Biomedical Engineering Reference
In-Depth Information
The fundamental problem with most polymers in biomedical application is poor endothe-
lial cell adhesion due to lack of cell recognition sites. This has led to a broad spectrum of
surface modification methods to promote endothelial cell adhesion. Generally, these are
classified into three categories: topological modification, chemical modification, and pat-
terning (Goddard and Hotchkiss, 2007).
Topological Modification
(1) Creating surface roughness or porosity by means of base hydrolysis (Wang and
Cai, 2007)
(2) Micro/nano grade salt/sugar leaching (Mattioli-Belmonte, Vozzi et al., 2008; Sin,
Miao et al., 2010).
Chemical Modification
According to modification intention, there are three categories:
(1) Impartation of functional groups
The essence of these studies is to introduce functional groups on the biomedi-
cal polymeric surface by means of plasma treatment or wet chemical reaction to
improve EC adhesion (Favia and d'Agostino, 1998). Many types of gaseous plas-
mas have been used, including NH
3
(Chu et al., 1999; Lu and Sipehia, 2001; Pu
et al., 2002; Wan et al., 2003), Ar (Chen et al., 2007), air (Pratt et al., 1989), oxygen
(Ryu et al., 2005), helium (De et al., 2005), and H
2
O (Pompe et al., 2007). Functional
groups such as hydroxyl (-OH) and amine (-NH
2
) were imparted onto the poly-
meric surface to improve endothelial cell compatibility. It was believed that those
functional groups changed the wettability of the polymeric surface and sequen-
tially influenced cell adhesion.
Plasma polymerization and grafting are the alternative ways to introduce func-
tional groups on a surface, such as lactic acid grafting (Hsu and Chen, 2000) and
acrylamide polymerization (Croll et al., 2004).
Wet chemical reaction: Primary amines have been introduced to PLA and PLGA
by aminolysis using 1,6-hexanediamine (Eisenbarth et al., 2007).
Impartation of functional groups improves cell attachment marginally by
increasing hydrophilicity or protein adsorption. Bioactive molecules including
extracellular matrix proteins and adhesion ligands were immobilized/incorpo-
rated on biomaterials for specific cell adhesion.
(2) Immobilization of extra-cellular matrix materials
It has become evident that certain molecules in the basement membrane
(basal lamina) are responsible for adhesion of the endothelial cells (EC) and thus
essential for endothelial integrity. Researchers attempted to immobilize them
covalently on polymeric surface with the aim of better endothelial cell adhesion
(74). One of the most widely studied of these is fibronectin (Sheiban et al., 2008),
which accounts for approximately 15% of the protein synthesized and secreted
by EC. Another commonly studied protein is collagen (Yang et al., 2003; Cheng
and Teoh, 2004; De et al., 2005; Feugier et al., 2005); its denatured form, gelatin
