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Japanese researchers have developed a biomimetic gland that weaves artificial spider silk that closely resembles its natural counterpart. In particular, the device makes it possible to reproduce the complex molecular structure of spider silk by mimicking the physico-chemical changes caused by spiders, giving it incredible strength and lightness. Ultimately, the technology could have important implications for the sustainable textile industry and biomedicine.
Spider silk is a natural supermaterial that is light, flexible and as strong as steel – meaning it has a tensile strength comparable to that of a metal alloy of the same diameter. Its properties have aroused great scientific interest, particularly with regard to its application in industries such as textiles. In fact, its biodegradability could significantly reduce the environmental impact of this sector. Its biocompatibility could also enable use in biomedicine – for example, for surgical sutures or the design of artificial ligaments.
However, natural spider silk cannot be used without significant impacts on biodiversity, not to mention logistical challenges. In fact, spiders are either cannibalistic or fight violently among themselves to the death and therefore cannot be bred in captivity like silkworms. This led to significant efforts to develop technologies to produce spider silk artificially. However, replicating the properties of natural spider silk is a major challenge due to the complexity of its structure. Although various companies have invested in the production of artificial silk, the quality they achieve is still far from that of natural silk.
Spider silk: a great natural material
Spider silk is a biopolymer composed of repeating sequences of large proteins called spidroins that form structures called beta sheets. The mechanical performance of this silk is achieved through the precise arrangement of these structures. To do this, spiders use a complex mechanism that causes changes in the arrangement of protein sequences in real time. These changes are caused by very precisely coordinated chemical precursors as well as physical forces generated by the geometry of the silk gland ducts.
In a previous study, researchers at the Riken Center for Sustainable Resource Science (in Japan) also found that spiders use two types of ions to spin their silk, which have different effects on spidroin. Sodium and chlorine ions, for example, inhibit the formation of hydrogen bonds between silk proteins, keeping them in a liquid state. On the other hand, phosphate and sulfate promote their polymerization and thus cause the silk to solidify. Spiders would rely on an ion gradient at the level of their silk glands to structure the threads in a very precise way.
In their new study, published in the journal Nature communicationResearchers at the Riken Center for Sustainable Resource Science and the Riken Pioneering Research Cluster have developed a biomimetic silk gland device aimed at reproducing these complex physicochemical processes. Their results suggest that by replicating the right conditions, it is possible to obtain spider silk that is incredibly close in quality to its natural counterpart.
The biomimetic glandular device developed by the researchers. © Jianming Chen et al.
A device that uses negative pressure
The device developed by the Japanese researchers consists of a small rectangular box with a network of microfluidic channels etched inside. In fact, the spider silk gland would function like a natural microfluidic device. “ In this study, we attempted to mimic natural spider silk production using microfluidics, in which small amounts of fluid flow through narrow channels and are manipulated », explains Keiji Numata, co-lead author of the study and researcher at the University of Tokyo, in a press release from the Riken Center.
To produce silk, the spidroin solution is subjected to precise physicochemical changes induced by the system. Specifically, it is injected at one end of the box and then “pulled” to the other end by negative pressure (an internal pressure lower than that outside the box).
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Microfluidic weaving device consisting of three inlets and one outlet with a negative pressure control system. Spidroin was first mixed with 50 mM citrate phosphate (CPB) at pH 7 and then exposed to 1 M CPB buffer (pH 5) at the interface. © Jianming Chen et al.
By testing and optimizing a range of conditions, researchers were able to identify the ideal parameters that allow proteins to self-assemble into silk fibers with the complex structure characteristic of natural spider silk. What is also interesting is that the application of mechanical force other than negative pressure did not allow the beta sheets to be arranged correctly.
« It was surprising to see how robust the microfluidic system was once the various conditions were established and optimized. said Ali Malay from the Riken Center, who was also involved in the study. In particular, the silk fibers spontaneously and surprisingly quickly assembled into an artificial device. “ What is notable is that the fibers exhibit the distinct hierarchical structure found in natural spider silk fibers “, he added.
As a next step, the researchers plan to improve their device to establish a continuous spinning process. The quality of the artificial silk is also being further evaluated with the aim of identifying further potential for improvement.
Source: Nature Communications
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