3D printed material features controllable surface textures.

A team of mechanical engineers at Massachusetts Institute of Technology, has developed a way of making soft materials, using a 3D printer, with surface textures that can be controlled at will to be smooth, ridged, or bumpy. It can even be designed to have complex patterns that could be used to guide fluids.

Fig. 1 – Polymer material produced by a 3-D printer includes soft, flexible material (clear or lighter tone) with particles of hard material (black) embedded, in predetermined arrangements. When compressed, its surface become bumpy in a pattern determined by the hard particles. (Credit: Felice Frankel)
The process, developed using detailed computer simulations, involves a material that is composed of two different polymers with different degrees of stiffness. Rigid particles are embedded within a matrix of a flexible polymer. When squeezed, the material’s surface changes from smooth to a pattern determined by the spacing and shapes of the implanted harder particles. When released, the material reverts back to its original form.

Their findings, the researchers say, could lead to a new class of materials with dynamically controllable and reversible surface properties.

Depending on the arrangement of the particles, and using the same amount of compression, the researchers were able to get different surface topographies, including ridges and bumps, along the surface.

The system can produce simple, repetitive patterns of bumps or creases, which could be used to change aerodynamic resistance of an object, or its reflectivity. But, they found that by arranging the distribution of the hard particles, it can also produce highly complex surface textures. For example, it might be useful for creating microfluidic channels to control the movement of liquids inside a chemical or biological detector.

Such a device could have a smooth, tilted surface allowing fluids to flow evenly across its surface, then, upon demand, could create raised sections and depressions to separate the flow of liquids.

The team says that there are no previous techniques that provide comparable flexibility for creating dynamically and locally tunable and reversible surface changes. Since the system is based on the shapes and spacing of materials with different degrees of flexibility, it could be scaled to all different sizes, and the same principles should work.

While their current research addresses using physical pressure to control texture, the same design principles, they say, could be used to modify materials using other stimuli, such as through the application of an electric charge, or by changing temperature or humidity.

In addition, using embedded particles that are elongated instead of round could also allow for the creation of surface textures that are asymmetrical, which could create surfaces that have high friction in one direction but are slippery in another, allowing a passive means of controlling how things move over that surface.

For more information, visit www.newsoffice.mit.edu .