3 research outputs found
Patterned Enzymatic Degradation of Poly(ε-caprolactone) by High-Affinity Microcontact Printing and Polymer Pen Lithography
This
paper reports deposition of Candida antarctica Lipase B (CALB) on relatively thick poly(ε-caprolactone) (PCL)
films (300–500 nm) to create well-defined patterns using two
different writing techniques: high-affinity microcontact (HA-μCL)
and polymer pen (PPL) lithography. For both, an aqueous CALB ink is
absorbed onto a polydimethylsiloxane (PDMS) writing implement (PDMS
stamp or a PDMS pen tip), which is transferred to a spun-cast PCL
film. HA-μCL experiments demonstrated the importance of applied
pressure to obtain high-resolution patterns since uniform contact
is needed between raised 20 μm parallel line regions of the
PDMS stamp and the surface. AFM imaging shows pattern formation evolves
gradually over incubation time only in areas stamped with CALB cutting
through spherulites without apparent influence by grain boundaries.
Strong binding of CALB to PCL is postulated as the mechanism by which
lateral diffusion is limited. PPL enables formation of an arbitrary
image by appropriate programming of the robot. The PDMS pen tips were
coated with an aqueous CALB solution and then brought into contact
with the PCL film to transfer CALB onto the surface. By repeating
the ink transfer step multiple times where pen tips are brought into
contact with the PCL film at a different locations, a pattern of dots
is formed. After printing, patterns were developed at 37 °C and
95% RH. Over a 7-day period, CALB progressively etched the PCL down
to the silicon wafer on which it was spun (350 nm) giving round holes
with diameters about 10 μm. AFM images show the formation of
steep PCL walls indicating CALB degraded the PCL film in areas to
which it was applied. This work demonstrates that high-resolution
patterns can be achieved without immobilizing the enzyme on the surface
of polymeric stamps that limits the depth of features obtained as
well as the throughput of the process
High Throughput, High Resolution Enzymatic Lithography Process: Effect of Crystallite Size, Moisture, and Enzyme Concentration
By bringing enzymes into contact
with predefined regions of a surface,
a polymer film can be selectively degraded to form desired patterns
that find a variety of applications in biotechnology and electronics.
This so-called “enzymatic lithography” is an environmentally
friendly process as it does not require actinic radiation or synthetic
chemicals to develop the patterns. A significant challenge to using
enzymatic lithography has been the need to restrict the mobility of
the enzyme in order to maintain control of feature sizes. Previous
approaches have resulted in low throughput and were limited to polymer
films only a few nanometers thick. In this paper, we demonstrate an
enzymatic lithography system based on Candida antartica lipase B (CALB) and poly(ε-caprolactone) (PCL) that can resolve
fine-scale features, (<1 μm across) in thick (0.1–2.0
μm) polymer films. A
Polymer Pen Lithography (PPL) tool was developed to deposit an aqueous
solution of CALB onto a spin-cast PCL film. Immobilization of the
enzyme on the polymer surface was monitored using fluorescence microscopy
by labeling CALB with FITC. The crystallite size in the PCL films
was systematically varied; small crystallites resulted in significantly
faster etch rates (20 nm/min) and the ability to resolve smaller features
(as fine as 1 μm). The effect of printing conditions and relative
humidity during incubation is also presented. Patterns formed in the
PCL film were transferred to an underlying copper foil demonstrating
a “Green” approach to the fabrication of printed circuit
boards
Development of a Scalable, Chromatography-Free Synthesis of <i>t</i>‑Bu-SMS-Phos and Application to the Synthesis of an Important Chiral CF<sub>3</sub>‑Alcohol Derivative with High Enantioselectivity Using Rh-Catalyzed Asymmetric Hydrogenation
A chromatography-free,
asymmetric synthesis of the C2-symmetric
P-chiral diphosphine <i>t</i>-Bu-SMS-Phos was developed
using a chiral auxiliary-based approach in five steps from the chiral
auxiliary in 36% overall yield. Separtion and recovery of the auxiliary
were achieved with good yield (97%) to enable recycling of the chiral
auxiliary. An air-stable crystalline form of the final ligand was
identified to enable isolation of the final ligand by crystallization
to avoid chromatography. This synthetic route was applied to prepare
up to 4 kg of the final ligand. The utility of this material was demonstrated
in the asymmetric hydrogenation of trifluoromethyl vinyl acetate at
0.1 mol % Rh loading to access a surrogate for the pharmaceutically
relavent chiral trifluoroisopropanol fragment in excellent yield and
enantiomeric excess (98.6%)