Biomedical Engineering Reference
In-Depth Information
TABLE 7.2
Polymers Investigated for Oral Peptide Delivery
Category
Polymers
Synthetic biodegradable polymers
Poly(glycolic acid), poly(lactic acid),
and copolymers
Poly(hydroxy butyrate)
Poly(anhydrides)
Poly(cyanoacrylates)
Poly(ortho esters)
Poly(phosphazenes)
Nonbiodegradable synthetic polymers
Poly(acrylic acid) and derivatives
Poly(ethylene glycol)
Poly(hydroxymethyl methacrylate)
Poly(vinyl alcohol)/poly(vinyl acetate)
Poly(vinyl pyrrolidone)
Natural polymers
Chitosan and derivatives
Alginate
Cellulose and starch
Gelatin, casein and collagen
Pullulan
Xanthan
7.4.1 S
YNTHETIC
B
IODEGRADABLE
P
OLYMERIC
N
ANO
/M
ICROPARTICLES
A large number of biodegradable polymers have been investigated as carriers in the design of con-
trolled drug-delivery systems. Biodegradable nanoparticles are in much demand nowadays because
of their selective uptake by Peyer's patches, which gives them great potential as carriers for oral
peptide- or oral vaccine-delivery systems. Biodegradable polymers such as polylactide or glycolide,
polyanhydrides, and the like, are capable of moving across intestinal epithelium [31,32]. It was pro-
posed that the use of these nanoparticles would be benefi cial for oral delivery because of their
control release properties and their ability to protect drugs without exposing them to the gastric and
intestinal fl uids. However, a major issue with this approach is the insuffi cient absorption of nanopar-
ticulate drug carriers to achieve an acceptable degree of bioavailability [33].
Drugs administered through the gastrointestinal tract are normally transported into systemic
circulation by the portal vein. As a consequence, compounds can sometimes undergo extensive
metabolism during the fi rst pass through the liver. First-pass metabolism may result in reduced bio-
availability for many drugs compared with the parenteral administration, where drugs are directly
released into the systemic circulation. If a drug is absorbed through the lymphatic system rather
than by the portal circulation, it will fi nd its way into the blood through the thoracic duct and
will, therefore, avoid the fi rst-pass effect [34]. A drug absorbed lymphatically is incorporated into
chylomicrons (and other lipoproteins) produced by the fat digestion process. Numerous attempts
were made to utilize this route for developing oral peptide-delivery system.
The idea of using biodegradable hydrophobic nanoparticles was proposed as a possible system to
deliver proteins through the lymphatic circulation to achieve a higher degree of success. In the 1960s,
Volkheimer described intestinal uptake of particulate matter on the absorption of intact starch particles
[35]. This description awakened the hopes of achieving peptide and protein delivery using particles as
carriers. Thereafter numerous studies were undertaken to establish the phenomenon of particle uptake,
and now it is most accepted that the uptake happens mainly through phagocytosis [36]. Further studies
carried out using model particles (polystyrene latex, polymethylmethacrylate) in the range of 50 nm
