Innovation And Invention: Inspiration From Spider Silk Fiber Structure

 

Professor Meng Tao's team has significantly improved the water collection capacity of the fiber by constructing a hollow structure inside the spider silk like microfiber. It is found that the volume of the suspension droplet is 1663 times of that of the spindle node, and the water collecting capacity is far beyond the reported value.

The shortage of fresh water resources has become the main factor restricting the global social and economic development. According to statistics, seawater resources account for 96.54% of all water resources on the earth, while fresh water resources only account for 2.53%, and only 0.36% of fresh water resources can be directly used by human beings. How to obtain more available freshwater resources is an urgent problem to be solved.

Recently, the International Journal Journal Journal of material chemistry a reported the research results of Professor Meng Tao's team of Southwest Jiaotong University, namely, the use of spider like microfibers with hollow continuous channels for efficient water harvesting. By constructing hollow structures inside the spider silk like microfibers, the water collection capacity of the fibers has been significantly improved, The suspended droplet volume of the bionic microfiber is 1663 times of that of the spindle node, and the water collecting capacity is far beyond the reported value.

Inspiration from spider silk fiber structure

At present, due to the problems of water pollution and lack of fresh water resources, the water resources crisis has attracted more and more attention. Due to the applicability, simplicity and cost-effectiveness of seawater desalination and wastewater treatment technologies, some places can not use these technologies to obtain fresh water resources. Over the years, scientists in various fields have tried to get inspiration from nature and study bionic water harvesting technology.

In nature, most organisms have unique ability to deal with harsh environment. After long-term natural selection, some organisms have been able to obtain water from fog for their own survival, which provides inspiration for the design and manufacture of functional bionic materials in freshwater collection system. So far, researchers have developed a large number of bionic water collecting materials by using the water collecting mechanism of desert beetle, cactus and spider silk.

In the early morning after rain or in the humid corner, people can often find a large number of crystal drops hanging on the spider web. In fact, spider silk has a strong water collecting function, and its water collecting capacity is attributed to a unique fiber structure, which is composed of periodic spindle nodes and joints. The spindle node is composed of random and disordered nanofibers, and the joints are composed of aligned nanofibers. When the spider silk changes from dry condition to wet condition, the structure of spider silk changes and spindles (which can store water) appear. When the tiny water droplets condense on the spider silk, they will move towards the spindle node under the action of driving force to realize water collection.

Inspired by natural spider silk, the researchers plan to create microfibers that mimic the structure of spider silk and collect fresh water from the atmosphere. However, in recent years, research has focused on improving the capillary force by regulating the fiber surface morphology, which has limited effect on the improvement of fiber water collection performance. Therefore, it is still a continuous challenge to improve the water collection capacity of microfibers.

Hollow microfiber shows better water collection performance

Professor Meng Tao of Southwest University, based on his team's method of improving the water harvesting performance of fiber. In the process of research, the team tried the microfluidic technology of oil-water system and gas-liquid system, and carried out a lot of experiments, which did not achieve the desired results.

Finally, inspired by the structure of water-phase partition inside and outside the cell, the research team used microfluidic spinning technology based on aqueous two-phase laminar flow and the mechanism of partition effect of aqueous two-phase to form fibers through rapid cross-linking at the interface, which prevented the diffusion and continuous reaction of subsequent substances, and formed spider silk like hollow microfibers. "We conducted a comparative water harvesting experiment between spider silk like hollow microfibers and spider silk like solid microfibers under the same conditions, and proved that the hollow structure enhances the water collection performance of the fiber, and the spider silk like hollow microfiber has better and better water collection capacity," Meng Tao said

Why does spider like hollow microfibers exhibit better droplet suspension ability than solid spindle microfibers? "Due to the existence of the hollow channel, the length of the three-phase contact line between the droplet and the fiber is prolonged, and the capillary force on the droplet is enhanced, thus improving the ability of the fiber to hang the droplet." Meng Tao explained that when a droplet is suspended on a hollow microfiber, the liquid column in the hollow channel forms a capillary bridge, and the meniscus shaped depression at both ends of the liquid column provides additional capillary force for the suspended droplet, which has an important contribution to improving the ability of suspending the droplet.

Capillary action refers to the attraction of liquid surface to solid surface. The surface of a liquid is similar to a tensioned rubber membrane. If the liquid level is curved, it tends to flatten. "The liquid level of the wetting liquid in the capillary is concave. It exerts a pulling force on the liquid below to make the liquid rise along the pipe wall. When the upward pulling force is equal to the gravity of the liquid column in the tube, the liquid in the tube stops rising and reaches equilibrium." Meng Tao, for example, said that there are many examples of capillary phenomena in nature and daily life. For example, the vessel in the stem of a plant is a very thin capillary in the plant body, which can absorb water from the soil. In addition, brick water absorption, towel sweat absorption, chalk ink absorption are common capillary phenomenon, there are many small pores in these objects, all play the role of capillary.

Therefore, with the help of capillary force, it can increase the ability of spider like hollow microfibers to hang droplets. The larger the volume of the droplets, the more water will be captured from the air per unit time, thus improving the efficiency of microfibers collecting water from the air.

Widely used spider silk like microfibers

Nowadays, people can use the good mechanical properties of spider silk like hollow microfibers for long-term and large-scale water collection. Human beings can prepare a large number of microfibers and weave them into spider webs to collect water from the air in the humid morning and evening. "This method can also be applied to extreme environments such as arid deserts and water deficient islands to meet people's demand for fresh water shortage," Meng Tao said

Meng Tao said that in order to promote the application and innovation of spindle micro fiber in the field of water collection, the team will systematically and deeply study the interface mechanism of droplet fiber interaction in the water collection process and the technology of large-scale production of spider like hollow microfiber. "In addition, the water collection performance experiment of the fiber is carried out under a certain humidity fog. In future research, we should consider how the spindle micro fiber can collect water in the environment with extremely low humidity, and the influence of other external conditions such as wind speed, temperature and fog flow rate on the water collection performance."

It is reported that the microfiber can not only be used for water collection, but also be used in medicine, cosmetics, environmental protection, military industry and other fields. For example, spider silk like hollow microfibers can be used as wound dressings in the field of medicine. The material is a biocompatible material, covering the wound surface can effectively absorb the excess wound exudate, and can form gel to protect the wound. In addition, the fiber can accelerate the wound healing due to the introduction of the fiber as an anti-inflammatory and anti-inflammatory agent in the wound healing process.