• Volume 36, Issue 1

February 2013,   pages  1-182

• Carbon nanotubes purification constrains due to large Fe–Ni/Al2O3 catalyst particles encapsulation

Purification efficiency of carbon nanotubes (CNTs) by the method of chemical oxidation was considered as a function of position and size of catalyst remains and consequently of the tubes morphology. Oxidation of CNTs by means of both HNO3 and NaOH treatment efficiently removes small catalyst particles embedded in the tubes top, following tip-mode” CNTs growth mechanism. Destructive character of the purification can be assumed due to the resulting tiniest tube population increase as a consequence of their body tearing. However, limited purification efficiency was observed in the case of bigger metal particles with variable size and position in CNTs. Bigger particles occur on account of catalyst instability portrayed as small metal particles of active phase migration and merging. The formed agglomerates are not stable in the tubes hollow, but disintegrate leading to different sizes and position of metal particles in the tubes body. Consequently, CNT may be obtained with non-uniform thickness and morphology. The phenomenon is due to liquid-like behaviour of the active phase at reaction temperature (700 °C) which is higher than both Huttig and Tamman temperatures of applied metals. A mechanism is proposed assuming that an isolated bigger part of the mother particle stayed encapsulated inside the tube body inactive for further tube growth, while a smaller fragment of the collapsed particle resided at the tube top acting as a new-born active site. Owing to replica effect” the tube further grows thinner following the size of the new active site. Consequently CNTs of irregular morphology occur as they resemble metal particles of various sizes following their disintegration.

• X-ray reflectivity study of bias graded diamond like carbon film synthesized by ECR plasma

Diamond like carbon (DLC) coatings were deposited on silicon substrates by microwave electron cyclotron resonance (ECR) plasma CVD process using plasma of Ar and CH4 gases under the influence of negative d.c. self bias generated on the substrates by application of RF (13.56 MHz) power. The negative bias voltage was varied from −60 V to −150 V during deposition of DLC films on Si substrate. Detailed X-ray reflectivity (XRR) study was carried out to find out film properties like surface roughness, thickness and density of the films as a function of variation of negative bias voltage. The study shows that the DLC films constituted of composite layer i.e. the upper sub surface layer followed by denser bottom layer representing the bulk of the film. The upper layer is relatively thinner as compared to the bottom layer. The XRR study was an attempt to substantiate the sub-plantation model for DLC film growth.

• Investigation of magnetically enhanced swelling behaviour of superparamagnetic starch nanoparticles

The present study follows a novel strategy for the preparation of superparamagnetic nanoparticles of cross-linked starch impregnated homogeneously with nanosized iron oxide. The prepared magnetic nanoparticles were characterized by infra-red (FTIR) spectroscopy, transmission electron microscopy (TEM) and X-ray diffraction and magnetization studies. The size of the magnetic polymeric particles was found to lie in the range of 20–80 nm, and they exhibited superparamagnetic properties. The particles were allowed to swell in phosphate buffer saline (PBS) and the influence of factors such as chemical composition of nanoparticles, pH and temperature of the swelling bath and applied magnetic field was investigated on the water intake capacity of the nanoparticles. The prepared nanoparticles showed potential to provide a possible option for controlled and targeted delivery of anticancer drugs, applying external magnetic field.

• Discrepancy of room temperature ferromagnetism in Mo-doped In2O3

Molybdenum-doped indium oxide nanopowders were synthesized via mechanical alloying with subsequent annealing at a relatively low temperature of 600 °C. Themorphologies and crystal structures of the synthesized nanopowders were examined by using scanning electron microscopy (SEM) and X-ray diffraction patterns. X-ray diffraction pattern of the milled mixture shows the presence of both In2O3 phase and Mo element. The presence of broad peaks in the pattern confirms that the synthesized powders are nanosized. The X-ray diffraction of annealed samples at 600 °C shows the absence of Mo peaks revealing that the Mo was incorporated into the crystal lattices of In2O3. Interestingly, it was observed that the diffraction peaks were still broad in the annealed samples indicating the single phase at the nanoscale. From the XRD pattern, the calculated crystallite sizes were in the range of 12–18 nm. Magnetic properties of the synthesized Mo-doped In2O3 nanopowders were examined and it was found that the obtained nanopowders possess diamagnetic properties.

• Electrical and optical studies in polyaniline nanofibre–SnO2 nanocomposites

Polyaniline nanofibre–tin oxide (PAni-SnO2) nanocomposites are synthesized and mixed with polyvinyl alcohol (PVA) as stabilizer to cast free-standing films. Composite films are characterized by X-ray diffraction studies (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), photoluminescence spectroscopy (PL) and UV-visible spectroscopy. XRD confirms the formation of PAni nanofibre–SnO2 nanocomposite. From TEM images, diameter of the polyaniline nanofibre and SnO2 nanoparticles in the PAni-SnO2 nanocomposite are found to be 20–60 nm. SEM results show fibrous morphology of the PAni nanofibre and spherical morphology of polyaniline-SnO2 composites. The nanocomposites exhibit high relative photoluminescence intensity in violet as well as green–yellow region of visible spectrum. From electrical conductivity measurement, it is confirmed that PAni nanofibre–SnO2 nanocomposite follows Mott’s one-dimensional variable range hopping (VRH) model.

• Effect of different carbon fillers and dopant acids on electrical properties of polyaniline nanocomposites

Electrically conducting nanocomposites of polyaniline (PANI) with carbon-based fillers have evinced considerable interest for various applications such as rechargeable batteries, microelectronics, sensors, electrochromic displays and light-emitting and photovoltaic devices. The nature of both the carbon filler and the dopant acid can significantly influence the conductivity of these nanocomposites. This paper describes the effects of carbon fillers like carbon black (CB), graphite (GR) and muti-walled carbon nanotubes (MWCNT) and of dopant acids like methane sulfonic acid (MSA), camphor sulfonic acid (CSA), hydrochloric acid (HCl) and sulfuric acid (H2SO4) on the electrical conductivity of PANI. The morphological, structural and electrical properties of neat PANI and carbon–PANI nanocomposites were studied using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT–IR), UV–Vis spectroscopy and the four-point probe technique, respectively. Thermogravimetric analysis (TGA) and X-ray diffraction (XRD) studies were also conducted for different PANI composites. The results show that PANI and carbon–PANI composites with organic acid dopants show good thermal stability and higher electrical conductivity than those with inorganic acid dopants. Also, carbon–PANI composites generally show higher electrical conductivity than neat PANI, with highest conductivities for PANI–CNT composites. Thus, in essence, PANI–CNT composites prepared using organic acid dopants are most suitable for conducting applications.

• Synthesis and characterization of MoO3–WO3 composite thin films by liquid phase deposition technique: Investigation of its photochromic properties

In order to achieve high colouration efficiency, MoO3–WO3 composite thin films have been successfully deposited on sodium silicate glass and silicon wafer (111) at 30 °C by a very simple novel wet process known as liquid phase deposition. The deposited films were annealed at different temperatures and characterized by carrying out SEM, EDAX, UV-vis and XRD analyses. The EDAX and SEM analyses support the structure and existence of peaks corresponding to Mo, W and O. X-ray diffraction studies showed that MoO3–WO3 is amorphous at lower temperature and turns crystalline at higher annealing temperature and suggested the mixture of two crystalline phases such as orthorhombic–monoclinic. Photochromic properties of the MoO3–WO3 composite films were studied in the spectral region 400–1200 nm by illuminating them in polychromatic light. The photochromic behaviour is observed to be more effective in composites films in visible region.

• Electrochemical passivation behaviour of nanocrystalline Fe80Si20 coating in borate buffer solution

Passivation behaviour of nanocrystalline coating (Fe80Si20) obtained by in situ mechanical alloying route is studied and compared with that of the commercial pure iron and cast Fe80Si20 in sodium borate buffer solution at two different pH values (7.7 and 8.4). The coating reveals single passivation at a pH of 7.7 and double stage passivity at a pH of 8.4. The first passive layer is due to the dissolution mechanism and second passivity is related to stable passivation. The cast sample shows single stage passivity in the solution of pH 8.4. The difference in the passivation behaviour for the cast alloy (Fe80Si20) and the coating is related to the presence of highly iron-enriched localized regions, formed during the processing stage of coating.

• Effect of crystal structure on photoinduced superhydrophilicity of copper grafted TiO2 nanostructure thin film

In this work, copper grafted titanium dioxide (rutile and brookite) thin films were deposited on glass substrates using the dip-coatingmethod. Field emission scanning electron microscopy and X-ray photoelectron spectroscopy were used to evaluate the surface morphology and properties of the film surfaces. The water contact angle on the film surfaces during irradiation and storage in a dark place was measured by a contact angle analyser. The results indicate that copper grafted titanium dioxide brookite thin film showed higher hydrophilicity than copper grafted titania rutile thin film.

• Interpretation of anomalous normal state optical conductivity of K3C60 fullerides

The observed frequency dependent optical response of alkali–metal-doped fulleride superconductors (𝑇c ≈ 19 K) has been theoretically analysed. The calculations of the optical conductivity, 𝜎(𝜔), have been made within the two-component schemes: one is the coherent Drude carriers (electrons) responsible for superconductivity and the other is incoherent motion of carriers from one atom to other atom of C60 molecule to a pairing between Drude carriers. The approach accounts for the anomalies reported (frequency dependence of optical conductivity) in the optical measurements for the normal state. The model has only one free parameter, the relaxation rate. The frequency dependent relaxation rates are expressed in terms of memory functions. The coherent Drude carriers form a sharp peak at zero frequency and a long tail at higher frequencies, i.e. in the infrared region. However, the hopping of carriers from one atom to the other (incoherent motion of doped electrons) yields a peak value in the optical conductivity centred at mid-infrared region. It is found that both the Drude and hopping carriers will contribute to the optical process of conduction in the K3C60 and shows similar results on optical conductivity in the mid-infrared as well as infrared frequency regions as those revealed from experiments.

• A new approach for understanding ion transport in glasses; example of complex alkali diborate glasses containing lead, bismuth and tellurium oxides

Mechanism of ion transport in glasses continues to be incompletely understood. Several of the theoretical models in vogue fail to rationalize conductivity behaviour when d.c. and a.c. measurements are considered together. While they seem to involve the presence of at least two components in d.c. activation energy, experiments fail to reveal that feature. Further, only minor importance is given to the influence of structure of the glass on the ionic conductivity behaviour. In this paper, we have examined several general aspects of ion transport taking the example of ionically conducting glasses in pseudo binary, 𝑦Na2B4O7.(1−𝑦) M$_{a}$O$_{b}$ (with 𝑦 = 0.25–0.79 and M$_{a}$O$_{b}$ = PbO, TeO2 and Bi2O3) system of glasses which have also been recently characterized. Ion transport in them has been studied in detail. We have proposed that non-bridging oxygen (NBO) participation is crucial to the understanding of the observed conductivity behaviour. NBO–BO switching is projected as the first important step in ion transport and alkali ion jump is a subsequent event with a characteristically lower barrier which is, therefore, not observed in any study. All important observations in d.c. and a.c. transport in glasses are found consistent with this model.

• Synthesis, microstructure and thermal expansion studies on Ca0.5+𝑥/2Sr0.5+𝑥/2Zr4P6−2𝑥Si2𝑥O24 system prepared by co-precipitation method

We report on the synthesis, microstructure and thermal expansion studies on Ca0.5+𝑥/2Sr0.5+𝑥/2Zr4P6−2𝑥Si2𝑥O24 (𝑥 = 0.00 to 1.00) system which belongs to NZP family of low thermal expansion ceramics. The ceramics synthesized by co-precipitation method at lower calcination and the sintering temperatures were in pure NZP phase up to 𝑥 = 0.37. For 𝑥 ≥ 0.5, in addition to NZP phase, ZrSiO4 and Ca2P2O7 form as secondary phases after sintering. The bulk thermal expansion behaviour of the members of this system was studied from 30 to 850 °C. The thermal expansion coefficient increases from a negative value to a positive value with the silicon substitution in place of phosphorous and a near zero thermal expansion was observed at 𝑥 = 0.75. The amount of hysteresis between heating and cooling curves increases progressively from 𝑥 = 0.00 to 0.37 and then decreases for 𝑥 ≥ 0.37. The results were analysed on the basis of formation of the silicon based glassy phase and increase in thermal expansion anisotropy with silicon substitution.

• New observations on formation of thermally induced martensite in Fe–30%Ni–1%Pd alloy

Kinetical, morphological, crystallographical and thermal characteristics of thermally induced martensite in an Fe–30%Ni–1%Pd alloy has been studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), differential scanning calorimetry (DSC) and X-ray diffraction method. Kinetics of transformation was found to be as athermal. SEM and TEM observations and X-ray method revealed 𝛼' (𝑏𝑐𝑐) martensite formation in the austenite phase of alloy by thermal effect. The crystallographic orientation relationship between austenite and 𝛼' (𝑏𝑐𝑐) martensite was found to be having Kurdjumov–Sachs (K–S) type relationship. In addition, the lattice parameters of austenite and martensite phases were calculated from X-ray diffraction patterns.

• Laser cladding of Zr-based coating on AZ91D magnesium alloy for improvement of wear and corrosion resistance

To improve the wear and corrosion resistance of AZ91D magnesium alloy, Zr-based coating made of Zr powder was fabricated on AZ91D magnesium alloy by laser cladding. The microstructure of the coating was characterized by XRD, SEM and TEM techniques. The wear resistance of the coating was evaluated under dry sliding wear test condition at room temperature. The corrosion resistance of the coating was tested in simulated body fluid. The results show that the coating mainly consists of Zr, zirconium oxides and Zr aluminides. The coating exhibits excellent wear resistance due to the high microhardness of the coating. The main wear mechanism of the coating and the AZ91D sample are different, the former is abrasive wear and the latter is adhesive wear. The coating compared to AZ91D magnesium alloy exhibits good corrosion resistance because of the good corrosion resistance of Zr, zirconium oxides and Zr aluminides in the coating.

• Spin canting phenomenon in cadmium doped cobalt ferrites, CoCd𝑥Fe2−𝑥O4 (𝑥 = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0), synthesized using sol–gel auto combustion method

Synthesis of non-collinear (spin canted) ferrites having the formula, CoCd𝑥Fe2−𝑥O4 (𝑥 = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0), has been carried out using the sol–gel auto combustion method. The ferrite samples show an interesting magnetic transition from Neel to Yafet–Kittel configuration, as the Cd2+ concentration is increased beyond 𝑥 = 0.4. The FT–IR spectra confirm the formation of the metal oxide bond as they exhibit two frequency bands in the range of ∼595 cm-1 and ∼450 cm-1, corresponding to the tetrahedral and the octahedral stretching vibrations of the metal oxide, respectively. The structural evolutions of the nanophase investigated using powder X-ray diffraction (XRD) technique show that the average crystallite size is ∼35 nm. The magnetic studies reveal that the saturation magnetization, 𝑀s, increases up to 𝑥 = 0.4 and decreases when the value of 𝑥 is > 0.4. It is proposed that the incorporation of Cd2+ ion takes place into the tetrahedral sites and up to 𝑥 = 0.4, Neel’s model is followed. But for 𝑥 > 0.4, canting of spins occurs, as explained by Yafet–Kittel (Y–K) model. The d.c. resistivity decreases as a function of temperature, indicating semiconducting nature of the ferrites and the positive value of Seebeck coefficient establishes 𝑝-type conduction behaviour for all the ferrite samples.

• Study of polarization and relaxation phenomena of polyblend films of poly(vinyl chloride) and poly(methyl methacrylate)

Thermally stimulated discharge current (TSDC) studies were carried out on pure poly(methyl methacrylate), poly(vinyl chloride) and polyblends (of various weight ratios, 100:0, 90:10, 80:20 and 70:30) as a function of polarizing fields at constant temperature, to study the polarization and relaxation phenomena in them. For PVC and different blends a peak around 140–180 °C and for PMMA two peaks at around 95 and 165 °C were observed. No regular variation in peak position for PMMA and blends was observed. The various TSDC parameters i.e. activation energy, charge released and relaxation times were calculated. In the blend samples it is suggested that the chains are so entangled that in the total polarization the dipolar contribution is less and the observed polarization seems to be mainly due to the formation of induced dipoles and an increase in free volume and mobility of charge carriers due to a plasticization effect.

• in situ ring-opening polymerization of hydroxyapatite/poly(ethylene adipate)-𝑐𝑜-(ethylene terephthalate) biomimetic composites

Hydroxyapatite/poly(ethylene adipate)-𝑐𝑜-poly(ethylene terephthalate) biomaterials (HAp/PEA-𝑐𝑜-PET) have been prepared by ring opening polymerization (ROP) of cyclic oligo(ethylene adipate)-𝑐𝑜-oligo(ethylene terephthalate) (C-OEA-𝑐𝑜-C-OET) in the porous hydroxyapatite (HAp) scaffolds at 250 °C for 24 h under vacuum. The content of ROP-PEA-𝑐𝑜-PET in the HAp/PEA-𝑐𝑜-PET composite was about 20 wt% with the values of number average molecular weight ($\bar{M}$n) and weight average molecular weight ($\bar{M}$W) of 3380 and 7160 g/mol, respectively. Compressive strength and modulus of the HAp/PEA-𝑐𝑜-PET composites were about 29 and 246 MPa, respectively. These mechanical properties were higher than those of the porous HAp templates and natural cancellous bone. In vitro bioactivity of the HAp/PEA-𝑐𝑜-PET composites was studied by soaking in simulated body fluid (SBF) under the flowing system at the rate of 130 mL/day for 7, 14, 21 and 28 days. The formation of hydroxyapatite nanocrystals was observed on the composite surfaces through the consumption of calcium and phosphorus from the SBF solution, indicating the bioactivity of these HAp/PEA-𝑐𝑜-PET composites. These results indicated the competency of HAp/PEA-𝑐𝑜-PET composites for biomedical applications.

• Proton transport properties of tin phosphate, chromotropic acid anchored onto tin phosphate and tin phenyl phosphonate

Tin (IV) phosphates of the class of tetravalent metal acid (TMA) salts have been synthesized by sol–gel method. The functionalized materials of tin (IV) phosphate (SnP) like chromotropic acid anchored tin phosphate (SnPCA) and tin phenyl phosphonate (SnPP) were also synthesized. These materials have been characterized for elemental analysis (ICP–AES), thermal analysis, X-ray analysis and FTIR spectroscopy. Chemical resistivity of these materials has been accessed in acidic, basic and organic solvent media. The proton present in the structural hydroxyl groups indicates good potential for TMA salts to exhibit solid-state proton conduction. The transport properties of these materials have been explored by measuring specific proton conductance at different temperatures. Based on the specific conduction data and Arrhenius plots, a suitable mechanism has been proposed.

• Electrical characterization of zirconium substituted barium titanate using complex impedance spectroscopy

This paper reports complex impedance analysis of polycrystalline complex perovskite structured BaZr0.025Ti0.975O3 prepared by solid state reaction method. XRD analysis reveals the formation of single phase perovskite structure. SEM has been used to investigate grain morphology of the material. Impedance plots have been used as a tool to analyse electrical properties of the sample as a function of frequency and temperature. Bulk resistance is observed to decrease with an increase in temperature showing a typical negative temperature coefficient of resistance (NTCR) type behaviour. Nyquist (Cole–Cole) plots show both inter and intra grain boundary effects. Relaxation time is found to decrease with increasing temperature and it obeys the Arrhenius relationship. The variation of d.c. and a.c. conductivity as a function of temperature is also reported.

• Anisotropy in elastic properties of lithium sodium sulphate hexahydrate single crystal—An ultrasonic study

The double sulfate family of (ABSO4) where A and B are alkali metal cations, is the object of great interest owing to the complexity and richness of its sequence of phase transition induced by temperature variation. A new sulfate salt characterized by the presence of water molecule in the unit cell with the chemical formula, Li2Na3(SO4)2.6H2O (LSSW), was obtained. The ultrasonic velocity measurement was done with pulse echo overlap technique [PEO]. All the six second order elastic stiffness constants, 𝐶11 = 𝐶22, 𝐶33, 𝐶44 = 𝐶55, 𝐶12, 𝐶14 and 𝐶13 = 𝐶23, are reported for the first time. The anisotropy in the elastic properties of the crystal are well explained by the pictorial representation of the surface plots of phase velocity, slowness, Young’s modulus and linear compressibility in 𝑎–𝑏 and 𝑎–𝑐 planes.

• Crystal structure studies on plate/shelf like disodium ditungstate

The structure of plate/shelf like disodium ditungstate (Na2W2O7) synthesized by newmethod in the process of ultrasonic spray pyrolysis using acidified aqueous solutions of tungsten (VI) oxide clusters as a precursor was refined down to the 𝑅-factor of 8.9%. X-ray diffraction analysis undoubtedly confirmed formation of orthorhombic Na2W2O7 and refinement of the diffraction data showed that Na2W2O7 powder belongs to the base-centred orthorhombic type of structure with 64 space group, 𝐶𝑚𝑐𝑎. The structure of Na2W2O7 can be described as infinite chains formed from tetrahedral (WO4) and octahedral (WO6) building units joined together. It was found that the basic units of the precursor complexes exist in the structure of Na2W2O7. Scanning electron microscopy confirmed formation of plate/shelf like Na2W2O7 particles with an average thickness of about 1.2 𝜇m.

• Preparation of continuous alumina gel fibres by aqueous sol–gel process

Continuous alumina gel fibres were prepared by sol–gel method. The spinning sol was prepared by mixing aluminum nitrate, lactic acid and polyvinylpyrrolidone with a mass ratio of 10:3:1.5. Thermogravimetry–differential scanning calorimetry (TG–DSC), Fourier transform infrared (FTIR) spectra, X-ray diffraction (XRD), and scanning electron microscopy (SEM) were used to characterize the properties of the gel and ceramic fibres. The Al2O3 fibres with a uniform diameter can be obtained by sintering gel fibres at 1200 °C.

• Twinning in copper deformed at high strain rates

Copper samples having varying microstructures were deformed at high strain rates using a split-Hopkinson pressure bar. Transmission electron microscopy results show deformation twins present in samples that were both annealed and strained, whereas samples that were annealed and left unstrained, as well as samples that were unannealed and strained, are devoid of these twins. These deformation twins occurred at deformation conditions less extreme than previously predicted.

• A soluble-lead redox flow battery with corrugated graphite sheet and reticulated vitreous carbon as positive and negative current collectors

A soluble-lead redox flow battery with corrugated-graphite sheet and reticulated-vitreous carbon as positive and negative current collectors is assembled and performance tested. In the cell, electrolyte comprising of 1.5M lead (II) methanesulfonate and 0.9 M methanesulfonic acid with sodium salt of lignosulfonic acid as additive is circulated through the reaction chamber at a flow rate of 50 ml min-1. During the charge cycle, pure lead (Pb) and lead dioxide (PbO2) from the soluble lead (II) species are electrodeposited onto the surface of the negative and positive current collectors, respectively. Both the electrodeposited materials are characterized by XRD, XPS and SEM. Phase purity of synthesized lead (II) methanesulfonate is unequivocally established by single crystal X-ray diffraction followed by profile refinements using high resolution powder data. During the discharge cycle, electrodeposited Pb and PbO2 are dissolved back into the electrolyte. Since lead ions are produced during oxidation and reduction at the negative and positive plates, respectively there is no risk of crossover during discharge cycle, preventing the possibility of lowering the overall efficiency of the cell. As the cell employs a common electrolyte, the need of employing a membrane is averted. It has been possible to achieve a capacity value of 114 mAh g−1 at a load current-density of 20 mA cm-2 with the cell at a faradaic efficiency of 95%. The cell is tested for 200 cycles with little loss in its capacity and efficiency.

• Development of hydroxyapatite bone cement for controlled drug release via tetracycline hydrochloride

The purpose of this work was to study the preparation and characterization of drug–hydroxyapatite cement. The hydroxyapatite (HA) cement has been synthesized by using tricalcium phosphate, calcium carbonate and dicalcium phosphate anhydrous with sodium hydrogen phosphate as liquid phase. The effect of added tetracycline hydrochloride (TCH) as drug on final phases, microstructure, setting behaviour and compressive strength has been studied. The drug release rate was first order within the first day and then was zero order. No obvious difference could be detected in XRD patterns of the TCH–HA cement with various amounts of drug. By increasing the drug concentration, mechanical strength of cement was decreased and its setting time was increased. The results of this study demonstrate the potential of using HA cement as a carrier for drug delivery.

• Characterization and in vitro and in vivo evaluation of cross-linked chitosan films as implant for controlled release of citalopram

The aim of the present study is to develop cross-linked chitosan (CH) films that can release drug over an extended period of time and that too in a controlled manner. A solution of different percentages of CH, is prepared in 1% lactic acid, followed by addition of citalopram (CTP) and then reacted with increasing amounts of glutaraldehyde (GL) to obtain films with different cross-linking densities. Prepared films are characterized for their physical and mechanical properties. The films are then subjected to in vitro drug release studies using pH 7.4 phosphate buffer saline (PBS) as dissolution medium and cumulative amount of drug released is calculated. Kinetic analysis of drug release is performed using Power law model and Higuchi’s model.With increase in concentration of CH, water absorption capacity and mechanical strength are increased; whereas, water vapour permeability and elasticity of the films are decreased. The effect of cross-linking agent, GL, is such that with an increase in the amount of GL, water vapour permeability, water absorption capacity and elasticity of the films are decreased; whereas, mechanical strength increased to some extent and then decreased. In vitro release studies indicate that films containing 3% CH, cross-linked with 2–3% GL and films containing 4%CH, cross-linked 1%GL are able to sustain the drug release for a prolonged time along with releasing almost complete drug in a desired period. Out of these batches, films containing 3% CH, cross-linked with 2–3% GL are having sufficient strength, water vapour permeation, water absorption capacity and elongation at break for implantation purpose. The in vitro degradation studies and histopathological studies were carried out with a sample film (batch C3 as in table 1) in rabbit model. In vitro degradation study indicates that the films maintained their integrity for desired implantation. The histopathological studies under optical microscope indicates that on implanting, there is no evidence of any inflammation, any foreign body granuloma or any necrosis or hemorrhage. Tissue configuration remains unaltered after 30 days of implantation. So, it can be suggested that cross-linked CH films of above said composition can be used as implant for long term application in depression and related disorders.

• # Bulletin of Materials Science

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June 2018