Effect of Fe³⁺ on the Silk Fibroin Regulated Direct Growth of Nacre-like Aragonite Hybrids

Silk fibroin (SF), which has been used as an analogue of the silk-like proteins in studying the biomineralization process of calcium carbonate in vitro, shows a high preference for the formation of aragonite polymorph. In this study, Fe³⁺, which has been found with relatively high levels in the shells of marine mollusks, was introduced into the SF-regulated biomineralization system. The addition of Fe³⁺ into the SF aqueous solutions induced a conformational transition of SF from random coil to β-sheet. The promoted β-sheet structures provided Ca²⁺-binding sites for SF and, accordingly, enabled the formation of an amorphous calcium carbonate precursor. Such a precursor has an aligned parallel structure and acts as a template for the direct growth of aragonite. The corresponding aragonite products showed similar organic–inorganic hierarchical structure to nacre building in vivo as well as higher thermal stability compared with that of the other Fe³⁺-free aragonite products in terms of the polymorph. It is indicated that Fe³⁺ plays multiple roles in this nacre-mimetic biomineralization process. By examining the coeffect of SF and Fe³⁺ as multiple additives, this study has provided a deeper understanding on the valuable contribution of Fe³⁺ in the nacre-mimetic system, which could facilitate the fabrication of similar synthetic materials with good mechanical performance from cheap abundant materials

Effect of Various Dissolution Systems on the Molecular Weight of Regenerated Silk Fibroin

Effect of Various Dissolution Systems on the Molecular Weight of Regenerated Silk Fibroi

Colloidal Stability of Silk Fibroin Nanoparticles Coated with Cationic Polymer for Effective Drug Delivery

Generally, silk fibroin nanoparticles (SFNPs) are great candidates to deliver drugs or other bioactive substances in vivo. However, their further applications are largely limited by the low colloidal stability of SFNPs, as they tend to aggregate in biological media. To address this issue, SFNP composite materials with a core–shell structure (CS-SFNPs) were fabricated by coating SFNPs with four different selected cationic polymers, glycol chitosan, <i>N</i>,<i>N</i>,<i>N</i>-trimethyl chitosan, polyethylenimine, and PEGylated polyethylenimine, through electrostatic interaction. According to the DLS and NTA results, compared with the bare SFNPs, the CS-SFNPs showed much higher colloidal stability in biological media. When treated with human cervical carcinoma (HeLa) cells, the CS-SFNPs were efficiently internalized and accumulated in lysosome; and when loaded with an anticancer drug, DOX, the CS-SFNPs also showed higher cytotoxicity against HeLa cells. Our results suggest that the fabricated CS-SFNPs with desirable colloidal stability in biological media have the potential to be employed as drug carriers for the anticancer drug delivery system

Silk Fibroin Acts as a Self-Emulsifier to Prepare Hierarchically Porous Silk Fibroin Scaffolds through Emulsion–Ice Dual Templates

Silk fibroin (SF) has shown enormous potentials in various fields; however, application of SF in emulsion technology is quite limited. Here, we use SF as a self-emulsifier to form an oil-in-water (O/W) emulsion by emulsifying 1-butanol in SF aqueous solution. This showed that SF possessed strong surface activity to stabilize the O/W emulsion without the need for any other surface-active agent until its solidification because of 1-butanol-induced conformational transition of SF to β-sheet. After freezing the preformed emulsions at −20 °C, robust three-dimensional porous SF scaffolds were prepared without the need for any further post-treatment. The evolution from the O/W emulsion to porous scaffold formation under freezing was tracked, and an emulsion–ice dual template mechanism was proposed for scaffold formation, based on which SF scaffolds with controllable hierarchically porous structures were achieved by tuning the dispersed droplet volume fraction. Furthermore, SF scaffolds with hierarchical porosity showed significantly higher bioactivity toward L929 fibroblasts than that of SF scaffolds with mono macroporosity, highlighting the great asset of this hierarchically porous SF scaffold for broad applications in tissue engineering. Therefore, the strong surface-active characteristic of SF presented here, in addition to its distinct advantages, sheds a bright light on the application of SF in the vast range of emulsion technologies, especially in cosmetic-, food-, and biomedical-related areas

Understanding the Mechanical Properties and Structure Transition of Antheraea pernyi Silk Fiber Induced by Its Contraction

Like most major ampullate silks of spider, the length of Antheraea pernyi silkworm silk can shrink to a certain degree when the fiber is in contact with water. However, what happens in terms of molecule chain level and how it correlates to the mechanical properties of the silk during its contraction is not yet fully understood. Here, we investigate the water-induced mechanical property changes as well as the structure transition of two kinds of A. pernyi silk fiber, which are forcibly reeled from two different individuals (silkworm <i>a</i> and silkworm <i>b</i>; the silk fiber from either one represents the lower and upper limit of the distribution of mechanical properties, respectively). The tensile test results present that most of the mechanical parameters except the post-yield modulus and breaking strain for both silk fibers have the same variation trend before and after their water contraction. Synchrotron FTIR and Raman spectra show that the native filament from silkworm <i>a</i> contains more α-helix structures than that in silkworm <i>b</i> filament, and these α-helices are partially converted to β-sheet structures after the contraction of the fibers, while the order of both β-sheet and α-helix slightly increase. On the other side, the content and orientation of both secondary structural components in silkworm <i>b</i> fiber keep unchanged, no matter if it is native or contracted. ¹³C CP/MAS NMR results further indicate that the α-helix/random coil to β-sheet conformational transition that occurred in the silk of silkworm <i>a</i> corresponds the Ala residues. Based upon these results, the detailed structure transition models of both as-reeled A. pernyi silk fibers during water contraction are proposed finally to interpret their properties transformation

Protein Biomineralized Nanoporous Inorganic Mesocrystals with Tunable Hierarchical Nanostructures

Mesocrystals with the symmetry defying morphologies and highly ordered superstructures composed of primary units are of particular interest, but the fabrication has proved extremely challenging. A novel strategy based on biomineralization approach for the synthesis of hematite mesocrystals is developed by using silk fibroin as a biotemplate. The resultant hematite mesocrystals are uniform, highly crystalline, and porous nanostructures with tunable size and morphologies by simply varying the concentration of the silk fibroin and iron­(III) chloride in this biomineralization system. In particular, we demonstrate a complex mesoscale biomineralization process induced by the silk fibroin for the formation of hematite mesocrystals. This biomimetic strategy features precisely tunable, high efficiency, and low-cost and opens up an avenue to access new novel functional mesocrystals with hierarchical structures in various practical applications

A Recycling-Free Nanocatalyst System: The Stabilization of In Situ-Reduced Noble Metal Nanoparticles on Silicone Nanofilaments via a Mussel-Inspired Approach

The recovery and reuse of costly nanocatalysts is an essential operation in modern nanocatalysis, and improvements in catalyst reusability can contribute significantly to the economic viability and sustainable development of nanocatalysis. Herein, starting with the application of a silicone nanofilament (SNF) coating on a target substrate, a mussel-inspired approach in the form of polydopamine (PDA) deposition on the SNF surface was used to form in situ-reduced Pd nanoparticles (Pd NPs) and to stabilize them on the SNFs. This PDA-mediated approach enabled a high integrity nanocatalyst system to be built on a free-standing SNF support while retaining the porosity in the original SNF architecture. The SNFs-Pd nanocomposites prepared as such were applied to the inside walls of laboratory chemical reactors and used as recycling-free nanocatalyst systems for Pd-catalyzed organic reactions without the laborious conventional catalyst recovery and redispersion processes. The SNFs-Pd catalyst system exhibited high activity and high selectivity in single and successive Heck coupling reactions; and a reusability as high as 90% was still possible in the 20th cycle. This mussel-inspired approach is highly versatile and can be applied to laboratory chemical reactors in different shapes, sizes, and configurations to scale up the nanocatalyst applications. Furthermore, the general utility of the chemistry involved allows this surface modification technique to apply to other supported noble metal (e.g., Ag, Au, and Pt) catalysts, thereby increasing the usability and the performance of nanocatalyst systems

The Robust Hydrogel Hierarchically Assembled from a pH Sensitive Peptide Amphiphile Based on Silk Fibroin

Supramolecular polymers can be formed by self-assembly of designed subunits to yield highly ordered materials. In this paper, hierarchically structured materials, from molecules to nanofibers to macroscopical hydrogel, were fabricated by pH-induced assembly of C₁₂-GAGAGAGY, a peptide amphiphile (PA) based on silk fibroin. Due to the different acid dissociation constants of the carboxyl and phenolic hydroxyl groups on tyrosine residue (Y), the PAs showed unique pH sensitive assembly and aggregation behaviors. It was found that not only the molecular-scale assemblies of these PAs gradually changed from cylindrical nanofibers to nanoribbons with the decreasing of pH value from 11 to 8 but also most of nanoribbons aggregated into parallel bundles in such a case. Further decrease of pH value resulted in a hierarchically structured robust and plastic hydrogel, of which the rheological moduli reached around 10⁵ Pa. Moreover, noodle-like hydrogel fibers with bundles of nanoribbons aggregated parallel along the long axis in them could be steadily prepared under shear force. Taking the pH-sensitive reversible sol–gel transition, high modulus and plasticity into account, the hydrogel is believed to have significant potential applications in tissue engineering or as the biocompatible adhesives