Biomedical Engineering Reference
In-Depth Information
S0142961206007630 - ref_bib35
). Only a few studies are dedicated to understand
the degree to which nanomaterials interact with various cells to describe why nano-
materials demonstrate unique biological properties. One possible explanation lies
in the nanostructures of the natural tissues and associated extracellular matrices. A
more plausible explanation is that nanomaterials mimic dimensions of components
of tissues for tissue engineering applications that relies on their unique surface
energetics. Prior to adherence of cells, proteins are adsorbed to a material surface to
potentially interact with selected cell membrane receptors.
112
Specific amino acid
sequences of adsorbed vitronectin, fibronectin, and laminin may either enhance
or inhibit cellular adhesion and growth. The surface chemistry, hydrophilicity or
hydrophobicity, charge, topography, roughness, and energy affect the type, concen-
tration, conformation, and bioactivity of plasma proteins adsorbed.
112,113
The unique properties of nanomaterials include higher surface areas, higher
surface roughness, higher amounts of surface defects (including grain boundaries),
altered electron distributions, improved topography, and biocompatibility.
112
These
affect interactions with proteins and other biomolecules which are nanoscale enti-
ties. The nanoscale surface features on nanomaterials can provide for more avail-
able sites for protein adsorption affecting the amount of cellular interactions.
112
The cellular interactions with artificial surfaces are complex and still cur-
rent unresolved.
114,115
Ideally, cell adhesion to surfaces and neighboring cells
involves formation of specific short-range attractive forces that are formed
through molecular ligand-receptor recognition steps to overcome specific
long-range repulsive forces between hydrophilic surfaces and glycocalyx mac-
romolecules.
114,116
After the occurrence of a short-term cell adhesion, further
adhesion and spreading are governed by a subtle combination of molecular rec-
ognition and mechanosensing, which depends on surface topography, nature of
functional groups, surface energy (wettability), stiffness, and the contact area
between cell and substrate.
117,118
The surface parameters modulate the start of
adhesion when cells are cultured without serum or when adsorbed cell-adhesive
glycoproteins such as fibronectin or vitronectin are present.
119
However, cell
adhesion to polystyrene surfaces can be triggered by hydroxyl groups even in
the absence of serum or cell-produced fibronectin
120
(
Figure 6.3
)
77
.
6.3.1 Nanomaterials for Bones
Natural bone is a nanostructured composite material.
112
It has three levels of struc-
tures namely: (1) the nanostructure (a few nanometers to a few hundred nano-
meters) that includes noncollageneous organic proteins, fibrillar collagen, and
embedded mineral hydroxyapatite (HA) crystals; (2) the microstructure (from 1 to
500 µm) that includes lamellae, osteons, and Haversian systems; and (3) the mac-
rostructure that includes cancellous and cortical bone.
121
These three levels of ori-
ented structures assemble into heterogeneous and anisotropic bone
112
using natural
porcine femur bone as seen by scanning electron microscopy (SEM) and AFM.
112
