Physicists at Leiden University in the Netherlands have created a 3D-printed microscopic version of the USS Voyager from the Star Trek franchise, in keeping with a recent paper in the journal Soft Matter. These sorts of artificial “microswimmers” are of great interest to scientists as a result of they may at some point result in tiny swimming robots for autonomous drug supply by the bloodstream, or for cleansing wastewater, amongst different potential functions. Such research might additionally shed light on how pure “microswimmers” like sperm and micro organism journey by the human physique.
Because of their small dimension, microswimmers face distinctive challenges after they transfer by fluids. As we’ve reported previously in the context of completely different analysis, organic microorganisms stay in environments with a low so-referred to as Reynolds number—a quantity that predicts how a fluid will behave based mostly on the variables viscosity, size, and velocity. Named after the nineteenth-century physicist Osborne Reynolds, the idea is particularly helpful for predicting when a fluid will transition to turbulent move.
In sensible phrases, it implies that inertial forces (e.g., pushing in opposition to the water to propel your self ahead while swimming) are largely irrelevant at very low Reynolds numbers, the place viscous forces dominate as a substitute. So as a result of micro organism or sperm swim at low Reynolds numbers, they will barely coast any distance at all if you push them to set them in movement. It’s akin to a human attempting to swim in molasses.
“By studying synthetic microswimmers, we would like to understand biological microswimmers,” co-writer Samia Ouhajji told CNN. “This understanding could aid in developing new drug delivery vehicles; for example, microrobots that swim autonomously and deliver drugs at the desired location in the human body.”
Shape seems to be a major factor affecting the movement and interactions of microswimmers, and that is the main focus of this newest paper. “Shape and motion in synthetic and biological micro swimmers are intimately connected,” the authors wrote. Prior research have proven that L-formed particles comply with round trajectories, for occasion. And in 2016, scientists at Southern Methodist University constructed microswimmer robots resembling a series of magnetic beads, whose motion might be managed by way of a rotating magnetic field. They discovered that microswimmers of completely different lengths had completely different swimming properties. Most notably, longer ones swim quicker.
The Leiden group wanted a sturdy technique of making microswimmers in a range of advanced shapes. Synthetic microswimmers are sometimes made by way of chemical or evaporation strategies, which, while efficient, restrict the attainable shapes to spheres or rod-like colloids. Biological microswimmers are far more various and asymmetrical with regard to form. So the Leiden researchers opted to make use of “two-photon polymerization,” or 2PP, a technique that allows the 3D printing of microstructures while nonetheless having some flexibility in phrases of form and symmetry. It additionally allowed them to manage how a particle is oriented relative to the fused-silica substrate on which it is printed, giving them further management over the ensuing movement.
“The potential of 2PP to create microswimmers with a wide range of geometries is immense, allowing the production of almost any desired shape,” the authors wrote. According to co-writer Daniela Craft, a Leiden University physicist, the group centered a laser inside a droplet and used it to “write” no matter construction they desired. They had been capable of create a range of shapes at the micrometer scale with a excessive-decision 3D printer. Once printed, the objects had been positioned in propylene glycol methylether acrylate for half-hour, and dipped 5 instances in isopropanol. As a ending touch, every construction was coated with a catalytically lively nanolayer of platinum/palladium.
The group began by printing spherical particles in the 1 to 10 micrometer vary as proof of precept and had been capable of conclude that 4 micrometers was the bottom they may go and nonetheless produce fairly spherical shapes. Next, they confirmed that, when positioned in water, their spherical particles exhibited Brownian motion, the random motion of particles in a fluid as they continually collide with different molecules—i.e., they behaved like true colloids. (Fun truth: one of the seminal papers Albert Einstein printed in 1905—his annus mirabilis —modeled particular person water molecules as a mechanism for the noticed random movement of pollen particles in a puddle.)
Then the Leiden scientists positioned their microswimmers right into a water and hydrogen peroxide resolution; the platinum/palladium coating reacted with the answer to create self-propulsion, or lively movement. “The difference in the passive trajectories in water and those in hydrogen peroxide solution show that through a simple coating procedure, 3D printed colloids can be made active,” the authors wrote.
For the following section of their analysis, the Leiden group expanded their repertoire to 3D print more advanced buildings: a spiky sphere, a spiral, a helix, and a so-referred to as “3DBenchy” boat measuring 30 micrometers long—short for “benchmark,” a construction generally used to check 3D printers to see how nicely they deal with fantastic element. The Benchy boat, for instance, sports activities such difficult geometrical options as portholes and an open cabin.
And of course, they made the micro version of the USS Voyager, measuring simply 15 micrometers long. That was at the behest of co-writer Jonas Hoecht, who was given the selection of printing any 3D form he preferred for the final pattern. Hoecht is a diehard Star Trek fan and picked the Voyager. All the 3D-printed micro objects had been imaged utilizing a scanning electron microscope (SEM).
“We hope to learn about what is now a good design principle for creating a little drug delivery vehicle—if you have a little particle that goes to a specific part of the body to deliver drugs, then it has to propel itself, and it may have to deal with the environment in your body, which is very complex,” co-writer Daniela Kraft told CNN. “What we are trying to answer is: what would be a good design? What would be a great shape so that it can go around and be efficient?”
The group’s analysis demonstrated that particles created in a helix form confirmed probably the most promising motion. “When it moves forward, often it needs to rotate, and that helps, for example, to speed it up,” mentioned Kraft. “If you think about applications, if you want to have a little machine that goes somewhere, it might be more useful to have a helix shape, because it swims faster.”