Lignocellulosic Biomass for the Fabrication of Triboelectric Nano-Generators (TENGs)-A Review.

Growth in population and increased environmental awareness demand the emergence of new energy sources with low environmental impact. Lignocellulosic biomass is mainly composed of cellulose, lignin, and hemicellulose. These materials have been used in the energy industry for the production of biofuels as an eco-friendly alternative to fossil fuels. However, their use in the fabrication of small electronic devices is still under development. Lignocellulose-based triboelectric nanogenerators (LC-TENGs) have emerged as an eco-friendly alternative to conventional batteries, which are mainly composed of harmful and non-degradable materials. These LC-TENGs use lignocellulose-based components, which serve as electrodes or triboelectric active materials. These materials can be derived from bulk materials such as wood, seeds, or leaves, or they can be derived from waste materials from the timber industry, agriculture, or recycled urban materials. LC-TENG devices represent an eco-friendly, low-cost, and effective mechanism for harvesting environmental mechanical energy to generate electricity, enabling the development of self-powered devices and sensors. In this study, a comprehensive review of lignocellulosic-based materials was conducted to highlight their use as both electrodes and triboelectric active surfaces in the development of novel eco-friendly triboelectric nano-generators (LC-TENGs). The composition of lignocellulose and the classification and applications of LC-TENGs are discussed.

Carbon Quantum Dots Based on Marine Polysaccharides: Types, Synthesis, and Applications.

The marine environment offers a vast array of resources, including plants, animals, and microorganisms, that can be utilized to extract polysaccharides such as alginate, carrageenan, chitin, chitosan, agarose, ulvan, porphyra, and many more. These polysaccharides found in marine environments can serve as carbon-rich precursors for synthesizing carbon quantum dots (CQDs). Marine polysaccharides have a distinct advantage over other CQD precursors because they contain multiple heteroatoms, including nitrogen (N), sulfur (S), and oxygen (O). The surface of CQDs can be naturally doped, reducing the need for excessive use of chemical reagents and promoting green methods. The present review highlights the processing methods used to synthesize CQDs from marine polysaccharide precursors. These can be classified according to their biological origin as being derived from algae, crustaceans, or fish. CQDs can be synthesized to exhibit exceptional optical properties, including high fluorescence emission, absorbance, quenching, and quantum yield. CQDs' structural, morphological, and optical properties can be adjusted by utilizing multi-heteroatom precursors. Moreover, owing to their biocompatibility and low toxicity, CQDs obtained from marine polysaccharides have potential applications in various fields, including biomedicine (e.g., drug delivery, bioimaging, and biosensing), photocatalysis, water quality monitoring, and the food industry. Using marine polysaccharides to produce carbon quantum dots (CQDs) enables the transformation of renewable sources into a cutting-edge technological product. This review can provide fundamental insights for the development of novel nanomaterials derived from natural marine sources.

Bacterial Cellulose-Graphene Based Nanocomposites.

Bacterial cellulose (BC) and graphene are materials that have attracted the attention of researchers due to their outstanding properties. BC is a nanostructured 3D network of pure and highly crystalline cellulose nanofibres that can act as a host matrix for the incorporation of other nano-sized materials. Graphene features high mechanical properties, thermal and electric conductivity and specific surface area. In this paper we review the most recent studies regarding the development of novel BC-graphene nanocomposites that take advantage of the exceptional properties of BC and graphene. The most important applications of these novel BC-graphene nanocomposites include the development of novel electric conductive materials and energy storage devices, the preparation of aerogels and membranes with very high specific area as sorbent materials for the removal of oil and metal ions from water and a variety of biomedical applications, such as tissue engineering and drug delivery. The main properties of these BC-graphene nanocomposites associated with these applications, such as electric conductivity, biocompatibility and specific surface area, are systematically presented together with the processing routes used to fabricate such nanocomposites.

Molecular α-relaxation process of exopolysaccharides extracted from Nostoc commune cyanobacteria.

Broadband dielectric spectroscopy was used to investigate the molecular α-relaxation of the exopolysaccharides (EPS) extracted from Nostoc commune cyanobacteria. The EPS were modified in different ways. EPS were carboxymethylated to obtain carboxymethyl-exopolysaccharides (CEPS). EPS and CEPS were doped with ammonium iodide and 1-butyl-3-methylimidazolium chloride. An α relaxation process was observed for all specimens. The temperature dependence of the relaxation times for pure and doped, EPS and CEPS polymers exhibited non-Arrhenius behavior. This relaxation process was associated with the glass transition of the complex heteropolysaccharides produced by the cyanobacteria. The molecular mobility at the glass transition, Tg, was affected by both the carboxymethylation treatment and the doping. The fragility index also decreased for the doped specimens, which may be attributed to an increase in the mobility of the polymer chains due to the plasticizing effect of the doping agents.

Application of the Spider Silk Standardization Initiative (S3I) methodology to the characterization of major ampullate gland silk fibers spun by spiders from Pantanos de Villa wetlands (Lima, Peru).

Spider silk is a natural material with unique properties and a great potential for engineering and biomedical applications. In spite of its simple composition and highly conserved and stereotypical production, spider silks show a wide range of variability in their mechanical properties which, for long, have defied their classification and standardization. Here we propose to launch the Spider Silk Standardization Initiative (S3I), a methodology based on the definition of the α* parameter, in an attempt to define a systematic procedure to classify the tensile properties exhibited by major ampullate gland silk (MAS) spun by Entelegynae spiders. The α* parameter is calculated from the comparison of the true stress-true strain curve of any MAS fiber after being subjected to maximum supercontraction, with the true stress-true strain curve of the species Argiope aurantia, which is set as a reference curve. This work presents the details of the S3I methodology and, as an example, shows its application to an assemblage of Entelegynae spiders from different families collected at the Pantanos de Villa wetlands (Lima, Peru). The systematic and objective classification of the tensile properties of MAS fibers allowed by the S3I will offer insights into key aspects of the biological evolution of the material, and address questions such as how history and adaptation contributed to shape those properties. In addition, it will surely have far reaching consequences in fields such as Materials Science, and Molecular and Evolutionary Biology, by organizing the range of tensile properties exhibited by spider silk fibers.

Natural Polysaccharide Nanomaterials: An Overview of Their Immunological Properties.

Natural occurring polymers, or biopolymers, represent a huge part of our planet biomass. They are formed by long chains of monomers of the same type or a combination of different ones. Polysaccharides are biopolymers characterized by complex secondary structures performing several roles in plants, animals, and microorganisms. Because of their versatility and biodegradability, some of them are extensively used for packaging, food, pharmaceutical, and biomedical industries as sustainable and renewable materials. In the recent years, their manipulation at the nanometric scale enormously increased the range of potential applications, boosting an interdisciplinary research attempt to exploit all the potential advantages of nanostructured polysaccharides. Biomedical investigation mainly focused on nano-objects aimed at drug delivery, tissue repair, and vaccine adjuvants. The achievement of all these applications requires the deep knowledge of polysaccharide nanomaterials' interactions with the immune system, which orchestrates the biological response to any foreign substance entering the body. In the present manuscript we focused on natural polysaccharides of high commercial importance, namely, starch, cellulose, chitin, and its deacetylated form chitosan, as well as the seaweed-derived carrageenan and alginate. We reviewed the available information on their biocompatibility, highlighting the importance of their physicochemical feature at the nanoscale for the modulation of the immune system.

Hydrazine treatment improves conductivity of bacterial cellulose/graphene nanocomposites obtained by a novel processing method.

A novel method to prepare BC nanocomposites reinforced with reduced graphene oxide (RGO) is reported. A simple hydrazine treatment is shown to in-situ reduce the graphene oxide (GO) incorporated to BC films while increasing their conductivity. Raman spectroscopy was used to confirm the presence of graphene and assess the effect of the hydrazine treatment on its structure. XRD tests revealed no changes on BC structure. We hypothesize that this treatment removes the hydroxyl and epoxy groups present on the reduced graphene and increases the content of nonoxygenated carbon. These changes account for the increase in conductivity of the BC-based films, which behaved as an insulating material before the hydrazine treatment and reach an average conductivity value of 12S/m after such a treatment.

Failure of flight feathers under uniaxial compression.

Flight feathers are light weight engineering structures. They have a central shaft divided in two parts: the calamus and the rachis. The rachis is a thinly walled conical shell filled with foam, while the calamus is a hollow tube-like structure. Due to the fact that bending loads are produced during birds' flight, the resistance to bending of feathers has been reported in different studies. However, the analysis of bent feathers has shown that compression could induce failure by buckling. Here, we have studied the compression of feathers in order to assess the failure mechanisms involved. Axial compression tests were carried out on the rachis and the calamus of dove and pelican feathers. The failure mechanisms and folding structures that resulted from the compression tests were observed from images obtained by scanning electron microscopy (SEM). The rachis and calamus fail due to structural instability. In the case of the calamus, this instability leads to a progressive folding process. In contrast, the rachis undergoes a typical Euler column-type buckling failure. The study of failed specimens showed that delamination buckling, cell collapse and cell densification are the primary failure mechanisms of the rachis structure. The role of the foam is also discussed with regard to the mechanical response of the samples and the energy dissipated during the compression tests. Critical stress values were calculated using delamination buckling models and were found to be in very good agreement with the experimental values measured. Failure analysis and mechanical testing have confirmed that flight feathers are complex thin walled structures with mechanical adaptations that allow them to fulfil their functions.

Unusual reversible elastomeric gels from Nostoc commune.

Nostoc commune cyanobacteria grow in extreme conditions of desiccation and nutrient-poor soils. Their colonies form spherical gelatinous bodies are composed of a variety of polysaccharides that allow them to store water and nutrients. In this paper, we study this type of biological gel that shows characteristics of both chemical and physical gels. The structure of this gel was assessed by means of scanning electron microscopy, plate-plate rheometry, Fourier transform infrared spectroscopy and absorption/desorption tests. The storage modulus of this gel was found to be frequency independent, as is usual for chemical gels. The stress sweeps showed a reversible stress softening behaviour that was explained in terms of the physical nature of the interactions of this network. The high density of physical crosslinks probably allows this physical network to behave as a highly elastomeric chemical network, limiting the relaxation of individual chains. On the other hand, reversibility is associated with the physical nature of its bonds.

Characterization of dermal plates from armored catfish Pterygoplichthys pardalis reveals sandwich-like nanocomposite structure.

Dermal plates from armored catfish are bony structures that cover their body. In this paper we characterized structural, chemical, and nanomechanical properties of the dermal plates from the Amazonian fish Pterygoplichthys pardalis. Analysis of the morphology of the plates using scanning electron microscopy (SEM) revealed that the dermal plates have a sandwich-like structure composed of an inner porous matrix surrounded by two external dense layers. This is different from the plywood-like laminated structure of elasmoid fish scales but similar to the structure of osteoderms found in the dermal armour of some reptiles and mammals. Chemical analysis performed using Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and X-ray diffraction (XRD) results revealed similarities between the composition of P. pardalis plates and the elasmoid fish scales of Arapaima gigas. Reduced moduli of P. pardalis plates measured using nanoindentation were also consistent with reported values for A. gigas scales, but further revealed that the dermal plate is an anisotropic and heterogeneous material, similar to many other fish scales and osteoderms. It is postulated that the sandwich-like structure of the dermal plates provides a lightweight and tough protective layer.

Failure analysis of porcupine quills under axial compression reveals their mechanical response during buckling.

Porcupine quills are natural structures formed by a thin walled conical shell and an inner foam core. Axial compression tests, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FT-IR) were all used to compare the characteristics and mechanical properties of porcupine quills with and without core. The failure mechanisms that occur during buckling were analyzed by scanning electron microscopy (SEM), and it was found that delamination buckling is mostly responsible for the decrease in the measured buckling stress of the quills with regard to predicted theoretical values. Our analysis also confirmed that the foam core works as an energy dissipater improving the mechanical response of an empty cylindrical shell, retarding the onset of buckling as well as producing a step wise decrease in force after buckling, instead of an instantaneous decrease in force typical for specimens without core. Cell collapse and cell densification in the inner foam core were identified as the key mechanisms that allow for energy absorption during buckling.

Physical characterization of the liquid adhesive from orb-weaving spiders.

Orb-weaving spiders produce bioadhesives that are used to capture their prey. In this paper, the physical properties of these adhesives are characterised. The liquid adhesive from Argiope argentata spiders has been studied and the morphological properties of the droplets, including size, shape and volume were determined. An estimation of viscosity and Young's modulus using atomic force microscopy has also been carried out. Morphological characterization confirmed that the liquid adhesive displayed a typical beads-on-a-string (BOAS) morphology on the silk fibres. The experimental data confirmed that the elastic modulus of the liquid adhesive from A. argentata was in the range 20-100kPa which is in agreement with the Dahlquist criterion for adhesives.

An experimental confirmation of thermal transitions in native and regenerated spider silks.

Biological structures such as spider silks are formed by proteins. The physical properties of such proteins are determined by environmental conditions such as temperature and humidity. In this paper, we confirm the thermal transitions that take place in spider silks using differential scanning calorimetry and study how the interaction of spider silk proteins with water affects the onset temperatures for these thermal processes. Native fibres and regenerated films of dragline silk and egg sac silk from Argiope argentata spiders were used to study thermal transitions of protein based structures. For the first time, differential scanning calorimetry (DSC) tests were carried out with spider silk samples of relatively large mass (10mg). Previous attempts of DSC tests applied to spider silk samples failed to detect thermal transitions in a conclusive way. The tests reported here, however, show thermal transitions on both natural and regenerated samples that are in agreement with results from dynamic mechanical analysis (DMA) tests reported in the literature. The water content on spider silks seems to lower the temperatures at which such thermal transitions take place. The results also confirm that the amorphous regions of native and regenerated spider silk and silk worm silk give rise to similar thermal transitions.

Biocompatibility of bacterial cellulose based biomaterials.

Some bacteria can synthesize cellulose when they are cultivated under adequate conditions. These bacteria produce a mat of cellulose on the top of the culture medium, which is formed by a three-dimensional coherent network of pure cellulose nanofibers. Bacterial cellulose (BC) has been widely used in different fields, such as the paper industry, electronics and tissue engineering due to its remarkable mechanical properties, conformability and porosity. Nanocomposites based on BC have received much attention, because of the possibility of combining the good properties of BC with other materials for specific applications. BC nanocomposites can be processed either in a static or an agitated medium. The fabrication of BC nanocomposites in static media can be carried out while keeping the original mat structure obtained after the synthesis to form the final nanocomposite or by altering the culture media with other components. The present article reviews the issue of biocompatibility of BC and BC nanocomposites. Biomedical aspects, such as surface modification for improving cell adhesion, in vitro and in vivo studies are given along with details concerning the physics of network formation and the changes that occur in the cellulose networks due to the presence of a second phase. The relevance of biocompatibility studies for the development of BC-based materials in bone, skin and cardiovascular tissue engineering is also discussed.

Structure-property relationships of a biopolymer network: the eggshell membrane.

The eggshell membrane (ESM) is a biopolymer network that may have potential applications in biomedicine, but it also may reveal important details regarding the behaviour of biopolymer networks. In this paper, we have studied the mechanical and morphological properties of the ESM in order to reveal important structure-property relationships. Light optical microscopy and atomic force microscopy were used to assess the morphology of the ESM. The mechanical properties of membranes and individual fibres were studied by means of tensile tests and nanoindentation tests, respectively. The mechanical behaviour of ESM networks in different environmental conditions showed a non-linear and a linear regime. As for elastomers and other biopolymer systems, the non-linear regime was modelled by the Mooney-Rivlin relation. The Young's modulus in the linear regime of the network was related to the Young's modulus of the individual fibres using Gibson and Ashby analysis for cellular solids. The results of morphological characterization were used to relate the properties of individual fibres to the properties of the whole networks. This enabled us to predict the macroscopical properties of the network based on the properties of the individual fibres. It was found that the ESM networks behaved as both Mooney-Rivlin and Hookean materials in different environmental conditions. This study helps elucidate the properties of the biopolymer networks found in nature and describes important mechanical properties for the use of the ESM as a biomaterial.

Processing and characterization of porous structures from chitosan and starch for tissue engineering scaffolds.

Natural biodegradable polymers were processed by different techniques for the production of porous structures for tissue engineering scaffolds. Potato, corn, and sweet potato starches and chitosan, as well as blends of these, were characterized and used in the experiments. The techniques used to produce the porous structures included a novel solvent-exchange phase separation technique and the well-established thermally induced phase separation method. Characterization of the open pore structures was performed by measuring pore size distribution, density, and porosity of the samples. A wide range of pore structures ranging from 1 to 400 microm were obtained. The mechanisms of pore formation are discussed for starch and chitosan scaffolds. Pore morphology in starch scaffolds seemed to be determined by the initial freezing temperature/freezing rate, whereas in chitosan scaffolds the shape and size of pores may have been determined by the processing route used. The mechanical properties of the scaffolds were assessed by indentation tests, showing that the indentation collapse strength depends on the pore geometry and the material type. Bioactivity and degradation of the potential scaffolds were assessed by immersion in simulated body fluid.