Solvent-assisted Micromolding Research Articles

Well-Defined Polyethylene Glycol Microscale Hydrogel Blocks Containing Gold Nanorods for Dual Photothermal and Chemotherapeutic Therapy.

Local drug delivery offers a means of achieving a high concentration of therapeutic agents directly at the tumor site, whilst minimizing systemic toxicity. For heterogenous cancers such as glioblastoma, multimodal therapeutic approaches hold promise for better efficacy. Herein, we aimed to create a well-defined and reproducible drug delivery system that also incorporates gold nanorods for photothermal therapy. Solvent-assisted micromolding was used to create uniform sacrificial templates in which microscale hydrogels were formed with and without gold nanorods throughout their structure. The microscale hydrogels could be loaded with doxorubicin, releasing it over a period of one week, causing toxicity to glioma cells. Since these microscale hydrogels were designed for direct intratumoral injection, therefore bypassing the blood–brain barrier, the highly potent breast cancer therapeutic doxorubicin was repurposed for use in this study. By contrast, the unloaded hydrogels were well tolerated, without decreasing cell viability. Irradiation with near-infrared light caused heating of the hydrogels, showing that if concentrated at an injection site, these hydrogels maybe able to cause anticancer activity through two separate mechanisms.

AFM-Based nanofabrication and quality inspection of three-dimensional nanotemplates for soft lithography

Soft lithography is one of the most promising nanofabrication technologies for scalable nanomanufacturing. It uses flexible molds or stamps to fabricate extremely high-resolution nanopatterns in a low cost and rapid fashion on both flat and curved surfaces. Although two-dimensional soft lithography has been widely investigated and applied for some applications, there is a lack of quantitative research on using nanometer scale 3D patterns fabricated by atomic force microscope (AFM) for 3D soft lithography. In this paper, we demonstrated the effectiveness of ultrasonic vibration assisted AFM-based nanomachining in fabricating 3D master nanotemplates for 3D soft lithography. We successfully applied Polydimethylsiloxane (PDMS) daughter molds, casted from a nanometer scale 3D master template, using a soft lithography technique solvent-assisted micromolding. In addition, we investigated the quality and reusability of the master nanotemplates, and the quality of the PDMS patterns by quantifying the volume differences using an automatic imaging registration algorithm. Results show that there are zero or little PDMS residuals in the polymethyl methacrylate (PMMA) master nanotemplate with a simple contour for the first and second daughter mold casting, but 7% residuals for the third casting. And a more complex master nanotemplate shows slightly higher residual levels.

Solvent‐assisted prototyping of microfluidic and optofluidic microsystems in polymers

ABSTRACTDue to their low‐cost and processing simplicity, polymers have made a substantial impact on everyday life and scientific discoveries. Such discoveries include the use of microanalysis and optical microsystems, which—albeit simpler to prototype than their inorganic counterparts—still require dedicated procedures at high temperatures and pressures. Here, recent developments in microsystem prototyping are highlighted, based on solvent‐assisted polymer stimulation. These developments—largely inspired by the earlier demonstration of solvent‐assisted micromolding (SAMIM) for nanoimprinting—enable micronscale imprinting, but also bonding to substrates and three‐dimensional chemical functionalization via strict benchtop procedures. These solvent‐assisted strategies are categorized into two groups: those based on solvent immersion and those based on complete polymer dissolution. Recent embodiments within each group are discussed and compared in performance. Solvent‐assisted prototyping further narrows the gap of processing complexity and costs between the PDMS elastomer and thermoplastic polymer microfluidics, and also enables novel architectures and thus new opportunities in microscale Life Sciences and Chemistry investigations. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 1681–1686

Simple replica micromolding of biocompatible styrenic elastomers

In this work, we introduce a simple solvent-assisted micromolding technique for the fabrication of high-fidelity styrene-ethylene/butylene-styrene (SEBS) microfluidic devices with high polystyrene (PS) content (42 wt% PS, SEBS42). SEBS triblock copolymers are styrenic thermoplastic elastomers that exhibit both glassy thermoplastic and elastomeric properties resulting from their respective hard PS and rubbery ethylene/butylene segments. The PS fraction gives SEBS microdevices many of the appealing properties of pure PS devices, while the elastomeric properties simplify fabrication of the devices, similar to PDMS. SEBS42 devices have wettable, stable surfaces (both contact angle and zeta potential) that support cell attachment and proliferation consistent with tissue culture dish substrates, do not adsorb hydrophobic molecules, and have high bond strength to wide range of substrates (glass, PS, SEBS). Furthermore, SEBS42 devices are mechanically robust, thermally stable, as well as exhibit low auto-fluorescence and high transmissivity. We characterize SEBS42 surface properties by contact angle measurements, cell culture studies, zeta potential measurements, and the adsorption of hydrophobic molecules. The PS surface composition of SEBS microdevices cast on different substrates is determined by time-of-flight secondary ion mass spectrometry (ToF-SIMS). The attractive SEBS42 material properties, coupled with the simple fabrication method, make SEBS42 a quality substrate for microfluidic applications where the properties of PS are desired but the ease of PDMS micromolding is favoured.

Simultaneous fabrication of an alignment layer and a wall structure for a liquid crystal display by solvent-assisted micromolding

Patterning and aligning are the most distinctive research areas in surface science. In this paper, we demonstrate a fabrication method for the simultaneous formation of a wall-structured surface relief and a molecular aligning region between the walls. A photoreactive polymer, poly(vinyl cinnamate) (PVCi), was used as the matrix; it was coated either onto a rigid glass substrate or a flexible plastic substrate. We used a solvent-assisted micro-molding poly(dimethylsiloxane) stamp to form 10-μm-wide and 10-μm-high walls every 100 μm on the matrix. The direction of the molecular alignment in the region between the walls was perpendicular to the direction of the walls; this finding was confirmed by the subsequent liquid crystal (LC) alignment investigation. The alignment of this wide region between the wall structures is uncommon and differs from the molecular alignment induced by the microgroove topology due to the patterning. Additionally, the application of linearly polarized ultraviolet irradiation onto the photoreactive PVCi improved the molecular alignment either on the region between the walls or on the lateral side of the walls; this finding was confirmed by polarized light microscopy imaging. The simultaneous formation of the wall support in the molecular aligning region can be used in flexible LC displays, in which the maintenance of cell gaps and the aligning of the LC material play a critical role in display performance. Open image in new window

UV-driven in-plane rotation of a liquid crystal director in poly(vinyl cinnamate) films having microscale grooves

The micropatterned poly(vinyl cinnamate) (PVCi) alignment layers are fabricated by a solvent-assisted micromolding method. Without UV irradiation, the alignment layer can induce the unidirectional liquid crystal (LC) orientation, which is influenced by topography-based anchoring energies. With photodimerization of PVCi by UV irradiation, we could modulate the anchoring energies caused by chemical interactions of the alignment layer. It is observed that these two different contributions compete against each other in determining LC rotation on the surface of the alignment layer. The rotation angle of LC directors could be controlled from 45° to 70° by simply changing the UV exposure dose.

Soft lithography for micro- and nanoscale patterning

This protocol provides an introduction to soft lithography--a collection of techniques based on printing, molding and embossing with an elastomeric stamp. Soft lithography provides access to three-dimensional and curved structures, tolerates a wide variety of materials, generates well-defined and controllable surface chemistries, and is generally compatible with biological applications. It is also low in cost, experimentally convenient and has emerged as a technology useful for a number of applications that include cell biology, microfluidics, lab-on-a-chip, microelectromechanical systems and flexible electronics/photonics. As examples, here we focus on three of the commonly used soft lithographic techniques: (i) microcontact printing of alkanethiols and proteins on gold-coated and glass substrates; (ii) replica molding for fabrication of microfluidic devices in poly(dimethyl siloxane), and of nanostructures in polyurethane or epoxy; and (iii) solvent-assisted micromolding of nanostructures in poly(methyl methacrylate).

Selective Protein Adsorption on Polymer Patterns Formed by Self-Organization and Soft Lithography

Thin films, with both isotropic and ordered patterns of polymer domains, are used as substrates to study selective adsorption of two proteins (concanavalin A and lentil lectin) and to test reconstruction of polymer patterns by these proteins. Integral geometry approach is used to compare quantitatively fluorescence micrographs of protein patches with AFM images of original isotropic patterns, formed during blend casting of polystyrene/poly(methyl methacrylate) and PS/poly(ethylene oxide). Preferential adsorption of both lectins to PMMA phase domains, enhanced for PS/PMMA interfaces is concluded. In turn, protein binding to PS phase regions of PS/PEO blends is highly selective. Ordered protein grouping is obtained as a result of selective adsorption to alternating stripes of polystyrene (partly brominated to enable identification) and cross-linked PEO, prepared with solvent-assisted micromolding applied to PBrS/PEO bilayers. Biological activity test, performed with concanavalin A, confirms preserved functionality of a complementary protein, carboxypeptidase Y, adsorbed to polymer patterns.

Solvent-assisted polymer micro-molding

The micro-molding technology has played an important role in fabrication of polymer micro-patterns and development of functional devices. In such a process, suitable solvent can swell or dissolve the polymer films to decrease their glass transition temperature (Tg) and viscosity and thereby improve flowing ability. Consequently, it is easy to obtain the 2D and 3D patterns with high fidelity by the solvent-assisted micro-molding. Compared with the high temperature molding, this technology overcomes some shortcomings such as shrinking after cooling, degradation at high temperature, difficulty in processing some functional materials having high Tg, etc. It can be applied to making patterns not only on polymer monolayers but also on polyelectrolyte multilayers. Moreover, the compression-induced patterns on the multilayers are chemically homogenous but physically heterogeneous. In this review, the controlling factors on the pattern quality are also discussed, including materials of the mold, solvent, pressure, temperature and pattern density.

Hydrophilic Composite Elastomeric Mold for High-Resolution Soft Lithography

Here, we introduce a nanopatternable hydrophilic composite elastomer highly desirable for both nanostructure patterning via solvent-assisted micromolding (SAMIM) and microcontact printing of polar inks. This composite precursor is prepared by blending two UV-curable materials, Norland Optical Adhesives (NOA) 63 and poly(ethylene glycol) diacrylate (PEGDA), in an appropriate ratio; upon UV polymerization, a nanopatternable elastomer with preferential permeability both to aqueous and organic solvent is fabricated. Using this composite mold, nanoscale SAMIM of poly(4-vinylpyridine) (P4VP) and microcontact printing of a polar biomolecule, bovine serum albumin (BSA), was successfully demonstrated, paving the way for facile and efficient reproduction of various nanopatterns and a biomolecule-printed array platform.

SOFT LITHOGRAPHY

Abstract Soft lithography represents a non-photolithographic strategy based on self-assembly and replica molding for carrying out micro- and nanofabrication. It provides a convenient, effective, and low-cost method for the formation and manufacturing of micro- and nanostructures. In soft lithography, an elastomeric stamp with patterned relief structures on its surface is used to generate patterns and structures with feature sizes ranging from 30 nm to 100 μm. Five techniques have been demonstrated: microcontact printing (μCP), replica molding (REM), microtransfer molding (μTM), micromolding in capillaries (MIMIC), and solvent-assisted micromolding (SAMIM). In this chapter we discuss the procedures for these techniques and their applications in micro- and nanofabrication, surface chemistry, materials science, optics, MEMS, and microelectronics.

Fabrication of patterned electroluminescent polymers that emit in geometries with feature sizes into the submicron range

This letter describes the fabrication of structured polymer light-emitting devices (LEDs) that produce patterns of light with feature sizes as small as ∼0.8 μm. Solvent-assisted micromolding of a film of a precursor to poly(p-phenylene vinylene) (PPV), produces variations in its thickness that replicate the relief on the mold. Thermal conversion of this precursor produces a film of PPV with the same surface relief. LEDs formed with the structured PPV emit preferentially in the thin regions of the film. Devices fabricated in this manner may be important for constructing plastic visual displays, and could eventually lead to new subwavelength sources of light suitable for applications in near field optics.