Biomedical Engineering Reference
In-Depth Information
shape. To do this, the matrix material can be added before or after
the dispersed material has been placed into a mold cavity or onto
the mold surface. The matrix material experiences a melding event
that, depending upon the nature of the matrix material, can occur
in various ways such as chemical polymerization, setting, curing or
solidification from a melted state. Due to a general inhomogeneity,
the physical properties of many composite materials are not
isotropic but rather orthotropic (i.e
, there are different properties
or strengths in different orthogonal directions) [64, 94, 95].
In order to prepare any type of a composite, at least two different
materials must be mixed. Thus, a phase miscibility phenomenon
appears to be of the paramount importance [97, 98]. Furthermore,
the interfacial strength among the phases is a very important factor
because a lack of adhesion among the phases will result in an early
failure at the interface and thus in a decrease in the mechanical
properties, especially the tensile strength. From a chemical point
of view, we can distinguish several types of the interaction among
the composite components: materials with strong (covalent,
coordination, ionic) interactions; those with weak interactions
(van der Waals forces, hydrogen bonds, hydrophilic-hydrophobic
balance) or without chemical interactions among the components
[99]. Wetting is also important in bonding or adherence of the
materials. It depends on the hydrophilicity or polarity of the filler(s)
and the available polar groups of the matrix.
Biocomposites are defined as nontoxic composites able to
interact well with the human body
.
and, ideally, contain one
or more component(s) that stimulate(s) the healing process and
uptake of the implant [100]. Thus, for biocomposites the biological
compatibility appears to be more important than any other type
of compatibility [63, 101, 102]. Interestingly, but, according to the
databases, the first paper with the term “biocomposite” in the title
was published in 1987 [103] and the one containing a combination
of terms “biocomposite” and HA in the title was published in
1991 [104]. Thus, this subject appears to be quite new. The most
common properties from the bioorganic and inorganic domains to
be combined in biocomposites have been summarized in Table 6.2
[40]. For general advantages of the modern calcium orthophosphate-
based biocomposites over calcium orthophosphate bioceramics and
bioresorbable polymers individually, the interested readers are
advised to get through “Composite materials strategy” section of Ref.
[50].
in vivo
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