Pharmaceutical Manufacturing Handbook: Production and

1302 PHARMACEUTICAL NANOSYSTEMS
TABLE 4 Chemical Vapour Deposition Methods and Their Key Features
CVD Method
Key Features
Atmospheric pressure CVD [178,
Operates at atmospheric pressure
179]
Atomic layer CVD (atomic layer
High - precision fi lm thickness and uniformity
epitaxy) [180, 181]
requirements
Aerosol - assisted CVD [182, 183]
For use with involatile precursors
Direct liquid injection CVD [184,
High fi lm growth rates possible
185]
Hot - wire CVD [186] High growth rate, low temperature, and use
of inexpensive materials such as plastics
as substrate
Low - pressure CVD [187]
Improved fi lm uniformity
Metal organic CVD [188]
Uniform and conformal deposition
Microwave plasma - assisted CVD
No external heating required
[189]
Plasma - enhanced CVD [190]
Reduced substrate temperatures can be
used
Rapid thermal CVD [191]
Conformal coverage over high - aspect - ratio
features is possible, i.e., improved control
of interfacial properties
Remote plasma - enhanced CVD
Excellent conformal coverage of complex
[192]
structures
Can produce multilayer and graded layers
with tailored functional group attachment
Ultrahigh vacuum CVD [193]
Reduced surface contamination
7.3.5.2 Nanostructuring Processes for Polymeric Materials
Numerous microfabrication techniques have been used to produce a wide range of
implantable and oral drug delivery systems using materials ranging from silicon,
glass, silicone elastomer, and plastics. Fabrication techniques have rapidly evolved
to produce nanoscale objects and therapeutic systems using polymeric materials as
the substrate due to their biodegradable nature. There are a number of different
synthetic polymer systems that have been developed for this type of application,
and the most common ones are listed below:
Poly( d - lactic acid) (PDLA)
Poly( ε - caprolactone) (PCL)
Poly(vinyl alcohol) (PVA)
Polyalkylcyanoacrylates (PACA)
Poly( l - lactide) (PLLA)
Poly(lactide - co - glycolide) (PLGA)
Polymethylcyanoacrylate (PMCA)
Techniques for the production of micrometer - sized features using polymers are
well established and apply primarily to device construction. The techniques listed