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Author(s): Christopher M. Elvin (corresponding author) [1]; Andrew G. Carr [1]; Mickey G. Huson [2]; Jane M. Maxwell [2]; Roger D. Pearson [1]; Tony Vuocolo [1]; Nancy E. Liyou [1]; [...]

Carbon fibre composites are lightweight, high performance materials with outstanding mechanical properties. However, the use of carbon fibre is limited to high-end applications largely due to their high manufacturing cost. A significant portion of the cost results from the energy input required to convert the precursor into carbon fibre. Stabilization is the first critical step whereby the fibre undergoes a series of thermal treatments creating a stabilized fibre ready for carbonization. In this study, we demonstrate the use of ionic liquids as polyacrylonitrile fibre impregnation agents, resulting in substantially lower fibre stabilization temperatures and thus significant energy savings. The use of infrared, calorimetric, and thermogravimetric studies indicated that the beneficial effect of ionic liquids is due to higher stabilization chemical reaction rates. [ABSTRACT FROM AUTHOR]

We demonstrate the utilisation of an azomethine 1,3-dipolar cycloaddition reaction with carbon fibre to graft complex molecules onto the fibre surface. In an effort to enhance the interfacial interaction of the fibre to the matrix, the functionalised fibres possessed a pendant amine that is able to interact with epoxy resins. Functionalisation was supported by X-ray photoelectron spectroscopy and the grafting process had no detrimental effects on tensile strength compared with the control (untreated) fibres. Also, microscopic roughness (as determined by atomic force microscopy) and fibre topography were unchanged after the described treatment process. This methodology complements existing methodology aimed at enhancing the surface of carbon fibres for advanced material applications while not compromising the desirable strength profile. Single-fibre fragmentation tests show a statistically significant decrease in fragment length compared with the control fibres in addition to transverse cracking within the curing resin, both of which indicate an enhanced interaction between fibre and resin. [ABSTRACT FROM AUTHOR]

Collagen is ubiquitous throughout the animal kingdom, where it comprises some 28 diverse molecules that form the extracellular matrix within organisms. In the 1960s, an extracorporeal animal collagen that forms the cocoon of a small group of hymenopteran insects was postulated. Here we categorically demonstrate that the larvae of a sawfly species produce silk from three small collagen proteins. The native proteins do not contain hydroxyproline, a post translational modification normally considered characteristic of animal collagens. The function of the proteins as silks explains their unusual collagen features. Recombinant proteins could be produced in standard bacterial expression systems and assembled into stable collagen molecules, opening the door to manufacture a new class of artificial collagen materials. [ABSTRACT FROM AUTHOR]

Honeybee larvae produce silken cocoons that provide mechanical stability to the hive. The silk proteins are small and nonrepetitive and therefore can be produced at large scale by fermentation in E. coli. The recombinant proteins can be fabricated into a range of forms; however the resultant material is soluble in water and requires a post production stabilizing treatment. In this study, we describe the structural and mechanical properties of sponges fabricated from artificial honeybee silk proteins that have been stabilized in aqueous methanol baths or by dry heating. Aqueous methanol treatment induces formation of ß-sheets, with the amount of ß-sheet dictated by methanol concentration. Formation of ßsheets renders sponges insoluble in water and generates a reversibly compressible material. Dry heat treatments at 190°C produce a water insoluble material, that is stiffer than the methanol treated equivalent but without significant secondary structural changes. Honeybee silk proteins are particularly high in Lys, Ser, Thr, Glu and Asp. The properties of the heat treated material are attributed to generation of lysinoalanine, amide (isopeptide) and/or ester covalent cross-links. The unique ability to stabilize material by controlling secondary structure rearrangement and covalent cross-linking allows us to design recombinant silk materials with a wide range of properties. [ABSTRACT FROM AUTHOR]

Honeybee silk is composed of four fibrous proteins that, unlike other silks, are readily synthesized at full-length and high yield. The four silk genes have been conserved for over 150 million years in all investigated bee, ant and hornet species, implying a distinct functional role for each protein. However, the amino acid composition and molecular architecture of the proteins are similar, suggesting functional redundancy. In this study we compare materials generated from a single honeybee silk protein to materials containing all four recombinant proteins or to natural honeybee silk. We analyse solution conformation by dynamic light scattering and circular dichroism, solid state structure by Fourier Transform Infrared spectroscopy and Raman spectroscopy, and fiber tensile properties by stress-strain analysis. The results demonstrate that fibers artificially generated from a single recombinant silk protein can reproduce the structural and mechanical properties of the natural silk. The importance of the four protein complex found in natural silk may lie in biological silk storage or hierarchical self-assembly. The finding that the functional properties of the mature material can be achieved with a single protein greatly simplifies the route to production for artificial honeybee silk. [ABSTRACT FROM AUTHOR]

This work investigates the mechanisms involved in the improvement of flexural properties of a jute/polyester composite when the reinforcement material has been atmospherically plasma treated using helium gas. All composites were laid-up by hand and cured using a Quickstep™ cure cycle. Surface characterization techniques including scanning probe microscopy (SPM), and surface wettability combined with fabric tensile strength, composite flexural strength and composite Mode-I properties have been used to quantify the effects of plasma modification. Flexural strength and modulus increased with plasma treatment time, reaching a maximum at 25 passes before decreasing. SPM topographical analysis showed that roughness of the fibre decreased as the plasma treatment time increased until 25 passes after which the roughness was found to increase again. The coefficient of friction increased rapidly after only a short plasma treatment time (5 passes) whilst wettability continued to increase until 25 passes after which it remained constant. The fabric tensile strength followed the same trend as the flexural properties of the composites. Decreasing fibre surface roughness is postulated as a reason for decreasing Mode-I interlaminar fracture toughness properties of the composites. [ABSTRACT FROM AUTHOR]

Recombinant proteins are polymers that offer the materials engineer absolute control over chain length and composition: key attributes required for design of advanced polymeric materials. Through this control, these polymers can be encoded to contain information that enables them to respond as the environment changes. However, despite their promise, protein-based materials are under-represented in materials science. In this chapter we investigate why this is and describe recent efforts to address this. We discuss constraints limiting rational design of structural proteins for advanced materials; advantages and disadvantages of different recombinant expression platforms; and, methods to fabricate proteins into solid-state materials. Finally, we describe the silk proteins used in our laboratory as templates for information-containing polymers.

The effects of moisture and thermal denaturation on the solid-state structure and molecular mobility of soy glycinin powder were investigated using multiple techniques that probe over a range of length and time scales. In native glycinin, increased moisture resulted in a decrease in both the glass transition temperature and the denaturation temperature. The sensitivity of the glass transition temperature to moisture is shown to follow the Gordon-Taylor equation, while the sensitivity of the denaturation temperature to moisture is modeled using Flory's melting point depression theory. While denaturation resulted in a loss of long-range order, the principal conformational structures as detected by infrared are maintained. The temperature range over which the glass to rubber transition occurred was extended on the high temperature side, leading to an increase in the midpoint glass transition temperature and suggesting that the amorphous regions of the newly disordered protein are less mobile. (13)C NMR results supported this hypothesis.

Two novel recombinant proteins An16 and Dros16 have recently been generated. These recombinant proteins contain, respectively, sixteen copies of an 11 amino acid repetitive domain (AQTPSSQYGAP) observed in a resilin-like gene from Anopheles gambiae and sixteen copies of a 15 amino acid repetitive domain (GGRPSDSYGAPGGGN) observed in the first exon of the Drosophila melanogaster CG15920 gene. We compare structural characteristics of the proteins and material properties of resulting biopolymers relative to Rec1-resilin, a previously characterized resilin-like protein encoded by the first exon of the Drosophila melanogaster CG15920 gene. While the repetitive domains of natural resilins display significant variation both in terms of amino acid sequence and length, our synthetic polypeptides have been designed as perfect repeats. Using techniques including circular dichroism, atomic force microscopy, and tensile testing, we demonstrate that both An16 and Dros16 have similar material properties to those previously observed in insect and recombinant resilins. Modulus, elasticity, resilience, and dityrosine content in the cross-linked biomaterials were assessed. Despite the reduced complexity of the An16 and Dros16 proteins compared to natural resilins, we have been able to produce elastic and resilient biomaterials with similar properties to resilin.

Concerns for the environment and consumer demand are driving research into environmentally friendly fibers as replacements for part of the 38 million tonnes of synthetic fiber produced annually. While much current research focuses on cellulosic fibers, we highlight that protein fibers regenerated from waste or byproduct sources should also be considered. Feather keratin and wheat gluten may both be suitable. They are annually renewable, commercially abundant, of consistent quality, and have guaranteed supply. They contain useful amino acids for fiber making, with interchain cross-linking possible via cysteine residues or through the metal-catalyzed photocrosslinking of tyrosine residues. Previous commercially produced fibers suffered from poor wet strength. Contemporary nanoparticle and cross-linking technology has the potential to overcome this, allowing commercial production to resume. This would bring together two existing large production and processing pipelines, agricultural protein production and textile processing, to divert potential waste streams into useful products.

When provoked, Notaden bennetti frogs secrete an exudate which rapidly forms a tacky elastic solid ("frog glue"). This protein-based material acts as a promiscuous pressure-sensitive adhesive that functions even in wet conditions. We conducted macroscopic tests in air to assess the tensile strength of moist glue (up to 78 +/- 8 kPa) and the shear strength of dry glue (1.7 +/- 0.3 MPa). We also performed nanomechanical measurements in water to determine the adhesion (1.9-7.2 nN or greater), resilience (43-56%), and elastic modulus (170-1035 kPa) of solid glue collected in different ways. Dry glue contains little carbohydrate and consists mainly of protein. The protein complement is rich in Gly (15.8 mol %), Pro (8.8 mol %), and Glu/Gln (14.1 mol %); it also contains some 4-hydroxyproline (4.6 mol %) but no 5-hydroxylysine or 3,4-dihydroxyphenylalanine (L-Dopa). Denaturing gel electrophoresis of the glue reveals a characteristic pattern of proteins spanning 13-400 kDa. The largest protein (Nb-1R, apparent molecular mass 350-500 kDa) is also the most abundant, and this protein appears to be the key structural component. The solid glue can be dissolved in dilute acids; raising the ionic strength causes the glue components to self-assemble spontaneously into a solid which resembles the starting material. We describe scattering studies on dissolved and solid glue and provide microscopy images of glue surfaces and sections, revealing a porous interior that is consistent with the high water content (85-90 wt %) of moist glue. In addition to compositional similarities with other biological adhesives and well-known elastomeric proteins, the circular dichroism spectrum of dissolved glue is almost identical to that for soluble elastin and electron and scanning probe microscopy images invite comparison with silk fibroins. Covalent cross-linking does not seem to be necessary for the glue to set.