Microwave-assisted synthesis of crosslinked ureido chitosan for hemostatic applications.

In this study, we present a facile method for introducing hydrophilic ureido groups (NH2-CO-NH-) into chitosan using a microwave-assisted reaction with molten urea, with the aim of enhancing chitosan's interaction with blood components for improved hemostasis. The formation of the ureido groups through nucleophilic addition reaction between the amine groups in chitosan and in situ generated isocyanic acid was confirmed by FTIR, CP/TOSS 13C NMR, and CP/MAS 15N NMR spectroscopic techniques. However, in stark contrast to the glucans, the said modification introduced extensive crosslinking in chitosan. Spectroscopic studies identified these crosslinks as carbamate bridges (-NH-COO-), which were likely formed by the reaction between the ureido groups and hydroxyl groups of adjacent chains through an isocyanate intermediate. These carbamate bridges improved ureido chitosan's environmental stability, making it particularly resistant to changes in pH and temperature. In comparison to chitosan, the crosslinked ureido chitosan synthesized here exhibited good biocompatibility and cell adhesion, rapidly arrested the bleeding in a punctured artery with minimal hemolysis, and induced early activation and aggregation of platelets. These properties render it an invaluable material for applications in hemostasis, particularly in scenarios that necessitate stability against pH variations and degradation.

Improving Hydrophobicity of Collagen with Silica Nanoparticles: Probing a Noncovalent Approach.

Collagen-based materials have a wide range of applications in wound care, tendon repair, cartilage repair, etc. Improving certain properties such as hydrophobicity can diversify the application areas. In this work, we investigated the noncovalent interactions of suitably functionalized silica nanoparticles with collagen for the possibility of improving hydrophobicity. Functionalization on silica nanoparticles was achieved via Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) or "click" reaction using surface grafting methods. Furthermore, we synthesized two different silica nanoparticles (SiNPs) functionalized with the fluorine-containing substrate or only with an aryl moiety (silica-g-4EMB and silica-g-ETFMB) for comparison. The functionalized SiNPs immobilized along with the model system trans-4-hydroxy-l-proline (HPA) (usually present in abundant quantities in collagen) have been probed using nuclear magnetic resonance (NMR) spin relaxation to appreciate the influence of SiNPs on HPA. Furthermore, we effectively utilized a saturated transfer difference (STD) NMR experiment to measure the interaction parameters between judiciously functionalized silica nanoparticles and substrates of interest. In essence, such a detailed study on noncovalent interactions employing an arsenal of experimental approaches facilitated the immobilization of suitably functionalized silica nanoparticles to collagen and leather (where collagen is a major constituent), leading to improvements in hydrophobicity.

Blocking and Deblocking of Diisocyanate to Synthesize Polyurethanes.

Diisocyanates, particularly toluene diisocyanate (TDI), are useful for the preparation of various polyurethanes with specific applications as leather-like materials, adhesives and insoles, etc. Blocking agents can be used for the operational simplicity and to reduce the hazards of TDI. In this paper, we reported the use of 3-(4-bromo-phenyl)-1H-pyrazole to block toluene diisocyanate (TDI). FTIR, NMR, thermogravimetric analysis, contact angle analysis and differential scanning calorimetry (DSC) were used for the characterization. The effectiveness of the blocking was confirmed by spectroscopic techniques. The DSC thermogram showed that blocked adducts deblock at 240 °C, causing the regeneration of TDI, and causing the diisocyanates to react with polyols of different molecular weights, forming polyurethanes. The characterization of the polyurethanes was performed by infrared spectroscopy, nuclear magnetic resonance spectroscopy, thermogravimetric analysis, differential scanning calorimetry and a contact angle study.

Hydroxyapatite nanophases augmented with selenium and manganese ions for bone regeneration: Physiochemical, microstructural and biological characterization.

Hydroxyapatite (HAP) nanopowders with different manganese (Mn) and selenium (Se) contents with Mn/Ca and Se/P molar ratio of 1 mol%, 2.5 mol% and 5 mol% were synthesized by wet-co-chemical precipitation method. The results revealed that with either Mn or Se doping, ion-substituted apatite phase was achieved with good crystallographic features. The combined evidence obtained from spectrometric techniques revealed that nanocrystalline HAP was effectively doped with Mn and Se ions, where Se in form of SeO32- replaced PO43- and Mn2+ replaced Ca2+. Mn and Se doped HAP samples exhibited rod-like and needle-like morphology with strong tendency to form agglomerates. HAP enriched with Mn and Se represented a strong antibacterial effect and also showed prominent blood compatibility. From the biocompatibility testing, it was evident that Mn and Se doped HAP augmented the osteoblasts adhesion, migration and proliferation in a dose-dependent manner. To conclude from this study, it is clearly evident that the doping amount of both Mn and Se ions can determine the size and morphology of the final HAP product. Therefore, Mn and Se HAP nanopowders with molar ratio less than 5 mol% without any heat treatment can provide good crystallographic features to HAP with satisfying micro-structural, thermal and biological properties.

Interplay between surface chemistry and osteogenic behaviour of sulphate substituted nano-hydroxyapatite.

Surface potential and chemical compositions of the bioceramics are the core of therapeutic effect and are key factors to trigger the interfacial interactions with surrounding hard and soft tissues to repair and regeneration. Ionic substitution in hydroxyapatite (Hap) lattice significantly influences the zeta potential from -16.46 ± 0.66 mV to -6.01 ± 0.68 mV as well as an average nano-rod length from ~40 nm to ~26 nm with respect to SO42- ion content. Moreover, the surface chemistry of Hap is mainly inter-related to SO42- substitution rate at PO42- site. Specifically, nano-sized feature with lowered negative surface potential influences the protein adsorption via their weak repulsive or attractive forces. Bovine serum albumin (BSA) and lysozyme (LSZ) adsorption studies confirmed the increased affinity to active binding sites of Hap's surface. Further, SO42- ion substituted Hap (SNHA) showed improved in vitro biomineralization activity and alkaline phosphatase activity. Expression of osteogenic biomarkers such as collagen I, V, osteopontin and osteocalcin were evaluated in Saos-2 and MC3T3-E1 cells. Gene expression of these markers was influenced by SO42- ion content in Hap (maximum with 10SNHA). Altogether, these data emphasizes that chemical composition and surface properties are dominant aspect in bioceramic development towards bone regeneration.

Copper (0) Mediated Single Electron Transfer-Living Radical Polymerization of Methyl Methacrylate: Functionalized Graphene as a Convenient Tool for Radical Initiator.

Polymer nanocomposites have been synthesized by the covalent addition of bromide-functionalized graphene (Graphene-Br) through the single electron transfer-living radical polymerization technique (SET-LRP). Graphite functionalized with bromide for the first time via an efficient route using mild reagents has been designed to develop a graphene based radical initiator. The efficiency of sacrificial initiator (ethyl α-bromoisobutyrate) has also been compared with a graphene based initiator towards monitoring their Cu(0) mediated controlled molecular weight and morphological structures through mass spectroscopy (MOLDI-TOF) and field emission scanning electron microscopy (FE-SEM) analysis, respectively. The enhancement in thermal stability is observed for graphene-grafted-poly(methyl methacrylate) (G-g-PMMA) at 392 °C, which may be due to the influence ofthe covalent addition of graphene, whereas the sacrificial initiator used to synthesize G-graft-PMMA (S) has low thermal stability as analyzed by TGA. A significant difference is noticed on their glass transition and melting temperatures by DSC. The controlled formation and structural features of the polymer-functionalized-graphene is characterized by Raman, FT-IR, UV-Vis spectroscopy, NMR, and zeta potential measurements. The wettability measurements of the novel G-graft-PMMA on leather surface were found to be better in hydrophobic nature with a water contact angle of 109 ± 1°.

Synthesis of Fluorophore Decorated Single-Walled Carbon Nanotubes for In-Vitro Cytocompatibility.

We report rhodamine based fluorophore derivative for the stable dispersion of single-walled carbon nanotubes (SWCNTs), which can afford better fluorescent label to carbon nanotubes (CNTs). The nanotubes-fluorophore conjugates are helpful in achieving stable dispersion in polar and non-polar solvents with intense fluorescence. The product was characterized through NMR, Mass spectrometry, Raman, XPS, SEM, AFM and Fluorescence measurements. The formation of SWCNT-g- Rhodamine was confirmed by the presence of D and G bands in Raman spectrum. The alkyl and aryl groups in the range of 14.8, 17.6, 38.1 and 96.3 ppm confirms the grafting of the nanocomposite through NMR. The morphological studies were carried out intensively for analyzing SWCNTs stable dispersion and the results from EDAX measurements shows the elements weight% of C: 35.09 and N: 30.1 concludes that SWCNTs are completely grafted onto rhodamine derivatives. The application of SWCNTs fluorophore conjugates were analyzed by cell viability studies using MTT assay and exhibits less toxic compare to other functionalized CNTs. The viability of percentage increases with decrease in the concentration of SWCNT-COCl with 91.7% of live cells even after 24 h at a concentration of 250 µg for SWCNT-g-Rhodamine. The fluorescent images obtained during viability analysis shows enhanced fluorescence for living cells in case of SWCNT-g-Rhodamine compared to SWCNT-COCl, which clearly shows the utility of decorating nanotubes with fluorophore. This research work further extends its application for molecular sensing and other biological process.

Carbon Nanotube Reinforced Polymer-Stabilized Liquid Crystal Device: Lowered and Thermally Invariant Threshold with Accelerated Dynamics.

Polymer-stabilized liquid crystal (PSLC) devices comprise a polymer matrix in an otherwise continuous phase of liquid crystal. The fibrils of the polymer provide, even in the bulk, virtual surfaces with finite anchoring energy resulting in attractive electro-optic properties. Here, we describe a novel variation of the PSLC device fabricated by reinforcing the polymer matrix with polymer-capped single-walled carbon nanotubes (CNTs). The most important outcome of this strengthening of the polymer strands is that the threshold voltage associated with the electro-optic switching becomes essentially temperature independent in marked contrast to the significant thermal variation seen in the absence of the nanotubes. The reinforcement reduces the magnitude of the threshold voltage, and notably accelerates the switching dynamics and the effective splay elasticity. Each of these attributes is quite attractive from the device operation point of view, especially the circuit design of the required drivers. The amelioration is caused by the polymer decorating CNTs being structurally identical to that of the matrix. The resulting good compatibility between CNTs and the matrix prevents the CNTs from drifting away from the matrix polymer, a lacuna in previous attempts to have CNTs in PSLC systems. The difference in the morphology, perhaps the primary cause for the effects seen, is noted in the electron microscopy images of the films.

Single-Walled Carbon Nanotubes Decorated with Polypyrrole-TiO2 Nanocomposites.

Nanomaterials decorated with polypyrrole were synthesized using two types of oxidants by chemical oxidative polymerization method. The interaction and influence of the addition of single-walled carbon nanotubes (SWCNTs) and titanium dioxide (TiO2) nanoparticles in polypyrrole (PPy) were studied using Fourier transform infrared spectroscopy and Raman spectroscopy. Thermal stability has been observed by using thermogravimetric analysis. Electrochemical properties were calculated by using Cyclic Voltammetry to study comparative analysis between samples. Particle size measurements and morphology were determined by Field emission transmission electron microscopy. All the nanocomposites exhibit better thermal and electrochemical properties than native polymer. The size of the polypyrrole particles were in the range of 50 nm to 60 nm.

Controlled decoration of the surface with macromolecules: polymerization on a self-assembled monolayer (SAM).

Polymer functionalized surfaces are important components of various sensors, solar cells and molecular electronic devices. In this context, the use of self-assembled monolayer (SAM) formation and subsequent reactions on the surface have attracted a lot of interest due to its stability, reliability and excellent control over orientation of functional groups. The chemical reactions to be employed on a SAM must ensure an effective functional group conversion while the reaction conditions must be mild enough to retain the structural integrity. This synthetic constraint has no universal solution; specific strategies such as "graft from", "graft to", "graft through" or "direct" immobilization approaches are employed depending on the nature of the substrate, polymer and its area of applications. We have reviewed current developments in the methodology of immobilization of a polymer in the first part of the article. Special emphasis has been given to the merits and demerits of certain methods. Another issue concerns the utility - demonstrated or perceived - of conjugated or non-conjugated macromolecules anchored on a functionally decorated SAM in the areas of material science and biotechnology. In the last part of the review article, we looked at the collective research efforts towards SAM-based polymer devices and identified major pointers of progress (236 references).

The influence of applied silica nanoparticles on a bio-renewable castor oil based polyurethane nanocomposite and its physicochemical properties.

Novel bio-renewable castor oil based polyurethane (PU)-silica nanocomposite films were prepared using castor oil, 1,6-hexamethylene diisocyanate and dibutyltin dilaurate in tetrahydrofuran at room temperature. ATR-FTIR spectra confirm the formation of polyurethane and the presence of silica nanoparticles in the polyurethane matrix. The increase of Si nanoparticle content shifts the peak position of N-H and C[double bond, length as m-dash]O (both hydrogen and non-hydrogen bonded) groups present in the polyurethane structure. Furthermore, Raman spectra confirmed the urethane-amide interaction present in the polyurethane-silica nanocomposites. (29)Si CP/MAS NMR spectra evidence the formation and the presence of completely condensed SiO2 species in the polyurethane nanocomposite films. The incorporation of silica nanoparticles increases the thermal stability of the above-mentioned polyurethane films, which can be seen from the increase in activation energy (Ea) values of the degradation process. The Ea values at two stages (Tmax1 and Tmax2) of the degradation process are 133, 139 and 157, 166 kJ mol(-1) for PU control and PU-5AMS (5 wt% amine modified silica nanoparticles), respectively. DSC results prove the interfacial interaction present between silica nanoparticles and the polyurethane hard segment, which decreases the melting temperature. Optical transmittance of the polyurethane films decreased with increasing silica content due to the scattering at the interfaces between the silica nanoparticles and polyurethane. It is interesting to note that the presence of silica nanoparticles gives reinforcement to polyurethane film, thereby increasing the storage modulus up to 24% for PU-5AMS. FE-SEM and HR-TEM images confirm the presence of silica nanoparticles in the polyurethane matrix.

The pH-sensitive polyampholyte nanogels: inclusion of carbon nanotubes for improved drug loading.

We report a simple and facile method to prepare a novel pH sensitive polyampholyte nanogel by copolymerizing vinylimidazole (VIM) with acrylic acid (AA) using functionalized single-walled carbon nanotubes (f-SWCNTs) (as reinforcing material) and cyanuric chloride via an intermolecular quaternization reaction. The polyampholyte nanogels have been characterized by various microscopic and spectroscopic methods. These studies reveal that incorporation of nanotubes in cross-linked copolymer of poly(vinylimidazole-co-acrylic acid) (PVI-co-AA) form polyampholyte nanogel with enhanced physical properties. The thermal experiments show that the introduction of f-SWCNTs into PVI-co-AA has significant impact on the thermal stability of nanogels. The rheological study showed that the nanogel is more viscoelastic than native gel. MTT assay indicates that the prepared polyampholyte gels possess biocompatibility and cell viability. The nanogel is also useful material to load water-soluble drug such as promethazine hydrochloride. The releasing profile of the drug from the nanogel clearly shows the pH-sensitive property of the material.

Physicochemical studies on polyurethane/siloxane cross-linked films for hydrophobic surfaces by the sol-gel process.

A series of castor oil based polyurethane/siloxane cross-linked films were prepared using castor oil, isophorone diisocyanate, and 3-aminopropyl trimethoxysilane by the sol-gel process. Fourier transform infrared (FT-IR) spectra reveal the cross-linking interaction between polyurethane and siloxane moieties, thereby shifting the peak position of characteristic N-H and C═O groups to higher wavenumber. (29)Si (silica) solid state nuclear magnetic resonance spectra were used to prove the formation of siloxane network linkage in the polyurethane system, thereby analyzing the Si environment present in the polyurethane/siloxane cross-linked films. The activation energy values at two stages (Tmax1 and Tmax2) for the degradation of polyurethane films were increased with increasing silane ratio. The calculated activation energy values for the higher silane ratio (1.5) are 136 and 170 kJ/mol at Tmax1 and Tmax2, respectively. From contact angle measurements, we observed that increasing siloxane cross-linking increased the hydrophobicity of the films. The optical transmittance obtained from ultraviolet-visible spectra indicated that the film samples are transparent in the region 300-800 nm. The moisture sorption/desorption isotherm curve shows a characteristic behavior of type III isotherm corresponds to hydrophobic materials. Dynamic mechanical studies show that the increase in storage modulus reveals siloxane cross-linking gives rigidity to the films. Atomic force microscopic images show that the introduction of siloxane changes the surface roughness of the polyurethane films. It is found that the siloxane cross-linking can be used to obtain hydrophobic surface films having good thermal stability and optical transmittance.

Sol-gel network silica/modified montmorillonite clay hybrid nanocomposites for hydrophobic surface coatings.

Sol-gel silica/nanoclay composites were prepared through sol-gel polymerization technique using tetraethylorthosilicate precursor and montmorillonite (MMT) clay in aqueous media. In this study, both montmorillonite-K(+) and organically modified MMT (OMMT) clays were used. The prepared composites were coated on glass substrate by making 1 wt% solution in ethyltrichlorosilane. The incorporation of nanoclay does not alter the intensity of characteristic Si-O-Si peak of silica network. Thermogravimetric studies show that increasing clay content increased the degradation temperature of the composites. Differential scanning calorimetry (DSC) results of organically modified MMT nanoclay incorporated composite show a shift in the melting behavior up to 38°C. From DSC thermograms, we observed that the ΔH value decreased with increasing clay loading. X-ray diffraction patterns prove the presence of nanoclay in the composite and increase in the concentration of organically modified nanoclay from 3 to 5 wt% increases the intensity of the peak at 2θ=8° corresponds to OMMT. Morphology of the control silica gel composite was greatly influenced by the incorporation of OMMT. The presence of nanoclay changed the surface of control silica gel composite into cleaved surface with brittle in nature. Contact angle measurements were done for the coatings to study their surface behavior. These hybrid coatings on glass substrate may have applications for hydrophobic coatings on leather substrate.

Mesoporous and biocompatible surface active silica aerogel synthesis using choline formate ionic liquid.

In this paper, we report the preparation and characterization of mesoporous and biocompatible transparent silica aerogel by the sol-gel polymerization of tetraethyl orthosilicate using ionic liquid. Choline cation based ionic liquid allows the silica framework to form in a non collapsing environment and controls the pore size of the gel. FT-IR spectra reveal the interaction of ionic liquid with surface -OH of the gel. DSC thermogram giving the evidence of confinement of ionic liquid within the silica matrix, which helps to avoid the shrinkage of the gel during the aging process. Nitrogen sorption measurements of gel prepared with ionic liquid exhibit a low surface area of 100.53 m2/g and high average pore size of 3.74 nm. MTT assay proves the biocompatibility and cell viability of the prepared gels. This new nanoporous silica material can be applied to immobilize biological molecules, which may retain their stability over a longer period.