Biomedical Engineering Reference
In-Depth Information
Figure 2.13. SEM images showing the osteoclastic resorption of HAP, CHA and CFA showing
that apatite containing F (CFA) had the least number and smallest size of osteoclastic resorp-
tion pits.
Composites consisting of polymer and HA, BCP and other calcium phos-
phates are also being used as scaffolds for bone regeneration by tissue engineer-
ing [96,119]. The polymers used are either natural (e.g., collagen, chitosan) or
synthetic (e.g., PLA, PLGA).
Reactivity of apatites and related calcium phosphates considered as potential
candidates for biomaterials are usually evaluated in vitro by the cell response.
Different substitutions in the apatite elicit different cell responses [29,36,122,123].
For example, osteoclasts (bone-resorbing cells) were shown to have greater activ-
ity (greater number and larger resorption pits) on carbonate-substituted apatites
compared to F-substituted apatites, as shown in Figure 2.13 [29]. Osteoblasts
(bone-forming cells) were shown to have greater activity on F-containing apatites
compared to F-free apatites, in vitro [28,36] .
In vivo , the amount of bone formation or type of bone (lamellar or woven)
also depends on the composition [111]. Figure 2.14 shows histological pictures of
similar size granules of carbonate apatite and HA implanted in bone defect in rat
cranium after 12 weeks. The size of the HA granule was not changed signifi cantly,
while the size of the CHA granule was greatly reduced. In addition, greater
amount of new bone surrounded the CHA granule compared to that around HA
granule.
The properties of calcium phosphate based biomaterials that make them
superior materials include: similarity in composition to the bone mineral,
bioactivity, and osteoconductivity [65]. Bioactivity is the ability to directly bond
with bone thus forming a uniquely strong interface [104]. In vitro, bioactivity is
usually determined by the formation of carbonate apatite on the material surface
after immersion in “simulated biologic fl uid” (SBF) with electrolyte composition
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