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Functional Bulk Nanocomposites Created Using Aerosol-Assisted Biosynthesis Strategy

One of the coolest scenes in the movie Avengers: Infinity War takes place when Iron Man switches on his nanotech armor and manipulates nanoparticles to generate the armor upon his skin. In fact, forming such a method to assemble nanomaterials into macroscopic bulk materials that preserve their unique nanoscale properties is still a difficult task for researchers in the real world. In the meantime, it is also a major problem that hinders the practical industrial application of nanomaterials.

One likely solution is to make a skeleton that can contain the individual nanomaterials together and thus construct functional bulk nanocomposites, similar to the steel reinforcing bars in reinforced concrete. Among many candidates, bacterial cellulose (BC) nanofibrils, one of the most copious biomaterials that can be created in large quantities at low cost via bacterial fermentation, are preferred by researchers for their high tensile strength that is similar to Kevlar and steel, as well as for the strong 3D nanofibrous network they develop.

However, the traditional process of BC nanocomposites fabrication necessitates the disintegration of this kind of a 3D network structure, which critically weakens the mechanical properties of the fabricated nanocomposites. Therefore, researchers cannot help but contemplate if there is a method that can procure the best of the two worlds: integrating nanoscale building blocks into a BC matrix while maintaining the 3D network structure of BC.

In reaction to this challenge, now, scientists led by Professor Yu Shu-Hong from the University of Science and Technology of China (USTC) formulated a basic and scalable biosynthesis strategy, which involves concurrent growth of cellulose nanofibrils via microbial fermentation and co-deposition of different kinds of nanoscale building blocks (NBBs) via aerosol feeding (intermittent spray of liquid nutrients and NBBs suspension) on solid culture substrates.

In comparison with static fermentation in liquid nutrients dispersed with NBBs, this technique surpasses the diffusion limitation of nanoscale units from the bottom liquid medium to the upper surface layer of new-grown BC, successfully creating a series of uniform bulk nanocomposites made up of BC and nanoscale building blocks of varying shapes, dimension, and sizes. Mainly, the technique can be easily expanded for potential industrial applications by using large reactors and adding more nozzles.

As a result of the even distribution of NBBs in the biosynthesized nanocomposites, scientists were able to tweak the content of carbon nanotubes (CNTs) in a broad range from 1.5 wt% to 75 wt% by altering the concentration of CNTs suspensions. It is important to keep in mind that conventional fabrication technique for CNTs nanocomposites that require the blending of CNTs dispersions with polymer solutions is only valid for preparation of polymer nanocomposites with low CNTs (<10 wt%), as it is very difficult to homogeneously scatter high-concentration CNTs in polymeric hosts.

To further prove the benefits of the biosynthesis strategy for preparing mechanically reinforced nanocomposites, CNTs/BC nanocomposite films were also prepared for comparison by mixing of CNTs and disintegrated BC suspensions. Both Young’s modulus and tensile strength of the biosynthesized CNTs/BC nanocomposites were unusually higher than that of the blended samples. Consequently, the biosynthesized CNTs/BC nanocomposites simultaneously attain a very high mechanical strength and electrical conductivity, which is of critical importance for practical application.

Despite the fact that we are currently focusing on CNT-based nanocomposite aerogels and films in this work, all the biosynthesized pellicles can be converted into corresponding functional bulk nanocomposites.

Guan Qing-Fang, Study First Author, University of Science and Technology of China

For instance, the biosynthesized Fe3O4/BC nanocomposite films displayed superparamagnetic behavior and high tensile strength, which are projected to be useful in different fields such as biomedicine electromagnetic actuators, and smart microfluidics devices.

By upgrading the state-of-the-art production line that produces pure bacterial cellulose pellicles, industrial-scale production of these bulk nanocomposite materials for practical applications can be expected in the near future,” the scientists provide a positive viewpoint.

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