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The Process
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.
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