Distinct Roles of Tensile and Compressive Stresses in Graphitizing and Properties of Carbon Nanofibers

It is generally accepted that inducing molecular alignment in a polymer precursor via mechanical stresses influences its graphitization during pyrolysis. However, our understanding of how variations of the imposed mechanics can influence pyrolytic carbon microstructure and functionality is inadequate. Developing such insight is consequential for different aspects of carbon MEMS manufacturing and applicability, as pyrolytic carbons are the main building blocks of MEMS devices. Herein, we study the outcomes of contrasting routes of stress-induced graphitization by providing a comparative analysis of the effects of compressive stress versus standard tensile treatment of PAN-based carbon precursors. The results of different materials characterizations (including scanning electron microscopy, Raman and X-ray photoelectron spectroscopies, as well as high-resolution transmission electron microscopy) reveal that while subjecting precursor molecules to both types of mechanical stresses will induce graphitization in the resulting pyrolytic carbon, this effect is more pronounced in the case of compressive stress. We also evaluated the mechanical behavior of three carbon types, namely compression-induced (CIPC), tension-induced (TIPC), and untreated pyrolytic carbon (PC) by Dynamic Mechanical Analysis (DMA) of carbon samples in their as-synthesized mat format. Using DMA, the elastic modulus, ultimate tensile strength, and ductility of CIPC and TIPC films are determined and compared with untreated pyrolytic carbon. Both stress-induced carbons exhibit enhanced stiffness and strength properties over untreated carbons. The compression-induced films reveal remarkably larger mechanical enhancement with the elastic modulus 26 times higher and tensile strength 2.85 times higher for CIPC compared to untreated pyrolytic carbon. However, these improvements come at the expense of lowered ductility for compression-treated carbon, while tension-treated carbon does not show any loss of ductility. The results provided by this report point to the ways that the carbon MEMS industry can improve and revise the current standard strategies for manufacturing and implementing carbon-based micro-devices

Stress-induced stabilization of pyrolyzed polyacrylonitrile and carbon nanotubes electrospun fibers

The unique properties of graphitic carbons have gained widespread attention towards their development and application. Carbon materials can be synthesized by thermal decomposition and, more specifically, carbon pyrolysis from polymer precursors. The paper shows the pyrolysis process of polyacrylonitrile (PAN) in the presence of multi-walled carbon nanotubes (MWCNTs) according to different manufacturing process conditions. The electrospinning process of the PAN-MWCNTs solution on multi-plates collectors was firstly analyzed. The morphology and the particles arrangement of the electrospun fibers was studied under scanning and transmission electron microscopes. Moreover, the composite fibrous mats were characterized by RAMAN spectroscopy to identify the effects of a mechanical tension application during the thermal stabilization phase performed before the pyrolysis treatment to obtain carbon fibers from the precursor polymer. The results show that the graphitization of the pyrolyzed fibers is enhanced by the combination of MWCNTs and a mechanical stress applied during the thermal treatment

Nanocellulose Paper Semiconductor with a 3D Network Structure and Its Nano-Micro-Macro Trans-Scale Design

Semiconducting nanomaterials with 3D network structures exhibit various fascinating properties such as electrical conduction, high permeability, and large surface areas, which are beneficial for adsorption, separation, and sensing applications. However, research on these materials is substantially restricted by the limited trans-scalability of their structural design and tunability of electrical conductivity. To overcome this challenge, a pyrolyzed cellulose nanofiber paper (CNP) semiconductor with a 3D network structure is proposed. Its nano-micro-macro trans-scale structural design is achieved by a combination of iodine-mediated morphology-retaining pyrolysis with spatially controlled drying of a cellulose nanofiber dispersion and paper-crafting techniques, such as microembossing, origami, and kirigami. The electrical conduction of this semiconductor is widely and systematically tuned, via the temperature-controlled progressive pyrolysis of CNP, from insulating (1012 ω cm) to quasimetallic (10-2 ω cm), which considerably exceeds that attained in other previously reported nanomaterials with 3D networks. The pyrolyzed CNP semiconductor provides not only the tailorable functionality for applications ranging from water-vapor-selective sensors to enzymatic biofuel cell electrodes but also the designability of macroscopic device configurations for stretchable and wearable applications. This study provides a pathway to realize structurally and functionally designable semiconducting nanomaterials and all-nanocellulose semiconducting technology for diverse electronics.Koga H., Nagashima K., Suematsu K., et al. Nanocellulose Paper Semiconductor with a 3D Network Structure and Its Nano-Micro-Macro Trans-Scale Design. ACS Nano, 16(6), 8630-8640, 2022. https://doi.org/10.1021/acsnano.1c10728

Smart dressings based on bacterial cellulose for chronic wounds healing and monitoring

In recent years, there has been an upward trend for novel biomass based green materials for dressing chronic wounds, which can assist in wound healing and monitoring. This research focuses on candidate components for smart chronic wound dressings based on bacterial cellulose (BC), which is comprised of two parts: antimicrobial BC nanocomposites for wound dressing, and a BC-derived pH sensor for monitoring chronic wounds. This research demonstrates a novel ability to utilise BC and BC-derived nanocomposites in potential applications for smart wound dressings. In the chapter regarding BC production, samples grown in static from four different Acetobacter bacterial strains are characterized and compared for the first time. SEM and BET results demonstrate a large surface area (>100 m2/g) and XRD analysis reveals high crystallinity (>60%). In vitro cell tests indicate potential biocompatibility. In the BC based pH sensor chapter, a pyrolyzed BC (p-BC) aerogel was incorporated with polyaniline (PANI) and polydimethylsiloxane (PDMS), exhibiting near-Nernst pH sensitivity (50.4 mV/pH). In the chapter on antimicrobial BC nanocomposites, the inorganic BC/silver nanoparticle (BC/AgNP) and organic BC/lysozyme, BC/eggshell membrane (BC/ESM), BC/methylglyoxal (BC/MGO) nanocomposites were fabricated and characterized, with BC/ESM and BC/MGO nanocomposites proposed for the first time. The antimicrobial properties were tested via a disk diffusion method, with BC/MGO exhibiting the greatest antimicrobial activity, with diameters of inhibition zone (DIZ) up to 17.1 ± 0.6 mm against S. aureus and 15.5 ± 0.5 mm against E. coli. Tensile tests show the nanocomposites still retain the high tensile strength of plain BC (>2 MPa). These results indicate that BC and BC-derived nanocomposites are promising candidate materials for smart wound dressings. The future work will focus on more detailed in vitro biocompatibility tests and in vivo wound healing assays

Nanocellulose from the Appalachian Hardwood Forest and Its Potential Applications

Nanofibrillated cellulose (NFCs) are nanoscale fibers of high aspect ratio that can be isolated from a wide variety of cellulosic sources, including wood and bacterial cellulose. With high strength despite of their low density, NFCs are a promising renewable building block for the preparation of nanostructured materials and composites. To fabricate NFC-based materials with improved mechanical and chemical properties and additional new functionalities for different applications, it is essential to tailor the surface properties of individual NFCs. The surface structures control the interactions between NFCs and ultimately dictate the structure and macroscale properties of the bulk material. This research was focused on determining the feasibility of using hardwood residues from the Appalachian Hardwood Forest for the production of nanofibrillated cellulose (NFC). In addition, some modifications during the NFC production process were performed to evaluate their improvement to incorporate more antimicrobial copper in the cellulosic backbone. This thesis has been divided in the following main chapters: 1) Literature review regarding to nanocellulosic materials and their production processes, 2) Nanocellulose current and potential applications, 3) Nanofibrillated cellulose from the Appalachian Hardwood logging residues, 4) Modified nanofibrillated from the Appalachian Hardwood logging residues, 5) Preparation of nanocellulose using ionic liquids -- A review, 6) Nanocellulose-based drug delivery system -- A review, 7) Safety aspects on the utilization of lignocellulosic based materials - A review

Beyond Covalent Crosslinks: Applications of Supramolecular Gels

Traditionally, gels have been defined by their covalently cross-linked polymer networks. Supramolecular gels challenge this framework by relying on non-covalent interactions for self-organization into hierarchical structures. This class of materials offers a variety of novel and exciting potential applications. This review draws together recent advances in supramolecular gels with an emphasis on their proposed uses as optoelectronic, energy, biomedical, and biological materials. Additional special topics reviewed include environmental remediation, participation in synthesis procedures, and other industrial uses. The examples presented here demonstrate unique benefits of supramolecular gels, including tunability, processability, and self-healing capability, enabling a new approach to solve engineering challenges. Keywords: supramolecular gel; self-assembly; gels; applied soft matte

Protein and Polysaccharide-Based Fiber Materials Generated from Ionic Liquids: A Review.

Natural biomacromolecules such as structural proteins and polysaccharides are composed of the basic building blocks of life: amino acids and carbohydrates. Understanding their molecular structure, self-assembly and interaction in solvents such as ionic liquids (ILs) is critical for unleashing a flora of new materials, revolutionizing the way we fabricate multi-structural and multi-functional systems with tunable physicochemical properties. Ionic liquids are superior to organic solvents because they do not produce unwanted by-products and are considered green substitutes because of their reusability. In addition, they will significantly improve the miscibility of biopolymers with other materials while maintaining the mechanical properties of the biopolymer in the final product. Understanding and controlling the physicochemical properties of biopolymers in ionic liquids matrices will be crucial for progress leading to the ability to fabricate robust multi-level structural 1D fiber materials. It will also help to predict the relationship between fiber conformation and protein secondary structures or carbohydrate crystallinity, thus creating potential applications for cell growth signaling, ionic conductivity, liquid diffusion and thermal conductivity, and several applications in biomedicine and environmental science. This will also enable the regeneration of biopolymer composite fiber materials with useful functionalities and customizable options critical for additive manufacturing. The specific capabilities of these fiber materials have been shown to vary based on their fabrication methods including electrospinning and post-treatments. This review serves to provide basic knowledge of these commonly utilized protein and polysaccharide biopolymers and their fiber fabrication methods from various ionic liquids, as well as the effect of post-treatments on these fiber materials and their applications in biomedical and pharmaceutical research, wound healing, environmental filters and sustainable and green chemistry research

Development of electrochemical biosensors and sensors for the determination of interest analytes

Se han puesto a punto varios métodos electroquímicos para la determinación de varios analitos de interés, como lactato, cloruro, bromuro y yoduro utilizando sistemas electródicos serigrafiados (SPEs). Su bajo costo, tamaño pequeño, portabilidad para aplicaciones in situ, así como su facilidad de modificación, les confiere gran versatilidad, para ser usados como transductores en sensores y biosensores electroquímicos con gran precisión y sensibilidad en distintas matrices. Concretamente, se ha desarrollado un biosensor amperométrico para la determinación de lactato, basado en la utilización de la enzima lactato oxidasa. El biosensor ha permitido la determinación de este ácido orgánico en líquidos biológicos como saliva y sudor y en productos alimentarios como vinos. Se incluyen también estudios de los mecanismos de inhibición de las enzimas utilizadas en los biosensores. También se han puesto a punto sensores para la determinación de haluros, que han mostrado su aplicabilidad para su cuantificación en varios tipos de muestras

Advanced liposome-loaded scaffolds for therapeutic and tissue engineering applications

Liposome is one of the most commonly used drug delivery systems in the world, due to its excellent biocompatibility, satisfactory ability in controlling drug release, and passive targeting capability. However, some drawbacks limit the application of liposomes in clinical, such as problems in transporting, storing, and difficulties in maintaining the drug concentration in the local area. Scaffolds usually are used as implants to supply certain mechanical supporting to the defective area or utilized as diagnosis and imaging methods. But, in general, unmodified scaffolds show limited abilities in promoting tissue regeneration and treating diseases. Therefore, liposome-scaffold composite systems are designed to take advantages of both liposomes’ biocompatibility and scaffolds’ strength to provide a novel system that is more suitable for clinical applications. This review introduces and discusses different types of liposomes and scaffolds, and also the application of liposome-scaffold composite systems in different diseases, such as cancer, diabetes, skin-related diseases, infection and human immunodeficiency virus, and in tissue regeneration like bone, teeth, spinal cord and wound healing.Peer reviewe