration; after dose correction, retention performance improved by approximately 4.57 times and was accompanied by a stronger cancer-cell-killing effect. The results suggest that first delivering the payload near the lesion and then allowing the nanoparticles to adhere locally may better resist flow-induced loss than administering the nanoparticle drug alone.

However, the evidence currently remains at an early preclinical stage. The anticancer effect has been tested only in cell and microfluidic models. Although the researchers have moved magnetized robots across the surfaces of ex vivo pig stomach and intestinal tissues, this still cannot reproduce the full range of peristalsis, immune responses, food interference, and excretion processes in a living body. Whether an external magnetic field can maintain stable positioning deep within the human body is also an engineering challenge for future work.

The next step is to confirm the robots’ passage, release, and recovery or excretion in animals, and to assess the safety of the materials, the source of the platelet membranes, and doxorubicin leakage. What the platform currently demonstrates is that the multilayer delivery concept can operate in a coordinated manner—not that it can already treat colorectal cancer. To become a precision oral drug-delivery tool, it must still overcome hurdles including manufacturing consistency, efficacy in living organisms, and long-term safety.