Scientists at Leiden University in the Netherlands have created a 3D-printed version of Star Trek’s USS Voyager spaceship that measures a ultra-tiny 15 um (micrometers) long. By comparison, the width of a human hair is 50 um. The USS Voyager spaceship is so tiny, it can only be viewed through a microscope!
Scientists create microscopic models so they can study “microswimmers”. Microswimmers are important because they will one day lead to tiny swimming robots that can be turned loose in the human body to repair tiny injuries or deliver drugs to a precise location inside the body.
Because they are so tiny, microswimmers face a variety of challenges that scientists must solve. For instance, their small size and shape means they are impacted by the fluid’s viscosity and turbulence. These factors are measured by a so-called Reynolds number.
The Reynolds number
The Reynolds number predicts how a fluid will act based in the fluid’s viscosity and speed. The Reynolds number measurement is especially important when dealing with microswimmers. Microscopic creatures swim at low Reynolds numbers and thus, the thickness of a fluid greatly impacts their ability to travel through it.
Two-photon polymerization 3D printers
The machine used to print the microscopic swimmers is called a 2PP or two-photon polymerization. It works by using a fine laser focused on a droplet that can then be used to “write” the structure they want to create. Once the object is printed, it is placed in a propylene glycol methylether acrylate for 30 minutes, then coated with a layer of platinum/palladium.
How scientists use microscopic models
To test the microswimmer’s effectiveness in a fluid, scientists 3D-print the microswimmers in a wide variety of shapes. They printed object is placed in a solution of hydrogen peroxide. The platinum/palladium coating reacts with the hydrogen peroxide causing the object to propel itself through the fluid. Scientists can then study the microswimmer’s movement through the fluid.
As it turns out, the microswimmer’s shape great impacts it ability to swim through a fluid. For instance, scientists found that longer objects are able to swim faster. Unfortunately, the Star Trek USS Voyager microswimmer is not the best candidate for swimming through the human bloodstream. Scientists prefer a helix-shaped object which spins and allows the microswimmer to swim faster.