Microscale 3-D Printing

Information Technology; Computer Engineering

Microscale 3-D printing is a type of 3-D printing that makes it possible to construct objects at an extremely small scale. Some processes can create objects as small as 100 micrometers. 3-D printing at this scale has a number of applications for computing and medicine. It makes it possible to produce microscopic structures out of organic materials for biomedical applications.

3-D printing is a relatively new technology. However, it has already revolutionized manufacturing. It takes its name from traditional computer printers that produce pages of printed images. Regular printers operate by depositing small amounts of ink at precise locations on a piece of paper. Instead of ink, a 3-D printer uses a material, such as a polymer, metallic powder, or even organic material. It builds an object by depositing small amounts of that material in successive layers. In some cases, 3-D printing fastens materials to a substrate using heat, adhesives, or other methods. 3-D printing can produce incredibly intricate objects that would be difficult or impossible to create through traditional manufacturing methods.

Microscale 3-D printing advances the innovation of standard 3-D printing to create microscopic structures. The potential applications for microscale 3-D printing are still being explored. However, microscale 3-D printing presents the possibility of creating tissue for transplant. For example, full-scale 3-D printing has already produced some types of tissue, such as muscle, cartilage, and bones. One problem is the printed tissue sometimes did not survive because it had no circulatory system to bring blood and nutrients to the new tissue. Microscale 3-D printing makes it possible to create the tiny blood vessels needed in living tissue, among other potential applications.

3-D PRINTING METHODS

Other methods melt or fuse materials after they have been deposited. In powder bed fusion, the printer heats a bed of powdered glass, metal, ceramic, or plastic until the materials fuse together in the desired locations. Another layer of powder is then added and fused onto the first. Binder jetting uses a printer head to deposit drops of glue-like liquid into a powdered medium. The liquid soaks into and solidifies the medium. Sheet lamination fuses together thin sheets of paper, metal, or plastic with an adhesive. The layers are then cut with a laser into the desired shape. In directed energy deposition, a metal wire or powder is deposited in thin layers before being melted with a laser.

The method used depends on the physical properties of the material being printed. Metal alloys, for example, cannot easily be liquefied for vat polymerization, material jetting, or material extrusion. Instead, they are printed using binder jetting, powder bed fusion, or sheet lamination.

Microscale 3-D printing requires more exact methods to create objects that are just a few micrometers wide. Microscopic objects require tiny droplets of materials and precise locations of deposition. One microscale 3-D printing technique is optical lithography. This technique uses light to create patterns in a photosensitive resist, where material is then deposited. Optical transient liquid molding (TLM) uses UV light patterns and a custom flow of liquid polymer to create objects that are smaller than the width of a human hair. Optical TLM combines a liquid polymer, which will form the structure of the printed object, with a liquid mold in a series of tiny pillars. The pillars are arranged based on software that determines the shape of the liquids' flow. Patterned UV light then cuts into the liquids to further shape the stream. The combination of the liquid mold and the UV light pattern allow the creation of highly complex structures that are just 100 micrometers in size.

Microscale 3-D printing makes it possible to create extremely small circuits. This will enable the creation of new devices, such as “smart clothing” that can sense the wearer's body temperature and adjust its properties based on this information. Microscale 3-D printing may also revolutionize the creation of new medicines. Because drug uptake by cells is shape-dependent, the precision of microscale 3-D printing may allow researchers to design custom drugs for specific brain receptors.

Some refer to the build materials used in 3-D printing as “inks” because they take the place of ink as it is used in regular document printers. This can stretch the definition of “ink.” Most people think of ink as either the liquid in a pen or the toner of a computer printer. In microscale 3-D printing, the ink might be human cells used to create an organ or metallic powder that will be fused into tiny circuits.

—Scott Zimmer, JD