For the regeneration or creation of functional tissues, biodegradable biomaterials including polylactic acid (PLA) are widely preferred. Modifications of the material surface are quite common to improve cell−material interactions and thereby support the biological outcome. Typical approaches include a wet chemical treatment with mostly hazardous substances or a functionalization with plasma. In the present study, gas-phase fluorination was applied to functionalize the PLA surfaces in a simple and one-step process. The biological response including biocompatibility, cell adhesion, cell spreading, and proliferation was analyzed in cell culture experiments with fibroblasts L929 and correlated with changes in the surface properties. Surface characterization methods including surface energy and isoelectric point measurements, X-ray photoelectron spectroscopy, and atomic force microscopy were applied to identify the effects of fluorination on PLA. Gas-phase fluorination causes the formation of C−F bonds in the PLA backbone, which induce a shift to a more hydrophilic and polar surface. The slightly negatively charged surface dramatically improves cell adhesion and spreading of cells on the PLA even with low fluorine content. The results indicate that this improved biological response is protein-but not integrin-dependent. Gas-phase fluorination is therefore an efficient technique to improve cellular response to biomaterial surfaces without losing cytocompatibility.

Layers of recombinant spider silks and native silks from silk worms were prepared by sincoating and casting of various solutions. FT-IR spectra were recorded to investigate the influence of the different mechanic stress occurring during the preparation of the silk layers. The solubility of the recombinant spider silk proteins SO1-ELP, C16, AQ24NR3 and of the silk fibroin from Bombyx mori were investigated in hexafluorisopropanol, ionic liquids and concentrated salt solutions. The morphology and thickness of the layers were determined by Atomic Force Microscopy (AFM) or with a profilometer. The mechanical behaviour was investigated by acoustic impedance analysis by using a quartz crystal microbalance (QCMB) as well as by microindentation. The density of silk layers (d<300 nm) was determined based on AFM and QCMB measurements. At silk layers thicker than 300 nm significant changes of the half-band-half width can be correlated with increasing energy dissipation. Microhardness measurements demonstrate that recombinant spider silk and sericine-free Bombyx mori silk layers achieve higher elastic penetration moduls EEP and Martens hardness values HM than those of polyethylenterephthalate (PET) and polyetherimide (PEI) foils

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Aerosol droplets made from respiratory liquid are of fundamental importance for airborne transmission of several virus-based diseases, such as COVID-19. While the transmission route in the air has been intensively studied in the last two years, only few papers deal with the formation of these droplets. It seems to be accepted that such droplets are generated by upper airway activity such as talking, sneezing or coughing. Especially talking is associated with disease transmission, although the droplet formation mechanisms have not been fully resolved, yet. Thus, we focus on the investigation of the atomization process of respiratory liquid attached to the vocal folds. A new experimental setup has been installed that emulates the vocal folds and their oscillating movement in a simplified manner. A model liquid mimicking the respiratory mucus is dispersed at the vocal folds. The primary atomization of the model liquid into an air stream is observed qualitatively. This new insight shows that, in contrast to the typical assumption that only liquid bridges form between the vocal folds and break up into droplets, rather bubbles are generated, which can break up into much smaller particles than filaments. Further, droplet size distributions downstream of the vocal folds are evaluated. The influence of the oscillation frequency and amplitude as well as air flow rate on the droplet size distributions are analyzed. It is found that an increase in both frequency and amplitude leads to smaller particle sizes, while raising the air flow rate results in a higher proportion of larger particles.

Films made of a recombinant spider silk protein and silk fibroin were prepared by spincoating and casting. Therefore the solubility of these substances was investigated in hexafluoroisopropa-nol, ionic liquids and concentrated salt solutions. The roughness and the thickness of the protein films were determined by the Atomic Force Microscopy (AFM) and by mechanical profilometry. The micromechanical behaviour was investigated by acoustic impedance analysis using a quartz crystal microbalance (QCMB) as well as by microindentation. Films with thickness less than 350 nm revealed an almost ideal elastic behaviour in the range of 5 to 75 MHz. At a higher film thickness the half-band-half width increases considerably and the films show a viscoelastic be-haviour with a considerable dissipation. The relative humidity significantly influences the me-chanical behaviour of protein films. Hence the micro-hardness and the ability of water adsorption were determined in dependence on the relative humidity.