Biomedical Engineering Reference
In-Depth Information
Hybrid
Nanostructured
material
Biomaterial
FIGURE 12.1
Hybridization between nanostructured materials and biomaterials.
restricted freedom in their motions, conformational changes, and selected access to external signals,
including chemical and physical stimuli. The latter scientifi c aspects would be much more worthy of
research, because many sciences still remain unexplored for biomolecules in nanostructured media.
Since nanofabrication methods based on top-down approaches such as photolithography are
expected to encounter fabrication size limitations in the near future, bottom-up approaches based
on supramolecular assemblies are now receiving much attention as novel techniques to obtain pre-
cisely structured materials [1-4]. In contrast to the processes in silicon-based nanofabrication, these
approaches are suitable for hybridization of biomaterials with simple procedures under rather mild
conditions. In this background, several examples of biohybrid nanomaterials prepared by supramo-
lecular approaches are introduced in this chapter. This chapter describes fabrication strategies and
outstanding functions of three kinds of biohybrid nanomaterials, lipid-based hybrid nanomaterials,
hybrid nanomaterials with other small bioactive molecules, and hybrid nanomaterials with proteins.
12.2 LIPID-BASED HYBRID NANOMATERIALS
The simplest but most important biocomponents can be lipids and their families, which are the major
components of cell membranes. A cell membrane is mainly formed through the spontaneous assem-
bly of lipids, proteins, oligosaccharides, and others. The basic structure of the cell membrane is the
lipid-bilayer membrane and it is mimicked often by supramolecular chemistry, as seen in liposome
and vesicle structures [5-7]. In these structures, the lipid bilayer structure extends two-dimensionally
and forms the “skin” of a closed sphere that has a water pool inside. The lipid-bilayer structures are
known to behave as a thermotropic liquid crystal. At low temperature, the lipid bilayer is in a gel (or
crystalline) state with motional freezing of the alkyl chains. As the temperature rises, the alkyl chains
melt and attain a fl exible motional state, though the bilayer structure is maintained. Since permeability
of the small molecules through the lipid-bilayer membranes depends much on the states of the lipid
bilayer, permeation control upon the gel (or crystalline)-liquid crystalline phase transition of the lipid
bilayer membrane are extensively researched, which is sometimes aimed at development of drug deliv-
ery systems (DDS) [8,9]. However, the lipid-bilayer membranes themselves are mechanically weak
supermolecules, which characteristic is not always advantageous in practical usage. In order to over-
come such a weak feature of the lipid bilayer membranes, hybridization of the lipid bilayer membranes
with mechanically stable supporting materials have been widely investigated. One of the examples is
