Biomedical Engineering Reference
In-Depth Information
Particles are cross-linked with glutaraldehyde. Particles produced by this method have
better acid stability than those prepared by other methods.
7.2.1.3 Spray Drying
Spray drying is a well-known technique to produce powders, granules, and agglomerates
from a mixture of drug and excipient solutions as well as suspensions. The method is
based on drying atomized droplets in a stream of hot air. In this method, CMs are first
dissolved in an aqueous acetic acid solution, and then the drug is dissolved or dispersed
in the solution and, finally, a suitable cross-linking agent is added. This solution or dis-
persion is then atomized in a stream of hot air. Atomization leads to the formation of
small droplets, from which the solvent evaporates instantaneously leading to the forma-
tion of free flowing particles [6] as depicted in Figure 7.3 [1]. Various process parameters
have to be controlled to get the desired size of particles. Particle size depends on the size
of the nozzle, the spray flow rate, atomization pressure, inlet air temperature, and extent
of cross-linking.
7.2.1.4 Emulsion-Droplet Coalescence Method
The novel emulsion-droplet coalescence method was developed by Tokumitsu et al. [7],
which utilized the principles of both emulsion cross-linking and precipitation. However,
instead of cross-linking the stable droplets, this method induces precipitation by allow-
ing coalescence of CS droplets with NaOH droplets. First, a stable emulsion containing
an aqueous solution of CS along with drug is produced in liquid paraffin oil and then,
another stable emulsion containing CS aqueous solution of NaOH is produced in the
same manner. When both emulsions are mixed under high-speed stirring, droplets of
each emulsion would collide at random and coalesce, thereby precipitating CS droplets
Compressed air
Chitosan solution
Hot air
Exhaust
Drying chamber
Cyclone
Microparticles
Figure 7.3
Schematic representation of preparation of chitosan particulate systems by means of spray drying method.
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