The Silk Route to Green Catalysis: Silk Fibroin as a Recyclable Ligand for Iron-Catalyzed Olefin Epoxidation.

Silk fibroin spheres as a platform for controlled drug delivery

Silk Fibroin Microfluidic Devices.

Silk fibroin supported Pd (Pd/SF) has been prepared and used as catalyst in Suzuki–Miyaura cross‐coupling reactions in water/ethanol (4:1 v/v) mixture. The reactions proceed rapidly with aryl iodides and boronic acids with different electronic properties using low metal loading (0.38 mol‐%). Pd/SF exhibits better recyclability compared to other biopolymer‐supported Pd catalysts, up to nineteen cycles without loss of activity.

A silk fibroin gel system (e-gel) formed under weak electric fields has potential utility in drug delivery systems. By controlling the nanostructure of silk fibroin in aqueous solution, an e-gel containing silk fibroin microspheres could be formed even from silk fibroin solutions of low concentration (1%). The size of the microspheres was controlled from about 200 nm to 3 μm by changing the incubation time at 60°C. Silk fibroin microspheres containing bovine serum albumin labeled with fluorescein isothiocyanate (FITC-BSA) were then prepared under weak electric fields to form FITC-BSA-loaded carriers. The uptake of FITC-BSA by the microspheres was increased near a positive electrode because of the negative charge of FITC-BSA following its incorporation into the silk fibroin nano/microspheres. The microspheres showed a sustained release of FITC-BSA over 120 h with 75% initial loading. Considering the mild preparation conditions (low-voltage electric field, room temperature and aqueous environment), the method developed for preparing silk fibroin drug-loaded systems provides a promising way to load proteins and gene medicines with negative charge.

The goal of this proof-of-concept study was the fabrication of porous silk fibroin (SF) microspheres which could be used as cell culture carriers under very mild processing conditions. The SF solution was differentiated into droplets which were induced by a syringe needle in the high-voltage electrostatic field. They were collected and frozen in liquid nitrogen and water in droplets formed ice crystals which sublimated during lyophilization and a great quantity of micropores shaped in SF microspheres. Finally, the microspheres were treated in ethanol so as to transfer the molecular conformation into β-sheet and then they were insoluble in water. SF particles were spherical in shape with diameters in the range of 208.4 μm to 727.3 μm, while the pore size on the surface altered from 0.3 μm to 10.7 μm. In vitro, the performances of SF microspheres were assessed by culturing L-929 fibroblasts cells. Cells were observed to be tightly adhered and fully extended; also a large number of connections were established between cells. After 5-day culture, it could be observed under a confocal laser scanning microscope that the porous microenvironment offered by SF particles accelerated proliferation of cells significantly. Furthermore, porous SF particles with smaller diameters (200 - 300 μm) might promote cell growth better. These new porous SF microspheres hold a great potential for cell culture carriers and issue engineering scaffolds.

Functionalized silk fibroin dressing with topical bioactive insulin release for accelerated chronic wound healing

The formation of C–C bonds is a prerequisite for all life on earth. Understanding the role of proteins in mediating the formation of these bonds is important for understanding biological mechanisms in evolution, as well as for designing “green catalysts”. In this work, the ability of silk fibroin (SF) proteins to mediate selective C–C bond formation under mild conditions was comprehensively evaluated and compared between different SF-based materials and other proteins. Aqueous SF solution (ASFS), freeze-dried SF (FDSF), mesoporous SF (MPSF), and SF hydrogel (SFHG) materials were prepared and characterized by a variety of techniques including, among others, FE-SEM, ICP-OES, FT-IR, and TGA. The nitroaldol (Henry) reaction, Knoevenagel condensation, and direct aldol reaction were used as models for this study, in which the recovery and reusability of the protein was also evaluated.

Silk fibroin/hyaluronan scaffolds for human mesenchymal stem cell culture in tissue engineering

Supported catalysts have attracted extensive attention due to their excellent catalytic performance and reliability in heterogeneous catalysis. In this work, we report a general synthesis strategy that achieves the self‐coupling reaction of acetylene derivatives to 1,3‐diyne efficiently under conditions of copper catalyst impregnated on the precursor formed by acetone and urea. The experiments were performed by screening the base, solvent, temperature, and so forth to determine the optimum reaction conditions and then characterization and analysis of the catalyst. The results demonstrate that the Cu/CuO@CN(8) exhibits extraordinary reactivity to the self‐coupling reaction and achieves a high turnover frequency (TOF = 96.8). Typically, the conversion of phenylacetylene reaches 99.9% under the optimal reaction conditions of NaOH (2 mmol) and tert‐butanol (2 ml) and O2 (1 atm) at 60°C for 1 h. Nevertheless, it is worth noting that Cu/CuO@CN(8) has a large specific surface area (626.07 m2 g−1) and low metal loading (3.3%) measured by Brunauer Emmett–Teller (BET) and ICP‐OES, respectively. Simultaneously, kinetics and mechanism are also discussed and analyzed, and the thermodynamic energy value is calculated as 22.74 kJ mol−1. Besides, the optimum catalyst can be reused five times under optimal conditions without a significant decrease in reactivity.

Bombyx mori silk fibroin (SF) is a promising natural biocompatible protein. However, its interaction with graphene oxide (GO) has never been studied and the resultant SF/GO matrix has not been used to direct stem cell fate. Herein, we found out that mixing SF molecules and GO nanosheets in an aqueous solution can trigger the assembly of SF nanoparticles into oriented nanofibrils due to the guidance of GO nanosheets, forming SF/GO films with unique nanotopographies and improved modulus upon the removal of the solvent. When GO mass percentage in the SF/GO films is 2 and 10%, the SF assemblies are necklace-like nanofibrils (assembled from loosely linked SF nanoparticles) and solid nanofibrils (assembled from densely linked SF nanoparticles) in the resultant films, termed SG2 and SG10, respectively. GO nanosheets guided the SF assembly into nanofibrils by triggering the structural change of SF molecules from random coils to β-sheets, as confirmed by Fourier transform infrared spectroscopy and circular dichroism measurements. Furthermore, oxidative groups in the GO nanosheets were reduced by the reducing groups in SF during the nanofibril formation according to X-ray photoelectron spectroscopy and Raman spectroscopy. The reduction of the oxidative groups in GO by SF was further verified by the good cell viability on the SF/GO films. The unique nanotopographies of the SF/GO films were found to accelerate the early cell adhesion and induce the osteogenic differentiation of human mesenchymal stem cells (MSCs) even in the absence of additional inducers in the medium. More importantly, SG10 presents a stronger capability in promoting early MSC adhesion by promoting F-actin assembly, increasing cell spreading area, and inducing the osteogenic differentiation of the MSCs by the unique SF/GO nanofibrous matrix. To the best of our knowledge, it is the first report that the SF/GO substrates can induce the osteogenic differentiation of MSCs in the absence of osteogenic differentiation medium. Therefore, SF/GO composite materials would have a potential application in the field of bone tissue engineering.

Tissue-engineering scaffolds must balance mechanical compatibility with biological performance to support effective tissue regeneration. Bioactive glass (BG), valued for its strength and bone-bonding ability, often suffers from high stiffness, risking stress shielding. To address this limitation, we hybridized BG with silk fibroin (SF), a soft, biocompatible protein, to create (3-glycidyloxypropyl)trimethoxysilane (GPTMS)-crosslinked BG-SF scaffolds with tunable mechanics and enhanced cellular interactions. Fabricated via the sol-gel technique with varying BG-to-SF ratios, the scaffolds demonstrated increased porosity with higher SF content, positioning SF as a natural alternative to chemical porogens. Mechanical testing revealed that incorporating SF reduced BG stiffness, improved flexibility, and enhanced toughness, aligning the scaffold properties with those of native tissues. Fatigue testing confirmed greater durability in SF-enriched scaffolds, while degradation studies highlighted controllable rates conducive to tissue regeneration. Remarkably, as little as 10 wt% SF increased cell survival by 6.5-fold in biocompatibility assays. These findings underscore the synergy between BG and SF, presenting a soft matter strategy for designing scaffolds with customizable properties for tissue-engineering applications.

Aqueous and chemical extraction of saponin of Acacia concinna (Willd.) Dc.: An effective Bio-surfactant solution to extract silk fibroin from muga silk cocoons

The oxygen reduction reaction on palladium with low metal loadings: The effects of chlorides on the stability and activity towards hydrogen peroxide

The last decade has witnessed significant progress in the development of photosensitive polymers for in situ polymerization and 3D printing applications. Light-mediated sol-gel transitions have immense potential for tissue engineering applications as cell-laden materials can be crosslinked within minutes under mild environmental conditions. Silk fibroin (SF) is extensively explored in regenerative medicine applications due to its ease of modification and exceptional mechanical properties along with cytocompatibility. To efficiently design SF materials, the in vivo assembly of SF proteins must be considered. During SF biosynthesis, changes in pH, water content, and metal ion concentrations throughout the silkworm gland divisions drive the transition from liquid silk to its fiber form. Herein, we study the effect of the glycidyl-methacrylate-modified SF (SilkMA) solution pH on the properties and secondary structure of SilkMA hydrogels by testing formulations prepared at pH 5, 7, and 8. Our results demonstrate an influence of the prepolymer solution pH on the hydrogel rheological properties, compressive modulus, optical transmittance, and network swellability. The hydrogel pH did not affect the in vitro viability and morphology of human dermal fibroblasts. This work demonstrates the utility of the solution pH to tailor the SilkMA conformational structure development toward utility and function and shows the need to strictly control the pH to reduce batch-to-batch variability and ensure reproducibility.

The formation of C N bonds is one of the most important transformations in chemistry because nitrogen-containing compounds, particularly amines and their derivatives, are versatile building blocks for various organic molecules and essential precursors to a variety of biologically active compounds. Although several methods are known for the synthesis of C N bonds, preparation under mild and wastefree conditions using simple, inexpensive, and readily available feedstock is still a challenging goal. The transitionmetal-catalyzed coupling of amines with alcohols by using a hydrogen-borrowing strategy (also known as a hydrogenautotransfer process) has proven to be an atom-economical and environmentally attractive method for the construction of C N bonds, especially for secondary amine preparation. Although many efficient catalysts for such transformations have been reported, 4] the development of easily recoverable and recyclable heterogeneous catalysts that can solve the problem of the homogeneous systems has attracted special attention. To the best of our knowledge, few heterogeneous catalyst systems have been reported that enable efficient and selective N-alkylation of amines with alcohols under simple, mild, and environmentally benign conditions. Nitroarenes are cheap and readily available organic compounds and the reduction of nitro compounds is a key step in the preparation of many pharmaceutical agents and fine chemicals. Despite numerous established procedures for the reduction of nitro compounds, the development of catalytic methodologies that afford high chemoand regioselectivity under mild reaction conditions is still a challenging problem. As for the synthesis of secondary amines, the direct use of commercially available and inexpensive nitroarenes and alcohols as starting materials is highly attractive, especially when a single catalyst system could be employed. In this valuable one-pot multistep transformation, the alcohol may conceivably serve two possible functions: as the hydrogen source for nitro reduction and as the alkylating reagent based on the catalytic hydrogen transfer. Although excess alcohol is required to ensure the completion of the reaction (see the Supporting Information for possible reaction stoichiometries), the operational simplicity of such transformations may have practical advantages for a concise synthesis of N-substituted amines in a more straightforward manner. Compared to the great progress being made in the amination of amines with alcohols, there are scarcely available reports dealing with the direct amination of nitroarenes with alcohols. To date, only three Ru-based homogeneous systems have been reported. However, these homogeneous catalysts are problematic in terms of the recovery/ recycling of the catalyst and the necessity of special handling of metal complexes. From a sustainable point of view, a more efficient reaction with a ligand-free heterogeneous catalyst is highly desired. Over the last five years, we have been interested in the unique catalytic properties of supported gold nanoparticles (NPs) and involved in their application to sustainable organic synthesis. Recently, we have shown that very small Au NPs (approx. 1.8 nm) deposited on TiO2 (Au/TiO2-VS; VS=very small) acts as an efficient heterogeneous catalyst for the clean and atom-efficient mono-N-alkylation of a range of amines with alcohols in excellent yields under hydrogen-borrowing conditions. In view of the prominent efficiency of the gold system for the amination of amines with alcohols, we envisioned that the Au-mediated hydrogen-borrowing strategy could afford a green and efficient protocol for the direct amination of nitroarenes with alcohols under mild conditions. Herein, we report for the first time that the simple Au/TiO2-VS system can catalyze the selective secondary or tertiary amine formation from the direct condensation of nitroarenes and alcohols. Notably, the reaction can proceed effectively under ligandand basefree conditions without any external hydrogen resources. To the best of our knowledge, this study also forms the first report of a one-pot selective preparation of imines from nitroarenes and alcohols by using a heterogeneous gold-mediated “catalytic hydrogen-transfer” procedure. Based on our previous results in heterogeneous Au-catalyzed amine/alcohol coupling chemistry, the optimization study was initiated with the direct amination of nitrobenzene (1a) with eight equivalents of benzyl alcohol (2a) in the presence of Au/TiO2-VS (0.5 mol% of Au, see the Sup[a] C.-H. Tang, L. He, Dr. Y.-M. Liu, Prof. Dr. Y. Cao, Prof. Dr. H.-Y. He, Prof. K.-N. Fan Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials Department of Chemistry, Fudan University Shanghai 200433 (P.R. China) Fax: (+86)21-65643774 E-mail : yongcao@fudan.edu.cn Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201100393.