Aerosols and droplets from expiratory events play an integral role in transmitting pathogens such as SARS-CoV-2 from an infected individual to a susceptible host. However, there remain significant uncertainties in our understanding of the aerosol droplet microphysics occurring during drying and sedimentation and the effect on the sedimentation outcomes. Here, we apply a new treatment for the microphysical behavior of respiratory fluid droplets to a droplet evaporation/sedimentation model and assess the impact on sedimentation distance, time scale, and particle phase. Above a 100 μm initial diameter, the sedimentation outcome for a respiratory droplet is insensitive to composition and ambient conditions. Below 100 μm, and particularly below 80 μm, the increased settling time allows the exact nature of the evaporation process to play a significant role in influencing the sedimentation outcome. For this size range, an incorrect treatment of the droplet composition, or imprecise use of RH or temperature, can lead to large discrepancies in sedimentation distance (with representative values >1 m, >2 m, and >2 m, respectively). Additionally, a respiratory droplet is likely to undergo a phase change prior to sedimenting if initially <100 μm in diameter, provided that the RH is below the measured phase change RH. Calculations of the potential exposure versus distance from the infected source show that the volume fraction of the initial respiratory droplet distribution, in this size range, which remains elevated above 1 m decreases from 1 at 1 m to 0.125 at 2 m.

Polysaccharide-based microgels are effective vectors for biopharmaceutics delivery and functional components in tissue engineering due to their bioactivity and biocompatibility. Currently, the synthesis of chemically crosslinked microgels typically requires long reaction times, high energy input and are low yielding due to low volumes of water phase used. Herein, we report the synthesis of norbornene-derivatized chitosan (CS-nbn-COOH), which can undergo rapid gelation in the presence of a thiolated crosslinker through the highly efficient thiol-ene photoclick reaction. This water-soluble photocrosslinkable derivative, synthesized on scale via a single step

Aerosols and droplets from expiratory events play an integral role in transmitting pathogens such as SARS-CoV-2 from an infected individual to a susceptible host. However, there remain significant uncertainties in our understanding of the aerosol droplet microphysics occurring during drying and sedimentation, and the effect on the sedimentation outcomes. Here, we apply a new treatment for the microphysical behaviour of respiratory fluid droplets to a droplet evaporation / sedimentation model and assess the impact on sedimentation distance, timescale and particle phase. Above 100 µm initial diameter, the sedimentation outcome for a respiratory droplet is insensitive to composition and ambient conditions. Below 100 µm, and particularly below 80 µm, the increased settling time allows the exact nature of the evaporation process to play a significant role in influencing the sedimentation outcome. For this size range, an incorrect treatment of the droplet composition, or imprecise use of RH or temperature can lead to large discrepancies in sedimentation distance (>1 m, >3 m and >2 m respectively). Additionally, a respiratory droplet is likely to undergo phase change prior to sedimenting if initially <100 µm diameter, provided the RH is below the measured phase change RH. Calculations of the potential exposure at distances away from the infected source show that volume fraction of the initial respiratory droplet distribution in this size range which remains elevated above 1 m decreases from 1 at 1 m to 0.125 at 2 m.

No abstract

Access to biocompatible self-assembled gels and microgels is of great interests for a variety of biological applications from tissue engineering to drug delivery. Here, the facile synthesis of supramolecular hydrogels of norbornene (nb)-functionalised chitosan (CS-nb) via UV-triggered self-assembly in the presence of Irgacure 2959 (IRG) is reported. The in vitro stable hydrogels are injectable and showed pH-responsive swelling behaviour, while their structure and mechanical properties could be tuned by tailoring the stereochemistry of the norbornene derivative (e.g. endo-or-exo). Interestingly, unlike other nb-type hydrogels, the gels possess nanopores within their structure, which might lead to potential drug delivery applications. A gelation mechanism was proposed based on hydrophobic interactions following the combination of IRG on norbornene, as supported by 1H NMR. This self-assembly mechanism was used to access microgels of size 100-150 nm which could be further functionalised and showed no significant toxicity to human dermofibroblast cells. File list (2) download file view on ChemRxiv exo-endo-gels .pdf (1.14 MiB) download file view on ChemRxiv ESI exo-endo gels.pdf (1.17 MiB)