Misleading Pore Size Measurements in Gelatin and Alginate Hydrogels revealed by Confocal Microscopy.

It is a well-documented phenomenon that the porous structure of hydrogels observed with vacuum-based imaging techniques is generated during the freezing and drying process employed prior to observation. Nevertheless, vacuum-based techniques, such as scanning electron microscopy (SEM), are still being commonly used to measure pore sizes in hydrogels, which is often not representative of the actual pore size in hydrated conditions. The frequent underestimation of the impact of freezing and drying on hydrogel structures could stem from a lack of cross-fertilization between materials science and biomedical or food science communities, or from the simplicity and visually appealing nature of SEM imaging which may lead to an overemphasis on its use. Our study provides a straightforward and impactful way of pinpointing this phenomenon exploiting two hydrogels ubiquitously applied in tissue engineering, including gelatin methacryloyl (GelMA) and alginate as proof-of-concept hydrogels. By comparing images of the samples in the native hydrated state, followed by freezing, freeze-drying and rehydration using SEM and confocal microscopy, we highlight discrepancies between hydrogel pore sizes in the hydrated versus the dry state. To conclude, our study offers recommendations for researchers seeking insight in hydrogel properties and emphasizes key factors that require careful control when using SEM as a characterization tool.

The importance of mechanical and biological cues of tympanic membrane grafts to ensure optimal regeneration.

Chronic suppurative otitis media (CSOM) is often associated with permanent tympanic membrane (TM) perforation and conductive hearing loss. The current clinical gold standard, using autografts and allografts, suffers from several drawbacks. Artificial replacement materials can help to overcome these drawbacks. Therefore, scaffolds fabricated through digital light processing (DLP) were herein created to support TM regeneration. Various UV-curable printing inks, including gelatin methacryloyl (GelMA), gelatin-norbornene-norbornene (GelNBNB) (crosslinked with thiolated gelatin (GelSH)) and alkene-functionalized poly-ε-caprolactone (E-PCL) (crosslinked with pentaerythritol tetrakis(3-mercaptopropionate) (PETA4SH)) were optimized regarding photo-initiator (PI) and photo-absorber (PA) concentrations through viscosity characterization, photo-rheology and the establishment of working curves for DLP. Our material platform enabled the development of constructs with a range of mechanical properties (plateau storage modulus varying between 15 and 119 kPa). Excellent network connectivity for the GelNBNB and E-PCL constructs was demonstrated (gel fractions >95 %) whereas a post-crosslinking step was required for the GelMA constructs. All samples showed excellent biocompatibility (viability >93 % and metabolic activity >88 %). Finally, in vivo and ex vivo assessments, including histology, vibration and deformation responses measured through laser doppler vibrometry and digital image correlation respectively, were performed to investigate the effects of the scaffolds on the anatomical and physiological regeneration of acute TM perforations in rabbits. The data showed that the most efficient healing with the best functional quality was obtained when both mechanical (obtained with the PCL-based resin) and biological (obtained with the gelatin-based resins) material properties were taken into account.

Surface Functionalization of 4D Printed Substrates Using Polymeric and Metallic Wrinkles.

Wrinkle topographies have been studied as simple, versatile, and in some cases biomimetic surface functionalization strategies. To fabricate surface wrinkles, one material phenomenon employed is the mechanical-instability-driven wrinkling of thin films, which occurs when a deforming substrate produces sufficient compressive strain to buckle a surface thin film. Although thin-film wrinkling has been studied on shape-changing functional materials, including shape-memory polymers (SMPs), work to date has been primarily limited to simple geometries, such as flat, uniaxially-contracting substrates. Thus, there is a need for a strategy that would allow deformation of complex substrates or 3D parts to generate wrinkles on surfaces throughout that complex substrate or part. Here, 4D printing of SMPs is combined with polymeric and metallic thin films to develop and study an approach for fiber-level topographic functionalization suitable for use in printing of arbitrarily complex shape-changing substrates or parts. The effect of nozzle temperature, substrate architecture, and film thickness on wrinkles has been characterized, as well as wrinkle topography on nuclear alignment using scanning electron microscopy, atomic force microscopy, and fluorescent imaging. As nozzle temperature increased, wrinkle wavelength increased while strain trapping and nuclear alignment decreased. Moreover, with increasing film thickness, the wavelength increased as well.

Radical Intermediates in the Degradation of Hop Acids.

Radical formation in isohumulones was investigated under different types of stress, including temperature, transition metal ions, and hydrogen peroxide. Including dihydroisohumulones and tetrahydroisohumulones, as relevant analogues, allowed us to evaluate critical functionalities in radical formation. Using spin-trapping methodology with 5,5-dimethyl-1-pyrroline N-oxide and N-tert-butyl-α-phenylnitrone as relevant traps, followed by simulation of corresponding spin adducts, identification of incipient radicals was attempted. The isohexenoyl side chain in isohumulones, but not present in dihydro- and tetrahydroisohumulones, was most sensitive to radical formation. Kinetic profiles further demonstrated that radical formation in this moiety was accelerated in the presence of ferrous ions. Reactivity of parent six-membered-ring humulones in radical formation was different, as scavenging of free radical species was more important. Lupulones, despite similarity with humulones, showed a different behavior with an obvious radical decay pathway during ageing, mainly ascribed to radical formation on the ring structure. Quantification of final spin adducts allowed us to determine absolute importance of the different degradation pathways. Eventually, mechanisms are presented explaining why isohumulones are more prone to radical processes in (aut)oxidation and thermal decay than close relatives such as dihydroisohumulones.