Additionally, this model does not consider changes in the carrier volume that may be induced by drug release and/or matrix degradation. In configuration (c) (Figure 1(c)), the thin membranes (e.g., the lipid bilayers of liposomes are only several nanometer thick) may selleckchem render the convection of polymer-soluble drug at the carrier surface dominant. As a result, the release Inhibitors,research,lifescience,medical of drug molecules from the outer surfaces of drug carriers to the extracarrier medium follows dm/dt = −Ah(c − c∞) [20]. Here, h is the convection coefficient, which is determined by the

flow characteristics of the extracarrier medium; and c∞ is the drug concentration in the extracarrier medium. In the porous and monolithic configurations (Figures 1(d) and 1(e)), transport of drug molecules in the carrier may be mediated by diffusion, excipient erosion/degradation, Inhibitors,research,lifescience,medical and/or osmotic pressure. The osmotically mediated flux of drug molecules can be written as dm/dt = − AP(c − c∞), where P is the permeability. Under perfect sink conditions, the convection-dominated and osmotic pressure-mediated Inhibitors,research,lifescience,medical release follows the first-order kinetics in (1), leading to an analytical solution of an exponential function. In contrast, a solution to diffusion-driven release in the monolithic systems is comprised of an infinite series of exponential terms [21]. Because this study

focuses Inhibitors,research,lifescience,medical on the effects of drug-carrier interaction on drug release, transport of drug molecules via various mechanisms is described by the first-order kinetic model in (1). While the model provides

an accurate description of several release mechanisms, it only approximates diffusion-driven release. Nevertheless, this simplification is necessary for obtaining an analytical solution when drug-carrier interaction is considered in drug release from various nanomaterials. 2.2. Drug-Carrier Interaction In addition to the transport of drug molecules, drug-carrier interaction is another important mechanism Inhibitors,research,lifescience,medical dictating the drug release profiles. Drug molecules may directly interact with drug carriers, lowering their solubility and/or retarding others their release from drug carriers. Drug molecules may complex with each other or additives and then interact with drug carriers. To simplify the model, drug molecules that are not molecularly dispersed in the system are assigned collectively into a group called associated molecules, which need to be disassociated from carriers prior to release. The association and disassociation processes are assumed to be reversible. Furthermore, the reversible association of a drug molecule with a carrier is assumed to follow the first-order kinetics, in a fashion similar to reversible drug-stent interactions [22, 23].