Biomedical Engineering Reference
In-Depth Information
Fig. 5
Human mesenchymal stem cells plated either on an unpatterned (
left
) or patterned (
right
)
nanofi brous PCL substrate. The
white diagonal line
drawn in the
right panel
schematically illus-
trates the spatial orientation of the underlying PCL fi bers (not fl uorescently visualized). Cell
viability assay indicates that cells plated on the PCL nanofi bers are live (
green color
)
may be critical in engineering functional tissue by controlling the cell and ECM
spatial patterns. In addition, high degree of control of cell orientation and alignment
may also have signifi cant implication for regulation of stem cell proliferation and
differentiation. However, one diffi culty in nanofi ber technology has been seeding
cells within a nanofi brillar structure with pore spaces much smaller than a cellular
diameter. Somehow, the network must be formed in situ, around the cells, without
cellular damage.
A class of nanofi brillar gels has been recently developed, which can self-assem-
ble around the cells under appropriate near-physiologic conditions, and the cells
survive this process (Hartgerink et al.
2002
; Silva et al.
2004
). The unit blocks of the
3D nanofi ber matrix are peptide-amphiphile molecules, which incorporate specifi c
biomolecular signals. The synthesized peptide-amphiphile molecule consists of
long alkyl tail, amino acid spacer, and peptide sequence for a specifi c cell response
(e.g., cell adhesion ligand RGD, laminin peptide). The nanofi bers 5-8 nm diameter
and up to few microns long are driven to assemble in aqueous media of high ionic
strength by hydrogen bonding and hydrophobic interactions. This promising tech-
nique can potentially produce biosystems that can be delivered to living tissues by
simply injecting peptide-amphiphile solution. This solution should self-assemble in
vivo into artifi cial scaffolds directing cell differentiation, proliferation, and other
crucial cell functions. The wide choice of amphiphile building-block molecules pro-
vides a versatile tool with environment-controllable and reversible self-assembly
mechanism for engineering various types of tissues. For example, the self-assem-
bled peptide-amphiphile nanofi bers are shown to direct hydroxyapatite crystal
nucleation and growth to form a composite material in which the alignment between
hydroxyapatite and nanofi bers is the same as that found in natural bone (Hartgerink
