Biomedical Engineering Reference
In-Depth Information
drug component. In this chapter, release-controlled coatings are categorized as polymer-
based, inorganic-based, and matrix-free. Under each category, the primary matrix materi-
als will be described in terms of materials, structures and forming techniques, and release
kinetics. With the introduction of individual cases, the perspectives of release-controlled
coatings will be discussed.
MatrixMaterials
The materials used for fabricating the matrix of stents, indicated in the constructive tri-
angle for DES (Figure 6.1), have undergone continuous and rapid development since 2002.
Traditional, simple, nonerodible polymers have been replaced by erodible, inorganic-based
systems.
Polymer-Based Matrix
Synthetic and natural polymers that are biocompatible and biodegradable are widely
used in medical and surgical applications. Among these, nonerodible polymers, such
as acrylic polymers or copolymers and erodible polymers, such as polylactic acid (PLA)
and poly(lactide-
co
-glycolide) (PLGA), are used as the matrix materials for loading drugs
onto coronary stents (Raval et al., 2007). As a reservoir for the controlled release of drugs,
the polymer-based matrix materials that first received FDA approval were nonerodible.
The sirolimus-eluting CYPHER stent (Cordis, Warren, NJ) consists of a stainless steel
platform coated with a nonerodible polymer (poly(ethylene-
co
-vinyl acetate) [PEVA] and
Platform—delivery
Strut thickness
Flexibility
Type of metal
Drugs—ecacy
Dose
Release kinetics
Polymer—safety
Degradability
Vascular toxicity
FIGURE 6.1
Constructive triangle for DES.
