Fine Structural Analysis of Degummed Fibroin Fibers Reveals Its Superior Mechanical Capabilities.

Bombyx mori silk fibroin fibers constitute a class of protein building blocks capable of functionalization and reprocessing into various material formats. The properties of these fibers are typically affected by the intense thermal treatments needed to remove the sericin gum coating layer. Additionally, their mechanical characteristics are often misinterpreted by assuming the asymmetrical cross-sectional area (CSA) as a perfect circle. The thermal treatments impact not only the mechanics of the degummed fibroin fibers, but also the structural configuration of the resolubilized protein, thereby limiting the performance of the resulting silk-based materials. To mitigate these limitations, we explored varying alkali conditions at low temperatures for surface treatment, effectively removing the sericin gum layer while preserving the molecular structure of the fibroin protein, thus, maintaining the hierarchical integrity of the exposed fibroin microfiber core. The precise determination of the initial CSA of the asymmetrical silk fibers led to a comprehensive analysis of their mechanical properties. Our findings indicate that the alkali surface treatment raised the Young's modulus and tensile strength, by increasing the extent of the fibers' crystallinity, by approximately 40 % and 50 %, respectively, without compromising their strain. Furthermore, we have shown that this treatment facilitated further production of high-purity soluble silk protein with rheological and self-assembly characteristics comparable to those of native silk feedstock, initially stored in the animal's silk gland. The developed approaches benefits both the development of silk-based materials with tailored properties and the proper mechanical characterization of asymmetrical fibrous biological materials made of natural building blocks.

Micro and nano-scale compartments guide the structural transition of silk protein monomers into silk fibers.

Silk is a unique, remarkably strong biomaterial made of simple protein building blocks. To date, no synthetic method has come close to reproducing the properties of natural silk, due to the complexity and insufficient understanding of the mechanism of the silk fiber formation. Here, we use a combination of bulk analytical techniques and nanoscale analytical methods, including nano-infrared spectroscopy coupled with atomic force microscopy, to probe the structural characteristics directly, transitions, and evolution of the associated mechanical properties of silk protein species corresponding to the supramolecular phase states inside the silkworm's silk gland. We found that the key step in silk-fiber production is the formation of nanoscale compartments that guide the structural transition of proteins from their native fold into crystalline ß-sheets. Remarkably, this process is reversible. Such reversibility enables the remodeling of the final mechanical characteristics of silk materials. These results open a new route for tailoring silk processing for a wide range of new material formats by controlling the structural transitions and self-assembly of the silk protein's supramolecular phases.

Cognitive impairment and its associations with the path of illness in affective disorders: a comparison between patients with bipolar and unipolar depression in remission.

The goals of this study were to investigate differences in neurocognitive performance between groups of patients with unipolar major depressive disorder (MDD) or bipolar I disorder (BD-I) in a euthymic state, and to analyze associations among cognitive performance, sociodemographic and clinical variables, and global functioning. The study evaluated 25 outpatients with MDD and 25 outpatients with BD-I. Controls consisted of a sample of 29 healthy adult volunteers. All of the subjects were administered a battery of neuropsychological tests (Babcock Story Recall Test, Wisconsin Card Sorting Test, Trail Making Test Part B, Stroop Color and Word Test, Symbol- Number Association Test, and Digit Span). Patients demonstrated reduced performance on tasks involving executive functions (Trail Making Test Part B and Wisconsin Card Sorting Test) and attention (Digit Span and Symbol-Number Association Test) compared with healthy controls. Performance on neurocognitive tasks did not differentiate patients with MDD from those with BD-I. Improved performance on tasks that assessed executive functions by patients with BDI and MDD, considered as a single group, was associated with better global functioning, even when controlling for several sociodemographic and clinical confounders. Patients with MDD and BD-I showed a similar profile of information-processing deficits and similar global functioning. Global functioning was also moderately associated with performance on executive function tasks.