Effects of expanded graphite's structural and elemental characteristics on its oil and heavy metal sorption properties.

Expanded graphite has promising potential environmental applications due to its porous structure and oleophilic nature, which allow it to absorb large quantities of oil. The material is produced by intercalating graphite and applying heat to convert the intercalant into gas to cause expansion between the layers in the graphite. Using different intercalants and temperature conditions results in varying properties of expanded graphite. This work has proven that the sorption properties of commercial expanded graphite differ significantly due to the material's structural and elemental characteristics, which can be attributed to the intercalation method. This resulted in various degrees of exfoliation of the graphite and possible functionalisation of the graphene sheets within the structure. This affected the material's sorption capacity and its affinity for heavy metal sorption by incorporating selectivity towards the sorption of certain metals. It was found that sample EG3, which underwent a less harsh expansion, exhibited lower porosity than EG1, and thus, the sample absorbed less oil at 37.29 g/g compared to the more expanded samples EG1 and EG2 with 55.16 g/g and 48.82 g/g, respectively. However, it was able to entrap a wider variety of metal particles compared to EG1 and EG2, possibly due to its smaller cavities allowing for a capillary effect between the graphene sheets and greater Van der Waals forces. A second possibility is that ionic or coordination complexes could form with certain metals due to the possible functionalisation of the expanded graphite during the intercalation process. This would be in addition to coordination between the metals and expanded graphite carbon atoms. The findings suggest that there is evidence of functionalisation as determined by XRD and elemental analyses. However, further investigation is necessary to confirm this hypothesis. The findings in this work suggest that the first mechanism of sorption was more likely to be related to the degree of expansion of the expanded graphite. Various metals are present in used oil, and their removal can be challenging. Some metals in oil are not considered heavy since they have a relatively low density but can be associated with heavy metals in terms of toxicity.

Poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) as an insulin carrier in silk fibroin hydrogels for transdermal delivery via iontophoresis.

In this study, silk fibroin (SF) was utilized as the starting material to fabricate physically crosslinked hydrogels. Poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) was synthesized and characterized as a drug carrier, with insulin as the model drug. PEDOT:PSS, with a high electrical conductivity of 1666 ± 49 S cm-1, interacted with insulin molecules via electrostatic interaction by replacing the dopant PSS molecules. Insulin-loaded PEDOT:PSS embedded in the SF hydrogel resulted in an increase in the degree of swelling, pore size, and mesh size of the hydrogel. In the in vitro release and release-permeation experiments, the amounts of insulin release and release-permeation were investigated using a modified Franz diffusion cell, under the effects of SF concentrations, electric fields, and pH values. The amounts of insulin release and release-permeation from the pristine SF hydrogel and the PEDOT:PSS/SF hydrogel followed the power laws with the scaling exponents close to 0.5, indicating the Fickian diffusion or the concentration gradient. Under electric fields, with or without PEDOT:PSS used as the drug carrier, the insulin amount and diffusion coefficient were shown to increase with the increasing electric field due to the electro-repulsive forces between the cathode and insulin molecules and SF chains, electroosmosis, and SF matrix swelling. The SF hydrogel and PEDOT:PSS as the drug carrier are demonstrated herein as new components in the transdermal delivery system for the iontophoretically controlled insulin basal release applicable to diabetes patients.

Metformin delivery via iontophoresis based on κ-carrageenan cryogels.

Transdermal drug delivery system (TDDS) is the system for transmitting a drug through the skin into the blood circulation. In this work, κ-Carrageenan (κC) was used as the drug matrix material. The porous κC matrices were fabricated by dissolving the κC in deionized water to obtain hydrogels and then using the freeze-dryer to obtain cryogels. The porous (κC) matrices showed interconnected pore sizes varying between 6.05 to 25.8 nm. In the drug release experiments, the drug diffusion coefficient increased and the drug release duration was reduced with decreasing κC concentration due to the larger κC pore sizes. The diffusion coefficient increased with a shorter release time under the applied electric strength of +1.0 V due to the electro-repulsive force between the Metformin and the anode. For the drug release-permeation of the κC 0.8 % v/v cryogel through the pig skin under applied positive electrical potentials, the amounts of drug release-permeation and diffusion coefficients were enhanced with shorter durations relative to without electrical potential. The κC 0.8 % v/v matrix at the applied electric strength of +6.0 V has been shown here to be potential to be used as the Metformin transdermal controlled delivery patch for abdominal obesity and diabetes.

Synthesis of Highly Conductive Poly(3-hexylthiophene) by Chemical Oxidative Polymerization Using Surfactant Templates.

Poly(3-hexylthiophene) (P3HT) was systematically synthesized by chemical oxidative polymerization in chloroform with ferric chloride (FeCl3) as the oxidizing agent and various surfactants of the shape templates. The effects of 3HT: FeCl3 mole ratios, polymerization times, and surfactant types and concentrations on the electrical conductivity, particle shape and size were systematically investigated. Furthermore, dodecylbenzenesulfonic acid (DBSA), p-toluenesulfonic acid (PTSA), sodium dodecyl sulfate (SDS), and sodium dioctyl sulfosuccinate (AOT) were utilized as the surfactant templates. The P3HT synthesized with DBSA at 6 CMC, where CMC stands for the Critical Micelle Concentration of surfactant, provided a higher electrical conductivity than those with PTSA, SDS and AOT. The highest electrical conductivity of P3HT using DBSA was 16.21 ± 1.55 S cm-1 in which the P3HT particle shape was spherical with an average size of 1530 ± 227 nm. The thermal analysis indicated that the P3HT synthesized with the surfactants yielded higher stability and char yields than that of P3HT without. The P3HT_DBSA electrical conductivity was further enhanced by de-doping and doping with HClO4. At the 10:1 doping mole ratio, the electrical conductivity of dP3HT_DBSA increased by one order of magnitude relative to P3HT_DBSA prior to the de-doping. The highest electrical conductivity of dP3HT_DBSA obtained was 172 ± 5.21 S cm-1 which is the highest value relative to previously reported.

Electrically controlled transdermal delivery of naproxen and indomethacin from porous cis-1,4-polyisoprene matrix.

This study is focused on the inquiry of using a porous polymeric structure to absorb and release transdermally two drugs through a skin from deproteinized natural rubber latex (DPNR). The porous DPNR films were fabricated from the internal formation of surfactant micelles and their subsequent leaching out to generate porous structures. The pore size of DPNR films increased with increasing surfactant amount. The model drugs were naproxen and indomethacin; their releases and release-permeations were investigated under the effects of surfactant amount, electrical potential, and drug size. Without electric field, the drug release mechanism was mainly driven by concentration gradient. The higher amount of drug released was obtained from the matrix with a larger pore size. Under electric field, the higher amounts of drug release were obtained in the shorter drug release durations, via the electrorepulsive force between the negatively charged drugs and the cathode electrode. The molecular drug size was a factor for the drug absorption, release rate and amount. For the drug release-permeation experiment through the pig skin, there were two release-permeation periods as governed by the combination of concentration gradient and swelling in the first period, and the matrix erosion in the second period. The fabricated porous DPNR films have been shown here to be potential to be used as a transdermal patch with electrically controllable drug release rate, amount and duration along with the facile drug-matrix loading and absorption.

The Soft and High Actuation Response of Graphene Oxide/Gelatin Soft Gel.

The high actuation response of soft gel from a graphene oxide/gelatin composite was prepared as an alternative material in soft robotics applications. Graphene oxide (GO) was selected as the electroresponsive (ER) particle. GO was synthesized by modifying Hummer's method at various ratios of graphite (GP) to potassium permanganate (KMnO4). To study the effect of ER particles on electromechanical properties, GO was blended with gelatin hydrogel (GEL) at various concentrations. The electrical properties of the ER particles (GO and GP) and matrix (GEL) were measured. The capacitance (C), resistance (R), and dielectric constant of the GO/GEL composite were lower than those of the GO particles but higher than those of the GEL and GP/GEL composite at the given number of particles. The effects of external electric field strength and the distance between electrodes on the degree of bending and the dielectrophoresis force (Fd) were investigated. When the external electric field was applied, the composite bent toward electrode, because the electric field polarized the functional group of polymer molecules. Under applied 400 V/mm, the GO/GEL composite (5% w/w) showed the highest deflection angle (θ = 82.88°) and dielectrophoresis force (7.36 N). From the results, we conclude that the GO/GEL composite can be an alternative candidate material for electromechanical actuator applications.

Effects of conductive polyazulene and plasticizer embedded in deproteinized natural rubber transdermal patch on electrically controlled naproxen release-permeation.

Naproxen (Npx) was utilized as an anionic drug and loaded in the deproteinized natural rubber (DPNR) films prepared by the UV irradiation. The in-vitro drug release-permeation from the DPNR films and through the pig skin was investigated under the effects of the plasticizer type and amount, silicone oil (Si) and dibutyl phthalate (DBP), applied electric potential, and used conductive polyazulene as the drug encapsulation host. The drug release-permeation consisted of 2 successive periods: the pore formation period and release-permeation period. In the first period, the scaling exponent n1 values were between 0.5 and 1 indicating the decreasing drug rate with time. In the second stage, the scaling exponent n2 values were higher than 1 indicating the increasing drug rate with time. The Npx release-permeation amount increased with increasing amount of hydrophilic plasticizers. The efficiency of plasticizers on the Npx release-permeation amount was ranked as follows: DBP > Si. The Npx release-permeation amount was drastically enhanced from the applied electrical potential due to the electro-repulsive force between the negatively charged drug and the negatively charged electrode, and the presence of the Npx-doped conductive polyazulene. Other characteristics were also investigated in details namely the matrix morphology, and the pore formation during the two periods.

Permeation study of indomethacin from polycarbazole/natural rubber blend film for electric field controlled transdermal delivery.

Transdermal drug delivery is an alternative route to transport the drug into the blood system. This method has been continuously developed to overcome limitations and is now suitable for a wide variety of drug molecules. In this work, the influences of electric field and conductive polymer were investigated for developing a unique drug delivery system from double-centrifuged natural rubber (DCNR) matrix. Indomethacin (IN) was loaded into polycarbazole (PCz) as a conductive polymer drug host to promote the efficient transportation of the drug. The IN-loaded PCz was blended with DCNR to form a transdermal patch. The permeation of IN through the PCz/NR film and pig skin was carrried out by a modified Franz diffusion cell. The IN diffused from DCNR film by the diffusion controlled combined with erosion mechanism depending on the pore formation period. The drug permeation increased with decreasing cross-link ratio because of more accessible pathways for the drug permeation. Moreover, an electric field and the inclusion of PCz as the drug carrier dramatically improved the diffusion of the drug from the membrane by through the electrorepulsive force and electro-reduced PCz expansion. Thus, the PCz/DCNR films are shown here as a potential transdermal patch under applied electric field.

Controlled Aloin Release from Crosslinked Polyacrylamide Hydrogels: Effects of Mesh Size, Electric Field Strength and a Conductive Polymer.

The aim of this paper is to investigate the effects of hydrogel mesh size, a conductive polymer, and electric field strength on controlled drug delivery phenomena using drug-loaded polyacrylamide hydrogels prepared at various crosslinking ratios both with and without a conductive polymer system. Poly(p-phenylene vinylene), PPV, as the model conductive polymer, was used to study its ability to control aloin released from aloin-doped poly(p-phenylene vinylene)/polyacrylamide hydrogel (aloin-doped PPV/PAAM). In the passive release, the diffusion of aloin from five aloin-doped PPV/PAAM hydrogel systems each was delayed ranging from during the first three hours to during the first 14 h due to the ionic interaction between the anionic drug and PPV. After the delayed periods, aloin could diffuse continuously into the buffer solution through the PAAM matrix. The amount of aloin released from the aloin-doped PPV/PAAM rose with increasing electric field strength as a result of the three mechanisms: the expansion of PPV chains inside the hydrogel, iontophoresis, and the electroporation of the matrix pore size, combined. Furthermore, the conductive polymer and the electric field could be used in combination to regulate the amount of release drug to a desired level, to control the release rate, and to switch the drug delivery on/off.

Electric field-controlled benzoic acid and sulphanilamide delivery from poly(vinyl alcohol) hydrogel.

The controlled release of benzoic acid (3.31 Å) and sulphanilamide (3.47 Å) from poly(vinyl alcohol), PVA, hydrogels fabricated by solution casting at various cross-linking ratios, were investigated. The PVA hydrogels were characterized in terms of the degree of swelling, the molecular weight between cross-links, and the mesh size. The drug release experiment was carried out using a modified Franz diffusion cell, at a pH value of 5.5 and at temperature of 37°C. The amount of drug release and the diffusion coefficients of the drugs from the PVA hydrogels increased with decreasing cross-linking ratio, as a larger mesh size was obtained with lower cross-linking ratios. With the application of an electric field, the amount of drug release and the diffusion coefficient increased monotonically with increasing electric field strength, since the resultant electrostatic force drove the ionic drugs from the PVA matrix. The drug size, matrix pore size, electrode polarity, and applied electric field were shown to be influential controlling factors for the drug release rate.

Effects of crosslinking ratio, model drugs, and electric field strength on electrically controlled release for alginate-based hydrogel.

The drug release characteristics of calcium alginate hydrogels, (Ca-Alg), under an electric field assisted transdermal drug delivery system were systematically investigated. The Ca-Alg hydrogels were prepared by the solution-casting using CaCl(2) as a crosslinking agent. The diffusion coefficients and the release mechanism of the anionic model drugs, benzoic acid and tannic acid, and a cationic model drug, folic acid on the Ca-Alg hydrogels were determined and investigated using a modified Franz-Diffusion cell in an MES buffer solution of pH 5.5, at a temperature of 37°C, for 48 h. The influences of the crosslinking ratio, -the mole of the crosslinking agent to the mole of the alginate monomer-mesh size, model drug size, drug charge, electric field strength, and electrode polarity were systematically studied. The drug diffusion coefficient decreased with an increasing crosslinking ratio and drug size for all of the model drugs. The drug diffusion coefficient is precisely controlled by an applied electric field and the electrode polarity depending on the drug charge, suitable for a tailor-made transdermal drug delivery system.

Electrical conductivity response of poly(phenylene-vinylene)/zeolite composites exposed to ammonium nitrate.

Poly(p-phenylenevinylene) (PPV) was chemically synthesized via the polymerization of p-xylene-bis(tetrahydrothiophenium chloride) monomer and doped with H(2)SO(4). To improve the electrical conductivity sensitivity of the conductive polymer, Zeolites Y (Si/Al = 5.1, 30, 60, 80) were added into the conductive polymer matrix. All composite samples show definite positive responses towards NH(4)NO(3). The electrical conductivity sensitivities of the composite sensors increase linearly with increasing Si/Al ratio: with values of 0.201, 1.37, 2.80 and 3.18, respectively. The interactions between NH(4)NO(3) molecules and the PPV/zeolite composites with respect to the electrical conductivity sensitivity were investigated through the infrared spectroscopy.

Controlled transdermal iontophoresis of sulfosalicylic acid from polypyrrole/poly(acrylic acid) hydrogel.

A conductive polymer-hydrogel blend between sulfosalicylic acid-doped polypyrrole (PPy) and poly(acrylic acid) (PAA) was used as a carrier/matrix for the transdermal drug delivery under applied electrical field. PAA films and the blend films were prepared by solution casting with ethylene glycol dimethacrylate (EGDMA) as a cross-linking agent, followed by the blending of PPy particles and the PAA matrix. The effects of cross-linking ratio and electric field strength on the diffusion of the drug from PAA and PPy/PAA hydrogels were investigated using a modified Franz-diffusion cell with an acetate buffer of pH 5.5 and at 37 degrees C, for a period of 48h. The diffusion coefficient of the drug is calculated using the Higuchi equation, with and without an electric field, at various cross-linking ratios. The drug diffusion coefficient decreases with increasing drug size/mesh size ratio, irrespective of the presence of the conductive polymer as the drug carrier. The diffusion coefficient, at the applied electric field of 1.0V, becomes larger by an order of magnitude relative to those without the electric field.

Electric field assisted transdermal drug delivery from salicylic acid-loaded polyacrylamide hydrogels.

The apparent diffusion coefficients, D(app), and the release mechanisms of salicylic acid from polyacrylamide hydrogels through pigskin were investigated. D(app) increases with increasing electric field strength and reaches the maximum value at electric field strength of 0.1 V; beyond that it decreases with increasing electric field strength and becomes saturated at 5 V. The increase in D(app) at low electric field strength can be attributed to the combination of iontophoresis, electroporation of matrix pore, and induced pathway in pigskin. D(app) obeys the scaling behavior D(app)/D(o) = (drug size/pore size)m with m equal to 0.67 and 0.49 at the electric field strengths of 0 and 0.1 V, respectively.

Electrically controlled release of salicylic acid from poly(p-phenylene vinylene)/polyacrylamide hydrogels.

The apparent diffusion coefficients, Dapp, and the release mechanisms of salicylic acid from salicylic acid-loaded polyacrylamide hydrogels, SA-loaded PAAM, and salicylic acid-doped poly(phenylene vinylene)/polyacrylamide hydrogels, SA-doped PPV/PAAM, were investigated. In the absence of an electric field, the diffusion of SA from the SA-doped PPV/PAAM is delayed in the first 3 h due to the ionic interaction between the anionic drug (SA anion) and the PPV. Beyond this period, SA is dissolved in and can diffuse into the buffer solution through the PAAM matrix. The Dapp of the SA-doped PPV/PAAM is higher than that of the SA-loaded PAAM, and the former increases with increasing electric field strength due to combined mechanisms: the expansion of PPV chains inside the hydrogel; the reduction reaction under a negative potential driving the anionic SA through the PAAM matrix; and the expansion of the matrix pore. The Dapp of SA from the SA-loaded PAAM and the SA-doped PPV/PAAM apparently obey the scaling behavior: Dapp/D0 = (drug size/pore size)m with the scaling exponent m equal to 0.50 at 0.1 V for both SA-loaded PAAM and SA-doped PPV/PAAM. Thus, the presence of the conductive polymer and the applied electric field can be combined to control the drug release rate at an optimal desired level.

Fabrication of Poly(p-Phenylene)/Zeolite Composites and Their Responses Towards Ammonia.

Poly(p-phenylene) (PPP) was chemically synthesized via oxidative polymerization using benzene and doped with FeCl(3). The electrical conductivity response of the doped PPP (dPPP) towards CO, H(2) and NH(3) is investigated. dPPP shows no electrical conductivity response towards the first two gases (CO and H(2)), but it shows a definite negative response towards NH(3). The electrical conductivity sensitivity of dPPP increases linearly with increasing NH(3) concentration. To improve the sensitivity of the sensor towards NH(3), ZSM-5 zeolite is added into the conductive polymer matrix. The electrical sensitivity of the sensor increases with increasing zeolite content up to 30%. The effect of the type of cation in the zeolite pores is investigated: namely, Na(+), K(+), NH(4) (+) and H(+). The electrical conductivity sensitivity of the composites with different cations in the zeolite can be arranged in this order: K(+) < no zeolite < Na(+) < NH(4) (+) < H(+). The variation in electrical sensitivity with cation type can be described in terms of the acid-base interaction, the zeolite pore size and surface area. The PPP/Zeolite composite with H(+) possesses the highest electrical sensitivity of -0.36 since H(+) has the highest acidity, the highest pore volume and surface area, which combine to induce a more favorable NH(3) adsorption and interaction with the conductive polymer.

Electrically controlled release of sulfosalicylic acid from crosslinked poly(vinyl alcohol) hydrogel.

Electrically controlled drug delivery using poly(vinyl alcohol) (PVA) hydrogels as the matrix/carriers for a model drug was investigated. The drug-loaded PVA hydrogels were prepared by solution-casting using sulfosalicylic acid as the model drug and glutaraldehyde as the crosslinking agent. The average molecular weight between crosslinks, the crosslinking density, and the mesh size of the PVA hydrogels were determined from the equilibrium swelling theory as developed by Peppas and Merril, and the latter data were compared with those obtained from scanning electron microscopy. The release mechanisms and the diffusion coefficients of the hydrogels were studied using modified Franz-Diffusion cells in an acetate buffer with pH 5.5 and temperature 37 degrees C during a period of 48 h, in order to determine the effects of crosslinking ratio, electric field strength, and electrode polarity. The amounts of drug released were analyzed by UV-vis spectrophotometry. The amounts of drug released vary linearly with square root of time. The diffusion coefficients of drug-loaded PVA hydrogels decrease with increasing crosslink ratio. Moreover, the diffusion coefficients of the charged drug in the PVA hydrogels depend critically on the electric field strength between 0 and 5 V as well as on the electrode polarity. Thus, the release rate of sulfosalicylic acid can be altered and controlled precisely through electric field stimulation.