Enhanced cytochrome P450 IA1 activity of self-assembled rat hepatocyte spheroids

Estimation of energy pathway fluxes in cancer cells - Beyond the Warburg effect

Glycolytic and respiratory fluxes were analyzed in cancer and non-cancer cells. The steady-state fluxes in energy metabolism were used to estimate the contributions of aerobic glycolytic and oxidative phosphorylation (OxPhos) pathways to the cellular ATP supply. The rate of lactate production - corrected for the fraction generated by glutaminolysis - is proposed as the appropriate way to estimate glycolytic flux. In general, the glycolytic rates estimated for cancer cells are higher than those found in non-cancer cells, as originally observed by Otto Warburg. The rate of basal or endogenous cellular O₂ consumption corrected for non-ATP synthesizing O₂ consumption, measured after inhibition by oligomycin (a specific, potent and permeable ATP synthase inhibitor), has been proposed as the appropriate way to estimate mitochondrial ATP synthesis-linked O₂ flux or net OxPhos flux in living cells. Detecting non-negligible oligomycin-sensitive O₂ consumption rates in cancer cells has revealed that the mitochondrial function is not impaired, as claimed by the Warburg effect. Furthermore, when calculating the relative contributions to cellular ATP supply, under a variety of environmental conditions and for different types of cancer cells, it was found that OxPhos pathway was the main ATP provider over glycolysis. Hence, OxPhos pathway targeting can be successfully used to block in cancer cells ATP-dependent processes such as migration. These observations may guide the re-design of novel targeted therapies.

17-β Estradiol up-regulates energy metabolic pathways, cellular proliferation and tumor invasiveness in ER+ breast cancer spheroids

Several biological processes related to cancer malignancy are regulated by 17-β estradiol (E2) in ER+-breast cancer. To establish the role of E2 on the atypical cancer energy metabolism, a systematic study analyzing transcription factors, proteins, and fluxes associated with energy metabolism was undertaken in multicellular tumor spheroids (MCTS) from human ER+ MCF-7 breast cancer cells. At E2 physiological concentrations (10 and 100 nM for 24 h), both ERα and ERβ receptors, and their protein target pS2, increased by 0.6-3.5 times vs. non-treated MCTS, revealing an activated E2/ER axis. E2 also increased by 30-470% the content of several transcription factors associated to mitochondrial biogenesis and oxidative phosphorylation (OxPhos) (p53, PGC1-α) and glycolytic pathways (HIF1-α, c-MYC). Several OxPhos and glycolytic proteins (36-257%) as well as pathway fluxes (48-156%) significantly increased being OxPhos the principal ATP cellular supplier (>75%). As result of energy metabolism stimulation by E2, cancer cell migration and invasion processes and related proteins (SNAIL, FN, MM-9) contents augmented by 24-189% vs. non-treated MCTS. Celecoxib at 10 nM blocked OxPhos (60%) as well as MCTS growth, cell migration and invasiveness (>40%); whereas the glycolytic inhibitor iodoacetate (0.5 µM) and doxorubicin (70 nM) were innocuous. Our results show for the first time using a more physiological tridimensional cancer model, resembling the initial stages of solid tumors, that anti-mitochondrial therapy may be useful to deter hormone-dependent breast carcinomas.

Application and research progress of in vitro liver cancer cell culture models

Liver cancer is gradually becoming an important burden on public health around the world, and many drugs are currently available for the treatment of liver cancer, so the correct choice of drugs will significantly improve the prognosis of patients. In vitro liver cancer cell culture model is an important way to study the pathogenesis of liver cancer and drug screening. Long-term practice has proved that the traditional two-dimensional (2D) drug screening method cannot truly reproduce the complex drug resistance mechanism of tumor. The emergence of in vitro three-dimensional (3D) hepatocellular carcinoma cell model enriches the selection of methods for hepatoma experiments in vitro. The experimental sensitivity of hepatoma drugs in vitro and the study of pathology and physiology of hepatoma cells in vitro have also been greatly improved. In this paper, we review the main types of liver cancer cells cultured in vitro and discuss their advantages and disadvantages, in order to clarify the development and research direction of in vitro liver cancer culture models.

Challenges and Opportunities in the Design of Liver-on-Chip Microdevices

The liver is the central hub of xenobiotic metabolism and consequently the organ most prone to cosmetic- and drug-induced toxicity. Failure to detect liver toxicity or to assess compound clearance during product development is a major cause of postmarketing product withdrawal, with disastrous clinical and financial consequences. While small animals are still the preferred model in drug development, the recent ban on animal use in the European Union created a pressing need to develop precise and efficient tools to detect human liver toxicity during cosmetic development. This article includes a brief review of liver development, organization, and function and focuses on the state of the art of long-term cell culture, including hepatocyte cell sources, heterotypic cell-cell interactions, oxygen demands, and culture medium formulation. Finally, the article reviews emerging liver-on-chip devices and discusses the advantages and pitfalls of individual designs. The goal of this review is to provide a framework to design liver-on-chip devices and criteria with which to evaluate this emerging technology.

A perfusion incubator liver chip for 3D cell culture with application on chronic hepatotoxicity testing

Liver chips have been developed to recapitulate in vivo physiological conditions to enhance hepatocyte functions for assessing acute responses to drugs. To develop liver chips that can assess repeated dosing chronic hepatotoxicity, we need to ensure that hepatocyte functions be maintained at constant values over two weeks in stable culture conditions of sterility, temperature, pH, fluidic-flow of culture media and drugs. We have designed a perfusion-incubator-liver-chip (PIC) for 3D cell culture, that assures a tangential flow of the media over the spheroids culture. Rat hepatocyte spheroids constrained between a cover glass and a porous-ultrathin Parylene C membrane experienced optimal mass transfer and limited shear stress from the flowing culture media; maintained cell viability over 24 days. Hepatocyte functions were significantly improved and maintained at constant values (urea, albumin synthesis, and CYP450 enzyme activities) for 14 days. The chip act as an incubator, having 5% CO₂ pressure-driven culture-media flow, on-chip heater and active debubbler. It operates in a biosafety cabinet, thus minimizing risk of contamination. The chronic drug response to repeated dosing of Diclofenac and Acetaminophen evaluated in PIC were more sensitive than the static culture control.

Cell-cell adhesion accounts for the different orientation of columnar and hepatocytic cell divisions

Mitotic spindle alignment with the basal or substrate-contacting domain ensures that dividing epithelial cells remain in the plane of the monolayer. Spindle orientation with respect to the substratum is established in metaphase coincident with maximal cell rounding, which enables unobstructed spindle rotation. Misaligned metaphase spindles are believed to result in divisions in which one daughter loses contact with the basal lamina. Here we describe a rescue mechanism that drives substrate-parallel spindle alignment of quasi-diagonal metaphase spindles in anaphase. It requires a Rho- and E-cadherin adhesion-dependent, substrate-parallel contractile actin belt at the apex that governs anaphase cell flattening. In contrast to monolayered Madin-Darby canine kidney cells, hepatocytic epithelial cells, which typically feature tilted metaphase spindles, lack this anaphase flattening mechanism and as a consequence maintain their spindle tilt through cytokinesis. This results in out-of-monolayer divisions, which we propose contribute to the stratified organization of hepatocyte cords in vivo.

Isolated Hepatocytes versus Hepatocyte Spheroids: In Vitro Culture of Rat Hepatocytes

The use of hepatocytes that express liver-specific functions to develop an artificial liver is promising. Unfortunately, the loss of specialized liver functions (dedifferentiation) is still a major problem. Different techniques, such as collagen entrapment, spherical multicellular aggregates (spheroids), and coculture of hepatocytes with extracellular matrix, have been used to improve the performance of hepatocytes in culture. The aim of this study was to compare two different models of hepatocyte isolation in culture: isolated hepatocytes (G1) and hepatocyte spheroids (60% hepatocytes, 40% nonparenchymal cells, and extracellular matrix) (G2). To test functional activity of hepatocytes, both synthetic and metabolic, production of albumin and benzodiazepine transformation into metabolites was tested. G2 showed a high albumin secretion, while a decrease after 15 days of culture in G1 was noted. Diazepam metabolites were higher in G2 than in G1 in all samples, but had statistical significance at days 14 and 21 (p < 0.01). The glycogen content, after 30 days of culture, was very low in G1 (14.2 ± 4.4%), while in G2 it was 72.1 ± 2.6% (p < 0.01). Our study confirms the effectiveness of a culture technique with extracellular matrix and nonparenchymal cells. Maintenance of a prolonged functional activity has been related to restoration of cell polarity and close cell-to-cell contact. We showed that isolated hepatocytes maintain their functional activity for a period significantly reduced, when compared to the hepatocyte spheroids. We confirmed the role of extracellular matrix as a crucial component to promote hepatocyte homeostasis, and the close link between cellular architecture and tissue-specific functions.

Hypothermic Maintenance of Hepatocyte Spheroids

Primary hepatocytes form spheroids under some culture conditions. These spheroids exhibit many tissuelike ultrastructures and retain many liver-specific functions over a long period of time. They are attractive for many applications employing liver cells. The ability to maintain their viability and functions at a reduced temperature to allow for transportation to the site of their application will facilitate their use. Furthermore, with their structural and functional similarity, they could possibly be used as a model system for studying various liver ischemias. The effect of hypothermic treatment was assessed by oxygen consumption rate, ATP, H2O2, and caspase 8 content, as well as albumin and urea synthesis, during and posttreatment. No single outcome variable gives a superlative quantification of hypothermic damage. Taken together, the hypothermic treatment can be seen as increasingly damaging as the temperature decreases from 21°C to 15°C and 4°C. The addition of the chemical protectants glutathione, N-acetyl-L-cystein (NAC), and tauroursodeoxycholic acid (TUDCA) decreased the damaging effect of hypothermic treatment. This protection effect was even more profound when spheroids were preincubated with the protectant for 24 h, and was most prominent at 4°C. The viability of the hypothermically treated hepatocyte spheroids was confirmed by laser scanning confocal microscopy. The method reported provides a means of maintaining spheroids' viability and may allow for their distribution to application sites at a distance.

Regulation of Human Pluripotent Stem Cell-Derived Hepatic Cell Phenotype by Three-Dimensional Hydrogel Models

Human-induced pluripotent stem cell (hiPSC)-derived hepatocytes are anticipated as important surrogates for primary human hepatocytes in applications ranging from basic research to drug discovery and regenerative medicine. Although methods for differentiating hepatocyte-like cells (HLCs) from hiPSCs have developed remarkably, the limited yield of fully functional HLCs is still a major obstacle to their utility. A three-dimensional (3D) culture environment could improve the in vitro hepatic maturation of HLCs. Here we compare 3D hydrogel models of hiPSC-derived HLCs in agarose microwells (3D Petri Dish; 3DPD), nanofibrillar cellulose hydrogels (Growdex; 3DNFC), or animal extracellular matrix-based hydrogels (3D Matrigel; 3DMG). In all the tested 3D biomaterial systems, HLCs formed aggregates. In comparison with two-dimensional monolayer culture, 3DPD and 3DMG models showed both phenotypic and functional enhancement in HLCs over 2.5 weeks of 3D culture. Specifically, we found higher hepatocyte-specific gene expression levels and enhanced cytochrome P450 functions. Our work suggests that transferring HLCs into 3D hydrogel systems can expedite the hepatic maturation of HLCs irrespective of the biochemical nature of the 3D hydrogel. Both plant-based nonembedding and animal-based embedding 3D hydrogel models enhanced the maturation.

A microfluidically perfused three dimensional human liver model

Within the liver, non-parenchymal cells (NPCs) are critically involved in the regulation of hepatocyte polarization and maintenance of metabolic function. We here report the establishment of a liver organoid that integrates NPCs in a vascular layer composed of endothelial cells and tissue macrophages and a hepatic layer comprising stellate cells co-cultured with hepatocytes. The three-dimensional liver organoid is embedded in a microfluidically perfused biochip that enables sufficient nutrition supply and resembles morphological aspects of the human liver sinusoid. It utilizes a suspended membrane as a cell substrate mimicking the space of Disse. Luminescence-based sensor spots were integrated into the chip to allow online measurement of cellular oxygen consumption. Application of microfluidic flow induces defined expression of ZO-1, transferrin, ASGPR-1 along with an increased expression of MRP-2 transporter protein within the liver organoids. Moreover, perfusion was accompanied by an increased hepatobiliary secretion of 5(6)-carboxy-2',7'-dichlorofluorescein and an enhanced formation of hepatocyte microvilli. From this we conclude that the perfused liver organoid shares relevant morphological and functional characteristics with the human liver and represents a new in vitro research tool to study human hepatocellular physiology at the cellular level under conditions close to the physiological situation.

Photolithographic patterning of 3D-formed polycarbonate films for targeted cell guiding

A facile photolithographic platform for the design of cell-guiding polymeric substrates is introduced. Specific areas of the substrate are photo-deactivated for the subsequent growth of bioresistant polymer brushes, creating zones for cell proliferation, and protein adhesion.

Cell and tissue engineering for liver disease

Despite the tremendous hurdles presented by the complexity of the liver's structure and function, advances in liver physiology, stem cell biology and reprogramming, and the engineering of tissues and devices are accelerating the development of cell-based therapies for treating liver disease and liver failure. This State of the Art Review discusses both the near- and long-term prospects for such cell-based therapies and the unique challenges for clinical translation.

Roles of spheroid formation of hepatocytes in liver tissue engineering

The liver plays an important role in a broad spectrum of physiological functions and detoxifies endogenous and exogenous substances. The liver failure is associated with a high risk of mortality because it is one of important organs in our body. Various bioartificial liver (BAL) systems have been used for clinical trials as a bridge for liver transplantations in patients with liver failure. Long term and stable liver-specific functions of hepatocytes in the development of BAL support systems should be considered. Spheroid formation of hepatocytes enhances liver-specific functions. In this review, hepatocyte spheroid formation methods such as galactose density, topology of extracellular matrix, micro-molding technique, hanging-drop culture, non-adhesive surface, positive charged surface, spinner culture, rocked technique, medium component, external forces, coculture system and polymeric nanospheres are explained for enhancing liver-specific functions.

Pluripotent stem cell-derived hepatocyte-like cells

Liver disease is an important clinical problem, impacting over 30 million Americans and over 600 million people worldwide. It is the 12th leading cause of death in the United States and the 16th worldwide. Due to a paucity of donor organs, several thousand Americans die yearly while waiting for liver transplantation. Unfortunately, alternative tissue sources such as fetal hepatocytes and hepatic cell lines are unreliable, difficult to reproduce, and do not fully recapitulate hepatocyte phenotype and functions. As a consequence, alternative cell sources that do not have these limitations have been sought. Human embryonic stem (hES) cell- and induced pluripotent stem (iPS) cell-derived hepatocyte-like cells may enable cell based therapeutics, the study of the mechanisms of human disease and human development, and provide a platform for screening the efficacy and toxicity of pharmaceuticals. iPS cells can be differentiated in a step-wise fashion with high efficiency and reproducibility into hepatocyte-like cells that exhibit morphologic and phenotypic characteristics of hepatocytes. In addition, iPS-derived hepatocyte-like cells (iHLCs) possess some functional hepatic activity as they secrete urea, alpha-1-antitrypsin, and albumin. However, the combined phenotypic and functional traits exhibited by iHLCs resemble a relatively immature hepatic phenotype that more closely resembles that of fetal hepatocytes rather than adult hepatocytes. Specifically, iHLCs express fetal markers such as alpha-fetoprotein and lack key mature hepatocyte functions, as reflected by drastically reduced activity (~0.1%) of important detoxification enzymes (i.e. CYP2A6, CYP3A4). These key differences between iHLCs and primary adult human hepatocytes have limited the use of stem cells as a renewable source of functional adult hepatocytes for in vitro and in vivo applications. Unfortunately, the developmental pathways that control hepatocyte maturation from a fetal into an adult hepatocyte are poorly understood, which has hampered the field in its efforts to induce further maturation of iPS-derived hepatic lineage cells. This review analyzes recent developments in the derivation of hepatocyte-like cells, and proposes important points to consider and assays to perform during their characterization. In the future, we envision that iHLCs will be used as in vitro models of human disease, and in the longer term, provide an alternative cell source for drug testing and clinical therapy.

Recent advances in 2D and 3D in vitro systems using primary hepatocytes, alternative hepatocyte sources and non-parenchymal liver cells and their use in investigating mechanisms of hepatotoxicity, cell signaling and ADME

This review encompasses the most important advances in liver functions and hepatotoxicity and analyzes which mechanisms can be studied in vitro. In a complex architecture of nested, zonated lobules, the liver consists of approximately 80 % hepatocytes and 20 % non-parenchymal cells, the latter being involved in a secondary phase that may dramatically aggravate the initial damage. Hepatotoxicity, as well as hepatic metabolism, is controlled by a set of nuclear receptors (including PXR, CAR, HNF-4α, FXR, LXR, SHP, VDR and PPAR) and signaling pathways. When isolating liver cells, some pathways are activated, e.g., the RAS/MEK/ERK pathway, whereas others are silenced (e.g. HNF-4α), resulting in up- and downregulation of hundreds of genes. An understanding of these changes is crucial for a correct interpretation of in vitro data. The possibilities and limitations of the most useful liver in vitro systems are summarized, including three-dimensional culture techniques, co-cultures with non-parenchymal cells, hepatospheres, precision cut liver slices and the isolated perfused liver. Also discussed is how closely hepatoma, stem cell and iPS cell-derived hepatocyte-like-cells resemble real hepatocytes. Finally, a summary is given of the state of the art of liver in vitro and mathematical modeling systems that are currently used in the pharmaceutical industry with an emphasis on drug metabolism, prediction of clearance, drug interaction, transporter studies and hepatotoxicity. One key message is that despite our enthusiasm for in vitro systems, we must never lose sight of the in vivo situation. Although hepatocytes have been isolated for decades, the hunt for relevant alternative systems has only just begun.

Morphological and Functional Analysis of Hepatocyte Spheroids Generated on Poly-HEMA-Treated Surfaces under the Influence of Fetal Calf Serum and Nonparenchymal Cells

Poly (2-hydroxyethyl methacrylate) (HEMA) has been used as a clinical material, in the form of a soft hydrogel, for various surgical procedures, including endovascular surgery of liver. It is a clear liquid compound and, as a soft, flexible, water-absorbing material, has been used to make soft contact lenses from small, concave, spinning molds. Primary rat hepatocyte spheroids were created on a poly-HEMA-coated surface with the intention of inducing hepatic tissue formation and improving liver functions. We investigated spheroid formation of primary adult rat hepatocyte cells and characterized hepatic-specific functions under the special influence of fetal calf serum (FCS) and nonparencymal cells (NPC) up to six days in different culture systems (e.g., hepatocytes + FCS, hepatocytes – FCS, NPC + FCS, NPC – FCS, co-culture + FCS, co-culture – FCS) in both the spheroid model and sandwich model. Immunohistologically, we detected gap junctions, Ito cell/Kupffer cells, sinusoidal endothelial cells and an extracellular matrix in the spheroid model. FCS has no positive effect in the sandwich model, but has a negative effect in the spheroid model on albumin production, and no influence in urea production in either model. We found more cell viability in smaller diameter spheroids than larger ones by using the apoptosis test. Furthermore, there is no positive influence of the serum or NPC on spheroid formation, suggesting that it may only depend on the physical condition of the culture system. Since the sandwich culture has been considered a “gold standard” in vitro culture model, the hepatocyte spheroids generated on the poly-HEMA-coated surface were compared with those in the sandwich model. Major liver-specific functions, such as albumin secretion and urea synthesis, were evaluated in both the spheroid and sandwich model. The synthesis performance in the spheroid compared to the sandwich culture increases approximately by a factor of 1.5. Disintegration of plasma membranes in both models was measured by lactate dehydrogenase (LDH) release in both models. Additionally, diazepam was used as a substrate in drug metabolism studies to characterize the differences in the biotransformation potential with metabolite profiles in both models. It showed that the diazepam metabolism activities in the spheroid model is about 10-fold lower than the sandwich model. The poly-HEMA-based hepatocyte spheroid is a promising new platform towards hepatic tissue engineering leading to in vitro hepatic tissue formation.

Biophysical microenvironment and 3D culture physiological relevance

Force and substrate physical property (pliability) is one of three well established microenvironmental factors (MEFs) that may contribute to the formation of physiologically more relevant constructs (or not) for cell-based high-throughput screening (HTS) in preclinical drug discovery. In 3D cultures, studies of the physiological relevance dependence on material pliability are inconclusive, raising questions regarding the need to design platforms with materials whose pliability lies within the physiological range. To provide more insight into this question, we examine the factors that may underlie the studies inconclusiveness and suggest the elimination of redundant physical cues, where applicable, to better control other MEFs, make it easier to incorporate 3D cultures into state of the art HTS instrumentation, and reduce screening costs per compound.

Human liver cell spheroids in extended perfusion bioreactor culture for repeated-dose drug testing

Primary cultures of human hepatocyte spheroids are a promising in vitro model for long-term studies of hepatic metabolism and cytotoxicity. The lack of robust methodologies to culture cell spheroids, as well as a poor characterization of human hepatocyte spheroid architecture and liver-specific functionality, have hampered a widespread adoption of this three-dimensional culture format. In this work, an automated perfusion bioreactor was used to obtain and maintain human hepatocyte spheroids. These spheroids were cultured for 3-4 weeks in serum-free conditions, sustaining their phase I enzyme expression and permitting repeated induction during long culture times; rate of albumin and urea synthesis, as well as phase I and II drug-metabolizing enzyme gene expression and activity of spheroid hepatocyte cultures, presented reproducible profiles, despite basal interdonor variability (n = 3 donors). Immunofluorescence microscopy of human hepatocyte spheroids after 3-4 weeks of long-term culture confirmed the presence of the liver-specific markers, hepatocyte nuclear factor 4α, albumin, cytokeratin 18, and cytochrome P450 3A. Moreover, immunostaining of the atypical protein kinase C apical marker, as well as the excretion of a fluorescent dye, evidenced that these spheroids spontaneously assemble a functional bile canaliculi network, extending from the surface to the interior of the spheroids, after 3-4 weeks of culture.

CONCLUSION

Perfusion bioreactor cultures of primary human hepatocyte spheroids maintain a liver-specific activity and architecture and are thus suitable for drug testing in a long-term, repeated-dose format.

Tethered spheroids as an in vitro hepatocyte model for drug safety screening

Hepatocyte spheroids mimic many in vivo liver-tissue phenotypes but increase in size during extended culture which limits their application in drug testing applications. We have developed an improved hepatocyte 3D spheroid model, namely tethered spheroids, on RGD and galactose-conjugated membranes using an optimized hybrid ratio of the two bioactive ligands. Cells in the spheroid configuration maintained 3D morphology and uncompromised differentiated hepatocyte functions (urea and albumin production), while the spheroid bottom was firmly tethered to the substratum maintaining the spheroid size in multi-well plates. The oblate shape of the tethered spheroids, with an average height of 32 μm, ensured efficient nutrient, oxygen and drug access to all the cells within the spheroid structure. Cytochrome P450 induction by prototypical inducers was demonstrated in the tethered spheroids and was comparable or better than that observed with hepatocyte sandwich cultures. These data suggested that tethered 3D hepatocyte spheroids may be an excellent alternative to 2D hepatocyte culture models for drug safety applications.

A novel 3D liver organoid system for elucidation of hepatic glucose metabolism

Hepatic glucose metabolism is a key player in diseases such as obesity and diabetes as well as in antihyperglycemic drugs screening. Hepatocytes culture in two-dimensional configurations is limited in vitro model for hepatocytes to function properly, while truly practical platforms to perform three-dimensional (3D) culture are unavailable. In this work, we present a practical organoid culture method of hepatocytes for elucidation of glucose metabolism under nominal and stress conditions. Employing this new method of culturing cells within a hollow fiber reactor, hepatocytes were observed to self-assemble into 3D spherical organoids with preservation of tight junctions and display increased liver-specific functions. Compared to both monolayer culture and sandwich culture, the hepatocyte organoids displayed higher intracellular glycogen content, glucose consumption, and gluconeogenesis and approached the in vivo values, as also confirmed by gene expression of key enzymes. Moreover, hepatocyte organoids demonstrated more realistic sensitivity to hormonal challenges with insulin, glucagon, and dexamethasone. Finally, the exposure to high glucose demonstrated toxicities including alteration of mitochondrial membrane potential, lipid accumulation, and reactive oxygen species formation, similar to the in vivo responses, which was not captured by monolayer cultures. Collectively, hepatocyte organoids mimicked the in vivo functions better than hepatocyte monolayer and sandwich cultures, suggesting suitability for applications such as antihyperglycemic drugs screening.

Three-dimensional co-culture of hepatocytes and stellate cells

Hepatocytes self-assemble in culture to form compacted spherical aggregates, or spheroids, that mimic the structure of the liver by forming tight junctions and bile canalicular channels. Hepatocyte spheroids thus resemble the liver to a great extent. However, liver tissue contains other cell types and has bile ducts and sinusoids formed by endothelial cells. Reproducing 3-D co-culture in vitro could provide a means to develop a more complex tissue-like structure. Stellate cells participate in revascularization after liver injury by excreting between hepatocytes a laminin trail that endothelial cells follow to form sinusoids. In this study we investigated co-culture of rat hepatocytes and a rat hepatic stellate cell line, HSC-T6. HSC-T6, which does not grow in serum-free spheroid medium, was able to grow under co-culture conditions. Using a three-dimensional cell tracking technique, the interactions of HSC-T6 and hepatocyte spheroids were visualized. The two cell types formed heterospheroids in culture, and HSC-T6 cell invasion into hepatocyte spheroids and subsequent retraction was observed. RT-PCR revealed that albumin and cytochrome P450 2B1/2 expression were better maintained in co-culture conditions. These three-dimensional heterospheroids provide an attractive system for in vitro studies of hepatocyte-stellate cell interactions.

Enhanced differentiation of adult bone marrow-derived stem cells to liver lineage in aggregate culture

Hepatocyte-like cells derived from stem cells hold great potential for clinical and pharmaceutical applications, including high-throughput drug toxicity screening. We report a three-dimensional aggregate culture system for the directed differentiation of adult rat bone marrow-derived stem cells, rat multipotent adult progenitor cells, to hepatocyte-like cells. Compared to adherent monolayer cultures, differentiation in the aggregate culture system resulted in significantly higher expression level of liver-specific transcripts, including an increased albumin mRNA level, and higher levels of albumin and urea secretion. This coincides with the presence of significantly more cells that express intracellular albumin at levels found in primary hepatocytes. The differentiated cell aggregates exhibited cytochrome P450-mediated ethoxyresorufin-O-dealkylation and pentoxyresorufin-O-dealkylation activity. Consistent with these increased mature functions, cells within the aggregates were shown to have many ultrastructural features of mature hepatocytes by transmission electron microscopy. With the scalability of the aggregate culture system and the enhanced differentiation capability, this system may facilitate translation of generating hepatocytes from stem cells to technology.

Microcapsules embedded with three-dimensional fibrous scaffolds for cell culture and tissue engineering

Aggregating into multicellular spheroids within alginate–poly-L-lysine–alginate (APA) microcapsules is important in maintaining the cellular viability and specific functions. However, in the absence of a vascular network, cells in the core of large-sized spheroids are gradually necrotic because of oxygen transfer limitations. In this study, a novel APA microcapsule embedded with three-dimensional fibrous scaffolds (called APA-FS) was proposed to eliminate cellular necrosis by regulating cells to form multi-small spheroids. HepG2 cells were embedded within the APA-FS to form spheroids and the state of these spheroids was evaluated via 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazoliumbromide assay, glucose/lactate metabolism, live/dead staining, and hematoxylin and eosin staining. Comparing with the conventional APA microcapsules, the cells within APA-FS organized into multi-small spheroids. The size of these spheroids depended on the concentration of fibrous scaffolds embedded within the microcapsules. In the APA-FS embedded with 5% (v/v) fibrous scaffolds, the average size of cellular spheroids was controlled below 100 microm and the cellular viability was increased by 50% than the control. The results of live/dead staining and hematoxylin and eosin staining showed that the improved cellular viability might be attributed to the decreased necrosis in the core of these spheroids. The improved viability of cells demonstrated the efficiency of this technology. These findings implied that this system might provide a more suitable culture environment for a variety of tissue engineering applications.

Stimuli-responsive microwells for formation and retrieval of cell aggregates

Generating cell aggregates is beneficial for various applications ranging from biotechnology to regenerative therapies. Previously, poly(ethylene glycol) (PEG) microwells have been demonstrated as a potentially useful method for generating controlled-size cell aggregates. In addition to controlling cell aggregate size and homogeneity, the ability to confine cell aggregates on glass adhesive substrates and subsequently retrieve aggregates from microwells for further experimentation and analysis could be beneficial for various applications. However, it is often difficult to retrieve cell aggregates from these microwells without the use of digestive enzymes. This study describes the stable formation of cell aggregates in responsive microwells with adhesive substrates and their further retrieval in a temperature dependent manner by exploiting the stimuli responsiveness of these microwells. The responsive polymer structure of the arrays can be used to thermally regulate the microwell diameters causing a mechanical force on the aggregates, subsequently facilitating the retrieval of cell aggregates from the microwells with high efficiency compared to PEG arrays. This approach can be potentially integrated into high-throughput systems and may become a versatile tool for various applications that require aggregate formation and experimentation, such as tissue engineering, drug discovery, and stem cell biology.

The famous versus the inconvenient - or the dawn and the rise of 3D-culture systems

One of the greatest impacts on in vitro cell biology was the introduction of three-dimensional (3D) culture systems more than six decades ago and this era may be called the dawn of 3D-tissue culture. Although the advantages were obvious, this field of research was a "sleeping beauty" until the 1970s when multicellular spheroids were discovered as ideal tumor models. With this rebirth, organotypical culture systems became valuable tools and this trend continues to increase. While in the beginning, simple approaches, such as aggregation culture techniques, were favored due to their simplicity and convenience, now more sophisticated systems are used and are still being developed. One of the boosts in the development of new culture techniques arises from elaborate manufacturing and surface modification techniques, especially micro and nano system technologies that have either improved dramatically or have evolved very recently. With the help of these tools, it will soon be possible to generate even more sophisticated and more organotypic-like culture systems. Since 3D perfused or superfused systems are much more complex to set up and maintain compared to use of petri dishes and culture flasks, the added value of 3D approaches still needs to be demonstrated.

The famous versus the inconvenient - or the dawn and the rise of 3D-culture systems

One of the greatest impacts on in vitro cell biology was the introduction of three-dimensional (3D) culture systems more than six decades ago and this era may be called the dawn of 3D-tissue culture. Although the advantages were obvious, this field of research was a "sleeping beauty" until the 1970s when multicellular spheroids were discovered as ideal tumor models. With this rebirth, organotypical culture systems became valuable tools and this trend continues to increase. While in the beginning, simple approaches, such as aggregation culture techniques, were favored due to their simplicity and convenience, now more sophisticated systems are used and are still being developed. One of the boosts in the development of new culture techniques arises from elaborate manufacturing and surface modification techniques, especially micro and nano system technologies that have either improved dramatically or have evolved very recently. With the help of these tools, it will soon be possible to generate even more sophisticated and more organotypic-like culture systems. Since 3D perfused or superfused systems are much more complex to set up and maintain compared to use of petri dishes and culture flasks, the added value of 3D approaches still needs to be demonstrated.

The three-dimensional cultivation of the carcinoma cell line HepG2 in a perfused chip system leads to a more differentiated phenotype of the cells compared to monolayer culture

We describe a polymer chip with a grid-like architecture that it is intended for the three-dimensional cultivation of cells with an active nutrient and gas supply. The chip is typically made from polymethyl methacrylate or polycarbonate but can also be manufactured from biodegradable polymers, such as poly(lactic-co-glycolic acid). Different designs of the chip can be realized. In this study, we evaluated a chip with 506 microcontainers of the size of 300 x 300 x 300 microm that are capable of housing up to 6 million cells, and its suitability as a tissue-specific culture system for the carcinoma cell line HepG2 instead of primary liver cells. Related to an earlier study, where we could show the principal suitability of the system for rat primary cells, we here investigated the system's suitability for the human carcinoma cell line HepG2. The carcinoma cells were used in two different types of chip-containing bioreactors. By confocal laser scanning microscopy, we could show that cellular integrity in the chip culture was maintained and that there were no signs of apoptosis as confirmed by the absence of K18 fragmentation. Gene expression analysis of some liver-specific genes revealed a significantly higher expression of the phase II metabolism genes uridine-diphosphate- glucosyl-transferase (UGT1A1) and glutathione-S-transferase (GSTpi1) as a marker. Therefore, we conclude that by using a three-dimensional instead of a conventional monolayer culture system, hepatocellular carcinoma cells display a phenotype that resembles more closely the tissue of origin.

Vitrification Successfully Preserves Hepatocyte Spheroids

This is the first report on low-temperature preservation of self-assembled cell aggregates by vitrification, which is both a time- and cost-effective technology. We developed an effective protocol for vitrification (ice-free cryopreservation) of hepatocyte spheroids that employs rapid stepwise exposure to cryoprotectants (10.5 min) at room temperature and direct immersion into liquid nitrogen (-196°C). For this, three vitrification solutions (VS) were formulated and their effects on vitrified-warmed spheroids were examined. Cryopreservation using ethylene glycol (EG)-sucrose VS showed excellent preservation capability whereby highly preserved cell viability and integrity of vitrified spheroids were observed, through confocal and scanning electron microscopy imaging, when compared to untreated control. The metabolic functions of EG-sucrose VS-cryopreserved spheroids, as assessed by urea production and albumin secretion, were not significantly different from those of control within the same day of observation. In both the vitrification and control groups, albumin secretion was consistently high, ranging from 47.57 ± 14.39 to 70.38 ± 11.29 μg/106 cells and from 56.84 ± 14.48 to 71.79 ± 16.65 μg/106 cells, respectively, and urea production gradually increased through the culture period. The efficacy of vitrification procedure in preserving the functional ability of hepatocyte spheroids was not improved by introduction of a second penetrating cryoprotectant, 1,2-propanediol (PD). Spheroids cryopreserved with EG-PD-sucrose VS showed maintained cell viability; however, in continuous culture, levels of both metabolic functions were lower than those cryopreserved with EG-sucrose VS. EG-PD VS, in which nonpenetrating cryoprotectant (sucrose) was excluded, provided poor protection to spheroids during cryopreservation. This study demonstrated that sucrose plays an important role in the effective vitrification of self-assembled cell aggregates. In a broad view, the excellent results obtained suggest that the developed vitrification strategy, which is an alternative to freezing, may be effectively used as a platform technology in the field of cell transplantation.

Energy metabolism transition in multi-cellular human tumor spheroids

It is thought that glycolysis is the predominant energy pathway in cancer, particularly in solid and poorly vascularized tumors where hypoxic regions develop. To evaluate whether glycolysis does effectively predominate for ATP supply and to identify the underlying biochemical mechanisms, the glycolytic and oxidative phosphorylation (OxPhos) fluxes, ATP/ADP ratio, phosphorylation potential, and expression and activity of relevant energy metabolism enzymes were determined in multi-cellular tumor spheroids, as a model of human solid tumors. In HeLa and Hek293 young-spheroids, the OxPhos flux and cytochrome c oxidase protein content and activity were similar to those observed in monolayer cultured cells, whereas the glycolytic flux increased two- to fourfold; the contribution of OxPhos to ATP supply was 60%. In contrast, in old-spheroids, OxPhos, ATP content, ATP/ADP ratio, and phosphorylation potential diminished 50-70%, as well as the activity (88%) and content (3 times) of cytochrome c oxidase. Glycolysis and hexokinase increased significantly (both, 4 times); consequently glycolysis was the predominant pathway for ATP supply (80%). These changes were associated with an increase (3.3 times) in the HIF-1alpha content. After chronic exposure, both oxidative and glycolytic inhibitors blocked spheroid growth, although the glycolytic inhibitors, 2-deoxyglucose and gossypol (IC(50) of 15-17 nM), were more potent than the mitochondrial inhibitors, casiopeina II-gly, laherradurin, and rhodamine 123 (IC(50) > 100 nM). These results suggest that glycolysis and OxPhos might be considered as metabolic targets to diminish cellular proliferation in poorly vascularized, hypoxic solid tumors.

Design and fabrication of sub-mm-sized modules containing encapsulated cells for modular tissue engineering

We have proposed modular tissue engineering as a strategy to construct vascularized tissues containing multiple cell types. To create a modular construct, instead of seeding a preformed scaffold, cells were encapsulated within sub-mm modules, and the outer surface of these modules was covered with a layer of endothelial cells. Modules were then added to a larger structure (here by filling a tube) to form the modular construct. Through a systematic process of materials selection, collagen, human umbilical vein endothelial cells (HUVECs), and HepG2 cells, a human hepatoma cell line, were identified as suitable components for module formation, at least for initial studies. A method, which involved cutting and shaping the modules within a tubular mold, was developed to fabricate sub-mm, cylindrical, collagen modules that contained viable, functioning HepG2 cells and that could be seeded with a surface layer of HUVECs. Module dimensions were reproducible and easily altered in a controlled fashion if desired. The module fabrication process developed here not only generated modules suitable for the assembly of a prototype modular construct, but also could potentially be used more generally for other applications for which the goal is to form submm-diameter cylinders from soft hydrogels.

Vitreous Cryopreservation of Cell–Biomaterial Constructs Involving Encapsulated Hepatocytes

We put forward a new strategy for cryopreservation, namely vitrification or ice-free preservation, of cell-biomaterial constructs for tissue-engineering applications. In this study, for a period of 6 days, we tested vitrified and control hepatocytes entrapped at 2 different cell densities (1.5 x 10(6) and 5 x 10(6) cells/mL) in 2 types of engineered collagen matrices (M- and G-collagen) as models to evaluate efficacy and universality of the developed vitrification method. The nature of collagens caused differences in capsule sizes (100-200 microm versus 350-450 microm). The developed method included rapid step-wise introduction of microencapsulated hepatocytes to vitrification solution (40v/v% ethylene glycol 0.6 M sucrose in medium) and their direct immersion in liquid nitrogen. Vitrification did not affect viability and functions of the microencapsulated hepatocytes, which exhibited trends similar to those of untreated controls in the decline of their functions and the rate of cell death during continuous culture, irrespective of physical and chemical properties of the biomaterial and cell density. For control and vitrification, the percentage of live cells varied from 80.3% +/- 0.9% to 82.3% +/- 1.4% in capsules formed by M-collagen, from 82.8% +/- 1.1% to 85.0% +/- 3.3% in capsules formed by G-collagen with cells entrapped at low density, and from 84.4% +/- 1.3% to 86.8% +/- 0.6% in capsules formed by G-collagen with cells entrapped at high density (p > 0.05). Within the same day, the maximum relative change in cell viability and functions between control and vitrification was 4% and 16%, respectively. The developed vitrification approach, which is an alternative to freezing, can be applied to other tissue-engineered constructs with comparable sizes, various cell numbers, and various properties of the biomaterials involved.

A novel formulation of oxygen‐carrying matrix enhances liver‐specific function of cultured hepatocytes

Oxygen is an important component of the cellular microenvironment, mediating cell survival, differentiation, and function. Oxygen supply is a limiting factor during culture of highly metabolic cells such as hepatocytes. Here we present a simple formulation of a fluorocarbon-based oxygen carrier embedded in collagen gel that increases oxygen concentration in culture 6-fold. Rat hepatocytes cultured on oxygen carrier-collagen showed a significant increase in viability and function. Cytochrome P450IA1 activity was increased by 140% in serum-free cultures and by 820% in serum-containing cultures. The significantly higher hepatocellular function on oxygen carrier-collagen matrix persisted and increased during long-term culture. Long-term albumin secretion was increased by 350% in serum-free cultures and by 166% in serum-containing culture. Long-term urea secretion was increased by 79% in serum-free cultures and by 76% in serum-containing cultures. We conclude that oxygen supply may limit hepatocyte function in vitro. This limitation can be overcome by addition of an oxygen carrier to the extracellular matrix. Culture of hepatocytes on oxygen-carrying matrix mimics the oxygen-rich environment of the liver and provides a simple method for enhanced long-term function.

A method for the effective formation of hepatocyte spheroids using a biodegradable polymer nanosphere

Cultures of hepatocytes in spheroid form are known to maintain higher cell viability and exhibit better hepatocyte functions than those in monolayer cultures. In this study, a method for the formation of hepatocyte spheroids was developed using biodegradable polymer nanospheres. The addition of poly(lactic-co-glycolic acid) nanospheres to hepatocyte cultures in spinner flasks increased the efficiency of hepatocyte spheroid formation (the number of cells in spheroids divided by the total cell number) as compared with hepatocyte cultures without nanospheres (control). The viability and mitochondrial activity of the hepatocyte spheroids in the nanosphere-added cultures were significantly higher than those in the control. In addition, the mRNA expression levels of albumin and phenylalanine hydroxylase, both of which are hepatocyte-specific proteins, were significantly higher in the nanosphere-added cultures than in the control. This new culture method improves upon the conventional method of forming hepatocyte spheroids in terms of spheroid formation efficiency, cell viability, and hepatocyte function.

Integration of technologies for hepatic tissue engineering

The liver is the largest internal organ in the body, responsible for over 500 metabolic, regulatory, and immune functions. Loss of liver function leads to liver failure which causes over 25,000 deaths/year in the United States. Efforts in the field of hepatic tissue engineering include the design of bioartificial liver systems to prolong patient's lives during liver failure, for drug toxicity screening and for the study of liver regeneration, ischemia/reperfusion injury, fibrosis, viral infection, and inflammation. This chapter will overview the current state-of-the-art in hepatology including isolated perfused liver, culture of liver slices and tissue explants, hepatocyte culture on collagen "sandwich" and spheroids, coculture of hepatocytes with non-parenchymal cells, and the integration of these culture techniques with microfluidics and reactor design. This work will discuss the role of oxygen and medium composition in hepatocyte culture and present promising new technologies for hepatocyte proliferation and function. We will also discuss liver development, architecture, and function as they relate to these culture techniques. Finally, we will review current opportunities and major challenges in integrating cell culture, bioreactor design, and microtechnology to develop new systems for novel applications.

Micromolding of photocrosslinkable chitosan hydrogel for spheroid microarray and co-cultures

Bioengineering approaches, such as co-cultures of multiple cell types, that aim to mimic the physiological microenvironment may be beneficial for optimizing cell function and for engineering tissues in vitro. This study describes a novel method for preparing a spheroid microarray on microfabricated hydrogels, alone or in co-cultures. Photocrosslinkable chitosan was synthesized and utilized for fabricating hydrogel microstructures through a micromolding process. The chitosan surface was initially cell repellent but became increasingly cell adhesive over time. By using this unique property of chitosan hydrogels, it was possible to generate patterned co-cultures of spheroids and support cells. In this scheme, cells were initially microarrayed within low shear stress regions of microwells. Human hepatoblastoma cells, Hep G2, seeded in these wells formed spheroids with controlled sizes and shapes and stably secreted albumin during the culture period. The change of cell adhesive properties in the chitosan surface facilitated the adhesion and growth of a second cell type, NIH-3T3 fibroblast, and therefore enabled co-cultures of hepatocyte spheroids and fibroblast monolayers. This co-culture system could be a useful platform for studying heterotypic cell-cell interactions, for drug screening, and for developing implantable bioartificial organs.

Liver endothelial cells promote LDL-R expression and the uptake of HCV-like particles in primary rat and human hepatocytes

Low-density lipoprotein (LDL) is an important carrier of plasma cholesterol and triglycerides whose concentration is regulated by the liver parenchymal cells. Abnormal LDL regulation is thought to cause atherosclerosis, while viral binding to LDL has been suggested to facilitate hepatitis C infection. Primary hepatocytes quickly lose the ability to clear LDL during in vitro culture. Here we show that the coculture of hepatocytes with liver sinusoidal endothelial cells (LSEC) significantly increases the ability of hepatocytes to uptake LDL in vitro. LDL uptake does not increase when hepatocytes are cocultured with other cell types such as fibroblasts or umbilical vein endothelial cells. We find that LSECs induce the hepatic expression of the LDL receptor and the epidermal growth factor receptor. In addition, while hepatocytes in single culture did not take up hepatitis C virus (HCV)-like particles, the hepatocytes cocultured with LSECs showed a high level of HCV-like particle uptake. We suggest that coculture with LSECs induces the emergence of a sinusoidal surface in primary hepatocytes conducive to the uptake of HCV-like particles. In conclusion, our findings describe a novel model of polarized hepatocytes in vitro that can be used for the study of LDL metabolism and hepatitis C infection.

Nitric oxide attenuates resistance to doxorubicin in three-dimensional aggregates of human breast carcinoma cells

Compared with monolayer culture, tumour cells cultured as multicellular aggregates (spheroids) exhibit much higher levels of resistance to chemotherapeutic agents, a phenomenon known as multicellular resistance (MCR). Associated with multicellular aggregates is a heterogeneous microenvironment characterised by gradients in oxygen, pH, and nutrients. We previously showed that nitric oxide (NO) signalling plays an important role in the regulation of chemosensitivity in cancer cells cultured as monolayer, and that hypoxia increases resistance to anti-cancer agents largely through a mechanism involving the inhibition of NO signalling. The goal of the present study was to determine whether NO mimetics chemosensitize breast cancer cells in spheroid cultures. Survival of MDA-MB-231 breast carcinoma cells was determined by clonogenic assay following spheroid culture, doxorubicin exposure, and NO mimetic administration. When spheroids were incubated for 24 h with the NO mimetics diethylenetriamine/nitric oxide adduct (DETA/NO) and glyceryl trinitrate (GTN), cell survival after doxorubicin (200 microM) exposure was decreased by 33% (p<0.006) and by up to 47% (p<0.02), respectively. Nitric oxide-mediated signalling involves the generation of the second messenger cyclic guanosine monophosphate (cGMP). Administration of a non-hydrolysable cGMP analogue, 8-Bromo-cGMP, significantly decreased MCR (p<0.04). The effect of NO mimetic exposure on tumour cell chemosensitivity was not due to increased penetration of doxorubicin into spheroids, nor was it associated with an increase in cell proliferation. These results suggest that NO mimetics attenuate MCR to doxorubicin through a mechanism involving cGMP-dependent signalling. Therefore, NO-mimetics may potentially be used as chemosensitizers in cancer therapy.

Dexamethasone effects on rat hepatocyte spheroid formation and function

Hepatocytes cultured on moderately adhesive surfaces or in spinner flasks spontaneously self-assemble into spherical tissue-like aggregates (spheroids). These spheroids have smooth surfaces and tissue-like polarized cell morphology, including bile canalicular-like channels, and maintain high viability and liver-specific functions for extended culture periods. Dexamethasone (DEX), a synthetic glucocorticoid, is known to elicit various responses in gene expression, and is often added to hepatocyte culture medium. The morphology and liver-specific protein production of hepatocyte spheroids were assessed under DEX concentrations ranging from 50 nM to 10 microM. DEX altered the kinetics of spheroid formation in a concentration-dependent fashion, with increasing concentrations inhibiting aggregation and promoting aggregate disassembly on culture dishes. DEX addition to spinner cultures resulted in smaller, more irregularly shaped spheroids and a higher incidence of aggregate clumping. Albumin and urea production were also higher in DEX cultures, but this effect was not as sensitive to concentration and occurred irrespective of the state of aggregation. RTPCR was utilized to assess the mRNA levels of extracellular matrix proteins, E-cadherin, and cytochrome P-450 enzymes. Results indicated a slight increase in fibronectin and collagen III mRNA early in the cultures, possibly contributing to the changes in morphology observed.

Rapid, large-scale formation of porcine hepatocyte spheroids in a novel spheroid reservoir bioartificial liver

We have developed a novel bioreactor based on the observation that isolated porcine hepatocytes rapidly and spontaneously aggregate into spheroids under oscillation conditions. The purpose of this study was to characterize the influence of oscillation frequency (0.125 Hz, 0.25 Hz), cell density (1-10 x 10(6) cells/mL), and storage condition (fresh, cryopreserved) of porcine hepatocytes on the kinetics of spheroid formation. The viability and metabolic performance of spheroid hepatocytes was also compared to monolayer culture. We observed that both fresh and cryopreserved porcine hepatocytes began formation of spheroids spontaneously at the onset of oscillation culture. Spheroid size was directly related to cell density and time in culture, though inversely related to oscillatory frequency. Spheroid formation by fresh porcine hepatocytes was associated with decreased cell death (lactate dehydrogenase release, 1.3 +/- 1.0 vs. 3.1 +/- 0.7 U/mL, P < 0.05) and increased metabolic performance (albumin production, 14.7 +/- 3.3 vs. 4.6 +/- 1.4 fg/c/h, P < 0.0001; ureagenesis from ammonia, 267 +/- 63 vs. 92 +/- 13 micromol/L/h, P < 0.001) compared with monolayer culture. In conclusion, based on the favorable properties of rapid spheroid formation, increased hepatocellular function, and ease of scale-up, the spheroid reservoir bioreactor warrants further investigation as a bioartificial liver for support of liver failure.

Scalable encapsulation of hepatocytes by electrostatic spraying

Encapsulating cells by polyelectrolyte complex coacervation can be accomplished at physiological temperature and buffer conditions. One of the oppositely charged polyelectrolytes in the microcapsule core can be collagen or any other natural extra-cellular matrices suitable for cellular support while the other polyelectrolyte forms the ultra-thin shell to ensure efficient mass transfer. These microcapsules with ultra-thin shell are difficult to produce in large quantities due to their fragility. In this study, electrostatic spraying technique was used to achieve a scalable production of one such type of microcapsules formed by complex coacervation between the cationic methylated collagen and anionic terpolymer of hydroxylethyl methacrylate, methyl methacrylate and methylacrylic acid (HEMA-MMA-MAA). It was found that the microcapsule sizes were dependent on several important operational parameters, such as the diameter of the spraying needle, the flow rate of the hepatocytes-collagen mixture and the voltage of the electrical field. The microcapsules with diameters of 200-800 microm and a narrow size distribution (standard deviation of 5-28%) were successfully produced. The above parameters also influenced the hepatocyte viability and functions. With a practical encapsulation rate of up to 55 ml/h per orifice required in bio-artificial liver-assisted device applications, we have produced large quantities of microcapsules maintaining comparable cell viability (>87%), mechanical stability and bio-functions to the manually extruded microcapsules.

Formation of melanocyte spheroids on the chitosan-coated surface

The search for biocompatible materials that can maintain function of melanocytes as the cellular patch is a feasible alternative for use in the autologous melanocyte transplantation for vitiligo. In this study, we demonstrated that the surface of chitosan-coated polystyrene wells supported the growth and phenotype expression of melanocytes. Depending on the seeding density and culture time, melanocytes were monolayered or spheroidal in morphology. At seeding densities above 10 x 10(3) cells/cm2, human melanocytes started to aggregate on the surface of chitosan after 2 days in culture. These aggregates grew into compact melanocyte spheroids on day 3 and more melanocyte spheroids were observed when a higher seeding density was used. Cells remained viable in the spheroids and grew into dendritic melanocytes when they were reinoculated on polystyrene wells. Conversely, the time for the formation of melanocyte spheroids needed a longer period at lower seeding density. For example, melanocytes at as low as 1.25 x 10(3) cells/cm2 did not aggregate until the 20th day of culture. In order to interpret the phenomenon further, we proposed the formation of melanocyte spheroids on the chitosan is mediated by a balance between two competing forces: the interactions of cell-chitosan and cell-cell.