A mechanism on the drug release into a perfect sink from a coated planar matrix with a super-saturation loading in the core

Minimization of initial burst in poly(vinyl alcohol) hydrogels by surface extraction and surface-preferential crosslinking

Surface extraction and surface-preferential crosslinking were investigated as effective methods to reduce the burst effect for proxyphylline release from poly(vinyl alcohol) hydrogels. Both these techniques involved changing the surface characteristics to reduce drug diffusion during the early stages of release, with the goal of subtracting the burst effect from the release profile without altering the long-term release rate. The extraction process was carried out on both relaxed and dry gels. Proxyphylline was extracted from both freshly made and dried hydrogel samples, with the extraction from dried samples providing better control of the burst effect with smaller amounts of drug removed from the gels. The success of extracting from the dried samples was attributed to the lack of drug diffusivity and redistribution after extraction when the majority of the device remained dry. Surface-preferential crosslinking, by dipping preformed proxyphylline-loaded samples in a concentrated crosslinking solution, effectively diminished the burst effect by slowing macromolecular relaxation near the surface. Notably, this technique maintained the same long-term drug release rate as the untreated gels and less than 0.2% of the loaded proxyphylline was removed during the crosslinking step.

Finite element analysis of slow drug release through deformed coating film: effects of morphology and average thickness of coating film

This paper, a continuation of our previous work, is a presentation of the effect of the morphology and the average thickness of the deformed coating films on the slow diffusional release characteristics analyzed numerically under the constraints of the constant volume of the drug matrices and the coating films, if the films have the same average thickness. Increasing the average thickness of the coating films slows down the fractional release and the average release rate of the drug and smoothen the initial burst of the drug, as well as increase the initial lag time. The effect due to deformation of the coating films on these diffusional release characteristics are found to be less significant with the increasing average thickness of the coating films. Interestingly initial lag times are found to be the same for the coated particles having the same smallest thickness but different average thickness of coating films. The effect due to the change in the average thickness of the coating films on the characteristics of the slow controlled-release is discussed to shed light on the design of a better controlled-release device.

Slow release of drug through deformed coating film: effects of morphology and drug diffusivity in the coating film

The effects of the morphology and drug diffusivity in the coating film on the slow release characteristics have been analyzed numerically under the constraint that the volume of the coating film and the drug matrix is maintained constant. Two different systems of coated particles with deformed coating films were studied and their release characteristics compared with those of the coated particles having spherical coating films. The average release rate, fractional release, drug concentration profiles, and the initial burst of drug were found to be strongly influenced by the ratio of drug diffusivity in the coating film to that in the drug matrix D(r) (i.e., dimensionless drug diffusivity in the coating film). Increasing D(r) always increased the release rate, the fractional release, and the initial burst of drug, but reduced the initial lag times of drug release. The effect of shape deformation was very significant in the drug concentration profiles and the initial lag times; in contrast, it was not so substantial on the fractional release and the average release rates. The morphology difference in the deformed systems was also found to affect the release characteristics to different extents. Increasing the degree of the shape deformation, represented by the perturbation parameter epsilon, always reduced the effective surface area for the controlled release of drug. Because of the compensation effects between decreasing surface area and the non-uniform mass flux distribution, even though the heterogeneity of surface mass flux distribution would become more considerable, the effects of increasing shape deformation to the overall release rate would be less than expected unless the coating film was deformed significantly enough. The effect of the shape deformation and the morphology difference become less effective to differentiate the release characteristics with increasing D(r).