Tom Gheysens

Regenerative potential of silk conduits in repair of peripheral nerve injury in adult rats

Various attempts have been made to develop artificial conduits for nerve repair, but with limited success. We describe here conduits made from Bombyx mori regenerated silk protein, and containing luminal fibres of Spidrex(®), a silk-based biomaterial with properties similar to those of spider silk. Assessment in vitro demonstrated that Spidrex(®) fibres support neurite outgrowth. For evaluation in vivo, silk conduits 10 mm in length and containing 0, 100, 200 or 300 luminal Spidrex(®) fibres, were implanted to bridge an 8 mm gap in the rat sciatic nerve. At 4 weeks, conduits containing 200 luminal Spidrex(®) fibres (PN200) supported 62% and 59% as much axon growth as autologous nerve graft controls at mid-conduit and distal nerve respectively. Furthermore, Spidrex(®) conduits displayed similar Schwann cell support and macrophage response to controls. At 12 weeks, animals implanted with PN200 conduits showed similar numbers of myelinated axons (81%) to controls, similar gastrocnemius muscle innervation, and similar hindpaw stance assessed by Catwalk footprint analysis. Plantar skin innervation was 73% of that of controls. PN200 Spidrex(®) conduits were also effective at bridging longer (11 and 13 mm) gaps. Our results show that Spidrex(®) conduits promote excellent axonal regeneration and function recovery, and may have potential for clinical application.

Silkworm and spider silk scaffolds for chondrocyte support.

Objective To create scaffolds with silkworm cocoon, spider egg sac and spider dragline silk fibres and examine their use for chondrocyte attachment and support. Methods Three different kinds of scaffolds were developed with Bombyx mori cocoon, Araneus diadematus egg sac and dragline silk fibres. The attachment of human articular cartilage cells were investigated on these bioprotein matrices. The chondrocytes produced an extracellular matrix which was studied by immunostaining. Moreover, the compression behaviour in relation to the porosity was studied. Results The compression modulus of a silkworm silk scaffold was related to its porosity. Chondrocytes were able to attach and to grow on the different fibres and in the scaffolds for several weeks while producing extracellular matrix products. Conclusion Porous scaffolds can be made out of silkworm and spider silk for cartilage regeneration. Mechanical properties are related to porosity and pore size of the construct. Cell spreading and cell expression depended on the porosity and pore-size.

Modulation of cell growth on exposure to silkworm and spider silk fibers

Recent years have seen an increased interest in the use of natural and modified silks for tissue engineering. Despite longstanding concerns regarding the biocompatibility of silk sutures, only a few studies have been carried out to investigate the biocompatibility of natural silk fibers. Here, we report an in vitro assessment of the effect of nonmodified, degummed silks on cells. We describe the effects of degummed silk fibers as well as extracted sericin on cell metabolism and proliferation. Endothelial cells directly exposed to native degummed Bombyx mori and Antheraea pernyi silks showed lower rates of proliferation and metabolism than nonexposed cells. A similar but milder effect was observed for cells in direct contact with Nephila edulis egg sack fibers. Sericin and silk-conditioned medium had no negative effect on cell proliferation except in medium supplemented with 5% bovine serum prior to conditioning with A. pernyi silk. The toxicity of A. pernyi was negligible after thorough enzymatic treatment of the fibers with trypsin. It is, therefore, proposed that A. pernyi silk contain one or more cytotoxic components, which need to be removed prior to medical use.

Silk inverse opals from template-directed β-sheet transformation of regenerated silk fibroin

We describe a novel and facile method for the fabrication of reconstituted silk monoliths with ordered interconnected air spheres based on intercalation and β-sheet transformation of regenerated silk fibroin solutions within the interstitial spaces of a sacrificial colloidal crystal template. The silk inverse opals are elastic and can withstand and recover from compressive loads of up to 112 MPa by reversible pore deformation. They also exhibit super-hydrophobicity with water droplet contact angles of up to 140° due to periodic nanoscale protrusions associated with the surface texture of the inverse opal architecture. These properties indicate that silk inverse opals could have potential applications as biocompatible elastic scaffolds, storage-release, barrier and self-cleaning materials, and in the design of load-responsive microfluidic devices.

A poisonous surprise under the coat of the African crested rat

Plant toxins are sequestered by many animals and the toxicity is frequently advertised by aposematic displays to deter potential predators. Such ‘unpalatability by appropriation’ is common in many invertebrate groups and also found in a few vertebrate groups. However, potentially lethal toxicity by acquisition has so far never been reported for a placental mammal. Here, we describe complex morphological structures and behaviours whereby the African crested rat, Lophiomys imhausi, acquires, dispenses and advertises deterrent toxin. Roots and bark of Acokanthera schimperi (Apocynaceae) trees are gnawed, masticated and slavered onto highly specialized hairs that wick up the compound, to be delivered whenever the animal is bitten or mouthed by a predator. The poison is a cardenolide, closely resembling ouabain, one of the active components in a traditional African arrow poison long celebrated for its power to kill elephants.

EGG SAC STRUCTURE OF ZYGIELLA X-NOTATA (ARACHNIDA, ARANEIDAE)

Abstract A detailed examination of the egg sac of Zygiella x-notata (Clerck 1757) revealed its structure, composition and different fibers. All egg sacs were composed of a basic layer, an insulation layer and an outer layer. The insulation layer consisted of two layers of cylindrical (or tubuliform) fibers with different diameters and probably with different mechanical properties. Knowing the complete structure of the egg sac allows us to locate and extract the needed fibers for further research and to observe how the egg sac composition alters in relation to the habitat.

MODELING OF THE STRESS-STRAIN BEHAVIOR OF EGG SAC SILK OF THE SPIDER ARANEUS DIADEMATUS

Abstract Spider silk has attracted the attention of many scientists because of its desirable physical properties. Most of this attention has been devoted to dragline silk, a thread that has high tensile strength, high strain and ultra-low weight. To help understand structure-property relationships in spider silks, the tensile behavior of egg sac (cylindrical gland) silk of Araneus diadematus Clerck 1757 was compared with dragline (major ampullate gland) and silkworm silks. In addition, stress-strain curves of egg sac silk were simulated by a spring-dashpot model, specifically a Standard Linear Solid (SLS) model. The SLS model consists of a spring in series with a dashpot and in parallel with another spring, resulting in three unknown parameters. The average stress-strain curve of fibers from five different egg sacs could be accurately described by the model. Closer examination of the individual stress-strain curves revealed that in each egg sac two populations of fibers could be distinguished based on the parameters of the SLS model. The stress-strain curves of the two populations clearly differed in their behavior beyond the yield point and were probably derived from two different layers within the egg sac. This indicates that silks in the two layers of A. diadematus egg sacs probably have different tensile behavior.

Dry-Spun Silk Produces Native-Like Fibroin Solutions

Silk’s outstanding mechanical properties and energy efficient solidification mechanisms provide inspiration for biomaterial self-assembly as well as offering a diverse platform of materials suitable for many biotechnology applications. Experiments now reveal that the mulberry silkworm Bombyx mori secretes its silk in a practically “unspun” state that retains much of the solvent water and exhibits a surprisingly low degree of molecular order (β-sheet crystallinity) compared to the state found in a fully formed and matured fiber. These new observations challenge the general understanding of silk spinning and in particular the role of the spinning duct for structure development. Building on this discovery we report that silk spun in low humidity appears to arrest a molecular annealing process crucial for β-sheet formation. This, in turn, has significant positive implications, enabling the production of a high fidelity reconstituted silk fibroin with properties akin to the gold standard of unspun native silk.

Enzymatic Mineralization of Silk Scaffolds

The present study focuses on the alkaline phosphatase (ALP) mediated formation of apatitic minerals on porous silk fibroin protein (SFP) scaffolds. Porous SFP scaffolds impregnated with different concentrations of ALP are homogeneously mineralized under physiological conditions. The mineral structure is apatite while the structures differ as a function of the ALP concentration. Cellular adhesion, proliferation, and colonization of osteogenic MC3T3 cells improve on the mineralized SFP scaffolds. These findings suggest a simple process to generate mineralized scaffolds that can be used to enhanced bone tissue engineering-related utility.

Spider silk : a novel optical fibre for biochemical sensing

Whilst being thoroughly used in the textile industry and biomedical sector, silk has not yet been exploited for fibre optics-based sensing although silk fibres directly obtained from spiders can guide light and have shown early promises to being sensitive to some solvents. In this communication, a pioneering optical fibre sensor based on spider silk is reported, demonstrating for the first time the use of spider silk as an optical fibre sensor to detect polar solvents such as water, ammonia and acetic acid.