Biomedical Engineering Reference
In-Depth Information
(a)
(b)
100nm
100nm
Fig. 9. TEM images of MBG (a) and BG (b) powders [7].
morphology (Fig. 10a), whereas the MBG or BG composite scaffolds had a more open pore
morphology (Fig. 10b and c) compared to the silk scaffolds. The pore size of the pure silk
scaffolds ranged from several tens to one hundred micrometers; the pore size of the
composite scaffolds is larger than that of pure silk scaffolds [33].
The compressive strength and modulus of MBG/silk scaffolds were 420kPa and 0.70MPa,
respectively, figures that were comparable with those of pure silk scaffolds and greater than
those of BG/silk scaffolds (300kPa for compressive strength and 0.5MPa for modulus). It is
speculated that the incorporation of BG particles into silk scaffolds may destroy the inner
structure of silk and lead to the detrimental effect of the mechanical strength of silk
scaffolds. Although MBG particles may also destroy the inner structure of silk, however,
MBG has high surface area and pore volume, and parts of silk solution may enter into the
nanopores of MBG during preparation, which leads to a strong bond between MBG particles
and silk after freeze-drying. Thus, the incorporation of MBG into silk will not decrease the
mechanical strength of silk scaffolds [33].
The apatite-mineralization ability and ion release of scaffolds were carried out using
acellular simulated body fluids (SBF). The morphology of the three scaffold species, after
soaking in SBF, is shown in Figure 11. There was no apatite particles deposit visible on the
pore wall surfaces for pure silk and BG/silk scaffolds (Fig. 11a and b). However, a layer of
apatite microparticles formed on the pore wall of MBG/silk scaffolds (Fig. 11c) and at
higher magnification apatite was seen as nano-sized particles (Fig. 11d). EDS analysis
revealed the ratio of Ca/P of the apatite to be 2.3 [33]. Apatite mineralization of silicate
materials, such as CaSiO
3
ceramics, 45S5 bioglass, etc. is thought to be an important
phenomenon in the chemical interactions between the implant materials and the bone tissue,
which ultimately affects the
in vivo
osteogenesis of the bone grafting materials [34-36]. In
this study, MBG/silk scaffolds had an obvious apatite mineralization in SBF, whereas
neither BG/silk nor pure silk scaffolds induced apatite mineralization. This suggests that
MBG/silk scaffolds have an improved “
in vitro
bioactivity”, a term that has been used in
previous studies [25,37,38].
There was a sustained release of Si ions from both the MBG/silk and BG/silk scaffolds, even
across an extended period of soaking and the MBG/silk scaffolds had a faster rate of Si ion
release than BG/silk scaffolds. The pH value of SBF with MBG/silk scaffolds stayed within
a range of 7.25-7.5 throughout the 6 weeks of soaking. The pH values of the pure silk and
