Biomedical Engineering Reference
In-Depth Information
For human bone, the microstructure-property relationship and the relative
importance of bone mineral density and bone architecture on fracture behavior
need further investigation [
117
,
133
-
135
].
4.3 In-Vitro and In-Vivo Studies
In an early study by Vrouwenvelder et al. [
136
] osteoblasts were seeded on pol-
ished bioactive glass (45S5) slides and cultured for several days. Figure
6
shows
the morphology of osteoblasts after 2 days' cultivation. The cells in the center
show a well-developed morphology; they are well spread and tend to form a
monolayer.
In addition to providing excellent in vitro bioactivity, suitable cellular behavior
and favorable mechanical properties, bioactive glass-ceramic scaffolds have
shown also superior in vivo behavior (e.g., bone formation, mineralization, higher
interfacial strength between implant and bone) compared to the glass in particulate
form [
90
] or compared to other bioactive materials (e.g., HA, tricalcium phos-
phate) [
48
].
For example, Wang et al. [
137
] implanted sol-gel-derived porous bioactive
glass discs of 1 cm diameter in New Zealand rabbits. After 5 weeks, histological
results showed newly formed tissue in the form of widely distributed collagen fiber
strands (Fig.
7
). San Miguel et al. [
107
] reported superior osteoconductive
behavior using a rabbit calvarial bone model (i.e., significantly higher bone for-
mation, bone deposition) of SBF-pretreated scaffolds (BG fiber constructs) com-
pared with non-treated porous BG scaffolds, bioactive glass granules (PerioGlas
)
and empty bone defects.
Fu et al. [
138
] reported on the implantation of a 13-93 bioactive glass scaffold
into subcutaneous pockets in the dorsum of rats. Scaffolds with both a ''trabecular''
microstructure (processed via the polymer sponge method, porosity 65%, pore size
between 100-500 lm), and with a columnar microstructure (processed via uni-
directional freezing of the suspension, porosity 65%, pore size between 90 and 110
lm) were investigated. After 4 weeks the columnar scaffolds showed abundant
tissue ingrowth whereas the trabecular scaffolds showed only limited tissue
infiltration.
5 Bioactive Glass Containing Composite Scaffolds
Most glass-ceramic scaffolds analyzed in the literature show a suitable intercon-
nected macroporous network and compressive strengths [2 MPa, which is in the
range of the compressive strength of cancellous bone (Table
2
). The scaffolds can
therefore fulfill the requirement in terms of compressive strength. However, load-
bearing bone defect sites are usually under cyclic loading and, as the scaffolds are
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