Survival, proliferation, and functions of porcine hepatocytes encapsulated in coated alginate beads: a step toward a reliable bioartificial liver

Plant-Derived Biomaterials and Their Potential in Cardiac Tissue Repair

Cardiovascular disease remains the leading cause of mortality worldwide. The inability of cardiac tissue to regenerate after an infarction results in scar tissue formation, leading to cardiac dysfunction. Therefore, cardiac repair has always been a popular research topic. Recent advances in tissue engineering and regenerative medicine offer promising solutions combining stem cells and biomaterials to construct tissue substitutes that could have functions similar to healthy cardiac tissue. Among these biomaterials, plant-derived biomaterials show great promise in supporting cell growth due to their inherent biocompatibility, biodegradability, and mechanical stability. More importantly, plant-derived materials have reduced immunogenic properties compared to popular animal-derived materials (e.g., collagen and gelatin). In addition, they also offer improved wettability compared to synthetic materials. To date, limited literature is available to systemically summarize the progression of plant-derived biomaterials in cardiac tissue repair. Herein, this paper highlights the most common plant-derived biomaterials from both land and marine plants. The beneficial properties of these materials for tissue repair are further discussed. More importantly, the applications of plant-derived biomaterials in cardiac tissue engineering, including tissue-engineered scaffolds, bioink in 3D biofabrication, delivery vehicles, and bioactive molecules, are also summarized using the latest preclinical and clinical examples.

Bilirubin Removal by Polymeric Adsorbents for Hyperbilirubinemia Therapy

Hyperbilirubinemia, presenting as jaundice, is a life-threatening critical illness in newborn babies and acute severe hepatic failure patients. Over the past few decades, extracorporeal hemoadsorption by adsorbent therapy has been widely applied in the treatment of hyperbilirubinemia. The capability of hemoadsorption depends on the adsorbents. Most of the clinically used bilirubin adsorbents are made up of styrene/divinylbenzene copolymer and quaternary ammonium salt, which usually have poor biocompatibility and weak mechanical strength. To overcome the drawbacks of commercial polymer adsorbents, advanced synthetic and natural polymers with/without nanomaterials have been designed, and novel adsorbent fabrication technologies have also been developed. In this review, the adsorption mechanism of bilirubin adsorbents has been summarized, which is the basic criterion in adsorbent development. Furthermore, the preparation method, adsorption mechanism, relative merits and practicability of the emerging bilirubin adsorbents have been evaluated. Based on the existing studies, this work highlights the future direction of the efforts on how to design and develop bilirubin adsorbents with good overall clinical performance. Perhaps this study can change traditional perspectives and propose new strategies for bilirubin clearance from the aspects of pathogenic mechanisms, metabolic pathways, and material-based innovation.

Preclinical characterization of alginate-poly-L-lysine encapsulated HepaRG for extracorporeal liver supply

We recently demonstrated that HepaRG cells encapsulated into 1.5% alginate beads are capable of self-assembling into spheroids. They adequately differentiate into hepatocyte-like cells, with hepatic features observed at Day 14 post-encapsulation required for external bioartificial liver applications. Preliminary investigations performed within a bioreactor under shear stress conditions and using a culture medium mimicking acute liver failure (ALF) highlighted the need to reinforce beads with a polymer coating. We demonstrated in a first step that a poly-l-lysine coating improved the mechanical stability, without altering the metabolic activities necessary for bioartificial liver applications (such as ammonia and lactate elimination). In a second step, we tested the optimized biomass in a newly designed perfused dynamic bioreactor, in the presence of the medium model for pathological plasma for 6 h. Performances of the biomass were enhanced as compared to the steady configuration, demonstrating its efficacy in decreasing the typical toxins of ALF. This type of bioreactor is easy to scale up as it relies on the number of micro-encapsulated cells, and could provide an adequate hepatic biomass for liver supply. Its design allows it to be integrated into a hybrid artificial/bioartificial liver setup for further clinical studies regarding its impact on ALF animal models.

Decellularization and Solubilization of Porcine Liver for Use as a Substrate for Porcine Hepatocyte Culture: Method Optimization and Comparison

Biologic substrates, prepared by decellularizing and solubilizing tissues, have been of great interest in the tissue engineering field because of the preservation of complex biochemical constituents found in the native extracellular matrix (ECM). The integrity of the ECM is critical for cell behavior, adhesion, migration, differentiation, and proliferation that in turn affect homeostasis and tissue regeneration. Previous studies have shown that various processing methods have a distinctive way of affecting the composition of the decellularized ECM. In this study, we developed a bioactive substrate for hepatocytes in vitro, made of decellularized and solubilized liver tissue. The present work is a comparative approach of 2 different methods. First, we decellularized porcine liver tissue with ammonium hydroxide versus a sodium deoxycholate method, then characterized the decellularized tissue using various methods including double stranded DNA (dsDNA) content, DNA size, immunogenicity, and mass spectrometry. Second, we solubilized the decellularized porcine liver with hydrochloric acid versus acetic acid (AA) and characterized the resultant solubilized tissues using relevant methodologies including protein yield, immunogenicity, and bioactivity. Finally, we isolated primary porcine hepatocytes, cultured, and evaluated their bioactivity on the optimized decellularized–solubilized liver substrate. The decellularized porcine liver ECM processed by the ammonium hydroxide method and solubilized with AA displayed higher ECM integrity, low dsDNA, no evidence of intact nuclei, low human monocyte chemoattraction, and the presence of key molecules typically found in the native liver, a very important element for normal cell function. In addition, primary porcine hepatocytes showed enhanced functionality including albumin and urea production and bile canaliculi formation when cultured on the developed liver substrate compared to type I collagen.

Three Dimensional Culture Upregulates Extracellular Matrix Protein Expression in Human Liver Cell Lines - a Step towards Mimicking the Liver in Vivo?

Extracellular matrix (ECM) in the liver affects the phenotype of both hepatocytes and non-parenchymal cells. To be able to mimic in vivo liver function for extracorporeal hepatic support using human cell lines, a necessary step is to upregulate the function normally seen in monolayer culture. 3-D spheroid colonies were formed by culturing single HepG2 cells encapsulated in alginate beads. ECM expression in these cultures was compared to monolayer Hep G2 cultures. The following ECM proteins were detected immunohistochemically:- collagens I, III, V and VI, the glycoproteins fibronectin, tenascin and vitronectin, and the basement membrane protein laminin. In 3-D cultures, all proteins except tenascin were strongly expressed, as compared with weak or undetectable expression in monolayer cultures, even with 10-fold increases in the antibody concentration used. In conclusion, we have demonstrated that the 3-D environment created by alginate encapsulation of cell lines leads to cell behaviour mimicking that in vivo.

Comparison of Porcine Hepatocytes with Human Hepatoma (C3A) Cells for Use in a Bioartificial Liver Support System

Cells from primary porcine hepatocytes (PPH) and the immortalized human hepatoma cell line C3A are both used in bioartificial liver support systems (BALSS). In this work the viability and metabolic capacity of PPH and C3A cells cultured in different media were compared. Also, because the cells come into direct or indirect contact with human blood components in BALSS, the effects of human complement on survival and functions of the cells was evaluated. For short-term culture, maintenance of PPH viability was essential for retention of P450IA1 activity ( r = 0.882, p < 0.01) and effective ammonia clearance ( r = −0.791, p < 0.01). When cell viability was below 60% P450IA1 activity could not be recorded and nitrogen elimination activity significantly diminished. In contrast to PPH, ammonia levels were markedly increased for C3A cells in all culture media tested ( p < 0.01). Ammonia increase correlated with C3A viability ( r = 0.896, p < 0.05). PPH metabolic function was superior to that of the C3A cell line when evaluated by P450IA1 activity, ammonia removal, and amino acid metabolism. When PPH were incubated in human plasma (HP) or human serum (HS) there was rapid and irreversible deterioration of viability occurring within 9 h. This toxic effect could be prevented by the inactivation of complement. When sodium citrate dissolved in dextrose was added to medium, there was considerable damage to both PPH and the C3A cell line. However, there was no demonstrable toxic effect when hepatic cells of either type were exposed to heparin. We conclude that PPH cultivated in complement-inactivated HP or HS are to be preferred to C3A for clinical application of BALSS, and that heparin should be preferred for anticoagulation in BALSS. © 1998 Elsevier Science Inc.

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

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

Comparison of Bioenergetic Activity of Primary Porcine Hepatocytes Cultured in Four Different Media

Primary hepatocytes have extensively been used in biochemical, pharmacological, and physiological research. Recently, primary porcine hepatocytes have been regarded as the cells of choice for bioartificial liver support systems. The optimum culture medium for hepatocytes to be used in such devices has yet to be defined. In this study we investigated the effectiveness of four culture media in driving energy metabolism of primary porcine hepatocytes. The media selected were William's E medium, medium 1640, medium 199, and hepatocyte medium. Cells (3 × 1010; viability 87 ± 6%) were isolated from weanling piglets and seeded on 90-mm plates in the above media supplemented with antibiotics and hormones at a density of 8 × 106 viable cells per plate. Using 1H NMR spectroscopy we looked at indices of glycolysis, gluconeogenesis, ketogenesis, and ureagenesis on days 2, 4, and 6 of the experiments (n = 9). We also studied urea and albumin synthesis and total P450 content. The examined metabolic pathways of the hepatocytes were maintained by all media, although there were statistically significant differences between them. All media performed well in glycolysis, ureagenesis, and albumin synthesis. William's E medium and medium 199 outperformed the rest in gluconeogenesis. Medium 199 was best in ketogenesis. Overall, medium 199 was the best at driving energy metabolism from its constituent substrates and we think that it preferentially should be used in the culture of primary porcine hepatocytes.

Polysaccharide matrices used in 3D in vitro cell culture systems

Polysaccharides comprise a diverse class of polymeric materials with a history of proven biocompatibility and continual use as biomaterials. Recent focus on new matrices appropriate for three-dimensional (3D) cell culture offers new opportunities to apply polysaccharides as extracellular matrix mimics. However, chemical and structural bases for specific cell-polysaccharide interactions essential for their utility as 3-D cell matrices are not well defined. This review describes how these naturally sourced biomaterials satisfy several key properties for current 3D cell culture needs and can also be synthetically modified or blended with additional components to tailor their cell engagement properties. Beyond their benign interactions with many cell types in cultures, their economical and high quality sourcing, optical clarity for ex situ analytical interrogation and in situ gelation represent important properties of these polymers for 3D cell culture applications. Continued diversification of their versatile glycan chemistry, new bio-synthetic sourcing strategies and elucidation of new cell-specific properties are attractive to expand the polysaccharide polymer utility for cell culture needs. Many 3D cell culture priorities are addressed with the portfolio of polysaccharide materials available and under development. This review provides a critical analysis of their properties, capabilities and challenges in 3D cell culture applications.

p53, cathepsin D, Bcl-2 are joint prognostic indicators of breast cancer metastatic spreading

Background

Traditional prognostic indicators of breast cancer, i.e. lymph node diffusion, tumor size, grading and estrogen receptor expression, are inadequate predictors of metastatic relapse. Thus, additional prognostic parameters appear urgently needed. Individual oncogenic determinants have largely failed in this endeavour. Only a few individual tumor growth drivers, e.g. mutated p53, Her-2, E-cadherin, Trops, did reach some prognostic/predictive power in clinical settings. As multiple factors are required to drive solid tumor progression, clusters of such determinants were expected to become stronger indicators of tumor aggressiveness and malignant progression than individual parameters. To identify such prognostic clusters, we went on to coordinately analyse molecular and histopathological determinants of tumor progression of post-menopausal breast cancers in the framework of a multi-institutional case series/case-control study.

Methods

A multi-institutional series of 217 breast cancer cases was analyzed. Twenty six cases (12 %) showed disease relapse during follow-up. Relapsed cases were matched with a set of control patients by tumor diameter, pathological stage, tumor histotype, age, hormone receptors and grading. Histopathological and molecular determinants of tumor development and aggressiveness were then analyzed in relapsed versus non-relapsed cases. Stepwise analyses and model structure fitness assessments were carried out to identify clusters of molecular alterations with differential impact on metastatic relapse.

Results

p53, Bcl-2 and cathepsin D were shown to be coordinately associated with unique levels of relative risk for disease relapse. As many Ras downstream targets, among them matrix metalloproteases, are synergistically upregulated by mutated p53, whole-exon sequence analyses were performed for TP53, Ki-RAS and Ha-RAS, and findings were correlated with clinical phenotypes. Notably, TP53 insertion/deletion mutations were only detected in relapsed cases. Correspondingly, Ha-RAS missense oncogenic mutations were only found in a subgroup of relapsing tumors.

Conclusions

We have identified clusters of specific molecular alterations that greatly improve prognostic assessment with respect to singularly-analysed indicators. The combined analysis of these multiple tumor-relapse risk factors promises to become a powerful approach to identify patients subgroups with unfavourable disease outcome.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-016-2713-3) contains supplementary material, which is available to authorized users.

Injectable Hydrogels for Cardiac Tissue Repair after Myocardial Infarction

Cardiac tissue damage due to myocardial infarction (MI) is one of the leading causes of mortality worldwide. The available treatments of MI include pharmaceutical therapy, medical device implants, and organ transplants, all of which have severe limitations including high invasiveness, scarcity of donor organs, thrombosis or stenosis of devices, immune rejection, and prolonged hospitalization time. Injectable hydrogels have emerged as a promising solution for in situ cardiac tissue repair in infarcted hearts after MI. In this review, an overview of various natural and synthetic hydrogels for potential application as injectable hydrogels in cardiac tissue repair and regeneration is presented. The review starts with brief discussions about the pathology of MI, its current clinical treatments and their limitations, and the emergence of injectable hydrogels as a potential solution for post MI cardiac regeneration. It then summarizes various hydrogels, their compositions, structures and properties for potential application in post MI cardiac repair, and recent advancements in the application of injectable hydrogels in treatment of MI. Finally, the current challenges associated with the clinical application of injectable hydrogels to MI and their potential solutions are discussed to help guide the future research on injectable hydrogels for translational therapeutic applications in regeneration of cardiac tissue after MI.

Stiffness of hyaluronic acid gels containing liver extracellular matrix supports human hepatocyte function and alters cell morphology

Tissue engineering and cell based liver therapies have utilized primary hepatocytes with limited success due to the failure of hepatocytes to maintain their phenotype in vitro. In order to overcome this challenge, hyaluronic acid (HA) cell culture substrates were formulated to closely mimic the composition and stiffness of the normal liver cellular microenvironment. The stiffness of the substrate was modulated by adjusting HA hydrogel crosslinking. Additionally, the repertoire of bioactive molecules within the HA substrate was bolstered by supplementation with normal liver extracellular matrix (ECM). Primary human hepatocyte viability and phenotype were determined over a narrow physiologically relevant range of substrate stiffnesses from 600 to 4600Pa in both the presence and absence of liver ECM. Cell attachment, viability, and organization of the actin cytoskeleton improved with increased stiffness up to 4600Pa. These differences were not evident in earlier time points or substrates containing only HA. However, gene expression for the hepatocyte markers hepatocyte nuclear factor 4 alpha (HNF4α) and albumin significantly decreased on the 4600Pa stiffness at day 7 indicating that cells may not have maintained their phenotype long-term at this stiffness. Function, as measured by albumin secretion, varied with both stiffness and time in culture and peaked at day 7 at the 1200Pa stiffness, slightly below the stiffness of normal liver ECM at 3000Pa. Overall, gel stiffness affected primary human hepatocyte cell adhesion, functional marker expression, and morphological characteristics dependent on both the presence of liver ECM in gel substrates and time in culture.

3D liver models on a microplatform: well-defined culture, engineering of liver tissue and liver-on-a-chip

The liver, the largest organ in the human body, is a multi-functional organ with diverse metabolic activities that plays a critical role in maintaining the body and sustaining life. Although the liver has excellent regenerative and recuperative properties, damages caused by chronic liver diseases or viral infection may lead to permanent loss of liver functions. Studies of liver disease mechanism have focused on drug screening and liver tissue engineering techniques, including strategies based on in vitro models. However, conventional liver models are plagued by a number of limitations, which have motivated the development of 'liver-on-a-chip' and microplatform-based bioreactors that can provide well-defined microenvironments. Microtechnology is a promising tool for liver tissue engineering and liver system development, as it can mimic the complex in vivo microenvironment and microlevel ultrastructure, by using a small number of human cells under two-dimensional (2D) and three-dimensional (3D) culture conditions. These systems provided by microtechnology allow improved liver-specific functions and can be expanded to encompass diverse 3D culture methods, which are critical for the maintenance of liver functions and recapitulation of the features of the native liver. In this review, we provide an overview of microtechnologies that have been used for liver studies, describe biomimetic technologies for constructing microscale 2D and 3D liver models as well as liver-on-a-chip systems and microscale bioreactors, and introduce applications of liver microtechnology and future trends in the field.

Liver tissue engineering and cell sources: issues and challenges

Liver diseases are of major concern as they now account for millions of deaths annually. As a result of the increased incidence of liver disease, many patients die on the transplant waiting list, before a donor organ becomes available. To meet the huge demand for donor liver, alternative approaches using liver tissue engineering principles are being actively pursued. Even though adult hepatocytes, the primary cells of the liver are most preferred for tissue engineering of liver, their limited availability, isolation from diseased organs, lack of in vitro propagation and deterioration of function acts as a major drawback to their use. Various approaches have been taken to prevent the functional deterioration of hepatocytes including the provision of an adequate extracellular matrix and co-culture with non-parenchymal cells of liver. Great progress has also been made to differentiate human stem cells to hepatocytes and to use them for liver tissue engineering applications. This review provides an overview of recent challenges, issues and cell sources with regard to liver tissue engineering.

Effect of oxygen concentration on viability and metabolism in a fluidized-bed bioartificial liver using ³¹P and ¹³C NMR spectroscopy

Many oxygen mass-transfer modeling studies have been performed for various bioartificial liver (BAL) encapsulation types; yet, to our knowledge, there is no experimental study that directly and noninvasively measures viability and metabolism as a function of time and oxygen concentration. We report the effect of oxygen concentration on viability and metabolism in a fluidized-bed NMR-compatible BAL using in vivo ³¹P and ¹³C NMR spectroscopy, respectively, by monitoring nucleotide triphosphate (NTP) and ¹³C-labeled nutrient metabolites, respectively. Fluidized-bed bioreactors eliminate the potential channeling that occurs with packed-bed bioreactors and serve as an ideal experimental model for homogeneous oxygen distribution. Hepatocytes were electrostatically encapsulated in alginate (avg. diameter, 500 μm; 3.5×10⁷ cells/mL) and perfused at 3 mL/min in a 9-cm (inner diameter) cylindrical glass NMR tube. Four oxygen treatments were tested and validated by an in-line oxygen electrode: (1) 95:5 oxygen:carbon dioxide (carbogen), (2) 75:20:5 nitrogen:oxygen:carbon dioxide, (3) 60:35:5 nitrogen:oxygen:carbon dioxide, and (4) 45:50:5 nitrogen:oxygen:carbon dioxide. With 20% oxygen, β-NTP steadily decreased until it was no longer detected at 11 h. The 35%, 50%, and 95% oxygen treatments resulted in steady β-NTP levels throughout the 28-h experimental period. For the 50% and 95% oxygen treatment, a ¹³C NMR time course (∼5 h) revealed 2-¹³C-glycine and 2-¹³C-glucose to be incorporated into [2-¹³C-glycyl]glutathione (GSH) and 2-¹³C-lactate, respectively, with 95% having a lower rate of lactate formation. ³¹P and ¹³C NMR spectroscopy is a noninvasive method for determining viability and metabolic rates. Modifying tissue-engineered devices to be NMR compatible is a relatively easy and inexpensive process depending on the bioreactor shape.

A three-dimensional microfluidic approach to scaling up microencapsulation of cells

Current applications of the microencapsulation technique include the use of encapsulated islet cells to treat Type 1 diabetes, and encapsulated hepatocytes for providing temporary but adequate metabolic support to allow spontaneous liver regeneration, or as a bridge to liver transplantation for patients with chronic liver disease. Also, microcapsules can be used for controlled delivery of therapeutic drugs. The two most widely used devices for microencapsulation are the air-syringe pump droplet generator and the electrostatic bead generator, each of which is fitted with a single needle through which droplets of cells suspended in alginate solution are produced and cross-linked into microbeads. A major drawback in the design of these instruments is that they are incapable of producing sufficient numbers of microcapsules in a short-time period to permit mass production of encapsulated and viable cells for transplantation in large animals and humans. We present in this paper a microfluidic approach to scaling up cell and protein encapsulations. The microfluidic chip consists of a 3D air supply and multi-nozzle outlet for microcapsule generation. It has one alginate inlet and one compressed air intlet. The outlet has 8 nozzles, each having 380 micrometers inner diameter, which produce hydrogel microspheres ranging from 500 to 700 μm in diameter. These nozzles are concentrically surrounded by air nozzles with 2 mm inner diameter. There are two tubes connected at the top to allow the air to escape as the alginate solution fills up the chamber. A variable flow pump 115 V is used to pump alginate solution and Tygon® tubing is used to connect in-house air supply to the air channel and peristaltic/syringe pump to the alginate chamber. A pressure regulator is used to control the flow rate of air. We have encapsulated islets and proteins with this high throughput device, which is expected to improve product quality control in microencapsulation of cells, and hence the outcome of their transplantation.

Alginate beads as immobilization matrix for hepatocytes perfused in a bioreactor: a physico-chemical characterization

Because of their peculiar physico-chemical properties, alginate beads have often been proposed as an alternative cell immobilization matrix for many biotechnological applications. For entrapped hepatocytes perfused in a bioreactor, alginate beads have been demonstrated to promote viability and three-dimensional cell organization. In order to optimise the hepatocyte cell culture, we investigated the relationship between alginate beads properties, at high and low content of guluronic acid (G), and the relative cell viability and reorganization when perfused in a bioreactor. The primary structure of alginates did not apparently influence the hepatocytes culture in 8 h of perfusion in a bioreactor. However, our results confirm a preference for beads with a high content of G due to their superior mechanical resistance.

New advances in MR-compatible bioartificial liver

MR-compatible bioartificial liver (BAL) studies have been performed for 30 years and are reviewed. There are two types of study: (i) metabolism and drug studies using multinuclear MRS; primarily short-term (< 8 h) studies; (ii) the use of multinuclear MRS and MRI to noninvasively define the features and functions of BAL systems for long-term liver tissue engineering. In the latter, these systems often undergo not only modification of the perfusion system, but also the construction of MR radiofrequency probes around the bioreactor. We present novel MR-compatible BALs and the use of multinuclear MRS ((13)C, (19)F, (31)P) for the noninvasive monitoring of their growth, metabolism and viability, as well as (1)H MRI methods for the determination of flow profiles, diffusion, cell distribution, quality assurance and bioreactor integrity. Finally, a simple flexible coil design and circuit, and life support system, are described that can make almost any BAL MR-compatible.

Energy metabolism and re-establishment of intercellularadhesion complexes of gel entrapped hepatocytes

We studied the effect of continuous medium flow on the viabilityand structural organization of hepatocytes high density entrapped inalginate gel beads in the first few hours after isolation.The metabolic energy status of the entrapped cells, monitored invivo by (31)P NMR spectroscopy, was stable during theexperimental time and a physiological redox ratio was reachedafter the first three hours of culture. The morphologicalanalysis revealed that the entrapped hepatocytes placed in a fixed-bed bioreactor under continuous flow showed a polyhedricalshape with numerous microvilli on cell surface and reconstitutedtight junctions as well as bile canalicular structures, closelyresembling those present in the liver.These results suggest that continuous flow allows the culture ofhepatocytes at very high cell density within a matrix withoutloss of viability and accelerates cellular tissue reconstructionat very short times after isolation. This type of culture couldrepresent a very useful model for physiological andtoxicological studies as well as a promising approach toward thedevelopment of a bioartificial hybrid support device in acuteliver failure.

The effectiveness of a novel cartridge-based bioreactor design in supporting liver cells

There are a number of applications--ranging from temporary strategies for organ failure to pharmaceutical testing--that rely on effective bioreactor designs. The significance of these devices is that they provide an environment for maintaining cells in a way that allows them to perform key cellular and tissue functions. In the current study, a novel cartridge-based bioreactor was developed and evaluated. Its unique features include its capacity for cell support and the adaptable design of its cellular space. Specifically, it is able to accommodate functional and reasonably sized tissue (>2.0 x 10(8) cells), and can be easily modified to support a range of anchorage-dependent cells. To evaluate its efficacy, it was applied to liver support in the current study. This involved evaluating the performance of rat primary hepatocytes within the unique cartridges in culture--sans bioreactor--and after being loaded within the novel bioreactor. Compared to collagen sandwich culture functional controls, hepatocytes within the unique cartridge design demonstrated significantly higher albumin production and urea secretion rates when cultured under dynamic flow conditions--reaching peak values of 170 +/- 22 microg/10(6) cells/day and 195 +/- 18 microg/10(6) cells/day, respectively. The bioreactor's effectiveness in supporting live and functioning primary hepatocytes is also presented. Cell viability at the end of 15 days of culture in the new bioreactor was 84 +/- 18%, suggesting that the new design is effective in maintaining primary hepatocytes for at least 2 weeks in culture. Liver-specific functions of urea secretion, albumin synthesis, and cytochrome P450 activity were also assessed. The results indicate that hepatocytes are able to achieve good functional performance when cultured within the novel bioreactor. This is especially true in the case of cytochrome P450 activity, where by day 15 of culture, hepatocytes within the bioreactor reached values that were 56.6% higher than achieved by the collagen sandwich functional control cultures. The success of the novel cartridge-based bioreactor in supporting hepatocytes with good viability and functional performance suggests that it is an effective design for supporting anchorage-dependent cells.

Progress technology in microencapsulation methods for cell therapy

Cell encapsulation in microcapsules allows the in situ delivery of secreted proteins to treat different pathological conditions. Spherical microcapsules offer optimal surface-to-volume ratio for protein and nutrient diffusion, and thus, cell viability. This technology permits cell survival along with protein secretion activity upon appropriate host stimuli without the deleterious effects of immunosuppressant drugs. Microcapsules can be classified in 3 categories: matrix-core/shell microcapsules, liquid-core/shell microcapsules, and cells-core/shell microcapsules (or conformal coating). Many preparation techniques using natural or synthetic polymers as well as inorganic compounds have been reported. Matrix-core/shell microcapsules in which cells are hydrogel-embedded, exemplified by alginates capsule, is by far the most studied method. Numerous refinement of the technique have been proposed over the years such as better material characterization and purification, improvements in microbead generation methods, and new microbeads coating techniques. Other approaches, based on liquid-core capsules showed improved protein production and increased cell survival. But aside those more traditional techniques, new techniques are emerging in response to shortcomings of existing methods. More recently, direct cell aggregate coating have been proposed to minimize membrane thickness and implants size. Microcapsule performances are largely dictated by the physicochemical properties of the materials and the preparation techniques employed. Despite numerous promising pre-clinical results, at the present time each methods proposed need further improvements before reaching the clinical phase.

Development of a hybrid liver-support device

The development of an extracorporeal hybrid liver-support system using hepatocytes and an artificial device has been long awaited for the treatment of patients with hepatic failure. During the past decade important progress has been made in biotechnology and bioengineering, and a hybrid liver-support device using metabolically active hepatocytes may well become a reality in the near future. This paper outlines recent developments in bioreactor systems used as bioartificial liver-support devices, and focuses on critical issues for bioreactor design, main transport features and culture techniques for hepatocytes. We describe our bioreactor, which uses porcine hepatocytes, and the scaling-up of the device. The biochemical performance of such a device is comparable to that of those developed by other researchers, and we feel encouraged to perform in vivo experiments on animal models in order to evaluate the potential of the device as a bioartificial liver.

Enhancement of posterolateral lumbar spine fusion using low-dose rhBMP-2 and cultured marrow stromal cells

We tested the hypothesis that the dose of recombinant human bone morphogenetic protein-2 (rhBMP-2) required to induce spine fusion can be reduced by combination with mesenchymal stem cells (MSCs). Twenty-four adult rabbits underwent posterolateral intertransverse fusion at the L4-L5 level. The animals were divided into four groups based on the implant material: autologous iliac graft, Alginate-MSCs composite, Alginate-BMP-2-MSCs composite, and Alginate-BMP-2 composite. After 16 weeks, the rabbits were euthanized for radiographic examination, manual palpation, biomechanical testing, and histology. Radiographic union of 12 intertransverse fusion areas for the autogenous iliac graft, Alginate-MSCs, Alginate-BMP-2-MSCs, and Alginate-BMP-2 groups was 11, 8, 11, and 0, respectively. Moreover, manual palpation of six fusion segments in each subgroup found solid union to be 6, 1, 5, and 0, respectively. The average torques at failure of the first three groups were 2278 +/- 135, 1943 +/- 140, and 2334 +/- 187 N-mm, respectively. The failure torque did not differ significantly between the autograft and Alginate-BMP-2-MSCs groups; both groups were significantly higher than the Alginate-MSCs group. The results indicate that MSCs delivered with in vitro cellular doses of rhBMP-2 are more osteoinductive than MSCs without rhBMP-2. In combination with MSCs, a low dose (2.5 microg) of rh-BMP-2 could enhance bone formation and posterolateral spine fusion success in the rabbit model.

Long-term maintenance of the drug transport activity in cryopreservation of microencapsulated rat hepatocytes

Transplantation of isolated hepatocytes has been proposed to compensate for essential functions lacking in liver failure or for genetic defects that alter a specific liver metabolic pathway. Hepatocyte utilization for these purposes would be facilitated with a reliable, reproducible, and effective method of long-term hepatocyte storage. We have recently developed a simple new system for cryopreservation of hepatocytes that encapsulates alginate microspheres and maintains liver-specific function. The aim of this study was to elucidate the transport and drug-metabolizing enzyme activities of cryopreserved microencapsulated hepatocytes stored for a long time. Morphological examinations showed there is no apparent injury of the hepatocytes during cryopreservation processes. A drug-metabolizing enzyme (testosterone 6beta-hydroxylase, a specific probe for CYP3A2) and drug transport activities [salicylate, allopurinol, and prostaglandin E2 (PGE2), typical substrates of rOat2] in cryopreserved microencapsulated hepatocytes were maintained up to 120 days. Our results thus demonstrate for the first time that cryopreservation of primary rat hepatocytes by the encapsulation technique allows long-term retention of drug metabolism and drug transport activities.

Development and characterization of a small-scale bioreactor based on a bioartificial hepatic culture model for predictive pharmacological in vitro screenings

A vast majority of pharmacons are beset by possible interactions and side effects which have usually been tested in laboratory animals. However, better methods are needed to reduce the number of animal experiments and interspecies differences with respect to drug metabolism, as well as to provide a faster and more cost-effective way of analysis. These facts have led to the development of in vitro models based on isolated primary hepatocytes to better assess drug metabolism, interactions, and toxicity. A new small-scale bioreactor with the hepatic sandwich model and a gas-permeable membrane at the bottom allowing a definable oxygen exchange, has been constructed and compared with the conventional well plates. Compared to hepatocytes cultured in conventional systems, the cells exhibited a stronger liver-specific capacity and remained in a differentiated state in the small-scale bioreactor over a cultivation period of 17 days. This in vitro model could serve as a tool to predict the liver response to newly developed drugs.

Development of a biodegradable alginate carrier system for antibiotics and bone cells

This study presents a novel biodegradable alginate delivery system for antibiotics and bone cells to treat infected bone defects. About 2 x 10(7) New Zealand rabbit mesenchymal stem cells (MSCs) and 5 mL vancomycin solution (50 mg/mL) were added to 5 mL of 2.5% (w/v) sodium alginate solution to form biodegradable antibiotic and MSCs alginate beads 3 mm in diameter. The alginate beads were then cultured in an osteogenic medium for 14 days. The profiles of antibiotics released from the alginate beads were evaluated using the method of high performance liquid chromatography (HPLC). The expression of osteogenic genes, including Cbfa1 and osteopontin, in the alginate beads was determined by reverse transcription-polymerase chain reaction (RT-PCR) analysis. The alkaline phosphatase activity, calcium level, and mineral deposition of the cultured cells within the alginate beads were assessed. Analytical results demonstrated that the concentrations of vancomycin eluted from the alginate beads were, for 14 days, well above the minimal inhibitory concentration of Staphylococcus aureus. Osteopontin and mRNA of Cbfa1 were detected and increased alkaline phosphatase activity and calcium levels were noted, as was a substantial mineral deposition in cultured MSCs. The PKH 26-labeled MSCs and vancomycin alginate beads were implanted in rabbit bony cavities for in vivo analysis. Implanted PKH 26-labeled MSCs were identified in the newly formed bony trabeculae in all specimens at 2 and 4 months after implantation and there was abundant mineral deposition. The results of in vitro study demonstrated sustained elution of vancomycin from the alginate carrier for 14 days and good osteogenic differentiation of cultured MSCs in the alginate carrier matrix. The results of in vivo study demonstrated the implanted MSCs participating in new bone formation. Based on experimental evidence, development of a biodegradable alginate carrier system for antibiotics and bone cells is possible, providing a potential treatment procedure for infected bone defects.

A novel method of cryopreservation of rat and human hepatocytes by using encapsulation technique and possible use for cell transplantation

Encapsulated hepatocyte transplantation is a promising approach to cell transplantation without immunosuppression as an alternative to whole organ liver transplantation. However, the shortage of donor cells for hepatocyte transplantation has not been resolved, and at this critical point, it seems necessary to establish a method of hepatocyte cryopreservation to allow clinical application of hepatocyte transplantation and the development of a bioartificial liver system in the near future. In this study we demonstrated that cryopreserved microencapsulated rat and human hepatocytes can retain their hepatic function and that cryopreserved microencapsulated human hepatocytes transplanted into rat spleen remain viable without immunosuppression. Rat and human hepatocytes were isolated by a collagenase digestion method, and they were microencapsulated with poly-L-lysine. The microencapsulated rat hepatocytes were transferred to culture medium (DMEM containing 10% FBS and 10% DMSO) and immediately frozen in liquid nitrogen. A warm water bath (37 degrees C) was used to thaw the microencapsulated hepatocytes. Hepatic function, drug metabolism, and cell morphology were assessed after 90 days of cryopreservation. After 1 week of cryopreservation, microencapsulated hepatocytes were cultured for up to 2 weeks to assess their hepatic function and morphology. The morphology of human hepatocytes was assessed after 30 days of cryopreservation. Cryopreserved human hepatocytes were transplanted into rat spleen to assess their morphology. Cryopreserved microencapsulated hepatocytes retained their viability and were strongly positive for expression of albumin, OAT2, CYP3A2, and CYP3A9. Two weeks after cultivation, the cryopreserved microencapsulated rat hepatocytes had retained their hepatic function (urea synthesis). Cryopreserved microencapsulated human hepatocytes also mainly survived and retained their hepatic function for at least 30 days after cryopreservation. Moreover, entrapped cryopreserved human hepatocytes also survived and expressed albumin in rat spleen after transplantation. We demonstrated a novel method of long-term cryopreservation of rat and human hepatocytes by using an encapsulation technique, with retention of biological activity and excellent survival of the cryopreserved microencapsulated human hepatocytes transplanted into rat spleen. We believe that this novel approach to hepatocytes cryopreservation provides a new direction in encapsulated cell therapy with the goal of clinical application in the near future.

Present and Future Developments in Hepatic Tissue Engineering for Liver Support Systems : State of the art and future developments of hepatic cell culture techniques for the use in liver support systems

The liver is the most important organ for the biotransformation of xenobiotics, and the failure to treat acute or acute-on-chronic liver failure causes high mortality rates in affected patients. Due to the lack of donor livers and the limited possibility of the clinical management there has been growing interest in the development of extracorporeal liver support systems as a bridge to liver transplantation or to support recovery during hepatic failure. Earlier attempts to provide liver support comprised non-biological therapies based on the use of conventional detoxification procedures, such as filtration and dialysis. These techniques, however, failed to meet the expected efficacy in terms of the overall survival rate due to the inadequate support of several essential liver-specific functions. For this reason, several bioartificial liver support systems using isolated viable hepatocytes have been constructed to improve the outcome of treatment for patients with fulminant liver failure by delivering essential hepatic functions. However, controlled trials (phase I/II) with these systems have shown no significant survival benefits despite the systems' contribution to improvements in clinical and biochemical parameters. For the development of improved liver support systems, critical issues, such as the cell source and culture conditions for the long-term maintenance of liver-specific functions in vitro, are reviewed in this article. We also discuss aspects concerning the performance, biotolerance and logistics of the selected bioartificial liver support systems that have been or are currently being preclinically and clinically evaluated.

Towards Injectable Cell-based Tissue-Engineered Bone: The Effect of Different Calcium Phosphate Microparticles and Pre-Culturing

Bone tissue engineering by combining bone marrow stromal cells (BMSCs) with a porous scaffold is a promising technology. Current major challenges are to upscale the technique for clinical application and to improve the handling characteristics. With respect to minimal invasive surgery, moldable and/or injectable formulations are highly preferable. Ceramic microparticles of different HA/TCP formulations (100/0, 70/30, 60/40, 40/60, and 0/100) with varying surface roughness were sieved to select 200 microg aliquots of the 212-300 microm fraction. Goat BMSCs were seeded on different aliquots one week prior to in vivo implantation. These constructs and remaining cells were cultured for one week. By then, the remaining cells were harvested and resuspended in a specific binder: hyaluronic acid, alginate, or blood plasma, combined with aliquots of 60/40 microparticles peroperatively. All constructs were implanted in nude rats (n = 10) and analyzed for their bone yield histomorphometrically after 6 weeks. All precultured constructs showed consistent bone formation of comparable quantity. No significant differences were observed between the different material compositions. Peroperatively prepared constructs hardly showed any bone formation. The present study demonstrated the osteogenic potential of a tissue- engineered bone substitute made of microparticles of various HA/TCP compositions. There was an obvious advantage when the constructs were pre-cultured.

Evaluation of human serum albumin as a substitute of foetal bovine serum for cell culture

Cell microencapsulation requires clinically approved materials for their use in pharmaceutical and/or biomedical applications. The overwhelming majority of the literature has used the classical alginate-poly-l-lysine-alginate (APA) capsules for cell immobilization. Although alginate is granted with the medical approval, some of the remaining components such as foetal bovine serum (FBS), an essential ingredient of cell culture media, are not in accordance with the guidelines affirmed by the American Society for Testing and Materials (ASTM) and Food and Drug Administration (FDA). In this paper, human serum albumin (HSA), a medically approved substance, was evaluated as a potential substitute of FBS. The effect of different percentages of FBS and HSA was studied on the proliferation rate, viability and protein production of two different cell lines (C2C12 and baby hamster kidney (BHK) cells), maintained in culture and immobilized in APA microcapsules. Results show that substitution of FBS by HSA reduced the functionality of both non-encapsulated and encapsulated BHK cells. However, immobilized C2C12 cells presented the highest level of viability and a reduction in protein production of 25% when 1% HSA was used. It can be concluded that HSA might be a possible substitute of FBS in order to maintain or transport encapsulated C2C12 cells for short periods of time before implantation.

Propagation and functional characterization of serum-free cultured porcine hepatocytes for downstream applications

Hepatocyte transplantation is considered an alternative to whole organ transplantation. However, the availability of human cadaveric livers for the isolation of transplantation-quality hepatocytes is increasingly restricted. Xenogeneic porcine hepatocytes may therefore serve as an alternate cell ressource. The propagation of hepatocytes is often necessary to yield a sufficient cell number for downstream applications in xenotransplantation and in, for example, bioartificial liver support or pharmacological and toxicological studies. Our goal has been to propagate primary porcine hepatocytes in vitro and to determine the functional maintenance of the propagated cells. Porcine hepatocytes were cultured under serum-free conditions in the presence of hepatocyte growth factor and epidermal growth factor and passaged several times. The viability, proliferation and maintenance of liver-specific functions were determined as culture proceeded. Total cell number increased by 12-fold during four sequential passages, although the proliferative capacity was higher in primary cells and early passages as compared with late passages. Xenobiotics metabolism and urea synthesis gradually decreased with ongoing culture but could be restored by treatment with appropriate stimuli such, as beta-naphthoflavone and cAMP. The expression of hepatocyte-specific genes was generally lower at the beginning than at later time-points of culture of individual passages. Porcine hepatocytes can thus be propagated in vitro. The partial loss of hepatocyte function may be restored in vitro by appropriate stimuli. This may also be achieved in a recipient liver after hepatocyte transplantation provided that the proper physiological environment for the maintenance of the differentiated hepatocyte phenotype is present.

Formation of microcapsules from polyelectrolyte and covalent interactions

A new approach combining electrostatic and covalent bonds was established for the formation of resistant capsules with long-term stability under physiological conditions. Three kinds of interactions were generated in the same membrane: (1) electrostatic bonds between alginate and poly-L-lysine (PLL), (2) covalent bonds (amides) between propylene-glycol-alginate (PGA) and PLL, and (3) covalent bonds (amides) between BSA and PGA. Down-scaling of the capsules size (< or =1 mm diameter) with a jet break-up technology was achieved by modifying the rheological properties of the polymer solution. Viscosity of the PGA solution was reduced by 95% with four successive pH stabilizations (pH 7), while filtration (0.2 microm) and sterilization was possible. Covalent bond formation was initiated by addition of NaOH (pH 11) using a transacylation reaction. Kinetics of the chemical reaction (pH 11) were simulated by two mathematical models and adapted in order to preserve immobilization of animal cells. It was demonstrated that diffusion of NaOH in the absence of BSA resulted in gelation of 94% of the bead and death of 94% of the cells after 10 s reaction. By addition of BSA only 46% of the cells were killed within the same reaction time (10 s). Mechanical resistance of this new type of capsule could be increased 5-fold over the standard polyelectrolytic system (PLL-alginate). Encapsulated CHO cells were successfully cultivated for 1 month in a repetitive batch mode, with the mechanical resistance of the capsules decreasing by only 10% during this period. The combination of a synthetic and natural protein resulted in enhanced stability toward culture medium and proteolytic enzymes (250%).

Factors influencing stem cell differentiation into the hepatic lineage in vitro

A major area of research in transplantation medicine is the potential application of stem cells in liver regeneration. This would require well-defined and efficient protocols for directing the differentiation of stem cells into the hepatic lineage, followed by their selective purification and proliferation in vitro. The development of such protocols would reduce the likelihood of spontaneous differentiation of stem cells into divergent lineages upon transplantation, as well as reduce the risk of teratoma formation in the case of embryonic stem cells. Additionally, such protocols could provide useful in vitro models for studying hepatogenesis and liver metabolism. The development of pharmokinetic and cytotoxicity/genotoxicity screening tests for newly developed biomaterials and drugs, could also utilize protocols developed for the hepatic differentiation of stem cells. Hence, this review critically examines the various strategies that could be employed to direct the differentiation of stem cells into the hepatic lineage in vitro.

Intrasplenic transplantation of encapsulated hepatocytes decreases mortality and improves liver functions in fulminant hepatic failure from 90% partial hepatectomy in rats

BACKGROUND

Encapsulated cell therapy might be a promising approach to enable cell transplantation without immunosuppression. This study investigates the viability and hepatic function of hepatocytes encapsulated with alginate/poly-L-lysine in vitro and the effect of the intrasplenic transplantation of cultured encapsulated hepatocytes on survival in 90% hepatectomized rats as a preliminary step toward allogeneic hepatocyte transplantation without immunosuppression.

MATERIALS AND METHODS

Rat hepatocytes were isolated and encapsulated using alginate/poly-L-lysine. Encapsulated hepatocytes were cultured for 28 days to measure cell viability, liver function, and morphology. Rats were treated with a 90% partial hepatectomy and then immediately underwent the intrasplenic transplantation of the cultured encapsulated hepatocytes, the capsule alone, or the allogeneic hepatocytes without the capsule. The survival rate, liver function, and cell morphology were assessed after transplantation.

RESULTS

The cultured encapsulated hepatocytes maintained their viability and showed better metabolic activity than day 0 cultured encapsulated hepatocytes. The encapsulated cells strongly expressed albumin and were positive for periodic acid-Schiff staining. Electron microscopy demonstrated that the microencapsulated hepatocytes retained the structural elements of hepatic cytoplasm and nuclei. Intrasplenic transplantation of the encapsulated hepatocytes increased the survival rate and improved the hepatic function. Encapsulated hepatocytes transplanted into rat spleen survived well and retained their hepatic function. Moreover, dramatic liver regeneration was observed 48 hr after transplantation in the group that received intrasplenic transplantations of encapsulated hepatocytes.

CONCLUSIONS

The intrasplenic transplantation of cultured encapsulated hepatocytes improved the survival rate of an acute liver failure rat model induced by a 90% partial hepatectomy.

Coating alginate microspheres with a serum albumin-alginate membrane: application to the encapsulation of a peptide

Calcium alginate gel microspheres coated with a human serum albumin (HSA)-alginate membrane were prepared adapting a transacylation method previously applied to large beads. The procedure involved emulsification of an aqueous solution of sodium alginate and propylene glycol alginate (PGA) in an oily phase, followed by addition of CaCl(2). The resulting gel microspheres were transferred in an aqueous solution of HSA. The addition of 0.5 M NaOH started the reaction between PGA and HSA, producing amide bonds and forming a membrane around the particles. An optimization study was conducted, notably exploring the addition of HSA to the internal phase. The microcapsules were studied with respect to morphology (optical and scanning electron microscopy) and size (laser granulometry), in comparison with uncoated gel microspheres. Biocompatibility was checked in osteoblast cultures. Lysine-arginine-phenylalanine-lysine (KRFK) was encapsulated and the release kinetics was studied in vitro. The method provided stable microspheres (size around 60 microm), with a membrane surviving a treatment with citrate and resisting lyophilization. The microcapsules were shown biocompatible. The release of KRFK was slower (release time>8 days) than that of uncoated microspheres. These microcapsules might be useful as peptide containers to be combined with prosthetic materials for improving osteointegration.

Preparation and characterization of an electrodeposited calcium phosphate coating associated with a calcium alginate matrix

A new way of optimizing osteoconduction of biomaterials is to bring to them biological properties. In this work, we associated a novel release system with an electrodeposited calcium phosphate (CaP) coated titanium alloy Ti6Al4V. The characterization of this material was performed by means of light microscopy, scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM) and X-ray energy dispersive spectroscopy (EDXS). The electrodeposited CaP coating was a tricalcium phosphate, and the release system was composed of microcapsules entrapped in an alginate film. We observed that the alginate matrix had a close contact with the coating. An intermediate layer containing calcium and phosphorus appeared at the interface between the alginate matrix and the CaP coating. These results allowed us to conclude that the association of two techniques, i.e. electrodeposition followed by deposition of a calcium alginate matrix, led to the elaboration of a new biomaterial.

Compression of a capsule: mechanical laws of membranes with negligible bending stiffness

The compression of a capsule between two plates is considered. The problem is solved numerically for a capsule made of an incompressible liquid drop surrounded by a thin elastic membrane which has a negligible bending stiffness. Numerical results are provided for three different mechanical laws of the membrane. By considering elastic moduli independent of the deformation, we show that the isotropic dilation plays the major role. In particular, an asymptotic behavior independent of the shear modulus is found for large deformations. For more complex models, the deformation limits beyond which the variation of elastic moduli starts to play a role are examined. The results indicate that the distinction between the different models requires a careful inspection of both small and large deformations. The theoretical predictions are compared with experimental results. For millimetric capsules with membranes made of covalently linked human serum albumin and alginate, the best agreement is obtained by considering that the elastic moduli are independent of the deformation and range from 0.1 to 4 N/m.

In vivo study of biodegradable alginate antibiotic beads in rabbits

The authors investigated the lyophilized poly-L-lysine-coated alginate antibiotic delivery system in vivo for the treatment of musculoskeletal infections. The sodium alginate was mixed with vancomycin, coated with poly-L-lysine and lyophilized to form 3 mm in diameter biodegradable antibiotic beads. The antibiotic beads were implanted in the distal femoral cavities of rabbits for in vivo investigation. The local concentration of vancomycin was well above the minimal inhibitory concentration of Staphylococcus aureus for 21 days. The release was most marked during the first two days. The diameters of sample inhibition zone ranged from 8 to 16 mm, the relative activity of vancomycin ranged from 12.5% to 100%. The blood level of vancomycin reached its peak (46.0 mg/l) two days after implantation and fell to 3.2 mg/l at two weeks. It was undetectable after three weeks. There was no increase in the concentration of blood urea nitrogen and serum creatinine after the implantation. Histological observations showed that bead materials were biodegradable, resorbed slowly and only cause mild host reaction. This study offers a biodegradable delivery system of antibiotics to treat musculoskeletal infections.

Hypothermic storage and cryopreservation of hepatocytes: the protective effect of alginate gel against cell damages

Hepatocyte-based therapy has been proposed as an alternative to organ transplantation in the treatment of liver disorders. In the clinical context, a major issue is the constant supply of quality assurance-controlled hepatocytes, thereby requiring their cold storage in good conditions. We have analyzed the protective effects of alginate entrapment of rat hepatocytes after either 24 or 48 h of hypothermic storage or cryopreservation on the cell viability, cell yield, both mitochondrial and other cytoplasmic functional activities, and apoptosis. Decrease in viability, as evaluated by the MTT inclusion test, was 4% and 13% (24 h at 4 degrees C), 15% and 33% (48 h at 4 degrees C), and 9% and 19% (liquid nitrogen) for entrapped and free suspended hepatocytes, respectively. Viable cell yields were 86 +/- 8% and 51 +/- 6% for cryopreserved entrapped and free suspended hepatocytes, respectively. The mitochondrial (MTS assay), 7-ethoxyresorufin O-deethylase (EROD), and glutathione-S-transferase (GST) activities were better preserved in entrapped than in free suspended hepatocytes. Both hypothermic storage and cryopreservation were found to induce early caspase-3-like activities, being always much lower in entrapped hepatocytes, particularly after cryopreservation (98.4 +/- 42.4 vs. 6.4 +/- 4.0 fluorescence arbitrary units/hours/microg protein). Thus, cold-induced apoptosis in hepatocytes can be significantly reduced following their entrapment within alginate gel beads and this is associated with an improvement of both their viability and function.

Rates of transport through a capsule membrane to attain Donnan equilibrium

The swelling of a capsule consisting of salt solution and polyelectrolyte, surrounded by a membrane, is studied. The membrane allows salt and water to pass, but is impermeable to polyelectrolyte molecules. Equilibrium swelling of the capsule is governed by Donnan equilibrium. Transport rates of a salt and water through the membrane are expressed in terms of a Darcy permeability and a salt diffusivity. The governing equations predict that the rate at which equilibrium is attained as the external salt concentration varies is controlled by the timescale for diffusion of salt, rather than by that for Darcy flow. Experiments were performed using capsules with membranes made of covalently linked HSA and alginate. The capsule volume varied with a single relaxation rate when the external salt concentration was changed, as predicted by theory. This constitutes the first step toward a simple method for determining the membrane properties of capsules by measuring rates of change of capsule volume.

Compression of biocompatible liquid-filled HSA-alginate capsules: determination of the membrane mechanical properties

Compression experiments between two parallel plates are performed on a series of biocompatible HSA-alginate capsules with two different membrane thicknesses. The capsule geometry and size as well as the average membrane thickness are first measured. The compression set-up is fitted with a sensitive force transducer that allows measurement of the compression force as a function of plate separation. The response of the capsule is analyzed by assuming different constitutive models for the membrane, where the shear and surface dilatation effects are accounted. An apparent area dilatation modulus is then computed for different values of the plate separation and required to remain constant as the capsule deformation increases. This allows identification of plausible constitutive laws for the membrane material.

Improving the next generation of bioartificial liver devices

Several extracorporeal bioartificial liver (BAL) devices are currently being evaluated as an alternative or adjunct therapy for liver disease. While these hybrid systems show promise, in order to become a clinical reality, BAL devices must clearly demonstrate efficacy in improving patient outcomes. Here, we present aspects of BAL devices that could benefit from fundamental advances in cell and developmental biology. In particular, we examine the development of human hepatocyte cell lines, strategies to stabilize the hepatocyte phenotype in vitro, and emphasize the importance of the cellular microenvironment in bioreactor design. Consideration of these key components of BAL systems will greatly improve next generation devices.

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.

Xenotransplantation for liver therapy or: Can porcine hepatocytes generate physiological functions sufficient for a human patient in ALF?

Detailed knowledge about physiology, biochemistry and function is required before artificial liver devices using porcine hepatocytes may be used successfully. Improvement of cell culture conditions and tissue engineering may permit the generation of human hepatocytes as substitutes for grafts in a transplantation setting. The physiological functions of xenografts have to be compatible with those of the recipient. However, first observations indicate that most physiological interaction in widely divergent species combinations such as pig and man are considerably different. This may be crucial for the selection of a suitable organ, tissue or cell for a clinical set-up. These differences vary from organ to organ and cell to cell. Only very conservative molecules, like for example insulin or calcitonin function properly in both species, while others such as complement, albumin and erythropoietin do not fulfill their task properly or not at all.

Follow-up by one- and two-dimensional NMR of plasma from pigs with ischemia-induced acute liver failure treated with a bioartificial liver

Hepatic encephalopathy may occur following acute hepatic failure (AHF), which results in the release of toxic compounds from the injured liver. These compounds, which induce cerebral edema, are not well characterized, yet. The aim of this study was to evaluate the potential interest of NMR spectroscopy in the follow-up of different plasma compounds in pigs with ischemia-induced fulminant hepatic failure treated or not with a bioartificial liver (BAL), which has been previously shown to improve the neurological status of the animals. Qualitative analysis of pig plasma was achieved by one-dimensional-(1)H CPMG, two-dimensional homonuclear (1)H-(1)H TOCSY CPMG and heteronuclear (1)H-(13)C HSQC sequences. Semi-quantitative analysis of selected plasma metabolites along the disease evolution was carried out on pigs with ischemia-induced AHF treated with the BAL containing alginate beads with or without hepatocytes. A quantitative longitudinal follow-up was performed on characteristic metabolites via a one-dimensional CPMG sequence, including choline, glutamine, N-acetyl-glucosamine (NAG), pyruvate and trimethylamine-N-oxide (TMAO). The concentrations of choline and TMAO increased from the beginning to the end in animals treated with the BAL containing alginate beads without hepatocytes. Treatment of pigs with BAL containing hepatocytes resulted in an improvement of survival, the plasma concentrations of choline and TMAO being decreased in three out of five animals. Thus, NMR spectroscopy is a useful approach for the identification of toxic compounds which are involved in hepatic encephalopathy associated with AHF. These compounds can be cleared by a BAL resulting in the improvement of survival and neurological parameters of the animals.