S. Woranuch, J. Arin, A. Pangon, K. Puagsuntia, N. Subjalearndee, V. Intasanta
National Nanotechnology Center, National Science and Technology Development Agency,
Keywords: nanofiber, rice flour, hydrogen bonding, nanofiltration, bio-nucleating agent, antibacterial, Tuberculosis, multifunction
Summary:Nature inspires material design through forms and functions. In this present contribution, we exemplify how bio-inspired functions can be manifested into multifunctional and potent antibacterial air nanofilters with mechanical strength and flexibility under nanostructural and compositional design theme. Firstly, a unique compositional theme as the rice-flour based nanofibrous membranes containing PVA for is developed via electrospinning (RSC Adv., 2017, 7, 19960-19966; Thai patent application number 1701001836). At the rice flour weight content of 25%, an optimal condition is discovered with reinforced hydrogen bonding between the two polymers as unveiled by the FTIR blue shift of hydroxyl groups’ 3290 wavenumber. The interaction enhances electropsinning precursor’s processability with 35% increase in viscosity and fibers’ uniformity unveiled by SEM. From structure-property study via XRD and DSC, the dissolved rice flour functions as a nucleating agent, promoting 38% crystallinity constituted from 4.29-nm PVA crystals, resulting in 23% and 19% increases in tensile strength and Young's modulus, respectively, in comparison with the pristine PVA nanofibers. The application of the versatile bio-based membrane is further differentiated by incorporation of silver nanoparticles and B-cyclodextrin to improve antimicrobial properties and volatile organic compound adsorption. As only tiny particles with sizes around 0.1 micron are able to pass through these rice-flour meshes, the bio-based nanocomposite membrane can be applied as low-environmental impact and high performance multipurpose nanofilters (RSC Advances, 2017, 7, 35368–35375 and Thai Patent Application 1701001837). Secondly, a novel structural approach is investigated in the development of an advanced type of bio-spired nanofiltration to counteract the spread of airborne multi-drug resistance tuberculosis (MDR-TB) bacteria which can be suspended in air or transmitted via respiratory aerosol (RSC Advances, 2017, 7, 46906-46915, Thai/PCT Patent Application 1601003407/PCT-TH2017-000045) and cannot be eliminated by conventional air filtration technologies due to their relatively small sizes and subtly thick cell walls. Even though fine filtration of HEPA filter could lead to effective blocking of small particles and bacteria, the device has no antibacterial functions, causing the trapped bacteria to form colonies, proliferate and eventually make the contaminated device biologically hazardous. Experimentally, water-based multicomponent solutions containing specially selected active polymers, antibacterial and water repellent agents are prepared and electrospun into nanofibrous membrane by a needle-free and scalable Nanospider process. The unique interplay among the functional components leads to mechanically-robust, flexible and petal-like water-resistant membranes with unique nanostructured mesh possibly due to the constituents’ phase separation. In the subsequent anti-TB testing under a direct contact mode, the antibacterial clear zone on the membrane’s surface is evident by a fluorescent confocal laser scanning microscope and Live/Dead staining kit. In another water-based, flow-through method, TB cells are physically blocked and killed by the miniscule pores of the potent antibacterial nanofibrous membranes. Subsequently, the membrane is assembled into a portable air filter that shows Tuberculosis killing efficiency of 90-99% during pilot scale TB-suspended aerosol filtration in a biosafety cabinet level 3. Finally, these bio-inspired nanomembranes are expected to make great economic and social impact.