Biomedical Engineering Reference
In-Depth Information
for the prevention of implant-associated infections. h e main principle
of such devices is that an antimicrobial drug bound superi cially to a
medical device either directly or by means of a carrier or incorporated
into the interior of the polymer. If such device comes into contact with
an aqueous environment, drug release occurs in the immediate vicinity.
h e amount of the antimicrobial substance released is inl uenced by some
parameters such as, loading dose, applied technique, molecular size of the
drug and the physico-chemical properties of the polymeric device. Most
materials exhibit a release pattern according to i rst-order kinetics, with
an initially high drug release and subsequent exponential decrease of the
released drug.
Medical devices built from a material that would be antiadhesive or
colonization-resistant in vivo would be the most suitable candidates to
avoid colonization and subsequent infection [112, 113]. However, the
most studies have focused on the incorporation or superi cial coating
of polymers with antimicrobials agents [114, 115]. Antimicrobials sub-
stances that dif er from antibacterials, such as antiseptics, have also used
to develop new medical devices [116]. Also, silver has raised the interest of
many investigators because of its good antimicrobial action and low tox-
icity [117]. Antimicrobial polymers that contain silver represent a great
challenge for academics and industry [118]. Silver is a metal known for its
broad-spectrum antimicrobial activity against Gram-positive and Gram-
negative bacteria, protozoa, fungi, and certain viruses [119], including
antibiotic-resistant strains [120] and therefore it can be used to prevent
bacterial colonization on medical devices [121-124]. Silver, as an antiseptic
agent, has been ef ective in a variety of materials, including glass, titanium
and polymers. h e antimicrobial activities of commercially available silver
impregnated dressings and catheters have been reported [125]. However,
the use of medical devices containing silver must be undertaken with cau-
tion, since a concentration-dependent toxicity has been demonstrated.
2.7.2 Bioi lm Formation
An ideal biomaterial should have good mechanical properties and a bio-
compatible surface. Also, an acceptable biomaterial must not generate
a strong foreign body or exogenous reaction or inl ammation response.
Nevertheless, while a few polymeric materials are truly biocompatible,
only a much smaller number fuli ll both requirements. Although there
is a great variety of microorganisms involved as pathogens, however,
staphylococci account for the majority of infections. h eir ability to
adhere to materials and promote formation of a bioi lm comprise the
