Biomedical Engineering Reference
In-Depth Information
SAMs was correlated to the affinities of the Fn-specific monoclonal antibodies.
Although antibody-based measurements could not distinguish between conforma-
tional (structural) and orientational changes in the adsorbed proteins, they provided
information about the biological activity of adsorbed proteins.
2.3.4 Cell Adhesion in Serum-Free Medium
Cells are sometimes cultured in serum-free medium. In this condition, the surface
should carry substituents of serum proteins that can directly interact with
cells. SAMs of alkanethiols with bioactive ligands have been used to control
interactions between the material surface and cells [
80
-
83
]. Several bioactive
ligands have been tested, including RGD [
80
], PHSRN [
81
], and laminin-derived
peptides [
82
,
83
]. These ligands were expected to directly interact with cell
surface integrins.
SAMs of alkanethiols that carried RGD peptides were tested to determine the
minimum amount of peptide required for cell adhesion to the substrate. Roberts et al.
employed SAMs of alkanethiols with mixtures of RGD and oligo(ethylene glycol)
moieties that resisted nonspecific protein and cell adsorption [
80
]. Bovine capillary
endothelial cells attached and spread on SAMs that had a mole fraction of RGD,
w
RGD
10
3
. This fraction
indicated that the RGD density was on the order of 10
11
RGD molecules/cm
2
,
assuming that the RGD occupied an alkanethiol area of ~0.25 nm
2
/molecule.
Arnold et al. designed a hexagonally close-packed rigid template of cell-adhesive
gold nanodots coated with cyclic RGDfK peptide. They used block-copolymer
micelle nanolithography to create a patterned surface [
84
]. The gold nanodots were
placed with 28, 58, 73, or 85 nm spacing, based on the molecular weight of
the block-copolymer. Adhesion tests with osteoblasts, fibroblasts, and melanocytes
showed that cells adhered and spread on the patterned gold nanodots with a spacing
of
10
5
. Cell spreading reached a maximum at
w
RGD
58 nm. This result also showed that the RGD density was on the order of 10
11
molecules/cm
2
.
3 Cell Culture Substrates for Specific Cell Proliferation
In standard cell culture methods, cells are plated in a cell culture flask or Petri dish,
and they are maintained in medium supplemented with FBS and various growth
factors. Cells adhere to the substrate through integrin and cell adhesion
glycoproteins that adsorb to the plastic surface of the flask or dish. Primary cells
isolated from embryonic and adult tissues are widely cultured with these methods.
Nevertheless, it appears that this conventional culture method is inefficient for the
production of specific cells in high purity and large quantities. Although different
kinds of cells isolated fromwidely different tissues can adhere and proliferate in cell
culture flasks, efficiency may be limited by the heterogeneity of cell populations.
