Since the outbreak of the COVID-19 pandemic, most countries have recommended their citizens to adopt social distance, hand hygiene, and face mask wearing. However, wearing face masks has not been well adopted by many citizens. While the reasons are complex, there is a general perception that the evidence to support face mask wearing is lacking, especially for the general public in a community setting. Face mask wearing can block or filter airborne virus-carrying particles through the working of colloid and interface science. This paper assesses current knowledge behind the design and functioning of face masks by reviewing the selection of materials, mask specifications, relevant laboratory tests, and respiratory virus transmission trials, with an overview of future development of reusable masks for the general public. This review highlights the effectiveness of face mask wearing in the prevention of COVID-19 infection.

Due to their structural simplicity and robust self-assembled nanostructures, short peptides prove to be an ideal system to explore the physical processes of self-assembly, hydrogels, semi-flexible polymers, quenched disorder and reptation. Rational design in peptide sequences facilitates cost-effective manufacturing, but the huge number of possible peptides has imposed obstacles for their characterisation to establish functional connections to the primary, secondary and tertiary structures. This review aims to cover recent advances in the self-assembly of designed short peptides, with a focus on physical driving forces, design rules, characterisation methods and exemplar applications. Super-resolution microscopy in combination with modern image analysis have been applied to quantify the structure and dynamics of peptide hydrogels whilst SANS and ssNMR continue to provide valuable information on structures over complementary lengths. Short peptides are attractive in biomedicine and nanotechnology, e.g., as antimicrobials, anticancer agents, vehicles for controlled drug release, peptide bioelectronics and responsive cell culture materials.

Antimicrobial peptides are promising alternatives to traditional antibiotics. A group of selfassembling lipopeptides was formed by attaching an acyl chain to the N-terminus of α-helix forming peptides with the sequence C x -G(IIKK) y I-NH 2 (C x G y , x = 4-12 and y = 2). C x G y selfassemble into nanofibers above their critical aggregation concentrations (CACs). With increasing x, the CACs decrease and the hydrophobic interactions increase, promoting secondary structure transitions within the nanofibers. Antimicrobial activity, determined by the minimum inhibition concentration (MIC), also decreases with increasing x, but the MICs are significantly smaller than the CACs, suggesting effective bacterial membrane disrupting power. Unlike conventional antibiotics, both C 8 G 2 and C 12 G 2 can kill S. aureus and E. coli after only minutes of exposure. C 12 G 2 nanofibers have considerably faster killing dynamics and lower cytotoxicity than their non-aggregated monomers. Antimicrobial activity of peptide aggregates has to date been underexploited and it is found to be a very promising mechanism for peptide design. Detailed evidence for the molecular mechanisms involved are provided, based on super-resolution fluorescence microscopy, ss-NMR, AFM, neutron scattering/reflectivity, CD and Brewster angle microscopy.

Molecular dynamics simulations are conducted to investigate the underwater oleophobicity of self-assembled monolayers (SAMs) with different head groups. Simulation results show that the order of underwater oleophobicity of SAMs is methyl < amide < oligo(ethylene glycol) (OEG) < ethanolamine (ETA) < hydroxyl < mixed-charged zwitterionic. The underwater-oil contact angles (OCAs) are <133° for all nonionic hydrophilic SAMs, while the mixed-charged zwitterionic SAMs are underwater superoleophobic (OCA can reach 180°). It appears that surfaces with stronger underwater oleophobicity have better antifouling performance. Further study on the effect of different alkyl ammonium ions on mixed-charged SAMs reveals that the underwater OCAs are >143.6° for all SAMs; mixed-charged SAMs containing primary alkyl ammonium ion are likely to possess the best underwater oleophobicity for its strong hydration capacity. It seems that alkyl sulfonate anion (SO) is more hydrophilic than alkyl trimethylammonium ion (NC) for the hydrophobic methyl groups on nitrogen atoms and that the hydration of SO in mixed-charged SAMs can be seriously blocked by NC. The monomer of SO should be slightly longer than that of NC to obtain better underwater oleophobicity in NC-/SO-SAMs. In addition, the underwater oleophobicity of SAMs might become worse at low grafting densities. This work systematically proves that a zwitterionic surface is more underwater oleophobic than a nonionic surface. These results will help for the design and development of superoleophobic surfaces.

Molecular dynamics (MD) simulations, stochastic optical reconstruction microscopy (STORM) and neutron reflection (NR) are combined to explore how antimicrobial peptides (AMPs) can be designed to promote the formation of nanoaggregates into bacterial membranes and impose effective bactericidal actions. Changes in the hydrophobicity of the designed AMPs were found to have strong influence on their bactericidal potency and cytotoxicity. G(IIKK) 3 I-NH 2 (G 3 ) achieved low minimum inhibition concentrations (MICs) and effective dynamic kills against both antibiotic resistant and susceptible bacteria. However, a G 3 derivative with weaker hydrophobicity, KI(KKII) 2 I-NH 2 (KI), exhibited considerably lower membrane-lytic activity. In contrast, the more hydrophobic G(ILKK) 3 L-NH 2 (GL) peptide achieved MICs similar to those observed for G 3 , but with worsened haemolysis. Both the model membranes studied by Brewster angle microscopy, Zeta-potential measurements and NR, and the real bacterial membranes examined with direct STORM, contained membrane inserted peptide aggregates upon AMP exposure. These structural features were well supported by MD simulations. By revealing how AMPs self-assemble in microbial membranes, this work provides important insights into their mechanistic actions and allows further fine-tuning of antimicrobial potency and cytotoxicity.