Biomedical Engineering Reference
In-Depth Information
9
Inorganic Nanostructures
for Drug Delivery
Ying-Jie Zhu
CONTENTS
9.1 Introduction...........................................................................................................................
217
9.2 Nanostructured Silica as Drug Carriers................................................................................
218
9.3 Nanostructured Calcium Carbonate and Calcium Phosphates as Drug Carriers .................
224
9.4 Magnetic Targeting Drug Delivery Systems.........................................................................
226
9.5 Concluding Remarks.............................................................................................................
231
References ......................................................................................................................................
231
9.1 INTRODUCTION
Nanotechnology has had a signifi cant impact on the development of drug delivery systems over the
past decade, leading to the emergence of entirely new research fi elds [1]. For the pharmaceutical
industry, novel drug delivery technologies represent a strategic tool for expanding drug markets,
evidenced by the fact that sales of products incorporating a drug delivery system account for approxi-
mately 13% of the current global pharmaceutical market. The demand for drug delivery systems in
the United States alone is expected to grow by nearly 9% annually, to more than US$ 82 billion by
2007. Controlled drug delivery provides the ability to control the release rate of the drug and the
delivery of the drug to a specifi c location in the body (i.e., targeting). Recently, some reviews on drug
delivery were published [1-4]; however, these reviews focused primarily on polymeric systems.
Many organic materials such as polymers [5], liposomes, and micelles have been investigated
as drug delivery carriers. However, unsolved problems regarding these organic systems continue
to exist. These problems include low chemical stability, swelling, susceptibility to microbiological
contamination, and inadequate control over the drug release rate. The release properties of many
biodegradable polymer-based drug delivery systems are dependent on the hydrolysis-induced ero-
sion of the carrier structure [2,3]. Such systems usually require the use of organic solvents for drug
loading, which could sometimes trigger undesirable modifi cations of the structure or the function
or both of the encapsulated molecules.
In contrast, many inorganic materials are nontoxic, biocompatible, hydrophilic, and chemically
stable. These materials hold promise for the development of drug delivery systems, especially for
controlled drug delivery. It is possible to produce the stable porous structures of inorganic materials,
which can often be tailored to control the drug loading and the drug release rate. In addition, there is
no swelling or porosity change under different pH values, which is a common problem encountered
when using organic materials. Because of the abovementioned reasons, the research on inorganic
nanostructures as drug carriers has gained momentum in recent years and is currently a fast grow-
ing fi eld. In this chapter, the recent progress in nanostr uctured inorganic dr ug ca r r iers and their dr ug
delivery properties will be briefl y reviewed. However, all the literature on this subject will not be
reviewed; instead, only some related papers will be included in this chapter. This chapter is divided
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