Jinrong Yao

The preparation of regenerated silk fibroin microspheres

The objective of the present study is to investigate the possibility of preparing pure protein microspheres from regenerated silk fibroin (RSF). It is found that RSF microspheres, with predictable and controllable sizes ranging from 0.2 to 1.5 µm, can be prepared mild self-assembling of silk fibroin molecular chains. The merits of this novel method include a rather simple production apparatus and no potentially toxic agents, such as surfactants, initiators, cross-linking agents, The results show that the particle size and size distribution of RSF microspheres are greatly affected by the amount of ethanol additive, the freezing temperature and the concentration of silk fibroin. Finally, the mechanism of RSF microspheres formation is also discussed based on our experimental results.

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 C(12)-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 10(5) 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.

Crystallization of calcium carbonate on chitosan substrates in the presence of regenerated silk fibroin.

The crystallization of calcium carbonate (CaCO3) was investigated using a mineralization system composed of a chitosan membrane and regenerated silk fibroin (RSF). Such a system may resemble the mineralization in molluscs, where chitosan is a derivative of chitin and RSF an analogue of nacreous protein. It was found that the vaterite disks generally formed on the chitosan membrane while the aragonite disks also appeared with changes of pH value or temperature of the solution. The crystallization of CaCO3 in the vicinity of the chitosan membrane was much more affected by the environment of crystallization, compared to that in bulk solution. Detailed observation from high-resolution scanning and transmission electron microscopy (HRSEM and TEM) showed that these disks consisted of nanoparticles about 20 nm in size, thus suggesting that the accumulation of hybrid CaCO3/RSF nanoparticles induced the formation of crystalline disks on the chitosan membrane.

Robust soy protein films obtained by slight chemical modification of polypeptide chains

Soy protein based materials are of great interest because of the merits of biocompatibility, biodegradability, renewability, etc. However, the poor mechanical properties and high water sensitivity limit their further application in many fields. In this paper, we tried to overcome these shortcomings through a slight chemical modification of the polypeptide chains of soy protein. 31P NMR and solid state 13C CP/MAS NMR spectroscopy confirmed that the diethoxy phosphoryl groups were successfully grafted onto soy protein chains with a molar grafting ratio of 0.15–1.18%, which almost did not change the nature of soy protein. The isoelectric point and rheological behavior of the modified soy protein sample varied with the grafting ratio, indicating that the tertiary structure of the protein was changed after phosphoryl modification. The FTIR spectra of the modified soy protein suggested that the increase of β-sheet conformation from the slight chemical modification could be the reason for the change of the globular structure of soy protein. Finally, we obtained a robust soy protein film as expected, and we did not use any crosslinking agent and plasticizer that were almost unavoidable in the previous studies reported in the literature. The tensile strength and the elongation at break of our soy protein films were 35 ± 5 MPa, 2.5 ± 0.5% in the dry state, and 3.8 ± 1.5 MPa, 125 ± 5% in the wet state, respectively. We believe that the method we developed in this communication provides a practical approach to improve the mechanical properties and broaden the applications of natural soy protein based materials.

Fabrication of an alternative regenerated silk fibroin nanofiber and carbonated hydroxyapatite multilayered composite via layer-by-layer

A novel multilayered composite consisting of regenerated silk fibroin (RSF) nanofiber and carbonated hydroxyapatite (CHA) was fabricated with the combination of electrospinning of RSF aqueous solution and soaking in CaCl2 and Na2HPO4 solutions alternately. The chemical composition and morphologies of RSF/CHA composite were characterized by FT-IR, XRD, TGA, EDX, and SEM. The results showed that such an organic/inorganic composite had an alternate layered structure, while the CHA mineral partly penetrated into the porous RSF mats, which was similar to the structure of natural nacre. By tuning the CHA deposition procedure and RSF electrospinning condition independently, the thickness of each layer of CHA and RSF, as well as the layer numbers of composite, could be easily regulated. For example, the average thickness of CHA layers with 5 and 10 mineralization cycles were 1.63 and 3.19 μm, while 9.03 and 30.12 μm of porous RSF nanofiber layers could be formed with 7 and 24 h electrospinning process, respectively. Thus, it may provide an efficient and general approach to produce a series of inorganic/organic multilayered biomaterials for biomedical engineering.

Silver sulfadiazine–immobilized celluloses as biocompatible polymeric biocides

Sulfadiazine was immobilized onto cotton cellulose using ethylene glycol diglycidyl ether as a binder. Upon treatment with diluted silver nitrate aqueous solution, the sulfadiazine moieties in the immobilized celluloses were transformed into silver–sulfadiazine coordination complexes. The resulting silver sulfadiazine–immobilized celluloses provided a 6-log reduction of 108 CFU mL−1 of Staphylococcus aureus (Gram-positive bacteria), Escherichia coli (Gram-negative bacteria), methicillin-resistant Staphylococcus aureus (drug-resistant bacteria), vancomycin-resistant Enterococcus faecium (drug-resistant bacteria), and Candida albicans (fungi) in 30–60 minutes, and a 5-log reduction of 107 PFU mL−1 of MS2 virus in 120 minutes. The antibacterial, antifungal, and antiviral activities were both durable and rechargeable. Additionally, trypan blue assay suggested that the new silver sulfadiazine–immobilized celluloses sustained excellent mammal cell viability, pointing to great potentials of the new materials for a broad range of health care–related applications.

Silk fibroin immobilization on poly(ethylene terephthalate) films: comparison of two surface modification methods and their effect on mesenchymal stem cells culture.

Silk fibroin (SF) has played a curial role for the surface modification of conventional materials to improve the biocompatibility, and SF modified poly(ethylene terephthalate) (PET) materials have potential applications on tissue engineering such as artificial ligament, artificial vessel, artificial heart valve sewing cuffs dacron and surgical mesh engineering. In this work, SF was immobilized onto PET film via two different methods: 1) plasma pretreatment followed by SF dip coating (PET-SF) and 2) plasma-induce acrylic acid graft polymerization and subsequent covalent immobilization of SF on PET film (PET-PAA-SF). It could be found that plasma treatment provided higher surface roughness which was suitable for further SF dip coating, while grafted poly(acrylic acid) (PAA) promised the covalent bonding between SF and PAA. ATR-FTIR adsorption band at 3284 cm(-1), 1623 cm(-1) and 1520 cm(-1) suggested the successful introduction of SF onto PET surface, while the amount of immobilized SF of PET-SF was higher than PET-PAA-SF according to XPS investigation (0.29 vs 0.23 for N/C ratio). Surface modified PET film was used as substrate for mesenchymal stem cells (MSCs) culture, the cells on PET-SF surface exhibited optimum density compared to PET-PAA-SF according to CCK-8 assays, which indicated that plasma pretreatment followed by SF dip coating was a simple and effective way to prepare biocompatible PET surface.

Soy protein-based polyethylenimine hydrogel and its high selectivity for copper ion removal in wastewater treatment

The pollution of water resources has become a worldwide concern because of the indiscriminate disposal of heavy metal ions and toxic organics in the past few decades. In this study, we use a sustainable, low cost, and abundant plant protein, soy protein isolate (SPI) as a matrix, polyethyleneimine (PEI) as a functional component to prepare the SPI/PEI composite hydrogels through a facile chemical crosslinking method. The results show that the SPI/PEI composite hydrogels can effectively adsorb Cu(II) ions from aqueous solution. In particular, the SPI/PEI composite hydrogel with a 50% PEI content demonstrates an excellent selectivity for the removal of Cu(II) ions when co-existing competitive heavy metal ions, including Zn(II), Cd(II), and Pb(II), especially the selectivity coefficient for Cu(II)/Zn(II), reaches about 250. Furthermore, the adsorbed Cu(II) ions in the composite hydrogel can be reduced easily in situ by NaBH4 to form uniformly dispersed copper nanoparticles (Cu NPs), which gives a Cu NP-loaded-SPI/PEI composite hydrogel. Such a material is found to be able to act as a catalyst to catalyse the model reaction, i.e., the reduction of 4-nitrophenol with a high efficiency. These results suggest that such a SPI-based hydrogel is a good candidate to selectively adsorb and recycle copper element for the waste disposal industry. In addition, we also provide a strategy to keep the natural resources sustainable, i.e., to select a natural and sustainable material (SPI) to protect the environment (wastewater treatment), and to recycle metals (copper and possibly others).

Tough protein-carbon nanotube hybrid fibers comparable to natural spider silks

Animal silks, especially spider dragline silks, have an excellent portfolio of mechanical properties, but it is still a challenge to obtain artificial silk fibers with similar properties to the natural ones. In this paper, we show how to extrude tough regenerated silk fibers by adding a small amount of commercially available functionalized multiwalled carbon nanotubes (less than 1%) through an environmentally friendly wet-spinning process reported by this laboratory previously. Most of the resulting regenerated silk fibers exhibited a breaking energy beyond 130 MJ m-3, which is comparable to spider dragline silks (∼160 MJ m-3). The best of these fibers in terms of performance show a breaking stress of 0.42 GPa, breaking strain of 59%, and breaking energy of 186 MJ m-3. In addition, we used several advanced characterization techniques, such as synchrotron radiation FTIR microspectroscopy and synchrotron radiation X-ray diffraction, to reveal the toughening mechanism in such a protein-inorganic hybrid system. We believe our attempt to produce such tough protein-based hybrid fibers by using cheap, abundant and sustainable regenerated silkworm protein and commercially available functionalized carbon nanotubes, with simplified industrial wet-spinning apparatus, may open up a practical way for the industrial production of super-tough fiber materials.

Preparation of 3D fibroin/chitosan blend porous scaffold for tissue engineering via a simplified method.

In this work, we developed a simple and flexible method to manufacture a 3D porous scaffold based on the blend of regenerated silk fibroin (RSF) and chitosan (CS). No crosslinker or other toxic reagents were used in this method. The pores of resulted 3D scaffolds were connected with each other, and their sizes could be easily controlled by the concentration of the mixed solution. Compared with pure RSF scaffolds, the water absorptivities of these RSF/CS blend scaffolds with significantly enhanced mechanical properties were greatly increased. The results of MTT and RT-PCR tests indicated that the chondrocytes grew very well in these blend RSF/CS porous scaffolds. This suggested that the RSF/CS blend scaffold prepared by this new method could be a promising candidate for applications in tissue engineering.