Aerogel films are interesting as coatings due to their unique properties including high surface area, sorption capacity and insulating properties. To date, silica-based aerogel films have been most widely explored due to their ultrahigh surface areas and well-known chemistry. However, the fragile nature of silica aerogels coupled with the limited control over film thickness and dimensions when using traditional deposition techniques limits their use in applications requiring films with good mechanical stability (e.g., in flexible devices). To address these challenges, we present a pressure-aided freeze casting method to pattern, on a variety of substrates (e.g., glass or flexible polyethylene terephthalate), mechanically robust aerogel films composed of covalently cross-linked cellulose nanocrystals (CNCs) with controlled dimensions and internal morphology. To accomplish this, a film of the desired aerogel thickness was deposited on the substrate and a mold with the specific shape for the aerogel was fabricated by xurography (>1 mm lateral dimensions, 7–85 μm thickness) or photolithography (2–500 μm lateral dimensions, 3 μm thickness). An aqueous gel of reactive CNCs or CNCs with poly(oligoethylene-glycol-methacrylate) was drop cast onto the substrate, and pressure was applied so that the gel adopted the mold shape. The gel was subsequently frozen and lyophilized, and the mold was lifted off the substrate, leaving behind patterned porous aerogel films, which were first explored as cell culture scaffolds. Human prostate cancer cells strongly adhered to the aerogels, where individual cells could be isolated on small aerogel arrays while cell clusters were obtained on larger arrays. This system has potential applications in studying single-cell phenotype and developing miniaturized cell-based assays. The simplicity of this freeze casting and lift-off patterning technique makes it attractive for the fabrication of cellulose-nanocrystal-based aerogels with a variety of compositions for applications requiring materials with high surface area, low density, and good mechanical stability.
Microcontact printing has become a versatile soft lithography technique used to produce molecular micro- and nano-patterns consisting of a large range of different biomolecules. Despite intensive research over the last decade and numerous applications in the fields of biosensors, microarrays and biomedical applications, the large-scale implementation of microcontact printing is still an issue. It is hindered by the stamp-inking step that is critical to ensure a reproducible and uniform transfer of inked molecules over large areas. This is particularly important when addressing application such as cell microarray manufacturing, which are currently used for a wide range of analytical and pharmaceutical applications. In this paper, we present a large-scale and multiplexed microcontact printing process of extracellular matrix proteins for the fabrication of cell microarrays. We have developed a microfluidic inking approach combined with a magnetic clamping technology that can be adapted to most standard substrates used in biology. We have demonstrated a significant improvement of homogeneity of printed protein patterns on surfaces larger than 1 cm2 through the control of both the flow rate and the wetting mechanism of the stamp surface during microfluidic inking. Thanks to the reproducibility and integration capabilities provided by microfluidics, we have achieved the printing of three different adhesion proteins in one-step transfer. Selective cell adhesion and cell shape adaptation on the produced patterns were observed, showing the suitability of this approach for producing on-demand large-scale cell microarrays.
To provide a robust platform for fluid handling, most microfluidic devices usually involve irreversible bonding methods to achieve a leak free interface between the microchannels and the holding substrate. Such an approach induces a major drawback when biological interactions are performed on a microarray format as it is difficult to recover the biochip for further fluorescence scanner analysis. This work describes an automated microfluidic platform using a reversible magnetic clamp for multiplexed immunodiagnostis. The microfluidic device is composed of a magnetic PDMS layer (containing iron powder) coated by PDMS, which is reversibly clamped to an epoxysilane glass slide containing an array of various antigens. The microfluidic device was validated for in vitro diagnosis of food allergies on an allergen microarray after serum interaction. The statistical analysis of spot intensities (Signal to noise ratios) on the microarray displayed excellent reproducibility. In addition to the reduction of volumes provided by miniaturization, this approach is versatile, easy-toproduce and provide an effective platform for multiplexed immunodiagnosis based on conventional fluorescent detection schemes.
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