Researchers from the School of Mechanical Engineering at Purdue University have developed an innovative new patterning approach for applications like drug delivery in biomedical applications. Detailing their research in the recently published ‘3D-Printed Microrobots with Integrated Structural Color for Identification and Tracking ,’ the authors give us insight into new patterns on the micro- and nanoscale using two-photon polymerization (TPP), a technique that offers submicron resolution.
While microrobots (divided into biological, hybrid, and synthetic groups) are helpful in applications like micromanipulation and advanced sensing, there are still obstacles in development of miniature structures because of the need to combine actuation and wireless control within one device. Size is the issue in many cases, although actuation is often provided externally. There are also extensive challenges for in vitro and in vivo processes with the use of microrobotic systems, visuals, and tracking.
“For 3D printed microrobots with smaller dimensions, alternative fabrication approaches are needed to integrate distinctive tracking features, including marking the microrobot surfaces with fluorescent materials such as quantum dots or using fluorophores selectively attached to specific functional groups,” stated the researchers. “Despite their success in tracking, these materials lose their fluorescence over time, limiting their duration of usefulness.”
In this study, color plays a large role, with patterns comprised of prism arrays pointing upward—permitting the team to integrate them onto different areas of the microrobot. Patterns were developed as follows:
- Red pattern – blocks with a 160 nm x 170 nm footprint
- Green pattern – blocks with a footprint of 120 nm x 90 nm
- Arrays on both of the helix and platform microrobots consist of all red (R), all green (G), or alternating red and green (RG) blocks
Depending on the light source, expressed colors may vary. The authors noted that for adding color contrast, they used a high-index dielectric layer of Ge; however, the result in samples for the study was only ‘minimal.’ The light source was set in a fixed position and then rotated by hand, with images recorded each time there was a substantial change in color.
“The RG pattern was shown to express a wider spectrum of colors in comparison to just R and the G patterns alone,” stated the researchers. “The R and G patterns expressed bright colors of blue and red only, whereas RG additionally expressed bright green.
“Fine tuning of color expression depending on the applied angle can potentially provide real-time information of a microrobot’s position in both x–y and z directions by identifying the change in color while it is moving in the 3D workspace.”
Helical microswimmers relied on rotating magnetic fields for actuators, while the control platform microrobots used gradient fields relying on the MagnebotiX coil system. The researchers noted that as the control platforms rotated, color was visible, as well as on the helical robots using low frequencies. The researchers did note though that color differed depending on orientation and light source.
“The variation of structural color block dimensions was used to explore the ability to manipulate color expression. In this study, the alternating block geometries provided a wider range of colors than arrays with a single type of block geometry,” concluded the researchers. “With increasing accuracy of micro-3D-printing technologies and by exploring complex patterns, noniridescent colors can be obtained.
“This has been recently demonstrated for 3D printed lamellar-like structures similar to the ones of the Morpho butterfly, though this type of pattern only expressed an artificial blue color and was not applied to structures while moving. By exploring new computationally designed structures and integrating them into 3D microrobotic systems, structural color can become a common element not only for tracking and identification but also for creating tunable surface properties.”
Microrobotics and drug delivery systems continue to be impacted by 3D printing in research projects involving innovative microstructures , spermbots , and a variety of different techniques . What do you think of this news? Let us know your thoughts! Join the discussion of this and other 3D printing topics at 3DPrintBoard.com .
[Source / Images: ‘3D-Printed Microrobots with Integrated Structural Color for Identification and Tracking