Establishment of self-organization system in rapidly formed multicellular heterospheroids

Acoustic levitation as a tool for cell-driven self-organization of human cell spheroids during long-term 3D culture

Acoustic levitation, which allows contactless manipulation of micro-objects with ultrasounds, is a promising technique for spheroids formation and culture. This acoustofluidic technique favors cell-cell interactions, away from the walls of the chip, which leads to the spontaneous self-organization of cells. Using this approach, we generated spheroids of mesenchymal stromal cells, hepatic and endothelial cells, and showed that long-term culture of cells in acoustic levitation is feasible. We also demonstrated that this self-organization and its dynamics depended weakly on the acoustic parameters but were strongly dependent on the levitated cell type. Moreover, spheroid organization was modified by actin cytoskeleton inhibitors or calcium-mediated interaction inhibitors. Our results confirmed that acoustic levitation is a rising technique for fundamental research and biotechnological industrial application in the rapidly growing field of microphysiological systems. It allowed easily obtaining spheroids of specific and predictable shape and size, which could be cultivated over several days, without requiring hydrogels or extracellular matrix.

Multidimensional controllable fabrication of tumor spheroids based on a microfluidic device

Multicellular tumor spheroids (MCTSs) are in vitro solid tumor models with physiological relevance. To achieve robust process control, a MCTS fabrication method that combines cell membrane engineering and droplet microfluidic techniques is designed. The fluidic control and the chemical interactions between biotin and streptavidin enable artificial cell aggregation to be accomplished in seconds. Then, spheroids with a uniform size are fabricated within alginate microcapsules. Microfluidic mixing-based cell aggregation regulates the cell aggregate size and the spheroid composition, and the microcapsules regulate the size of spheroids from 120 to 180 μm. The method shows applicability for various cancer cell lines, including HCT116, HepG2, and A549. In addition, composite colon cancer spheroids consisting of HCT116 and NIH3T3 with predetermined cell ratios and uniform distributions are produced. The generated MCTSs are assessed using the ELISA and UPLC-MS/MS techniques. The release of vascular endothelial growth factor (VEGF) and the 5-fluorouracil (5-FU) resistance differ in the monotypic and cocultured colon cancer models. Our method provides a robust way to produce consistent and customized MCTSs in cancer research and drug screening.

3D Tumor Spheroid Models for In Vitro Therapeutic Screening of Nanoparticles

The anticancer activity of compounds and nanoparticles is most often determined in the cell monolayer. However, three-dimensional (3D) systems, such as tumor spheroids, are more representing the natural tumor microenvironment. They have been shown to have higher invasiveness and resistance to cytotoxic agents and radiotherapy compared to cells growing in 2D monolayer. Furthermore, to improve the prediction of clinical efficacy of drugs, in the past decades, even more sophisticated systems, such as multicellular 3D cultures, closely representing natural tumor microenvironment have been developed. Those cultures are formed from either cell lines or patient-derived tumor cells. Such models are very attractive and could improve the selection of tested materials for clinical trials avoiding unnecessary expensive tests in vivo. The microenvironment in tumor spheroids is different, and those differences or the interaction between several cell populations may contribute to different tumor response to the treatment. Also, different types of nanoparticles may have different behavior in 3D models, depending on their nature, physicochemical properties, the presence of targeting ligands on the surface, etc. Therefore, it is very important to understand in which cases which type of tumor spheroid is more suitable for testing specific types of nanoparticles, which conditions should be used, and which analytical method should be applied.

3D perfusion culture of mouse insulinoma in macro-porous scaffolds enhanced insulin production response

To address the remaining issue of poor cell immobilization and insufficient mass transfer in scaffold-based tissue engineering approach for future islet transplantation, we employed a macro-porous poly-l-lactide (PLLA) scaffold immobilizing mouse insulinoma cells and studied its function toward an implantable pancreatic tissue in 7-day perfusion culture. The murine pancreatic β cells could be immobilized in the PLLA scaffold at a high density of 10⁷ cells per cm³ close to the estimated range in normal pancreas. The perfusion culture promoted the 3D cellular organization as observed with live/dead staining and histological staining. The insulin production was significantly enhanced in comparison with static 2D culture and 3D rotational suspension culture by two and six folds, respectively (p < 0.001). As enhanced insulin response was only observed where both the perfusion and 3D cellular organization were present, this could represent important elements in engineering a functional bioartificial pancreas.

Modular assembly-based approach of loosely packing co-cultured hepatic tissue elements with endothelialization for liver tissue engineering

Background

In liver tissue engineering, co-culturing hepatocytes with typical non-parenchymal hepatic cells to form cell aggregates is available to mimic the in vivo microenvironment and promote cell biological functions. With a modular assembly approach, endothelialized hepatic cell aggregates can be packed for perfusion culture, which enables the construction of large-scale liver tissues. Since tightly packed aggregates tend to fuse with each other and block perfusion flows, a loosely packed mode was introduced in our study.

Methods

Using an oxygen-permeable polydimethylsiloxane (PDMS)-based microwell device, highly dense endothelialized hepatic cell aggregates were generated as hepatic tissue elements by co-culturing hepatocellular carcinoma (HepG2) cells, Swiss 3T3 cells, and human umbilical vein endothelial cells (HUVECs). The co-cultured aggregates were then harvested and applied in a PDMS-fabricated bioreactor for 10 days of perfusion culture. To maintain appropriate interstitial spaces for stable perfusion, biodegradable poly-L-lactic acid (PLLA) scaffold fibers were used and mixed with the aggregates, forming a loosely packed mode.

Results

In a microwell co-culture, Swiss 3T3 cells significantly contributed to the formation of hepatic cell aggregates. HUVECs developed a peripheral distribution in aggregates for endothelialization. In the perfusion culture, compared with pure HepG2 aggregates, HepG2/Swiss 3T3/HUVECs co-cultured aggregates exhibited a higher level of cell proliferation and liver-specific function expression (i.e., glucose consumption and albumin secretion). Under the loosely packed mode, co-cultured aggregates showed a characteristic histological morphology with cell migration and adhesion to fibers. The assembled hepatic tissue elements were obtained with 32% of in vivo cell density.

Conclusions

In a co-culture of HepG2, Swiss 3T3, and HUVECs, Swiss 3T3 cells were observed to be beneficial for the formation of endothelialized hepatic cell aggregates. Loosely packed aggregates enabled long-term perfusion culture with high viability and biological function. This study will guide us in constructing large-scale liver tissue models by way of aggregate-based modular assembly.

Three-dimensional cell culture: from evolution to revolution

Recent advances in the isolation of tissue-resident adult stem cells and the identification of inductive factors that efficiently direct differentiation of human pluripotent stem cells along specific lineages have facilitated the development of high-fidelity modelling of several tissues in vitro Many of the novel approaches have employed self-organizing three-dimensional (3D) culturing of organoids, which offer several advantages over conventional two-dimensional platforms. Organoid technologies hold great promise for modelling diseases and predicting the outcome of drug responses in vitro Here, we outline the historical background and some of the recent advances in the field of three-dimensional organoids. We also highlight some of the current limitations of these systems and discuss potential avenues to further benefit biological research using three-dimensional modelling technologies.This article is part of the theme issue 'Designer human tissue: coming to a lab near you'.

A set of cancer stem cell homing peptides associating with the glycan moieties of glycosphingolipids

Cancer stem cells (CSCs) are currently believed to be involved in tumor metastasis and relapse. And treatments against CSCs are well concerned issues. Peptides targeting to mouse and human CSCs were screened from an M13 phage display library. The first subset of cancer stem cell homing peptides (CSC HPs), CSC HP-1 to -12, were screened with mouse EMT6 breast cancer stem cells. Among them, CSC HP-1, CSC HP-3, CSC HP-8, CSC HP-9, and CSC HP-10 can bind to mouse CT26 colon CSCs; CSC HP-1, CSC HP-2, CSC HP-3, and CSC HP-8 can bind to mouse Hepa1-6 liver CSCs; as well as CSC HP-1, CSC HP-2, CSC HP-3, CSC HP-8, CSC HP-9, CSC HP-10, and CSC HP-11 can bind to human PANC-1 pancreatic CSCs. The second subset of cancer stem cell homing peptides, CSC HP-hP1 to -hP3, were screened with human PANC-1 pancreatic CSCs. Both CSC HP-hP1 and CSC HP-hP2 were demonstrated able to bind mouse EMT6, CT26 and Hepa1-6 CSCs as well as human colorectal HT29 and lung H1650 CSCs. CSC HP-1 and CSC HP-hP1 could strongly associate with the Globo 4 and Lewis Y glycan epitopes coupled on a microarray chip or Globo 4 and Globo H conjugated on bovine serum albumin. CSC HP-10, CSC HP-11 and CSC HP-hP2 could associate with the disialylated saccharide Neu5Ac-α-2,6-Gal-β-1,3-(Neu5Ac-α-2,6)-GalNAc coupled on a microarray chip. These results indicate that the CSC HPs may target to the known stem cell glycan markers GbH and Lewis Y as well as the disialylated saccharide.

Controlled self-assembly of alginate microgels by rapidly binding molecule pairs

Controlled self-assembly of cell-encapsulating microscale polymeric hydrogels (microgels) could be advantageous in a variety of tissue engineering and regenerative medicine applications. Here, a method of assembly by chemical modification of alginate polymer with binding pair molecules (BPM) was explored. Alginate was modified with several types of BPM, specifically biotin and streptavidin and click chemistry compounds, and fabricated into 25-30 μm microgels using a microfluidic platform. These microgels were demonstrated to self-assemble under physiological conditions. By combining complementary microgels at a high ratio, size-defined assemblages were created, and the effects of BPM type and assembly method on the number of microgels per assemblage and packing density were determined. Furthermore, a magnetic process was developed to separate assemblages from single microgels, and allow formation of multilayer spheroids. Finally, cells were singly encapsulated into alginate microgels and assembled using BPM-modified alginate, suggesting potential applications in regenerative medicine.

Rapid Formation of Cell Aggregates and Spheroids Induced by a "Smart" Boronic Acid Copolymer

Cell surface engineering has emerged as a powerful approach to forming cell aggregates/spheroids and cell-biomaterial ensembles with significant uses in tissue engineering and cell therapeutics. Herein, we demonstrate that cell membrane remodeling with a thermoresponsive boronic acid copolymer induces the rapid formation of spheroids using either cancer or cardiac cell lines under conventional cell culture conditions at minute concentrations. It is shown that the formation of well-defined spheroids is accelerated by at least 24 h compared to non-polymer-treated controls, and, more importantly, the polymer allows for fine control of the aggregation kinetics owing to its stimulus response to temperature and glucose content. On the basis of its simplicity and effectiveness to promote cellular aggregation, this platform holds promise in three-dimensional tissue/tumor modeling and tissue engineering applications.

Spherical cancer models in tumor biology

Three-dimensional (3D) in vitro models have been used in cancer research as an intermediate model between in vitro cancer cell line cultures and in vivo tumor. Spherical cancer models represent major 3D in vitro models that have been described over the past 4 decades. These models have gained popularity in cancer stem cell research using tumorospheres. Thus, it is crucial to define and clarify the different spherical cancer models thus far described. Here, we focus on in vitro multicellular spheres used in cancer research. All these spherelike structures are characterized by their well-rounded shape, the presence of cancer cells, and their capacity to be maintained as free-floating cultures. We propose a rational classification of the four most commonly used spherical cancer models in cancer research based on culture methods for obtaining them and on subsequent differences in sphere biology: the multicellular tumor spheroid model, first described in the early 70s and obtained by culture of cancer cell lines under nonadherent conditions; tumorospheres, a model of cancer stem cell expansion established in a serum-free medium supplemented with growth factors; tissue-derived tumor spheres and organotypic multicellular spheroids, obtained by tumor tissue mechanical dissociation and cutting. In addition, we describe their applications to and interest in cancer research; in particular, we describe their contribution to chemoresistance, radioresistance, tumorigenicity, and invasion and migration studies. Although these models share a common 3D conformation, each displays its own intrinsic properties. Therefore, the most relevant spherical cancer model must be carefully selected, as a function of the study aim and cancer type.

Engineering of pseudoislets: effect on insulin secretion activity by cell number, cell population, and microchannel networks

Engineered pseudoislets reconstituted from a suspension of pancreatic α and β cells have the potential to relieve the shortage of donor islets for transplantation in the treatment of type 1 diabetes. However, the methods to fabricate pseudoislets are not well developed. In this study, we attempted to generate pseudoislets, which show a higher potential for glucose-induced insulin secretion, by altering total cell number, adjusting the cell ratio of pancreatic α and β cells, and fabricating microchannel networks with the use of alginate hydrogel beads. To effectively aggregate α and β cells and hydrogel beads, we used a previously established rapid aggregation method. When pseudoislets were reconstituted with 8,000 cells in a 1:8 α/β-cell ratio, we observed that the glucose-induced insulin secretion was enhanced by 3.1 times compared with the pseudoislets formed with β cells only. In addition, embedding of microchannel networks increased the insulin secretion rate by 4.4 times compared with the pseudoislets without the microstructures. These findings demonstrated that active modification was effective in reconstituting higher functional pseudoislets, which may be useful for islet transplantation.

Macromolecular cell surface engineering for accelerated and reversible cellular aggregation

Two simple cell membrane interacting copolymers are reported that induce rapid cell aggregation and act as self-supporting “cellular glues” at minute concentrations.

Formation of Cell Aggregates Using Microfabricated Hydrogel Chambers for Assembly into Larger Tissues

This paper presents a fabrication process for cell aggregates with controlled shapes that can be used as building units for constructing relatively large tissue models. Microfabricated hydrogel-based chambers with non-adhesive surface characteristics were prepared via a micromolding process. Alginate was used as the hydrogel matrix, which facilitated the efficient formation of aggregates from cells retained inside the microchamber. We employed several types of toroidal and lattice-shaped hydrogel microchambers with different geometries. We examined the effect of cell type on the aggregate formation process using NIH-3T3, C2C12, and HepG2 cells and clearly observed that aggregation behavior is highly dependent on cell type. In addition, we tried to construct 2-layered capillarylike tissues by stacking heterotypic toroidal cell aggregates, which mimic blood vessels. The presented cell aggregate-based tissue fabrication process could become a versatile approach for preparing complex and scaffold-free 3D tissue models.

Metre-long cell-laden microfibres exhibit tissue morphologies and functions

Artificial reconstruction of fibre-shaped cellular constructs could greatly contribute to tissue assembly in vitro. Here we show that, by using a microfluidic device with double-coaxial laminar flow, metre-long core-shell hydrogel microfibres encapsulating ECM proteins and differentiated cells or somatic stem cells can be fabricated, and that the microfibres reconstitute intrinsic morphologies and functions of living tissues. We also show that these functional fibres can be assembled, by weaving and reeling, into macroscopic cellular structures with various spatial patterns. Moreover, fibres encapsulating primary pancreatic islet cells and transplanted through a microcatheter into the subrenal capsular space of diabetic mice normalized blood glucose concentrations for about two weeks. These microfibres may find use as templates for the reconstruction of fibre-shaped functional tissues that mimic muscle fibres, blood vessels or nerve networks in vivo.

A multicellular 3D heterospheroid model of liver tumor and stromal cells in collagen gel for anti-cancer drug testing

Two-dimensional (2D) monolayer cultures are the standard in vitro model for cancer research. However, they fail to recapitulate the three-dimensional (3D) environment and quickly lose their function. In this study, we developed a new 3D multicellular heterospheroid tumor model in a collagen hydrogel culture system that more closely mimics the in vivo tumor microenvironment for anti-cancer drug testing. Three aspects of cancer were chosen to be modeled based on their ability to resist anti-cancer drugs: 3D, multicellularity, and extracellular matrix (ECM) barrier. The hanging drop method and co-culture of liver carcinoma with stromal fibroblasts were used to form controlled and uniform heterospheroids. These heterospheroids were then encapsulated in collagen gel in order to create a 3D model of liver cancer that would act more similarly to in vivo ECM conditions. The 3D heterospheroid tumor model was tested with an anti-cancer drug to determine how each of the above aspects affects drug resistance. The results demonstrate that the 3D heterospheroid model is more resistant to drug over 2D monolayer and homospheroid cultures, indicating stromal fibroblasts and collagen hydrogel culture system provides more resistance to anti-cancer drug. This study will provide useful information toward the development of improved biomimetic tumor models in vitro for cancer research in pre-clinical drug development.

Rapid aggregation of heterogeneous cells and multiple-sized microspheres in methylcellulose medium

We report a method for the rapid production of cellular aggregates without electric power and cell modification. We focused on the swelling property of a solution containing a high molecular material, methylcellulose (MC), which immediately absorbs a small amount of solvent and fills the space occupied by the solvent. When 1 μl of a suspension of 1000 animal cells in normal culture medium was injected into the 3% MC medium, the normal medium was rapidly absorbed by the surrounding MC medium. Suspended cells were simultaneously trapped on the interfaces between the normal and MC media; they were finally pulled together and held in the MC medium. This event was nearly complete within the first 10 min. Moreover, MC medium-dependent aggregation was observed when polystyrene microspheres of different sizes (diameter, 100 nm-100 μm) were added. Furthermore, we demonstrated the stepwise fabrication of multi-layered aggregates with embedded structures. These methods for creating engineered aggregates should enhance the study of three-dimensional cultures comprising two or more cell types with well-designed structures.