BLOGS

Medical applications Laboratory tests showed how the 3D printed material molds and sticks to organs such as this porcine heart. (Courtesy: Casey Cass/CU Boulder)

Topics: 3D Printing, Additive Manufacturing, Hydrogels, Polymer Science

A new method for 3D printing, described in Science, makes inroads into hydrogel-based adhesives for use in medicine.

3D printers, which deposit individual layers of a variety of materials, enable researchers to create complex shapes and structures. Medical applications often require strong and stretchable biomaterials that also stick to moving tissues, such as the beating human heart or tough cartilage covering the surfaces of bones at a joint.

Many researchers are pursuing 3D-printed tissues, organs and implants created using biomaterials called hydrogels, which are made from networks of crosslinked polymer chains. While significant progress has been made in the field of fabricated hydrogels, traditional 3D printed hydrogels may break when stretched or crack under pressure. Others are too stiff to sculpt around deformable tissues.

Researchers at the University of Colorado Boulder, in collaboration with the University of Pennsylvania and the National Institutes of Standards and Technology (NIST), realized that they could incorporate intertwined chains of molecules to make 3D printed hydrogels stronger and more elastic – and possibly even allow them to stick to wet tissue. The method, known as CLEAR, sets an object’s shape using spatial light illumination (photopolymerization) while a complementary redox reaction (dark polymerization) gradually yields a high concentration of entangled polymer chains.

3D printing creates strong, stretchy hydrogels that stick to tissue, Catherine Steffel, Physics World

A sample of the new titanium lattice structure 3D printed in cube form. Credit: RMIT. New titanium lattice structure 3D printed in cube form. Credit: RMIT

Topics: 3D Printing, Additive Manufacturing, Materials Science, Metamaterials

A 3D printed ‘metamaterial’ boasting levels of strength for weight not normally seen in nature or manufacturing could change how we make everything from medical implants to aircraft or rocket parts.

RMIT University researchers created the new metamaterial – a term used to describe an artificial material with unique properties not observed in nature – from common titanium alloy.

But it’s the material’s unique lattice structure design, recently revealed in the journal Advanced Materials, that makes it anything but common: tests show it’s 50% stronger than the next strongest alloy of similar density used in aerospace applications.

Nature-Inspired Designs and Innovations

Lattice structures made of hollow struts were originally inspired by nature: strong hollow-stemmed plants like the Victoria water lily or the hardy organ pipe coral (Tubipora musica) showed us the way to combine lightness and strength.

Supernatural Strength: 3D Printed Titanium Structure Is 50% Stronger Than Aerospace Alloy, SciTech Daily, RMIT University

Chromatic imaging of white light with a single lens (left) and achromatic imaging of white light with a hybrid lens (right). Credit: The Grainger College of Engineering at the University of Illinois Urbana-Champaign

Topics: 3D Printing, Additive Manufacturing, Applied Physics, Materials Science, Optics

Using 3D printing and porous silicon, researchers at the University of Illinois Urbana-Champaign have developed compact, visible wavelength achromats that are essential for miniaturized and lightweight optics. These high-performance hybrid micro-optics achieve high focusing efficiencies while minimizing volume and thickness. Further, these microlenses can be constructed into arrays to form larger area images for achromatic light-field images and displays.

This study was led by materials science and engineering professors Paul Braun and David Cahill, electrical and computer engineering professor Lynford Goddard, and former graduate student Corey Richards. The results of this research were published in Nature Communications.

"We developed a way to create structures exhibiting the functionalities of classical compound optics but in highly miniaturized thin film via non-traditional fabrication approaches," says Braun.

In many imaging applications, multiple wavelengths of light are present, e.g., white light. If a single lens is used to focus this light, different wavelengths focus at different points, resulting in a color-blurred image. To solve this problem, multiple lenses are stacked together to form an achromatic lens. "In white light imaging, if you use a single lens, you have considerable dispersion, and so each constituent color is focused at a different position. With an achromatic lens, however, all the colors focus at the same point," says Braun.

The challenge, however, is that the required stack of lens elements required to make an achromatic lens is relatively thick, which can make a classical achromatic lens unsuitable for newer, scaled-down technological platforms, such as ultracompact visible wavelength cameras, portable microscopes, and even wearable devices.

A new (micro) lens on optics: Researchers develop hybrid achromats with high focusing efficiencies,  Amber Rose, University of Illinois Grainger College of Engineering

Credit: Tom Mannion

Topics: Additive Manufacturing, Biology, Biotechnology, Environment, Genetics, Nanotechnology

For Hermes, the Greek god of speed, these bacterial sneakers would have been just the ticket. Modern Synthesis co-founders Jen Keane, CEO, and Ben Reeve, CTO, are now setting out to make them available to mere mortals, raising a $4.1 million investment to scale up production. Keane, a graduate from Central Saint Martins School of Art and Design in London, and synthetic biologist Reeve, then at Imperial College London, set up Modern Synthesis in 2020 to pursue ‘microbial weaving’.

Their goal is to produce a new class of material, a hybrid/composite that will replace animal- and petrochemical-made sneakers with a biodegradable, yet durable, alternative. The shoe's upper is made by bacteria that naturally produce nanocellulose—Komagataeibacter rhaeticus—and can be further genetically engineered to also self-dye by producing melanin for color.

The process begins with a two-dimensional yarn scaffold shaped by robotics, which the scientists submerge in a fermentation medium containing the cellulose-producing bacteria. The K. rhaeticus ‘weave’ the sneaker upper by depositing the biomaterial on the scaffold. Once the sheets emerge from their microbial baths, they are shaped on shoe lasts following traditional footwear techniques. “It’s more than the sum of its parts,” Reeves says of the biocomposite. “Initially the scaffold helps the bacteria grow, then the microbial yarn reinforces the material: it holds the scaffold together.” Once the shoe is made, it is sterilized and the bacteria are washed out.

Cellulose shoes made by bacteria, Lisa Melton, Nature Biotechnology

Beetling along: Under the influence of moisture, the color of the 3D-printed beetle changes from green to red, and back again to red. (Courtesy: Bart van Overbeeke)

Topics: 3D Printing, Additive Manufacturing, Biomimetics

Researchers in the Netherlands have produced models of a beetle that changes color and a scallop shell that opens and closes in response to changing humidity in the surrounding air. Inspired by iridescent structures in nature, Jeroen Sol and colleagues at the Eindhoven University of Technology showed that they could integrate a specialized liquid crystal into standard 3D-printing techniques, creating “4D printed” devices that react to their changing environments.

Over millions of years, many organisms have evolved micro-scale structures in their anatomies that allow them to change their vibrant iridescent colors in response to stimuli. Recently, researchers have developed inks that change color in the same way and have begun to experiment with incorporating them into 3D-printed structures.

This technology has been dubbed 4D printing, where the fourth dimension represents reversible, time-varying changes to the structures after printing. One widely used technique in 4D printing is to deposit ink directly onto 3D printed structures. This approach can accommodate many types of material, as well as a versatile range of printing temperatures, speeds, and path designs.

4D-printed material responds to environmental stimuli, Sam Jarman, Physics World