A new magnetorheological fluid-based soft robot created by the researchers includes reversible t robot with reversible gastrointestinal tract medical applications.
Millions of people around the world are infected with gastrointestinal tract diseases and the conventional drug delivery system lacks high targeting capacity with chances of side effects of systemic drug delivery. The development of magnetic soft robots has become an innovative solution to minimally invasive medical procedures, due to their miniaturity, untethered locomotion and their agile movements. Nonetheless, the current magnetic soft robots have severe constraints of multi-angle folding, real time reconfigurable magnetization, and compliance with the irregular and constrained gastrointestinal cavity, which are the barriers to clinical use of targeted drug delivery.
In order to solve these problems, a research team, comprising of researchers at China University of Mining and Technology, Soochow University, RWTH Aachen University and the University of Oxford created a magnetic soft sheet robot with magnetorheological fluids. The robot takes the form of a four-layered fully-soft sheet, which consists of upper and bottom layers of linear low-density polyethylene surface, a core layer of magnetorheological fluids and a polyamide nylon mesh support layer. The robot is non-magnetized in zero magnetic field, weighing 0.55 g (a weight of 30 mm in length, 10 mm in width, 1.5 mm in thickness), which is small (30 mm in length, 10 mm in width, 1.5 mm in thickness), which removes unwanted magnetic interference in the human body.
The main novelty of such robot is the magnetization, which can be reconfigured in real time, and the performance by reversible folding. The magnetic particle chains along the magnetic field direction can be generated by the internal magnetorheological fluids within milliseconds under the external magnetic and the magnetization direction can be dynamically readjusted using the spatial magnetic field. Propelled by a 5 degree of freedom magnetic field platform, the robot can be folded to a one third size of the original to move in slender intestinal tracts and unfolded to a large surface area to move in a stable fashion within the stomach cavity-achieving the flexible adaptation to the different spatial sizes of the gastrointestinal tract.
- The research group used the fabrication of five prototypes of the soft sheet robot with varying magnetorheological fluid densities (3.0 g/mL to 4.2 g/mL) and a series of motion performance tests under various environments.
- The robot was found to have a stable flip, steering and folding motion on smooth surfaces, on flexible fluff surfaces and on slope surfaces and also in environment with underwater. It was also able to maintain consistent performance of movement even under load (carrying biodegradable hydrogel drugs with a mass of 0.15 g, which is about 30 percent of the own mass of the robot).
- The ex vivo porcine stomach experiments, which mimicked the human gastrointestinal environment, were done to have critical validation. The robot was able to reach any predetermined location in the porcine stomach in an average of 5 minutes and firmly secured to the point of drug release with the loaded hydrogel drugs dissolving within 30 minutes to create localized targeted therapy in 10 repetitions.
- Also, the ultrasonic detection technology (Voluson E10), was able to trace real-time movements of the robot in closed gastric cavity, which proved traceable and controllable in closed biological environments- a technical assurance in monitoring robots in clinical practices.
The biocompatibility tests continued to confirm the safety of the robot when used in human body: the robot was immersed in the simulated gastric juice (pH 1.2) and intestinal juice (pH 6.8) at 37degC after 24 hours and no rupture of its surfaces, expansion of its volume and deformation of the shape were observed. It was revealed that no exceeding of the safety levels was detected in the extract solutions by the heavy metals and harmful substances and no bacterial colonies were obtained in the tests related to the growth of microbial cultures, which indicates the biocompatibility and non-toxicity of the robot in the gastrointestinal tract environment.
The research team observed that the magnetic soft sheet robot has overcome the technical bottlenecks of the conventional magnetic soft robots in terms of folding capability and magnetization ability. It has the benefit of untethered drive, complete soft-structure, and excellent targeting precision, which render it the best noninvasive medical device to deliver drugs to the gastrointestinal tract.