Effect of Bombyx mori silk-fiber volume on flexural strength of fiber-reinforced composite

Dental glass fiber is one of dental synthetic fibers that are widely used in dentistry as a dental resin reinforcement, such as in dentin replacement material. The availability of glass fiber is limited in Indonesia because it must be imported and relatively expensive. Bombyx mori silk-fiber is one of the strongest natural fiber derived from silkworm cocoon processing. Silk-fiber is used in medical applications as a post-surgical sutures, scaffolds for tissue engineering and drug delivery. The purpose of this study was to evaluate the effect of Bombyx mori silk-fiber volume on the flexural strength of fiber-reinforced composite (FRC). We used Bombyx mori silk-fiber (Perhutani Pati, Central Java, Indonesia) and flowable composite (Charmfil flow, Denkist, Korea) in this study. The FRC samples were divided into 4 groups consisting of fiber volumes of 0%, 5%, 10% and 15% (n = 4). Tests of flexural strength were performed according to ISO 4049. The results were analyzed using one way ANOVA (p<0.05). The study showed that the means of the flexural strength (MPa) of Bombyx mori silk-fiber FRC for volume of 0%, 5%, 10% and 15% were 149.2 ± 5.5; 127.6 ± 3.8; 110.9 ± 3.5; 71.2 ± 4.2. One-way ANOVA test showed that the means of FRC flexural strength on the four groups’ silk-fiber Bombyx mori volumetric were significantly different (p<0.05). This study concluded that Bombyx mori silk-fiber volumetric influences the flexural strength of fiber- reinforced composite. An increase in Bombyx mori silk-fiber volume decreases the flexural strength of FRC because there is a small gap due to the weak interfacial bonds between dental flowable composite and Bombyx mori silk-silk-fiber

Preparation of hexagonal GeO2 particles with particle size and crystallinity controlled by peptides, silk and silk-peptide chimeras

We demonstrate the use of silk based proteins to control the particle/crystallite size during GeO2 formation, using a bio-mimetic approach at circumneutral pH and ambient temperature. Multicrystalline GeO2 was prepared from germanium tetraethoxide (TEOG) in the presence of different silk-based proteins: Bombyx mori silk (native silk) and two chimeric proteins prepared by linking a germania binding peptide (Ge28: HATGTHGLSLSH) with Bombyx mori silk via chemical coupling at different peptide loadings (silk-Ge28 10% and silk-Ge28 50%). The mineralisation activity of the silk-based proteins was compared with that of peptide Ge28 as a control system. GeO2 mineralisation was investigated in water and in citric acid/bis-tris propane buffer at pH 6. Morphology, particle size, crystallinity, water and organic content of the materials obtained were analysed to study the effect of added biomolecules and mineralisation environment on material properties. In the presence of silk additives well-defined cube-shape hybrid materials composed of hexagonal germania and up to ca. 5 wt% organic content were obtained. The cubic particles ranged from 0.4 to 1.4m in size and were composed of crystalline domains in the range 35-106 nm depending on the additive used and synthesis conditions

Microrheological Studies of Regenerated Silk Fibroin Solution by Video Microscopy

We have carried out studies on the rheological properties of regenerated silk fibroin (RSF) solution using video microscopy. The degummed silk from the Bombyx mori silkworm was used to prepare RSF solution by dissolving it in calcium nitrate tetrahydrate-methanol solvent. Measurements were carried out by tracking the position of an embedded micron-sized polystyrene bead within the RSF solution through video imaging. The time dependent mean squared displacement (MSD) of the bead in solution and hence, the complex shear modulus of this solution was calculated from the bead's position information. An optical tweezer was used to transport and locate the bead at any desired site within the micro-volume of the sample, to facilitate the subsequent free-bead video analysis. We present here the results of rheological measurements of the silk polymer network in solution over a frequency range, whose upper limit is the frame capture rate of our camera, at full resolution. By examining the distribution of MSD of beads at different locations within the sample volume, we demonstrate that this probe technique enables us to detect local inhomogeneties at micrometer length scales, not detectable either by a rheometer or from diffusing wave spectroscopy.Comment: 5 page

Vibrational Study on the Structure, Bioactivity, and Silver Adsorption of Silk Fibroin Fibers Grafted with Methacrylonitrile

Natural fibers have received increasing attention as starting materials for innovative applications in many research fields, from biomedicine to engineering. Bombyx mori silk fibroin has become a material of choice in the development of many biomedical devices. Grafting represents a good strategy to improve the material properties according to the desired function. In the present study, Bombyx mori silk fibroin fibers were grafted with methacrylonitrile (MAN) with different weight gains. The potential interest in biomedical applications of MAN functionalization relies on the presence of the nitrile group, which is an acceptor of H bonds and can bind metals. IR and Raman spectroscopy were used to characterize the grafted samples and the possible structural changes induced by grafting. Afterward, the same techniques were used to study the bioactivity (i.e., the calcium phosphate nucleation ability) of MAN-grafted silk fibroins after ageing in simulated body fluid (SBF) for possible application in bone tissue engineering, and their interaction with Ag+ ions, for the development of biomaterials with enhanced anti-microbial properties. MAN was found to efficiently polymerize on silk fibroin through polar amino acids (i.e., serine and tryptophan), inducing an enrichment in silk fibroin-ordered domains. IR spectroscopy allowed us to detect the nucleation of a thin calcium phosphate layer and the uptake of Ag+ ions through the nitrile group, which may foster the application of these grafted materials in biomedical applications

Nuclear Magnetic Resonance (NMR) Spectroscopic Characterization of Nanomaterials and Biopolymers

abstract: Nanomaterials have attracted considerable attention in recent research due to their wide applications in various fields such as material science, physical science, electrical engineering, and biomedical engineering. Researchers have developed many methods for synthesizing different types of nanostructures and have further applied them in various applications. However, in many cases, a molecular level understanding of nanoparticles and their associated surface chemistry is lacking investigation. Understanding the surface chemistry of nanomaterials is of great significance for obtaining a better understanding of the properties and functions of the nanomaterials. Nuclear magnetic resonance (NMR) spectroscopy can provide a familiar means of looking at the molecular structure of molecules bound to surfaces of nanomaterials as well as a method to determine the size of nanoparticles in solution. Here, a combination of NMR spectroscopic techniques including one- and two-dimensional NMR spectroscopies was used to investigate the surface chemistry and physical properties of some common nanomaterials, including for example, thiol-protected gold nanostructures and biomolecule-capped silica nanoparticles. Silk is a natural protein fiber that features unique properties such as excellent mechanical properties, biocompatibility, and non-linear optical properties. These appealing physical properties originate from the silk structure, and therefore, the structural analysis of silk is of great importance for revealing the mystery of these impressive properties and developing novel silk-based biomaterials as well. Here, solid-state NMR spectroscopy was used to elucidate the secondary structure of silk proteins in N. clavipes spider dragline silk and B. mori silkworm silk. It is found that the Gly-Gly-X (X=Leu, Tyr, Gln) motif in spider dragline silk is not in a β-sheet or α-helix structure and is very likely to be present in a disordered structure with evidence for 31-helix confirmation. In addition, the conformations of the Ala, Ser, and Tyr residues in silk fibroin of B. mori were investigated and it indicates that the Ala, Ser, and Tyr residues are all present in disordered structures in silk I (before spinning), while show different conformations in silk II (after spinning). Specifically, in silk II, the Ala and Tyr residues are present in both disordered structures and β-sheet structures, and the Ser residues are present primarily in β-sheet structures.Dissertation/ThesisDoctoral Dissertation Chemistry 201

THERMAL & MECHANICAL ANALYSIS OF BOMBYX MORI SILK NANOFIBERS

This thesis presents a study on the thermomechanical properties of Bombyx Mori silk nanofibers. These nanofibers were obtained from silkworm cocoons which were degummed to separate the fibroin and the sericin, the two proteins that make up silk. The fibroin was then centrifuged to remove insoluble particles and stored and 4°C before the electrospinning process. A parametric study of the electrospinning process was carried out in order to identify the factors allowing to obtain optimal mechanical properties. The current as well as the flow rate applied, the diameter of the syringe, the distance separating the syringe from collector or even the environmental conditions and the concentration of the solution are all parameters influencing the specific characteristics of the nanofibers obtained, in particular their diameter, their distribution and their orientation. A range of concentrated solutions from 1% to 6% silk fibroin were prepared with Hexafluoroisopropanol (HFIP) as a solvent. These solutions were electrospun using process parameters which corresponded to the best conditions for electrospinning. The morphologies of these nanofibers were characterized by scanning electron microscopy (SEM). Their mechanical properties have also been evaluated using the lab nanomechanics testing system specially designed for single fiber tensile testing enabling to link the influence of electrospinning parameters to the final properties of silk nanofibers. The thermal properties of the degummed silk fibroin were also investigated using differential scanning calorimetry (DSC) which allowed to determine the specific phase transitions and crystallinity of degummed silk fibroin and silk nanofibers. Moreover, Raman spectroscopy has been performed to characterize the molecular composition and the external structure of degummed silk and silk nanofibers. Advisor: Yuris Dzeni

Emergence of supercontraction in regenerated silkworm (Bombyx mori) silk fibers

The conditions required for the emergence of supercontraction in regenerated silkworm (Bombyx mori) silk fibers are assessed through an experimental approach that combines the spinning of regenerated fibers with controlled properties and their characterization by 13C solid-state nuclear magnetic resonance (NMR). Both supercontracting and non-supercontracting regenerated fibers are produced using the straining flow spinning (SFS) technique from 13C labeled cocoons. The short-range microstructure of the fibers is assessed through 13C CP/MAS in air and 13C DD/MAS in water, and the main microstructural features are identified and quantified. The mechanical properties of the regenerated fibers and their microstructures are compared with those of natural silkworm silk. The combined analysis highlights two possible key elements as responsible for the emergence of supercontraction: (1) the existence of an upper and a lower limit of the amorphous phase compatible with supercontraction, and (2) the existence of two ordered phases, β-sheet A and B, which correspond to different packing arrangements of the protein chains.Ministerio de Economía y Competitividad MAT2016-75544- C2-1-RMinisterio de Economía y Competitividad MAT2016-79832-RMinisterio de Economía y Competitividad DPI2016-78887-C3-1-RConsejería de Educación Comunidad de Madrid NEUROCENTRO-B2017/BMD-3760Ministerio de Educación, Ciencia y Cultura JP26248050Ministerio de Economía y Competitividad DPI2016-78887-C3-1-

The interfacial behavior of Bombyx mori silk fibroin.

A new crystal structure has been observed for Bombyx mori silk fibroin at air-water interfaces. This structure, silk III, incorporates a left-handed three-fold polyglycine II conformation and an approximately hexagonal lattice. Detailed crystallographic studies using electron diffraction data have been used to characterize the silk III crystal structure. There is a hexapeptide repetitive sequence found in the crystallizable portions of silk fibroin. When this sequence, Gly-Ala-Gly-Ala-Gly-Ser, is in a threefold helical conformation, a row of alternating glycine and serine residues parallel to the helical axis results. One third of the helix thus becomes slightly hydrophilic, whereas the other two thirds consist of glycine and hydrophobic alanine residues. The data indicate that the helices are arranged so that the serine residues pack preferentially in serine-rich sheets in the (110) planes of the crystal. The result is a monoclinic crystal structure, where the basal plane angle $\gamma$ is 116\sp\circ rather than the 120\sp\circ expected for perfect hexagonal packing, due to the distortion in nearest neighbor interhelical packing distances that results when the serine residues have a preferred packing. The separation of hydrophobic and hydrophilic residues in a threefold helical conformation of fibroin suggests that the air-water interface may stabilize the threefold conformation because this conformation allows the fibroin to behave as a surfactant at the interface. The sheet-like arrangement of serine residues deduced for the monoclinic silk III crystallites also supports a role for surfactancy in stabilizing the silk III structure at the air-water interface. If the crystallizable portions of fibroin are behaving as a surfactant, then the three-fold helical silk III structure should be oriented with the axes of the three-fold fibroin helices in the plane of the interface. This orientation is observed in uncompressed fibroin films which were picked up onto TEM grids. In LB films compressed to 16.7 mN/meter on the trough prior to being picked up onto TEM grids a uniaxial orientation is observed for silk III, with the helical axes perpendicular to the plane of the sample film. A surface compression of 34 mN/meter results in films containing silk II crystallites with the same uniaxial orientation, placing the helical axes perpendicular to the plane of the film. In addition to air-water interface experiments several experiments were carried out using aqueous-organic interfaces. A hydrated crystal structure incorporating a left-handed 6/2 helix which is still roughly three-fold, is observed at the water-hexane and water-chloroform interfaces. Large lamellar crystallites possessing a hexagonal habit were observed at both of these interfaces. A banded cholesteric mesophase which in some regions crystallizes into the same silk III hydrate structure as the lamellae was also observed and characterized

Effect of water on Bombyx mori regenerated silk fibers and its application in modifying their mechanical properties

The effect of water on regenerated silkworm silk fibers has been studied and compared with that of water on natural silkworm silk fibers. Regenerated fibers are spun from an N-methylmorpholine-N-oxide (NMMO) fibroin solution through a wet-spinning process, leading to fibers with two distinct tensile behaviors, labeled as brittle and ductile, respectively. Regenerated fibers show a significant contraction when immersed in water. Contraction increases further after drying. In contrast, natural silkworm silk fibers show a negligible contraction when submerged in water. Regenerated fibers tested in water are considerably more compliant than samples tested in air, though their stiffness and tensile strength are significantly reduced. It has been shown that the tensile properties of brittle regenerated fibers can be modified by a wet-stretching process, which consists of deforming the fiber while immersed in water. Regenerated wet-stretched fibers always show a ductile behavior independent from their initial tensile behavior

Silk-fibronectin protein alloy fibres support cell adhesion and viability as a high strength, matrix fibre analogue

Silk is a natural polymer with broad utility in biomedical applications because it exhibits general biocompatibility and high tensile material properties. While mechanical integrity is important for most biomaterial applications, proper function and integration also requires biomaterial incorporation into complex surrounding tissues for many physiologically relevant processes such as wound healing. In this study, we spin silk fibroin into a protein alloy fibre with whole fibronectin using wet spinning approaches in order to synergize their respective strength and cell interaction capabilities. Results demonstrate that silk fibroin alone is a poor adhesive surface for fibroblasts, endothelial cells, and vascular smooth muscle cells in the absence of serum. However, significantly improved cell attachment is observed to silk-fibronectin alloy fibres without serum present while not compromising the fibres' mechanical integrity. Additionally, cell viability is improved up to six fold on alloy fibres when serum is present while migration and spreading generally increase as well. These findings demonstrate the utility of composite protein alloys as inexpensive and effective means to create durable, biologically active biomaterials.T32 EB006359 - NIBIB NIH HH