No description available.

No description available.

Cellulose nanofibers (CNFs) have established widespread attention in various industries with their potential applications. Production of CNFs from agricultural post harvesting wastes has several cost-effective and eco-friendly benefits. The objective of this research was to prepare four different types of CNFs from cotton stalks by different chemical treatments followed by ultra-sonication. CNFs via untreated bleached pulp, sulfuric acid hydrolysis, and TEMPO [(2,2,6,6-tetramethylpiperidin-1-yl) oxy radical]-mediated oxidation process were produced. Physical and chemical properties of these CNFs were investigated by morphological (FE-SEM, AFM), structural (FTIR), and thermal gravimetric analysis (TGA). Developed TEMPO-oxidized cellulose nanofibers (TEMPO-CNFs) were brighter and higher in yields (>90%). It was the first time uniform and very small sized (3-15 nm diameter and 10-100 nm length) nanofibers were produced. In application purpose, TEMPO-CNFs were introduced into chitosan matrix (prepared from shrimp exoskeletons) for the development of bionanocomposite food packaging films and into chitin for hydrogels preparation in order to eliminate heavy metals from water bodies. Development of bionanocomposite films (chitosan/TEMPO-CNFs compositions) was an effective and complete green approach with enhanced mechanical and barrier properties. Also use of TEMPO-CNFs in this method makes it possible to produce flexible, transparent, and low cost food packaging films with good antimicrobial activity against Salmonella enterica, E. coli O157:H7, and Listeria monocytogenes. In a similar way, generation of recyclable biobased adsorbents (chitin/TEMPO-CNFs compositions) with superior adsorption capacity and high surface area were effectively used in lead (Pb2+) removal from aqueous solutions, thus provide new opportunities as economical and environmentally friendly green remediation.

No description available.

No description available.

Anterior cruciate ligament (ACL) ruptures and tears are significant orthopedic problems that result in discomfort and limited mobility. Fully functional tissue engineered ligament replacements are promising alternatives to current graft choices for repair of ACL disruptions. The cell-based approach to construct engineered ligament grafts presented herein involves the culture of mesenchymal stem cells (MSC) on biodegradable, fibrous polymeric scaffolds to promote tissue formation. Multipotent MSCs are advantageous because of their in vitro proliferative capacity and ease of harvest; however; the promotion of MSC differentiation into mature fibroblasts and subsequent extracellular matrix (ECM) development is unknown. The proposed studies utilized three complementary methods to promote differentiation of MSCs: scaffold architecture, mechanical stretch and over-expression of the transcription factor, scleraxis. First, elastomeric scaffolds were fabricated by electrospinning a segmented poly(esterurethane urea) with variations in fiber diameter and fiber alignment. Primary mesenchymal stem cells and the mesenchymal stem cell line, C3H10T1/2, were seeded on these scaffolds and assumed spindle-shaped morphologies and oriented with the direction of fiber alignment. Fiber diameter affected cellular responses, including the expression of ECM genes (e.g. collagen type 1 and decorin) which were elevated on smaller mean fiber diameter scaffolds initially. However, scleraxis gene expression was greatest on larger mean fiber diameter scaffolds at the end of two weeks. Second, cyclic stretch was applied to C3H10T1/2 cells on semi-aligned scaffolds using a novel bioreactor. Cell attachment was verified during and after the application of mechanical stress by confocal microscopy. Cyclic stretch induced cells to assume a highly elongated morphology; however ECM gene expression changes were moderate. Third, forced constitutive expression of scleraxis was accomplished by nucleofection of C3H10T1/2 cells. Transient mRNA expression, accumulation of the gene product in the cell nucleus, and cell death were observed. Future work will seek to refine the experimental methods, including the development and testing of an inducible scleraxis transgene and the application of longer periods of mechanical stimulation. Finally, these complementary approaches may be combined to further extend this work in pursuit of directed differentiation of stem cells and the ensuing generation of a robust tissue graft. / Ph. D.

The state of adhesion of bacteria to nanofiber-textured model surfaces is analyzed at single-cell level. The results reveal similarities between the effect of topography on bacteria-surface interactions and vesicle-surface interactions. The results are discussed in the context of controlling bacterial adhesion to surfaces using nanofibrous topographical features. / Master of Science

In this study, we developed the manufacturing pathways of carbon nanofibers (CNF) and activated carbon nanofibers (ACNF) via the ¡§melt-spinning¡¨ method. A novel route based on the solvent-free core/sheath melt-spinning of polypropylene/ (phenol formaldehyde-polyethylene) (PP/(PF-PE)) to prepare CNF. The approach consists of three main steps: co-extrusion of PP (core) and a polymer blend of PF and PE (sheath), followed by melt-spinning, to form the core/sheath fibers; stabilization of core/sheath fibers to form the carbon fiber precursors; and carbonization of carbon fiber precursors to form the final CNF. Both scanning electron microscopy and transmission electron microscopy images reveal long and winding CNF with diameter 100 - 600 nm and length greater than 80 £gm. With a yield of ~ 45 % based on its raw material PF, the CNF exhibits regularly oriented bundles which curl up to become rolls of wavy long fibers with clean and smooth surface. Results from X-ray diffractometry, energy dispersive X-ray, Raman spectroscopy, and selected area electron diffraction patterns further reveal that the CNF exhibits a mixed phase of carbon with graphitic particles embedded homogeneously in an amorphous carbon matrix. The carbon atoms in CNF are evenly distributed in a matrix having a composition of 90 % carbon element and 10 % in oxygen element. A series of ACNF have also been prepared based on the chemical activation on the thus-prepared CNF; their morphological and microstructure characteristics were analyzed by scanning electron microscopy, atomic force microscopy (AFM), Raman spectroscopy, and X-ray diffractometry, with particular emphasis on the qualitative and quantitative AFM analysis. The effect of activating agent, potassium hydroxide and phosphorous acid, is compared; factors affecting the surface morphology and microstructure of ACNF are analyzed. The ACNF also exhibits a mixed phase of carbon with graphitic particles embedded homogeneously in an amorphous carbon matrix. The resulting ACNF consists of 73 % C element and 27 % O element. The total pore volume of the all activated ACNF is larger than that of un-activated CNF. It can be inferred that chemical activation by KOH results in increased micropore volume in carbon nanofibers; while the micropores produced by the chemical activation of H3PO4 may further be activated and then enlarged to become the mesopores at the expense of micropore volume. For the concentration effect of KOH on ACNF, it can be inferred that high concentration KOH activation results in increased SBET and micropore volume in carbon nanofibers. The average pore diameter of ACNF gradually decreases as the KOH concentration increases.

The objective of this work is to electrospin poly(acrylonitrile) (PAN) based nanofibers with controlled diameter and to stabilize and carbonize them for developing meso-porous carbon for application as electrochemical capacitor electrodes. A sacrificial polymer, poly(styrene-co-acrylonitrile) (SAN) has been used to control porosity. Carbon nanotubes (CNT) have been used to increase electrode conductivity and hence power density. The study has been divided into two parts. In part I, electrospinning behavior of PAN and PAN/CNT has been studied. The diameter of electrospun PAN fibers was monitored as a function of polymer molecular weight, solution concentration, solution flow rate, distance between the spinneret and the target, and the applied voltage. Bead free PAN fibers of 60 nm diameter have been electrospun. Various electrospun fibers have been characterized by wide angle X-ray diffraction and by Raman spectroscopy. Electrospinning process has been observed by high speed photography. In part II, the electrospun PAN, PAN/SAN, and PAN/SAN/CNT fiber mats were stabilized, carbonized, and processed into electrochemical capacitor electrodes. The performance of the electrochemical capacitors was tested by the constant current charge/discharge and cyclic voltammetry in 6 molar potassium hydroxide aqueous solution. The surface area and pore size distribution of the electrodes were measured using N2 adsorption and desorption. The effect of surface area and pore size distribution on the capacitance performance has been studied. The capacitance performance of various carbonized electrospun fibers mats have been compared to those of the PAN/SAN/CNT film, carbon nanotube bucky paper, and activated carbon pellet. The capacitance of PAN/SAN/CNT fiber mat over 200 F/g (at a current density of 1 A/g) and the power density approaching 1 kW/kg have been observed. Addition of 1 wt% carbon nanotubes in PAN/SAN, improves the power density by a factor of four. For comparison, the capacitance of single wall carbon nanotube bucky paper at a current density of 1 A/g is about 50 F/g.

Yes / In this study, we prepared chitosan (Cs_P) nanofibers (NFs) membrane by electrospinning. The Cs_P NFs membrane was then chemically functionalized (CsF) by a novel stepwise chemical process. The CsF NFs membrane was electrospray with TiO2 nanoparticles (NPs) to prepare the CsF_Coa NFs membrane. A second NFs membrane with embedded TiO2 NPs (Cs_Co) was also prepared by electrospinning. The TiO2 NPs, Cs_P, CsF s, CsF_Coa NFs, and Cs_Co NFs membranes were analyzed by standard spectroscopic, microscopic, X-ray, and thermal methods. Fourier transform infrared (FTIR) analysis confirmed the incorporation of the new functional group into the Cs structure. X-ray photoelectron spectroscopy (XPS) data confirmed the FTIR results and the fabrication of the CsF NFs membrane. Scanning electron microscope (SEM) micrographs showed a smooth morphology for the Cs_P NFs membrane and a denser morphology for the CsF NFs membrane (NFs swelled with functionalization). The SEM micrographs also showed a dense cloud of TiO2 NPs on the surface of the Cs_Coa NFs membrane. Transmission electron microscope (TEM) showed that the particle size of TiO2 NPs varied between 20 and 35 nm and tended to be spherical. The X-ray diffraction (XRD) pattern confirmed the existence of the anatase phase of the TiO2 NPs. The presence of TiO2 in the Cs_Coa and Cs_Co NFs membranes was also confirmed by energy-dispersive x-ray spectroscopy (EDX). Surface profilometry confirmed an increase in the surface roughness of the CsF and Cs_Coa NFs membranes. Brunauer–Emmett–Teller (BET) analysis revealed that the isotherms and hystereses for all NFs membranes were of the IV and H3 types, respectively, corresponding to mesopores and slit pores. The higher photocatalytic activity of the Cs_Coa NFs membrane (89%) compared to the Cs_Co NFs membrane (40%) was attributed to a balance between the short band gap, high surface roughness, and lower surface area.