Ultrasound regulated flexible protein materials: Fabrication, structure and physical-biological properties

Facile construction of a flexible metal-silk fibroin film with excellent flame retardancy for early fire warning

Early warning materials play a pivotal role in both minimizing property damage and containing the spread of fires. Herein, we report a set of flexible metal-silk fibroin (SF-M) films, which integrates early fire warning capability and excellent flame retardancy in single material. The dissolution of silk fibroin is facilitated by various metal ions (CaCl2, MgCl2, MnCl2, ZnCl2, FeCl3) and formic acid. A two-stage response to the fire alarm in the present study is firstly reported. The obtained SF-M films can not only achieve super-fast warning responses (only 1-3 s) based on ionic conduction at low temperatures, but also maintain long-lasting alarms after rapid carbonization. Meanwhile, the SF-M films illustrate excellent flame retardant properties, which can easily reach the V-0 rating, and achieve an LOI of as high as 80 % with extremely low heat and smoke release during combustion. The biomass derived SF-M films is expected to show great potential in emerging fields.

Structural and mechanical comparison of Eri and Mulberry silk fibroin nanofibers films through advanced mechanical treatments for sustainable applications

Mulberry silk (Bombyx mori) and eri silk (Samia/Philosamia ricini) are widely used silks. Eri silk is a wild silk that contains an arginine-glycine-aspartic acid tripeptide sequence within its structure, making it a potential and sustainable biomaterial. However, its poor solubility using conventional methods has resulted in limited research compared with that of mulberry silk fibroin. This study investigated the differences between nanofibrillated fibroins from both silks to assess their biomedical potential, focusing on their structural, morphological, and mechanical properties, as well as their biodegradability. Both silks were degummed and processed into fibroin microfibers (FMF) and fibroin nanofibers (FNF) via high-pressure ultrasonication and grinding in an aqueous solution. Analyses were performed using fourier transform infrared spectroscopy (FT-IR), X-ray diffractometry (XRD), atomic force microscopy (AFM), scanning electron microscope (SEM), UV-visible spectrometry, and thermogravimetric analysis (TGA) techniques. The results showed that both silks were prepared by high-pressure ultrasonication and exhibited microfibers when treated with a grinder machine, which can produce fibroin nanofibers. In terms of the type of fibroin, when comparing the properties of both silks, it was found that they have similar chemical structures but differ in their physical properties. Moreover, eri fibroin films showed superior transparency, high thermal resistance, and high strength, but were more brittle than mulberry fibroin films, which was attributed to amino acid differences. Eri silk has unique features that are interesting for the development of new materials and can create new pathways for utilizing non-mulberry silk.

Natural bioink of interpenetrating network hydrogels mimicking extracellular polymeric substances for microbial immobilization in water pollution control

Artificial biomanufacturing has been developed as a promising biotechnology for water pollution control. Effective bioimmobilization techniques are limited in application because of low productivity and the difficulty in achieving both mechanical strength and biocompatibility. Bioprinting technology, using biomaterials as bioink to enable the rapid on-demand production of bioactive structures, opens a new path for bioimmobilization. In this study, mimicking extracellular polysaccharide and protein of aerobic granular sludge (AGS), sodium alginate (SA) and silk fibroin methacryloyl (SilMA) were developed as the dual-component bioink with a suitable viscosity for bioprinting hydrogel. Interpenetrating network (IPN) hydrogel beads were manufactured using 1.5% (w/v) SA combined with 20% (w/v) SilMA through physical and covalent crosslinking, which exhibited excellent structural stability and bioactivity. The addition of SilMA provided a solution to the poor mechanical stability of SA-Ca hydrogels limited by Ca2+-Na+ ionic exchange. The unique structure of SilMA contributed to the reduction of hydrogel swelling as well as the prevention of SA loss. IPN hydrogels showed a swelling rate of less than 20% compared to the high swelling rate of more than 60% for SA hydrogels. On the other hand, SA controlled the hardening induced by excessive self-assembly of SilMA and improved mass transport in SilMA hydrogels. Compared to IPN hydrogels, SilMA hydrogels experienced a 15% volumetric shrinkage and exhibited a low water content of 92%. Sonication pretreatment of the dual-component bioink not only increased the intermolecular chain entanglement to form IPN, but also led to β-sheet content in SiMA reaching 46%-48%, which resulted in the formation of stable IPN hydrogels dominated entirely by physical crosslinking. Satisfactory proliferation and viability were achieved for the encapsulated bacteria in IPN hydrogels (μmax 1.49-2.18 d-1). Further, the IPN biohydrogels could maintain structural stability as well as achieve pollutant removal for treating synthetic wastewater with high Na+ concentration of 300 mg/L. The novel SA/SilMA hydrogel bioprinting strategy established in this study offers a new direction for bioimmobilization in water pollution control and other environmental applications.

Revolutionizing wild silk fibers: Ultrasound enhances structure, properties, and regenerability of protein biomaterials in ionic liquids

Ultrasound-assisted regulation of biomaterial properties has attracted increasing attention due to the unique reaction conditions induced by ultrasound cavitation. In this study, we explored the fabrication of wild tussah silk nanofiber membranes via ultrasound spray spinning from an ionic liquid system, characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), atomic force microscopy (AFM), water contact angle, cytocompatibility tests, and enzymatic degradation studies. We investigated the effects of ultrasound propagation in an ionic liquid on the morphology, structure, thermal and mechanical properties, surface hydrophilicity, biocompatibility, and biodegradability of the fabricated fibers. The results showed that as ultrasound treatment time increased from 0 to 60 min, the regenerated silk fiber diameter decreased by 0.97 μm and surface area increased by 30.44 μm2, enhancing the fiber surface smoothness and uniformity. Ultrasound also promoted the rearrangement of protein molecular chains and transformation of disordered protein structures into β-sheets, increasing the β-sheet content to 54.32 %, which significantly improved the materials' thermal stability (with decomposition temperatures rising to 256.38 °C) and mechanical properties (elastic modulus reaching 0.75 GPa). In addition, hydrophilicity, cytocompatibility, and biodegradability of the fiber membranes all improved with longer ultrasound exposure, highlighting the potential of ultrasound technology in advancing the properties of natural biopolymers for applications in sustainable materials science and tissue regeneration.

Physical-chemical double crosslinked silk fibroin hydrogel for high-performance bone screws

Hydrogels are widely used due to their exceptional biocompatibility and adaptability, but their weak mechanical properties limit their application in biomedical engineering. Herein, we rapidly attained a comprehensive enhancement of silk fibroin hydrogels in mechanical properties by employing a physical-chemical double crosslinking strategy. The SF was ultrasonicated and simultaneously photo-crosslinked to form a di-tyrosine network interspersed with β-sheet blocks, resulting in a SF hydrogel network structure with both rigid and flexible domains. The SF hydrogels exhibited a maximum breaking strength of 59.7 kPa and a Young's modulus of 82.2 MPa, demonstrating significant rigidity and flexibility. Subsequently, the silk screws prepared by this double crosslinking strategy showed extraordinary compressive strength and Young's modulus of 41.8 MPa and 10.9 MPa, respectively. The silk screws cocultured with osteoblasts showed optimal biocompatibility, and the rate of biodegradation could be matched to the rate of osteogenesis. The screw also exhibited high adaptability in the requirements of bone screws. In this study, the SF hydrogels prepared by physical-chemical double crosslinking have extraordinary mechanical properties and biocompatibility, which provides a new avenue for the preparation of high-performance hydrogels and has great potential in bone tissue engineering.

Regulation of Protein Flexibility and Promoting the Cod Protein Gel Formation Using Ultrasound Treatment

In order to obtain a soft-textured protein gel suitable for the elderly, the cod protein gel was prepared by improving the protein flexibility under ultrasound treatment. It has been found that the increase in ultrasonic power, protein flexibility, particle size, ζ-potential, surface hydrophobicity, and α-helix content of preheated cod protein exhibited an increasing trend. The improvement of protein flexibility promoted uniformity and density of the gel network, water retention, and texture properties. The flexibility of preheated cod protein increased to 0.189, the water holding capacity of the gel reached up to 99.41%, and the hardness increased to 49.12 g, as the ultrasonic power level increased to 400 W. Protein flexibility was correlated well with the cohesiveness of the gel. The storage modulus (G') initially decreased and then increased during the heating-cooling process. The attractive forces forming between the flexible protein molecules during cooling in the ultrasound treatment groups promoted protein self-assembly aggregation and formed the cod protein gel. The gel obtained at 100-400 W could be categorized as Level 6─soft and bite-sized according to the International Dysphagia Diet Standardization Initiative (IDDSI) framework, indicating that the cod protein gel has potential as an easy-to-swallow diet for the elderly.

Manipulating supramolecular gels with surfactants: Interfacial and non-interfacial mechanisms

Gel is a class of self-supporting soft materials with applications in many fields. Fast, controllable gelation, micro/nano structure and suitable rheological properties are essential considerations for the design of gels for specific applications. Many methods can be used to control these parameters, among which the additive approach is convenient as it is a simple physical mixing process with significant advantages, such as avoidance of pH change and external energy fields (ultrasound, UV light and others). Although surfactants are widely used to control the formation of many materials, particularly nanomaterials, their effects on gelation are less known. This review summarizes the studies that utilized different surfactants to control the formation, structure, and properties of molecular and silk fibroin gels. The mechanisms of surfactants, which are interfacial and non-interfacial effects, are classified and discussed. Knowledge and technical gaps are identified, and perspectives for further research are outlined. This review is expected to inspire increasing research interest in using surfactants for designing/fabricating gels with desirable formation kinetics, structure, properties and functionalities.

Effects of quinoa flour (Chenopodium Quinoa Willd) substitution on wheat flour characteristics

Quinoa is a pseudo-cereal with great nutritional and functional qualities, serving as an excellent substitution to develop quinoa-containing foods. This study aimed to explore the influence of quinoa flour substitution on quality characteristics of wheat flour (WF). WF was substituted with different level of quinoa core flour, ground quinoa whole flour and recombined quinoa whole flour. Increasing levels of quinoa flour in WF declined dough swelling index, while increased falling number of composite flours. Besides, quinoa flour substitution considerably decreased the chemical forces of gluten in composite flours. The proportions α-helix and β-sheets reduced, while the random coil proportion increased in gluten secondary structure. SEM images revealed that the gluten network structure was severely damaged. Our findings indicated that substitution of WF with quinoa flours was promising to be developed as an ingredient for food products.

Development of Silk Fibroin Scaffolds for Vascular Repair

Silk fibroin (SF) is a biocompatible natural protein with excellent mechanical characteristics. SF-based biomaterials can be structured using a number of techniques, allowing the tuning of materials for specific biomedical applications. In this study, SF films, porous membranes, and electrospun membranes were produced using solvent-casting, salt-leaching, and electrospinning methodologies, respectively. SF-based materials were subjected to physicochemical and biological characterizations to determine their suitability for tissue regeneration applications. Mechanical analysis showed stress-strain curves of brittle materials in films and porous membranes, while electrospun membranes featured stress-strain curves typical of ductile materials. All samples showed similar chemical composition, melting transition, hydrophobic behavior, and low cytotoxicity levels, regardless of their architecture. Finally, all of the SF-based materials promote the proliferation of human umbilical vein endothelial cells (HUVECs). These findings demonstrate the different relationship between HUVEC behavior and the SF sample's topography, which can be taken advantage of for the design of vascular implants.

Ultrasound-assisted air-jet spinning of silk fibroin-soy protein nanofiber composite biomaterials

Ultrasound utilizes a non-radiation technology that can meet modern standards to gain access to cheap, reliable and sustainable modern energy. Ultrasound technology can be implemented in the field of biomaterials for its exceptional potential in controlling the shape of nanomaterials. This study presents the first example of the production of soy and silk fibroin protein composite nanofibers in various ratios via combining ultrasonic technology with air-spray spinning. Characterization of ultrasonic spun nanofibers was performed by scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetric (TG) analysis, water contact angle, water retention, enzymatic degradation, and cytotoxicity assays. The effects that adjustments on the ultrasonic time have on the surface morphology, structures, thermal properties, hydrophilicity, water-uptake, bio-enzyme degradability, mechanical properties, and cytocompatibility of the material were examined. It was discovered that as the sonication time increased from 0 to 180 min, the beading phenomenon disappeared, forming nanofibers with uniform diameter and porosity; while the content of β-sheet crystals in the composites and their thermal stability gradually increased, the materials glass transition temperature decreased, and preferred mechanical properties were obtained. Additional studies show that the hydrophilicity, water retention capacity and enzymatic degradation rate were also enhanced by ultrasound, providing a favorable environment for cell attachment and proliferation. This study highlights the experimental and theoretical methods for ultrasound assisted air-jet spinning of biopolymer nanofibrous materials with tunable properties and high biocompatibility, which provide a wide range of applications in wound dressings and drug-carrying systems. This work shows great potential for a direct road to sustainable development of protein based fibers in the industry, thus promoting economic growth, and improving the health of the general population and well-being of wounded patients worldwide.

Silk fibroin hydrogels for biomedical applications

Silk fibroin hydrogels occupy an essential position in the biomedical field due to their remarkable biological properties, excellent mechanical properties, flexible processing properties, as well as abundant sources and low cost. Herein, we introduce the unique structures and physicochemical characteristics of silk fibroin, including mechanical properties, biocompatibility, and biodegradability. Then, various preparation strategies of silk fibroin hydrogels are summarized, which can be divided into physical cross-linking and chemical cross-linking. Emphatically, the applications of silk fibroin hydrogel biomaterials in various biomedical fields, including tissue engineering, drug delivery, and wearable sensors, are systematically summarized. At last, the challenges and future prospects of silk fibroin hydrogels in biomedical applications are discussed.

Freeze-casting osteochondral scaffolds: The presence of a nutrient-permeable film between the bone and cartilage defect reduces cartilage regeneration

Microfracture treatment that is basically relied on stem cells and growth factors in bone marrow has achieved a certain progress for cartilage repair in clinic. Nevertheless, the neocartilage generated from the microfracture strategy is limited endogenous regeneration and prone to fibrosis due to the influences of cell inflammation and vascular infiltration. To explore the crucial factor for articular cartilage remodeling, here we design a trilaminar osteochondral scaffold with a selective permeable film in middle isolation layer which can prevent stem cells, immune cells, and blood vessels in the bone marrow from invading into the cartilage layer, but allow the nutrients and cytokines to penetrate. Our findings show that the trilaminar scaffold exhibits a good biocompatibility and inflammatory regulation, but the osteochondral repair is far less effective than the control of double-layer scaffold without isolation layer. These results demonstrate that it is not adequate to rely only on nutrients and cytokines to promote reconstruction of articular cartilage, and the various cells in bone marrow are indispensable. Consequently, the current study illustrates that cell infiltration involving stem cells, immune cells and other cells from bone marrow plays a crucial role in articular cartilage remodeling based on the integrated scaffold strategy. STATEMENT OF SIGNIFICANCE: Clinical microfracture treatment plays a certain role on the restoration of injured cartilage, but the regenerative cartilage is prone to be fibrocartilage due to the modulation of bone marrow cells. Herein, we design a trilaminar osteochondral scaffold with a selective permeable film in middle isolation layer. This specific film made of dense electrospun nanofiber can prevent bone marrow cells from invading into the cartilage layer, but allow the nutrients and cytokines to penetrate. Our conclusion is that the cartilage remodeling will be extremely inhibited when the bone marrow cells are blocking. Owing to the diverse cells in bone marrow, we will further explore the influence of each cell type on cartilage repair in our continuous future work.

Ultrasound-assisted fabrication of biopolymer materials: A review

There is an urgent need to develop technologies that can physically manipulate the structure of biocompatible and green polymer materials in order to tune their performance in an efficient, repeatable, easy-to-operate, chemical-free, non-contact, and highly controllable manner. Ultrasound technology produces a cavitation effect that promotes the generation of free radicals, the fracture of chemical chain segments and a rapid change of morphology. The cavitation effects are accompanied by thermal, chemical, and biological effects that interact with the material being studied. With its high efficiency, cleanliness, and reusability applications, ultrasound has a vast range of opportunity within the field of natural polymer-based materials. This work expounds the basic principle of ultrasonic cavitation and analyzes the influence that ultrasonic strength, temperature, frequency and induced liquid surface tension on the physical and chemical properties of biopolymer materials. The mechanism and the influence that ultrasonic modification has on materials is discussed, with highlighted details on the agglomeration, degradation, morphology, structure, and the mechanical properties of these novel materials from naturally derived polymers.