Development of low-fluorescence thick photoresist for high-aspect-ratio microstructure in bio-application

Selective cell retrieval method using light-responsive gas-generating polymer-based microarrays

Selective cell retrieval from base material is necessary for developing and improving cell analyzing technologies as well as regenerative medicine. Many conventional technologies, such as micromanipulators, are developed for selective cell retrieval. However, selective cell retrieval at the single-cell level remains challenging because it is quite difficult to retrieve adhered single cells from base material with ease, rapidity, and no damage. Here, we propose a novel selective cell retrieval method using microarrays made of a light-responsive gas-generating polymer (LGP microarray). The convex LGP microarray was fabricated by a molding process using polystyrene microarray chips. LGP microarrays generate N₂ gas when exposed to a specific light used for fluorescence microscopy. A human cervical cancer cell (HeLa) suspension was spread on the LGP microarray coated by fibronectin. After these HeLa cells were adhered to the surface of the LGP microarray structure, light at a wavelength of 365 nm was used to irradiate the LGP microarray. All the target HeLa cells were selectively released from the light-irradiated surface area of the LGP microarray by the generated N₂ gas. The LGP microarray system was also applied to single-cell retrieval, and we easily and rapidly retrieved 100% of the single HeLa cells from the microarrays. In addition, approximately 90% of single HeLa cells retrieved from the LGP microarray proliferated on a chamber of a 96-well plate. Therefore, the LGP microarray system enables easy and selective retrieval of adhered cell groups or single cells with only harmless light irradiation.

Cell Culture on Low-Fluorescence and High-Resolution Photoresist

2D and 3D topographic cues made of photoresist, a polymer, are used for cell culture and cell analysis. Photoresists used for cell analysis provide the surface conditions necessary for proper cell growth, along with patterning properties of a wide range and high precision, and low auto-fluorescence that does not affect fluorescence imaging. In this study, we developed a thick negative photoresist SJI-001 possessing the aforementioned properties. We evaluated the surface conditions of SJI-001 affecting cell culture. First, we studied the wettability of SJI-001, which was changed by plasma treatment, conducted as a pretreatment on a plastic substrate before cell seeding. SJI-001 was more chemically stable than SU-8 used for fabricating the micro-electromechanical systems (MEMS). Furthermore, the doubling time and adhesion rate of adherent HeLa cells cultured on untreated SJI-001 were 25.2 h and 74%, respectively, thus indicating its suitability for cell culture over SU-8. In addition, we fabricated a cell culture plate with a 3D lattice structure, three micrometers in size, using SJI-001. HeLa cells seeded on this plate remained attached over five days. Therefore, SJI-001 exhibits surface conditions suitable for cell culture and has several bioapplications including microstructures and cell chips for cell culture and cell analysis.

Micropatterning Method for Porous Materials Using the Difference of the Glass Transition Temperature between Exposed and Unexposed Areas of a Thick-Photoresist

A cell culture on a scaffold has the advantages of functionality and easy handling, because the geometry of the cellular tissue is controlled by designing the scaffold. To create complex cellular tissue, scaffolds should be complex two-dimensional (2D) and three-dimensional (3D) structures. However, it is difficult to fabricate a scaffold with a 2D and 3D structure because the shape, size, and fabrication processes of a 2D structure in creating a cell layer, and a 3D structure containing cells, are different. In this research, we propose a micropatterning method for porous materials using the difference of the glass transition temperature between exposed and unexposed areas of a thick-photoresist. Since the proposed method does not require a vacuum, high temperature, or high voltage, it can be used for fabricating various structures with a wide range of scales, regardless of the materials used. Additionally, the patterning area can be fabricated accurately by photolithography. To evaluate the proposed method, a membrane integrated scaffold (MIS) with a 2D porous membrane and 3D porous material was fabricated. The MIS had a porous membrane with a pore size of 4 μm or less, which was impermeable to cells, and a porous material which was capable of containing cells. By seeding HUVECs and HeLa cells on each side of the MIS, the cellular tissue was formed with the designed geometry.

Microphotonic needle for minimally invasive endoscopic imaging with sub-cellular resolution

Ultra-compact micro-optical elements for endoscopic instruments and miniaturized microscopes allow for non-invasive and non-destructive examination of microstructures and tissues. With sub-cellular level resolution such instruments could provide immediate diagnosis that is virtually consistent with a histologic diagnosis enabling for example to differentiate the boundaries between malignant and benign tissue. Such instruments are now being developed at a rapid rate; however, current manufacturing technologies limit the instruments to very large sizes, well beyond the sub-mm sizes required in order to ensure minimal tissue damage. We show here a platform based on planar microfabrication and soft lithography that overcomes the limitation of current optical elements enabling single cell resolution. We show the ability to resolve lithographic features that are as small as 2 μm using probes with a cross section that is only 100 microns in size. We also show the ability to image individual activated neural cells in brain slices via our fabricated probe.

Thermal nanoimprint lithography for drift correction in super-resolution fluorescence microscopy

Localization-based super-resolution microscopy enables imaging of biological structures with sub-diffraction-limited accuracy, but generally requires extended acquisition time. Consequently, stage drift often limits the spatial precision. Previously, we reported a simple method to correct for this by creating an array of 1 μm³ fiducial markers, every ~8 μm, on the coverslip, using UV-nanoimprint lithography (UV-NIL). While this allowed reliable and accurate 3D drift correction, it suffered high autofluorescence background with shorter wavelength illumination, unstable adsorption to the substrate glass surface, and suboptimal biocompatibility. Here, we present an improved fiducial micro-pattern prepared by thermal nanoimprint lithography (T-NIL). The new pattern is made of a thermal plastic material with low fluorescence backgrounds across the wide excitation range, particularly in the blue-region; robust structural stability under cell culturing condition; and a high bio-compatibility in terms of cell viability and adhesion. We demonstrate drift precision to 1.5 nm for lateral (x, y) and 6.1 nm axial (z) axes every 0.2 seconds for a total of 1 min long image acquisition. As a proof of principle, we acquired 4-color wide-field fluorescence images of live mammalian cells; we also acquired super-resolution images of fixed hippocampal neurons, and super-resolution images of live glutamate receptors and postsynaptic density proteins.