New Insights into the Molecular Structure of Tear Film Lipids Revealed by Surface X-ray Scattering.

The tear film lipid layer (TFLL) is a unique biological membrane that serves a pivotal role in the maintenance of ocular surface health. Reaching an overarching understanding of the functional principle of the TFLL has been hampered by a lack of insights into the structural and functional roles played by individual lipid classes. To bridge this knowledge gap, we herein focus on studying films formed by principal lipid classes by surface scattering methods. Through grazing incidence X-ray diffraction and X-ray reflectivity studies, we reveal quantitative data about the lattice distances, molecular tilt angles, and mono/multilayer thickness and density profiles for central TFLL lipid classes under close to simulated physiological conditions. In addition, we discuss the correlation of the results to those obtained previously with the natural lipid composition of meibum.

Early-Stage Development of an Anti-Evaporative Liposomal Formulation for the Potential Treatment of Dry Eyes.

Dry eye disease (DED), the most common ocular disorder, reduces the quality of life for hundreds of millions of people annually. In healthy eyes, the tear film lipid layer (TFLL) stabilizes the tear film and moderates the evaporation rate of tear fluid. In >80% of DED cases, these central features are compromised leading to tear film instability and excessive evaporation of tear fluid. Herein we assess the potential of liposomal formulations featuring phosphatidylcholines and tailored lipid species from the wax ester and O-acyl-ω-hydroxy fatty acid categories in targeting this defect. The developed lead formulation displays good evaporation-resistant properties and respreadability over compression-expansion cycles in our Langmuir model system and a promising safety and efficacy profile in vitro. Preclinical in vivo studies will in the future be required to further assess and validate the potential of this concept in the treatment of DED.

Structure of cellulose in birch phloem fibres in tension wood: an X-ray nanodiffraction study.

BACKGROUND: To gain a better understanding of bark layer structure and function, especially of the phloem fibres and their contribution to the posture control of trees, it is important to map the structural properties of these cells. The role of bark can also be linked to the reaction wood formation and properties which are essential when it comes to studying the questions related to tree growth. To offer new insights into the role of bark in the postural control of trees, we studied the micro- and nanoscale structures of the phloem and its nearest layers. This study is the first time, in which phloem fibres in trees have been extensively examined using X-ray diffraction (XRD). We determined the orientation of cellulose microfibrils in phloem fibres of Silver birch saplings by using scanning synchrotron nanodiffraction. The samples consisted of phloem fibres extracted from tension, opposite and normal wood (TW, OW, NW). RESULTS: Using scanning XRD, we were able to obtain new information about the mean microfibril angle (MFA) in cellulose microfibrils in phloem fibres connected to reaction wood. A slight but consistent difference was detected in the average MFA values of phloem fibres between the TW and OW sides of the stem. Using scanning XRD, different contrast agents (intensity of the main cellulose reflection or calcium oxalate reflection, mean MFA value) were used to produce 2D images with 200 nm spatial resolution. CONCLUSIONS: Based on our results, the tension wood formation in the stem might be related to the structure and properties of phloem fibres. Thus, our results suggest that the nanostructure of phloem fibres is involved in the postural control of trees containing tension and opposite wood.

Visualizing Degradation of Cellulose Nanofibers by Acid Hydrolysis.

Cellulose hydrolysis is an extensively studied process due to its relevance in the fields of biofuels, chemicals production, and renewable nanomaterials. However, the direct visualization of the process accompanied with detailed scaling has not been reported because of the vast morphological alterations occurring in cellulosic fibers in typical heterogeneous (solid/liquid) hydrolytic systems. Here, we overcome this distraction by exposing hardwood cellulose nanofibers (CNFs) deposited on silica substrates to pressurized HCl gas in a solid/gas system and examine the changes in individual CNFs by atomic force microscopy (AFM). The results revealed that hydrolysis proceeds via an intermediate semi-fibrous stage before objects reminiscent of cellulose nanocrystals were formed. The length of the nanocrystal-like objects correlated well with molar mass, as analyzed by gel permeation chromatography, performed on CNF aerogels hydrolyzed under identical conditions. Meanwhile, X-ray diffraction showed a slight increase in crystallinity index as the hydrolysis proceeded. The results provide a modern visual complement to >100 years of research in cellulose degradation.

Molecular Insights on Successful Reconstitution of Freeze-Dried Nanofibrillated Cellulose Hydrogel.

The diversity and safety of nanofibrillated cellulose (NFC) hydrogels have gained a vast amount of interest at the pharmaceutical site in recent years. Moreover, this biomaterial has a high potential to be utilized as a protective matrix during the freeze-drying of heat-sensitive pharmaceuticals and biologics to increase their properties for long-term storing at room temperature and transportation. Since freeze-drying and subsequent reconstitution have not been optimized for this biomaterial, we must find a wider understanding of the process itself as well as the molecular level interactions between the NFC hydrogel and the most suitable lyoprotectants. Herein we optimized the reconstitution of the freeze-dried NFC hydrogel by considering critical quality attributes required to ensure the success of the process and gained insights of the obtained experimental data by simulating the effects of the used lyoprotectants on water and NFC. We discovered the correlation between the measured characteristics and molecular dynamics simulations and obtained successful freeze-drying and subsequent reconstitution of NFC hydrogel with the presence of 300 mM of sucrose. These findings demonstrated the possibility of using the simulations together with the experimental measurements to obtain a more comprehensive way to design a successful freeze-drying process, which could be utilized in future pharmaceutical applications.

Defect-Driven Enhancement of Electrochemical Oxygen Evolution on Fe-Co-Al Ternary Hydroxides.

Efficient, abundant and low-cost catalysts for the oxygen evolution reaction (OER) are required for energy conversion and storage. In this study, a doping-etching route has been developed to access defect rich Fe-Co-Al (Fe-Co-Al-AE) ternary hydroxide nanosheets for superior electrochemical oxygen evolution. After partial etching of Al, ultrathin Fe3 Co2 Al2 -AE electrocatalysts with a rich pore structure are obtained with a shift of the cobalt valence state towards higher valence (Co2+ →Co3+ ), along with a substantial improvement in the catalytic performance. Fe3 Co2 Al2 -AE shows a notably lower overpotential of only 284 mV at a current density of 10 mA cm-2 and double the OER mass activity of the etching-free Fe3 Co2 Al2 with an overpotential of 350 mV. Density functional theory shows the leaching of Al changes the rate-determining step of the OER from conversion of *OOH into O2 on Fe3 Co2 Al2 to formation of OOH from *O on the Al-defective catalysts. This work demonstrates an effective route to design and synthesize transition metal electrocatalysts and provides a promising alternative for the further development of oxygen evolution catalysts.