26
2 Surface Reactions and Fabrication of Bioreactive Platforms …
In summary, “grafting from” has several attractive features: (a) very high surface
density of up to 85 mg/mm
2 of a polymer can be obtained. (b) A linear increase in
the polymer thickness with polymer molecular mass is observed because the high
surface density of the polymer forces the polymer chains into a brush conformation
to minimize steric constraints. (c) The procedure is easy, because the synthesized
polymer is solely localized at the interface so that the need for extraction of loosely
physisorbed polymer is eliminated.
2.2.2.3 Reactive Polymer Coatings
Reactive polymer coatings, as a platform for immobilization of bioactive molecules,
proteins, or cells, are becoming very important for several technologies such as
the development of certain biosensors, and for fundamental studies of cell biology.
For many applications, polymer substrates are more desirable compared to metal
substrates. In principle, polymers may be deposited as thin films by different techniques, such as dipping, spin-coating, electrografting, and chemical vapor deposition,
to provide suitable interfaces for further surface modification.
Spin-coating has been widely used to prepare substrate-supported polymer films
with defined thickness, among these thin and ultrathin (d < 100 nm) films of
block copolymers. For example, for potential nanoelectronic research, spin-coated
triblock copolymer films of polystyrene–polybutadiene–polystyrene have been used
to pattern barium titanate precursor with nanoscale modulations. The reorganized thin
films of polymer are selectively OH-functionalized in situ on the unsaturated carbon
bonds in the polybutadiene matrix. The regioselective deposition of the barium titanium alkoxide on the original polybutadiene matrix of the polymer thin films was
achieved. Selective decoration of a phase-separated diblock copolymer prepared by
spin-coating with thiol-passivated gold nanocrystals also has been reported [40].
As an appropriate technique to improve the adhesion to organic coatings, electrochemistry has been used to irreversibly deposit polymeric materials onto conductive
solid inorganic surface. It was found that electrografting of (meth)acrylates is a
very powerful approach for the chemisorption of synthetic polymers onto conductive substrates. For example, epoxy and fluorinated groups have been immobilized
at the conductive surface by the electrografting of poly(glycidyl methacrylate) and
poly(trifluoroethylacrylate), respectively. Using electrografting technique, reactive
polymer surfaces containing highly activated N-succinimidyl acrylate (NHSA) ester
groups have been prepared (Fig. 2.14). These activated groups make the electrografted surface appropriate to immobilize a number of amino-functionalized
molecules, e.g., proteins.
Alternatively, chemical vapor deposition (CVD) polymerization, which is a
substrate-independent method for surface modification, has been used to deposit
polymer films. Compared to the deposition of polymer films by solvent-based
methods, CVD has several advantages. For instance, CVD provides a wide range
of functional groups, excellent adhesion to various substrates, and is applicable to
2 Surface Reactions and Fabrication of Bioreactive Platforms …
In summary, “grafting from” has several attractive features: (a) very high surface
density of up to 85 mg/mm
2 of a polymer can be obtained. (b) A linear increase in
the polymer thickness with polymer molecular mass is observed because the high
surface density of the polymer forces the polymer chains into a brush conformation
to minimize steric constraints. (c) The procedure is easy, because the synthesized
polymer is solely localized at the interface so that the need for extraction of loosely
physisorbed polymer is eliminated.
2.2.2.3 Reactive Polymer Coatings
Reactive polymer coatings, as a platform for immobilization of bioactive molecules,
proteins, or cells, are becoming very important for several technologies such as
the development of certain biosensors, and for fundamental studies of cell biology.
For many applications, polymer substrates are more desirable compared to metal
substrates. In principle, polymers may be deposited as thin films by different techniques, such as dipping, spin-coating, electrografting, and chemical vapor deposition,
to provide suitable interfaces for further surface modification.
Spin-coating has been widely used to prepare substrate-supported polymer films
with defined thickness, among these thin and ultrathin (d < 100 nm) films of
block copolymers. For example, for potential nanoelectronic research, spin-coated
triblock copolymer films of polystyrene–polybutadiene–polystyrene have been used
to pattern barium titanate precursor with nanoscale modulations. The reorganized thin
films of polymer are selectively OH-functionalized in situ on the unsaturated carbon
bonds in the polybutadiene matrix. The regioselective deposition of the barium titanium alkoxide on the original polybutadiene matrix of the polymer thin films was
achieved. Selective decoration of a phase-separated diblock copolymer prepared by
spin-coating with thiol-passivated gold nanocrystals also has been reported [40].
As an appropriate technique to improve the adhesion to organic coatings, electrochemistry has been used to irreversibly deposit polymeric materials onto conductive
solid inorganic surface. It was found that electrografting of (meth)acrylates is a
very powerful approach for the chemisorption of synthetic polymers onto conductive substrates. For example, epoxy and fluorinated groups have been immobilized
at the conductive surface by the electrografting of poly(glycidyl methacrylate) and
poly(trifluoroethylacrylate), respectively. Using electrografting technique, reactive
polymer surfaces containing highly activated N-succinimidyl acrylate (NHSA) ester
groups have been prepared (Fig. 2.14). These activated groups make the electrografted surface appropriate to immobilize a number of amino-functionalized
molecules, e.g., proteins.
Alternatively, chemical vapor deposition (CVD) polymerization, which is a
substrate-independent method for surface modification, has been used to deposit
polymer films. Compared to the deposition of polymer films by solvent-based
methods, CVD has several advantages. For instance, CVD provides a wide range
of functional groups, excellent adhesion to various substrates, and is applicable to