Biomedical Engineering Reference
In-Depth Information
In our search for additional functional motifs, we found that a class of bone
marrow homing peptides (BMHPs) (Gelain et al.
2006,
2007a,
b
) is one of the most
promising active motifs for stimulating adult mouse neural stem cells (NSC) adhesion
and differentiation. Likewise, we also found a newly designed two units of cell adhe-
sion motif that enhanced bone cell differentiation and 3-D migration (Horii et al.
2007
). These observations suggest a new class of designer self-assembling peptides
for 3-D cell biology studies.
4.5.1
Designer Peptide Scaffolds for Bone Cells and 3-D Migration
The designer self-assembling peptide nanofi ber scaffolds has been shown to be an
excellent biological material for 3-D cell cultures and capable to stimulate cell migra-
tion into the scaffold as well for repairing tissue defects in animals. We developed
several peptide nanofi ber scaffolds designed specifi cally for osteoblasts (Horii et al.
2007
). We designed one of the pure self-assembling peptide scaffolds RADA16-I
through direct coupling to short biologically active motifs. The motifs included
osteogenic growth peptide ALK (ALKRQGRTLYGF) bone-cell secreted-signal
peptide, osteopontin cell adhesion motif DGR (DGRGDSVAYG) and 2-unit RGD
binding sequence PGR (PRGDSGYRGDS). We made the new peptide scaffolds by
mixing the pure RADA16-I and designer peptide solutions, and we examined the
molecular integration of the mixed nanofi ber scaffolds using AFM. Compared to
pure RADA16-I scaffold, we found that these designer peptide scaffolds signifi cantly
promoted mouse pre-osteoblast MC3T3-E1 cell proliferation. Moreover, alkaline
phosphatase (ALP) activity and osteocalcin secretion, which are early and late markers
for osteoblastic differentiation, were also signifi cantly increased. We demonstrated
that the designer, self-assembling peptide scaffolds promoted the proliferation and
osteogenic differentiation of MC3T3-E1. Under the identical culture medium condi-
tion, confocal images unequivocally demonstrated that the designer PRG peptide
scaffold stimulated cell migration into the 3-D scaffold (Fig.
15
) (Horii et al.
2007
) .
Without the modifi ed motif, cells did not migrate into 3-D.
4.6
Why Designer Self-Assembling Peptide Scaffolds?
One may ask why one should choose designer self-assembling peptide scaffolds
while there are a large number of biomaterials on the market and some have already
been approved by the U.S Food and Drug Administration (FDA). The advantage of
using the designer peptide nanofi ber scaffolds is severalfold. (1) One can readily
modify the designer peptides at the single amino acid level at will, inexpensively and
quickly. This level of modifi cation is impossible with Matrigel and other polymer
scaffolds. (2) Unlike Matrigel, which contains unknown ingredients and quality that
varies from batch to batch, the designer self-assembling peptide scaffolds belong to
a class of synthetic biological scaffolds that contains pure components and every
ingredient is completely defi ned. (3) Because these designer peptide scaffolds are
