Self-Assembly of Nanostructures as Biomaterials - Biomaterials Fabrication and Processing - page 245

TABLE 10.1
Summary of Cell Adhesion on Different Polyion Films
Outermost
Layer

Alternating
Component

Surface Charge
at Neutral pH Cell Types Reference

PSS PDDA Negative Hepatocyte, fi broblast 65

PAH Negative Smooth muscle cells 67

PAH PSS Positive HUVEC 63

Gelatin PDL Negative Endothelial cells 27

PDL Fibronectin, laminin Positive Neuron 59

PGA Positive HUVEC 63

Hyaluronic acid Positive Fibroblast 64

Collagen PAA Negative Muscle myoblast cells 35

Hyaluronic acid Negative Chondrosarcoma cells 68

Hyaluronic acid PLL Negative Chondrosarcoma cells 66

CH PSS Positive HUVEC 69

factors that control the cell adhesion behavior. Even for the same fi lm, different cells respond differ-
ently. For example, from Table 10.1, one can fi nd that hepatocytes, fi broblasts, and smooth muscle
cells (SMCs) adhered well on synthetic polyelectrolyte multilayered fi lms with an outermost layer
PSS, while HUVEC cells adhered well on a PAH layer. In contrast, poor endothelial cell adhesion
was found on a (PSS/PEI) 8 /PSS fi lm with the outermost layer PSS [27].
Polydimethylsiloxane (PDMS) (also called silicone rubber) is an interesting substrate for the
deposition of LbL thin fi lms and studying cell behavior on such a surface. First, it is used extensively
to study cell-substrate interactions because its mechanical properties are easily tuned in physiologi-
cally relevant ranges. Second, it can be used to make different medical devices (e.g., intraocular lens,
contact lens, catheters, etc.) because of its good biocompatibility and inertness. But the strong hydro-
phobicity of silicone rubber prevents cell adsorption in vitro , and it nonspecifi cally absorbs proteins
in vivo with shortened lifetime. How to coat a thin and uniform hydrophilic fi lm on silicone is an
important, but not an easy step. Several surface modifi cation methods have already been reported,
including chemical immobilization [70], plasma treatment [71,72], and gelatin-glutaraldehyde cross-
linking [73]. Plasma treatment could deposit a high-quality thin fi lm, but application was limited to
surface areas that can be easily accessed. Tube-shaped vascular grafts are not suitable for plasma
deposition. In addition, the adsorption of matrix proteins to silicone rubber substrates through pas-
sive adsorption is relatively ineffi cient [74]. In an earlier attempt, we discovered that polyelectrolyte
fi lms can be used to modify silicone rubber surface hydrophobic property and the coating is stable
for endothelial cell adhesion and growth [27]. LbL self-assembly of polyelectrolyte was simple and
effi cient in surface modifi cation of silicone rubber. Without the help of any surface pretreatment,
polyelectrolytes can be directly applied onto such a surface through alternate coating of oppositely
charged polymers. Usually, highly charged polyelectrolytes PSS and PEI were used as precursor
layers in fi lm assembly; polypeptides were further coated to establish biocompatible coatings for
cell adhesion. Based on QCM quantifi cation, a PEI/PSS bilayer was about 2-3 nm, and a PDL/
gelatin bilayer has a thickness of 5 nm [27]. The thickness of the gelatin/PDL multilayers was linear
according to the number of layers. A fi lm composed of (PEI/PSS) 4 /(PDL/gelatin) 12 coated on a QCM
electrode was directly observed under SEM without metal coating (Figure 10.4a). The calculated
total fi lm thickness was 70 nm, which closely matched with the cross-section thickness of the fi lm in
this SEM image. When coating polyelectrolytes on silicone rubber, we found that using PSS as the
fi rst layer was more effi cient than a PEI layer. The reason is not clear, but we suspect hydrophobic
force between silicone rubber and PSS plays a major role here because silicone rubber is not charged.