When it comes to 3D printing, the sky is the limit. As 3D printing technology continues to advance, applications can be as far reaching as airplane and automobile parts to medical devices and even anatomically correct, biocompatible models. Although 3D printing technology is developing at a rapid pace, the technology itself is not new. It emerged in the 1980s as a means of creating rapid prototypes. In recent years the applications for 3D printed models have evolved with the available hardware, software, and printable materials. Evolving technology, paired with the creative and innovative minds of scientists, engineers, and physicians, has been the launching pad for developments within 3D printing technology specific to healthcare. One way 3D printing technology is poised to create better patient outcomes is in creating an anatomically and patient-specific models to aid in surgery and medical procedures. With the capability to 3D ...
As Leonardo da Vinci once said, “simplicity is the ultimate sophistication.”
Scientists have found a way to make artificial muscles, or materials that repeatedly contract and expand in response to external stimuli, from regular nylon 6,6 – a polyamide polymertypically used to make fishing lines. Research into artificial muscles (or polymer actuators) is traditionally associated with exotic electroactive polymers and liquid crystal elastomers, so using common nylon fibers to make artificial muscles is pretty amazing – and the low cost should allow rapid integration of the technology into many applications.
A team of scientists from The Alan G. MacDiarmid NanoTech Institute at the University of Texas at Dallas (U.S.A.), collaborated with scientists from the University of Wollongong (Australia), the University of British Columbia (Canada), Hanyang University (South Korea), Namik Kemal University (Turkey) and Jilin University (China) on the discovery, which is described in Science:
We demonstrated that inexpensive high-strength polymer fibers used for fishing line and sewing thread can be easily transformed by twist insertion to provide fast, scalable, nonhysteretic, long-life tensile and torsional muscles. Extreme twisting produces coiled muscles that can contract by 49%, lift loads over 100 times heavier than can human muscle of the same length and weight, and generate 5.3 kilowatts of mechanical work per kilogram of muscle weight, similar to that produced by a jet engine. Woven textiles that change porosity in response to temperature and actuating window shutters that could help conserve energy were also demonstrated. Large-stroke tensile actuation was theoretically and experimentally shown to result from torsional actuation.
Thermal Contraction
The researchers had a goal “to convert inexpensive (~$5/kg) high-strength polymer fibers into artificial muscles that match or exceed the performance of mammalian skeletal muscle to deliver millions of reversible contractions and over 20% tensile stroke, while rapidly lifting heavy loads.”
The key property of many strong polymer fibers, consisting of long highly oriented polymer molecules, is reversible thermal contraction, i.e., they contract when heated and expand when cooled down. Thermal contraction of nylon 6,6 fibers can reach 4%, a value similar to that of NiTi shape-memory wires. Twisting the fibers into tight coils greatly enhances the contraction effect. The video below explains the principle behind the artificial muscle design:
By controlling the degree of twisting and the tightness of the resulting coil, it was possible to adjust the properties of the resulting muscle. Even more interesting, if the direction of twisting (chirality) was the opposite to the direction of the coil, the temperature effect was reversed, i.e., “muscles” expanded upon heating, instead of contracting.
By controlling the degree of twisting and the tightness of the resulting coil, it was possible to adjust the properties of the resulting muscle. Even more interesting, if the direction of twisting (chirality) was the opposite to the direction of the coil, the temperature effect was reversed, i.e., “muscles” expanded upon heating, instead of contracting.
Other Fibers Tested
In addition to nylon, other low-cost high tensile strength fibers were tested, including ultra-high molecular weight polyethylene (UHMWPE), polyvinylidene difluoride (PVDF), Kevlar, polyester, and polypropylene. Twisting and coiling the fibers had the most dramatic effect on nylon 6,6 (with reversible thermal contraction between 20° and 240°C increasing from 4 to 34%) and polyethylene (0.3% for noncoiled fiber and 16% for the coiled fiber, heated between 20° and 130°C). The higher strength of polyethylene fibers (exceeding nylon almost 10 times) would be beneficial for heavier loads.
To make the “muscles” move, the twisted coils were combined and woven together with electrothermal heating elements ( thin steel wires), which could be further braided, resulting in cool textiles, such as an actuating nylon textile, woven from nylon “muscle” coils and silver-plated nylon heating elements, a breathing textile, driven by a coiled nylon muscle, and others ( see videos in supplementary materials).
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