Micropatterned photodegradable hydrogels for the sorting of microbeads and cells

Designing Inherently Photodegradable Cell-Adhesive Hydrogels for 3D Cell Culture

Light-based microfabrication techniques constitute an indispensable approach to fabricate tissue assemblies, benefiting from noncontact spatially and temporarily controlled manipulation of soft matter. Light-triggered degradation of soft materials, such as hydrogels, is important in tissue engineering, bioprinting, and related fields. The photoresponsiveness of hydrogels is generally not intrinsic and requires complex synthetic procedures wherein photoresponsive crosslinking groups are incorporated into the hydrogel. This paper demonstrates a novel biocompatible and inherently photodegradable poly(ethylene glycol) methacrylate (PEGMA)-based gelatin-methacryloyl (GelMA)-containing hydrogel that can be used to culture cells in 3D for at least 14 d. These gels are conveniently and quickly degraded via UV irradiation for 10 min to produce structured hydrogels of various geometries, sizes, and free-standing cell-laden hydrogel particles. These structures can be flexibly produced on demand. In particular, photodegradation can be temporarily delayed from photopolymerization, offering an alternative to hydrogel array production via photopolymerization with a photomask. The paper investigates the influences of hydrogel composition and swelling liquid on both its photodegradability and biocompatibility.

Core-shell hydrogel microcapsules enable formation of human pluripotent stem cell spheroids and their cultivation in a stirred bioreactor

Cellular therapies based on human pluripotent stem cells (hPSCs) offer considerable promise for treating numerous diseases including diabetes and end stage liver failure. Stem cell spheroids may be cultured in stirred bioreactors to scale up cell production to cell numbers relevant for use in humans. Despite significant progress in bioreactor culture of stem cells, areas for improvement remain. In this study, we demonstrate that microfluidic encapsulation of hPSCs and formation of spheroids. A co-axial droplet microfluidic device was used to fabricate 400 μm diameter capsules with a poly(ethylene glycol) hydrogel shell and an aqueous core. Spheroid formation was demonstrated for three hPSC lines to highlight broad utility of this encapsulation technology. In-capsule differentiation of stem cell spheroids into pancreatic β-cells in suspension culture was also demonstrated.

Next-Generation Biomaterials for Culture and Manipulation of Stem Cells

Stem cell fate decisions are informed by physical and chemical cues presented within and by the extracellular matrix. Despite the generally attributed importance of extracellular cues in governing self-renewal, differentiation, and collective behavior, knowledge gaps persist with regard to the individual, synergistic, and competing effects that specific physiochemical signals have on cell function. To better understand basic stem cell biology, as well as to expand opportunities in regenerative medicine and tissue engineering, a growing suite of customizable biomaterials has been developed. These next-generation cell culture materials offer user-defined biochemical and biomechanical properties, increasingly in a manner that can be controlled in time and 3D space. This review highlights recent innovations in this regard, focusing on advances to culture and maintain stemness, direct fate, and to detect stem cell function using biomaterial-based strategies.

Photo-Cleavable Peptide-Poly(Ethylene Glycol) Conjugate Surfaces for Light-Guided Control of Cell Adhesion

Photo-responsive cell attachment surfaces can simplify patterning and recovery of cells in microdevices for medicinal and pharmaceutical research. We developed a photo-responsive surface for controlling the attachment and release of adherent cells on a substrate under light-guidance. The surface comprises a poly(ethylene glycol) (PEG)-based photocleavable material that can conjugate with cell-adhesive peptides. Surface-bound peptides were released by photocleavage in the light-exposed region, where the cell attachment was subsequently suppressed by the exposed PEG. Simultaneously, cells selectively adhered to the peptide surface at the unexposed microscale region. After culture, the adhered and spread cells were released by exposure to a light with nontoxic dose level. Thus, the present surface can easily create both cell-adhesive and non-cell-adhesive regions on the substrate by single irradiation of the light pattern, and the adhered cells were selectively released from the light-exposed region on the cell micropattern without damage. This study shows that the photo-responsive surface can serve as a facile platform for the remote-control of patterning and recovery of adherent cells in microdevices.

Microfluidic Generation of Amino-Functionalized Hydrogel Microbeads Capable of On-Bead Bioassay

Microfluidic generation of hydrogel microbeads is a highly efficient and reproducible approach to create various functional hydrogel beads. Here, we report a method to prepare crosslinked amino-functionalized polyethylene glycol (PEG) microbeads using a microfluidic channel. The microbeads generated from a microfluidic device were evaluated by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and confocal laser scanning microscopy, respectively. We found that the microbeads were monodisperse and the amino groups were localized on the shell region of the microbeads. A swelling test exhibited compatibility with various solvents. A cell binding assay was successfully performed with RGD peptide-coupled amino-functionalized hydrogel microbeads. This strategy will enable the large production of the various functional microbeads, which can be used for solid phase peptide synthesis and on-bead bioassays.

Capture and "self-release" of circulating tumor cells using metal-organic framework materials

Capturing circulating tumor cells (CTCs) from peripheral blood for subsequent analyses has shown potential in precision medicine for cancer patients. Broad as the prospect is, there are still some challenges that hamper its clinical applications. One of the challenges is to maintain the viability of the captured cells during the capturing and releasing processes. Herein, we have described a composite material that could encapsulate a magnetic Fe3O4 core in a MIL-100 shell (MMs), which could respond to pH changes and modify the anti-EpCAM antibody (anti-EpCAM-MMs) on the surface of MIL-100. After the anti-EpCAM-MMs captured the cells, there was no need for additional conditions but with the acidic environment during the cell culture process, MIL-100 could realize automatic degradation, leading to cell self-release. This self-release model could not only improve the cell viability, but could also reduce the steps of the release process and save human and material resources simultaneously. In addition, we combined clinical patients' case diagnosis with the DNA sequencing and next generation of RNA sequencing technologies in the hope of precision medicine for patients in the future.

Machine learning metrology of cell confinement in melt electrowritten three-dimensional biomaterial substrates

Tuning cell shape by altering the biophysical properties of biomaterial substrates on which cells operate would provide a potential shape-driven pathway to control cell phenotype. However, there is an unexplored dimensional scale window of three-dimensional (3D) substrates with precisely tunable porous microarchitectures and geometrical feature sizes at the cell's operating length scales (10-100 μm). This paper demonstrates the fabrication of such high-fidelity fibrous substrates using a melt electrowriting (MEW) technique. This advanced manufacturing approach is biologically qualified with a metrology framework that models and classifies cell confinement states under various substrate dimensionalities and architectures. Using fibroblasts as a model cell system, the mechanosensing response of adherent cells is investigated as a function of variable substrate dimensionality (2D vs. 3D) and porous microarchitecture (randomly oriented, "non-woven" vs. precision-stacked, "woven"). Single-cell confinement states are modeled using confocal fluorescence microscopy in conjunction with an automated single-cell bioimage data analysis workflow that extracts quantitative metrics of the whole cell and sub-cellular focal adhesion protein features measured. The extracted multidimensional dataset is employed to train a machine learning algorithm to classify cell shape phenotypes. The results show that cells assume distinct confinement states that are enforced by the prescribed substrate dimensionalities and porous microarchitectures with the woven MEW substrates promoting the highest cell shape homogeneity compared to non-woven fibrous substrates. The technology platform established here constitutes a significant step towards the development of integrated additive manufacturing-metrology platforms for a wide range of applications including fundamental mechanobiology studies and 3D bioprinting of tissue constructs to yield specific biological designs qualified at the single-cell level.

Preparation of tri(ethylene glycol) grafted core-shell type polymer support for solid-phase peptide synthesis

A core-shell type polymer support for solid-phase peptide synthesis has been developed for high coupling efficiency of peptides and versatile applications such as on-bead bioassays. Although various kinds of polymer supports have been developed, they have their own drawbacks including poor accessibility of reagents and incompatibility in aqueous solution. In this paper, we prepared hydrophilic tri(ethylene glycol) (TEG) grafted core-shell type polymer supports (TEG SURE) for efficient solid-phase peptide synthesis and on-bead bioassays. TEG SURE was prepared by grafting TEG derivative on the surface of AM PS resin via biphasic diffusion control method and subsequent acetylation of amine groups which are located at the core region of AM PS resin. The performance of TEG SURE was evaluated by synthesizing several peptides. Three points can be highlighted: (1) easy control of loading level of TEG, (2) improved efficiency of peptide synthesis compared with the conventional resins, and (3) applicability of on-bead bioassays.

Metallo-Supramolecular Gels that are Photocleavable with Visible and Near-Infrared Irradiation

A photolabile ruthenium-based complex, [Ru(bpy)2 (4AMP)2 ](PF6 )2 , (4AMP=4-(aminomethyl)pyridine) is incorporated into polyurea organo- and hydrogels via the reactive amine moieties on the photocleavable 4AMP ligands. While showing long-term stability in the dark, cleavage of the pyridine-ruthenium bond upon irradiation with visible or near-infrared irradiation (in a two-photon process) leads to rapid de-gelation of the supramolecular gels, thus enabling spatiotemporal micropatterning by photomasking or pulsed NIR-laser irradiation.

One step fabrication of hydrogel microcapsules with hollow core for assembly and cultivation of hepatocyte spheroids

3D hepatic microtissues can serve as valuable liver analogues for cell-based therapies and for hepatotoxicity screening during preclinical drug development. However, hepatocytes rapidly dedifferentiate in vitro, and typically require 3D culture systems or co-cultures for phenotype rescue. In this work we present a novel microencapsulation strategy, utilizing coaxial flow-focusing droplet microfluidics to fabricate microcapsules with liquid core and poly(ethylene glycol) (PEG) gel shell. When entrapped inside these capsules, primary hepatocytes rapidly formed cell-cell contacts and assembled into compact spheroids. High levels of hepatic function were maintained inside the capsules for over ten days. The microencapsulation approach described here is compatible with difficult-to-culture primary epithelial cells, allows for tuning gel mechanical properties and diffusivity, and may be used in the future for high density suspension cell cultures.

STATEMENT OF SIGNIFICANCE

Our paper combines an interesting new way for making capsules with cultivation of difficult-to-maintain primary epithelial cells (hepatocytes). The microcapsules described here will enable high density suspension culture of hepatocytes or other cells and may be used as building blocks for engineering tissues.

Near-Infrared Light-Responsive Hydrogel for Specific Recognition and Photothermal Site-Release of Circulating Tumor Cells

Isolation of single circulating tumor cells (CTCs) from patients is a very challenging technique that may promote the process of individualized antitumor therapies. However, there exist few systems capable of highly efficient capture and release of single CTCs with high viability for downstream analysis and culture. Herein, we designed a near-infrared (NIR) light-responsive substrate for highly efficient immunocapture and biocompatible site-release of CTCs by a combination of the photothermal effect of gold nanorods (GNRs) and a thermoresponsive hydrogel. The substrate was fabricated by imprinting target cancer cells on a GNR-pre-embedded gelatin hydrogel. Micro/nanostructures generated by cell imprinting produce artificial receptors for cancer cells to improve capture efficiency. Temperature-responsive gelatin dissolves rapidly at 37 °C; this allows bulk recovery of captured CTCs at physiological temperature or site-specific release of single CTCs by NIR-mediated photothermal activation of embedded GNRs. Furthermore, the system has been applied to capture, individually release, and genetically analyze CTCs from the whole blood of cancer patients. The multifunctional NIR-responsive platform demonstrates excellent performance in capture and site-release of CTCs with high viability, which provides a robust and versatile means toward individualized antitumor therapies and also shows promising potential for dynamically manipulating cell-substrate interactions in vitro.

Biosensors for Cell Analysis

Biosensors first appeared several decades ago to address the need for monitoring physiological parameters such as oxygen or glucose in biological fluids such as blood. More recently, a new wave of biosensors has emerged in order to provide more nuanced and granular information about the composition and function of living cells. Such biosensors exist at the confluence of technology and medicine and often strive to connect cell phenotype or function to physiological or pathophysiological processes. Our review aims to describe some of the key technological aspects of biosensors being developed for cell analysis. The technological aspects covered in our review include biorecognition elements used for biosensor construction, methods for integrating cells with biosensors, approaches to single-cell analysis, and the use of nanostructured biosensors for cell analysis. Our hope is that the spectrum of possibilities for cell analysis described in this review may pique the interest of biomedical scientists and engineers and may spur new collaborations in the area of using biosensors for cell analysis.

A microsystem integrating photodegradable hydrogel microstructures and reconfigurable microfluidics for single-cell analysis and retrieval

We developed a micropatterned photodegradable hydrogel array integrated with reconfigurable microfluidics to enable cell secretion analysis and cell retrieval at the single-cell level. The activity of protease molecules secreted from single cells was monitored using FRET peptides entrapped inside microfabricated compartments. Antibody-modified gel islands tethering cells to the surface could be degraded by UV exposure to release specific single cells of interest.

Multifunctional "smart" particles engineered from live immunocytes: toward capture and release of cancer cells

Multifunctional "smart" particles with magnetic, topographic, cell-targeting, and stimulus-responsive properties are obtained using a "live template" strategy. These particles exhibit improved efficiency in capture of target cancer cells by introducing synergistic topographic interactions, and enable the release of captured cells with high viability via reduction of disulfide bonds. Diverse multifunctional particles can be designed using the "live template" strategy.

DNA hydrogel by multicomponent assembly for encapsulation and killing of cells

In this work, a new multifunctional assembled hydrogel was prepared by incorporating gadolinium ions (Gd(3+)) with salmon-sperm DNA and polythiophene derivative (PT-COOH) through chelation interactions. Efficient energy transfer from PT-COOH to Gd(3+) ions takes place followed by sensitization of oxygen molecule to generate reactive oxygen species (ROS) under light irradiation. Cancer cells can be encapsulated into the hydrogel in situ as the formation of hydrogel followed by killing by the ROS. Integration of imaging modality with therapeutic function within a single assembled hydrogel is therefore anticipated to be a new and challenging design element for new hydrogel materials.

Photodegradable hydrogels for capture, detection, and release of live cells

Cells may be captured and released using a photodegradable hydrogel (photogel) functionalized with antibodies. Photogel substrates were used to first isolate human CD4 or CD8 T-cells from a heterogeneous cell suspension and then to release desired cells or groups of cells by UV-induced photodegradation. Flow cytometry analysis of the retrieved cells revealed approximately 95% purity of CD4 and CD8 T-cells, suggesting that this substrate had excellent specificity. To demonstrate the possibility of sorting cells according to their function, photogel substrates that were functionalized with anti-CD4 and anti-TNF-α antibodies were prepared. Single cells captured and stimulated on such substrates were identified by the fluorescence "halo" after immunofluorescent staining and could be retrieved by site-specific exposure to UV light through a microscope objective. Overall, it was demonstrated that functional photodegradable hydrogels enable the capture, analysis, and sorting of live cells.