A review: permeability, porosity, tortuosity and physicochemical properties of controlled release oral dosage formulations
Drug dissolution is a part of drug flux governed by biopharmaceutical properties in correlation with fluid dynamic principles. It is essentially significant to determine the importance of fluid dynamics by observing the fate of essential fluids, namely, the air intake, foods eaten, water consumed, and body fluids. This study aimed to observe the correlation between different factors that influence fluid mechanics, specifically, permeability, porosity, and tortuosity with various physicochemical characteristics of drug substances, namely, drug solubility and dissolution rate, particle size and punch surface, polymorphism and amorphism, pseudo polymorphism (hydrates/solvates), and drug stability. Thus, this literature review aimed to compare the permeability of ambient conditions to different dosage forms of varying properties and determine its effects and liberation of active components to its ambient context of diffusion. Ergun equation is a tool for mathematical modelling of the fluid dynamics that can be used to calculate the fluid flow transition resulting to drug dissolution. Several imaging techniques, namely, x-ray microcomputed microtomography, magnetic resonance imaging (MRI) and nuclear magnetic resonance (NMR) can be used in determining the permeability of Newtonian fluid and analysis of ratio of porosity and tortuosity needed for regulation of the release of active therapeutic components. Flow rate control is necessary in controlled release oral dosage formulations in order to reduce adverse effects brought about by conventional release. Permeability of Newtonian fluid is influenced by the inverse relationship of porosity and tortuosity. The size of the void space in porous medium is affected by the degree of compression of drug materials. Hence, punch surface and other physicochemical properties of drugs, namely, solubility, particle size, polymorphism, solvates, hydrates and drug stability are coerced by the permeability of Newtonian fluid into the drug. Therefore, porosity and tortuosity are modified by change in physicochemical properties of drugs.