In-situ synthesis of gold nanoparticles for multifunctionalization of silk fabrics

A simple in-situ synthesis route for gold nanoparticles (NPs) was developed to realize multifunctions for silk fabrics. The gold NPs were prepared in a heated solution containing white silk fabric samples. The silk fabrics were colored red and brown by the gold NPs because of their localized surface plasmon resonance (LSPR) property. Gold nanospheres on silk were obtained at a low gold content, and gold nanoplates were synthesized as the gold content increased. The silk fabrics treated with gold NPs showed good light fastness. Moreover, the gold NPs endowed silk fabrics with strong antibacterial activity, excellent UV protection property and enhanced thermal conductivity. © 2013 Elsevier Ltd. All rights reserved.

Silk powder for regenerative medicine

Two approaches are used for silk particle production: bottom up and top down. In the bottom up approach, different liquid-solid phase transfer techniques are adapted to fabricate particles from silk solution. In the top down approach, silk fibres are milled by various means to prepare ultrafine silk particles. Many important properties of particles such as size, geometry, porosity, stability and biodegradability are dependent on the specific methods of particle production. These properties influence drug loading and release, delivery modes, biocompatibility and their clearance from the body. Particle properties also determine biomechanical properties of particle reinforced composite scaffolds. Thus correlation between preparation, characterisation and application of silk particles for a specific biomedical application is critical. Progress made in this direction and challenges ahead are discussed in this chapter. © 2014 Woodhead Publishing Limited. All rights reserved.

Intrinsic tensile properties of cocoon silk fibres can be estimated by removing flaws through repeated tensile tests

 ilk fibres from silkworm cocoons have lower strength than spider silk and have received less attention as a source of high-performance fibres. In this work, we have used an innovative procedure to eliminate the flaws gradually of a single fibre specimen by retesting the unbroken portion of the fibre, after each fracture test. This was done multiple times so that the final test may provide the intrinsic fibre strength. During each retest, the fibre specimen began to yield once the failure load of the preceding test was exceeded. For each fibre specimen, a composite curve was constructed from multiple tests. The composite curves and analysis show that strengths of mass-produced Muga and Eri cocoon silk fibres increased from 446 to 618 MPa and from 337 to 452 MPa, respectively. Similarly, their toughness increased from 84 to 136 MJ m(-3) and from 61 to 104 MJ m(-3), respectively. Composite plots produced significantly less inter-specimen variations compared to values from single tests. The fibres with reduced flaws as a result of retests in the tested section have a tensile strength and toughness comparable to naturally spun dragline spider silk with a reported strength of 574 MPa and toughness of 91-158 MJ m(-3), which is used as a benchmark for developing high-performance fibres. This retesting approach is likely to provide useful insights into discrete flaw distributions and intrinsic mechanical properties of other fatigue-resistant materials.

Wettability gradient-driven directional water transport across thin fibrous materials

Recently, novel properties have been observed when superhydrophobic and superhydrophilic surfaces are combined. For example, the Stenocara beetle, an insect in the Namib Desert, has an incredible ability to capture fresh water from air for its survival in the dry desert environment [1]. Such a feature derives from its special wing that has a hydrophilic-patterned superhydrophobic surface. Materials having a similar surface feature also exhibited a similar water-harvesting function [2]. A spider silk has been reported to show a periodic alternation of hydrophobic and hydrophilic surfaces along the fiberlength direction [3], which can quickly collect water from air. It was also observed that water droplets moved in one direction along a superhydrophobic-to-superhydrophilic gradient surface [4]. However, all these works are based on two dimension surfaces. The work on water transfer through porous media induced by a gradient wettability change has received little attention until very recently [5]. In this study, we have developed a simple, but very effective and versatile, method to produce wettability gradient across the thickness of fabrics, and demonstrated that the fabrics have the ability to spontaneously transfer water unidirectionally through the fibrous architecture. A plain weave polyester fabric was mainly used as a sample material.

Bioinspired strategy to reinforce PVA with improved toughness and thermal properties via hydrogen-bond self-assembly

Despite the high strength and stiffness of polymer nanocomposites, they usually display lower deformability and toughness relative to their matrices. Spider silk features exceptionally high stiffness and toughness via the hierarchical architecture based on hydrogen-bond (H-bond) assembly. Inspired by this intriguing phenomenon, we here exploit melamine (MA) to reinforce poly(vinyl alcohol) (PVA) via H-bond self-assembly at a molecular level. Our results have shown that due to the formation of physical cross-link network based on H-bond assembly between MA and PVA, yield strength, Young’s modulus, extensibility, and toughness of PVA are improved by 22, 25, 144, and 200% with 1.0 wt % MA, respectively. Moreover, presence of MA can enhance the thermal stability of PVA to a great extent, even exceeding some nanofillers (e.g., graphene). This work provides a facile method to improve the mechanical properties of polymers via H-bond self-assembly.

Bio-inspired hydrogen-bond cross-link strategy toward strong and tough polymeric materials

It remains a huge challenge to create advanced polymeric materials combining high strength, great toughness, and biodegradability so far. Despite enhanced strength and stiffness, biomimetic materials and polymer nanocomposites suffer notably reduced extensibility and toughness when compared to polymer bulk. Silk displays superior strength and toughness via hydrogen bonds (H-bonds) assembly, while cuticles of mussels gain high hardness and toughness via metal complexation cross-linking. Here, we propose a H-bonds cross-linking strategy that can simultaneously strikingly enhance strength, modulus, toughness, and hardness relative to polymer bulk. The H-bond cross-linked poly(vinyl alcohol) exhibits high yield strength (140 MPa), reduced modulus (22.5 GPa) in nanoindention tests, hardness (0.5 GPa), and great extensibility (40%). More importantly, there exist semiquantitive linear relationships between the number of effective H-bond and macroscale properties. This work suggests a promising methodology of designing advanced materials with exceptional mechanical by adding low amounts (1.0 wt %) of small molecules multiamines serving as H-bond cross-linkers.

Improvement of coating durability, interfacial adhesion and compressive strength of UHMWPE fiber/epoxy composites through plasma pre-treatment and polypyrrole coating

Ultra-high-molecular-weight polyethylene (UHMWPE) fibers have exceptionally higher specific strength and stiffness compared with other high-performance fibers. However, the interfacial adhesion and compressive performance of UHMWPE fiber-reinforced polymer composites (FPCs) are extremely low. The challenges are to achieve load transfer at the interface between the fiber and matrix at a molecular level. Here, we show that plasma pre-treatment of UHMWPE fibers followed by coating with polypyrrole (PPy) results in an 848% improvement in the interfacial adhesion and 54% enhancement in compressive performance. This method takes advantage of a toughening mechanism observed in spider silk and collagen, which the hydrogen bond power the load transfer. The results showed that these improvements of interfacial adhesion and compressive strength were attributed to hydrogen-bonding interactions between the plasma pre-treated UHMWPE and PPy, which improves the fiber-matrix-fiber load transfer process. In addition, the hydrogen-bonded PPy coatings also endowed durability electrical conductivity properties of the UHMWPE fiber.

Eri silk fibre attributes and sliver preparation

Eri silk produced by Philosamia cynthia ricini silkworm is a fibre not well-known to the silk industry, in spite of the fact that Eri silk is finer, softer, and has better mechanical and thermal properties than most animal fibres. Eri silk has a high commercial potential, as the host plants of Eri silk worms are widespread in diverse geographical locations, and the worms also have a higher degree of disease resistance than most other silk worms. Mills are often not aware of the properties of Eri for designing appropriate end products. Thus, Eri silk yarn is traditionally produced by hand spinning, and Eri silk usually ends up as material for handwoven shawls. The potential for bulk fibre processing and the development of soft luxurious novel Eri silk products is yet to be discovered. To better understand the material and its processing behaviour, Eri silk was characterised and cocoons were processed into tops through degumming, opening, and cutting filaments into different lengths, followed by a worsted spun silk processing route. Fibre properties such as fineness, crimp, strength and length at different processing stages up to combed tops were measured. The results indicate that staple Eri silk can be processed via the worsted topmaking route, using a cut length of 200 mm or 150 mm for filament sheets prepared from degummed cocoons.

Silk Road project

Choreographer Kim Vincs and Scenographer Matthew Delbridge worked with dancer, Carlee Mellow, musicians Rob Vincs, Scott Dunbabin and Eugene Ughetti to create a virtual visual performance where performer's movement was rendered using a motion capture system and projected onto translucent screens.

Maternity waiting homes in Southern Lao PDR : the unique 'silk home'

The concept of maternity waiting homes (MWH) has a long history spanning over 100 years. The research reported here was conducted in the Thateng District of Sekong Province in southern Lao People’s Democratic Republic (PDR) to establish whether the MWH concept would be affordable, accessible, and most importantly acceptable, as a strategy to improve maternal outcomes in the remote communities of Thateng with a high proportion of the population from ethnic minority groups. The research suggested that there were major barriers to minority ethnic groups using existing maternal health services (reflected in very low usage of trained birth attendants and hospitals and clinics) in Thateng. Unless MWH are adapted to overcome these potential barriers, such initiatives will suffer the same fate as existing maternal facilities. Consequently, the Lao iteration of the concept, as operationalized in the Silk Homes project in southern Lao PDR is unique in combining maternal and infant health services with opportunities for micro credit and income generating activities and allowing non-harmful traditional practices to co-exist alongside modern medical protocols. These innovative approaches to the MWH concept address the major economic, social and cultural barriers to usage of safe birthing options in remote communities of southern Lao PDR.

Fabrication of ultrafine powder from eri silk through attritor and jet milling

Fibroin protein derived from silk fibres has been extensively studied with exciting outcomes for a number of potential advanced biomaterial applications. However, one of the major challenges in applications lies in engineering fibroin into a  desired form using a convenient production technology. In this paper, fabrication of ultrafine powder from eri silk is reported. The silk cocoons were degummed and the extracted silk fibres were then chopped into snippets prior to attritor and air jet milling. Effects of process control agents, material load and material to water ratio during attritor milling were studied. Compared to dry and dry–wet attritor milling, wet process emerged as the preferred option as it caused less colour change and facilitated easy handling. Ultrafine silk powder with a volume based particle size d(0.5) of around 700 nm could be prepared following the sequence of chopping ➔ wet attritor milling ➔ spray drying ➔ air jet milling. Unlike most reported powder production methods, this method could fabricate silk particles in a short time without any pre-treatment on degummed fibre. Moreover, the size range obtained is much smaller than that previously produced using standard milling devices. Reduction in fibre tenacity either shortened the milling time even further or helped bypassing media milling to produce fine powder directly through jet milling. However, such reduction in fibre strength did not help in increasing the ultimate particle fineness. The study also revealed that particle density and particle morphology could be manipulated through appropriate changes in the degumming process.

Graphical Abstract:  Fabrication of eri silk powder using attritor and jet milling is reported. Volume based particle size d(0.5) of around 700 nm could be prepared following the sequence chopping ➔ wet attritor milling ➔ spray drying ➔ air jet milling. No pre-treatments were used and the particle size range obtained is much smaller than that previously produced using standard milling devices. Particle density morphology could be manipulated through appropriate changes of cocoon degumming conditions.

Grafts in myringoplasty : utilizing a silk fibroin scaffold as a novel device

Chronic perforations of the eardrum or tympanic membrane represent a significant source of morbidity worldwide. Myringoplasty is the operative repair of a perforated tympanic membrane and is a procedure commonly performed by otolaryngologists. Its purpose is to close the tympanic membrane, improve hearing and limit patient susceptibility to middle ear infections. The success rates of the different surgical techniques used to perform a myringoplasty, and the optimal graft materials to achieve complete closure and restore hearing, vary significantly in the literature. A number of autologous tissues, homografts and synthetic materials are described as graft options. With the advent and development of tissue engineering in the last decade, a number of biomaterials have been studied and attempts have been made to mimic biological functions with these materials. Fibroin, a core structural protein in silk from silkworms, has been widely studied with biomedical applications in mind. Several cell types, including keratinocytes, have grown on silk biomaterials, and scaffolds manufactured from silk have successfully been used in wound healing and for tissue engineering purposes. This review focuses on the current available grafts for myringoplasty and their limitations, and examines the biomechanical properties of silk, assessing the potential benefits of a silk fibroin scaffold as a novel device for use as a graft in myringoplasty surgery.

Fabricating and characterising silk powder for biomedical and sorption applications

This research developed a milling technology for ultrafine silk particles and designed novel biocompatible and biodegradable silk composites for repairing hard tissue defects. It also demonstrated high and rapid reversible ion binding properties of silk particles and thereby opened up their application opportunities as advanced green sorbents.