Sumonman Niamlang

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.

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.

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.

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 H2SO4. 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 NH4NO3. 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 NH4NO3 molecules and the PPV/zeolite composites with respect to the electrical conductivity sensitivity were investigated through the infrared spectroscopy.

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 FeCl3. The electrical conductivity response of the doped PPP (dPPP) towards CO, H2 and NH3 is investigated. dPPP shows no electrical conductivity response towards the first two gases (CO and H2), but it shows a definite negative response towards NH3. The electrical conductivity sensitivity of dPPP increases linearly with increasing NH3 concentration. To improve the sensitivity of the sensor towards NH3, 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+, NH4+ 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+ < NH4+ < 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 NH3 adsorption and interaction with the conductive polymer.

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

The apparent diffusion coefficients, Dapp, and the release mechanisms of salicylic acid from polyacrylamide hydrogels through pigskin were investigated. Dapp 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 Dapp at low electric field strength can be attributed to the combination of iontophoresis, electroporation of matrix pore, and induced pathway in pigskin. Dapp obeys the scaling behavior Dapp/Do = (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.

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.

Interactions between CO and Poly(p-phenylene vinylene) as Induced by Ion-Exchanged Zeolites

The effects of zeolite type, ion-exchanged level, and ion type on the electrical conductivity responses of poly(p-phenylene vinylene) (PPV), doped poly(p-phenylene vinylene) (dPPV) and zeolite composites under CO exposures were investigated. The electrical sensitivity of dPPV/Cu+-ZSM5(Si/Al = 23) system shows a negative sensitivity value of −0.154, while the Na+ system gives a positive sensitivity of 1.48. Based on FTIR and TPD data, the positive response of PPV/Na+-ZSM5 stems from the CO molecules acting as a secondary dopant. On the other hand, the negative response of PPV/Cu+-ZSM5 originates from the fact that CO molecules are selectively adsorbed on Cu+ sites rather than C+ sites of doped PPV.

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.

Oscillatory shear induced droplet deformation and breakup in immiscible polymer blends

Deformation and breakup of droplets in polybutadiene/polydimethylsiloxane blends subject to oscillatory shear flow were investigated experimentally using an optical shear flow cell. The apparent major axis (a∗) and the minor axis (c) in the vorticity direction of the droplets were measured as functions of time. From the time series of a∗ and c and the deformation parameter, (a∗−c)/(a∗+c), we define the deformation amplitudes as one-half the differences between the maximum and minimum values. The deformation amplitude parameters generally decrease with increasing viscosity ratio, time scale ratio, and droplet elasticity. The dependences of the deformation amplitude parameters on capillary number are generally linear up to a certain value for Newtonian droplets regardless of viscosity ratio and time scale ratio. The dependences become totally nonlinear with increasing droplet elasticity. Droplet viscosity and elasticity generally impede breakup under oscillatory shear. Critical capillary number for breakup,...