Biomedical Engineering Reference
In-Depth Information
Alginate solution reservoir
High-voltage power suppl
y
Syringe pump
Needle
Gelling solution
FIGURE 20.7
A schematic illustration of a typical electrostatic bead generator. The electrostatic potential
between the needle delivering the alginate solution and the electroconductive gelling solution forces the drop-
lets to fall from the needle tip before they grow to a point where they would fall due to their own weight.
2 h before washing in distilled water and drying at room temperature. Increasing the chitosan
concentration was found to improve the number of beads attaching to the surface of the intestine
after 1 h [64].
20.6.1.3
Nanoparticle Drug Delivery Systems
The effi ciency of delivering drugs via oral routes to colon can be reduced in gastrointestinal dis-
eases, such as infl ammatory bowel disease, where symptoms may include diarrhea. This can lead to
the accelerated elimination of microscopic drug delivery systems and a reduction of possible drug
release at the target site. One suggested approach to overcome this problem is the reduction in size
of the drug carrier down to nanoparticle-sized systems [72].
Nanoparticles are submicron colloidal carriers composed of natural or synthetic polymers.
Various methods can be used to fabricate polymeric nanoparticles, but these processes can be
broadly divided into two categories: those based on physiochemical properties such as phase sepa-
ration and solvent evaporation (frequently used for hydrophobic or cross-linked water-insoluble
hydrophilic polymers) and those based on chemical reactions such as emulsion polymerization and
polycondensation (using, for example, hydrophobic vinyl monomers) [73]. Poly(lactic-
co
-glycolic
acid) nanoparticles have been successfully prepared using an “in-water” emulsion solvent diffusion
method [74]. Poly(lactic-
co
-glycolic acid) and a drug were dissolved in a solvent mix of acetone
and ethanol, both of which dissolved in aqueous solution. When the polymer solution was poured
into aqueous poly(vinyl alcohol) solution, the rapid diffusion of solvent into the aqueous phase
(the Marangoni effect) resulted in the immediate formation of a submicron oil-in-water emulsion
due to the immediate reduction of the interfacial tension and rapid diffusion of organic solvent into
the aqueous phase. The nanosphere suspension was centrifuged and washed in distilled water to
remove the aqueous phase containing solvent and freeze-dried to produce a free-fl owing powder
consisting of monodispersed nanoparticles approximately 250 nm in diameter [74]. Although this
technique is relatively simple, its major drawback is the low entrapment effi ciency when used with
water-soluble drugs that leach from the nanoparticles during the solvent diffusion process. This
problem was reduced by changing the dispersion medium from an aqueous solution (“in-water”)
to an oily medium (“in-oil”) such as the medium chain triglyceride caprylate. Because the rapid
diffusion of solvent into the oil medium did not occur, a surfactant, such as Span 80, was added
