194 K.Yu,G.GaoandJ.N.Kizhakkedathu
Figure 8.22. Fluorescence photographs of BSA-adsorbed (a) bare gold and (b) linear
mPEG-2000-, (c) linear mPEG-5000-, (d) low molecular weight HPG-SH-L-, and (e) high
molecular weight HPG-SH-H grafted surfaces. Polymer films were produced by incubating
the gold surface in polymer solution at 6 g/L for 16 h. (f) Effect of the graft density on the
BSA adsorption of mPEG-, HPG-SH-L-,and HPG-SH-H-grafted surfaces. Images adapted
from Ref. 120. For color reference, see page 272.
molecular weight or lower molecular weight HPG. With increasing graft density
of the HPG chains on the surface, the protein adsorption was decreased( Fig. 8.22).
Our results show that HPG could be a good alternative to PEG in the development
of nonfouling functional surfaces.
8.7 PEPTIDE AND PROTEIN GRAFTED POLYMERIC SURFACES
There are lots of interests in recent years in the development of surfaces with
specific interaction to a certain biological system.
121
Short chain peptides or protein
coupled surfaces were used for this purpose.
122
Although there are several tech-
niques reported for the immobilization of peptides or proteins on the surface,
123
we will confine our discussion on the use of non-fouling polymer surfaces synthe-
sized by surface initiated polymerization in this section.
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Polymer-Based Biocompatible Surface Coatings 195
Table 8 . 2 Commonly Available Functional Groups in Proteins
and Functionalities of the Required Surfaces.
124
Side groups Amino acids Surfaces
NH
2
Lys.hydroxy-Lys carboxylic acid active
ester (NHS) epoxy
aldehyde
SH Cys maleimide pyridyil
disulfide vinyl sulfone
COOH Asp, Glu amine
OH Ser,Thr epoxy
Most often proteins or peptides were covalently bound to the surfaces through
accessible functional groups of exposed amino acids by irreversible binding to the
functional groups on the substrate. Table 2 gives the name of functional groups
typically used for the peptide/protein immobilization on the support surface.
124
Kang and coworkers grafted the Collagen I onto the titanium surface. Initially
the titanium surface was functionalized with an ATRP initiator through a silane
coupling agent. PHEMA chains were tethered on the Ti substrate via surface-
initiated ATRP. Antibiotics (gentamicin and penicillin) and collagen molecules
were covalently immobilized to the grafted polymer brushes after converting the
hydroxyl groups of P(HEMA) to carboxyl groups (Fig. 8.23).
125
Collard and coworkers used polyPOEGMA brushes for the coupling of helical
peptide sequence ((GGYGGGPC(GPP)5(GFOGER)(GPP)5GPC onto the titanium
surface. POEGMA brushes were prepared by surface initiated ATRP and the
peptides were coupled using 4-nitrophenyl chloroformate as coupling reagent
Figure 8.23. Schematic Diagram Illustrating the Route for the Immobilization of Collagen
on the Tig P(HEMA) Surface. Images adapted from Ref. 125.
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196 K.Yu,G.GaoandJ.N.Kizhakkedathu
Figure 8.24. Formation of a peptide-modified poly(OEGMA) brush on titanium. Images
adapted from Ref. 126. For color reference, see page 272.
Figure 8.25. RGD functionalized PHEMA and PPEGMA brushes. Images adapted from
Ref. 128. For color reference, see page 273.
(Fig. 8.24).
126
In another work Ober and coworkers used poly(acrylic acid) (PAA)
brushes for the attachment of proteins. PAA brushes acted as robust templates
for protein immobilization by providing a high density of –COOH groups on the
surface.
127
They used both bovine serum albumin and avidin for immobilization.
In a related work, Tugulu et al. demonstrated the feasibility of surface-initiated
atom transfer radical polymerization to prepare thin polymer brushes that can
be functionalized with short peptide ligands which could be used as coatings to
promote endothelialization of blood-contacting biomaterials. The grafted polymer
layer was composed of PHEMA or POEGMA. A protocol was developed to allow
the functionalization of the brushes with RGD containing peptide ligands resulting
in surface concentrations ranging from 0.5-12 pmol/cm
2
(Fig. 8.25).
128
They also
investigated the use of polymer brushes as platforms for the covalent immobi-
lization of fusion proteins. The AGT-mediated immobilization allowed selective
functionalization of polymer brushes with proteins in a defined orientation and the
surface density. All of these features make protein-modified polymer brushes very
attractive candidates for the development of protein microarrays (Fig. 8.26).
129
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