Biomedical Engineering Reference
In-Depth Information
available to improve the procedures. Moreover organic contaminants are always present on
high energy solids. They are mainly of hydrocarbon nature and are readily adsorbed from
surrounding air or in surface analysis spectrometers (Caillou et al., 2008; Landoulsi et al.,
2008a). The possible influence of contaminants on the silanization process and product is
usually not considered. In the case of silicon wafer silanized with
3-[methoxy(polyethyleneoxy)]propyl trimethoxysilane and trichlorosilane in organic
solvents under a controlled atmosphere, the surface obtained was described as a 1 to 2 nm
thick grafted silane layer covered by a thin layer of adventitious contaminants, suggesting
that contamination was posterior to the silanization reaction. On the other hand, the silane
layer was not stable in phosphate buffered saline at 37°C (Dekeyser et al., 2008).
Aminopropylalkoxysilanes are attractive for surface modification (Plueddemann, 1991), as
their bifunctional nature is expected to offer the possibility of covalently attaching a
biomolecule, either directly or through a linker. 3-Aminopropyl(triethoxysilane) (APTES) is
one of the most frequently used organosilane agents for the preparation of amine-
terminated films (Asenath Smith & Chen, 2008; Howarter & Youngblood, 2006; Kim et al.,
2009a; Lapin & Chabal, 2009; Pasternack et al., 2008).
Table 1 presents a list of references in which APTES was used to hopefully graft
biomolecules on different substrates. The survey is exhaustive for stainless steeel substrates
relevant for the field of biomaterials and illustrative for other substrates. Additional
references are: El-Ghannam et al., 2004; Kim et al., 2010; Sasou et al., 2003; Sarath Babu et al.,
2004; Quan et al., 2004 ; Subramanian et al., 1999 ; Jin et al., 2003 ; Cho & Ivanisevic, 2004 ;
Katsikogianni & Missirlis, 2010 ; Sordel et al., 2007 ; Toworfe et al., 2006 ; Balasundaram et
al., 2006 ; Doh & Irvine, 2006 ; Palestino et al., 2008 ; Son et al., 2011 ; Koh et al., 2006 ; Mosse
et al., 2009 ; Weng et al., 2008 ; Charbonneau et al., 2011 ; Iucci et al., 2007 ; Chuang et al.,
2006 ; Schuessele et al., 2009 ; Ma et al., 2007 ; Toworfe et al., 2009 ; Zile et al., 2011 ; Sargeant
et al., 2008 ; Lapin & Chabal, 2009. Table 1 indicates the substrate and linker used, the main
conditions of the APTES treatment and the evaluation of the surface treatment regarding
biomolecule activity with the blank used for comparison. The table also presents the main
data obtained by surface characterization. In some systems, no covalent grafting was aimed.
In other systems, although it was aimed, there is no direct evidence for the formation of
covalent bonds between the biomolecules and the substrate surface. On the other hand, the
evaluation of the bio-efficacy was never based on comparisons involving a complete set of
blanks: treatment with the biomolecule without silanization, without linker, without
silanization and linker. In a study of surface modification with the aim to enhance
mineralization, it has been demonstrated that APTES-coated glass retains a homopolymer
with monoester phosphate groups, poly[(2-methacryloyloxy)ethyl phosphate], by proton
transfer and electrostatic interaction, while the retention of a neutral homopolymer, poly[2-
(acatoacetoxy)ethyl methacrylate], was attributed to covalent linkage by reductive
amination between the keto groups of the polymer and the surface amine functions
(Jasienak et al., 2009). The retention of the diblock copolymer seemed to occur via segments
allowing covalent bonds to be formed. In Table 1, several systems show an improved
behavior which may only be attributed to non covalent bonding between the biomolecule
and the silanized substrate. In contradiction with frequent implicit considerations, the
occurrence or improvement of bioactivity as a result of surface treatments does not
demonstrate that the chemical schemes which motivated the treatments worked in reality.
This question is crucial as many organic reactions that work well in solution are difficult to
apply at solid surfaces (Kohli et al., 1998).
