Micropatterned Polymer Films Research Articles

Laser-Induced fluorinated graphene for superhydrophobic surfaces with anisotropic wetting and switchable adhesion

We present a facile direct-write approach for patterning fluorine-doped nanocarbons directly on molecularly engineered polymers for superhydrophobic and parahydrophobic surfaces. We first synthesized two different polymer films, non-fluorinated and fluorinated polyimides (PIs), by two-step procedure to create poly(amic acid) precursors, followed by thermal curing. Morphology and chemical composition were controlled by adjusting the programmed scan line pitch from 101.6 to 508 μm during lasing to achieve superhydrophobicity with a water contact angle (CA) up to 156° in the direction perpendicular to carbonized lines. Droplets exhibited strong adhesion on our porous graphene micropatterns even when held at vertical and inverted orientations, indicating a Cassie impregnating state of wetting. Parahydrophobic F-LINC with line pitch of 355.6 μm exhibits high dynamic CAs along both perpendicular (θA⊥ = 165°, θR⊥ = 127°) and parallel directions (θA‖ = 147°, θR‖ = 87°) as well as highly anisotropic CA hysteresis (Δθ⊥ = 38°, Δθ‖ = 60°). Moreover, we demonstrate strain-induced switchable adhesion by leveraging substrate curvature control. Further, we show that our micropatterned polymer films can be used for transferring droplets without any loss or contamination. Hence, our approach offers new insights into designing interfaces for droplet manipulation, pick-and-place applications, and localized control of reactions.

Enzymes as Biodevelopers for Nano- And Micropatterned Bicomponent Biopolymer Thin Films.

The creation of nano- and micropatterned polymer films is a crucial step for innumerous applications in science and technology. However, there are several problems associated with environmental aspects concerning the polymer synthesis itself, cross-linkers to induce the patterns as well as toxic solvents used for the preparation and even more important development of the films (e.g., chlorobenzene). In this paper, we present a facile method to produce micro- and nanopatterned biopolymer thin films using enzymes as so-called biodevelopers. Instead of synthetic polymers, naturally derived ones are employed, namely, poly-3-hydroxybutyrate and a cellulose derivative, which are dissolved in a common solvent in different ratios and subjected to spin coating. Consequently, the two biopolymers undergo microphase separation and different domain sizes are formed depending on the ratio of the biopolymers. The development step proceeds via addition of the appropriate enzyme (either PHB-depolymerase or cellulase), whereas one of the two biopolymers is selectively degraded, while the other one remains on the surface. In order to highlight the enzymatic development of the films, video AFM studies have been performed in real time to image the development process in situ as well as surface plasmon resonance spectroscopy to determine the kinetics. These studies may pave the way for the use of enzymes in patterning processes, particularly for materials intended to be used in a physiological environment.

Inverted tetrahedron-pyramidal micropatterned polymer films for boosting light output power in flip-chip light-emitting diodes.

We report the improved light output power in gallium nitride-based green flip-chip light-emitting diodes (FCLEDs) employed with inverted tetrahedron-pyramidal micropatterned polydimethylsiloxane (ITPM PDMS) films as an encapsulation and protection layer. The micropatterns are transferred into the surface of PDMS films from the sapphire substrate master molds with two-dimensional periodic hexagonal TPM arrays by a soft imprint lithography method. The ITPM PDMS film laminated on the sapphire dramatically enhances the diffuse transmittance (T(D)) in a wavelength (λ) range of 400-650 nm, exhibiting the larger T(D) value of ~53% at λ = 525 nm, (cf., T(D) ~1% for planar sapphire). By introducing the ITPM PDMS film on the outer surface of sapphire in FCLEDs, the light output power is enhanced, indicating the increment percentage of ~11.1% at 500 mA of injection current compared to the reference FCLED without the ITPM PDMS film, together with better electroluminescence intensity and far-field radiation pattern.

Constructing robust 3-dimensionally conformal micropatterns: vulcanization of honeycomb structured polymeric films

Here, we present the static breath figure process for constructing 3-dimensionally conformal microporous films on nonplanar substrates, with a commercially available triblock polymer, polystyrene-b-polyisoprene-b-polystyrene. The polymer can cover the surface of nonplanar substrates with ordered porous morphology despite the sharp corners and irregular shapes, which was ascribed to the fluid-like character of the matrix. In the subsequent vulcanization, the micro-patterned polymer films were effectively crosslinked and became self-supported even after removing the sacrificial templates. The 3D structures became resistant to a wide range of organic solvents and thermally stable up to 350 °C, an increase of more than 300 K as compared to the un-crosslinked films. The surface features on the 3D structures along the direction of the descending solvent level were investigated in detail by scanning electron microscopy. Furthermore, the versatility of this patterning method was also demonstrated by forming hierarchical micro-structures on bas-relief Si substrates with different patterns. Particularly, hydroxy groups were introduced into another commercially available triblock polymer, polystyrene-b-polybutadiene-b-polystyrene by hydroboration. The functionalized 3D micro-patterns feasible for site-directed grafting were created by the hydroxyl-containing polymers.

Micropatterned Polymer Films by Vapor-Induced Phase Separation Using Permeable Molds

Microstructured polymeric films are fabricated by a novel replication method. A polymer solution is applied and contained between two substrates, of which at least one is a patterned PDMS mold. The ensemble is then put in an atmosphere containing water vapor, which diffuses through the PDMS. The absorption of water into the polymer solution causes the precipitation (phase separation) of the polymer while in contact with the microstructured molds. The thickness of the PDMS slab can be exploited to tune the water vapor transport and hence the phase separation kinetics and resulting polymer morphology. Removal of excess polymer solution from between two PDMS slabs, followed by vapor induced phase separation, can also result in microperforated polymer films with great control over the dimensions.

Robust and hydrophilic polymeric films with honeycomb pattern and their cell scaffold applications

Starting from a commercially available block copolymer, polystyrene-b-polybutadiene-b-polystyrene (SBS), micro-patterned polymer films were successfully prepared by evaporating SBS/carbon disulfide solutions with different concentrations under high humidity. The influence of solution concentration on the pore size and array was investigated in detail. With the increase of solution concentration, regular pore arrays turned into random because of weakened convention. Once the concentration was more than 60 mg mL−1, a bimodal size distribution appeared. Photo-chemical cross-linking was achieved by exposing the polymer films in deep UV light (wavelength = 254 nm), monitored by attenuated total reflective Fourier transform infrared and X-ray photoelectron spectroscopy. After 1 h cross-linking, either solvent resistance or thermal stability or surface wettability of the films was significantly improved. The cross-linked honeycomb structured films became resistant to a wide range of organic solvents and thermally stable up to 350 °C, an increase of more than 250 K as compared to the un-crosslinked films. Another beneficial effect of the photo-chemical process was the formation of polar groups on the film surface, changing surface wettability from hydrophobicity to hydrophilicity, enhanced by the micro-patterned surface. The resultant films were non-cytotoxic and hence suitable as cell scaffolds. It was found that hydrophilic, micro-patterned polymer films with a uniform pore size of 3 µm facilitated cell attachment and proliferation.

Ultrathin Patterned Polymer Films on Surfaces Using Thiol−Ene Polymerizations

A simple and straightforward method for growing ultrathin, micropatterned polymer films on surfaces with precise thickness and spatial control is presented. A difunctional ene monomer and a difunctional thiol were photopolymerized on a surface terminated with thiol groups. The surface thiols participate in the polymerization, and a linear polymer is formed on the surface. Brush growth was spatially controlled by selectively polymerizing the monomers through a photomask, while the brush thickness was controlled by changing the ratio of thiol and ene monomers or by changing the monomer functionality. Further, the surface was passivated by attaching a patterned, cross-linked polymer film, which was then backfilled with another monomer, demonstrating the attachment of multiple functionalities on the surface in a controlled, photolithographically patternable manner. Thiol−ene polymerizations were carried out without an initiator and used to graft patterned, polymer films. The films were observed using scanning...

Growth and Differentiation of Astrocytes and Neural Progenitor Cells on Micropatterned Polymer Films

This paper investigates the influence of micropatterned polymers and chemical modification on neural progenitor cell growth and differentiation in co-culture systems with astrocytes. We sought to develop strategies to facilitate nerve regeneration using a synergistic combination of guidance cues, investigating the cellular mechanisms of nerve repair using adult rat hippocampal progenitor cells (AHPCs). Our studies have shown that this synergistic combination of physical, chemical, and biological cues can lead to oriented growth of astrocytes and progenitor cells, can control and accelerate neurite outgrowth and alignment in vitro, and may influence differentiation of progenitor cells.

Phase-Separation-Induced Micropatterned Polymer Surfaces and Their Applications

We report a route to fabricate micropatterned polymer films with micro- or nanometer-scale surface concavities by spreading polymer solutions on a non-solvent surface. The route is simple, versatile, highly efficient, low-cost, and easily accessible. The concavity density of the patterned films is tuned from 106 to 109 features cm–2, and the concavity size is controlled in the range from several micrometers to less than 100 nm, by changing the film-forming parameters including the polymer concentration, the temperature of the non-solvent and the interactions between polymer, solvent, and non-solvent. We further demonstrate that these concavity-patterned films have significantly enhanced hydrophobicity, owing to the existence of the surface concavities, and their hydrophobicity could be controlled by the concavity density. These films have been used as templates to successfully fabricate convex-patterned polymer films, inorganic TiO2 microparticles, and NaCl nanocrystals. Their other potential applications are also discussed.

Preparation of Self-Organized Micro-Patterned Polymer Films Having Cell Adhesive Ligands

This article describes novel three methods for micro-patterning of cell adhesive ligands by using the self-organized honeycomb-patterned structure formed by the simple cast method. A first method is a direct preparation of a patterned film by casting an amphiphilic polymer containing lactose residue which is one of cell adhesive ligands. A benzene solution of the amphiphilic polymer was cast at high humidity on a glass substrate. Atomic force microscopy (AFM) observation of the film showed that a honeycomb pattern with microporousness with as large as micrometer size in diameter was formed. The film was immersed into an aqueous fluorescence-labeled lectin solution to investigate the distribution of lactoses on the patterned film. Consistence of a fluorescence image of the lectin bound film with the honeycomb pattern showed that the lactose residues were existed not at the holes but at the rims of the honeycomb-patterned film. A second method is to immobilize gelatin, which is one also one of cell adhesive ligands, on the honeycomb-patterned film by chemical reaction. A honeycomb-patterned film was prepared from chloroform solution of an amphiphilic polymer containing reactive succinimide ester groups, and then the film was immersed into an aqueous fluorescence-labeled gelatin solution to introduce gelatin on the film surface. Immobilization of gelatin onto honeycomb-patterned film was confirmed by the fluorescence microscope. A third method is another way to introduce gelatin onto the honeycomb film by the specific avidin-biotin interaction. A honeycomb-patterned film was prepared from amphiphilic polymer containing biotin residues and dodecyl groups, and then the film was immersed into a avidin solution and a biotinylated fluorescence labeled gelatin solution successively. By the fluorescence microscopic observation of the film, gelatin was confirmed to be immobilized at the rims of the honeycomb pattern via the avidin-biotin interaction. Cell culture was performed on the gelatin immobilized patterned film prepared by second method. Bioactivity of gelatin immobilized honeycomb-patterned film was confirmed by adhesion of cell onto the film.

Stabilization of Micropatterned Polymer Films as Artificial Extracellular Matrices for Tissue Engineering

Honeycomb-patterned polymer films are formed upon self-organization of water microspheres stabilized by amphiphilic polymers. The honeycomb films can work as cell culture substrates. The films composed of heparin-cationic lipid complex, however, gradually lost the honeycomb structure when immersed in culture medium. Crosslinking of the films was carried to stabilize the honeycomb pattern. A bisazido derivative was used as a crosslinker connecting the constituent polymer of the honeycomb films. Morphological study of the immersed films revealed that the crosslinked films maintained the honeycomb structure in the phosphate buffer solution.