SciCombinator

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Journal: Biomacromolecules

32

Hagfish slime threads, which make up the fibrous component of the defensive slime of hagfishes, consist primarily of proteins from the intermediate filament family of proteins and possess impressive mechanical properties that make them attractive biomimetic models. To investigate whether solubilized intermediate filament proteins can be used to make high-performance, environmentally sustainable materials, we cast thin films on the surface of electrolyte buffers using solubilized hagfish slime thread proteins. The films were drawn into fibers, and the tensile properties were measured. Fiber mechanics depended on casting conditions and postspinning processing. Postsecondary drawing resulted in fibers with improved material properties similar to those of regenerated silk fibers. Structural analyses of the fibers revealed increased molecular alignment resulting from the second draw, but no increase in crystallinity. Our findings show promise for intermediate filament proteins as an alternative source for the design and production of high performance protein-based fibers.

Concepts: Cytoskeleton, Tensile strength, Fiber, Materials, Dietary fiber, Spider silk, Hagfish, Fibers

28

Alkyne-functionalized cellulose fibers have been generated through etherification under basic water or hydroalcoholic conditions (NaOH/H2O/Isopropanol). For a given NaOH content, the medium of reaction and more particularly the water/IPA ratio, was shown to be of crucial importance to derivatize the fibers without altering their integrity and their crystalline nature. It was shown that the DS of the fibers increases concomitantly with isopropanol weight ratio and that contrary to water or water-rich conditions, derivatization of fibers under isopropanol-rich conditions induces an alteration of the fibers. Optimization of etherification conditions in aqueous media afforded functionalized cellulose materials with DS up to 0.20. Raman confocal microscopy on derivatized fibers cross-sections stressed that alkyne moieties are incorporated all over the fibers. The resulting fibers were post-functionalized by molecular probes and macromolecules in aqueous or water-rich conditions. The effectiveness of the grafting was strongly impacted by the nature of the coupling agents.

Concepts: Molecule, Ethanol, Chemistry, Cellulose, Confocal microscopy, The Medium, Derivatization, Cellulose fiber

28

Enamel matrix self-assembly has long been suggested as the driving force behind aligned nanofibrous hydroxyapatite formation. We tested if amelogenin, the main enamel matrix protein, can self-assemble into ribbon-like structures in physiologic solutions. Ribbons 17 nm wide were observed to grow several micrometers in length, requiring calcium, phosphate, and pH 4.0-6.0. The pH range suggests that the formation of ion bridges through protonated histidine residues is essential to self-assembly, supported by a statistical analysis of 212 phosphate-binding proteins predicting 12 phosphate-binding histidines. Thermophoretic analysis verified the importance of calcium and phosphate in self-assembly. X-ray scattering characterized amelogenin dimers with dimensions fitting the cross-section of the amelogenin ribbon, leading to the hypothesis that antiparallel dimers are the building blocks of the ribbons. Over 5-7 days, ribbons self-organized into bundles composed of aligned ribbons mimicking the structure of enamel crystallites in enamel rods. These observations confirm reports of filamentous organic components in developing enamel and provide a new model for matrix-templated enamel mineralization.

Concepts: DNA, Scientific method, Protein, Histidine, Observation, Hypothesis, Amorphous calcium phosphate, Tooth enamel

28

Biodegradable polymers with high elasticity, low thrombogenicity, and drug loading capacity continue to be pursued for vascular engineering applications, including vascular grafts and stents. A biodegradable elastomeric polyurethane was designed as a candidate material for use as a drug-eluting stent coating, such that it was nonthrombogenic and could provide antiproliferative drug release to inhibit smooth muscle cell proliferation. A phosphorylcholine containing poly(ester urethane) urea (PEUU-PC) was synthesized by grafting aminated phosphorylcholine onto backbone carboxyl groups of a polyurethane (PEUU-COOH) synthesized from a soft segment blend of polycaprolactone and dimethylolpropionic acid, a hard segment of diisocyanatobutane and a putrescine chain extender. Poly(ester urethane) urea (PEUU) from a soft segment of polycaprolactone alone was employed as a control material. All of the synthesized polyurethanes showed high distensibility (>600%) and tensile strengths in the 20-35 MPa range. PEUU-PC experienced greater degradation than PEUU or PEUU-COOH in either a saline or lipase enzyme solution. PEUU-PC also exhibited markedly inhibited ovine blood platelet deposition compared with PEUU-COOH and PEUU. Paclitaxel loaded in all of the polymers during solvent casting continued to release for 5 d after a burst release in a 10% ethanol/PBS solution, which was utilized to increase the solubility of the releasate. Rat smooth muscle cell proliferation was significantly inhibited in 1 wk cell culture when releasate from the paclitaxel-loaded films was present. Based on these results, the synthesized PEUU-PC has promising functionality for use as a nonthrombogenic, drug eluting coating on metallic vascular stents and grafts.

Concepts: Enzyme, Cardiac muscle, Stent, Skeletal muscle, Smooth muscle, Muscular system, Polyurethane, Carbamate

28

Modular proteins have emerged as powerful tools in tissue engineering because both the mechanical and biochemical properties can be precisely controlled through amino acid sequence. Resilin is an attractive candidate for use in modular proteins because it is well-known for having low stiffness, high fatigue lifetime, and high resilience. However, no studies have been conducted to assess resilin’s compressive properties, cytocompatibility with clinically relevant cells, or effect on cell spreading. We designed a modular protein containing repeating sequences of a motif derived from Anopheles gambiae and cell-binding domains derived from fibronectin. Rapid cross-linking with tris(hydroxymethyl)phosphine was observed. The hydrogels had a complex modulus of 22 ± 1 kPa and yield strain of 63%. The elastic modulus in compression, or unconfined compressive modulus, was 2.4 ± 0.2 MPa, which is on the same order as human cartilage. A LIVE/DEAD assay demonstrated that human mesenchymal stem cells cultured on the resilin-based protein had a viability of 95% after three days. A cell-spreading assay revealed that the cells interacted with the fibronectin-derived domain in a sequence-specific manner and resulted in a mean cell area ∼1.4-fold larger than when cells were seeded on a sequence-scrambled negative control protein. These results demonstrate that our resilin-based biomaterial is a promising biomaterial for cartilage tissue engineering.

Concepts: DNA, Protein, Gene, Amino acid, Stem cell, Cell biology, Young's modulus, Elasticity

28

Single-molecule total internal reflection fluorescence microscopy was used to observe the dynamic behavior of polycytosine single-stranded DNA (ssDNA) (1-50 nucleotides long) at the interface between aqueous solution and hydrophilic (oligoethylene glycol-modified fused silica, OEG) and hydrophobic (octadecyltriethoxysilane-modified fused silica, OTES) solid surfaces. High throughput molecular tracking was used to determine >75 000 molecular trajectories for each molecular length, which were then used to calculate surface residence time and squared displacement (i.e., “step-size”) distributions. On hydrophilic OEG surfaces, the surface residence time increased systematically with ssDNA chain length, as expected due to increasing molecule-surface interactions. Interestingly, the residence time decreased with increasing ssDNA length on the hydrophobic OTES surface, particularly for longer chains. Similarly, the interfacial mobility of polynucleotides slowed with increasing chain length on OEG, but became faster on OTES. On OTES surfaces, the rates associated with desorption and surface diffusion exhibited the distinctive anomalous temperature dependence that is characteristic of hydrophobic interactions for short-chain species but not for longer chains. These combined observations suggest that long oligonucleotides adopt conformations minimizing hydrophobic interactions, e.g., by internal sequestration of hydrophobic nucleobases.

Concepts: DNA, Gene, Polymerase chain reaction, Base pair, Total internal reflection fluorescence microscope, Chemical properties, Nucleotide, Hydrophobicity scales

27

A new biologically compatible Zn(II) sensor was fabricated by embedding Zn(II) sensing spiropyran within the surface of a liposome derived from E.coli lipids (LSP2). Solution-based experiments with increasing Zn(II) concentrations show improved aqueous solubility and sensitivity compared to the isolated spiropyran molecule (SP2). LSP2 is capable of sensing Zn(II) efflux from apoptotic cells with preliminary data indicating that sensing is localized near the surface membrane of HEK 293 cells. Finally, LSP2 is suitable for development into a nanoliter scale, dip-sensor for Zn(II) using microstructured optical fiber as the sensing platform to detect Zn(II) in the range of 100 ρM with no signs of photobleaching. Existing spiropyran based sensing molecules can thus be made biologically compatible, with an ability to operate with improved sensitivity using nanoscale liquid sample volumes. This work represents the first instance where photochromic spiropyran molecules and liposomes are assembled to create a new and multifunctional sensing entity for Zn(II).

Concepts: DNA, Optical fiber, Chemistry, Cell culture, Solubility, Cell lines, HEK cell, Photonic-crystal fiber

27

The classic nanocomposite approach aims at percolation of low fraction of exfoliated individual reinforcing nanoscale elements within a polymeric matrix. By contrast, many of the mechanically excellent biological nanocomposites involve self-assembled and space-filled structures of hard reinforcing and soft toughening domains, with high weight fraction of reinforcements. Here we inspect a new concept towards mimicking such structures by studying whether percolation of intercalated domains consisting of alternating rigid and reinforcing, and soft rubbery domains could allow a transition to a reinforced state. Towards that, we present the functionalization of rigid native cellulose nanocrystals (CNC) by esterification with a dense hydrocarbon chain brush containing cross-linkable double bonds. Composite films with 0-80 wt% of such modified CNCs (mCNC) within a poly(butadiene) (PBD) rubber matrix were prepared via cross-linking by UV-light initiated thiol-ene click reaction. Transmission electron microscopy showed structures at two length scales, where the mCNCs and PBD form domains having internal aligned self-assemblies of alternating hard mCNCs and soft PBD with periodicity of 40 nm, and where additional PBD connects such domains. Increasing the weight fraction of mCNCs causes an uncommon abrupt transition from PBD-dominated soft materials to significantly reinforced mCNC-dominated mechanical properties, suggesting that the intercalated self-assembled mCNC/PBD domains percolate in PBD upon passing 30-35 wt% of mCNCs. Maximum stress of 16 MPa at mCNC fraction 80 wt% was obtained. The mechanical properties of the composites show exceptional insensitivity to air humidity. The shown simple concept of percolative intercalated nanocomposites suggests searching for more general biomimetic compositions involving several deformation mechanisms for improved mechanical properties.

Concepts: Electron, Click chemistry, Reinforcement, Percolation threshold, Percolation

27

Injectable, in situ-gelling magnetic composite materials have been fabricated by using aldehyde-functionalized dextran to cross-link superparamagnetic nanoparticles surface-functionalized with hydrazide-functionalized poly(N-isopropylacrylamide) (pNIPAM). The resulting composites exhibit high water contents (82-88 wt.%) while also displaying significantly higher elasticities (G' >60 kPa) than other injectable hydrogels previously reported. The composites hydrolytically degrade via slow hydrolysis of the hydrazone cross-link at physiological temperature and pH into degradation products that show no significant cytotoxicity. Subcutaneous injections indicate only minor chronic inflammation associated with material degradation, with no fibrous capsule formation evident. Drug release experiments indicate the potential of these materials to facilitate pulsatile, “on-demand” changes in drug release upon the application of an external oscillating magnetic field. The injectable but high-strength and externally-triggerable nature of these materials, coupled with their biological degradability and inertness, suggest potential biological applications in tissue engineering and drug delivery.

Concepts: Magnetism, Composite material, Boeing 787, Thermoplastic, Superparamagnetism, Fiberglass, Aramid, Pykrete

27

The purpose of this study is to investigate the effects of oxygen plasma treatments on PLGA and its silver nanoparticles (Ag) based nanocomposites in order to modulate the surface antimicrobial properties through tuneable bacteria adhesion mechanisms. PLGA nanocomposite films, produced by solvent casting with 1% wt, 3% wt and 7% wt of Ag nanoparticles were investigated. The PLGA and PLGA/Ag nanocomposite surfaces were treated with oxygen plasma. Surface properties of PLGA were investigated by field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), static contact angle (CA), and high resolution X-ray photoelectron spectroscopy (XPS). Antibacterial tests were performed using an Escherichia coli RB (a Gram negative) and Staphylococcus aureus 8325-4 (a Gram positive). The PLGA surface becomes hydrophilic after the oxygen treatment and its roughness increases with the treatment time. The synergism of these surface effects, due to the treatment action, and Ag nanoparticle introduction has a dominant influence on the bacteria adhesion and growth. Oxygen treated PLGA/Ag systems promote higher reduction of the bacteria viability in comparison to the untreated samples and neat PLGA. The combination of Ag nanoparticles with the oxygen plasma treatment opens new perspectives for the studied biodegradable systems in biomedical applications.

Concepts: Electron, Bacteria, Microbiology, Pneumonia, Escherichia coli, Nanomaterials, X-ray photoelectron spectroscopy, Scanning electron microscope