Recently, researchers at BASF Corporation, Pharma Solutions (Ledgewood, NJ), used a Thorlabs’ OCM1300SS swept source optical coherence tomography system (central wavelength 1325 nm, 10 dB spectral bandwidth > 130 nm, 16 kHz scan rate, ~10 mW output power) to monitor the change in inert cores in a delayed-release drug delivery system. Delayed-release drug delivery systems provide controlled drug release after a predetermined lag time. Due to increasing demand, various types of single unit (tablet or capsule) and multiple unit delayed release systems are being developed. The experiments completed by BASF demonstrate the usefulness of swept source OCT for visualizing the layered configuration in this particular drug design, while observing the dissolving layers under a fluid bed.

Multi-layered delayed-release systems usually consist of an inert core and three layers of coating, coating: a drug layer, a swellable polymer layer, and a water insoluble polymer outer coating. The last layer protects the system and is designed to rupture from the pressure caused by the swelling of the underlying layer as it absorbs water. Using the swept source OCT system, the BASF researchers evaluated several different formulations involving a new type of outer coating based on a polyvinyl acetate dispersion (Kollicoat® SR 30D). In order to evaluate its potential use in delayedrelease drug systems under normal conditions, a drug bead was formulated based on an inert sugar core and multilayer polymers with the Kollicoat® SR 30D outer coating, and studied under a bed of water. Thorlabs’ high-speed OCT imaging system was chosen to evaluate the performance of this coating due to the ability of the OCT laser to penetrate the top polymer film and probe the microstructure of the layers below (see Figure 3).

The high speed and high resolution provided by the swept source OCT system provided real-time cross-sectional data at 20 frames per second, which proved useful for monitoring the dissolving process. These results suggest that OCT is a useful imaging tool for monitoring dynamic physical processes such as pill dissolution, as well as other potential pharmaceutical applications such as determination of layer thickness and 3D surface profiling for quality control purposes.

Figure 1: The OCT image reveals the layered structure of the drug bead with coatings (scale bar is 500 µm). This image was obtained prior to exposing the drug bead to the water bath.

Figure 2: A 3D OCT image is shown of the ruptured bead with multiple coatings (imaging volume is approximately 1.5 mm x 1.5 mm x 1.5 mm). This image shows the ruptured coating of the bead and release of its inert core.

Figure 3: 3D cross-sectional imaging of the bead shows the ruptured coating and partial release (imaging volume ~0.8 mm x 0.8 mm x 1.8 mm).