Development of a bioartificial liver using isolated hepatocytes

A Simple Method for Hepatocyte Attachment in Hollow Fibre Bioreactors

A new method for hepatocyte attachment in hollow fibre (HF) bioreactors was proposed and verified. A flow of medium with suspended hepatocytes, evoked by transmembrane pressure (TMP), and directed across the membrane into the fibre lumen, has accelerated and improved hepatocyte contact with the HF. It was found that seeding of hepatocytes onto the membrane was optimal at TMP of 50–80 mmHg. Ammonia utilisation and ureagenesis rates in hepatocytes seeded in the bioreactor suggests that the proposed method warrants proper conditions for cell functionality and allows for extended culture of hepatocytes in HF bioreactors. It is speculated that time cutback between introduction of hepatocytes into the bioreactor and the start of the cell attachment process, accomplished by the presented method, leads to substantially improved recovery of freshly isolated hepatocytes, and consequently to better overall performance of HF bioreactor.

Comparative Evaluation of Different Membranes for the Construction of an Artificial Liver Support System

During the past decades, many technological improvements have been made in the construction of extracorporeal liver support systems. Among these achievements, membranes of artificial capillary system, used as substrates of hepatocyte growth, aroused our interest in their application for the construction of bioreactors. The present paper studied the comparison of hepatocyte growth and function on six different membranes. Four of them are cellulose based membranes, Cuprophan, Hemophan, Cellulose acetate, and Bioflux; two are synthetic polymer SPAN and Polysulphone. Human hepatoma cell line SMMC-7721, with moderately differentiated hepatocyte-specific functions, was inoculated into the hollow fiber cartridges. These cells were allowed to attach and to grow over these membranes. It was found that there existed differences in hepatocyte immobilization and growth among these membranes. They influenced the growth and functions of hepatoma cells in vitro to some extent. These results show that membrane is an important factor in the construction of capillary membrane bioreactors for artificial liver support.

Development of a Hybrid Liver Support System: A Review

Hybrid liver support systems (LSS) for the use of the detoxifying, metabolic synthetic and regulatory capabilities of liver cells are under development for extracorporeal therapy of acute liver failure and for bridging to liver transplantation. A summary of our development is discussed. A five-step technique for primary liver cell isolation has been introduced in order to address larger scale procurement of hepatocytes. Immobilisation of the cells after isolation appears to be one of the main factors in maintaining hepatocyte function in vitro. Different techniques have been investigated. Using the cell-cell adhesion technique, a culture model was developed for the immobilisation of hepatocytes between capillary membranes. Four separate capillary membrane systems, each forming independent compartments are woven in order to create a three dimensional network. A bioreactor design has been developed. The construction provides different functions, including decentralised cell perfusion. The bioreactor enables 3 dimensional reorganisation of cells, integral oxygenation and decentralised metabolite exchange. The bioreactor has been scaled-up to allow hepatocytes and sinusoidal endothelial cells to be cultured in quantities sufficient for therapeutic application. In a healthy pig model, possible limiting side effects of therapy with this device were excluded. The efficacy of the system has been demonstrated in a hepatectomised pig model. Subsequently, a complete hybrid liver support system for human studies was introduced and applied clinically.

Extracorporeal Artificial Liver: The Influence of a Second Cell Layer on the Morphology and Function of Immobilized Human Hepatocytes

Hepatocytes in long-term cultures represent a promising approach to preserve liver function under standard culture conditions. Hepatocyte cultures as the key components in an extracorporeal artificial liver (EAL) in the treatment of hepatic insufficiency, would be a great advantage. However, one of the numerous unsolved problems is the limitation of the surface area of a future EAL. To decrease the dimensions of same, we modified the cell immobilization technique by placing a second layer of immobilized human hepatocytes onto a layer of pre-immobilized hepatocytes creating a “sandwich immobilization” (SI) system. Immobilization and sandwich immobilization were compared over an investigation period of 30 days: functional performance mirrored by cholinesterase (CHE) and albumin secretion showed remarkable differences only in the course of the first week, whereas we found almost no differences from day 8 on. The total DNA-values on days 0, 1, 7, 14, 21 and 30 varied strongly after the first week but were very similar up to day 30. Finally, it appears disadvantageous to enlarge number/cm2 of (human) hepatocytes in long-term cultures or for application in an EAL by means of sandwich immobilization.

Highly Porous Polymer Matrices as a Three-Dimensional Culture System for Hepatocytes

Hepatocyte-based therapies (e.g., hepatocyte transplantation and extracorporeal support devices) may provide alternative therapies to treat patients with liver disease, but suitable approaches to localize these cells to a given location while maintaining liver-specific gene expression must be developed. The suitability of highly porous three-dimensional sponges fabricated from poly (l-lactic acid) [PLLA] as an hepatocyte culture system was evaluated in this study. Sponges were fabricated utilizing a particulate leaching technique, and were approximately 95% porous, with an average pore diameter of 180 μm. Hepatocytes seeded into these sponges adhered and remained viable for 14 days. However, the secretion rate of albumin from these cells, an indication of liver-specific gene expression, was low (approximately 6 pg/cell/day at day 1), and decreased steadily over the 14 days of the experiment. Coating sponges with collagen, and more preferably, immobilizing cells within the PLLA sponges with a collagen gel, led to enhanced cell survival and albumin secretion at all time points. These data suggest that porous PLLA sponges may provide a novel system for long-term culture of hepatocytes, and proper design of the system may allow the liver-specific gene expression of hepatocytes transplanted in these matrices to be enhanced.

Freezing Characteristics of Isolated Pig and Human Hepatocytes

The cellular response of isolated hepatocytes from pigs, humans, and human hepatoblastoma cells to freezing was characterized using cryomicroscopy and analyzed using a thermodynamic model for water transport and Intracellular Ice Formation (IIF). The value for the reference permeability, Lpg, was found to be 5.8(10)-13, 1.62(10)13, and 2.7(10)-14 m/Ns for pig, human, and Hep G2/C3A cells, respectively. The activation energy, Elp, was found to be 480 kJ/mol for pig hepatocytes, 216 kJ/mol for human, and 121 kJ/mol for Hep G2/C3A cells. The average temperature at which IIF (TavgIIF) occurs was calculated to be -7.24 + 2.3°C for pig hepatocytes, -8.5 + 2.6°C for human hepatocytes, and -9.6 + 4.5°C for Hep G2/C3A cells. These results indicate that the freezing characteristics of pig and human cells are distinct and that the specific freezing characteristics need to be understood for the development of appropriate freezing protocols.

Adipogenesis of human adipose-derived stem cells within three-dimensional hollow fiber-based bioreactors

To further differentiate adipose-derived stem cells (ASCs) into mature adipocytes and create three-dimensional (3D) adipose tissue in vitro, we applied multicompartment hollow fiber-based bioreactor technology with decentral mass exchange for more physiological substrate gradients and integral oxygenation. We hypothesize that a dynamic 3D perfusion in such a bioreactor will result in longer-term culture of human adipocytes in vitro, thus providing metabolically active tissue serving as a diagnostic model for screening drugs to treat diabetes. ASCs were isolated from discarded human abdominal subcutaneous adipose tissue and then inoculated into dynamic 3D culture bioreactors to undergo adipogenic differentiation. Insulin-stimulated glucose uptake from the medium was assessed with and without TNF-alpha. 3D adipose tissue was generated in the 3D-bioreactors. Immunohistochemical staining indicated that 3D-bioreactor culture displayed multiple mature adipocyte markers with more unilocular morphologies as compared with two-dimensional (2D) cultures. Results of real-time polymerase chain reaction showed 3D-bioreactor treatment had more efficient differentiation in fatty acid-binding protein 4 expression. Repeated insulin stimulation resulted in increased glucose uptake, with a return to baseline between testing. Importantly, TNF-alpha inhibited glucose uptake, an indication of the metabolic activity of the tissue. 3D bioreactors allow more mature adipocyte differentiation of ASCs compared with traditional 2D culture and generate adipose tissue in vitro for up to 2 months. Reproducible metabolic activity of the adipose tissue in the bioreactor was demonstrated, which is potentially useful for drug discovery. We present here, to the best of our knowledge for the first time, the development of a coherent 3D high density fat-like tissue consisting of unilocular structure from primary adipose stem cells in vitro.

Encapsulated arrays of self-assembled microtissues: an alternative to spherical microcapsules

Micro-encapsulation and immuno-isolation of allogenic and xenogenic tissues and cells is a promising method for the treatment of a variety of metabolic disorders. Many years have been spent optimizing spherical microcapsules, yet micro-encapsulation has not achieved its full clinical potential. As an alternative to spherical microcapsules, this study presents an alginate-encapsulated array of self-assembled three-dimensional (3D) microtissues. Monodispersed HepG2 cells were seeded onto a micro-molded agarose gel. Cells settled to the bottom of the mold recesses and self-assembled 3D microtissues (n = 822) within 24 h. This array of densely packed microtissues was encapsulated in situ using alginate. When separated from the agarose micro-mold, the encapsulated array had HepG2 microtissues in close proximity to its surface. This surface could be further modified by a simple dipping process. Microtissue size, viability, and albumin secretion were all controllable by the number of cells seeded onto the original agarose micro-mold, and microtissue shape and spacing were controllable by the design of the micro-mold. This approach to encapsulation and the use of self-assembled/self-packing 3D microtissues offers new design possibilities that may help to address certain limitations of conventional microcapsules.

Preparation and HL-7702 cell functionality of titania/chitosan composite scaffolds

Titania/chitosan composite scaffolds were prepared through a freeze-drying technique. The composite scaffolds were highly porous with the average pore size of 120-300 microm, and the titania (TiO(2)) powders were uniformly dispersed on the surface of the pore walls. The compressive strength of the composite scaffolds was significantly improved compared to that of pure chitosan scaffolds. Composite scaffold with 0.3 of TiO(2)/chitosan weight ratio showed the maximum compressive strength of 159.7 +/- 21 kPa. Hepatic immortal cell line HL-7702 was used as seeding cells on the scaffolds, and after different culture periods, cell attachment and function was analyzed. HL-7702 cells attached on the pore walls of the scaffolds with the spheroid shape after 1 day of culture, but more cell aggregations formed within the TiO(2)/chitosan composite scaffolds as compared to pure chitosan scaffolds. Liver-specific functions, albumin secretion and urea synthesis were detected using a spectrometric method. The results showed that albumin secretion and urea synthesis rate of HL-7702 cells slightly decreased with the culture time, and there was no significant difference between composite scaffolds and pure chitosan scaffolds. In conclusion, the TiO(2)/chitosan composite scaffolds possessed an improved mechanical strength compared to pure chitosan scaffolds and supported the attachment and functional expression of hepatocyte, implying their potential application in liver tissue engineering.

Bioartificial liver systems: why, what, whither?

Acute liver disease is a life-threatening condition for which liver transplantation is the only recognized effective therapy. While etiology varies considerably, the clinical course of acute liver failure is common among the etiologies: encephalopathy progressing toward coma and multiple organ failure. Detoxification processes, such as molecular adsorbent recirculating system (MARS®) and Prometheus, have had limited success in altering blood chemistries positively in clinical evaluations, but have not been shown to be clinically effective with regard to patient survival or other clinical outcomes in any Phase III prospective, randomized trial. Bioartificial liver systems, which use liver cells (hepatocytes) to provide metabolic support as well as detoxification, have shown promising results in early clinical evaluations, but again have not demonstrated clinical significance in any Phase III prospective, randomized trial. Cell transplantation therapy has had limited success but is not practicable for wide use owing to a lack of cells (whole-organ transplantation has priority). New approaches in regenerative medicine for treatment of liver disease need to be directed toward providing a functional cell source, expandable in large quantities, for use in various applications. To this end, a novel bioreactor design is described that closely mimics the native liver cell environment and is easily scaled from microscopic (<1 ml cells) to clinical (∼600 ml cells) size, while maintaining the same local cell environment throughout the bioreactor. The bioreactor is used for study of primary liver cell isolates, liver-derived cell lines and stem/progenitor cells.

Lactose Modified Chitosan Scaffold for Hepatocytes Culture

The chitosan scaffold we prepared have a high porosity of about 90% with pore sizes from 50 to 200m. Lactose was conjugated onto the inner surface of the highly porous chitosan scaffold. It was used as substrate for rat hepatocytes culture. The cell attachment ratio was much higher than on monolayer membrane and non-modified porous scaffold. Metabolic activities of the cells were evaluated in terms of albumin secretion and urea synthesis. It was found that hepatocytes cultured on the modified scaffolds showed an increase in albumin secretion during the first 4 days and were more stable than that on non-modified scaffold. The results showed that the microstructure of porous scaffolds provides large surface for cells to adhere and facilitates nutrient and oxygen transportation. Such lactose modified scaffold has a potential application in bioartificial liver support system.

Hybrid braided 3-D scaffold for bioartificial liver assist devices

Three-dimensional ex vivo hepatocyte culture is a tissue-engineering approach to improve the treatment of liver disease. The extracorporeal bioartificial liver (BAL) assists devices that are used in patients until they either recover or receive a liver transplant. The 3-D scaffold plays a key role in the design of bioreactor that is the most important component of the BAL. Presently available 3-D scaffolds used in BAL have shown good performance. However, existing scaffolds are considered to be less than ideal in terms of high-density cultures of hepatocytes maintaining long-term metabolic functions. This study aims to develop a 3-D hybrid scaffold for a BAL support system that would facilitate high-density hepatocyte anchorage with long-term metabolic functions. The scaffolds were fabricated by interlacing polyethylene terephthalate (PET) fibers onto the polysulfone hollow fibers utilizing a modern microbraiding technique. Scaffolds with various pore sizes and porosities were developed by varying braiding angle which was controlled by the gear ratio of the microbraiding machine. The morphological characteristics (pore size and porosity) of the scaffolds were found to be regulated by the gear ratio. Smaller braiding angle yields larger pore and higher porosity. On the other hand, a larger braiding angle causes smaller pore and lower porosity. In hepatocyte culture it was investigated how the morphological characteristics (pore size and porosity) of scaffolds influenced the cell anchorage and metabolic functions. Scaffolds with larger pores and higher porosity resulted in more cell anchorage and higher cellular functions, like albumin and urea secretion, compared to that of smaller pores and lower porosity.

Hepatocyte hollow-fibre bioreactors: design, set-up, validation and applications

Hepatocytes carry out many vital biological functions, such as synthetic and catabolic reactions, detoxification and excretion. Due to their ability to restore a tissue-like environment, hollow-fibre bioreactors (HFBs) show great potential among the different systems used to culture hepatocytes. Several designs of HFBs have been proposed in which hepatocytes or hepatocyte-derived cell lines can be cultured in suspensions or on a solid support. Currently the major use of hepatocyte HFBs is as bioartificial livers to sustain patients suffering from acute liver failure, but they can also be used to synthesize cell products and as cellular models for drug metabolism and transport studies. Here, we present an overview of the set-up of hepatocyte HFBs and aim to provide potential users with the basic knowledge necessary to develop their own system. First, general information on HFBs is given, including basic principles, transport phenomena, designs and cell culture conditions. The importance of the tests necessary to assess the performance of the HFBs, i.e. the viability and functionality of hepatocytes, is underlined. Special attention is paid to drug metabolism studies and to adequate analytical methods. Finally, the potential uses of hepatocyte HFBs are described.

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An engineered microenvironment for multidimensional microscopy of live cells

Multidimensional imaging (MD) of live cells is gaining importance in biomedical research as the commercial availability of confocal, nonlinear optical microscopes, environmental chambers, and specific fluorescence probes grows. One crucial aspect of the MD live cell imaging involves the proper immobilization of cells, which refers to the rapid and sufficient immobilization of cells on the microscope stage, neither disrupting the cellular structure and functions nor affecting the optical properties of the cells and the environments. Conventional cell immobilization methods glue the anchoring cells to coated surfaces, but such methods require centrifugation or extended incubation and are not suitable for cells in suspension. Most of the current three-dimensional (3-D) gels either exhibit unsatisfactory optical properties or have adverse effects on cell functions in culture. Recently, an engineered 3-D microcapsule has been developed that involves the complex coacervation of a positively charged collagen and a negatively charged polymer of 2-hydroxyethyl methacrylate--methacrylic acid--methyl methacrylate (HEMA-MMA-MAA). Hence, confocal imaging of live cells in this engineered 3-D microenvironment was investigated for its optical properties and cellular function compatibility. We report here that this microenvironment facilitates efficient cell immobilization, exhibits good optical properties, and can preserve cellular structures and functions, which will be useful in MD imaging of live cells for various applications.

Protein-coated poly(L-lactic acid) fibers provide a substrate for differentiation of human skeletal muscle cells

Tissue engineering represents a potential method for repairing damaged skeletal muscle tissue. Extracellular matrix (ECM) proteins were evaluated for their ability to aid in cell attachment, whereas a poly(L-lactic acid) (PLLA) fiber scaffold was tested as a substrate for the differentiation of human skeletal muscle cells. In comparison to uncoated or gelatin-coated PLLA films, cell attachment increased significantly (p < 0.001) on PLLA films coated with ECM gel, fibronectin, or laminin. Myoblasts differentiated into multinucleated myofibers on ECM gel-coated PLLA fibers, and expressed muscle markers such as myosin and alpha-actinin. Oligonucleotide microarray analysis showed similar gene expression profiles for human skeletal muscle cells on ECM gel-coated PLLA fibers as to that observed for myofibers on tissue culture plates. Therefore, PLLA fibers coated with ECM proteins provide a scaffold for the development of skeletal muscle tissue for tissue engineering and cell transplantation applications.

Cellular therapies for liver replacement

Insufficient donor organs for orthotopic liver transplantation worldwide have urgently increased the requirement for new therapies for acute and chronic liver disease. Whilst none are yet clinically proven there are at least two different approaches for which there is extensive experimental data, some human anecdotal evidence and some data emerging from Phase 1 clinical trials. Both approaches involve bio-engineering. In vivo tissue engineering involves isolated liver cell transplantation into the liver and/or other ectopic sites and in vitro tissue engineering, using an extracorporeal hepatic support system or bioartificial liver. Some questions are common to both these approaches, such as the best cell source and the therapeutic mass required, and are discussed. Others are specific to each approach. For cell transplantation in vivo the initial engraftment and repopulation will make a critical difference to the outcome, and development of markers for transplanted cells has enabled significant advances in understanding, and therefore manipulating, the process. Moreover, the role of immunosuppression is also important and novel approaches to natural immunosuppression are discussed. For use in a bioartificial liver, the ability for hepatocytes to perform ex vivo at in vivo levels is critical. Three dimensional culture improves cell performance over monolayer cultures. Alginate encapsulated cells offer a suitable 3-D environment for a bioartificial liver since they are both easily manipulatable and cryopreservable. The use of cells derived from stem cells or foetal rather than adult liver cells is also emerging as a potential human cell source which may overcome problems associated with xenogeneic cells.

Development of highly functional long-term culture method of liver slice embedded in agarose gel for bioartificial liver

It is difficult to a produce highly functional bioartificial liver (BAL) using only hepatocytes, because it is believed that liver-specific three-dimensional structure is necessary to maintain high function for BAL. But it is difficult to construct a culture system with liver-specific three-dimensional structure in vitro. To realize a highly functional culture system with liver-specific three-dimensional structure, we developed a culture system using liver slices that keep liver-specific architecture, such as liver lobule and hepatic microvascular system. Liver slices were embedded in agarose gel to maintain them under a moist and three-dimensional environment. We examined the viability and function of liver slices by using various shapes of agarose gel. Liver slices were cultured 1) under stationary condition (control), 2) directly embedded in gel, and 3) embedded in cylindrical gel for good drainage of medium and ventilation of air. The viability and function of the incubated liver slices were evaluated by LDH leakage, histomorphology, and immunohistochemistry. At 10 days, the morphological condition and function of liver slices embedded in cylindrical gel were maintained better than liver slices directly embedded in gel or in the stationary condition. We suggest that high functionality and morphological condition of liver slices could be maintained by embedding in cylindrical gel. In the future, it is possible that this method could be used to develop a highly functional bioartificial liver.

Polyvinylalcohol three-dimensional matrices for improved long-term dynamic culture of hepatocytes

Rat hepatocytes were seeded on three-dimensional highly porous polyvinylalcohol (PVA) and aminoethyl-modified polyvinylalcohol (AE-PVA) matrices. Hepatocytes were cultured under static and dynamic conditions. The three-dimensional matrices offered an improved extracellular microenvironment for long-term (5 days) maintenance of hepatocytes, compared to reference monolayer cultures on collagen. Cellular adhesion exceeded 80% with a viability superior to 70%. The preservation of albumin secretion after 5 days of culture was two times higher for static cultures on three-dimensional matrices (18% on PVA, 13% on AE-PVA) and three times higher for dynamic three-dimensional cultures (25% PVA and AE-PVA), compared to the static two-dimensional culture on collagen film (8%). The biotransformation of ammonia into urea was also maintained throughout the culture period. The addition of the aminoethyl function demonstrated no toxicity for the hepatocyte cultures. This function could be suitable eventually to further improve the hepatocyte culture system by linking more specific adhesion molecules on the polymer surface. This study demonstrated the efficiency of polyvinylalcohol as a three-dimensional matrix coupled to a perfusion culture system, which improves extracellular conditions for hepatocyte survival and promotes preservation of long-term hepatospecific functions.

Bioartificial liver support devices: historical perspectives

Fulminant hepatic failure (FHF) is an important cause of death worldwide. Despite significant improvements in critical care therapy there has been little impact on survival with mortality rates approaching 80%. In many patients the cause of the liver failure is reversible and if short-term hepatic support is provided, the liver may regenerate. Survivors recover full liver function and a normal life expectancy. For many years the only curative treatment for this condition has been liver transplantation, subjecting many patients to replacement of a potentially self-regenerating organ, with the lifetime danger of immunosuppression and its attendant complications, such as malignancy. Because of the shortage of livers available for transplantation, many patients die before a transplant can be performed, or are too ill for operation by the time a liver becomes available. Many patients with hepatic failure do not qualify for liver transplantation because of concomitant infection, metastatic cancer, active alcoholism or concurrent medical problems. The survival of patients excluded from liver transplantation or those with potentially reversible acute hepatitis might be improved with temporary artificial liver support. With a view to this, bioartificial liver support devices have been developed which replace the synthetic, metabolic and detoxification functions of the liver. Some such devices have been evaluated in clinical trials. During the last decade, improvements in bioengineering techniques have been used to refine the membranes and hepatocyte attachment systems used in these devices, in the hope of improving function. The present article reviews the history of liver support systems, the attendant problems encountered, and summarizes the main systems that are currently under evaluation.

Use of Ultrathin Shell Microcapsules of Hepatocytes in Bioartificial Liver-Assist Device

We previously encapsulated hepatocytes in ultrathin shell microcapsules and showed them to have enhanced differentiated functions over cells cultured in monolayer. Here we have used these microencapsulated hepatocytes in a bioartificial liver-assisted device (BLAD) with a rat hepatectomy model. Primary rat hepatocytes were encapsulated in 150- to 200-microm microcapsules, using an electrostatic droplet generator. The microencapsulated hepatocytes exhibited good in vitro urea synthesis activity in plasma from rats with fulminant hepatic failure (FHF). The ex vivo hemoperfusion was conducted in FHF rats by perfusing plasma at a rate of 1-2 mL/min through 1.5-2 x 10(8) encapsulated hepatocytes packed into a packed-bed bioreactor. Hemoperfusion with the bioreactor was initiated 5 h after operative induction of liver failure and continued for 7 h. The BLAD-treated rats showed improvements over the control groups in survival time and metabolic indicators, including ammonia and total bilirubin levels. Furthermore, expanded bed adsorption (EBA) detoxification technology using Streamline-SP resin was explored to complement the bioreactor with microencapsulated hepatocytes. In vitro experiments indicated that serum ammonia could be specifically removed in dose-dependent manner, whereas the total serum proteins were unaffected by the resin. In ex vivo experiments, hemoperfusion with the resin was initiated 3 h after operative induction of liver failure and continued for 7 h. The resin-treated rats showed obvious serum ammonia removal with no observable total blood protein and blood cell adsorption. Therefore, Streamline-SP resin can potentially be integrated into a BLAD for improved efficacy.

Culture of hepatocytes on fructose-modified chitosan scaffolds

Fructose was conjugated onto the inner surface of highly porous chitosan scaffold prepared by lyophilization. The modified scaffold with average pore size 50-200 microm was used to cultivate rat hepatocytes harvested by portal vein collagenase perfusion. The results indicated that while chitosan sponge alone supported cell attachment and growth, the scaffold modified with fructose accommodated a much larger number of hepatocytes due to the specific interaction between seeded hepatocytes and fructose moieties conjugated onto the surface of the scaffold. Hepatocytes exhibited a round cellular morphology with many microvilli evident on the surface of the cells, indicating healthy cells. Metabolic activities in terms of albumin secretion and urea synthesis were evaluated. It was found that hepatocytes cultured within fructose-modified scaffold resulted in much higher activities than within unmodified chitosan sponge. Scanning electron microscopy results showed that fructose-modified porous scaffold promoted the formation of cellular aggregates.

Morphological studies on the culture of kidney epithelial cells in a fiber-in-fiber bioreactor design with hollow fiber membranes

A hollow fiber-in-fiber-based bioreactor system was tested for the applicability to host kidney epithelial cells as a model system for a bioartificial kidney. Hollow fibers were prepared from polyacrylonitrile (PAN), polysulfone-polyvinylpyrollidinone (PVP) blend (PSU) and poly(acrylonitrile-N-vinylpyrollidinone) copolymer P(AN-NVP). Hollow fibers with smaller and larger diameters were prepared so that the smaller fitted into the larger, with a distance of 50-100 microm in between. The following material combinations as outer and inner fiber were applied: PAN-PAN; PSU-PSU, PSU-P(AN-NVP). Madin-Darby kidney epithelial cells (MDCK) were seeded in the interfiber space and cultured for a period up to 14 days. Light, scanning, and transmission electron microscopy were used to follow the adhesion and growth of cells, and to characterize their morphology. As a result, we found that MDCK cells were able to grow in the interfiber space in mono- and multilayers without signs of systemic degeneration. Comparison of the different materials showed that PAN and P(AN-NVP) provided the best growth conditions, indicated by a tight attachment of cells on hollow fiber membrane, and subsequent proliferation and development of structural elements of normal epithelia, such as tight junctions and microvilli. In conclusion, the fiber-in-fiber design seems to be an interesting system for the construction of a bioartificial kidney.

The development of a new bioartificial liver and its application in 12 acute liver failure patients

AIM: Bioartificial liver is a hope of supporting liver functions in acute liver failure patients. Using polysulfon fibers, a new bioartificial liver was developed. The aim of this study was to show whether this bioartificial liver could support liver functions or not.

METHODS: Hepatocytes were procured from swine using Seglen’s methods. The bioartificial liver was constructed by polysulfon bioreactor and more than 10¹⁰ hepatocytes. It was applied 14 times in 12 patients, who were divided into 7 cases of simultaneous HBAL and 5 cases of non-simultaneous HBAL. Each BAL treatment lasted 6 hours. The general condition of the patients and the biochemical indexes were studied.

RESULTS: After treatment with bioartificial liver, blood ammonia, prothrombin time and total bilirubin showed significant decrease. 2 d later, blood ammonia still showed improvment. within one month period, 1 case (1/7) in simultaneous group died while in non-simultaneous group 2 cases (2/5) died. The difference was significant. Mortality rate was 25%.

CONCLUSION: The constructed bioartificial liver can support liver functions in acute liver failure. The simultaneous HBAL is better than non-simultaneous HBAL.

The development of a new bioartificial liver and its application in 12 acute liver failure patients

AIM

Bioartificial liver is a hope of supporting liver functions in acute liver failure patients. Using polysulfon fibers, a new bioartificial liver was developed. The aim of this study was to show whether this bioartificial liver could support liver functions or not.

METHODS

Hepatocytes were procured from swine using Seglen's methods. The bioartificial liver was constructed by polysulfon bioreactor and more than 10(10) hepatocytes. It was applied 14 times in 12 patients, who were divided into 7 cases of simultaneous HBAL and 5 cases of non-simultaneous HBAL. Each BAL treatment lasted 6 hours. The general condition of the patients and the biochemical indexes were studied.

RESULTS

After treatment with bioartificial liver, blood ammonia, prothrombin time and total bilirubin showed significant decrease. 2 days later, blood ammonia still showed improvment. within one month period, 1 case (1/7) in simultaneous group died while in non-simultaneous group 2 cases (2/5) died. The difference was significant. Mortality rate was 25 %.

CONCLUSION

The constructed bioartificial liver can support liver functions in acute liver failure. The simultaneous HBAL is better than non-simultaneous HBAL.

Evaluation of a galactose-carrying gelatin sponge for hepatocytes culture and transplantation

This study proposes a new three-dimensional culture of mouse hepatocytes in a porous galactose-carrying modified gelatin sponge matrix. The modification of gelatin using galactose residues significantly increased the attachment of hepatocytes on the substrate. A modified gelatin sponge with lactobionic acid (MGLA) was prepared to increase the specific interaction between the hepatocytes and the matrix. Hepatocytes cultured in a three-dimensional MGLA sponge released much less lactate dehydrogenase than those cultured on a collagen Type I-coated monolayer. Moreover, the survival rate of hepatocytes cultured on an MGLA sponge was longer than the survival rate of hepatocytes cultured on a collagen Type I-coated monolayer. Hepatic specific metabolic functions, namely, the secretion of serum albumin and the synthesis of urea, were well maintained and promoted by spheroidal hepatocytes formed in the MGLA sponge.

Fibroblast culture on surface-modified poly(glycolide-co-epsilon-caprolactone) scaffold for soft tissue regeneration

Novel porous matrices made of a copolymer of glycolide (G) and epsilon-caprolactone (CL) (51 : 49, Mw 103000) was prepared for tissue engineering using a solvent-casting particulate leaching method. Poly(glycolide-co-epsilon-caprolactone) (PGCL) copolymer showed a rubber-like elastic characteristic, in addition to an amorphous property and fast biodegradability. In order to investigate the effect on the fibroblast culture, PGCL scaffolds of varying porosity and pore size, in addition to surface-hydrolysis or collagen coating, were studied. The large pore-sized scaffold (pore size >150 microm) demonstrated a much greater cell adhesion and proliferation than the small pore-sized one. In addition, the higher porosity, the better the cell adhesion and proliferation. The surface-hydrolyzed PGCL scaffold showed enhanced cell adhesion and proliferation compared with the unmodified one. Type I collagen coating revealed a more pronounced contribution for increased cell interactions than the surface-hydrolyzed one. These results demonstrate that surface-modified PGCL scaffold can provide a suitable substrate for fibroblast culture, especially in the case of soft tissue regenerations.

Polyetherimide: a new membrane-forming polymer for biomedical applications

Membranes for biohybrid organs such as the biohybrid liver support system have to face 2 different environments, namely blood and tissue cells. Accordingly, the respective membrane surfaces must have optimal properties in terms of biocompatibility for blood or tissue. Flat membranes prepared by a phase inversion process from polyetherimide were modified by binding of tris-(hydroxymethyl)-aminomethane to obtain a surface with hydroxyl groups by binding of polyethylene imine to attach a hydrophilic macromolecule with amine groups useful as a spacer for later bonding of further ligands and by attachment of heparin. The binding of the different ligands was successful as monitored by different physicochemical methods. The blood response of plain polyetherimide was comparable to that of polyacrylonitrile, and it could be further improved by the binding of heparin. The tissue compatibility of polyetherimide and its different modifications was compared with commercial cell culture substrate membranes (Millicell) and found to be comparable for polyetherimide and even better after the modification with tris-(hydroxymethyl)-aminomethane. In conclusion, polyetherimide seems to be an interesting material for the production of membranes for application in biohybrid organ systems.

Multi-layered microcapsules for cell encapsulation

Mechanical stability, complete encapsulation, selective permeability, and suitable extra-cellular microenvironment, are the major considerations in designing microcapsules for cell encapsulation. We have developed four types of multi-layered microcapsules that allow selective optimization of these parameters. Primary hepatocytes were used as model cells to test these different microcapsule configurations. Type-1 microcapsules with an average diameter of 400 microm were formed by complexing modified collagen with a ter-polymer shell of 2-hydroxyethyl methylacrylate (HEMA), methacrylic acid (MAA) and methyl methacrylate (MMA), resulting in a capsule thickness of 2-5 microm. Cells in these microcapsules exhibited improved cellular functions over those cultured on collagen monolayers. Type-II microcapsules were formed by encapsulating the Type-I microcapsules in another 2-5 microm ter-polymer shell and a approximately 5 microm collagen layer between the two ter-polymer shells to ensure complete cell encapsulation. Type-II microcapsules comprised of a macro-porous exoskeleton with materials such as alumina sol-gel coated on the Type-I microcapsules. Nano-indendation assay indicated an improved mechanical stability over the Type-I microcapsules. Type-IV microcapsules were created by encapsulating Type-III microcapsules in another 2-5 microm ter-polymer shell, with the aim of imparting a negatively charged smooth surface to minimize plasma protein absorption and ensure complete cell encapsulation. The permeability for nutrient exchange, cellular functions in terms of urea production and mechanical stability of the microcapsules were characterized. The advantages and limitations of these microcapsules for tissue engineering are discussed.

Extracorporeal tissue engineered liver-assist devices

The treatment of acute liver failure has evolved to the current concept of hybrid bioartificial liver (BAL) support, because wholly artificial systems have not proved efficacious. BAL devices are still in their infancy. The properties that these devices must possess are unclear because of our lack of understanding of the pathophysiology of liver failure. The considerations that attend the development of BAL devices are herein reviewed. These considerations include choice of cellular component, choice of membrane component, and choice of BAL system configuration. Mass transfer efficiency plays a role in the design of BAL devices, but the complexity of the systems renders detailed mass transfer analysis difficult. BAL devices based on hollow-fiber bioreactors currently show the most promise, and available results are reviewed herein. BAL treatment is designed to support patients with acute liver failure until an organ becomes available for transplantation. The results obtained to date, in this relatively young field, point to a bright future. The risks of using xenogeneic treatments have yet to be defined. Finally, the experience gained from the past and current BAL systems can be used as a basis for improvement of future BAL technology.

A novel reactor for making uniform capsules

A novel chemical reactor was designed and developed for the continuous high-rate production of uniform capsules. This reactor helps to control precisely the reaction time between the reacting liquids (anion drops and the cation bath, or vice versa), thereby leading to the formation of uniform capsules with walls of identical thickness. In addition, mild tumbling of the capsules during transit through the reactor ensures that every capsule wall is uniformly thick all around.

Advances in bioartificial liver assist devices

Rapid advances in development of bioartificial liver assist devices (BLADs) are exciting clinical interest in the application of BLAD technology for support of patients with acute liver failure. Four devices (Circe Biomedical HepatAssist, Vitagen ELAD, Gerlach BELS, and Excorp Medical BLSS) that rely on hepatocytes cultured in hollow-fiber membrane technology are currently in various stages of clinical evaluation. Several alternative approaches for culture and perfusion of hepatocytes have been evaluated in preclinical, large animal models of liver failure, or at a laboratory scale. Engineering design issues with respect to xenotransplantation, BLAD perfusion, hepatocyte functionality and culture maintenance, and ultimate distribution of a BLAD to a clinical site are delineated.

Improved survival and ammonia metabolism by intraperitoneal transplantation of microencapsulated hepatocytes in totally hepatectomized rats

BACKGROUND

We evaluated the effects of intraperitoneal transplantation of microencapsulated hepatocytes in a 3-stage total hepatectomy rat model.

METHODS

A new model of total hepatectomy was created as follows. First, the infrahepatic inferior vena cava was ligated just above the right renal vein. Seven days later, the portal vein was ligated and a portacaval shunt was established using a Teflon catheter over a venipuncture needle. Another 7 days later, total hepatectomy was completed by ligating and dividing the suprahepatic inferior vena cava, the hepatic artery, and the bile duct. Next, 4 x 10(7) hepatocytes (4% of the normal liver hepatocyte mass) isolated from male Wistar rats were microencapsulated within a collagen matrix enveloped by a 3-layer membrane of sodium alginate-poly-L-lysine-sodium alginate copolymer. Capsules containing hepatocytes (diameter, 500-800 microm) and empty capsules (control) were transplanted intraperitoneally 4 days before the total hepatectomy. Survival time and selected blood chemistry concentrations after the total hepatectomy were measured. The capsules were also examined histologically with hematoxylin and eosin staining and modified Gmelin's stain for bile pigments.

RESULTS

The survival time was greater in the rats given the microencapsulated hepatocytes than in the control rats (17.3 +/- 3 vs 3.7 +/- 0.1 hours; P <.01). The blood ammonia concentrations increased soon after total hepatectomy but remained significantly lower in the rats with microencapsulated hepatocytes (P <.05). The microcapsules contained numerous viable hepatocytes with abundant bile pigments and no lymphocytic infiltration.

CONCLUSIONS

Microencapsulated hepatocytes with an ultrathin polymer layer that protects them from inflammatory and lymphocytic reactions may facilitate their ability to function. In this study, 4 x 10(7) hepatocytes significantly prolonged the survival of rats that underwent hepatectomy and supported ammonia metabolism. Further development of this technique may permit its use in patients with hepatic failure.

Survival and differentiation of porcine hepatocytes encapsulated by semiautomatic device and allotransplanted in large number without immunosuppression

BACKGROUND/AIMS

The aim of this study was to evaluate the survival and functions of porcine hepatocytes transplanted in large quantities in the peritoneal cavity of allogeneic animals following semiautomatic encapsulation.

METHODS

Isolated porcine hepatocytes and a polymer solution composed of AN69 were coextruded through a double lumen spinneret. Minitubes containing hepatocytes were transplanted in the peritoneal cavity of 12 pigs (4 x 10(9) cells/animal) in the absence of immunosuppressive therapy. Seven, 15, and 21 days after transplantation, minitubes was collected and processed for analyses. The morphology was examined under light and electron microscopy. Albumin synthesis was assessed by semi-quantitative reverse transcription-polymerase chain reaction. Cytochrome P450 3A (CYP3A) gene expression was analyzed by Western blot and by testosterone 6-beta-hydroxylation assay.

RESULTS

The device allowed to encapsulate 55 x 10(6) hepatocytes/min. Hepatocytes exhibited normal structural and ultrastructural features up to day 21. Albumin gene expression decreased progressively between days 0 and 21. The amount of CYP3A protein and 6-beta-hydroxylase activity were approximately 2-fold lower at days 7 and 15 than in freshly encapsulated hepatocytes, and further decreased thereafter.

CONCLUSIONS

The preservation of hepatocyte functions during 1-2 weeks is encouraging for potential short-term use of such bioartificial liver in future clinical application.

Survival and functions of encapsulated porcine hepatocytes after allotransplantation or xenotransplantation without immunosuppression

BACKGROUND

This study evaluated the survival and functions of encapsulated porcine hepatocytes after intraperitoneal allotransplantation and xenotransplantation without immunosuppression.

METHODS

Isolated porcine hepatocytes were encapsulated in AN 69 polymer capsules (45.10(6)/capsule) and transplanted intraperitoneally in 12 rats and 12 pigs. Fifteen, 30, and 60 days after transplantation, capsules were removed and the viability and morphology of explanted hepatocytes were examined under light and electronic microscopy. The potential to produce albumin was assessed by evaluating the level of albumin messenger RNA, using semiquantitative reverse transcription-polymerase chain reaction. 6beta-Hydroxylase activity was measured by high-performance liquid chromatography. In addition, cytochrome P450 3A proteins were detected by Western blot only in allogeneic hepatocytes.

RESULTS

Similar results were observed after allotransplantation and xenotransplantation. Histologic studies showed that hepatocytes were well-preserved and arranged in cords for up to 30 days. The expression of porcine albumin gene was maintained up to 15 days. 6beta-Hydroxylase activity was 2.5-fold lower at day 15 than in freshly encapsulated hepatocytes, which were not transplanted. In allogeneic hepatocytes, the expression of CYP 3A protein was detected up to 60 days after transplantation.

CONCLUSIONS

Encapsulated porcine hepatocytes remain viable and functional for at least 15 days after allotransplantation and xenotransplantation without immunosuppression. The demonstration of maintained hepatic functions in transplanted porcine hepatocytes up to 15 days is a first step toward application in the treatment of acute liver failure.

Artificial liver support devices for fulminant liver failure

Artificial liver-support devices attempt to bridge patients with fulminant hepatic failure until either a suitable liver allograft is obtained for transplantation or the patient's own liver regenerates sufficiently to resume normal function. It is thought that toxins contribute to the clinical picture of fulminant hepatic failure. The earliest reports of successful toxin removal were blood- and plasma-exchange transfusions. Given these successful case reports, mechanical liver-support devices were designed to filter toxins. These mechanical devices used hemodialysis, charcoal hemoperfusion, hemoperfusion through cation-exchange resins, hemodiabsorption, and combinations of all of these techniques as in the MARS liver-support device. Despite promising case reports and small series, no controlled studies of mechanical devices have ever showed a long-term survival benefit. Thus, the removal of presumed toxins seems to be insufficient to support patients with fulminant hepatic failure, and the biologic function of the liver must also be replaced. Attempts at replacing the biologic function have included extracorporeal liver perfusion, cross-circulation, and hepatocyte transplantation. Current technologies have combined mechanical and biologic support systems in hybrid liver-support devices. The mechanical component of these hybrid devices serves both to remove toxins and to create a barrier between the patient's serum and the biologic component of the liver-support device. The biologic component of these hybrid liver support devices may consist of liver slices, granulated liver, or hepatocytes from low-grade tumor cells or porcine hepatocytes. These biologic components are housed within bioreactors. Currently the most clinically studied bioreactors are those that use capillary hollow-fiber systems. Both the bioartificial liver by Demetrious and the extracorporeal liver-assist device by Sussman and Kelly are in clinical trials. Although the trials seemed to have yielded good survival data when the devices are used as a bridge to transplantation, the type and degree of liver support provided by these devices remains uncertain. Thus, despite decades of great progress in the field of artificial liver support, no one technique alone yet provides sufficient liver support. A hybrid system seems to be the best option at present. Still to be determined is the best tissue to use, how much liver tissue should be used, and the optimal design of the bioreactor.

On bioartificial liver assist system: theoretical exploration and strategies for further development

The major difficulty in establishing a clinical effective bioartificial liver assist device for treatment of fulminate hepatic failure is limitation of our knowledge and technologies about fresh cell behaviors in culture and a lack of knowledge about the etiology and pathogenesis of hepatic coma. Increasing data from clinical and laboratory investigation have accrued indicating that toxins from necrotic liver tissue, mainly as oxygen reactive substances, have a role in the pathogenesis of hepatic encephalopathy and even multiple system organs failure. This paper presents the data available and suggests a new pathway for artificial and bioartificial liver assist system.

Hepatocyte encapsulation for enhanced cellular functions

An efficient bioartificial liver-assisted device can sustain the lives of patients with acute liver failure. Among different configurations of the bioreactor design, hepatocyte encapsulation has important features that satisfy most requirements of the device. We have encapsulated rat hepatocytes in a two-layer polymeric membrane by complex coacervation using a simple setup and demonstrated enhanced cellular functions up to three times higher than those of the monolayer control. These microcapsules of the functioning hepatocytes have a 2- to 3-microm outer layer of synthetic polymer with 25% 2-hydroxyethyl methacrylate, 25% methacrylic acid, and 50% methyl methacrylate and an inner layer of positively charged modified collagen as a suitable substrate for the enhanced cellular functions. Permeable only to small molecules up to albumin, the microcapsules should allow unimpeded exchange of nutrients, oxygen, growth factors, and metabolites but prevent attack by immunoglobulins of the immune system, and no "skin effect" of the collagen has been observed. Mechanical properties of the microcapsules measured with a nano-indentation method suggest that the microcapsules should be suitable for use in a bioartificial liver-assisted device.

A novel configuration of bioartificial liver support system based on circulating microcarrier culture

The purpose of this investigation is to initiate a new bioartificial liver support system that utilizes circulating microcarrier cultures in the extracapillary space of a hollow fiber cartridge. The material exchange occurs on the membranes of the hollow fiber. Toxins are metabolized by the circulating cells on the microcarriers driven by a centrifugal pump. We inoculated 2-3 x 10E8 Hep G2 cells on 2.5 grams of Cytodex 3 microcarriers, and allowed them flowing in the extracapillary space of a modified plasma filter. 10% FCS Medium was pumped through the capillaries at different rates. Cells keep morphological integrity and functionality during the circulation. These preliminary results suggest that this configuration of a bioartificial liver support system offers a future investigation.

Semiautomatic macroencapsulation of large numbers of porcine hepatocytes by coextrusion with a solution of AN69 polymer

We have previously demonstrated that allogenic and xenogenic hepatocytes macroencapsulated manually in AN-69 polymer and transplanted intra-peritoneally in rats remained viable for several weeks. However, this manual technique is inadequate to encapsulate several billions of hepatocytes which would be required to correct hepatic failure in big animals or humans. In the present study, we developed an original semiautomatic device in which isolated pig hepatocytes and the polymer solution containing 6% poly(acrylonitrile-sodium methallylsulfonate), 91% dimethylsulfoxide and 3% 0.9% NaCl solution were coextruded through a double-lumen spinneret. The extruded minitube (inner diameter: 1.8 mm, wall thickness: 0.07-0.1 mm) containing the encapsulated hepatocytes fell and coiled up in a 0.9% NaCl solution at 4 degrees C and was cut down in 4 m units containing about 120 million hepatocytes. This process allowed to encapsulate 50 million hepatocytes by minute with a preserved immediate cell viability (92 +/- 5%). To test prolonged cell viability after coextrusion, the minitubes were implanted intraperitoneally in rats. Three and seven days after implantation, they were explanted and analyzed. Cells were viable and well-preserved. Therefore, the semiautomatic device appears able to efficiently macroencapsulate in a limited time several billions of porcine hepatocytes which remain viable after transplantation in xenogenic conditions.

Matrices for tissue engineering-scaffold structure for a bioartificial liver support system

This study proposes a new composite scaffold system. A woven polyethylenterephtalate (PET) fabric was coated on one side with a biodegradable PLGA film, in order to obtain a geometrically polarized scaffold structure for an bioartificial liver support system. The composite structure ensures the stability of the membrane during degradation of the membrane polymer. The mesh size of the composite does not significantly influence the degradation behavior. Hepatocyte culturing studies reveal that the formation of aggregates depends on the mesh size and on the pretreatment: The largest aggregates could be observed after 48 h when PVLA coating, large mesh size and EGF were combined. Thus, the combination of a geometrically structured, partially degradable scaffold with receptor-mediated cell attachment sites offers promising possibilities in liver tissue engineering.

Morphologic studies of hepatocytes entrapped in hollow fibers of a bioartificial liver

A bioartificial liver cartridge was prepared by inoculating porcine hepatocytes into the inner space of hollow fibers of a hemodialyzer. The hepatocytes formed rod shaped cell aggregates during in vitro perfusion culture within 1 day. Morphologic examination was carried out on the aggregates by optical and electron microscopy. Each hepatocyte was in direct contact with adjacent cells and a bile canaliculus-like structure was occasionally seen between hepatocytes. High magnification observation showed that the canaliculus was separated from the remainder of the intercellular space by a tight junction. These facts suggest that the hepatocytes formed functionally associated cell aggregates with a compact morphology not unlike hepatocyte spheroids. These structures were well maintained for 7 days in culture, and then the amorphous area in the aggregates and the nonviable cell number increased with lengthening culture period. The bioartificial liver maintained the ability to metabolize lidocaine, ammonia, and galactose for 7 days and then deteriorated with time.