Biomedical Engineering Reference
In-Depth Information
proliferation on these films are very good, which may be attributed partly to the pres-
ence of sulfonate groups. The importance of such groups was evidenced in hepatocytes
by using films made from PDDA and PSS (Kidambi et al. 2004). The hepatocytes adhered
only on the films terminated with a PSS layer and not on PDDA ending films. However,
other cells lines, such as fibroblasts, were less sensitive and adhered on both the PDDA and
PSS. Of note, certain serum proteins present in the cell culture medium, such as bovine
serum albumin (BSA), adsorb onto the PSS-ending films, although only weakly (Ladam
et al. 2000). PAH/PAA films are also widely studied. PAA-ending films were found to be
resistant to the adsorption of BSA, fibrinogen or even to lysozyme, which is oppositely
charged to PAA (Salloum and Schlenoff 2004). This was explained not only by the low
charge density of PAA, but also by its strong hydration that creates an exclusion volume
above the PAA layer.
Usually, proteins adsorb preferentially onto films of opposite charge (Gergely et al. 2004;
Ladam et al. 2001; Salloum and Schlenoff 2004). However, it now seems to be accepted
that protein adsorption cannot account for the significant differences in cell adhesion
(Mendelsohn et al. 2003; Olenych et al. 2005). For PAH/PAA films, the nonadhesiveness
of the films built at pH 2 and the high adhesion observed for films built at pH 6.5 were
instead attributed to the ability of the former to swell (Mendelsohn et al. 2003).
Synthetic polymers were also employed by Salloum et al. (2005) to investigate the com-
bined effects of increasing surface charge and hydrophobicity on vascular smooth muscle
cell (SMCs) adhesion. On the most hydrophobic surfaces, the A7R75 SMCs spread and
were not very motile, whereas on the most hydrophilic surfaces, these cells adhered poorly
and displayed characteristics of being highly motile.
If synthetic polymers are to be used for in vivo implantations, their possible toxicity must
also be evaluated. The biocompatibility of a single PEI layer was tested on both fibroblastic
and osteoblastic cells. Pure titanium (Ti) and nickel-titanium (NiTi) alloy were coated with
PEI and morphology, adhesion and viability were assessed for up to 7 days after seeding.
The results show that the cells were less viable and proliferated less on PEI-coated tita-
nium than on the control, suggesting that PEI is potentially cytotoxic (Brunot et al. 2007).
On the other hand, PSS/PAH films deposited on human umbilical arteries showed good
grafting behavior and no inflammation in a rabbit model after 12 weeks of implantation
(Kerdjoudj et al. 2008). Systematic studies for each specific case are thus required.
Film as Mimics of Extracellular Matrix for Specific Cell Cultures
A step closer to recreating the original matrix into which cells develop in vivo is to use
ECM components as building blocks for the films. One advantage of these natural compo-
nents is their bioavailability and their possible biodegradability, as specific enzymes are
present in tissue and biological fluids. Thus, besides being used as natural mimics, they
can be potentially employed as biodegradable delivery systems.
PEM made of ECM proteins such as collagen (COL) (Gong et al. 2007; Sinani et al. 2003;
Zhang et al. 2005) or gelatin (GEL) (Zhu et al. 2003) and of glycoaminoglycans such as HA
(Picart et al. 2001b), CS (Liu et al. 2005c; Tezcaner et al. 2006), and HEP (Mao et al. 2005;
Tan et al. 2003; Wood et al. 2005) have been reported. Other polysaccharides, which are not
present in the human body but can be found in algae, crustacean shells, or fungi, are also
used. This is the case for ALG (Elbert et al. 1999; Yuan et al. 2007), dextran sulfate (DEXS)
(Nakahara et al. 2007), and CHI (Richert et al. 2004c; Serizawa et al. 2002; Yuan et al. 2007),
which are already being used in tissue engineering (Kumar 2000; Coviello et al. 2006) and
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