Single Cell Array Enclosed with a Photodegradable Hydrogel in Microwells for Image-Based Cell Classification and Selective Photorelease of Cells

Advances in high throughput cell culture technologies for therapeutic screening and biological discovery applications

Cellular phenotypes and functional responses are modulated by the signals present in their microenvironment, including extracellular matrix (ECM) proteins, tissue mechanical properties, soluble signals and nutrients, and cell-cell interactions. To better recapitulate and analyze these complex signals within the framework of more physiologically relevant culture models, high throughput culture platforms can be transformative. High throughput methodologies enable scientists to extract increasingly robust and broad datasets from individual experiments, screen large numbers of conditions for potential hits, better qualify and predict responses for preclinical applications, and reduce reliance on animal studies. High throughput cell culture systems require uniformity, assay miniaturization, specific target identification, and process simplification. In this review, we detail the various techniques that researchers have used to face these challenges and explore cellular responses in a high throughput manner. We highlight several common approaches including two-dimensional multiwell microplates, microarrays, and microfluidic cell culture systems as well as unencapsulated and encapsulated three-dimensional high throughput cell culture systems, featuring multiwell microplates, micromolds, microwells, microarrays, granular hydrogels, and cell-encapsulated microgels. We also discuss current applications of these high throughput technologies, namely stem cell sourcing, drug discovery and predictive toxicology, and personalized medicine, along with emerging opportunities and future impact areas.

Displacement Mapping as a Highly Flexible Surface Texturing Tool for Additively Photopolymerized Components

Displacement mapping is a computer graphics technique that enables the design of components with regularly or randomly textured surfaces that can be quickly materialized on a three-dimensional (3D) printer when needed. This approach is, in principle, more flexible, faster, and more economical compared to conventional texturing methods, but the accuracy of the texture depends heavily on the parameters used. The purpose of this study is to demonstrate how to produce a surface-textured part using polygonal (mesh) modeling software and a photopolymerizable resin and to develop a universal methodology to predict the dimensional accuracy of the model file log combined with a resin 3D printer. The printed components were characterized on a scanning confocal microscope. In the setup used in this study, the mesh size had to be reduced to 10% of the smallest feature size, and the textured layer had to be heavily (×4.5) overexposed to achieve the desired accuracy. As a practical application, two functional stamps with a regular (honeycomb) and a random texture, respectively, were successfully manufactured. The insights gained will be of great benefit for quickly and cost-effectively producing components with innovative patterns and textures for a variety of hobby, industrial, and biomedical applications.

Dynamic DNA Nanostructures for Cell Manipulation

Dynamic DNA nanostructures are DNA nanostructures with reconfigurable elements that can undergo structural transformations in response to specific stimuli. Thus, anchoring dynamic DNA nanostructures on cell membranes is an attractive and promising strategy for well-controlled cell manipulation. Here, we review the latest progress in dynamic DNA nanostructures for cell manipulation. Commonly used mechanisms for dynamic DNA nanostructures are first introduced. Subsequently, we summarize the anchoring strategies for dynamic DNA nanostructures on cell membranes and list possible applications (including programming cell membrane receptors, controlling ligand activity and drug delivery, capturing and releasing cells, and assembling cells into clusters). Finally, insights into the remaining challenges are presented.

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.

Selective retrieval of antibody-secreting hybridomas in cell arrays based on the dielectrophoresis

A cascade of the formation of cell arrays, the discrimination of cells secreting specific molecules, and the selective retrieval of cells has been developed to harvest antibody-secreting hybridomas in heterogeneous cell populations simply and rapidly. The microwell array device consisted of three-dimensional microband electrodes by assembling both upper and lower substrates perpendicularly. Arrays of hybridomas secreting specific antibodies were prepared by aligning hybridomas in each microwell based on the attractive force of positive dielectrophoresis (p-DEP). Antibody secreted by the hybridomas in the microwells was recognized by the antigen immobilized on the microwells or the membrane surfaces of hybridomas to discriminate hybridomas with the secretion ability. Thereafter, a repulsive force of negative dielectrophoresis (n-DEP) was applied to release the target hybridomas from the microwell array. To harvest the target hybridoma, AC signals could be modulated in the n-DEP frequency region and applied to a pair of microband electrodes located above and below each microwell containing target hybridoma. Thus, the cell-based array system described in this study allowed selective retrieval of single target hybridomas by merely switching from p-DEP to n-DEP after selecting the antibody-secreting hybridomas trapped in each microwell. The development of this high-affinity device could be useful to recover hybridomas producing antibodies in large populations of cells rapidly and effectively.

Star polymer networks: a toolbox for cross-linked polymers with controlled structure

The synthesis of precisely controlled polymer networks has been a long-cherished dream of polymer scientists. Traditional random cross-linking strategies often lead to uncontrolled networks with various kinds of defects. Recent...

Stimuli-responsive destructible polymeric hydrogels based on irreversible covalent bond dissociation

Covalently crosslinked stimuli-destructible hydrogels with the ability of irreversible bond dissociation have attracted great attentions due to their biodegradability, stability against hydrolysis, and controlled solubility upon insertion of desired triggers.

Photodegradable avidin-biotinylated polymer conjugate hydrogels for cell manipulation

Protein-synthetic polymer hybrid hydrogels crosslinked via protein-ligand binding are promising materials for the three-dimensional culture of various cells, while photo-responsive hydrogels have been widely used for the spatio-temporal control of cell functions and patterning. Photo-responsive protein-polymer hybrid hydrogels are therefore attractive candidates for use in cell and artificial tissue fabrication; however, no examples combining these properties have been reported to date. Herein, a photodegradable hydrogel consisting of avidin and biotinylated polyethylene glycol (PEG) was developed as a multi-functional matrix for cell culture and sorting. A four-branched PEG with a biotinylated photocleavable group at the end of each chain was crosslinked with avidin to produce a photodegradable hydrogel. A cytokine-dependent immunocyte was successfully cultured in the hydrogel by supplying cytokine from a medium layered on the hydrogel. Additionally, the adhesion and survival of fibroblasts could be controlled by decorating the hydrogel with a biotinylated cell-adhesive peptide. Cells embedded in the hydrogels could be recovered without cell damage as a result of light-induced hydrogel degradation. Moreover, model target cells expressing red fluorescent protein were selectively liberated from a hydrogel containing cells of different colors by irradiating with a targeted light. Owing to both the selective biotin-binding ability of avidin and the photocleavable properties of the synthetic polymer, the hydrogels were easy to prepare and decorate with functional molecules; they provided an internal structure suitable for cell culture, and allowed light-guided cell manipulation. The hydrogels are therefore expected to contribute to various cell fabrication processes as useful cell engineering and sorting tools.