P. P. Kundu

pH-sensitive chitosan/alginate core-shell nanoparticles for efficient and safe oral insulin delivery

Chitosan-alginate (CS/ALG) nanoparticles were prepared by formation of an ionotropic pre-gelation of an alginate (ALG) core entrapping insulin, followed by chitosan (CS) polyelectrolyte complexation, for successful oral insulin administration. Mild preparation process without harsh chemicals is aimed at improving insulin bio-efficiency in in vivo model. The nanoparticles showed an average particle size of 100-200 nm in dynamic light scattering (DLS), with almost spherical or sub-spherical shape and ∼ 85% of insulin encapsulation. Again, retention of almost entire amount of encapsulated insulin in simulated gastric buffer followed by its sustained release in simulated intestinal condition proved its pH sensitivity in in vitro release studies. Significant hypoglycemic effects with improved insulin-relative bioavailability (∼ 8.11%) in in vivo model revealed the efficacy of these core-shell nanoparticles of CS/ALG as an oral insulin carrier. No systemic toxicity was found after its peroral treatment, suggesting these core-shell nanoparticles as a promising device for potential oral insulin delivery.

pH sensitive N-succinyl chitosan grafted polyacrylamide hydrogel for oral insulin delivery.

pH sensitive PAA/S-chitosan hydrogel was prepared using ammonium persulfate (APS) as an initiator and methylenebisacrylamide (MBA) as a crosslinker for oral insulin delivery. The synthesized copolymer was characterized by Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD) study; morphology was observed under scanning electron microscope (SEM). The PAA/S-chitosan with ∼ 38% of insulin loading efficiency (LE) and ∼ 76% of insulin encapsulation efficiency (EE), showed excellent pH sensitivity, retaining ∼ 26% of encapsulated insulin in acidic stomach pH 1.2 and releasing of ∼ 98% of insulin in the intestine (pH 7.4), providing a prolonged attachment with the intestinal tissue. The oral administration of insulin loaded PAA/S-chitosan hydrogel was successful in lowering the blood glucose level of diabetic mice. The bioavailability of insulin was ∼ 4.43%. Furthermore, no lethality or toxicity was documented after its peroral administration. Thus, PAA/S-chitosan hydrogel could serve as a promising oral insulin carrier in future.

Oral insulin delivery by self-assembled chitosan nanoparticles: in vitro and in vivo studies in diabetic animal model.

We have developed self-assembled chitosan/insulin nanoparticles for successful oral insulin delivery. The main purpose of our study is to prepare chitosan/insulin nanoparticles by self-assembly method, to characterize them and to evaluate their efficiency in vivo diabetic model. The size and morphology of the nanoparticles were analyzed by dynamic light scattering (DLS), atomic force microscopy (AFM) and scanning electron microscopy (SEM). The average particle size ranged from 200 to 550 nm, with almost spherical or sub spherical shape. An average insulin encapsulation within the nanoparticles was ~85%. In vitro release study showed that the nanoparticles were also efficient in retaining good amount of insulin in simulated gastric condition, while significant amount of insulin release was noticed in simulated intestinal condition. The oral administrations of chitosan/insulin nanoparticles were effective in lowering the blood glucose level of alloxan-induced diabetic mice. Thus, self-assembled chitosan/insulin nanoparticles show promising effects as potential insulin carrier system in animal models.

Effect of salts and surfactant and their doses on the gelation of extremely dilute solutions of methyl cellulose

The effect of different salts and surfactant and their doses on the gel temperature of extremely dilute solutions (below 1%) of methyl cellulose (MC) has been studied. The gel temperature decreases non-linearly (concave downward) with increase in MC concentration. The addition of salts like NaCl, (NH4)2SO4 and (Na)2CO3 lowers the gel temperature of MC due to its dehydration. But increase in gel temperature is also observed on addition of 0.5 and 1% NaCl to 0.6 and 0.7% MC solutions, respectively. The addition of 1% sodium carbonate causes appearance of clouds only up to 0.2% MC, cloudy gel followed by clear gel up to 0.3% MC, thereafter phase separation occurs even at room temperature. The effect of addition of a surfactant, sodium lauryl sulphate (SLS) on the process of gelation of aqueous MC solutions has been studied in detail. The gelation process depends on r, the ratio of weight% of surfactant and that of MC present in the aqueous solution. Gels are formed for the limit 0.02<r<0.1 for all MC solutions, beyond which phase separation occurs. With increase in r (from the lower limit), gel temperature increases, reaches a maximum and then decreases.

Tensile property and interfacial dewetting in the calcite filled HDPE, LDPE, and LLDPE composites

Abstract Mechanical properties and complex melt viscosity of unfilled and the calcite (calcium carbonate: CaCO 3 ) filled high density polyethylene (HDPE), low density polyethylene (LDPE), and linear low density polyethylene (LLDPE) composites using dumbbell bar and film specimens are studied. In addition, the formation of air holes between calcium carbonate and the resin matrix was investigated from the phase morphology and interfacial behavior between the above constituents upon stretching using scanning electron microscopy. The tensile stress and the complex melt viscosity of the calcite filled (50%) polyethylene composites were higher than that of unfilled ones, implying that the reinforcing effect of calcium carbonate. The crack was initiated up to first 50% elongation along the transverse direction and the formation of air holes was originated by dewetting occurring through machine direction in the interface between calcium carbonate surface and HDPE. The propagation mechanism of the air hole formation was proposed to firstly originate by dewetting up to 300% elongation, and enlarged not only by breaking of a superimposed fibril structure, but also by merging effect air holes between fibrous resin matrix. However, the crack propagation was not observed at the very beginning elongation for the calcite filled LDPE and LLDPE systems. Less fibril structure was observed in LLDPE, then LDPE composites. The observed shape and the average size of the air holes were different from system to system. This sort of different interfacial behavior and mechanical properties may arise from different configuration of polyethylene.

Influence of film preparation procedures on the crystallinity, morphology and mechanical properties of LLDPE films

Abstract Influence of various film preparation procedures on the crystallinity, morphology and mechanical properties of pure linear low-density polyethylene and its calcite filled composite films has been studied using differential scanning calorimeter (DSC), wide-angle X-ray diffractometer (WAXRD), atomic force microscope (AFM) and ultimate tensile testing machine (UTM). The film preparation procedures include variation in cooling rates such as quenching, force (fan) and natural cooling and in techniques such as extrusion followed by melt squeezing and compression molding. The heat of fusion (from DSC), the degree of crystallinity (from WAXRD) and the crystallite size (from WAXRD and AFM) are found to be the highest for naturally cooled specimen, followed by fan cooled and quenched ones. The AFM images of surface topology exhibit stacked lamellar morphology for forcefully cooled (fan cooled and quenching) samples and spherulitic ‘lozenges’ for naturally cooled ones. The Young’s modulus and yield stress (from UTM) are the highest for naturally cooled samples, followed by fan cooled and quenched ones. Amongst the calcite filled composites, the ‘base film’, which is prepared by extrusion followed by melt squeezing and natural cooling, exhibits the lowest heat of fusion, degree of crystallinity and Young’s modulus, but the highest yield stress, elongation at break and tensile strength compared to the compression molded ones.

Utilization of Conducting Polymers in Fabricating Polymer Electrolyte Membranes for Application in Direct Methanol Fuel Cells

Search for suitable materials for fabricating polymer electrolyte membranes (PEMs) for application in polymer electrolyte membrane fuel cells, and particularly in direct methanol fuel cells (DMFCs), has been an important field of research for the last several decades. Notable candidates that have emerged from this extensive and seemingly exhaustive research are Nafion®, poly(vinylidenefluoride), sulfonated poly(etheretherketone), poly(benzimidazole), Dow XUS®, Flemion® R, 3P-energy, Aciplex-S®, Gore-Tex®, Gore-Select®, and their different blends, copolymers and interpenetrating networks with compounds, such as poly(hexafluoropropylene), poly(acrylonitrile), poly(styrenesulfonate), and poly(methylmethacrylate). Nevertheless, the objective of achieving a much reduced methanol crossover, while maintaining a substantial level of proton conductivity, has remained by and large elusive. However, a ray of hope has been provided by conducting polymers (CPs), and this has led to a considerable number of researchers to plunge into the exploitation of this possibility. This review focuses on the application of CPs, mainly polyaniline and polypyrrole, as PEM constituents. Detailed comparisons between their functioning, and their respective utility in terms of achieving this objective have been provided. We have also discussed the following critical points: first, the effect of CPs on methanol crossover, proton conductivity, and gas diffusion, and second, thermal stability of CPs in the temperature range within which DMFC operates.

Enhancements of Catalyst Distribution and Functioning Upon Utilization of Conducting Polymers as Supporting Matrices in DMFCs: A Review

Fuel cells (FCs) have evolved as a potential alternative energy harnessing device, with direct methanol fuel cell (DMFC) as one of the front-runners. Although it has achieved significant progress, and is currently getting available in the commercial market; however, from a broader perspective, DMFCs, like most other devices, suffer from certain critical drawbacks. This, in turn, demands considerable progress to be made in order to realize ultimate commercialization, i.e., cheap, reliable, durable, and portable DMFCs with easily accessible fuel. In this respect, one important area of real concern is the DMFC electrodes, consisting of catalysts and catalyst-supporting matrices. Sluggish reaction rates and use of highly expensive and scarce catalysts are two critical drawbacks. Conducting polymers (CPs) have found extensive use in the fabrication of these matrices and have resulted in better dispersion, distribution and anchoring of catalysts, which is important to enhance their reaction efficiencies. This review attempts to summarize the potential contributions of CPs, their critical roles, and possible future trends toward fabricating catalyst-supporting matrices in DMFCs.

A Review on Aromatic Conducting Polymers-Based Catalyst Supporting Matrices for Application in Microbial Fuel Cells

Polymer electrolyte membrane fuel cells (PEMFCs) are being considered as a very important source of alternative energy for powering present and next generation electrical and electronic devices. Microbial fuel cell (MFC) is an important member of the PEMFC family. Compared to other members, such as hydrogen/oxygen and direct methanol fuel cells, MFC is a relatively new entity and is still largely in the research and developmental stage. In terms of fuel, MFC enjoys a huge advantage over other prospective competitors due to large availability of waste water and sludge. In addition, the prospect of waste water and sludge treatment, along with the production of electricity, in an MFC operation is an added bonus. Nevertheless, like most other devices, MFC also suffers from certain critical drawbacks. For example, sluggish electrode reaction rates are source of real concern. This necessitates considerable progress to be made in terms of catalyst and catalyst supports. In this respect, the use of aromatic conducting polymers (ACPs) based catalyst supports have resulted in realizing better dispersion, distribution, and anchoring of catalysts, which is important to enhance their performances towards electrode reactions. This review summarizes the potential roles of ACPs in the capacity as a catalyst-supporting matrix in MFCs.

Nickel nanocatalysts supported on sulfonated polyaniline: potential toward methanol oxidation and as anode materials for DMFCs

The development of potential anode catalysts and catalyst supporting matrices for application in direct methanol fuel cells (DMFCs) has been an active area of research for the last couple of decades. The conventionally used Pt catalyst suffers from (a) high cost, (b) limited abundance and (c) the catalyst poisoning effect induced by the in situ generated carbon monoxide. In this work, a comparatively less expensive and more abundant Ni metal catalyst [supported on Vulcan carbon, polyaniline (PAni) and partially sulfonated PAni (SPAni)] has been utilized as a potential alternative to the Pt metal catalyst for the oxidation of methanol. SPAni emerged as the best matrix for the deposited Ni catalyst nanoparticles. This combination generated a peak current density of 306 μA cm−2 at +0.57 V. In addition, the Ni/SPAni catalyst produced a higher IF/IB ratio compared to the commercial Pt–Ru/C catalyst. Furthermore, a current density of 135 mA cm−2 (at +0.2 V potential) and a maximum power density of 27 mW cm−2 were obtained at 60 °C upon utilizing Ni/SPAni as the anode catalyst for DMFCs. The results, thus obtained, were better than those obtained for the commercial Pt–Ru/C, as well as, the Ni/C and Ni/PAni catalysts.