New materials with advantageous properties have been developed by material scientists in recent years, which could enhance the performance of various devices and technologies. One such material is hydrogel-based fibers and artificial skins that could help create comfortable smart clothes, wearable devices, prosthetics, and even humanoid robots. Chinese researchers at Donghua University recently developed hydrogel-based microfibers that are self-healable, crack-resistant, and robust, mimicking the structure of spider silk.
The Research
The researchers noticed that most synthetic hydrogel fibers synthesized to mimic the basic functions of biological fibers such as muscle, silk, and nerve fibers have poor damage resistance, limiting their durability. The researchers discovered that the structure of spider silk represents the limit of toughness of known natural biological materials, and hydrogel fibers’ toughness could be improved by learning from spider silk’s structure.
Spiders spin their webs from an aqueous dope, a liquid crystalline solution where protein molecules can move freely, retaining some degree of order. The hierarchical nanoconfined structure of the webs they create has advantageous mechanical properties. The researchers hypothesized that the ionic complex of a hygroscopic, positively charged polyelectrolyte (PDMAEA-Q) and polymethacrylic acid (PMAA) could be an ideal system to produce damage-tolerant hydrogel fibers. In the formed fiber, PMAA would form strong hydrogen-bonded clusters embedded in the soft matrix of ionic complexes, mimicking the nanoconfined structure of spider silk for improved mechanical performance.
The researchers produced the hydrogel microfibers under ambient conditions using a technique called pultrusion spinning, the same process by which spiders produce their webs. They formed the fibers from an aqueous solution containing PMAA and PDMAEA-Q. During water evaporation, the spontaneous nanoconfinement of PMAA chains (H-bonded clusters) naturally occurred as separated nanophases embedded in the soft PDMAEA-Q/PMAA matrix. The hierarchical nanoconfinement imparts hydrogel microfibers with very high mechanical properties. For example, the hydrogel fiber is rather robust with a high Young’s modulus of 428 MPa and an elongation of 219%.
The microfibers created by the researchers exhibited highly promising properties in initial evaluations. They had a high damping capacity and crack resistance, as well as high sensitivity to moisture that allowed them to contract, retain specific shapes, and rapidly self-heal when damaged. The spider silk-inspired hydrogel microfibers created by the researchers could soon inspire the production of other highly performing fibrous materials based on nanoconfined structures and similar spinning processes.
The hydrogel microfibers could also be evaluated and applied in real-world settings, such as the actuating fibers of prosthetic limbs or wearable devices. Although the researchers showed that hydrogel fibers with a nanoconfined structure displayed excellent properties, the toughness of the fibers is not yet comparable to that of real spider silk. The researchers aim to introduce even stronger nanocrystals as nanoconfinement to further improve the hydrogel fibers’ mechanical properties.
The researchers at Donghua University developed hydrogel-based microfibers that are self-healable, crack-resistant, and robust, mimicking the structure of spider silk. The hierarchical nanoconfined structure imparts hydrogel microfibers with very high mechanical properties. The spider silk-inspired hydrogel microfibers could soon inspire the production of other highly performing fibrous materials based on nanoconfined structures and similar spinning processes. The hydrogel microfibers could also be evaluated and applied in real-world settings, such as the actuating fibers of prosthetic limbs or wearable devices.
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