(Nanowerk News) Smart textiles offer many applications of wearable technology, from therapy to sensing to communication. For such smart textiles to function effectively, they must be strong, stretchable and electrically conductive. However, the fabrication of fibers that have all three of these properties is challenging and requires complex conditions and systems.
Taking inspiration from how spiders spin silk to make webs, a team of researchers led by Assistant Professor Swee-Ching Tan from the Department of Materials Science and Engineering under the National University of Singapore’s College of Design and Engineering, together with their international collaborators, have developed a method innovative to produce soft fibers that have these three main properties, and at the same time can be easily reused to produce new fibers. The fabrication process can be performed at room temperature and pressure, and uses less solvents and less energy, making it an attractive option for producing functional soft fibers for a variety of intelligent applications.
“The technology for making soft fibers needs to be simple, efficient and sustainable to meet the high demand for smart textile electronics. Soft fibers made using our spider-inspired spinning method have proven versatile for a wide range of smart technology applications – for example, these functional fibers can be integrated into tension-sensing gloves for gaming purposes, and smart face masks to monitor breathing status for conditions such as obstructive sleep apnea. These are just a few of the many possibilities,” said Asst Prof Tan.
Their innovations are demonstrated and outlined in their papers which are published in scientific journals Natural Electronics (“Biomimetic spinning of soft functional fibers via spontaneous phase separation”).
Spinning soft fiber web
Conventional man-made spinning methods for making synthetic fibers require high pressure, high energy input, large volumes of chemicals, and special equipment. In addition, the resulting fiber usually has a limited function.
In contrast, the spinning process of spider silk is highly efficient and can form strong and versatile fibers under ambient temperature and pressure. To address today’s technological challenges, the NUS team decided to mimic this natural spinning process to create a strong, stretchable, electrically conductive one-dimensional (1D) functional soft fiber. They identified two unique steps in spider silk formation that they could replicate.
The formation of spider silk involves converting a highly concentrated solution of protein, known as silk anesthetic, into strands of fiber. The researchers first identified that protein concentrations and interactions in silk dope increased from dope synthesis to spinning. The second step identified is the arrangement of the proteins in the dope changing when triggered by external factors to help separate the liquid part of the silk dope, leaving behind the solid part – the spider silk fiber. This second step is known as liquid-solid phase separation.
The team reinvented both steps and developed a new spinning process known as the ambient spinning with phase separation (PSEA) approach.
The soft fiber is spun from a viscous gel solution consisting of polyacrylonitrile (PAN) and silver ions – referred to as PANSions – dissolved in dimethylformamide (DMF), a common solvent. This gel solution is known as spinning dope, which is formed into soft fiber strands through a spinning process when the gel is stretched and rotated under ambient conditions.
Once the PANSion gel is stretched and exposed to air, the water molecules in the air act as a trigger causing the liquid portion of the gel to separate in the form of droplets from the solid portion of the gel, a phenomenon known as nonsolvent. vapor-induced phase separation effect. When separated from the solid fiber, droplets from the liquid portion are removed by holding the fiber vertically or at an angle to gravity to do its job.
“Manufacturing 1D soft fibers with seamless integration of end-to-end functionality is much more difficult to achieve and requires complex fabrication or multiple post-treatment processes. This innovative method fills an unmet need to create a simple but efficient spinning approach to produce functional 1D soft fibers that simultaneously have integrated mechanical and electrical functions,” said Asst Prof Tan.
Three properties, one method
The biomimetic spinning process combined with the unique formulation of the gel solution allowed researchers to create a soft fiber that has three main properties – strong, stretchable and electrically conductive.
Researchers tested the mechanical properties, strength and elasticity of PANSion gel through a series of stress tests and demonstrated that this remarkable innovation has exceptional strength and elasticity. This test also allowed the researchers to conclude that the formation of strong chemical networks between metal-based complexes in the gel is responsible for its mechanical properties.
Further analysis of the PANSion soft fibers at the molecular level confirmed their electrical conductivity and showed that the silver ions present in the PANSion gel contributed to the electrical conductivity of the soft fibers.
The team then concluded that PANSion’s soft fiber fulfills all the properties that allow it to be versatile and potentially used in a wide range of smart technology applications.
Potential applications and next steps
The team demonstrated the capabilities of PANSion’s soft fibers in a number of applications, such as communications and temperature sensing. PANSion fibers are sewn to create an interactive glove that exemplifies a smart gaming glove. When connected to a computer interface, the gloves successfully detect human hand movements and allow users to play simple games.
PANSion fibers can also detect changes in electrical signals that can be used as a form of communication such as Morse code. Additionally, these fibers can sense changes in temperature, a property that could potentially be capitalized on to protect robots from environments with extreme temperatures. Researchers have also sewn PANSion fiber into smart face masks to monitor the breathing activity of the mask wearer.
On top of the various potential applications of PANSion soft fiber, this innovative invention earns points in sustainability. PANSion fibers can be recycled by dissolving them in DMF, allowing them to be converted back into a gel solution to spin new fibers. Comparison with other current fiber spinning methods reveals that this new spider-inspired method consumes a much lower amount of energy and requires a smaller volume of chemicals.
Moving forward to this cutting-edge discovery, the research team will continue to work to improve the sustainability of PANSion’s soft fiber throughout its production cycle, from raw materials to final product recycling.