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Engineering of Novel Drug Delivery Devices Based on Convex/Concave Geometries and Dynamic Analysis Using X-Ray Tomography

Nicholas A. Peppas and Elena Losi. Department of Chemical Engineering, The University of Texas at Austin, CPE 3.466, 1 University Station, Code C0400, Austin, TX 78712

A new strategy for preparing oral drug delivery formulations has been developed. Colombo and associates designed a novel release system based on hydrophilic polymers formulated as discs with two curved bases, one convex and the other concave. Since the axial section of the system or module appeared as a dome, the new system was named Dome Matrix The unusual shape of this release module was designed to favor the possible addition (stacking) of several of these systems through the firm insertion of the convex base of one module in the concave base of a second. Thus, the administered dose in the single unit can be adjusted or multi-kinetics drug delivery achieved when different modules were assembled. In addition, appropriate module assemblage can allow the delivery of two drugs in a single unit at a specific time and at a proper rate and duration.

The aim of this work was to study the drug release kinetics from cylindrical, dome-shaped hydrophilic matrices with applications in oral drug delivery. In our studies we used the vasodilating drug buflomedyl pyridoxal phosphate (BPP), as a model drug due to its high solubility and the intense yellow color that allowed the imaging of the gel layer and glassy core of the matrix. Comparison was made of BPP release kinetics from dome matrix or from classical (flat base) cylindrical matrices.

Nondestructive high-resolution visualization with high-resolution X-ray computed tomography (CT) was used for the first time to follow the process of swelling and dissolution of the swellable tablets. This new method can be applied on dry and slowly swelling samples. The fundamental principle behind computed tomography is to acquire multiple slices of an object over a range of angular orientations

In our experiment, the release system was placed in a test tube in which foam was put at the bottom to support the specimen, since it has not to move during the scan. The dome matrix was placed with the convex base in contact with the foam. The cylindrical tablet was placed with one of the two flat bases in contact with the foam. The test tube was then filled with distilled water at 37C. The tube was kept vertically.

Using a 21-23 micron resolution and an average 4-minute scanning time we have been able to obtain meaningful data from these matrices dry and at zero, 15 min, 30, 45 and 60 minutes in water.

Calibration was necessary to establish the characteristics of the X ray signal as read by the detector. CT data was then collected and then special software were required to reconstruct the raw CT images. In particular, Amira software was used to obtain 3 dimensional image data and a Blob 3D software was employed to calculate the surface area and the volume of the specimens.