Spider silk as a blueprint for greener materials : a review

Spider silk exhibits remarkable properties, especially its well-known tensile performances. They rely on a complex nanostructured hierarchical organisation that studies progressively elucidate. Spider silk encompasses a vast range of fibres that exhibit diverse and captivating physical and biological characteristics. The full understanding of the relation between structure and properties may lead in the future to the design of a variety of high-performance, tailored materials and devices. Reknown for being produced in mild and benign conditions, this outstanding biological material constitutes one of the more representative example of biomimetism. In addition, silk’s structure is produced with limited means, i.e. low energy and relatively simple renewable constituents (silk proteins). Then, if successfully controlled and adequately transposed in biomaterials, some properties of natural silk could lead to innovative green materials that may contribute to reduce the ecological footprint of societies. In fact, striking recent advanced applications made with B. mori silk suggest that spider silk-based materials may lead to advanced resistant and functional materials, then becoming among the most promising subject of study in material science. However, several challenges have to be overcome, especially our ability to produce native-like silk, to control biomaterials’ structure and properties and to minimise their ecological footprint. This paper reviews the characteristics of spider silk that make it so attractive and that may (or may not) contribute to reduce ecological footprint of materials and the challenges in producing innovative spider silk-based materials. First, from a biomimetic perspective, the structure and models that explain the tensile resistance of natural silk are presented, followed by the state of knowledge regarding natural silk spinning process and synthetic production methods. Biocompatibility (biosafety and biofunctionality) as well as biodegradability issues are then addressed. Finally, examples of applications are reviewed. Features that may lead to the design of green materials are emphasised throughout

Membrane assembly and ion transport ability of a fluorinated nanopore

A novel 21-residue peptide incorporating six fluorinated amino acids was prepared. It was designed to fold into an amphiphilic alpha helical structure of nanoscale length with one hydrophobic face and one fluorinated face. The formation of a fluorous interface serves as the main vector for the formation of a superstructure in a bilayer membrane. Fluorescence assays showed this ion channel's ability to facilitate the translocation of alkali metal ions through a phospholipid membrane, with selectivity for sodium ions. Computational studies showed that a tetramer structure is the most probable and stable supramolecular assembly for the active ion channel structure. The results illustrate the possibility of exploiting multiple Fd-:M+ interactions for ion transport and using fluorous interfaces to create functional nanostructures

Using infrared and raman microspectroscopies to compare ex vivo involved psoriatic skin with normal human skin

Psoriasis is a chronic dermatosis that affects around 3% of the world’s population. The etiology of this autoimmune pathology is not completely understood. The barrier function of psoriatic skin is known to be strongly altered, but the structural modifications at the origin of this dysfunction are not clear. To develop strategies to reduce symptoms of psoriasis or adequate substitutes for modeling, a deep understanding of the organization of psoriatic skin at a molecular level is required. Infrared and Raman microspectroscopies have been used to obtain direct molecular-level information on psoriatic and healthy human skin biopsies. From the intensities and positions of specific vibrational bands, the lipid and protein distribution and the lipid order have been mapped in the different layers of the skin. Results showed a similar distribution of lipids and collagen for normal and psoriatic human skin. However, psoriatic skin is characterized by heterogeneity in lipid/protein composition at the micrometer scale, a reduction in the definition of skin layer boundaries and a decrease in lipid chain order in the stratum corneum as compared to normal skin. A global decrease of the structural organization is exhibited in psoriatic skin that is compatible with an alteration of its barrier properties

Transdermal diffusion, spatial distribution and physical state of a potential anticancer drug in mouse skin as studied by diffusion and spectroscopic techniques

Background:Understanding the efficiency of a transdermal medical drug requires the characterization of its diffusion process, including its diffusion rate, pathways and physical state. Objective:The aim of this work is to develop a strategy to achieve this goal. Methods:FTIR spectroscopic imaging in conjunction with a Franz cell and HPLC measurements were used to examine the transdermal penetration of deuterated tert-butyl phenylchloroethylurea (tBCEU), a molecule with a potential anticancer action. tBCEU has been solubilized in an expedient solvent mixture and its diffusion in hairless mouse skin has been studied. Results:The results indicate that tBCEU diffuses across the skin for more than 10 hours with a rate comparable to selegiline, an officially-approved transdermal drug. IR image analyses reveal that after 10 hours, tBCEU penetrates skin and that its spatial distribution does not correlate with neither the distribution of lipids nor proteins. tBCEU accumulates in cluster domains but overall low concentrations are found in skin. FTIR spectroscopic imaging additionally reveals that tBCEU is in a crystalline form. Conclusions:The results suggest that tBCEU is conveyed through the skin without preferential pathway. FTIR spectroscopic imaging and transdermal diffusion measurements appear as complementary techniques to investigate drug diffusion in skin

Magnetic resonance imaging of human tissue-engineered adipose substitutes

Adipose tissue (AT) substitutes are being developed to answer the strong demand in reconstructive surgery. To facilitate the validation of their functional performance in vivo, and to avoid resorting to excessive number of animals, it is crucial at this stage to develop biomedical imaging methodologies, enabling the follow-up of reconstructed AT substitutes. Until now, biomedical imaging of AT substitutes has scarcely been reported in the literature. Therefore, the optimal parameters enabling good resolution, appropriate contrast, and graft delineation, as well as blood perfusion validation, must be studied and reported. In this study, human adipose substitutes produced from adipose-derived stem/stromal cells using the self-assembly approach of tissue engineering were implanted into athymic mice. The fate of the reconstructed AT substitutes implanted in vivo was successfully followed by magnetic resonance imaging (MRI), which is the imaging modality of choice for visualizing soft ATs. T1-weighted images allowed clear delineation of the grafts, followed by volume integration. The magnetic resonance (MR) signal of reconstructed AT was studied in vitro by proton nuclear magnetic resonance (1H-NMR). This confirmed the presence of a strong triglyceride peak of short longitudinal proton relaxation time (T1) values (200±53 ms) in reconstructed AT substitutes (total T1=813±76 ms), which establishes a clear signal difference between adjacent muscle, connective tissue, and native fat (total T1 ∼300 ms). Graft volume retention was followed up to 6 weeks after implantation, revealing a gradual resorption rate averaging at 44% of initial substitute's volume. In addition, vascular perfusion measured by dynamic contrast-enhanced-MRI confirmed the graft's vascularization postimplantation (14 and 21 days after grafting). Histological analysis of the grafted tissues revealed the persistence of numerous adipocytes without evidence of cysts or tissue necrosis. This study describes the in vivo grafting of human adipose substitutes devoid of exogenous matrix components, and for the first time, the optimal parameters necessary to achieve efficient MRI visualization of grafted tissue-engineered adipose substitutes

Crown ether modified peptide interactions with model membranes

A simple model of an uncharged antimicrobial peptide, carrying four crown ether side chains, is modified further by the selective incorporation of arginine side chains to control its secondary structure and its interaction with model membranes and living cells. Conformational studies show that shifting the position of a cationic residue in the peptide sequence allows to control its secondary structure and supramolecular self-assembly in solution. Results also demonstrate that the secondary structure influences the interaction with model membranes and cells. An α-helical peptide with greater amphiphilicity forms assemblies that interact with both prokaryotic and eukaryotic model membranes and cells. However, a β-stranded peptide with evenly distributed charges generates assemblies that interact more selectively with prokaryotic model membranes and cells. In addition, we observed differences in peptide orientation between uncharged and cationic α-helical peptides with different phospholipid bilayers. In general, the studied peptides have a higher affinity for thinner membranes, and cationic peptides interacted better with anionic membranes

Biological Membrane Structure by Solid-State NMR

Nuclear magnetic resonance (NMR) spectroscopy, and particularly solid-state NMR spectroscopy, is a method of choice to study the structure and dynamics of both the lipid and the protein components of model and biological membranes. Different approaches have been developed to study these systems in which the restricted molecular motions result in broad NMR spectra. This contribution will first present an overview of the different techniques used to study lipid bilayers, namely 31P, 2H and 13C solid-state NMR spectroscopy. On the other hand, the study of the structure of membrane peptides and proteins is a rapidly growing field and several methods developed in the last two decades will be presented. These methods allow the investigation of protein systems for which structural information is often difficult to obtain by techniques such as X-ray diffraction and multidimensional solution NMR

Deuterium NMR and high-pressure FT-IR studies of membranes: Anesthetic-lipid interactions and molecular dynamics in lipid bilayers.

The interactions of the local anesthetic tetracaine with multilamellar dispersions of dimyristoylphosphatidylcholine (DMPC) containing cholesterol have been investigated by deuterium nuclear magnetic resonance (\sp2H NMR). \sp2H NMR spectra of tetracaine indicate that the location of the anesthetic in the cholesterol-containing DMPC bilayers differs from that in pure phosphatidylcholine bilayers, the anesthetic being located closer to the lipid-water interface in the former system. Moreover, the incorporation of the anesthetic into DMPC bilayers with or without cholesterol results in a reduction of the lipid order parameters both in the plateau and in the tail regions of the acyl chains, but does not significantly affect the cholesterol ordering. The interactions of tetracaine with the glycolipid 1,2-di-O-tetradecyl-3-O-($\beta$-D-glucopyranosyl)-sn-glycerol ($\beta$-DTGL) and with $\beta$-DTGL (20 mole%) in DMPC have also been investigated by \sp2H NMR. The stability of the lamellar structure of the pure glycolipid system is very sensitive to the presence of anesthetic while the interaction of tetracaine with the mixed glycolipid-phospholipid system does not trigger the formation of non-lamellar phases but leads to a slight reduction in molecular ordering. The location of tetracaine in different lipid bilayers and in nerves has been studied by high-pressure Fourier transform infrared (FT-IR) spectroscopy. The results reveal a correlation between the location of the anesthetic in model membranes and that in nerves. They also indicate that tetracaine is expelled by pressure from both model and nerve membranes, and that for model membrane systems, low pH or cholesterol will assist pressure in squeezing the anesthetic out of the bilayer. On the other hand, high-pressure FT-IR has also been used to study the effects of tetracaine on the structural and dynamic properties of lipids in model membrane systems. A combination of \sp2H spin-lattice relaxation and lineshape analysis has been used to demonstrate that a simple model involving two motions is sufficient to describe the spectral and relaxation features of the glycerol-labelled glycolipid $\beta$-DTGL. The lineshape and relaxation features of this lipid in the gel phase are best simulated using the three-site jump model with relative site populations of 0.46, 0.34 and 0.20, and a correlation time of 6.7 $\times$ 10\sp{-10}s. A second motion, namely rotation about the long axis of the molecule as a whole, is needed to account for the observed variation in the quadrupolar echo amplitude and the spectral lineshape over the temperature range of 25 to 60\sp\circC. Similar results have been obtained for several phospholipid and glycolipid bilayers, which suggest that the glycerol backbone dynamics in all these systems can be described in terms of common fast internal motions and a slower whole molecule axial motion. Two-dimensional solid-state deuteron NMR spectroscopy has been used to confirm the presence of a slow whole molecule motion in the gel phase of the glycolipid $\beta$-DTGL at 35\sp\circC, with an associated correlation time of the order of milliseconds. Comparison of the experimental and simulated two-dimensional ridge patterns suggest that a large angle jump about the long molecular axis can best account for the 2D exchange spectra of $\beta$-DTGL in the gel phase in comparison to small step Brownian diffusion. On the other hand, it is demonstrated that lateral diffusion over curved membrane surface of dipalmitoylphosphatidylcholine bilayers in the liquid-crystalline phase can be detected by 2D deuteron NMR, with an associated correlation time of the order of $\approx$100 ms