Preparation of nanoparticles by crosslinking folate conjugated chitosan with vanillin and its characterization

Functionalized chitosan (CS) were widely used as drug delivery system in the chemotherapy of various disease. In this work, folate (FA) was conjugated into chitosan molecular as targeting ligand based on Schiff reaction between –NH₂ group of CS and –COOH group of FA. And nanoparticles were made by emulsion method with vanillin novel cross-linking agent. The FA modified CS and its nanoparticles were characterized by Fourier transform spectroscopy (FT-IR), scanning electron microscope (SEM) and Zeta potential. SEM results confirmed the nanoparticles made from FA-CS conjugate were spherical in shape and were about 100 nm in size. Zeta potential analysis revealed that the nanoparticles were negatively charged with charge density of -7.73mV.

Crosslinking neat ultrathin films and nanofibres of pH-responsive poly(acrylic acid) by UV radiation

Electrospun polyelectrolyte hydrogel nanofibres are being developed for many applications including artificial muscles, scaffolds for tissue engineering, wound dressings and controlled drug release. For electrospun polyelectrolytes, a post-spinning crosslinking process is necessary for producing a hydrogel. Typically, radiation or thermal crosslinking routines are employed that require multifunctional crosslinking molecules and crosslink reaction initiators (free radical producers). Here, ultraviolet subtype-C (UVC) radiation was employed to crosslink neat poly(acrylic acid) (PAA) nanofibres and films to different crosslink densities. Specific crosslink initiators or crosslinking molecules are not necessary in this fast and simple process providing an advantage for biological applications. Scanning probe microscopy was used for the first time to measure the dry and wet dimensions of hydrogel nanofibres. The diameters of the swollen fibres decrease monotonically with increasing UVC radiation time. The fibres could be reversibly swollen/contracted by treatment with solutions of varying pH, demonstrating their potential as artificial muscles. The surprising success of UVC radiation exposure to achieve chemical crosslinks without a specific initiator molecule exploits the ultrathin dimensions of the PAA samples and will not work with relatively thick samples.

Simultaneous polymerization and crosslinking for the synthesis of molecular-level graphene oxide-polyacryl amide-CeOx composites

Synthesis of molecular-level multiple-component composites are particularly challenging due to the lack of direct bonding among different components. In this study, molecular-level graphene oxide (GO)-polyacryl amide (PAM)-CeOx composites were successfully synthesized, using the simultaneous polymerization and crosslinking strategy. Attenuated total reflection Fourier transform infrared (ATR-FTIR) and nuclear magnetic resonance (NMR) techniques confirmed that polyacryl amide (PAM) chains were successfully grafted onto the surface of GO. X-ray photoelectron spectroscopic (XPS) and X-ray diffraction (XRD) analyses further revealed the characteristic signals of cerium elements and CeO2 phase respectively. Scanning electron microscopy (SEM) showed that the surface morphology of the GO-PAM-CeOx composites was substantially thicker and rougher than those of the original GO. Further exploration of the reaction mechanism clearly demonstrate the existence of strong chelating interaction among PAM chains and Ce(IV) ions. In particular, the polymerization of acryl amide monomers and the crosslinking reaction between PAM and Ce(IV) or Ce(III) ions were realized simultaneously, leading to the final formation of molecular-level GO-PAM-CeOx composites. Moreover, the as-synthesized GO-PAM-CeOx composites were capable of effectively decomposing Rhodamine B under simulated sunlight, making it a potential candidate as a new photo catalyst. To sum up, this report demonstrates the potential utility of simultaneous polymerization and crosslinking method for the synthesis of other multiple-component composites at molecular-level.

Studies on the crosslinking of electrospun starch nanofibers

The starch nanofiber mats were prepared by electrospinning, and crosslinked by deal with glutaraldehyde vapor in a sealed containers. The morphology and structure of the fibers (before and after crosslinking) were characterized by SEM and FT-IR, and the properties of the product were measured by tensile test and contact angle measurements. Test results show that, acetalization reaction occurred between the intermolecular of glutaraldehyde and starch, the morphology of crosslinked fibers can be grossly preserved compared with the uncrosslinked starch fibers, and tensile properties and water resistance of the fiber mats have been greatly improved after glutaraldehyde crosslinking.

Effect of vapor-phase glutaraldehyde crosslinking on electrospun starch fibers

In this work, we have proven that starch nanofibrous membranes with high tensile strength, water stability and non-cytotoxicity can be produced by electrospinning of starch solution and post-treatment with GTA in vapor phase. GTA vapor phase crosslinking plays a key role in forming water-stable nanofiber membrane and improving the mechanical properties. Comparing with non-crosslinked starch fibers, the crosslinked fibers are increased by nearly 10 times in tensile strength. The crosslinked starch fibrous membranes are non-cytotoxic. They may find applications in the fields of tissue engineering, pharmaceutical therapy and medical.

Effects of MWNT nanofillers on structures and properties of PVA electrospun nanofibres

In this study, we have electrospun poly(vinyl alcohol)(PVA) nanofibres and PVA composite nanofibres containing multi-wall carbon nanotubes (MWNTs) (4.5 wt%), and examined the effect of the carbon nanotubes and the PVA morphology change induced by post-spinning treatments on the tensile properties, surface hydrophilicity and thermal stability of the nanofibres. Through differential scanning calorimetry (DSC) and wide-angle x-ray diffraction (WAXD) characterizations, we have observed that the presence of the carbon nanotubes nucleated crystallization of PVA in the MWNTs/PVA composite nanofibres, and hence considerably improved the fibre tensile strength. Also, the presence of carbon nanotubes in PVA reduced the fibre diameter and the surface hydrophilicity of the nanofibre mat. The MWNTs/PVA composite nanofibres and the neat PVA nanofibres responded differently to post-spinning treatments, such as soaking in methanol and crosslinking with glutaric dialdehyde, with the purpose of increasing PVA crystallinity and establishing a crosslinked PVA network, respectively. The presence of carbon nanotubes reduced the PVA crystallization rate during the methanol treatment, but prevented the decrease of crystallinity induced by the crosslinking reaction. In comparison with the crosslinking reaction, the methanol treatment resulted in better improvement in the fibre tensile strength and less reduction in the tensile strain. In addition, the presence of carbon nanotubes reduced the onset decomposition temperature of the composite nanofibres, but stabilized the thermal degradation for the post-spinning treated nanofibres. The MWNTs/PVA composite nanofibres treated by both methanol and crosslinking reaction gave the largest improvement in the fibre tensile strength, water contact angle and thermal stability.

Toughened electrospun nanofibers from crosslinked elastomer-thermoplastic blends

A crosslink-able elastomeric polyester urethane (PEU) was blended with a thermoplastic, polyacrylonitrile (PAN), and electrospun into nanofibres. The effects of the PEU/PAN ratio and the crosslinking reaction on the morphology and the tensile properties of the as-spun fibre mats were investigated. With the same overall polymer concentration (9 wt %), the nanofibre containing higher composition of PEU shows a slight decrease in the average fibre diameter, but the tensile strength, the elongation at break and tensile modulus of the nanofibre mats are all improved. These tensile properties are further enhanced by slight crosslinking of the PEU component within the nanofibres.

Time-of-flight secondary ion mass spectrometry investigation of epoxy resin curing behavior in real time

Time-of-flight secondary ion mass spectrometry and principal components analysis were used in real time to monitor the progress of curing reactions on the surface of a diglycidyl ether of bisphenol A (DGEBA) and diglycidyl ether of bisphenol F (DGEBF) epoxy resin blend reacted with the diamine hardener isophorone diamine at different time intervals. Molecular ions in the mass spectra that characterized the curing reactions steps, including blocking, coupling, branching, and crosslinking, were identified. The aliphatic hydrocarbon ions were correlated to the curing reaction rate, and this indicated that coupling and branching occurred much faster than the blocking and crosslinking curing reactions steps. The total conversion of the coupling and branching reaction steps were followed on the basis of changes with time in the relative ion intensity of molecular ions assigned to the DGEBA/DGEBF, aliphatic hydrocarbon, epoxide, and aromatic ring structures. Indicative measures of crosslinking density were monitored through the observation of changes in the ratio of the relative intensities of the aliphatic hydrocarbon and hydroxyl molecular ions over time. The curing reaction conversion was established by the observation of the changes in the relative ion intensity of the molecular ions that were related to the DGEBA/ DGEBF molecules.

Polymer-in-ionic-liquid electrolytes

In order to achieve high conductivity in a polymer electrolyte, polymer-in-ionic-liquid electrolytes have been explored. It is found in this study that poly[vinylpyrrolidone-co-(vinyl acetate)] (P(VP-c-VA)) in 1-ethyl-3-methylimidazolium bis(trifluoromethyl sulfonyl) amide (EtMeIm+Tf2N−) and poly(N,N-dimethyl acrylamide) (PDMAA) in trimethyl butyl ammonium bis(trifluoromethane sulfonyl) amide (N1114+Tf2N−) produce ion-conducting liquids and gels. The P(VP-c-VA)/ EtMeIm+Tf2N− mixture has a conductivity around 10−3 S · cm−1 at 22 °C, for copolymer concentrations up to 30 wt.-%. Thermal analysis shows that the Tg of the P(VP-c-VA)/ EtMeIm+Tf2N− system is well described by the Fox equation as a function of polymer content. Poly(methyl methacrylate) (PMMA)/ EtMeIm+Tf2N− gel electrolytes were prepared by in-situ polymerisation of the monomer in the ionic liquid. In the presence of 0.5–2.0 wt.-% of a crosslinking agent, these PMMA-based electrolytes displayed elastomeric properties and high conductivity (ca. 10−3 S · cm−1) at room temperature.

Simultaneous incorporation of 5-fluorouracil and leucovorin into chitosan nanoparticle as drug carrier and its characterization

A combined drug loaded system containing two most common anti-cancer drugs 5-fluorouracil (5-FU) and leucovorin (LV) was designed and prepared by ion crosslinking technology. The resulted nanoparticles are spherical in shape, and the particle size becomes larger when drug combination are loaded. Efficient drug encapsulation efficiency (EE) and drug loading (LC) are obtained due to the strong interaction between drugs and polymer. The combined drugs are distributed in the particles in amorpholous state which are demonstrated by the XRD results.

Formulation of vanillin cross-linked chitosan nanoparticles and its characterization.

Chitosan nanoparticles were successfully prepared by chemical cross-linking with vanillin. The nanoparticles were spherical in shape with smooth surface, and the average particle size of chitosan nanoparticles was 141 nm. The formulation of chitosan nanoparticles is based on Shiff reaction between aldehyde group of vanillin and amino group of chitosan. Chitosan nanoparticles prepared by crosslinking with vanillin are promising vehicle for the drug delivery of various anticancer drugs in the chemotherapy of cancers.

Carbon Nanotube Biofiber Formation in a Polymer-Free Coagulation Bath

A novel solution spinning method to produce highly conducting carbon nanotube (CNT) biofibers is reported. In this process, carbon nanotubes are dispersed using biomolecules such as hyaluronic acid, chitosan, and DNA, and these dispersions are used as spinning solutions. Unlike previous reports in which a polymer binder is used in the coagulation bath, these dispersions can be converted into fibers simply by altering the nature of the coagulation bath via pH control, use of a crosslinking agent, or use of a biomolecule-precipitating solvent system. With strength comparable to most reported CNT fibers to date, these CNT biofibers demonstrate superior electrical conductivities. Cell culture experiments are performed to investigate the cytotoxicity of these fibers. This novel fiber spinning approach could simplify methodologies for creating electrically conducting and biocompatible platforms for a variety of biomedical applications, particularly in those systems where the application of an electrical field is advantageous?for example, in directed nerve and/or muscle repair.

Molding micropatterns of elasticity on PEG-based hydrogels to control cell adhesion and migration

We present an innovative and simple, soft UV lithographic method “FIll-Molding In Capillaries” (FIMIC) that combines soft lithography with capillary force driven filling of micro-channels to create smooth hydrogel substrates with a 2D micro-pattern on the surface. The lithographic procedure involves the molding of a polymer; in our case a bulk PEG-based hydrogel, via UV-curing from a microfabricated silicon master. The grooves of the created regular line pattern are consequently filled with a second hydrogel by capillary action. As a result, a smooth surface is obtained with a well-defined pattern design of the two different polymers on its surface. The FIMIC method is very versatile; the only prerequisite is that the second material is liquid before curing in order to enable the filling process. In this specific case we present the proof of principle of this method by applying two hydrogels which differ in their crosslinking density and therefore in their elasticity. Preliminary cell culture studies on the fabricated elasticity patterned hydrogels indicate the preferred adhesion of the cells to the stiffer regions of the substrates, which implies that the novel substrates are a very useful platform for systematic cell migration studies, e.g. more fundamental investigation of the concept of “durotaxis”

Carbon nanotube based elastomer composites-an approach towards multifunctional materials

The current study focuses on giving a basic understanding of tubular graphene sheets or carbon nanotubes (CNTs) and points towards their role in fabricating elastomer composites. Since the properties and the performance of CNT reinforced elastomer composites predominantly depend on the rate of dispersion of fillers in the matrix, the physical and chemical interaction of polymer chains with the nanotubes, crosslinking chemistry of rubbers and the orientation of the tubes within the matrix, here, a thorough study of these topics is carried out. For this, various techniques of composite manufacturing such as pulverization, heterocoagulation, freeze drying, etc. are discussed by emphasizing the dispersion and alignment of CNTs in elastomers. The importance of the functionalization technique as well as the confinement effect of nanotubes in elastomer media is derived. In a word, this article is aimed exclusively at addressing the prevailing problems related to the CNT dispersion in various rubber matrices, the solutions to produce advanced high-performance elastomeric composites and various fields of applications of such composites, especially electronics. Special attention has also been given to the non-linear viscoelasticity effects of elastomers such as the Payne effect, Mullin's effect and hysteresis in regulating the composite properties. Moreover, the current challenges and opportunities for efficiently translating the extraordinary electrical properties of CNTs to rubbery matrices are also dealt with.