Correction to "Accurate Representations of the Microphysical Processes Occurring during the Transport of Exhaled Aerosols and Droplets".

[This corrects the article DOI: 10.1021/acscentsci.0c01522.].

Accurate Representations of the Microphysical Processes Occurring during the Transport of Exhaled Aerosols and Droplets.

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.

Tunable Thiol-Ene Photo-Cross-Linked Chitosan-Based Hydrogels for Biomedical Applications.

Access to biocompatible hydrogels with tunable properties is of great interest in biomedical applications. Here we report the synthesis and characterization of a series of photo-cross-linked chitosan hydrogels from norbornene-functionalized chitosan (CS-nb) and various thiolated cross-linkers. The resulting materials were characterized by NMR, swelling ratio, rheology, SEM, and small angle neutron scattering (SANS) measurements. The hydrogels exhibited pH- and salt-dependent swelling, while the macro- and microscale properties could be modulated by the choice and degree of cross-linker or the polymer concentration. The materials could be molded in situ and loaded with small molecules that can be released overtime. Moreover, the incorporation of collagen in the hydrogels drastically improved cell adhesion, with excellent viabilities of human dermofibroblast cells on the hydrogels observed for up to 6 days, highlighting the potential use of these materials in the biomedical area.

Facile Synthesis of Chitosan-Based Hydrogels and Microgels through Thiol-Ene Photoclick Cross-Linking.

Polysaccharide-based microgels are effective vectors for the delivery of biopharmaceutics and functional components in tissue engineering due to their bioactivity and biocompatibility. Currently, the synthesis of chemically cross-linked microgels typically requires long reaction times and a high-energy input and are low yielding due to low volumes of the water phase used. Herein, we report the synthesis of norbornene-derived chitosan (CS-nbn-COOH), which can undergo rapid gelation in the presence of a thiolated cross-linker through the highly efficient thiol-ene photoclick reaction. This water-soluble photo-cross-linkable derivative, synthesized on scale via a single step from native chitosan and commercially available carbic anhydride, represents the first example of a norbornene-functionalized CS to the best of our knowledge. Microgels with controlled cross-linking densities and diameters varying between 100 and 400 nm were obtained via a low-energy water-in-oil nanoemulsion templating method at room temperature, with photo-cross-linking initiated in a flow reactor powered with a domestic UV-A lamp, a method that is suitable for the scale-up synthesis of the microgels. We also demonstrate that the resulting microgels were nontoxic to human dermofibroblasts (HDF) cell lines and that residual norbornene groups could be reacted in a late stage through tetrazine ligation, highlighting the potential of these microgels as scaffolds for functional nanomaterials with biomedical applications.