Biomedical Engineering Reference
In-Depth Information
A very high number of microreservoirs, matrix-based systems, and similar car-
rier systems using biocompatible, biodegradable, and sterilizable materials for protein
delivery have been worked out. Microelectrical mechanical systems (briefly known as
MEMS) have been studied for pulsatile drug delivery of proteins, peptides, and several
other macromolecules. Pulsatile drug delivery using MEMS is achieved using silicon
microparticles containing an inner reservoir loaded with the drug candidate [27] . The
devices have been found to provide pulsatile, sustained drug release and are patient-
friendly psychological context. They can be a potent substitute for transcutaneous cath-
eters and may facilitate patient mobility and reduce the risk of infections.
8.3.4  Magnetically Induced Pulsatile/Triggered Release Systems
One of the oldest methods of modifying drug release from a polymeric matrix was based
on exposing the system to a magnetic field. Fabrication of magnetically active devices
from metals like magnetite, iron, nickel, and so on, may facilitate sustained drug deliv-
ery of proteins and peptides along with providing water-based, biocompatible, nonim-
munogenic carrier systems. Saslawski et al. [28] have worked on in vitro magnetically
active devices for insulin delivery, using alginate spheres. In this experiment, ferrite
microparticles and insulin powder were dispersed in an aqueous solution of sodium algi-
nate, followed by the subsequent addition of the same solution to an aqueous calcium
chloride solution, resulting in the formation of alginate microspheres. These resultant
microspheres were further cross-linked with an aqueous solution of poly(l-lysine) or
polyethyleneimine. Researchers observed that the magnetic effect produced by ferrite
microparticles and the mechanical properties of the polymeric matrix are key factors in
controlling drug release rate. These experiments also corroborated that densely cross-
linked matrices would exhibit a more sustained release drug profile as compared to ones
that are cross-linked to a lesser degree. Similarly, novel vesicular delivery systems like
liposomes are also imparted with magnetic characteristics and thereby achieve a sustained
drug release pattern. Babincová [29] developed magnet-based liposomes that entrapped
model substances like dextran and 6-carboxyfluorescein, and used a laser beam to trigger
the release of the entrapped substance. The underlying mechanism is that the heat energy
generated on absorption of laser light will be transmitted to flexible lipid bilayers of lipo-
somes. Elevation of temperature due to heat absorption leads to transition of lipid bilayers
from gel to liquid at phase transition temperature.
This rise in temperature beyond phase transition temperature leads to localized
heating of bilayered liposomes and triggers the drug release. The magnetic-based
liposomal delivery system is perceived as a potentially promising delivery system for
drug delivery in ophthalmics and transdermal drug applications. However, the magnetic
material used should be biocompatible, stable, and free from potential toxicities. U.S.
Patent 20016251365 [30] discusses the magnet-based nanometric liposomes, called
magnetosomes, made up of magnetic monocrystals. These magnetosomes are used to
achieve controlled drug delivery. Preparation of charged magnetic micro- or nanopar-
ticulate systems leads to further enhancement in targeting peptides and antibodies to a
specific target, when tagged to these magnetosomes.
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