Microencapsulated hepatocytes: an in vitro and in vivo study

Collagen Gel Immobilisation Provides a Suitable Cell Matrix for Long Term Human Hepatocyte Cultures in Hybrid Reactors

An easy to apply culture technique is presented that protects a monolayer configuration of liver cells within an extracellular matrix. The Immobilising Gel (IG)-Technique not only preserves hepatocyte morphology and supports a variety of differentiated cell functions over long term periods, but also offers higher resistance of IG-culture systems against shear forces of fluids in a hybrid reactor device, as compared to other culture techniques. Human hepatocyte cultures in IG-Technique: DNA-normalised levels for the total production of cholinesterase, albumin, urea and lactate remained high throughout the investigational period (50 days). Glutamic-Pyruvic-Transaminase (GPT) release decreased after peak values during early culture adaptation. Electron Microscopic (EM) findings after the shear forces experiment revealed undisturbed subcellular structures and a preserved intercellular morphology, including bile canaliculi and desmosomes. We conclude that the IG-technique is of considerable advantage as compared to other culture systems, especially in the field of dynamic applications, e.g. hybrid reactors for artificial organ development.

Investigation of a New Microcapsule Membrane Combining Alginate, Chitosan, Polyethylene Glycol and Poly-L-Lysine for Cell Transplantation Applications

Microencapsulation of living cells may serve as an alternative therapy for patients requiring organ transplants. One of the limiting factors in the progress of such therapy is attaining a biocompatible and mechanically stable polymer. The current study investigates the potential of a novel membrane combining alginate, chitosan, polyethylene glycol (PEG) and poly-L-lysine (PLL) with the objective of proposing a membrane suitable for cell entrapment that may overcome some of the shortcomings of the widely studied alginate-poly-L-lysine-alginate (APA) capsules. The novel microcapsule was formulated using a 1.5% alginate solution coated with 0.05% chitosan, 0.1% PEG and 0.05% poly-L-lysine with a final layer of 0.1% alginate. Microcapsules having a diameter of 450 ± 30 μm were prepared. Upon citrate treatment, the membrane remained intact and retained its spherical structure. The membrane was able to support liver cell proliferation and the encapsulated cells were capable of secreting proteins. The study demonstrated that the new membrane can be used for cell entrapment. However, further investigations are needed to assess its potential for long term transplantation and usage in the development of bioartificial organs.

Bioengineering considerations in liver regenerative medicine

Background

Liver disease contributes significantly to global disease burden and is associated with rising incidence and escalating costs. It is likely that innovative approaches, arising from the emerging field of liver regenerative medicine, will counter these trends.

Main body

Liver regenerative medicine is a rapidly expanding field based on a rich history of basic investigations into the nature of liver structure, physiology, development, regeneration, and function. With a bioengineering perspective, we discuss all major subfields within liver regenerative medicine, focusing on the history, seminal publications, recent progress within these fields, and commercialization efforts. The areas reviewed include fundamental aspects of liver transplantation, liver regeneration, primary hepatocyte cell culture, bioartificial liver, hepatocyte transplantation and liver cell therapies, mouse liver repopulation, adult liver stem cell/progenitor cells, pluripotent stem cells, hepatic microdevices, and decellularized liver grafts.

Conclusion

These studies highlight the creative directions of liver regenerative medicine, the collective efforts of scientists, engineers, and doctors, and the bright outlook for a wide range of approaches and applications which will impact patients with liver disease.

Field Effect Microparticle Generation for Cell Microencapsulation

The diameter and sphericity of alginate-poly-L-lysine-alginate microcapsules, determined by the size and the shape of calcium alginate microspheres, affect their in vivo durability and biocompatibility and the results of transplantation. The commonly used air-jet spray method generates microspheres with a wider variation in diameter, larger sphere morphology, and evenly distributed encapsulated cells. In order to overcome these drawbacks, we designed a field effect microparticle generator to create a stable electric field to prepare microparticles with a smaller diameter and more uniform morphology. Using this electric field microparticle generator the encapsulated cells will be located at the periphery of the microspheres, and thus the supply of oxygen and nutrients for the encapsulated cells will be improved compared with the centrally located encapsulated cells in the air-jet spray method.

Microencapsulation for the Therapeutic Delivery of Drugs, Live Mammalian and Bacterial Cells, and Other Biopharmaceutics: Current Status and Future Directions

Microencapsulation is a technology that has shown significant promise in biotherapeutics, and other applications. It has been proven useful in the immobilization of drugs, live mammalian and bacterial cells and other cells, and other biopharmaceutics molecules, as it can provide material structuration, protection of the enclosed product, and controlled release of the encapsulated contents, all of which can ensure efficient and safe therapeutic effects. This paper is a comprehensive review of microencapsulation and its latest developments in the field. It provides a comprehensive overview of the technology and primary goals of microencapsulation and discusses various processes and techniques involved in microencapsulation including physical, chemical, physicochemical, and other methods involved. It also summarizes the state-of-the-art successes of microencapsulation, specifically with regard to the encapsulation of microorganisms, mammalian cells, drugs, and other biopharmaceutics in various diseases. The limitations and future directions of microencapsulation technologies are also discussed.

Investigation of alginate-ε-poly-L-lysine microcapsules for cell microencapsulation

Cell microencapsulation is a promising approach for cell implantation, cell-based gene therapy, and large-scale cell culture. The well-studied α-AP (alginate-α-poly-L-lysine) microcapsules have been restricted to large-scale cell-culture and clinical applications because of high costs and cytotoxic effects in some cases. This study used ε-poly-L-lysine (ε-PLL), a high-biocompatible and low-cost food additives produced by fermentation, to prepare ε-AP (alginate-ε-PLL) microcapsules with various thickness membranes and swelling behaviors. ε-AP microcapsules were permeable to BSA, a standard protein of culture medium. ε-AP-microencapsulated Chinese hamster ovary (CHO) cells proliferated with culture time; no obvious difference with α-AP-microencapsulated CHO cells during the early 19 days. Whereas ε-AP-microencapsulated CHO cells kept higher viability (OD = 0.646 ± 0.012) on the 22nd day and microcapsule strength (integrity rate of 88%) on the 24th day than that of α-AP microcapsules (OD = 0.558 ± 0.025, integrity rate of 80%). ε-AP (alginate-ε-PLL) microcapsules exhibited more superior properties and could lower the costs to broaden the applications of microencapsulation technology.

Transplantation of Co-Microencapsulated Hepatocytes and HUVECs for Treatment of Fulminant Hepatic Failure

Purpose:

Microencapsulated hepatocytes might solve immunological rejection, broadening a new perspective for the treatment of fulminant hepatic failure (FHF). However, the transplantation of microcapsulated hepatocytes is limited by low cell viability Nevertheless, the co-microencapsulation of hepatocytes and human umbilical vein endothelial cells (HUVECs) may make the treatment of FHF more promising.

Methods:

We prepared the microcapsules using the high-voltage electrostatic droplet spray method, transplanted the empty microcapsules, isolated hepatocytes, microcapsulated hepatocytes, and co-microencapsulated hepatocytes and HUVEC intraperitoneally into rat models of FHF induced by D-aminogalactose (D-gal). After 1, 3, and 7 days, and 2, 3, and 4 weeks posttransplantation, we calculated the mortality and assessed alanine aminotransferase (ALT), aspartate aminotransferase (AST), and albumin (ALB) levels in the serum of the model; evaluated the integrality and recovery of microcapsules; and stained with hematoxylin and eosin (H&E) the recovered microcapsules as well as the liver of the FHF rats.

Results:

Hepatocyte-specific functions, including the levels of ALT, AST, and ALB in the serum of the co-microencapsulation group, were significantly better than those in the other groups (p<0.05) from 2 to 4 weeks after transplantation. Moreover, cotransplantation of the microencapsulated hepatocytes and HUVECs decreased the mortality rate of the FHF rats. The recovered microcapsules were intact, and recovery was up to 90%. H&E staining showed that the microencapsulated cells were still alive, and the liver tissues had started to recover after 4 weeks posttransplantation.

Conclusion:

The microcapsules have good biocompatibility and immunoprotection to protect the hepatocytes from immunological rejection. Cotransplantation of the microencapsulated hepatocytes and HUVECs could decrease mortality rates and improve liver function in FHF.

Improving cell encapsulation through size control

Capsules based on the polyelectrolyte complexation between the polyanions sodium alginate and sodium cellulose sulphate with the polycation poly(methylene-co-guanidine) hydrochloride in the presence of calcium chloride have previously shown important advantages for cell encapsulation. However, in vivo long-term applications require capsule features that are well suited for the functionality of encapsulated cells. These should be targeted to the site of implantation with an appropriate size, a relative stability, and suitable diffusion properties. This study shows the effect of capsule size reduction, from 1 mm to 400 microm, on capsule quality control, mechanical stability, diffusion properties, and in vitro activities of the encapsulated cells. Following a controlled preparation, it was determined that the capsule mechanical stability was largely dependent on the volume ratio of the capsule over the membrane. The molecule diffusion time was related to the surface/volume ratio of the capsule even for the capsules exhibiting an identical cut-off towards the proteins and the dextran molecules. Finally, the in vitro cellular activities, for both primary cultures of rat islets and murine hepatocytes, were improved for cells encapsulated into the 400 microm capsules compared with those in the 1 mm capsules. All of these findings suggest that the smaller capsules present better properties for future clinical applications, at the same time widening the choice of implantation site, and strengthen the notion that slight changes in the capsular morphological parameters can largely influence the graft function in vivo.

Use of Magnetocapsules for In Vivo Visualization and Enhanced Survival of Xenogeneic HepG2 Cell Transplants

Hepatocyte transplantation is currently being considered as a new paradigm for treatment of fulminant liver failure. Xeno- and allotransplantation studies have shown considerable success but the long-term survival and immunorejection of engrafted cells needs to be further evaluated. Using novel alginate-protamine sulfate-alginate microcapsules, we have co-encapsulated luciferase-expressing HepG2 human hepatocytes with superparamagnetic iron oxide nanoparticles to create magnetocapsules that are visible on MRI as discrete hypointensities. Magnetoencapsulated cells survive and secrete albumin for at least 5 weeks in vitro. When transplanted i.p. in immunocompetent mice, encapsulated hepatocytes survive for at least 4 weeks as determined using bioluminescent imaging, which is in stark contrast to naked, unencapsulated hepatocytes, that died within several days after transplantation. However, in vivo human albumin secretion did not follow the time course of magnetoencapsulated cell survival, with plasma levels returning to baseline values already at 1 week post-transplantation. The present results demonstrate that encapsulation can dramatically prolong survival of xenotransplanted hepatocytes, leading to sustained albumin secretion with a duration that may be long enough for use as a temporary therapeutic bridge to liver transplantation.

Alginate-PLL microencapsulation: effect on the differentiation of embryonic stem cells into hepatocytes

The emergence of hepatocyte based clinical and pharmaceutical technologies, has been limited by the absence of a stable hepatocyte cell source. Embryonic stem cells may represent a potential solution to this cell source limitation problem since they are highly proliferative, renewable, and pluripotent. Although many investigators have described techniques to effectively differentiate stem cells into a variety of mature cell lineages, their practicality is limited by: (1) low yields of fully differentiated cells, (2) absence of large scale processing considerations, and (3) ineffective downstream enrichment protocols. Thus, a differentiation platform that may be modified to induce and sustain differentiated cell function and scaled to increase differentiated cell yield would improve current stem cell differentiation strategies. Microencapsulation provides a vehicle for the discrete control of key cell culture parameters such as the diffusion of growth factors, metabolites, and wastes. In addition, both cell seeding density and bead composition may be manipulated. In order to assess the feasibility of directing stem cell differentiation via microenvironment regulation, we have developed a murine embryonic stem cell (ES) alginate poly-l-lysine microencapsulation hepatocyte differentiation system. Our results indicate that the alginate microenvironment maintains cell viability, is conducive to ES cell differentiation, and maintains differentiated cellular function. This system may ultimately assist in developing scalable stem cell differentiation strategies.

Extracellular matrix-enriched polymeric scaffolds as a substrate for hepatocyte cultures: in vitro and in vivo studies

Tissue engineering is a promising approach to developing hepatic tissue suitable for the functional replacement of a failing liver. The aim of the present study was to investigate whether an extracellular cell matrix obtained from fibroblasts-cultured within scaffolds of hyaluronic acid (HYAFF) could influence the proliferation rate and survival of rat hepatocytes both during long-term culture and after in vivo transplantation. Cultures were evaluated by histological and morphological analysis, a proliferation assay and metabolic activity (albumin secretion). Hepatocytes cultured in extracellular matrix-enriched scaffolds exhibited a round cellular morphology and re-established cell-cell contacts, growing into aggregates of several cells along and/or among fibers in the fabric. Hepatocytes were able to secrete albumin up to 14 days in culture. In vivo results demonstrated the biocompatibility of HYAFF-11 implanted in nude mice, in which hepatocytes maintained small well-organised aggregates until the 35th day. In conclusion, the presence of a fibroblast-secreted extracellular matrix improved the biological properties of the hyaluronan scaffold, favoring the survival and morphological integrity of hepatocytes in vitro and in vivo.

Engineering liver therapies for the future

Treatment of liver disease has been greatly improved by the advent and evolution of liver transplantation. However, as demand for donor organs continues to increase beyond their availability, the need for alternative liver therapies is clear. Several approaches including extracorporeal devices, cell transplantation, and tissue-engineered constructs have been proposed as potential adjuncts or even replacements for transplantation. Simultaneously, experience from the liver biology community have provided valuable insight into tissue morphogenesis and in vitro stabilization of the hepatocyte phenotype. The next generation of cellular therapies must therefore consider incorporating cell sources and cellular microenvironments that provide both a large population of cells and strategies to maintain liver-specific functions over extended time frames. As cell-based therapies evolve, their success will require contribution from many diverse disciplines including regenerative medicine, developmental biology, and transplant medicine.

Standards and guidelines for biopolymers in tissue-engineered medical products: ASTM alginate and chitosan standard guides. American Society for Testing and Materials

The American Society for Testing and Materials (ASTM) is making a concerted effort to establish standards and guidelines for the entire field of tissue-engineered medical products (TEMPS). Safety, consistency, and functionality of biomaterials used as matrices, scaffolds, and immobilizing agents in TEMPS are a concern. Therefore, the ASTM has established a number of task groups to produce standards and guidelines for such biomaterials. Alginate is a naturally occurring biomaterial used for immobilizing living cells to form an artificial organ, such as encapsulated pancreatic islets. In order to aid in successful clinical applications and to help expedite regulatory approval, the alginate used must be fully documented. The ASTM alginate guide gives information on selection of testing methodologies and safety criteria. Critical parameters such as monomer content, molecular weight, and viscosity, in addition to more general parameters, such as dry matter content, heavy metal content, bioburden, and endotoxin content are described in the ASTM document. In a like manner, the characterization parameters for chitosan, a bioadhesive polycationic polysaccharide, are described in a separate guide. For chitosan, the degree of deacetylation is of critical importance. Control of protein content and, hence, potential for hypersensitivity, endotoxin content, and total bioburden are important in chitosan preparations for TEMPS. Together these two guides represent part of the effort on behalf of the ASTM and other interested parties to ensure quality and standardization in TEMPS.

Development of a coculture model of encapsulated cells

In the whole animal, metabolic regulations are set by reciprocal interactions between various organs, via the blood circulation. At present, analyses of such interactions require numerous and uneasily controlled in vivo experiments. In a search for an alternative to in vivo experiments, our work aims at developing a coculture system in which different cell types are isolated in polymer capsules and grown in a common environment. The signals exchanged between cells from various origins are, thus, reproducing the in vivo intertissular communications. With this perspective, we evaluated a new encapsulation system as an artificial housing for liver cells on the one hand and adipocytes on the other hand. Murine hepatocytes were encapsulated with specially designed multicomponent capsules formed by polyelectrolyte complexation between sodium alginate, cellulose sulphate and poly(methylene-coguanidine) hydrochloride, of which the permeability has been characterized. We demonstrated the absence of cytotoxicity and the excellent biocompatibility of these capsules towards primary culture of murine hepatocytes. Encapsulated hepatocytes retain their specific functions--transaminase activity, urea synthesis, and protein secretion--during the first four days of culture in minimum medium. Mature adipocytes, isolated from mouse epidydimal fat, were embedded in alginate beads. Measurement of protein secretion shows an identical profile between free and embedded adipocytes. We finally assessed the properties of encapsulated hepatocytes, cryopreserved over a periods of up to four months. The perspective of using encapsulated cells in coculture are discussed, since this system may represent a promising tool for fundamental research, such as analyses of drug metabolism, intercellular regulations, and metabolic pathways, as well as for the establishment of a tissue bank for storage and supply of murine hepatocytes.

Multilayer capsules: a promising microencapsulation system for transplantation of pancreatic islets

In 1980, Lim and Sun introduced a microcapsule coated with an alginate/polylysine complex for encapsulation of pancreatic islets. Characteristic to this type of capsule is, that it consists of a plain membrane which is formed during a single procedural step. With such a simple process it is difficult to obtain instantly a membrane optimized with respect to all the properties requested for islet transplantation. To overcome these difficulties, it is recommended to build up the membrane in several consecutive steps, each optimized for a certain property. In this study, we have analysed such a multilayer microcapsule for the encapsulation of pancreatic islets. Therefore, empty and islet containing alginate beads were coated with alternating layers of polyethyleneimine, polyacrylacid or carboxymethylcellulose and alginate. By scanning electron microscopy the thickness of the covering multilayer-membrane was estimated to be less than 800 nm by comparison with an apparatus scale. Ellipsometric measurements showed that the membrane thickness is in the range of 145 nm. Neither the encapsulation procedure, nor the membrane-forming step did impede the stimulatory response of the islets. The encapsulation even lead to a significantly better stimulatory response of the encapsulated islets during week three and five of cell culture. Furthermore, the multilayer-membrane did not deteriorate the biocompatibility of the transplanted microcapsules, allowing an easy tuning of the molecular cut-off and the mechanical stability depending on the polycation-polyanion combination used. The multilayer membrane capsule has obvious advantages compared to a one-step encapsulation procedure. These beads guarantee a high biocompatibility, a precisely adjusted cut-off, an optimal insulin-response and high mechanical stability although the membrane is only 145 nm thick.

Human hepatocyte cell lines proliferating as cohesive spheroid colonies in alginate markedly upregulate both synthetic and detoxificatory liver function

BACKGROUND/AIMS

Bio-artificial liver support systems for treatment of hepatic failure require maintained expression of hepatocyte function in vitro. We studied cultures of human hepatocyte cell-lines proliferating within alginate beads, investigating the hypothesis that 3-dimensional cohesive colonies of hepatocyte cell-lines would achieve polarity and cell-to-cell contact resulting in upregulation of function.

METHODS

HepG2 and HHY41 human cell lines in alginate beads were cultured for >20 days.

RESULTS

Proliferation was maintained for 20 days. Production of albumin, prothrombin, fibrinogen, alpha-1-acid glycoprotein and alpha-1-antitrypsin was maintained throughout, maximal at days 8-10, when upregulation was 300-1100% compared with monolayer cultures at similar cell number per unit volume. Detoxificatory functions: ethoxyresorufin deethylase activity, androstenedione metabolism, and urea synthesis from arginine was also increased several-fold. Function returned to pre-freezing levels within 18 h of thawing after cryopreservation of cells in alginate. Electron microscopy revealed spherical colonies of cells of cuboidal shape, with cell-to-cell contact via desmosomes and junctional complexes, abundant microvilli, and cytoplasmic appearances suggesting transcriptionally active hepatocytes.

CONCLUSION

Hepatocyte cell-lines, proliferating in alginate express a range of liver-specific functions at levels approaching those found in vivo, relevant to their use in liver support systems.

Maintenance of primary murine hepatocyte functions in multicomponent polymer capsules--in vitro cryopreservation studies

BACKGROUND/AIMS

The potential of a new encapsulation system has been evaluated as an artificial housing for liver cells.

METHODS

Murine hepatocytes were encapsulated in specially designed multicomponent capsules formed by polyelectrolyte complexation of sodium alginate, cellulose sulphate and poly(methylene-co-guanidine) hydrochloride, the permeability of which has previously been characterised.

RESULTS

We demonstrate here the absence of cytotoxicity and the excellent biocompatibility of these capsules towards primary culture of murine hepatocytes. Experimental results demonstrated that the encapsulated hepatocytes retained their specific functions--transaminase activity, urea synthesis and protein secretion--over the first 4 days of culture in minimum medium. The cryopreservation of encapsulated hepatocytes, for periods of up to 4 months, did not alter their functional capacities, as no major differences were observed between unfrozen and frozen encapsulated cells for the functions tested.

CONCLUSIONS

Because of the absence of cytotoxicity, and the ease of handling and cryopreservation, while maintaining liver specific functions, the described system appears to be valuable for murine liver cell encapsulation. It is also a promising tool for fundamental research into drug metabolism, intercellular regulation, metabolic pathways, and the establishment of banks for the supply and storage of murine hepatocytes.

Factors affecting hepatocyte viability and CYPIA1 activity during encapsulation

Hepatocytes encapsulated in alginate-poly-1-lysine-alginate (APA) are used in transplantation studies and in bioartificial liver support systems. Loss of cell viability in the process of APA encapsulation is usually 20-30% while the effect on cytochrome CYP450 activity is rarely reported. This work investigates the negative influences on hepatocyte viability and CYPIA1 activity during APA encapsulation, and reports methods to alleviate these influences by incorporating certain reagents into the encapsulation solution. The results show that loss of hepatocyte viability and CYPIA1 activity was caused almost entirely by extracellular calcium toxicity rather than by mechanical damage (p < 0.05). Use of 10 mM instead of 100 mM calcium chloride (CaCl2) in the encapsulation process improved CYPIA1 activity (p < 0.05), but did not improve hepatocyte viability (p > 0.05) or result in satisfactory microcapsules. Hepatocyte viability was 25% higher (p < 0.05) in CaCl2 than in calcium lactate (CaLa) when the cells were gelled by contact with these calcium solutions at room temperature (RT). Hepatocyte viability showed little improvement by processing at 4 degrees C than at RT in CaCl2 (p > 0.05) but was 23% higher at 4 degrees C than at RT in CaLa (p < 0.05). Calcium used in the process of encapsulation caused cell necrosis rather than apoptosis. Addition of Dulbecco's modified Eagle's medium (containing 10% foetal bovine serum) or 20 mM fructose to the calcium solution did not improve cell survival. However, nifedipine at a final concentration of 25 mM modestly improved hepatocyte survival in solution containing 100 mM CaCl2 (p = 0.003). Glutathione and taurine in certain concentrations showed protective effects against loss of CYPIA1 activity (p < 0.05 and <0.01 respectively). In conclusion, to optimise the use of calcium during the process of encapsulation, CaCl2 is preferred to CaLa and inclusion of nifedipine, glutathione or taurine in 100 mM CaCl2 solution is recommended.

Review article: liver support systems in acute hepatic failure

The treatment of acute hepatic failure has developed rapidly over the last 40 years, reducing morbidity and mortality from this syndrome. Whilst this has been partly attributed to significant improvements in the specialist medical management of these patients, advances in surgical techniques and pharmaceutical developments have led to the establishment of successful liver transplantation programmes, which have improved mortality significantly. This review will examine the clinical impact of alternative methods that have been used to provide extra-corporeal hepatic support. Non-biological, bio- logical and hybrid hepatic extra-corporeal support will be explored, offering a comprehensive historical overview and an appraisal of present and future advances.

Bioreactors for hybrid liver support: historical aspects and novel designs

A novel bioreactor construction has been designed for the utilization of hepatocytes and sinusoidal endothelial cells. The reactor is based on capillaries for hepatocyte aggregate immobilization. Three separate capillary membrane systems, each permitting a different function are woven in order to create a three dimensional network. Cells are perfused via independent capillary membrane compartments. Decentralized oxygen supply and carbon dioxide removal with low gradients are possible. The use of identical parallel units to supply hepatocytes facilitates scale up. In vitro studies demonstrate long-term external metabolic function in primary isolated hepatocytes within bioreactors. These systems are capable of supporting essential liver functions. Animal experiments have verified the possibility of scaling-up the bioreactors for clinical treatment. However, since there is no reliable animal model for investigation of the treatment of acute liver failure, the promising results obtained from these studies have limited relevance. The small number of clinical studies performed so far is not sufficient to reach conclusions about improvements in the therapy of acute liver failure. Although important progress has been made in the development of these systems, various hepatocyte culture models and bioreactor constructions are being discussed in the literature, which indicates competition in this field of medical research. An overview, which emphasizes the development of hepatocyte culture models for bioreactors, subsequent in vitro studies, animal studies, and clinical application, is also provided.

Glycol methacrylate embedding of alginate-polylysine microencapsulated pancreatic islets

A method for processing and embedding alginate-polylysine microencapsulated pancreatic tissue in glycol methacrylate resin (GMA) is described. Fixation in 4% phosphate buffered formaldehyde, processing in ascending concentrations of glycol methacrylate monomer and embedding in Technovit 7100 results in well preserved morphological details of hydrogels, hydrogel-cell interfaces, and encapsulated pancreatic tissue. Routine staining with Loeffler's methylene blue, hematoxylin and eosin, and Romanovsky-Giemsa gave excellent images of the GMA embedded alginate polylysine membrane and tissues allowing cells on the outside of the capsule to be analyzed effectively as part of the foreign body reaction against the capsule membrane.

Extended liver-specific functions of porcine hepatocyte spheroids entrapped in collagen gel

The potential use of porcine hepatocytes in a bioartificial liver device requires large quantities of viable and highly active cells. To facilitate the scaling up of the system, liver specific activities of hepatocytes should be maximized. One way of enhancing the specific activities is to cultivate hepatocytes as multicellular spheroids. Freshly isolated porcine hepatocytes form spheroids when cultivated in suspended cultures. These spheroids exhibit higher activities for a number of liver specific functions compared to hepatocytes cultivated as monolayers. However, these activities decreased in a few days in culture. Entrappment of spheroids in collagen gel sustained their metabolic activities at a stable level over 21 days. Production of albumin and urea by spheroid hepatocytes entrapped in collagen gels were 2 to 3 times higher than those by freshly isolated single cells. P-450 activity was demonstrated by metabolism of lidocaine to its main metabolite, monoethylglycinexylidide. Phase II drug metabolism was demonstrated by glucuronidation of 4-methylumbelliferone. This work shows that porcine hepatocyte spheroids entrapped in collagen maintain differentiated functions for an extended time period. Such hepatocyte spheroid entrappment system may facilitate the development of a bioartificial liver support device.

Hollow fibers for hepatocyte encapsulation and transplantation: studies of survival and function in rats

In this study, the feasibility of transplanting hepatocytes using hollow fibers (HF) was investigated. Experiments were carried out in vitro and in vivo to determine the viability and function of hepatocytes encapsulated in four different types of commercially available HF: regenerated cellulose HF (RCHF), polysulfone HF of two different sizes (PSHF-1 and PSHF-2), and polyvinylidine HF (PVDF). Hepatocytes remained viable in all types of HF for at least 1 wk in vitro as measured by light microscopy and their ability to synthesize protein and secrete albumin. However, the levels of protein synthesis and albumin secretion in these cells varied significantly between different HF (RCHF > PSHF-2 > PVDF approximately PSHF-1) and appeared to be inversely related to their internal diameters (215, 500, 1000, and 1100 microns for RCHF, PSHF-2, PVDF, and PSHF-1, respectively). While PSHF-2, PVDF, and PSHF-1 did not support long term viability in vivo, hepatocytes in RCHF survived after implantation in the mesentery. After 24 h in vivo, the hepatocytes appeared morphologically intact and exhibited a similar rate of protein synthesis when compared with cells cultured in parallel. The hepatocytes in RCHF also maintained the ability to synthesize protein after 7 days in vivo. These results suggest that HF of appropriate size may be useful for hepatocyte transplantation applications in which prevascularization is not possible.

Evolution of the bioartificial liver: the need for randomized clinical trials

The pursuit of a bioartificial liver is well documented in the literature. Early techniques of artificial liver support that have undergone clinical testing included simple exchange transfusions, extracorporeal xenogeneic or allogeneic liver perfusion, cross-circulation, hemodialysis, charcoal hemoperfusion, and plasmapheresis with plasma exchange. These techniques failed because they were unable to adequately support those hepatic functions essential for survival and because they lacked a back-up therapy, such as liver transplantation, for irreversible forms of liver disease. The concept evolved that hepatic functions essential for survival would be best performed by hepatocytes in an apparatus that allowed sustained or repetitive application. The best results have been achieved with bioartificial liver technologies that employ hepatocytes as implantable systems or extracorporeal devices. Implantable bioartificial liver systems include hepatocytes that have been on coated microcarrier beads, within microencapsulated gel droplets, within biodegradable polymeric substrates, or as spheroid hepatocyte aggregates. Extracorporeal systems include hepatocytes in suspension, on flat plates, and in hollow fiber bioreactors. Several extracorporeal systems have undergone extensive animal testing and are entering the early stages of human clinical trials. Randomized trials are needed to establish the value of bioartificial liver support in the treatment of patients with acute hepatic failure or as a bridge to liver transplantation.

Rapid formation of multicellular spheroids of adult rat hepatocytes by rotation culture and their immobilization within calcium alginate

Tyrosine aminotransferase (TAT) induction and albumin secretion abilities were examined in rat hepatocytes immobilized within calcium alginate; the immobilized hepatocytes lost these abilities within a week. An attempt was then made to immobilize multicellular spheroids of hepatocytes for the purpose of stabilizing the liver functions. Although it takes at least 4 days to form spheroids in the conventional method using monolayer-cultured cells, in this study we developed a new method for rapid spheroid formation. Isolated hepatocytes were seeded into a polystyrene dish and incubated on a rotary shaker. Hepatocytes started to aggregate after 6 h of the rotation culture, and spheroids approximately 100 microns in diameter formed within 24 h. The immobilized spheroids had higher TAT induction and albumin secretion abilities, which were maintained for a longer time, than the immobilized nonaggregated cells. Further stabilization was observed in immobilized heterospheroids formed in the presence of nonparenchymal liver cells. This method for the rapid formation of spheroids consisting of hepatocytes and nonparenchymal liver cells could be utilized in the construction of a bioartificial liver support system.

Microencapsulation of viable hepatocytes in HEMA-MMA microcapsules: a preliminary study

Viable rat hepatocytes were encapsulated in a HEMA-MMA copolymer (80% HEMA). Encapsulated hepatocytes continued to produce urea (a measure of viability) for approximately 2 wk although urea production rates fell steadily over the course of in vitro culture in a pattern similar to those of control hepatocytes in conventional culture. Urea production was slightly higher in 0.01 M Tris buffered glycerol precipitated capsules, relative to phosphate buffered saline precipitated capsules. Hepatocytes were not viable in 0.001 M Tris buffered glycerol precipitated capsules which had a dense wall without the macroporosity seen in the walls of the other capsules. More work is needed to show that HEMA-MMA encapsulated hepatocytes retain some of the differentiated functions of hepatocytes.

A novel two step procedure for immobilizing living cells in microcapsules for improving xenograft survival

Histologically identified surface irregularities caused by the physical entrapment of encapsulated cells in the microcapsular membrane matrix of standard alginate-polylysine microcapsules potentiated graft rejection in mice. We have therefore devised a novel two step procedure to prevent the entrapment of cells in the capsular membrane matrix. With the new method the capsular membrane appeared uniform and without the physical entrapment of cells in the capsular membrane matrix. Furthermore, after 7 days of intraperitoneal implantation of encapsulated rat hepatocytes in mice, microcapsular membrane perforations and leukocyte infiltrations were not observed. Also a greater percentage of the modified capsules, free from fibrous encapsulation, were recovered after 7 and 11 days of intraperitoneal implantation compared to the standard microcapsule preparations.

The microencapsulation of cells within alginate poly-L-lysine microcapsules prepared with the standard single step drop technique: histologically identified membrane imperfections and the associated graft rejection

Standard alginate-polylysine microcapsules containing isolated rat hepatocytes were prepared. These capsules were intraperitoneally implanted into mice, and retrieved after seven days. Histological sections of the recovered microcapsules showed peritoneal lymphocyte and macrophage infiltration. Additional microscopic observations at various stages of the microencapsulation procedure, and histological observations of control non-implanted microcapsules; illustrate that encapsulated cells became embedded within the microcapsular membrane matrix. The microcapsular membrane at these sites appeared thin and often poorly formed. The cellular infiltration into the implanted microcapsules can occur through holes developed in these thin and poorly formed areas found in the microcapsular membrane. Similar observations were seen in microcapsules prepared with 20 x 10(6) and at a lower cell concentration of 10 x 10(6) suspended cells per millilitre of sodium alginate.

Development and evaluation of a system of microencapsulation of primary rat hepatocytes

To determine the in vitro function of microencapsulated hepatocytes, viable hepatocytes were isolated from rats and encapsulated within biocompatible alginate-polylysine membranes for in vitro studies. Urea formation, prothrombin and cholinesterase activity, the incorporation of tritiated leucine into intracellular proteins and the immunolocation of synthesized albumin were monitored in culture. Despite a decrease in some of these activities, the cultured hepatocytes continued to function throughout the 5-week observation period, producing and excreting urea, prothrombin and cholinesterase activity into the medium. In addition, albumin could be demonstrated within encapsulated hepatocytes for up to 5 weeks. Scanning and transmission electron microscopy showed the cells to be embedded within the alginate matrix and to retain a globular shape.

Hepatocytes immobilised by microencapsulation in artificial cells: effects on hyperbilirubinemia in Gunn rats

The possibility of using hepatocytes encapsulated in a calcium-alginate-polylysine matrix to lower bilirubin levels in hyperbilirubinemia was investigated. The animal model was the Gunn rat. The microencapsulated hepatocytes were injected intraperitoneally. 15 X 10(6) microencapsulated hepatocytes from Wistar rats, lowered the bilirubin from 14 mg/100 ml to 6 mg/100 ml after 20 days. The bilirubin is still depressed after 90 days. After encapsulation, Sprague-Dawley hepatocytes were as effective as free hepatocytes in lowering bilirubin levels in Gunn rats. After 68 days, the free Sprague-Dawley hepatocytes were not rejected.

Microencapsulated hepatocytes for bioartificial liver support

Free hepatocytes, harvested from normal rat livers by portal vein collagenase perfusion, were encapsulated within alginate-polylysine membranes and served as a liver support system. The encapsulated hepatocytes remained viable and were able to synthesize protein for up to 3 weeks in culture. Allografts of encapsulated hepatocytes replaced the function of a damaged liver and reduced the mortality rate among rats with galactosamine-induced fulminant hepatic failure.