2.3 Patterned Organic and Polymeric Films for Tailored (Bio)Interfaces
33
and growth, and cell–cell interactions on the microscale have been demonstrated
using microfabricated metal templates, self-assembled monolayers, biopolymers,
extracellular matrix proteins, cell-adhesive peptides, and membranes. Kleinfeld et al.
prepared siloxane SAMs, containing regions terminated in methyl and amino groups
[51]. Cerebellar cells plated in media containing serum attached and grew only on
the ionic, rather than the hydrophobic, regions of the surface, whereas cells plated
in the absence of serum are attached to all regions of the surface. Presumably, there
is a kinetic preference for serum proteins that do not promote attachment of cells to
adsorb on the hydrophobic regions.
Hyun et al. report a simple and genetic method to micropattern surfaces with
an amphiphilic comb polymer (poly(ethylene glycol methacrylate)) presenting short
oligoethylene glycol side chains that enable long-term, spatially resolved attachment,
and growth of mammalian cells in a biologically relevant milieu on a variety of
substrates. In the first step, PDMS is inked with a comb polymer, which was then
transferred onto substrate. In the second step, incubation of the patterned surface
in a protein-containing solution (fibronectin (FN) because of its role in promoting
cell adhesion) allows back-filling of only the unstamped regions with the protein via
adsorption, because the micropatterned comb polymer is protein-resistant. Incubation
of micropatterns of the comb polymer on FN-preadsorbed polymer surfaces with
fibroblasts resulted in the formation of cellular micropatterns that were confined to
the underlying fibronectin pattern, indicating the affinity of cells for fibronectin and
the ability of the comb polymer to repel cells.
2.3.2 Selective Molecular Assembly Patterning (SMAP)
To address the limitations in biomolecular patterning by μCP using PDMS, a novel
patterning approach, called selective molecular assembly patterning (SMAP), has
been developed by the Textor group (see Fig. 2.20) [52]. This approach comprises
a simple and versatile patterning technique based on selective adsorption from
aqueous media of multifunctional organic molecules onto oxide substrate prepatterned by lithographic methods (also called molecular-assembly patterning by liftoff) [53]. The preparation of cell-adhesive patterns of arbitrary geometry has been
reported. Using this patterned film, Textor and co-workers investigated the relationship between pattern geometry and the organization of elements of the cell adhesion
apparatus, namely focal contacts and stress fibers. The molecular assembly system is
based on a polycationic copolymer: poly(lysine)-graft-poly(ethylene glycol) (PLLg-PEG), which can spontaneously adsorb from aqueous solutions onto negatively
charged surfaces. The subsequent layer can resist the biomolecular adsorption on
the films due to the existence of a PEG brush. The PLL-g-PEG adlayers also show
long-term stability while still retain the resistance to protein adsorption. In addition, another advantage is that the PEG can be further functionalized with bioactive molecules (ligands). Since the fraction of PEG chain can be adjusted during
polymerization, the density of ligand end-functionalized PEG can also be controlled.
33
and growth, and cell–cell interactions on the microscale have been demonstrated
using microfabricated metal templates, self-assembled monolayers, biopolymers,
extracellular matrix proteins, cell-adhesive peptides, and membranes. Kleinfeld et al.
prepared siloxane SAMs, containing regions terminated in methyl and amino groups
[51]. Cerebellar cells plated in media containing serum attached and grew only on
the ionic, rather than the hydrophobic, regions of the surface, whereas cells plated
in the absence of serum are attached to all regions of the surface. Presumably, there
is a kinetic preference for serum proteins that do not promote attachment of cells to
adsorb on the hydrophobic regions.
Hyun et al. report a simple and genetic method to micropattern surfaces with
an amphiphilic comb polymer (poly(ethylene glycol methacrylate)) presenting short
oligoethylene glycol side chains that enable long-term, spatially resolved attachment,
and growth of mammalian cells in a biologically relevant milieu on a variety of
substrates. In the first step, PDMS is inked with a comb polymer, which was then
transferred onto substrate. In the second step, incubation of the patterned surface
in a protein-containing solution (fibronectin (FN) because of its role in promoting
cell adhesion) allows back-filling of only the unstamped regions with the protein via
adsorption, because the micropatterned comb polymer is protein-resistant. Incubation
of micropatterns of the comb polymer on FN-preadsorbed polymer surfaces with
fibroblasts resulted in the formation of cellular micropatterns that were confined to
the underlying fibronectin pattern, indicating the affinity of cells for fibronectin and
the ability of the comb polymer to repel cells.
2.3.2 Selective Molecular Assembly Patterning (SMAP)
To address the limitations in biomolecular patterning by μCP using PDMS, a novel
patterning approach, called selective molecular assembly patterning (SMAP), has
been developed by the Textor group (see Fig. 2.20) [52]. This approach comprises
a simple and versatile patterning technique based on selective adsorption from
aqueous media of multifunctional organic molecules onto oxide substrate prepatterned by lithographic methods (also called molecular-assembly patterning by liftoff) [53]. The preparation of cell-adhesive patterns of arbitrary geometry has been
reported. Using this patterned film, Textor and co-workers investigated the relationship between pattern geometry and the organization of elements of the cell adhesion
apparatus, namely focal contacts and stress fibers. The molecular assembly system is
based on a polycationic copolymer: poly(lysine)-graft-poly(ethylene glycol) (PLLg-PEG), which can spontaneously adsorb from aqueous solutions onto negatively
charged surfaces. The subsequent layer can resist the biomolecular adsorption on
the films due to the existence of a PEG brush. The PLL-g-PEG adlayers also show
long-term stability while still retain the resistance to protein adsorption. In addition, another advantage is that the PEG can be further functionalized with bioactive molecules (ligands). Since the fraction of PEG chain can be adjusted during
polymerization, the density of ligand end-functionalized PEG can also be controlled.