Combinatorial and High-Throughput Screening of Materials ...

ACS Combinatorial Science
Overall, compositional variables that produced heterogeneous
surface morphologies provided the highest antimicrobial activity
suggesting that the antimicrobial activity was primarily derived
from the relationship between coating chemical composition and
self-assembly of QAS moieties at the coating/air interface. Using
data modeling software, a narrow region of the compositional
space was identified that provided broad-spectrum antimicrobial
activity. An optimized coating composition was further evaluated
by coating sections of a urinary catheter and comparing the
antimicrobial response of the coated catheter sections to uncoated
catheter sections. 300 The coated catheter sections showed
a 54%, 94%, 80%, and 89% reduction in biofilm formation for
E. coli, S. epidermidis, P. aeruginosa, and C. albicans, respectively,
compared to the uncoated catheter sections.
3.3.4. Polyurethane-Based Coatings Containing Tethered
Triclosan Groups. In addition to antimicrobial coatings derived
from tethered QAS moieties, researchers at the Center for
Nanoscale Science and Engineering of the North Dakota State
University have been investigating coatings derived from
tethered triclosan moieties. 303 308 Triclosan (i.e., 5-chloro-
2-(2,4-diclorophenoxy)phenol) is a broad-spectrum antimicrobial
agent used extensively in personal-care products, healthcare,
and household goods. It has been formulated into hand
soaps, surgical scrubs, shower gels, underarm deodorants,
toothpastes, hand lotions, and mouthwashes; incorporated
into fabrics and plastics, such as children’s toys, surgical drapes,
cutting boards and toothbrush handles; and even infused into
concrete for floors. 309 Kugel et al. investigated polyurethanebased
coatings containing tethered triclosan groups using
C/HT methods. 310 First, an array of acrylic polyols was
produced using free-radical copolymerization of triclosan acrylate
(i.e., 5-Chloro-2-(2,4-dichlorophenoxy)phenyl acrylate)
(TA), HEA, and BA, as shown in Figure 30. The compositional
parameters varied to produce the library included BA/TA ratio
and HEA concentration. The array of acrylic polyols were
characterized using nuclear magnetic resonance spectroscopy,
DSC, and a HT GPC system. In addition, polymer yield was
determined gravimetrically with the assistance of a parallel
evaporator and a weighing robot. High yield (>90%) was
obtained for each copolymerization and polymer composition
was consistent with the monomer feed. With regard to thermal
properties, Tg of the acrylic polyols increased with increasing
TA content which was attributed to the relatively bulky
triclosan-ester pendent group. From the array of acrylic polyols,
a 24-element array of polyurethane coatings was produced
using hexamethylene diisocyanate trimer and a 1.1/1.0 molar
ratio of isocyanate functionality to hydroxy functionality. The
coatings were characterized using a parallel DMTA measurements,
automated surface energy measurements, and HT
biological assays utilizing four different microorganisms,
namely, C. lytica, E. coli, Staphylococcus epidermidis, andNavicula
incerta. From parallel DMTA measurements, Tg was
determined and two distinct trends were observed. First, at
constant HEA content of the acrylic polyol, coating Tg
increased with increasing TA content of the polyol. Second,
at a given TA content, coating Tg increased with increasing
polyol HEA content, which was attributed to obtainment of
higher cross-link densities with higher HEA contents. With
regard to antimicrobial properties, the coatings were found to
be very effective at inhibiting S. epidermidis biofilm formation
without leaching triclosan or other toxic components from the
coating.
REVIEW
Figure 30. Synthetic scheme used to produce an array of polyols with
triclosan pendent groups. 310
3.3.5. Radiation-Curable Coatings. CHT methods have also
been used to develop structure property relationships for
radiation-curable coatings. Uhl and co-workers 311 investigated
a compositional space comprised of three different cycloaliphatic
epoxides and three different polyester polyols, as shown in
Figure 31. The experiment involved variations in epoxide composition,
polyol composition, and the ratio of epoxy equivalents
to hydroxy equivalents to produce three 24-element arrays of
coatings in which each array was based on a single cycloaliphatic
epoxide. The photoinitiator used for the study was a mixed
arylsulfonium hexafluoroantimonate salt (UVI-6974 from Dow
Chemical) that decomposes to produce a strong protic acid upon
absorption of ultraviolet light. With this initiator, cross-linking
occurs through a propagating oxonium ion. 312 The coatings
produced were characterized using parallel DMTA measurements,
automated surface energy measurements, and automated
adhesion measurements. Some of the general trends observed
were: (1) Tg varied as a function of cycloaliphatic epoxy
composition with the higher molecular weight epoxide (CAE
28) resulting in lower Tgs; (2) coating Tg increased with an
increase the ratio of epoxy equivalents to hydroxy equivalents;
(3) although the nominal chemical structure of CAE5 and
CAE10 were the same, differences in coating properties between
analogous compositions were consistently observed; (4) storage
modulus above and below the Tg was dependent on polyol
composition; and (5) water contact angles did not vary significantly
over the compositional space. Potyrailo and co-workers 313
also described the results of a C/HT experiment involving
radiation-curable coatings. This work was focused on the HT
screening of optical clarity and abrasion resistance of coatings
produced in array format on a transparent, plastic substrate (i.e.,
polycarbonate). The report basically involved validation of the
HT methods developed for screening optical clarity and abrasion
resistance.
3.3.6. Hybrid Organic Inorganic Coatings. Recently, a C/HT
workflow was reported that was focused on the development
608 dx.doi.org/10.1021/co200007w |ACS Comb. Sci. 2011, 13, 579–633