Medical microrobots to deliver drugs on demand

Advances in micro- and nanoscale engineering in the medical field have led to the development of various robotic designs that one day will allow a new level of minimally invasive medicine. These micro- and nanorobots will be able to reach a targeted area, provide treatments and therapies for a desired duration, measure the effects and, at the conclusion of the treatment, be removed or degrade without causing adverse effects. Ideally, all these tasks would be automated but they could also be performed under the direct supervision and control of an external user.

Several approaches have been explored for the wireless actuation of microrobots. Among these, magnetic fields have been the most widely employed strategy for propulsion because they do not require special environmental properties such as conductivity or transparency. This approach allows for the precise manipulation of magnetic objects toward specific locations, and magnetic fields are biocompatible even at relatively high field strengths (MRI). In a new work, a team of researchers from ETH Zurich and Harvard University demonstrate that additional intelligence – including sensing and actuation – can be instantiated in these microrobots by selecting appropriate materials and methods for the fabrication process. The work combines the design and fabrication of near infrared light (NIR) responsive hydrogel capsules and biocompatible magnetic microgels with a magnetic manipulation system to perform targeted drug and cell delivery tasks. The research team fabricated an untethered, self-folding, soft microrobotic platform, in which different functionalities are integrated to achieve targeted, on-demand delivery of biological agents.

Stimuli-responsive hydrogels are a class of materials closely resembling biological tissues in their physical and chemical properties. These swollen polymer networks are of interest in research and industry for many biomedical applications due to their unique capability of a reversible volume change in response to different stimuli (temperature, pH, ionic strength, etc.). They are used in tissue engineering, drug and cell delivery and wound healing. Bilayered hydrogel structures fold when two coupled layers swell or contract differently in response to a specific chemical or physical change. The fabricated microstructures can switch from a closed to an open configuration when their body temperature exceeds 40°C. More importantly, a short exposure to a NIR-laser source generates the required heat within the target structure. In this way, an external operator can stimulate the microstructures from a certain distance. This source of actuation was chosen as a controllable trigger mechanism, because it can penetrate body tissue without causing damage even at repeated doses.

These microparticles can be loaded with biological materials and can easily be encapsulated inside the hydrogel bilayers. Alginate, a natural biodegradable polysaccharide, is often chosen as a gelable polymer for long-term and sustained delivery of both drugs and cells. This part of the device allows external magnetic manipulation and sustained delivery. Despite being developed as a prototype, the proposed microrobotic platform possesses all the required features that the researchers envision for biomedical applications including 3D automated magnetic steering; the capacity to carry drugs and cells; and spatiotemporally controlled delivery.

(http://www.nanowerk.com/spotlight/spotid=33210.php)