Biomedical Engineering Reference
In-Depth Information
the bone marrow.
50
Thus, mechanical property is the first criteria taken into
consideration when designing a material to be used as a bone scaffold. For
this, the mechanical strength of CNTs and carbon nanofibers (CNFs) is excel-
lent making them largely studied nanostructures as reinforcing agents in com-
posite materials
171-173
and for bone scaffolds.
50,174,175
In addition, unlike other
metallic or ceramic-based bone scaffolds used in orthopedics single CNTs
are less dense making lighter scaffolds with very high strength.
50
Single-wall
carbon nanotubes (SWCNTs) offer additional properties such as high flex-
ibility and a very high Young's modulus (stiffness) in the range of terapascals
(TPa).
175,176
The tailorable electrical and mechanical properties of CNF/polymer com-
posites have attracted attention for orthopedic applications. CNFs-polyurethane
(PU) nanocomposites promoted osteoblast adhesion
177
in comparison with con-
ventional carbon fibers and Ti (ASTM F-67, Medical Grade 2). These show the
ability of nanophase composites to increase functions of bone cells whether
used alone or in polymer composite form but which is not yet fully explored
for orthopedic applications. The improved mechanical and biocompatibility
properties of CNF/polymer composites hold promise for alternative orthopedic
implant.
Like other nanomaterials, CNTs/CNFs can be functionalized with groups
that can improve their biocompatibility
178,179
and/or mechanical strength
180
of
the scaffolds.
50
Furthermore, the material surface free energies influenced cell
adhesion that eventually affected subsequent functions of different types of
cells causing enhanced tissue regeneration.
181-184
Hence, scaffolds containing
various amounts of CNFs lead to a composite that can be used to selectively
enhance functions of one type of cell but decrease functions of others.
50
These
versatile nanocomposites lead to numerous applications in biological scaffolds
particularly for orthopedic applications.
In an in vitro study, Price et al.
177
dispersed CNFs in polycarbonate
urethane (PCU) to create composites (a PCU/CNF composite) and tested the
adhesion of osteoblasts (bone-forming cells), fibroblasts (soft tissue-forming
cells), chondrocytes (cartilage-synthesizing cells), and smooth muscle cells
on the composite scaffolds. The results indicated that the composites with
nanometer dimension carbon fibers promoted osteoblast adhesion without
promoting the adhesion of other cells. Furthermore, when carbon nanofiber
surface energy was increased, the adhesion of smooth muscle cell, fibroblast,
and chondrocyte decreased, indicating that surface energy is an important
parameter that influences cell adhesion and therefore subsequent cell func-
tions. In this study, they reported that greater weight percentages of high
surface energy carbon nanofibers in the PCU/CNF composite increased
osteoblast adhesion while decreasing fibroblast adhesion. Such a material is
desirable because it can promote osteoblast adhesion and decrease competi-
tive cell adhesion that leads to faster integration of the bone to the implant
surface in vivo.
177
Their study showed the versatility of CNFs to tailor the
