Biomedical Engineering Reference
In-Depth Information
The 5.0%Silk-MBG scaffolds had a decreased burst release compared to MBG scaffolds, and
maintained a sustained release (Fig. 4). The most likely explanation for this is that the 5% silk
solution forms a relatively dense silk film on the surface of pore walls which slows the drug
release; however, over time the silk will begin to degrade and its effect on the release kinetics
will therefore abate. This was evident by the fact that there was no discernible difference of the
drug-release rate of the 5.0%Silk-MBG scaffold compared to the 2.5%Silk-MBG and the MBG
scaffolds (Fig. 4). Further study has shown that after the drug release in phosphate buffer
solution (PBS), a thin Ca-P layer of micro-particles was found to have been deposited on the
surface of pore walls (Fig. 5). The formed Ca-P layer, one the one hand, will have an inhibitory
effect on drug release [24]; On the other hand, it is indicated that silk-modified MBG scaffolds
maintained the bioactivity of the surface chemistry as the Ca-P formation ability was regarded
as one of important factor for bioceramics according to Kokubo's view [25].
(b)
(a)
Fig. 5. SEM images for silk-modified MBG scaffolds after drug release in PBS.
The biological properties of silk-modified MBG scaffolds were further investigated by
evaluating the attachment, proliferation, differentiation and bone cell-relative gene (alkaline
phosphatase activity (ALP) and osteocalcin (OCN)) expression of bone marrow stromal cells
(BMSC). After 1 day of culture, BMSCs were attached to the surface of the pore walls in all
three types of scaffolds (Fig. 6). There was no obvious difference in the cell numbers and
morphology of the attached cells among the scaffold types after one day. After 7 days,
however, the density of BMSCs on 2.5%Silk-MBG and 5.0Silk-MBG scaffolds was higher
than that of pure MBG scaffolds, the BMSCs on the 5.0%Silk-MBG scaffolds eventually
reaching confluence. High magnification images show that BMSCs on 5.0%Silk-MBG
scaffolds had a more spread out morphology than those on pure MBG scaffolds and that the
cells had close contact with the pore walls of 5.0%Silk-MBG scaffolds (Fig. 6).
Silk modification significantly improved the proliferation and ALP activity of BMSCs on
MBG scaffolds. At day 1, the number of cells on the silk-modified MBG scaffolds were
comparable with that of pure MBG scaffolds (Fig. 7a), whereas by day 7, the number of cells
on the silk-modified MBG scaffolds was significantly higher than that on the pure MBG
scaffolds (p<0.05). ALP activity was used as an early marker of BMSC differentiation on
scaffolds. After 7 days of culture, the ALP activity of the cells on all three scaffold types was
