Biomedical Engineering Reference
In-Depth Information
14.2.2 Substrate properties of composites for
bone tissue engineering
the sections dedicated to ceramics and polymeric biomaterials have
highlighted that, although promising biomaterials for bone tissue engineering
have been developed from these two classes, limitations are still present that
prevent the complete mimicking of bone extracellular matrix properties (i.e.
chemical composition, mechanical properties and biorecognition). indeed, if
analysed from a material viewpoint, bone can be considered to be a composite
material, the characteristics of which dynamically change during both repair
and remodelling processes. the formation of bone during its repair process
involves the synthesis and deposition of a polymeric scaffold (collagen type
i) by the osteoblasts which is gradually encased in a Ha-based mineral phase.
in the remodelling process, the osteoclasts gradually resorb old bone which
is replaced by new tissue produced by the oseoblasts; the combination of the
activity of these two cell types results in constant changes in the histological
features. in both processes, a tissue with a composite nature forms. in the
attempt to mimic the composite nature of bone, several polymer/ceramic
biomaterials have been developed with the intention of mimicking the
collagen template and the Ha-based mineral phase.
Here, examples are provided that are based on the use of the ceramics
and polymeric materials which were presented in the previous sections.
Before providing these examples, it is worth analysing the mechanisms of
biomineralisation; understanding them allows us to assess the strategies
that have been adopted by researchers to obtain bone biomimicking
composites.
Studies on the mechanisms of HA formation in natural systems
The mechanisms of crystal nucleation are very complex and difficult to
discern at both the experimental and theoretical level and, as a consequence,
understanding the underlying principles leading to the formation of polymeric/
matrix composite materials is not always easy. the study and understanding
of the mechanisms of crystal nucleation require a profound knowledge
of both ion solvation processes (i.e. ion/solvent interactions) and ion-ion
interactions. in the case of biocomposites, the study is complicated by the
presence of biomolecules and their effect on the crystal growth effect. Special
simulation strategies have recently been developed that extend considerably
the potential of computational studies in this field. These simulations have
been underpinned by experimental studies on the nucleation of biomimetic
apatite on gelatine hydrogels during composite preparation processes and
they have explained the mechanisms of hierarchical crystal growth at both
the micro- and mesoscopic scale. a review paper has been published that
