Biomedical Engineering Reference
In-Depth Information
eficiently enhance the drug uptake in target leukemia cells. These
new nanocomposites have good biocompatibility, ease of surface
chemistry modiication, and very high surface area, which may afford
the possibility for their promising application in pharmacology and
biomedical engineering areas.
3 . 5 CompositeBiomaterials
Composite materials may be deined as those materials that consist
of two or more fundamentally different components that are able
to act synergistically to give properties superior to those provided
by either component alone [72, 94, 128]. Natural composites
include bone, wood, dentin, cartilage, and skin. In biomaterials, it is
important that each constituent of the composite be biocompatible.
Some applications of composites in biomaterial applications are:
(i) dental illing composites, (ii) reinforced methyl methacrylate
bone cement and ultrahigh molecular weight polyethylene, and (iii)
dental/orthopedic implants with porous surfaces.
Composites made of bioinert and bioactive ceramics are produced
to achieve two important features, bioactivity and mechanical
strength [43, 113]. Alumina ceramic can form composites with
hydroxyapatite that are bioactive. The properties of composites
depend very much upon structure, shape, volume fraction, and
the interface among the constituents, as well as upon the chemical
composition and their inal microstructure.
For, example, the dental composite resins consist of a polymer
matrix and stiff inorganic inclusions [26]. The inorganic inclusions
confer a relatively high stiffness and high wear resistance on the
material. Available dental composite resins use quartz, barium glass,
and colloidal silica as illers. Fillers have particle size from 0.04 μm
to 13 μm, and concentrations from 33 to 78% by weight. In view
of the greater density of the inorganic iller phase, a 77% weight
percent of iller corresponds to a volume percent of about 55%. The
matrix consists of a polymer, typically BIS-GMA. Polymerization can
be initiated by a thermochemical initiator such as benzoyl peroxide,
or by a photochemical initiator (benzoin alkyl ether) which
generates free radicals when subjected to ultraviolet light. Dental
composites have a Young's modulus in the range of 10-16 GPa, and
the compressive strength from 170 to 260 MPa (Table 3.30).
 
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