Biomedical Engineering Reference
In-Depth Information
calcium phosphate coating for titanium-based hip joints (Epinette et al., 2004), whereas
cervical disks have also been coated (Helmut et al., 2004). Other coatings have been used
to minimize frictional resistance and wear debris; such coatings are not considered strictly
bioactive.
Coatings that elute bioactive compounds locally to enhance efficacy have also been the
focus of research for several decades. Stemming from the unprecedented success of drug-
eluting stents (DES), research has intensified in this area (Venkatraman and Boey, 2007).
Other applications include coatings that elute bone morphogenic protein (BMP) in osteo
implants (Sohier et al., 2010), antifouling or antibiotic coatings, and coated micro- and
nanoparticles that have controlled the release of a bioactive. In this chapter, we discuss
both types of bioactive surfaces, the ones that involve elution of a bioactive compound and
the ones that involve immobilization of bioactive molecules.
BioactiveCoatingsType1:ControlledBioactiveElution
These coatings may be on metallic devices (osteo implants, stents) or part of a fully poly-
meric device (biodegradable stents).
Applications
Invariably, the major objective of a drug-eluting coating on an implant is to localize and
sustain the release of a bioactive, thereby enhancing its bioavailability and minimizing
systemic side effects. The idea is simple, yet surprisingly this concept did not enjoy com-
mercial success until the advent of the drug-eluting coronary stents in 2002. Attempts to
improve the performance of osteo implants using BMP have not enjoyed a similar level of
success, however. Also, although incorporation of antibiotics into bone cement has been
successful, coating of the device (such as an artificial hip joint shaft) to release an antibi-
otic has not yet been clinically successful (Pioletti et al., 2008). Similarly, bisphosphonate
(BP)-releasing coatings are the subject of intensive investigation at present (Roussiere et al.,
2005), but clinically not yet proven to be effective. Therefore, in what follows, we will focus
on drug- and bioactive-eluting stents.
Cardiovascular Coating
The use of the so-called bare metal stents results in an unacceptable rate of restenosis
in coronary arteries. To overcome this problem, stents that elute antiproliferative drugs
were first approved in the US in April 2003. The first such stent was a sirolimus-eluting
stent (SES, Cypher
®
) developed by the Cordis division of Johnson and Johnson; the sec-
ond one to win approval was a paclitaxel-eluting stent (PES, Taxus
®
) developed by Boston
Scientific and approved in March 2004. The market acceptance of these stents was spec-
tacular, with the DES displacing about 90% of the implantations previously done with
BMS in 2006 (Venkatraman and Boey, 2007). Such successes led to several other com-
panies developing DES. Approved stents include Endeavor
®
, developed by Medtronic/
Abbott Labs and approved in February 2008 and Xience™ developed by Guidant/Abbott
Vascular and approved in July 2008. Other DES approved ex-US includes the Infinnium®
®
stent (Sahajanand Medical Technologies) as well as the Axxion
®
(Biosensors Int) stainless
