Structure of silk I (Bombyx mori silk fibroin before spinning) in the dry and hydrated states studied using 13C solid-state NMR spectroscopy

Phycocyanin-butterfly pea (Clitoria ternatea L.) anthocyanin nanoparticles as novel high internal phase Pickering emulsion stabilizers with antioxidant and UV shielding properties

Protein-based high internal phase Pickering emulsions (HIPPEs) possess versatile functionalities and extensive applications. However, the structural fragility of native proteins limits their direct use. Herein, butterfly pea anthocyanin (BPACN) was utilized to modify phycocyanin (PC), enhancing its interfacial properties and antioxidant capacity. Covalently crosslinked PC-BPACN nanoparticles (NPs) were synthesized and characterized to explore their interaction mechanisms. The most effective NPs were evaluated for their role as stabilizers in HIPPEs, emphasizing on their emulsifying properties and oxidative stability. The results revealed that PC forms strong interactions with BPACN via covalent bonds, hydrogen bonding, electrostatic interactions, and π-cation interactions. The PC-BPACN-10:1 NPs exhibited a higher negative zeta potential (-39.6 mV), improved surface wettability (81.2°), superior antioxidant capacity, and enhanced thermal stability compared to PC alone. NPs showed a marked increase in β-turns, accompanied by a notable decrease in α-helices, β-sheets, and random coils when compared to PC alone. HIPPEs stabilized by NPs formed a self-supporting gel network that offers excellent storage and oxidative stability, as well as improved retention of astaxanthin under both natural light and UV irradiation. This study highlights the role of BPACN in modifying PC, resulting in enhanced emulsification efficiency and antioxidant capacity, and improved UV shielding performance.

Designing Silk Biomaterials toward Better Future Healthcare: The Development and Application of Silk-Based Implantable Electronic Devices in Clinical Diagnosis and Therapy

Implantable medical electronic devices (IMEDs) have attracted great attention and shown versatility for solving clinical problems ranging from real-time monitoring of physiological/ pathological states to electrical stimulation therapy and from monitoring brain cell activity to deep brain stimulation. The ongoing challenge is to select appropriate materials in target device configuration for biomedical applications. Currently, silk-based biomaterials have been developed for the design of diagnostic and therapeutic electronic devices due to their excellent properties and abundant active sites in the structure. Herein, the aim is to summarize the structural characteristics, physicochemical properties, and bioactivities of natural silk biomaterials as well as their derived materials, with a particular focus on the silk-based implantable biomedical electronic devices, such as implantable devices for invasive brain-computer interfaces, neural recording, and in vivo electrostimulation. In addition, future opportunities and challenges are also envisioned, hoping to spark the interests of researchers in interdisciplinary fields such as biomaterials, clinical medicine, and electronics.

Comparison of adipose derived stromal cells cultured on fibroin scaffolds fabricated by salt-leaching and by freeze-thawing

Fibroin, the main structural protein of Bombyx mori silk, is known for its mechanical properties, its biocompatibility and degradation characteristics in vivo. Various studies investigate its uses as cell carrier and/or material for surgical implants. Multiple protocols have been established to isolate fibroin from silk fibers and to produce scaffolds and films from fibroin solution. There is only limited literature available on how fibroin scaffolds manufactured by different methods compare to each other in terms of performance as cell carriers. This study compares the behaviour of human adipose derived stromal cells (ADSC) seeded on fibroin scaffolds produced by (i) salt-leaching and (ii) freeze-thawing. One type of freeze-thawing scaffold (poresize ≪ 315 μm) and three types of salt-leaching scaffolds (poresize ranging from 315 μm to 1000 μm) were used for this comparison. Measuring the DNA concentration on the seeded scaffolds as well as the seeded cells metabolic activity, we were able to determine freeze-thawed scaffolds to be superior for cell-seeding. ADSC seeded on salt-leaching scaffolds displayed a stronger downregulation of serum deprivation response gene than cells seeded on freeze-thaw scaffolds. In sum, our findings show that salt-leaching scaffolds offering different pore sizes differed much less among each other than salt-leaching from freeze-thawing scaffolds in terms of cell accommodation. Our work underlines the importance of physicochemical scaffold properties directly linked to different manufacturing methods and their influence on the cell seeding capacity of silk fibroin based carriers.

Molecular organization of fibroin heavy chain and mechanism of fibre formation in Bombyx mori

Fibroins' transition from liquid to solid is fundamental to spinning and underpins the impressive native properties of silk. Herein, we establish a fibroin heavy chain fold for the Silk-I polymorph, which could be relevant for other similar proteins, and explains mechanistically the liquid-to-solid transition of this silk, driven by pH reduction and flow stress. Combining spectroscopy and modelling we propose that the liquid Silk-I fibroin heavy chain (FibH) from the silkworm, Bombyx mori, adopts a newly reported β-solenoid structure. Similarly, using rheology we propose that FibH N-terminal domain (NTD) templates reversible higher-order oligomerization driven by pH reduction. Our integrated approach bridges the gap in understanding FibH structure and provides insight into the spatial and temporal hierarchical self-assembly across length scales. Our findings elucidate the complex rheological behaviour of Silk-I, solutions and gels, and the observed liquid crystalline textures within the silk gland. We also find that the NTD undergoes hydrolysis during standard regeneration, explaining key differences between native and regenerated silk feedstocks. In general, in this study we emphasize the unique characteristics of native and native-like silks, offering a fresh perspective on our fundamental understanding of silk-fibre production and applications.

Regenerated Fiber's Ideal Target: Comparable to Natural Fiber

The toughness of silk naturally obtained from spiders and silkworms exceeds that of all other natural and man-made fibers. These insects transform aqueous protein feedstocks into mechanically specialized materials, which represents an engineering phenomenon that has developed over millions of years of natural evolution. Silkworms have become a new research hotspot due to the difficulties in collecting spider silk and other challenges. According to continuous research on the natural spinning process of the silkworm, it is possible to divide the main aspects of bionic spinning into two main segments: the solvent and behavior. This work focuses on the various methods currently used for the spinning of artificial silk fibers to replicate natural silk fibers, providing new insights based on changes in the fiber properties and production processes over time.

Real-Time Monitoring of the Structural Transition of Bombyx mori Liquid Silk under Pressure by Solid-State NMR

Silk fibroin is stored in the silk glands of Bombyx mori silkworms as a condensed aqueous solution called liquid silk. It is converted into silk fibers at the silkworm's spinnerets under mechanical forces including shear stress and pressure. However, the detailed mechanism of the structural transition of liquid silk to silk fibers under pressure is not well understood. Magic angle spinning (MAS) in solid-state nuclear magnetic resonance (NMR) can exert pressure on liquid samples in a quantitative manner. In this study, solid-state NMR was used to quantitatively analyze the impact of pressure on the structural transition of liquid silk. A combination of 13C DD-MAS and CP-MAS NMR measurements enabled the conformation and dynamics of the crystalline region of the silk fibroin (both before (Silk Ip) and after (Silk IIp) the structural transition) to be detected in real time with atomic resolution. Spectral analyses proposed that the pressure-induced structural transition from Silk Ip to Silk IIp proceeds by a two-step autocatalytic reaction mechanism. The first reaction step is a nucleation step in which Silk Ip transforms to single lamellar Silk IIp, and the second is a growth step in which the single lamellar Silk IIp acts as a catalyst that reacts with Silk Ip molecules to further form Silk IIp molecules, resulting in stacked lamellar Silk IIp. Furthermore, the rate constant in the second step shows a significant pressure dependence, with an increase in pressure accelerating the formation of large stacked lamellar Silk IIp.

Silk fibroin scaffolds with stable silk I crystal and tunable properties

It is crucial to develop a three-dimensional scaffold with tunable physical properties for the biomedical application of silk fibroin (SF). The crystallization of polymers dictates their bulk properties. The presence of two unique crystal types, silk I and silk II, provides a mechanism for controlling the properties of SF biomaterials. However, it remains challenging to manipulate silk I crystallization. In this study, we demonstrate the stability and tunability of SF scaffolds with silk I structure prepared by a freezing-annealing processing. The porous structure and mechanical properties of the scaffolds can be readily regulated by SF concentration. XRD results show that the typical peaks representing silk I do not shift when subjected to various post-treatments, such as ethanol soaking, heating, water vapor annealing, UV irradiation, and high-temperature/high-pressure, indicating the stability of silk I crystal type. Moreover, the crystallization kinetics can be regulated by changing annealing time. This physical process can regulate the transition from non-crystalline to silk I, in turn controlling the mechanical properties and degradation rate of the SF scaffolds. Our result show that this green, all-aqueous strategy provides new directions for the design of SF-based biomaterials with controllable properties.

A review on the structure of Bombyx mori silk fibroin fiber studied using solid-state NMR: An antipolar lamella with an 8-residue repeat

Silk fibroin (SF) fiber from the silkworm Bombyx mori in the Silk II form has been used as an excellent textile fiber for over 5000 years. Recently it has been developed for a range of biomedical applications. Further expansion of these uses builds on the excellent mechanical strength of SF fiber, which derives from its structure. This relationship between strength and SF structure has been studied for over 50 years, but it is still not well understood. In this review, we report the use of solid-state NMR to study stable-isotope labeled SF fiber and stable-isotope labeled peptides including (Ala-Gly)₁₅ and (Ala-Gly-Ser-Gly-Ala-Gly)₅ as models of the crystalline fraction. We show that the crystalline fraction is a lamellar structure with a repetitive folding using β-turns every eighth amino acid, and that the sidechains adopt an antipolar arrangement rather than the more well-known polar structure described by Marsh, Corey and Pauling (that is, the Ala methyls in each layer point in opposite directions in alternate strands). The amino acids Ser, Tyr and Val are the next most common in B. mori SF after Gly and Ala, and occur in the crystalline and semi-crystalline regions, probably defining the edges of the crystalline region. Thus, we now have an understanding of the main features of Silk II but there is still a long way to go.