Biomedical Engineering Reference
In-Depth Information
between strength and toughness with improved characteristics compared with
their individual components.
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For example, bone is a natural organic/inorganic
composite material consisting of collagen and apatites
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making composite
materials excellent choices to make bone tissue engineering scaffolds.
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A multitude of current opportunities for polymer nanocomposites in the bio-
medical field arise from the diverse applications with different functional require-
ments
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but the mechanical properties of available polymeric porous scaffolds
offer insufficient stiffness and compressive strength compared with human bone.
This leads to the use of inorganic/organic nanostructures as components of bio-
degradable polymers to increase and modulate mechanical, electrical, and deg-
radation properties.
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Since the interface adhesion between nanoparticles and
polymer matrix is the major factor affecting the nanocomposite properties, it
is important to consider the mechanical properties of nanocomposites that are
controlled by several microstructural parameters such as the properties of the
matrix, properties and distribution of the fillers, as well as interfacial bonding
and by the synthesis/processing methods.
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To promote improved disper-
sion of fillers that will enhance the interfacial adhesion between the matrix and
the nanostructures, surface modification of nanostructures is necessary.
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Scaffolds for tissue engineering that are either synthetic or natural must
be biocompatible and must have properties including optimal fluid transport,
delivery of bioactive molecules, material degradation, cell-recognizable surface
chemistries, mechanical integrity, and the ability to induce signal transduction.
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These properties are important in the overall success of tissue organization and
development since these can ultimately dictate cell adherence, nutrient/waste
transport, matrix synthesis, matrix organization, and cell differentiation. The
scaffolding materials should be chemically and physically modified to allow
manipulation of critical parameters for tissue engineering applications.
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6.5.1 Current Polymer Matrices for Bionanocomposites
In tissue engineering, polymers are the primary scaffold fabrication materials
using many types of biodegradable polymeric materials. These materials can
be classified as: (1) natural-based materials, including polysaccharides (starch,
alginate, chitin/chitosan, hyaluronic acid derivatives) or proteins (soy, collagen,
fibrin gels, silk) and (2) synthetic polymers, such as PLA, poly(glycolic acid)
(PGA), poly(3-caprolactone) (PCL), and poly(hydroxyl butyrate) (PHB).
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238
Each of these groups of materials offers many advantages and disadvantages.
Generally, synthetic polymers offer good mechanical strength with easily modi-
fiable shape and degradation rate, but their surfaces are hydrophobic and lack
cell recognition signals. On the other hand, naturally derived polymers have the
advantage of biological recognition that support cell adhesion and function but
they have poor mechanical properties and many are limited in supply and can
be costly. Thus, synthetic biodegradable polymers, which can be produced in
