Search

Twin tungsten electrode – wire electrode indirect arc welding (TTW IAW) was a novel welding method. In this paper, the wettability and spreading of weld bead of TTW IAW were investigated by comparing with single tungsten electrode – wire electrode indirect arc welding (STW IAW). Results showed that compared to STW IAW, TTW IAW possessed larger arc width and greater arc heat distribution range with smaller variation gradient, due to the lower velocity of charged particles toward the arc center, caused by the smaller electromagnetic force acting on the arc plasma. So did the temperature distribution of weld pool of TTW IAW. Moreover, the process stability of TTW IAW was better. Besides, at the molten pool front, the transverse convection of the melted metal of TTW IAW was adequate, because of the superior wettability and long flow duration of the melted metal; at the molten pool rear, the inward convection of the melted metal of TTW IAW was weak mainly owing to the low Marangoni force. Therefore, the weld bead width of TTW IAW increased by about 25.0% and the wetting angle of the weld bead decreased by about 25.7% compared to STW IAW, which indicated that the weld bead spreading of TTW IAW was better. [ABSTRACT FROM AUTHOR]

Glass beads from two maritime sites were analyzed: the Dutch East India Company vessel Rooswijk, wrecked in 1740 on Goodwin Sands off the Kent coast, UK, and an unidentified vessel known as the Bead Wreck, located off Saint Peter Port, Guernsey, in the Channel Islands. Both vessels were carrying drawn, lead glass beads, which are found mainly in 17th- and 18th-century contexts. The study demonstrates the value of analysing glass beads from wreck sites because the information has the potential to help characterize unidentified vessels and further refine bead chronologies at post-medieval archaeological sites. [ABSTRACT FROM AUTHOR]

A unique methodology has been developed with the compilation of two magnets to produce the double axial magnetic field, and the effect on the arc shape and the bead characteristics in the gas tungsten arc welding (GTAW) process have been investigated. The load-carrying capacity of the joint depends upon the bead geometry. The developed methodology is capable of altering the arc shape and consequently the bead geometry of weld as per the requirement. Experimental results show that the double axial magnetic field changes the arc shape from a conical to constricted conical. It is further observed that magnetic configurations North-South-South-North (N-S-S-N) and Zero-Zero-South-North (0-0-S-N) provided better results than other configurations. The North-South-South-North (N-S-S-N) configuration produced a minimum penetration (0.98 mm) and a maximum shape factor (7.81), along with good appearance of weld beads. This configuration is suitable for cladding and hardfacing applications. The increased penetration (3.03 mm) was achieved with the Zero-Zero-South-North (0-0-S-N) configuration compared with conventional welding (2.20 mm). Similarly, this configuration yielded a higher bead width (8.13 mm) than conventional welding (5.90 mm). This configuration is suggested for the single-pass welding operation. [ABSTRACT FROM AUTHOR]

In this work, a novel and eco-friendly biosorbent, regenerated silk fibroin bead (rSFB) was successfully produced and used as a low-cost adsorbent to remove silver ion from wastewater. Batch adsorption experiments demonstrated that rSFB could effectively remove silver ion in particular. Factors influencing the adsorption of silver ion, e.g. contact time, solution pH, and adsorbent dosage were systematically investigated. Isotherm equilibrium studies demonstrated that the silver ion adsorption process followed the Langmuir model. The maximum adsorption capacity for silver ion was estimated to be 62.50 mg/g and the removal efficiency could reach up to 98.82%. The kinetics study showed that the adsorption process followed the second-order kinetic model. The adsorbent was stable and active for up to four successive cycles. The batch experimental results suggested that rSFB could be used as an efficient adsorbent to remove silver from wastewater. [ABSTRACT FROM AUTHOR]

In the present investigation, stability of weld morphology was investigated in case of electrolytic tough pitch copper (12 mm thickness) processed by Hot Wire Gas Tungsten Arc Welding (HW GTAW) using CuNi filler wire with variations of processing conditions, using different combination of hot wire's parameters such as feed rate and current. The assessment of weld bead geometry was performed using visual examination (during and after welding), and macrographic dimensional measurements of weld bead geometry such as depth of penetration and depth to width ratio. In addition to the stability of weld bead geometries, microstructural variations and weld quality assessments were studied using optical microscopy, scanning electron microscopy, energy dispersive x-ray spectroscopy, and micro-hardness measurements in case of processed sample observed with most uniform weld bead geometry. The results revealed that minimum dimensional variations of weld bead geometry throughout the processed length was obtained with 5.42 mm bead width, 1.2 mm bead height, 1.8 mm penetration, and 0.36 depth to width ratio when hot wire's parameters were 0.6 m/min wire feed rate and 90 amps hot wire current. The bridging mode of metal transfer helps to receive more stable weld bead geometry with minimum dimensional variations. Ni filler wire of HW GTAW improves the hardness in the Heat affected zone (70 HV0.3) and weld zone (80 HV0.3), which were 33% and 17% higher of base material. The weld zone was consisting of mixed mode of grains such as dendrites just above the fusion line and cellular grains further above dendrites in case of processed sample of minimum dimensional variations of weld bead geometry throughout the processed length. [ABSTRACT FROM AUTHOR]

Ever-growing needs in pipeline welding relating to quality, frequent usage of advanced, heat-sensitive, and corrosion-resistant materials alongside high production costs encourage the evaluation of a welding process thoroughly. The only way to overcome those problems is the adaptation of technically evolved welding methods that combine the goodness of cutting-edge power supply sources and advanced software configuration. One such technique is Regulated Metal Deposition (RMDTM) welding. In this context, the current study explores the influence of the regulated metal deposition (RMDTM) welding variables on ASME SA387-11-2 steels. Current (A), voltage (V), and gas flow rate (GFR) are preferred regulated metal deposition (RMD™) welding variables, and at the same time the depth of penetration (DOP), heat-affected zone (HAZ), bead height (BH), and bead width (BW) are incorporated as performance evaluation attributes. Furthermore, the exploration of Rao algorithms is presented to evaluate the optimal welding settings. The obtained optimal welding settings is current = 92 A, voltage = 13 V, and gas flow rate = 21 litre/min. The results are also compared with the JAYA, and teaching learning-based optimization (TLBO) approaches to show the efficacy of the intended approach. [ABSTRACT FROM AUTHOR]

Stainless steel is a widely used material in various industries such as aerospace, chemical processing and transportation. Tungsten Inert Gas (TIG) or Gas Tungsten Arc Welding (GTAW) process is extensively used for joining thin sections of stainless steel. However, it is not useful in joining thick sections in a single pass. Activated TIG (A-TIG) significantly increases weld penetration up to 1.5– 4 times in a single pass. Because of its deep penetration ability, A-TIG is the focus of research amongst the researchers. This article reports the mechanisms associated with A-TIG, effects of various weld parameters on weld bead geometry and optimization techniques to optimize the process variable of the A-TIG welding process. The present work also analyzes the consequence of activated fluxes on microstructure and mechanical properties of A-TIG weld metal. Along with this, recent developments in the TIG welding process have been discussed. The study concludes that the A-TIG welding process enhances the weld penetration to a great extent, but a high amount of slug gets deposited on the weld surface. This drawback can be overcome by novel variants of the A-TIG welding process such as Flux Bounded TIG (FB-TIG) and Flux Zone TIG (FZ-TIG) welding processes which enhance the future scope of research. [ABSTRACT FROM AUTHOR]

In this paper, a novel adsorbent which used polyvinyl alcohol, alginate and biochar was successfully made and been used to remove lead from aqueous solutions. Batch experiments were carried out to evaluate the adsorption capacities of Pb (II) on this bead. Experimental data were analysed by the model equations like Langmuir and Freundlich and adsorption kinetic constants were determined using pseudo-first-order (PFO) and pseudo-second-order (PSO). In this study, the adsorption characteristics of Pb (II) were well fitted by the Langmuir isotherm model and pseudo-second-order (PSO) kinetic model. The adsorption of Pb (II) onto PVA-biochar beads are spontaneous and exothermic at 303–333 K by the evidence of the changes in standard Gibbs free energy, standard enthalpy and standard entropy. The maximum adsorption capacity for Pb (II) was estimated to be 176.40 mg/g, which is comparable with other adsorbents. While the maximum adsorption increased varying the pH of initial solution from 2 to 6, the effect on the adsorption amount by the sodium ion concentration is not very large. The results of EDS spectra indicated that the existence of lead in polyvinyl alcohol (PVA)-biochar bead after adsorption, which proving the adsorption of lead. In XPS spectrum, the observed Pb elements also demonstrated that the lead was adsorbed by PVA-biochar bead. [ABSTRACT FROM AUTHOR]

Keyhole gas tungsten arc welding (K-GTAW) was applied to characterize the weld bead geometry in case of the 6 mm thick electrolytic tough pitch copper. Various conditions of welding speeds and preheating on the bead geometry were studied for its uniformity. Visual examination, macro bead dimensional analysis, microhardness profile across the transverse section, microstructural analyses were performed to investigate the K-GTAW on electrolytic tough pitch copper. The results revealed that full penetration of 6 mm can be obtained in a single pass using keyhole mode in GTAW. Keyhole length and width were majorly affected by the welding speed and preheating temperature. Significant variations in weld bead geometry were observed even when high heat input conditions were applied without preheating. Uniform weld bead geometry of 5 mm bead width and depth to width ratio of 0.42 was obtained for a length of 80 mm using appropriate preheating of 300°C and heat input condition of 1.37 kJ/mm (resulted from 300 amperes welding current, 120 mm/min welding speed, and 15.3 volts voltage). In the uniform weld bead geometry, the weld and heat affected zones were consisted of coarse grains relative to base material, wherein the micro hardness variations were observed. [ABSTRACT FROM AUTHOR]

In the present study, the effect of process parameters in Wire Arc Additive Manufacturing (WAAM) of Stainless Steel 304 as filler wire and mild steel as a substrate has been investigated. The deposition was made by using the Cold Metal Transfer (CMT) process. Single-pass beads are most useful for remanufacturing and repairing purposes. The quality of cladding for additive manufacturing predominantly depends on bead geometry. Hence, it is required to have an optimum range of bead parameters to ensure the desired mechanical properties. Response surface methodology and ANOVA were used to estimate the effects of current, weld speed, standoff distance on bead characteristics. Multiple regression models were developed to relate process parameters to bead quality. [ABSTRACT FROM AUTHOR]

The present work investigates the effect of dynamic correction (DC) and the arc length correction (ALC) parameters on the deposition of Stellite 6 filler wire on AISI H13 steel by Cold Metal Transfer (CMT) welding. The changes in the current and voltage waveforms were studied along with high-speed camera imaging of the process during single bead deposition. The effect of the arc correction parameters on the area and volumetric dilution, bead geometry, microstructure, and hardness are presented. The DC parameter influences the current waveform whereas the ALC parameter affects the voltage waveform and duration of the CMT cycle. It is shown that the ALC parameter has a strong effect on the dilution as compared to DC parameter. A wide scatter in the dilution values with similar heat input for different arc correction parameters was observed. Lower heat-input results in lower dilution and finer microstructure resulting in high hardness of the bead. [ABSTRACT FROM AUTHOR]

Load-carrying capacity of weld joints could be identified by its shape and size where weld bead geometry and shape relationship parameters are of utmost importance. Heat input and preheating temperature together can control the cooling time of weld, which in turn determines the weld microstructure and its mechanical properties. To control the shape and geometry of weld bead, it is necessary to understand its relationship with cooling time. In present work, preheating temperature is used as process variable along with heat input varying parameters for understanding their effects on weld bead geometry and shape relationship parameters using submerged arc welding process on high-strength low alloy pipeline steel. The experimental investigation was then analyzed by using the mathematical modeling in context with response surface methodology. The mathematical model predicts the influential dependency of cooling time on the preheating temperature than the other weld process parameters. The associated effects in relation to the process parameters have been discussed and analyzed in the present study. [ABSTRACT FROM AUTHOR]

In this article, effects of advanced submerged arc welding process parameters on weld bead geometry have been investigated. A novel water-cooled torch has been developed which allow a use of higher preheat current values for a continuous advanced submerged arc welding (ASAW) operation. Weld beads have been deposited on AISI 1023 steel plates by varying open circuit voltage, wire feed rate, welding speed, nozzle to plate distance, and preheat current as per central composite design. The relationships between welding parameters and weldment characteristics namely bead width, penetration, reinforcement, and dilution have been developed using multiple linear regression. The effects of individual process parameters and their interactions on response parameters were examined. Finally, single and multiobjective optimization of process parameters were performed using desirability approach and Jaya algorithm. The results reveal that a smaller bead width and lower dilution can be achieved with the developed torch by allowing the use of higher preheat current values. [ABSTRACT FROM PUBLISHER]

This research investigates the effects of input parameters on discontinuities in bead formation during material deposition by the plasma transferred arc welding (PTAW) process. Experiments based on L27 orthogonal array have been carried out by deposition of stainless steel powder (SS304 L) on stainless steel plate (SS316). Three types of depositions have been observed, namely continuous, partially continuous and discontinuous deposition. A process map has been developed, based upon powder and energy deposition per length, where the above-mentioned three types of depositions are distributed. The discontinuities in the deposition can be overcome by increasing the energy deposition per length or by reducing the powder deposition per length. [ABSTRACT FROM PUBLISHER]

Currently, cell microencapsulation (CM) is a promising technology for a wide range of areas of interest in cellular and molecular biology. This technique can be used for large-scale cell culture, cell implantation, and cell-based gene therapy. Although several materials have been used for CM, alginate is considered to be quite effective. Alginate bead-containing cells can be prepared by extruding a cell-alginate mixture into a calcium chloride solution. It is possible to easily create calcium alginate (Ca-alginate) beads with a syringe. However, beads that are generated by syringes are not suitable for CM due to their large size (>1000 μm). Researchers have proposed a number of solutions for this problem. The use of certain equipment is an inseparable part of these solutions. This study demonstrated that small size (<400 μm) Ca-alginate beads can successfully be generated by modifying the syringe method. In this study, this method was successfully employed for CM and embryoid body (EB) formation in alginate. [ABSTRACT FROM AUTHOR]

A bead-based competitive fluorescence immunoassay for the detection of triazophos has been developed. In this method, a conjugate of hapten and ovalbumin covalently bound to carboxylated fluorescent bead was used as a coating antigen and goat anti-mouse IgG/R-phycoerythrin conjugate was used as the fluorescent molecular probe. For standards (in 5% methanol in phosphate-buffered saline), the detection range was 0.02–50 ng/ml and the average coefficient of variation (CV) was 8.9%. This bead-assay was highly specific for triazophos, and none of other the structurally similar compounds (diazinon, malathion, parathion and fenitrothion) were recognised (<0.01% cross-reactivity). Vegetable samples (cabbage, carrot, green pepper, spinach, eggplant) were spiked with triazophos in the range of 1.0–100.0 ng/g and analysed by the bead-based immunoassay. The mean recovery and CV were 90.6 and 11.9%, respectively. The results confirmed that the bead-based fluorescence immunoassay is applicable for analysis and quantification of highly hydrophobic pesticide residues in vegetables. [ABSTRACT FROM PUBLISHER]

Uawa Tolaga Bay on the East Coast of the North Island was the place of first positive contact between Māori and European with the visit of HMS Endeavour in October 1769. The renaissance of Te Aitanga-a-Hauiti traditional history and culture has been enriched by re-engagement with a dual heritage beginning with James Cook, Tupaea and those on the Endeavour. Recent educational initiatives, historical research, archaeological investigations and events surrounding the 2004 transit of Venus all contribute to new appreciation of this dual heritage and point towards an exciting shared future. [ABSTRACT FROM AUTHOR]

Objective: The aim of this study was to prepare pH-sensitive sodium alginate/calcined hydrotalcite (SA/CHT) hybrid bead with improved the burst release effect of the drug. Materials and methods: A series of pH-sensitive SA/CHT hybrid beads were prepared by using Ca2++ cross-linking in the presence of diclofenac sodium (DS) and SA. The structure and drug loading of the beads were characterized by Fourier transform infrared spectroscopy and X-ray diffraction. The swelling and the drug release of the fabricated beads were investigated by the pH of test medium and CHT content. Result: The formed positively charged hydrotalcite layers were adsorbed on the negatively charged SA polymer chains through electrostatic interaction and act as inorganic cross-linkers in the three-dimensional network. Compared to pure SA beads, the incorporation of CHT enhanced the drug encapsulation efficiency, improved the swelling behaviors and slowed the drug release from the hybrid beads. Discussion and conclusions: The electrostatic interaction between hydrotalcite and SA has restricted the movability of the SA polymer chains, and then slowed down swelling and dissolution rates in aqueous solutions. The results provided a simple method to moderate drug release and matrix degradation of the SA beads. [ABSTRACT FROM AUTHOR]

Calcium-pectinate (Ca-pectinate) beads have shown immense potential as colon-specific drug carrier. However, Ca-pectinate itself is unable to prevent its swelling/degradation in the upper gastro-intestinal (GI) conditions. Hence, polyethyleneimine (PEI) was added in the cross-linking solution to strengthen the Ca-pectinate network. Resveratrol was used as a model drug due to its promising therapeutic activity towards several colonic diseases. Beads were prepared by varying cross-linking solution pH and other formulation variables. The effects of these formulation variables were investigated on the bead's characteristics. Furthermore, surface morphology, drug--polymer interaction, stability, and in  vivo pharmacokinetic study of the optimized formulation were performed. The optimized PEI-modified beads prevented drug release in the upper GI conditions, while released the drug in simulated colonic fluid. Furthermore, in  vivo pharmacokinetics studies in rats demonstrated delayed appearance of drug in blood after oral administration. The optimized Ca-pectinate beads demonstrated both in  vitro and in  vivo colon-specific drug release. [ABSTRACT FROM AUTHOR]

Agar beads containing chitosan particles were prepared by dropping hot suspension of agar/chitosan (2/1, w/w) into cold distilled water. The bead size was 2-3 mm and the cross section of the bead revealed a porous structure on FE-SEM (Field Emission Scanning electron microscopy) photos. The pH-dependent release property of the bead was observed using either blue dextran or FITC-dextran (Fluorescein isothiocyanate-dextran) as a dye. The % releases of blue dextran for 6 h were 42% at pH 3.5, 48% at pH 5.5 and 52% at pH 8.0. Obviously, the release was significantly suppressed at acidic pHs. This is possibly because the positive charge intensity of chitosan becomes stronger at an acidic pH. As a result, it tends to interact with negatively charged blue dextran, leading to a suppressed release at acidic pHs. On the other hand, the % releases of FITC-dextran for 6 h were 88% at pH 4.5, 80% at pH 5.5 and 76% at pH 8.0. The release was somewhat promoted at acidic pHs. At an acidic pH such as pH 3.5, chitosan could be dissolved within agar beads, giving rise to cavities. In addition, there might be no electrostatic interaction between positively charged chitosan and neutral FITC-dextran. Therefore, FITC-dextran would readily release through the cavities, resulting in a higher release at an acidic pH. [ABSTRACT FROM AUTHOR]

In this presentation, we will outline our novel, integrated bead-based oligonucleotide selection procedures including the automation of the split-pool synthesis of a one-bead one-thioaptamer library, high-throughput flow cytometric sorting and a PCR-based sequencing. Additionally, we will also discuss one promising thioaptamer that has been shown in preliminary animal therapeutic dosing to increase survival in animal models of infection with West Nile virus. Moreover, we will present our ongoing work on a thioaptamer proteomics chip. [ABSTRACT FROM AUTHOR]

The objective of this study was to prepare and evaluate biodegradable alginate beads as a controlled-release system for a water-insoluble drug, mefenamic acid (MA), using 3 × 22 factorial design by ionotropic gelation method. Therefore, the mefenamic acid dispersion in a solution of alginate was dropped into the cross-linking CaCl2 solution and a fairly high yield (71-89%) of MA-alginate beads were obtained. Their encapsulation efficiencies were in the range of 79.3-98.99%. The effect of drug:polymer ratio, CaCl2 concentration, and curing time on the time for 50% of the drug to be released (t50%), and the drug entrapment efficiency were evaluated with factorial design method. It was found that drug:polymer ratio and interaction of drug:polymer ratio and curing time had an important effect on the drug to be released (t50%). The effect of CaCl2 concentration is also important on the drug release. On the other hand, all factors except CaCl2 concentration were effective on the drug entrapment efficiency. The swelling properties of beads were also studied. The release mechanism was described and found to be non-Fickian, Case II, and Super Case II transport for the formulations. This study suggested a new mefenamic acid alginate bead formulation for oral delivery of nonsteroidal anti-inflammatory drugs, which cause gastric irritation. [ABSTRACT FROM AUTHOR]

Hydrogel beads based on the carbohydrate biopolymers kappa-carrageenan and sodium alginate were newly prepared. Both classical and experimental design (Taguchi) methods were used to obtain the optimum conditions for the full-polysaccharide hydrogel preparation. The carrageenan-alginate (Caralgi) beads exhibited a surface morphology smoother than that of the one-polysaccharide network beads. Infrared spectroscopy and DSC/TGA thermal methods were used to study the chemical structure and thermal properties of the beads. The carrageenan parts appreciably enhanced thermostability of the networks. The fully carbohydrate-based hydrogel beads are expected to be biologically compatible and degradable. They are being considered as new carriers for drug loading and controlled delivery systems. [ABSTRACT FROM AUTHOR]

The viability, proliferation and insulin production of RIN-m5F cells when loaded into alginate beads to form a 3D culture system has been investigated. The mechanism of alginate cross-linking (calcium ions vs barium ions), the addition of poly(L-lysine) (PLL) and poly(L-ornithine (PLO) and presence of different extra-cellular matrix proteins (ECM) influence the RIN-m5F cell behaviour. Cells in calcium alginate beads (CAB) proliferated and produced more insulin per cell than monolayer culture, but the physical properties of the beads were poor and they ruptured within a few days of culture. Barium alginate beads (BABs) provided a stable encapsulation method. Addition of PLL and PLO at concentrations above 0.1% w/v with the culture medium increased cell proliferation. With the addition of ECMs after bead formation there was a further increase in cell proliferation for certain combinations of ECM and PLO. It was concluded that RIN-m5F-loaded Ba-alginate beads (BABs), when incorporated with varying concentrations of poly (L) lysine (PLL), poly (L) ornithine (PLO) in the presence of extra-cellular matrix proteins (ECMs) were superior to both tissue culture and RIN-m5F-loaded Ca-alginate beads (CABs) in terms of physical stability, cell proliferation and insulin production. [ABSTRACT FROM AUTHOR]

For the functional enhancement of chelating resins containing carboxylic acids, copolymer beads were prepared by suspension polymerization of styrene (St), methyl methacrylate (MMA), and divinylbenzene (DVB) in the presence of toluene as diluent. The phenyl rings of the beads were directly chloromethylated, and the carboxylic ester groups of the beads were converted into hydroxymethyl groups by reduction followed by chlorination to give chloromethyl groups, respectively. The chelating resins containing a pair of neighboring carboxylic acid groups (NCAGs) were obtained by the alkylation of chloromethyl groups in copolymer beads with diethyl malonate in the presence of sodium hydride followed by hydrolysis using aqueous alkali solution. Accordingly, the structural effects of the resins on the adsorption of heavy metal ions were investigated. Poly(St‐ co ‐DVB)‐based chelating resin containing NCAGs showed adsorption abilities toward heavy metal ions like Pb 2+ , Cd 2+ , and Cu 2+ , whereas poly(MMA‐ co ‐DVB)‐based chelating resin containing NCAGs showed adsorption abilities toward heavy metal ions like Cu 2+ , Cd 2+ , and Co 2+ . On the other hand, poly(St‐ co ‐MMA‐ co ‐DVB)‐based chelating resin containing NCAGs showed adsorption abilities toward heavy metal ions like Pb 2+ , Cd 2+ , Hg 2+ , Co 2+ , and Cu 2+ : a synergistic effect on the adsorption of heavy metal ions like Pb 2+ , Cd 2+ , Hg 2+ , and Co 2+ was observed. The adsorption ability of poly(St‐ co ‐MMA‐ co ‐DVB)‐based chelating resin among three kinds of chelating resins was relatively good. [ABSTRACT FROM AUTHOR]

This paper reports the properties of vitamin C encapsulated sodium alginate beads prepared by an alternative approach. The alternative encapsulation process mainly involves immobilization of vitamin C in hydrated zinc oxide layers and encapsulation of prepared immobilized particles in sodium alginate bead. The immobilization of vitamin C in hydrated zinc oxide layers was achieved by a coprecipitation process. Fourier transform infrared (FTIR) spectroscopy showed that the vitamin C was found to be stable after its immobilization. X-ray diffraction (XRD) studies revealed that anionic vitamin C molecules are adsorbed between positively charged zinc hydroxide layers with a 1:1 layer sequence, since well-defined change in basal spacing was observed. Well-defined change in surface morphology was observed by scanning electron microscopy (SEM) when vitamin C immobilized particles are encapsulated in sodium alginate bead. The biological activity of vitamin C was retained, even after its immobilization which was confirmed by 4-dihydroxy-L-phenylalanine (L-DOPA) oxidase inhibition and free radical scavenging activity studies. The release rate of vitamin C from immobilized particles and beads was sustained through an ion exchange process. A higher amount of stable vitamin C was recovered from the bead when compared to neat vitamin C itself. [ABSTRACT FROM AUTHOR]

Chitosan beads (CBs) incorporating Ca-alginate microspheres (CAMs), containing a drug, were prepared as an oral sustained delivery system. Stable and monodisperse Ca-alginate microspheres loaded with drug were obtained by a membrane emulsification method. The Ca-alginate microspheres were encapsulated in chitosan beads by the ionotropic gelation method with a polyelectrolyte complex reaction between two oppositely charged polyions. The surface and internal characteristics of the beads were improved by ionic cross-linking in tripolyphosphate (TPP) solution adjusted to pH 5.0. The release experiments were performed using lidocaine·HCl (cationic drug) and sodium salicylate (anionic drug) as model drugs. Initial release of drugs depended on the degree of swelling. Ca-alginate microspheres encapsulated in chitosan beads were superior to both drug-loaded CBs and CAMs beads for sustained release because they had a three-layer composition; a calcium alginate core bounded by an inter-phasic chitosan-alginate membrane, which itself was surrounded by a layer of chitosan-TPP. [ABSTRACT FROM AUTHOR]