Coating Technology

A - Particle Coating:

A novel use of the fine particle formation process is to perform the process in the presence of large particle, water-soluble substrates. In this embodiment of the technology, the solute chemical (drug or coating) is deposited as a fine film or nanoparticulate coating on the surface of the substrate.

In this embodiment of the technology, a substrate (e.g., drug particles) is fluidized, or lifted, by a stream of supercritical or near-critical CO2 flowing upward through a conical chamber. CritiTech’s coating process is similar to the commercial Wurster coater except that the hot air stream which serves to fluidize and to dry the spray droplets is replaced with the thermally mild supercritical CO2. As illustrated in figure 2, the beads are lifted and circulated in a continuous process that isolates each bead. Because the beads are suspended in a flowing stream of supercritical or near-critical CO2, chemical-laden (e.g.: drug; taste-masking coating; time-release coating) organic solvent can be sprayed into the flowing stream causing the chemical to precipitate on the surface of the substrate. In this way this process is analogous to the nanoparticle formation process except that the particles are allowed to aggregate on the surface of the substrate.

Schematic of particle coating device using SCF to lift particles and remove solvent

Potential uses of this embodiment are taste masking, delayed or sustained release of drug material, rapid dissolution of drug from the surface of slowly dissolving beads and sequential release of more than one drug substance. An advantage of this process versus the air fluidization process currently in use is that a variety of organic solvents can be used because the system is closed, solvent removal is quantitative and solvents can be recaptured, not released to the atmosphere. Another advantage is that operating temperatures are substantially lower since the process is not an evaporative one. Finally, because the coating chemical is dissolved in non-aqueous solvents, and supercritical CO2 is essentially non-polar, water-soluble substrates can be easily coated with this technique.

As with the production of nanoparticulate drugs, commercial utilization would begin with a research contract to optimize the conditions of coating for the client company and would progress through the various stages of drug approval until the ultimate stage of mass production was reached.

B - Stent Coating:

Using its patented supercritical fluid-based coating technology, CritiTech, Inc., has succeeded in coating cardiac stents with polymers containing dye to facilitate viewing of the coated stent and drug substance to monitor sustained release. Stents can be fluidized in a stream of near critical carbon dioxide in a chamber that is similar in design to a Wurster coater.
Polymer, dissolved in suitable organic solvent, is sprayed into the near critical carbon dioxide in close proximity to the fluidized stents. Thickness of coating can be controlled by duration of spraying. Texture can be controlled by alteration of temperature above and below the glass transition temperature of the polymer used.

This stent coating procedure is an extension of CritiTech’s patented technology that is used for coating water-soluble substrates with organic-soluble coating materials. CritiTech can coat substrates in the size range from 300 microns to 1/4-inch tablets uniformly, rapidly and in bulk.

continue to lyophobic precipitation