Implantable Microrobots: Using Hydrogels, Engineers Create Biocompatible Micromachines
A team of researchers led by Columbia Engineering’s Sam Sia has developed a way to manufacture microscale machines from biomaterials that can safely be implanted in the body. These tiny machines could carry out targeted drug delivery, allowing for lower doses, or be used to deploy stents, and they hold promise for major advances in precision medicine.
Magnetic actuation of the Geneva drive device. A magnet is placed about 1cm below and without contact with the device. The rotating magnet results in the rotational movement of the smaller driving gear. With each full rotation of this driving gear, the larger driven gear is engaged and rotates by 60º, exposing the next reservoir to the aperture on the top layer of the device.
Working with hydrogels, which are biocompatible materials that engineers have been studying for decades, Sia invented a new technique that stacks the soft material in layers to make devices that have three-dimensional, freely moving parts. He calls the manufacturing method “implantable microelectromechanical systems,” or iMEMS.
By exploiting the unique mechanical properties of hydrogels, the researchers developed a “locking mechanism” that can precisely trigger actions and created freely moving parts that can function as valves, manifolds, rotors, pumps, and drug delivery systems. They were able to control the devices after implantation without a sustained power supply, such as batteries, which can be toxic.
Working with an orthopedic surgeon at Columbia University Medical Center, the team tested the drug delivery system on mice with bone cancer. The targeted treatments, described in the journal Science Robotics, delivered chemotherapy adjacent to the cancer and limited tumor growth with less toxicity than chemotherapy administered throughout the body. Testing has shown high success rates at one-tenth of the standard chemotherapy dose.
“Overall, our iMEMS platform enables development of biocompatible implantable microdevices with a wide range of intricate moving components that can be wirelessly controlled on demand and solves issues of device powering and biocompatibility,” said Sia, a biomedical engineering professor. “We’re really excited about this because we’ve been able to connect the world of biomaterials with that of complex, elaborate medical devices.”
Sia’s iMEMS technique addresses some fundamental challenges that biomedical engineers have faced in building biocompatible microdevices, including how to power small robotic devices without using toxic batteries and how to communicate wirelessly once the device is implanted.
With the new technique, the researchers were able to precisely trigger the micromachines to release multiple payloads over days to weeks by using magnetic forces to induce gear movements that, in turn, bend structural beams made of hydrogels.
“These microscale components can be used for microelectromechanical systems, for larger devices ranging from drug delivery to catheters to cardiac pacemakers, and for soft robotics,” Sia said. “People are already making replacement tissues, and now we can make small implantable devices, sensors, or robots that we can talk to wirelessly. Our iMEMS system could bring the field a step closer to developing soft miniaturized robots that can safely interact with humans and other living systems.”