Concentration Of Hydrophilic Polymer Research Articles

Porous hydrophobic/hydrophilic composite membranes: Estimation of the hydrophobic-layer thickness

A porous hydrophobic/hydrophilic composite membrane can be prepared by the phase inversion method in one casting step from a polymer solution containing a hydrophilic polymer and a fluorinated surface modifying macromolecule (SMM). The surface analysis of these membranes indicate that there is a fluorine concentration gradient along the membrane thickness resulting from the migration of fluorinated blocks to the air side surface during membrane formation. In this paper, direct contact membrane distillation (DCMD) process has been applied, together with a new theoretical model, to estimate the hydrophobic-layer thickness of porous composite membranes. The theoretical model involves the structural characteristics of the membranes, the heat transfer mechanism and the physical nature of mass transport through porous composite membranes. The model was validated using two supported commercial poly-tetra-fluoro-ethylene membranes of different pore sizes and known thickness-layers. The effect of the hydrophilic polymer concentration in the casting solution on the formed hydrophobic-layer thickness of the composite membranes has been investigated. Also are studied the effects of stirring rate and temperature in the DCMD system on the determination of the hydrophobic-layer thickness. The results show that the hydrophobic-layer thickness increases with the concentration of the hydrophilic base polymer in the casting solution and is independent on the operational parameters selected to conduct the DCMD experiments. The proposed method can be used to measure the layer thickness of porous composite hydrophobic/hydrophilic membranes within random uncertainties less than 5%. The maximum deviation of each individual thickness from the corresponding average value is less than 9%. The estimated errors due to the different input membrane parameters associated in the mathematical model were discussed. The hydrophobic-layer thickness of the SMM blended membrane was found to be an order of magnitude lower than that of the commercial membranes frequently used in membrane distillation.

Controlled Porosity Osmotic Pumps of Highly Aqueous Soluble Drug Containing Hydrophilic Polymers as Release Retardants

Controlled porosity osmotic pumps (CPOPs) are devoid of delivery orifice to release core contents and essentially possess pore‐forming agent(s) in coating composition. When the pump comes in contact with aqueous media, pore‐forming agent(s) generate pores through which core contents are delivered. Diltiazem hydrochloride (DLTZ) is a freely water‐soluble drug and the release rates of DLTZ are higher from oral osmotic pumps including CPOPs, in which the drug release is controlled by concentration of pore‐forming agents. The effect of appropriate concentration of hydroxypropyl methyl cellulose and sodium carboxy methyl cellulose mixture on the release of DLTZ from CPOPs was studied. In vitro drug release profiles were compared with that of different marketed controlled release formulations and statistically analysed to examine the suitability of CPOP for twice or once daily administration. Dissolution models were applied to drug release data in order to establish the mechanism of drug release and kinetics. Drug release from the CPOPs was effectively modified with the concentration of pore‐forming agent in membrane and concentration of hydrophilic polymers in the core. CPOPs showed minimum 65% of consistent DLTZ release at 16 h. Statistical analysis confirmed that with an increase in the amount of hydrophilic polymers release rate decreased. Drug release from the systems follows Hixson‐Crowell cube root model and mechanism of release follow non‐Fickian diffusion.

Development and Characterization of Transdermal Drug Delivery Systems for Diltiazem Hydrochloride

Transdermal drug delivery system of diltiazem hydrochloride was developed to obtain a prolonged controlled drug delivery. Both the matrix diffusion controlled (MDC) and membrane permeation controlled (MPC) systems were developed. The matrix diffusion controlled systems used various combinations of hydrophilic and lipophillic polymers, whereas membrane permeation controlled systems were developed using the natural polymer chitosan. The MDC systems were prepared using the cast film method and the MPC systems by an adhesive sealing technique. Both the systems were characterized for in vitro and in vivo performance. The MDC systems were characterized for physicochemical properties such as tensile strength, moisture content, and water vapor transmission. The in vitro release studies showed that the release from the matrix diffusion controlled transdermal drug delivery systems follows a nonfickian pattern and that from the membrane permeation controlled transdermal drug delivery systems follow zero-order kinetics. The release from the matrix systems increased on increasing the hydrophilic polymer concentration, but the release from the membrane systems decrease on cross-linking of the rate controlling membrane and also on addition of citric acid to the chitosan drug reservoir gel. The in vivo studies of the selected systems showed that both systems are capable of achieving the effective plasma concentration for a prolonged period of time. The MPC system achieved effective plasma concentration a little more slowly than the MDC system, but it exhibited a more steady state plasma level for 24 hr.

Influence of hydrogels on liposome stability and on the transport of liposome entrapped substances into the skin

Different liposome-hydrogel formulations, which are used for topical application of liposomes, have been prepared and the role of hydrophilic polymers on the transport of liposome-entrapped hydrophilic substance into pig ear skin was investigated by one-dimensional electron paramagnetic resonance imaging (1D-EPRI) and reduction kinetic imaging methods. Using conventional EPR the influence of polymers on liposome stability was also determined. Multilamellar liposomes composed basically of hydrogenated soya lecithin and cholesterol, with the entrapped hydrophilic paramagnetic probe ASL ( N-(1-oxyl-2,2,6,6-tetramethyl-4-piperidinyl)- N-dimethyl-N-hydroxyethylammonium iodide), were prepared in water solution and then mixed into hydrogels with different concentrations of hydrophilic polymers: carboxymethylcellulose or xanthan gum. It was found that the polymers examined do not prevent efficient transport of liposome-entrapped substances into the skin. From the on-going stability study of liposomes in hydrogel formulations, it follows that carboxymethycellulose does not influence the stability of liposomes during the time course of 6 weeks, while in xanthan hydrogels leakage of liposome-entrapped hydrophilic substance was observed already after 10 days. The results support the use of hydrogels in liposome dermatics, but it should be taken into account that some hydrophilic polymers can influence the physical stability of liposomes appreciably.

Studies on the adsorption and solubility of nalidixic acid

The adsorption of nalidixic acid on certain pharmaceutical additives was investigated and its extent estimated. Also, the effects of various surface-active agents and hydrophilic polymers on the solubility of the drug was determined. The adsorption isotherms have revealed that the degree of adsorption increased in the order; microcrystalline cellulose < ethyl cellulose < silicon dioxide < aluminium magnesium silicate. Studies on the solubility of nalidixic acid at 37°C using different concentrations of hydrophilic polymers have demonstrated that methyl cellulose, polvinylpyrrolidone and polyethylene glycol 6000 have comparable effects. Polyvinyl alcohol caused only a marginal increase in solubility. The surface-active agents, sodium lauryl sulphate and polysorbate 80, also increased solubility of the drug. The values of the heat of solution and the free energy changes were calculated from the Van't Hoff plots. The values of heat of solution for all systems were comparable, but the free energy changes indicate that sodium lauryl sulphate causes the most marked effect on solubility.