Molecular organization of fibroin heavy chain and mechanism of fibre formation in Bombyx mori.

Fibroins' transition from liquid to solid is fundamental to spinning and underpins the impressive native properties of silk. Herein, we establish a fibroin heavy chain fold for the Silk-I polymorph, which could be relevant for other similar proteins, and explains mechanistically the liquid-to-solid transition of this silk, driven by pH reduction and flow stress. Combining spectroscopy and modelling we propose that the liquid Silk-I fibroin heavy chain (FibH) from the silkworm, Bombyx mori, adopts a newly reported β-solenoid structure.

Meniscal Replacement With a Silk Fibroin Scaffold Reduces Contact Stresses in the Human Knee.

The aim of the current study was to verify if a previously developed silk fibroin scaffold for meniscal replacement is able to restore the physiological distribution of contact pressure (CP) over the articulating surfaces in the human knee joint, thereby reducing peak loads occurring after partial meniscectomy. The pressure distribution on the medial tibial articular surface of seven human cadaveric knee joints was analysed under continuous flexion-extension movements and under physiological loads up to 2,500 N at different flexion angles. Contact area (CA), maximum tibiofemoral CP, maximum pressure under the meniscus and the pressure distribution were analysed for the intact meniscus, after partial meniscectomy as well as after partial medial meniscal replacement using the silk fibroin scaffold.

Articular cartilage and meniscus reveal higher friction in swing phase than in stance phase under dynamic gait conditions.

Most previous studies investigated the remarkably low and complex friction properties of meniscus and cartilage under constant loading and motion conditions. However, both load and relative velocity within the knee joint vary considerably during physiological activities. Hence, the question arises how friction of both tissues is affected by physiological testing conditions occurring during gait.

The challenge of implant integration in partial meniscal replacement: an experimental study on a silk fibroin scaffold in sheep.

Purpose: To restore meniscal function after excessive tissue damage, a silk fibroin implant for partial meniscal replacement was developed and investigated in an earlier sheep model. After 6 months implantation, it showed promising results in terms of chondroprotection and biocompatibility. To improve surgical fixation, the material was subjected to optimisation and a fibre mesh was integrated into the porous matrix.

Biomechanical, structural and biological characterisation of a new silk fibroin scaffold for meniscal repair.

Meniscal injury is typically treated surgically via partial meniscectomy, which has been shown to cause cartilage degeneration in the long-term. Consequently, research has focused on meniscal prevention and replacement. However, none of the materials or implants developed for meniscal replacement have yet achieved widespread acceptance or demonstrated conclusive chondroprotective efficacy.

Correction to: In vivo performance of a novel silk fibroin scaffold for partial meniscal replacement in a sheep model.

The author would like to correct the errors in the publication of the original article. The corrected details are given below for your reading.

Friction properties of a new silk fibroin scaffold for meniscal replacement.

The menisci protect the articular cartilage by reducing contact pressure in the knee. To restore their function after injury, a new silk fibroin replacement scaffold was developed. To elucidate its tribological properties, friction of the implant was tested against cartilage and glass, where the latter is typically used in tribological cartilage studies.

In vivo performance of a novel silk fibroin scaffold for partial meniscal replacement in a sheep model.

Purpose: Due to the negative effects of meniscectomy, there is a need for an adequate material to replace damaged meniscal tissue. To date, no material tested has been able to replace the meniscus sufficiently. Therefore, a new silk fibroin scaffold was investigated in an in vivo sheep model.

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.

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.

Transcriptional heterochrony of scute and changes in bristle pattern between two closely related species of blowfly.

Temporal shifts in the expression of regulatory genes, relative to other events taking place during development, can result in changes in morphology. Such transcriptional heterochrony can introduce dramatic morphological changes that involve rather few genetic events and so has the potential to cause rapid changes during evolution. We have shown previously that stereotyped species-specific bristle patterns on the notum of higher Diptera correlate with changes in the spatial regulation of scute expression.

Gene duplication at the achaete-scute complex and morphological complexity of the peripheral nervous system in Diptera.

The number of achaete-scute genes increased during insect evolution, particularly in the Diptera lineage. Sequence comparison indicates that the four achaete-scute genes of Drosophila result from three independent duplication events. After duplication, the new genes acquired individual expression patterns but, in Drosophila, their products can compensate for one another, which raises the question: why retain all four genes? The complexity of the spatial expression of these genes on the notum increased in the lineage leading to the higher Diptera, allowing the development of stereotyped bristle patterns.

Neurochemical fine tuning of a peripheral tissue: peptidergic and aminergic regulation of fluid secretion by Malpighian tubules in the tobacco hawkmoth M. sexta.

The actions of various peptides and other compounds on fluid secretion by Malpighian tubules in the tobacco hawkmoth Manduca sexta sexta are investigated in this study. Using a newly developed pharate adult Malpighian tubule bioassay, we show that three tachykinin-related peptides (TRPs), leucokinin I, serotonin (5-HT), octopamine, the cardioacceleratory peptides 1a, 1b and 2c, cGMP and cAMP each cause an increase in the rate of fluid secretion in pharate adult tubules. Whereas the possible hormonal sources of biogenic amines and some of the peptides are known, the distribution of TRPs has not been investigated previously in M.

scute expression in Calliphora vicina reveals an ancestral pattern of longitudinal stripes on the thorax of higher Diptera.

In Drosophila the stereotyped arrangement of sensory bristles on the notum is determined by the tightly regulated control of transcription of the achaete-scute (ac-sc) genes which are expressed in small proneural clusters of cells at the sites of each future bristle. Expression relies on a series of discrete cis-regulatory elements present in the ac-sc gene complex that are the target of the transcriptional activators pannier (pnr) and the genes of the iroquois complex. Stereotyped bristle patterns are common among species of acalyptrate Schizophora such as Drosophila, and are thought to have derived from an ancestral pattern of four longitudinal rows extending the length of the scutum, through secondary loss of bristles.

Genetic analysis of bristle loss in hybrids between Drosophila melanogaster and D. simulans provides evidence for divergence of cis-regulatory sequences in the achaete-scute gene complex.

The two closely related species of Drosophila, D. melanogaster and D. simulans, display an identical bristle pattern on the notum, but hybrids between the two are lacking a variable number of bristles.

Neuropeptide stimulation of the nitric oxide signaling pathway in Drosophila melanogaster Malpighian tubules.

Activation of the nitric oxide (NO) and guanosine 3', 5'-cyclic monophosphate (cGMP) signaling pathway stimulates fluid secretion by the Drosophila melanogaster Malpighian tubule. The neuropeptide cardioacceleratory peptide 2b (CAP2b) has been previously shown to stimulate fluid secretion in this epithelium by elevating intracellular cGMP levels. Therefore, it was of interest to investigate if CAP2b acts through NO in isolated tubules and thus presumably through stimulation of a tubule NO synthase (NOS).

CAP2b, a cardioacceleratory peptide, is present in Drosophila and stimulates tubule fluid secretion via cGMP.

A cardioacceleratory peptide, CAP2b, identified originally in the lepidopteran Manduca sexta, stimulates fluid secretion by Malpighian tubules of the dipteran Drosophila melanogaster. High-performance liquid chromatography analyses of adult D. melanogaster reveal the presence of a CAP2b-like peptide, that coelutes with M.

A novel role for the nitric oxide-cGMP signaling pathway: the control of epithelial function in Drosophila.

The nitric oxide (NO) signaling pathway plays major roles in the vertebrate vascular, nervous, and immune systems. Here we present evidence that all the elements in the NO pathway are present in, and act to control epithelial fluid secretion by, the Malpighian tubules of an insect, Drosophila melanogaster. This finding will allow both a physiological and a molecular genetic dissection of the NO pathway in the same tissue.