Biomedical Engineering Reference
In-Depth Information
(a)
Larger pores
Laminar channels
Smaller pores
200 μm
400 μm
400 μm
(b
)
150 μm
150 μm
200 μm
FIGURE 7.3
Silk fibroin scaffolds with various pore sizes prepared using regenerated silk solution. Unseeded silk
scaffolds (a) and human bone marrow stem cell-seeded scaffolds (b). Cells are stained with rhodamine-phalloidin
(actin-red) and Hoechst 33342 (nuclei-green false color).
leaching possess a useful combination of high compressive strength and uniform, interconnected pores
with controllable pore size and size distribution. In the case of the HFIP-derived scaffolds, a large range
of concentrations (6-20%, w/v) can be used that exceed those (4-10%, w/v) for the aqueous-derived
scaffolds. Stiffness, compressive strength, and modulus were elevated with an increase in percent silk
fibroin solution utilized in the process to form the sponges [82]. Further, enzymatic degradation of
aqueous-based sponges was more rapid than for the solvent-based sponges, likely due to higher poros-
ity of the matrices along with less β-sheets [82]. It has also been observed that aqueous-based sponges
have rougher surface morphology than solvent-based sponges due to the partial solubilization of the
surface of the salt particles. Improved cell attachment was noted for the aqueous silk fibroin sponges in
comparison to the solvent-based porous sponges, likely due to these rougher surfaces and high porosity.
Porous 3D silk sponges have been widely utilized in a number of cell studies to generate connective
tissues. RGD-coupled silk sponges seeded with hMSCs cultured in osteogenic media resulted in the dif-
ferentiation of the cells, with deposition of hydroxyapaptite and upregulation of bone markers
in vitro
[83]. Tissue-engineered silk sponges were found useful for healing critical-size femur defects in rats [84].
Further, studies using aqueous porous sponges with large pore sizes (900 μm) were used for bone tissue
engineering where structures similar to trabecular bone were observed after 28 days of hMSC differ-
entiation in osteogenic media [85]. Solvent-based silk sponges were cultured with hMSCs in chondro-
genic media resulting in the upregulation of collagen type II and glycosaminoglycan transcripts when
compared to sponges composed of collagen or cross-linked collagen [86]. The structural integrity of the
silk sponges compared with rapidly degrading collagen-based sponges was in part responsible for the
differences in gene regulation [86]. Chondrocytes from New Zealand white rabbits were cultured in silk
fibroin sponges and proliferated faster and generated a higher content of glycosaminoglycans compared
with collagen sponges [87]. Further, porous silk fibroin scaffold sponges seeded with rabbit chondro-
cytes, in chondrogenic media, yielded a frictional coefficient similar to that of native cartilage after 28
days of culture [88,89]. In skin-related study, sponges formed from a blend of poly(vinyl alcohol) (PVA),
chitosan, and silk fibroin showed the best healing of epidermis and dermis of rats when compared to the
paired or single polymers [90].
