In a paint and coating formulation, antibodies could behave
similarly, binding contaminants that come in contact with
the surface and leaving them exposed to attack by other
actives designed for that purpose. Researchers at the
University of Pittsburgh have developed coatings containing both antibodies and enzymes. 24 Antibodies for
pathogens such as anthrax and smallpox have been incorporated into the paint, with lysozyme enzymes present to
destroy the bacteria once bound by the antibody.
Viruses, cells and cell parts have been investigated as
independent actives as well as vehicles to deliver biofunctional additives. For example, the OPDtox additive produced by Reactive Surfaces has as its active component
the bacterial enzyme organophosphorous hydrolase
(OPH). The gene for the enzyme was modified to produce
an enzyme suitable for use as an additive in a coating.
When the gene is placed into a bacterial host cell (E. coli),
the enzyme can be manufactured in high concentrations
via a fermentation process. Once the fermentation process
is completed, the resulting whole cells of bacteria are subjected to commercial spray-drying, which ruptures the
cells and exposes the OPH enzyme active. The fine powder
that results is readily incorporated into many paint formulations. Delivering the enzyme active in this fashion
greatly enhances the thermal stability of the enzyme in
the applied film (see Figure 6).
FORMULATING THE
ADDED BENEFITS
As researchers have investigated the viability of incorporating bioactive compounds into paints and coatings, it has
become clear that the method of biomolecule inclusion is
critical for determining not only the level of activity and
stability, but even the type of reactivity. At the same time,
it has been shown that bioengineered additives can indeed
be successfully formulated into paints and coatings to produce materials that provide a variety of active functions
and responses along with protection and decoration.
The first step when developing a biofunctional coating is
selection of a biocompound that exhibits the desired activity and has a high likelihood of performing well in a coating
formulation. Therefore, not only the specific reactivity of
the bio-molecule, but its compatibility with the polymer in
terms of its physical and chemical properties, and the functionality of the bioactive in the solid state must be evaluated. Both choice of polymer and means of immobilizing the
biocompound in the coating will influence performance.
When selecting an enzyme for incorporation into a coating, for example, there are specific characteristics that
should be considered. Not only should the enzyme meet
defined application parameters such as temperature, pH
and type of substrate it will act upon, but also biochemical
characteristics including stability, catalytic rate and substrate specificity.
Proper assessment of application requirements and a
detailed understanding of the functionalities that are
available within an enzyme family is an essential consideration in enabling the development of a reactive coating.
Figure 5
Synergism in solution between ProteCoat and Verichem’s
N2000 biocide against B. atrophaeus. Solid circles
indicate observed values, dotted line demonstrates
expected result without synergism.
Figure 6
Thermal stability of OPDtox in epoxy coatings
subjected to 18-hour exposure of temperature
between 30-120˚ C.
One can choose from the immense diversity of function
that can be found in nature or through the tools of genetic engineering create unique functionalities for specific
purposes. For its DeGreez coating, Reactive Surfaces considered the extensive family of lipase enzymes that
hydrolyze or synthesize triglycerides with different chemical specificities and physical characteristics. The critical
parameters were judged to be: 1) broad specificity for
chain length, 2) minimal regioselectivity, and 3) good thermostability. Three different lipases were chosen to evaluate these parameters. 23
