Sperm-Like “Micro-Robots” Navigate Through Complex Environments for Minimally Invasive Surgery

A team of researchers has developed a cutting-edge magnetic actuation platform that efficiently creates sperm-like "micro-robots," exhibiting remarkable motility and precise drug delivery capabilities. This platform overcomes the drawbacks of traditional microfluidic devices that struggle with fabricating complex 3D structures, thus simplifying the production process and enhancing the potential biomedical applications of these micro-robots. Designed for navigating complex internal body areas for targeted drug delivery and minimally invasive procedures, these microswimmers demonstrate superior locomotion efficiency in fluidic environments compared to standard microfluidic systems. However, the challenges remain of mass production and ensuring effective propulsion and drug release control.

Inspired by the motility mechanism of the sperm of ray, a type of sea fish, the research team from the School of Engineering of the Hong Kong University of Science and Technology (HKUST, Kowloon, Hong Kong) developed a one-step method to create versatile sperm-like microswimmers using a Vortex Turbulence-Assisted Microfluidics (VTAM) platform activated by an external magnetic field. These microswimmers are designed with a flexible tail for controlled movement and a core-shell head for efficient drug encapsulation, managing to propel effectively through various viscosity fluids. The innovative VTAM platform integrates a conventional cross-shaped microfluidic chip with a vortex container, which is created by a magnetic stirrer inducing rotational flow. This setup produces uniform magnetic alginate droplets in the microfluidic chip, which are then transferred to a calcium chloride solution in the vortex container.

Image: Illustration of the production of polymorphous sperm-like microswimmers using the Vortex Turbulence-Assisted Microfluidics platform (Photo courtesy of HKUST)

Within the vortex flow, the droplets burst open, exposing the magnetic alginate solution inside and drawing it out along the direction of the vortex flow, forming an asymmetric sperm-like structure. Once the tail is drawn out, the droplets quickly solidify due to a crosslinking reaction with the calcium ions, taking mere milliseconds. The resulting microswimmers feature biodegradable core-shell heads and adjustable tail shapes, modifiable through vortex speed and solution concentration adjustments. To optimize drug delivery, the microswimmers' surfaces are coated with a pH-sensitive membrane, which facilitates controlled drug release in varying pH conditions. This innovative coating significantly enhances drug release performance under diverse environmental settings compared to non-coated counterparts. The researchers successfully tested the microswimmers in a simulated biological environment, where they precisely targeted and released drugs, as reported in their findings published in Nature Communications.

“This research not only demonstrates the potential of bionic design in biomedical engineering, but also offers new direction for future drug delivery systems,” said Prof. SHEN Yajing, Associate Professor from the Department of Electronic and Computer Engineering who led the research team. “With continuous technological advancements, it is believed that our new sperm-like micro-robots will make greater contributions to human health in the foreseeable future.”

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