Efficient One‐Step Production of Microencapsulated Hepatocyte Spheroids with Enhanced Functions

Hepatocyte spheroids microencapsulated in hydrogels can contribute to liver research in various capacities. The conventional approach of microencapsulating spheroids produces a variable number of spheroids per microgel and requires an extra step of spheroid loading into the gel. Here, a microfluidics technology bypassing the step of spheroid loading and controlling the spheroid characteristics is reported. Double‐emulsion droplets are used to generate microencapsulated homotypic or heterotypic hepatocyte spheroids (all as single spheroids <200 μm in diameter) with enhanced functions in 4 h. The composition of the microgel is tunable as demonstrated by improved hepatocyte functions during 24 d culture (albumin secretion, urea secretion, and cytochrome P450 activity) when alginate‐collagen composite hydrogel is used instead of alginate. Hepatocyte spheroids in alginate‐collagen also perform better than hepatocytes cultured in collagen‐sandwich configuration. Moreover, hepatocyte functions are significantly enhanced when hepatocytes and endothelial progenitor cells (used as a novel supporting cell source) are co‐cultured to form composite spheroids at an optimal ratio of 5:1, which could be further boosted when encapsulated in alginate‐collagen. This microencapsulated‐spheroid formation technology with high yield, versatility, and uniformity is envisioned to be an enabling technology for liver tissue engineering as well as biomanufacturing.     

Morphological and functional behaviors of rat hepatocytes cultured on single-walled carbon nanotubes

This study describes the morphological and functional behaviors of rat hepatocytes on single-walled carbon nanotube (CNT)-coated surfaces. Although the hydrophobic characteristics of CNT-coated surfaces increased with increasing CNT density, hepatocyte adhesion decreased, indicating that the interaction between hepatocytes and CNTs is weak. We found that hepatocytes on a CNT-coated surface gradually gather together and form spheroids (spherical multicellular aggregates). These spheroids exhibit compact spherical morphology with a smooth surface and express connexin-32, an intracellular communication molecule. In contrast, collagen treatment in conjunction with the CNT-coated surface improved hepatocyte adhesion, and the cells maintained a monolayer configuration throughout the culture period. The albumin secretion and ammonia removal activities of hepatocyte spheroids were maintained at elevated levels for at least 15 days of culturing as compared with hepatocyte monolayers. These results indicate that CNTs can be used for the formation and long-term culture of hepatocyte spheroids.     

Hepatocyte spheroid formation on a titanium dioxide gel surface and hepatocyte long-term culture

The cell morphology and expression of differentiated functions of primary rat hepatocytes on a titanium dioxide (TiO₂) gel surface were investigated. Polystyrene culture dishes were coated with TiO₂ gel by spin-coating an ethanol solution of titanium n-butoxide, hydrolyzing in a humidity chamber and drying with nitrogen gas. The TiO₂ gel layer formed on the polystyrene dishes was transparent and robust, and its surface was quite flat. Rat hepatocytes inoculated on the TiO₂ gel-coated polystyrene dishes gradually accumulated with increasing culture time, and then spontaneously formed many hepatocyte spheroids at 90 ± 21 μm diameter from about 3 days of culture. The diameter of the spheroids increased during the culture, and was 151 ± 43 μm at 14 days of culture. Ammonia removal and albumin secretion by hepatocytes on the TiO₂ gel-coated polystyrene dishes were maintained at a high level for at least 14 days of culture compared with on a type I collagen-coated dish and a non-coated polystyrene dish. These results indicate that TiO₂ gel is an adequate material for hepatocyte spheroid formation and long-term culture of spheroids.     

Induced albumin secretion from HepG2 spheroids prepared using poly(ethylene glycol) derivative with oleyl groups

We developed a poly(ethylene glycol) (PEG) derivative with oleyl groups, so-called “cell adhesive”, for the promotion of human hepatocellular carcinoma HepG2 cell spheroids. Our approach was based on crosslinking of the cell membrane with a cell adhesive via a hydrophobic interaction. A cell adhesive, PEG derivative with hydrophobic oleyl groups at both ends was synthesized and characterized. HepG2 spheroids formed when the adhesive was added to cell suspensions. The size of the spheroids increased with time in culture. In addition, Ammonia elimination of HepG2 spheroid with cell adhesive was 3.4 times higher than that without cell adhesive. Furthermore, albumin secretion from HeG2 spheroids grown with the cell adhesive for 7 days was 3.3 times that from HepG2 spheroids grown without cell adhesive. Fluorescence microscopy showed greater albumin staining in spheroids grown with cell adhesive compared with spheroids grown without adhesive. This cell adhesive may be useful not only for single type of cells but also for multi types of cells to form artificial organs. This cell adhesive will be a key material for liver tissue engineering when it will apply to primary hepatocytes.     

Chondrocyte spheroids on microfabricated PEG hydrogel surface and their noninvasive functional monitoring

Abstract

A two-dimensional microarray of 10 000 (100 × 100) chondrocyte spheroids was constructed with a 100 μm spacing on a micropatterned gold electrode that was coated with poly(ethylene glycol) (PEG) hydrogels. The PEGylated surface as a cytophobic region was regulated by controlling the gel structure through photolithography. In this way, a PEG hydrogel was modulated enough to inhibit outgrowth of chondrocytes from a cell adhering region in the horizontal direction, which is critical for inducing formation of three-dimensional chondrocyte aggregations (spheroids) within 24 h. We further report noninvasive monitoring of the cellular functional change at the cell membrane using a chondrocyte-based field effect transistor. This measurement is based on detection of extracellular potential change induced as a result of the interaction between extracellular matrix protein secreted from spheroid and substrate at the cell membrane. The interface potential change at the cell membrane/gate interface can be monitored during the differentiation of spheroids without any labeling materials. Our measurements of the time evolution of the interface potential provide important information for understanding the uptake kinetics for cellular differentiation.     

Precise and Arbitrary Deposition of Biomolecules onto Biomimetic Fibrous Matrices for Spatially Controlled Cell Distribution and Functions

Advances in nano‐/microfabrication allow the fabrication of biomimetic substrates for various biomedical applications. In particular, it would be beneficial to control the distribution of cells and relevant biomolecules on an extracellular matrix (ECM)‐like substrate with arbitrary micropatterns. In this regard, the possibilities of patterning biomolecules and cells on nanofibrous matrices are explored here by combining inkjet printing and electrospinning. Upon investigation of key parameters for patterning accuracy and reproducibility, three independent studies are performed to demonstrate the potential of this platform for: i) transforming growth factor (TGF)‐β1‐induced spatial differentiation of fibroblasts, ii) spatiotemporal interactions between breast cancer cells and stromal cells, and iii) cancer‐regulated angiogenesis. The results show that TGF‐β1 induces local fibroblast‐to‐myofibroblast differentiation in a dose‐dependent fashion, and breast cancer clusters recruit activated stromal cells and guide the sprouting of endothelial cells in a spatially resolved manner. The established platform not only provides strategies to fabricate ECM‐like interfaces for medical devices, but also offers the capability of spatially controlling cell organization for fundamental studies, and for high‐throughput screening of various biomolecules for stem cell differentiation and cancer therapeutics.     

Reduced myofibroblast differentiation on femtosecond laser treated 316LS stainless steel

In-stent restenosis is a common complication after stent surgery which leads to a dangerous wall narrowing of a blood vessel. Laser assisted patterning is one of the effective methods to modify the stent surface to control cell–surface interactions which play a major role in the restenosis. In this current study, 316LS stainless steel substrates are structured by focusing a femtosecond laser beam down to a spot size of 50 μm. By altering the laser induced spot density three distinct surfaces (low density (LD), medium density (MD) and high density (HD)) were prepared. While such surfaces are composed of primary microstructures, due to fast melting and re-solidification by ultra-short laser pulses, nanofeatures are also observed as secondary structures. Following a detailed surface characterization (chemical and physical properties of the surface), we used a well-established co-culture assay of human microvascular endothelial cells and human fibroblasts to check the cell compatibility of the prepared surfaces. The surfaces were analyzed in terms of cell adherence, proliferation, cell morphology and the differentiation of the fibroblast into the myofibroblast, which is a process indicating a general fibrotic shift within a certain tissue. It is observed that myofibroblast proliferation decreases significantly on laser treated samples in comparison to non-treated ones. On the other hand endothelial cell proliferation is not affected by the surface topography which is composed of micro- and nanostructures. Such surfaces may be used to modify stent surfaces for prevention or at least reduction of restenosis.     

Cellular uptake and cell-to-cell transfer of polyelectrolyte microcapsules within a triple co-culture system representing parts of the respiratory tract

Abstract

Polyelectrolyte multilayer microcapsules around 3.4 micrometers in diameter were added to epithelial cells, monocyte-derived macrophages, and dendritic cells in vitro and their uptake kinetics were quantified. All three cell types were combined in a triple co-culture model, mimicking the human epithelial alveolar barrier. Hereby, macrophages were separated in a three-dimensional model from dendritic cells by a monolayer of epithelial cells. While passing of small nanoparticles has been demonstrated from macrophages to dendritic cells across the epithelial barrier in previous studies, for the micrometer-sized capsules, this process could not be observed in a significant amount. Thus, this barrier is a limiting factor for cell-to-cell transfer of micrometer-sized particles.     

Facile One Step Formation and Screening of Tumor Spheroids Using Droplet‐Microarray Platform

Tumor spheroids or microtumors are important 3D in vitro tumor models that closely resemble a tumor's in vivo “microenvironment” compared to 2D cell culture. Microtumors are widely applied in the fields of fundamental cancer research, drug discovery, and precision medicine. In precision medicine tumor spheroids derived from patient tumor cells represent a promising system for drug sensitivity and resistance testing. Established and commonly used platforms for routine screenings of cell spheroids, based on microtiter plates of 96‐ and 384‐well formats, require relatively large numbers of cells and compounds, and often lead to the formation of multiple spheroids per well. In this study, an application of the Droplet Microarray platform, based on hydrophilic–superhydrophobic patterning, in combination with the method of hanging droplet, is demonstrated for the formation of highly miniaturized single‐spheroid‐microarrays. Formation of spheroids from several commonly used cancer cell lines in 100 nL droplets starting with as few as 150 cells per spheroid within 24–48 h is demonstrated. Established methodology carries a potential to be adopted for routine workflows of high‐throughput compound screening in 3D cancer spheroids or microtumors, which is crucial for the fields of fundamental cancer research, drug discovery, and precision medicine.     

Hierarchically Inverse Opal Porous Scaffolds from Droplet Microfluidics for Biomimetic 3D Cell Co-Culture

With the advantages of better mimicking the specificity of natural tissues, three-dimensional (3D) cell culture plays a major role in drug development, toxicity testing, and tissue engineering. However, existing scaffolds or microcarriers for 3D cell culture are often limited in size and show suboptimal performance in simulating the vascular complexes of living organisms. Therefore, we present a novel hierarchically inverse opal porous scaffold made via a simple microfluidic approach for promoting 3D cell co-culture techniques. The designed scaffold is constructed using a combined concept involving an emulsion droplet template and inert polymer polymerization. This work demonstrates that the resultant scaffolds ensure a sufficient supply of nutrients during cell culture, so as to achieve large-volume cell culture. In addition, by serially planting different cells in the scaffold, a 3D co-culture system of endothelial-cell-encapsulated hepatocytes can be developed for constructing certain functional tissues. It is also demonstrated that the use of the proposed scaffold for a co-culture system helps hepatocytes to maintain specific in vivo functions. These hierarchically inverse opal scaffolds lay the foundation for 3D cell culture and even the construction of biomimetic tissues.     

Cell phenotype characterization in vascular organotypic culture

An in vitro biocompatibility assessment test has been successfully applied to vascular prostheses. It consists of an organotypic culture of chick embryo vascular explant which preserves wall vessel cell interactions and enables cell growth and migration on biomaterial. This study is an attempt to identify the cell phenotype expressed by scanning electron microscopy, by immunostaining with specific monoclonal antibodies against smooth muscle cell (SMC) or von Willebrand factor (vWF), and by uptake of acetylated low-density lipoprotein. Early migrating cells had an endothelial-like phenotype independent of embryonic or adult vessel, veinous or arterial explants. SMC appeared labelled beyond the inner endothelial area. At the periphery, SMC displayed actin bundles specific to stationary phase. Adult cell cultures differed from embryonic cultures in that endothelial-like cells (EC) were more stable and increased their vWF labelling, whereas in embryonic cultures, some EC rounded up with subsequent detachment. Explant culture in liquid instead of agar medium activated this degenerative process suggesting the effect of diffusible chemotactic factors. Organotypic culture in agar medium provides an in vitro co-culture system of EC and SMC and enables further investigation of spatial and temporal evolution of vascular tissues in contact with various substrate.     

Molding of hydrogel microstructures to create multiphenotype cell microarrays

The fabrication of mammalian cell-containing poly(ethylene glycol) (PEG) hydrogel microstructures on glass and silicon substrates is described. Using photoreaction injection molding in poly(dimethylsiloxane) microfluidic channels, three-dimensional hydrogel microstructures encapsulating cells (fibroblasts, hepatocytes, macrophage) were fabricated with cells uniformly distributed to each hydrogel microstructure, and the number of cells in each hydrogel microstructure was controlled by changing the cell density of the precursor solution. PEG hydrogels were modified using an Arg-Gly-Asp (RGD) peptide sequence, with the incorporation of RGD into the hydrogel matrix promoting the spreading of encapsulated fibroblasts over a 24-h period in culture. Cells remained viable encapsulated in these hydrogel microstructures for a period in excess of 1 week in culture. Arrays of hydrogel microstructures encapsulating two or more phenotypes on a single substrate were successfully fabricated using multimicrofluidic channels, creating the potential for multiphenotype cell-based biosensors.     

Bioprinting of Multiscaled Hepatic Lobules within a Highly Vascularized Construct

Highly vascularized complex liver tissue is generally divided into lobes, lobules, hepatocytes, and sinusoids, which can be viewed under different types of lens from the micro‐ to macro‐scale. To engineer multiscaled heterogeneous tissues, a sophisticated and rapid tissue engineering approach is required, such as advanced 3D bioprinting. In this study, a preset extrusion bioprinting technique, which can create heterogeneous, multicellular, and multimaterial structures simultaneously, is utilized for creating a hepatic lobule (≈1 mm) array. The fabricated hepatic lobules include hepatic cells, endothelial cells, and a lumen. The endothelial cells surround the hepatic cells, the exterior of the lobules, the lumen, and finally, become interconnected with each other. Compared to hepatic cell/endothelial cell mixtures, the fabricated hepatic lobule shows higher albumin secretion, urea production, and albumin, MRP2, and CD31 protein levels, as well as, cytochrome P450 enzyme activity. It is found that each cell type with spatial cell patterning in bioink accelerates cellular organization, which could preserve structural integrity and improve cellular functions. In conclusion, preset extruded hepatic lobules within a highly vascularized construct are successfully constructed, enabling both micro‐ and macro‐scale tissue fabrication, which can support the creation of large 3D tissue constructs for multiscale tissue engineering.     

Two-dimensional microarray of HepG2 spheroids using collagen/polyethylene glycol micropatterned chip

A new cell chip technology in the form of a two-dimensional microarray of HepG2 spheroids was developed by using the microcontact printing technique. The chip consisted of several collagen spots in a triangular arrangement within a 100-mm² area at the center of a glass plate (24 × 24 mm), which served as the cell adhesion area; the region excluding the collagen spots that was modified with polyethylene glycol (PEG) served as the non-adhesion area. HepG2 cells inoculated onto the chip gradually formed spheroids with smooth surfaces and high circularity on each collagen spot due to cell proliferation; the spheroid diameters remained constant after 10 days of culture. Such a two-dimensional microarray configuration of HepG2 spheroids could be maintained for at least 2 weeks. The spheroid diameter was directly proportional to the pitch between the collagen spots on the chip. This indicates that we can factitiously control the spheroid diameter. In addition, albumin secretion activity of HepG2 spheroids increased with the increase of spheroid diameter. This chip technology may be applicable as a cellular platform for developing two-dimensional spheroid microarrays.     

Cellular uptake and cell-to-cell transfer of polyelectrolyte microcapsules within a triple co-culture system representing parts of the respiratory tract

Polyelectrolyte multilayer microcapsules around 3.4 micrometers in diameter were added to epithelial cells, monocyte-derived macrophages, and dendritic cells in vitro and their uptake kinetics were quantified. All three cell types were combined in a triple co-culture model, mimicking the human epithelial alveolar barrier. Hereby, macrophages were separated in a three-dimensional model from dendritic cells by a monolayer of epithelial cells. While passing of small nanoparticles has been demonstrated from macrophages to dendritic cells across the epithelial barrier in previous studies, for the micrometer-sized capsules, this process could not be observed in a significant amount. Thus, this barrier is a limiting factor for cell-to-cell transfer of micrometer-sized particles.     

The rotating disc as a device to study the adhesive properties of endothelial cells under differential shear stresses

Hemocompatibility can be conferred on a biomaterial by covering this material with a monolayer of endothelial cells. The endothelial cell is an epithelial cell of mesenchymal origin, that features a specific phenotype with homotypic intercellular interactions and with specialized cell-matrix interactions. These interactions are mandatory to the normal barrier function and the non-thrombogenicity of the endothelial monolayer and are maintained in vivo at shear stresses ranging from 10^-5 to 10^-3 N cm^-2. The endothelial monolayer grafted on a biomaterial should meet similar requirements. We have constructed a rotating disc device to investigate the effects of differential shear stresses on cell-cell and cell-matrix interactions in a monolayer of endothelial cells grafted on a disc-shaped biomaterial. The range of shear stresses that are being applied by the device vary from 0–10^-4 N cm^-2 to 0–2×10^-3 N cm^-2. In a series of experiments with discs of plasma discharge treated polycarbonate (PC) that are coated with fibronectin, it has been shown that a monolayer of endothelial cells grafted on these discs starts to lose intercellular contacts and cell-fibronectin interactions at shear stresses of 10^-4 N cm^-2. Coating of the PC discs with a complex extracellular matrix, synthesized by arterial smooth muscle cells in culture, prior to endothelial cell seeding results in the formation of a monolayer, which retains its integrity at shear stresses up to 2×10^-3 N cm^-2.     

Cell response of cultured macrophages, fibroblasts, and co-cultures of Kupffer cells and hepatocytes to particles of short-chain poly[(R)-3-hydroxybutyric acid]

The known biodegradability of poly[(R)-3-hydroxybutyric acid] (PHB) in certain biological environments has lead to its proposed use as biodegradable, biocompatible polymer. Recently, a new, rapidly biodegradable blockcopolymer has been synthesized that contains crystalline domains of PHB blocks. During degradation of these polymers, the PHB-domains are transformed in a first step into small crystalline particles of short-chain PHB. Therefore, particles of short-chain poly[(R)-3-hydroxybutyric acid] (M_n2300) (PHB-P), as possible degradation products, are investigated here for their effects on the viability and activation of macrophages, fibroblasts, and co-cultures of rat Kupffer cells and rat hepatocytes. Results obtained in the present study indicate that phagocytosis of particles of short-chain poly[(R)-3-hydroxybutyric acid] at high concentrations (higher than 10 g/ml) is dosedependent and associated with cell damage in macrophages but not in fibroblasts. At low concentrations, particles of PHB-P also failed to activate macrophages and are biocompatible. Besides the PHB phagocytosis by Kupffer cells, treatment of co-cultures of Kupffer cells and hepatocytes with 1 g PHB/ml showed neither cytotoxic (lactate dehydrogenase activity) effects nor any change in albumin secretion by hepatocytes.     

Engineering Cell Surface Function with DNA Origami

A specific and reversible method is reported to engineer cell‐membrane function by embedding DNA‐origami nanodevices onto the cell surface. Robust membrane functionalization across epithelial, mesenchymal, and nonadherent immune cells is achieved with DNA nanoplatforms that enable functions including the construction of higher‐order DNA assemblies at the cell surface and programed cell–cell adhesion between homotypic and heterotypic cells via sequence‐specific DNA hybridization. It is anticipated that integration of DNA‐origami nanodevices can transform the cell membrane into an engineered material that can mimic, manipulate, and measure biophysical and biochemical function within the plasma membrane of living cells.     

Biofunctionalized poly(ethylene glycol)-<Emphasis Type="Italic">block</Emphasis>-poly(ε-caprolactone) nanofibers for tissue engineering

Electrospun fibers with contrasting cell adhesion properties provided non-woven substrates with enhanced in vitro acceptance and controllable cell interactions. Poly(ethylene glycol)-block-poly(ε-caprolactone) (PEG-b-PCL) block copolymers with varying segment lengths were synthesized in two steps and characterized by NMR and GPC. A cell adhesive peptide sequence, GRGDS, was covalently coupled to the PEG segment of the copolymer in an additional step. The suitability of polymers with molecular weights ranging from 10 to 30 kDa for electrospinning and the influences of molecular weight, solvent, and concentration on the resulting morphologies were investigated. Generally, electrospun fibers were obtained by electrospinning polymers with molecular weight larger than 25 kDa and concentrations of 10 wt%. Methanol/chloroform (25/75, v/v) mixtures proved to be good solvent systems for electrospinning the PEG-b-PCL and resulted in hydrophilic, non-woven fiber meshes (contact angle 30°). The mesh without cell adhesive GRGDS ligands showed no attachment of human dermal fibroblasts after 24 h cell culture demonstrating that the particular combination of the material and electrospinnig conditions yielded protein and cell repellent properties. The GRGDS immobilized mesh showed excellent cellular attachment with fibroblasts viable after 24 h with spread morphology. Electrospun nanofibers based on block copolymers have been produced which are capable of specifically targeting cell receptor binding and are a promising material for tissue engineering and controlling cell material interactions.