Biomedical Engineering Reference
In-Depth Information
2.1 Introduction
Recently, due to their potential to signii cantly reduce the side ef ects of
therapeutics, there has been a remarkable growth in drug delivery sys-
tems used for biomedical research. h ese help signii cantly to control the
concentration and location of active drugs released in the body over long
periods of time (compared to the administration of equivalent levels of
free drugs).
h e increasing availability of biocompatible synthetic materials,
together with a continuously evolving understanding of the mechanical
details underlying disease pathology, have stimulated an explosion of new
ideas and approaches to develop interesting medical devices used as drug
delivery systems. Usually, because of their low production cost and easy
manufacturing and handling, the most widely-used materials for fabri-
cating medical devices are polymers. Among polymers with the greatest
potential for uses in this i eld, we i nd the stimuli-responsive polymers also
known as “smart”. h ese materials are able to modify their physical prop-
erties in response to a small variation of environmental factors (tempera-
ture, pH, light, magnetic and electric i eld, etc.). h e temperature-sensitive
polymers undergo an abrupt decrease of the solubility in water above a
certain temperature; this temperature is known as lower critical solution
temperature (LCST). h e stimuli-responsive polymers can be prepared in
various architectures, such as micelles, reversible hydrogels, cross-linked
(permanent) hydrogels, interpenetrating networks (IPNs), modii ed inter-
faces and comb-type and grat copolymers. h e swelling or shrinking of
smart polymers in response to small changes in pH or temperature can
be used successfully to control drug release, because the dif usion of the
drug depends on the polymer state. A thermo-responsive material can
load drugs under LCST because it has the capacity to swell drug solution.
h en, when temperature is increased further than LCST, it de-swells and
can release the drug.
However, it should be noted that temporary or permanent implanting of
medical devices usually causes injury, inl ammation and a wound healing
response, resulting in swelling and pain at the insertion site and discom-
fort for the patient. Also, some challenges such as infections, inl amma-
tion, bioi lm formation on surface, etc. must be taken into consideration.
For example, once a medical device is inserted, a race to colonize the sur-
face begins, in which proteins, host cells and microorganisms compete for
adsorption onto the material. Microbial contamination is a major concern
in this area because growth of bacteria on implanted medical devices can
lead to development of severe infections. A potential method to prevent
