Development of a bioartificial liver: properties and function of a hollow-fiber module inoculated with liver cells

Manufacturing and Functional Characterization of Bioengineered Liver Grafts for Extracorporeal Liver Assistance in Acute Liver Failure

Acute Liver Failure (ALF) is a life-threatening illness characterized by the rapid onset of abnormal liver biochemistries, coagulopathy, and the development of hepatic encephalopathy. Extracorporeal bioengineered liver (BEL) grafts could offer a bridge therapy to transplant or recovery. The present study describes the manufacture of clinical scale BELs created from decellularized porcine-derived liver extracellular matrix seeded entirely with human cells: human umbilical vein endothelial cells (HUVECs) and primary human liver cells (PHLCs). Decellularized scaffolds seeded entirely with human cells were shown to adhere to stringent sterility and safety guidelines and demonstrated increased functionality when compared to grafts seeded with primary porcine liver cells (PPLCs). BELs with PHLCs were able to clear more ammonia than PPLCs and demonstrated lower perfusion pressures during patency testing. Additionally, to determine the full therapeutic potential of BELs seeded with PHLCs, longer culture periods were assessed to address the logistical constraints associated with manufacturing and transporting a product to a patient. The fully humanized BELs were able to retain their function after cold storage simulating a product transport period. Therefore, this study demonstrates the manufacture of bioengineered liver grafts and their potential in the clinical setting as a treatment for ALF.

Mesenchymal Stem Cell Transplantation in Liver Diseases

Promising preclinical data suggested that bone marrow-derived mesenchymal stem cells (BM-MSC) can reduce hepatic fibrosis and stimulate liver regeneration. Preclinical studies moreover suggested that the immunomodulatory and anti-inflammatory functions of MSCs may reduce hepatic inflammation, improve liver function, and decrease infection incidences which are deemed especially important in the case of acute-on-chronic liver failure (ACLF). Studies in patients with decompensated cirrhosis demonstrated that injection of BM-MSC resulted in an improvement of biochemical tests and led to a survival benefit in ACLF. Most of these studies were performed in hepatitis B virus infected patients. However, two adequately powered studies performed in Europe could not confirm these data. A possible alternative to mobilize BM-MSC into the liver is the use of granulocyte colony-stimulating factor (G-CSF) which has proregenerative and immunomodulatory effects. In Indian studies, the use of G-CSF was associated with improvement of survival, although this finding could not be confirmed in European studies. Human allogeneic liver-derived progenitor cell therapy represents a potential treatment for ACLF, of which the main action is paracrine. These human liver-derived MSC can perform various functions, including the downregulation of proinflammatory responses. The clinical beneficial effect of these cells is further explored in patients with alcoholic cirrhosis and ACLF in Europe.

A novel, simplified, and reproducible porcine model of acute ischemic liver failure with portal vein preservation

The current ischemic models of liver failure are difficult and usually time-consuming to produce. The aim of this study was to develop a simplified and reproducible porcine model of acute liver failure for use in preclinical research. Eighteen Bama miniature pigs were randomly divided into Groups A, B, and C. The hepatic artery and common bile duct were ligated in all groups. While the portal vein was completely preserved in Group A, it was narrowed by 1/3 and 1/2 in Groups B and C, respectively. Results of biochemical analyses, encephalopathy scores, and survival times were compared among the groups. Results of hematoxylin-eosin staining, terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling, Masson staining, and Ki-67 analyses were recorded. Survival times in Groups B and C were 11.67 ± 1.86 and 2.16 ± 0.75 days, respectively, shorter than that in Group A (>15 days). Following surgery, alanine aminotransferase, aspartate aminotransferase, lactate dehydrogenase, alkaline phosphatase, total bilirubin, and direct bilirubin levels significantly increased relative to baseline values in all groups (P<0.05). Groups B and C exhibited a significant decrease in encephalopathy scores and a significant increase in ammonia levels, which were negatively correlated with one another. Pathological analysis revealed obvious necrosis of liver cells, which correlated closely with the degree of portal vein constriction. Our simple, highly reproducible model effectively mimics the clinical characteristics of acute liver failure in humans and provides a foundation for further research on artificial liver support system development.

The development of artificial livers

PURPOSE OF REVIEW

While liver transplantation is an established treatment for liver failure, the number of patients with liver failure amenable to such intervention far outnumbers the donor supply of livers. Technologies serving to bridge this gap are required. Artificial livers may serve as an alternative. In this review, we discuss the development of artificial liver technologies.

RECENT FINDINGS

The accrued clinical data suggest that current liver assist devices may serve a role in specific liver diseases, but for the most part no survival benefit has been demonstrated. More clinical trials are expected to elucidate their utilization. Simultaneously, recent advances in materials and tissue engineering are allowing for exciting developments for novel artificial livers.

SUMMARY

As there continues to be more clinical data regarding the use of current liver devices, new intricate artificial liver technologies, with the use of sophisticated three-dimensional materials, are being developed that may help improve outcomes of liver failure patients.

Kinetic Analysis of Lidocaine Elimination by Pig Liver Cells Cultured in 3D Multi-Compartment Hollow Fiber Membrane Network Perfusion Bioreactors

Liver cells cultured in 3D bioreactors is an interesting option for temporary extracorporeal liver support in the treatment of acute liver failure and for animal models for preclinical drug screening. Bioreactor capacity to eliminate drugs is generally used for assessing cell metabolic competence in different bioreactors or to scale-up bioreactor design and performance for clinical or preclinical applications. However, drug adsorption and physical transport often disguise the intrinsic drug biotransformation kinetics and cell metabolic state. In this study, we characterized the intrinsic kinetics of lidocaine elimination and adsorption by porcine liver cells cultured in 3D four-compartment hollow fiber membrane network perfusion bioreactors. Models of lidocaine transport and biotransformation were used to extract intrinsic kinetic information from response to lidocaine bolus of bioreactor versus adhesion cultures. Different from 2D adhesion cultures, cells in the bioreactors are organized in liver-like aggregates. Adsorption on bioreactor constituents significantly affected lidocaine elimination and was effectively accounted for in kinetic analysis. Lidocaine elimination and cellular monoethylglicinexylidide biotransformation featured first-order kinetics with near-to-in vivo cell-specific capacity that was retained for times suitable for clinical assist and drug screening. Different from 2D cultures, cells in the 3D bioreactors challenged with lidocaine were exposed to close-to-physiological lidocaine and monoethylglicinexylidide concentration profiles. Kinetic analysis suggests bioreactor technology feasibility for preclinical drug screening and patient assist and that drug adsorption should be accounted for to assess cell state in different cultures and when laboratory bioreactor design and performance is scaled-up to clinical use or toxicological drug screening.

Advances in removing mass transport limitations for more physiologically relevant in vitro 3D cell constructs

Spheroids and organoids are promising models for biomedical applications ranging from human disease modeling to drug discovery. A main goal of these 3D cell-based platforms is to recapitulate important physiological parameters of their in vivo organ counterparts. One way to achieve improved biomimetic architectures and functions is to culture cells at higher density and larger total numbers. However, poor nutrient and waste transport lead to low stability, survival, and functionality over extended periods of time, presenting outstanding challenges in this field. Fortunately, important improvements in culture strategies have enhanced the survival and function of cells within engineered microtissues/organs. Here, we first discuss the challenges of growing large spheroids/organoids with a focus on mass transport limitations, then highlight recent tools and methodologies that are available for producing and sustaining functional 3D in vitro models. This information points toward the fact that there is a critical need for the continued development of novel cell culture strategies that address mass transport in a physiologically relevant human setting to generate long-lasting and large-sized spheroids/organoids.

Experimental Evaluation of a Cell Module for Hybrid Liver Support

Aim of the study was to evaluate a hybrid liver support system in a porcine model of acute liver failure, after hepatectomy. Pigs with a body weight of 70±18 kg underwent total hepatectomy and porto - cavo - caval shunting as well as ligation of the bile duct and the hepatic artery. Control animals were connected to the system (including capillary membrane plasma separation) containing a four compartment bioreactor with integral oxygenation and decentralized mass exchange but without liver cells. The treatment group received hybrid liver support with the same system including 370±42 g primary isolated porcine parenchymal liver cells in co-culture with hepatocyte nursing cells, tissue engineered to liver- like structures at high density. Treatment started after complete recovery from anesthesia and was performed continuously. A positive influence on peripheral vascular resistance and a reduced need of catecholamine dosage was observed in the treatment group. Hybrid liver support with a cell module upscaled for clinical application significantly prolonged survival time in animals after hepatectomy with the longest survival being 26 hours in the control group an 57 hours in the treatment group.

Morphological and Functional Evaluation of Isolated Rat Hepatocytes in three Dimensional Culture Systems

Various three-dimensional configurations, such as polyester tissue and woven-nonwoven, hydrophilic polyester fabric, either collagen-coated or uncoated, were investigated as potential scaffold for hepatocyte culture, in view of their use in bioreactors for hybrid liver support systems. Attachment, morphology and ultrastructure of primary adult rat hepatocytes were evaluated, as well as urea production and ammonium detoxification during a 24h incubation period in serum-free tissue culture medium. As control, hepatocytes were also plated onto collagen-coated dextran microcarriers and on plastic petri dishes, either collagen-coated or uncoated. In all the three-dimensional cultures, hepatocytes appeared morphologically intact without any statistically significant difference in metabolic activity. Collagen-coating did not influence cell attachment to polyester substrates, whereas woven-nonwoven hydrophilic polyester fabric may offer some potential advantages as three-dimensional system for hepatocyte culture in hybrid liver support systems.

Efficacy of Nafamostat Mesilate for Improving the Performance of a Bioartificial Liver Using Porcine Hepatocytes

Our bioartificial liver (BAL) consists of porcine hepatocytes attached to beads and plasma perfused through the system. The function of our BAL lasts for approximately 7 hours. The objective of the present study was to investigate the efficacy of Nafamostat Mesilate (NM), a protease inhibitor and potent complement inhibitor, for improving the performance of the BAL. The experimental groups were divided as follows; the NM group (n=7) where the BAL had porcine hepatocytes with 3.8×10−4 M, of NM, and the control group where the BAL had no NM. Plasma obtained from patients suffering from hepatic failure was perfused through the BAL for 10 hours. The viability of the porcine hepatocytes and the levels of alanine aminotransferase (ALT) in the human plasma were measured during perfusion. After the 10-hour perfusion, another human hepatic failure plasma was perfused for an additional 1 hour and then the function of the BAL was evaluated. After the 10-hour perfusion, the viability of the hepatocytes in the NM group was 51± 7 %, whereas that in the control group was rapidly reduced by 35 ± 5 %. Although the levels of ALT in the human plasma in both groups increased with the perfusion time, those in the NM group were significantly lower than those in the control group (p < 0.05). These results suggest that NM prevented damage to the porcine hepatocytes in human hepatic failure plasma as compared to the control group. In the human hepatic failure plasma before perfusion, the partial thrombin time (PT) and the plasma ammonia (NH3) levels were 19.8 ± 12 % and 288 ± 102 μg/dl, respectively. Fischer's ratios were 0.98 ± 0.39. Even after the 10- hour perfusion, the BAL in the NM group significantly improved the levels of PT (38 ± 10 %; p < 0.05), NH3 (214 ± 34 μg/dl; p < 0.05) and Fischer's ratios (1.4 ± 0.3; p < 0.05). On the other hand, the BAL in the control group did not show any improvement in those parameters. In conclusion, NM was found to help in maintaining the viability of porcine hepatocytes in human hepatic failure plasma, thereby allowing the porcine hepatocyte-based BAL to function much better.

Characterization of the Distribution of Matter in Hybrid Liver Support Devices where Cells are Cultured in a 3-D Membrane Network or on Flat Substrata

Bioreactors for liver assist tested on small animal models are generally scaled-up to treat humans by increasing their size to host a given liver cell mass. In this process, liver cell function in different culture devices is often established based on the metabolite concentration difference between the bioreactor inlet and outlet irrespective of how matter distributes in the bioreactor.

In this paper, we report our investigation aimed at establishing whether bioreactor design and operating conditions influence the distribution of matter in two bioreactors proposed for liver assist. We investigated a clinical-scale bioreactor where liver cells are cultured around a three-dimensional network of hollow fiber membranes and a laboratory-scale bioreactor with cells adherent on collagen-coated flat substrata. The distribution of matter was characterized under different operating modes and conditions in terms of the bioreactor residence time distribution evaluated by means of tracer experiments and modeled as a cascade of N stirred tanks with the same volume. Under conditions recommended by the manufacturers, matter distributed uniformly in the clinical-scale bioreactor as a result of the intense backmixing (N=1) whereas axial mixing was negligible in the laboratory-scale bioreactor (N=8). Switching from recycle to single-pass operation definitely reduced axial mixing in the clinical-scale bioreactor (N=2). Increasing feed flow rate significantly enhanced axial mixing in the laboratory-scale bioreactor (N=4). The effects of design, operating mode and conditions on matter distribution in bioreactors for liver cell culture suggest that characterization of the distribution of matter is a necessary step in the scale-up of bioreactors for liver assist and when function of liver cells cultured in different bioreactors is evaluated and compared.

Development of a Non-Transformed Human Liver Cell Line with Differentiated-Hepatocyte and Urea-Synthetic Functions: Applicable for Bioartificial Liver

There is a need to develop human hepatocyte cell lines which retain both replicating capacity and highly differentiated functions to facilitate the development of an efficient bioartificial liver. The present study was undertaken to differentiate, using sodium butyrate, the actively replicating immortalized human liver cell line.

The effects of butyrate on cell growth and cell cycle were analyzed, and the albumin synthesis, cytochrome P450 and ammonia-detoxifying activity of the butyrate-treated cells were measured. Butyrate treatment resulted in G2/M arrest of the cell cycle and polygonal changes in the cell morphology. Neither the control nor the butyrate-treated cells showed transformed characteristics. Butyrate treatment increased the amount of albumin secretion, cytochrome P450 activity, and the urea production rate of the cells.

The present study provides non-transformed human hepatocytes, which can replicate unlimitedly and then restore differentiated hepatocyte-specific functions by butyrate, and therefore, have applications for the development of an efficient bioartiflcial liver

Conditions Required for a Hybrid Artificial Liver Support System using a PUF/Hepatocyte-Spheroid Packed-Bed Module and it's use in Dogs with Liver Failure

We studied the effects of a hybrid artificial liver support system we developed on dogs with hepatic failure. The system consisted of a multi-channel polyurethane foam packed-bed culture module, including primary dog hepatocyte spheroids.

Blood ammonia was well metabolized by 20 g hepatocytes, but the other functions such as glucose concentration, total bile acid concentration, and survival time required 30 g hepatocytes to improve conditions. We found that we should use a culture substratum that easily forms spheroids, and that an artificial liver module should be used as soon as possible after spheroid formation by hepatocytes in the module.

Matrix-Induced Liver Cell Aggregates (MILCA) for Bioartificial Liver Use

Ex vivo reproduction of liver microstructure using isolated hepatocytes is critical for bioartificial liver use. We have developed a method of producing matrix-induced liver cell aggregates (MILCA) using a small number of collagen-coated beads as a nidus for formation of hepatocyte aggregates. Porcine hepatocytes were obtained by EDTA/collagenase digestion. Cell viability was assessed by trypan blue exclusion and LDH release. Cytochrome P-450 activity was determined at 4 and 24 hours by measuring the formation of 7-hydroxycoumarine (7-HC) from 7-ethoxycoumarine (7-EC). At 4 hours, the viability of MILCA was 92±2%, LDH release was 100+22 U/L and 7-HC formation was 140±34 nM/g cells. At 24 hours, MILCA viability remained greater than 90%, but 7-HC formation was lower than that of parallel control monolayer hepatocyte cultures (194±43 vs 481±78 nM/g cells; p<0.002). On transmission electron microscopy, MILCA ultrastructure resembled that of a normal liver (maintenance of cell polarity, gap junctions, bile canaliculi, intact organellae, glycogen granules). MILCA were subsequently inoculated into hollow-fiber bioreactors which were perfused for 6 hours with plasma recovered from patients with fulminant hepatic failure (n=6; 5x109 cells/cartridge, recirculation of 350 ml of plasma at 400 ml/min). In these studies, lidocaine (20 μg/ml) was cleared in less than 3 hours and 7-HC production at 6 hours was 71+8 nM/g cells. Other MILCA effects noted in this system included lowering of plasma lactate, bilirubin and ammonia and increase in the level of several non-essential amino acids.

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.

Clinical Experience with a Porcine Hepatocyte-Based Liver Support System

The only clinically proven effective treatment of fulminant hepatic failure (FHF) is orthotopic liver transplant (OLT). However, many patients die before an organ becomes available. Thus, there is a need for development of an extracorporeal liver support system to “bridge” these patients either to OLT or spontaneous recovery. We developed a bioartificial liver (BAL) based on plasma perfusion through a circuit of a hollow-fiber cartridge seeded with matrix-anchored porcine hepatocytes to treat patients with severe acute liver failure. Two groups of patients were studied. Group 1 (n = 12): patients with FHF. All patients were successfully “bridged” to OLT. “Bridge” time to OLT was 21-96 hr (mean: 39.3 hr). All patients were discharged neurologically intact. Reversal of decerebration was noted in all 11 deep stage 4 coma patients. There was reduction in intracranial pressure (ICP mmHg, 18.2 ± 2.2 to 8.5 ± 1.2; p<0.004) and increase in cerebral perfusion pressure (CPP mmHg, 71.1 ± 4.0 to 84.7 ± 2.6; p<0.006). Laboratory values pre- and post- BAL treatment: glucose (mg/dl) 122 ± 11 to 183 ± 21, p<0.002; ammonia (μmol/l) 155.6 ± 13.2 to 121.6 ± 9.5, p<0.02; total bilirubin (mg/dl) 21.6 ± 2.8 to 18.2 ± 2.2, p<0.001; PT (sec) 23.2 ± 1.7 to 21.9 ± 1.0, p<0.3. Group II (n=8): patients with chronic liver failure experiencing acute exacerbation. Two patients survived and later underwent OLT. Six patients (not OLT candidates) died 1-14 days after last BAL treatment. Laboratory values pre- and post-treatment: ammonia (μmol/l) 201 ± 47 to 143 ± 25, p<0.06; total bilirubin (mg/dl) 22.8 ± 5.2 to 19.5 ± 4.4, p<0.01; PT (sec) 22.5 ± 2.0 to 21.8 ± 1.1, p<0.6. Conclusion: our clinical experience with the BAL suggests that it may serve as “bridge” to OLT in patients with FHF primarily by reversing intracranial hypertension, but it is not a substitute for OLT in patients with end-stage liver disease who are non-transplant candidates.

Evaluation of the BioLogic-DT sorbent-suspension dialyser in patients with fulminant hepatic failure

The BioLogic-DT sorbent suspension dialyser was developed to remove toxic substances from the blood of patients with liver failure. In the present study a randomised controlled trial was carried out in 10 patients with fulminant hepatic failure who had developed grade 4 encephalopathy to evaluate the safety and biocompatibility of the dialyser in such severely ill patients. A total of 18 treatments were performed in 5 patients. Haemodynamic stability was maintained throughout. There was a significant loss of platelets (163 ± 34 to 101 ± 13 x 109/l) and decrease in plasma fibrinogen (0.53 ± 0.09 to 0.31 ± 0.08 g/l) with a rise in blood activated clotting time (190 ± 17 to 223 ± 22 sec) — not seen in the controls —, which was a result of the dialysis being carried out without the use of heparin as anticoagulant. Removal of metabolites by treatment was limited, with no significant effect on blood ammonia level and further developments of the system will be needed for this very sick group of patients.

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

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

Isolation of Porcine Hepatocytes from Slaughterhouse Organs

Recent developments in the field of hybrid artificial liver research have increased the demand for an unlimited supply of primary hepatocytes. At present, liver cells are mainly isolated from anesthetized pigs, since slaughterhouse organs have been regarded as a cell-source of minor quality. A modified enzymatic isolation technique for the successful harvesting of viable porcine liver cells from slaughterhouse organs is introduced. Digestion of the left medial liver lobe (n=114) resulted in 1.2 ± 0.35 x 10E7 viable hepatocytes per gram tissue and an overall yield of 2.23 ± 0.48 x 10E9 cells per isolation (viability: 94 ± 2.4%). Morphological integrity of hepatocytes in long-term immobilization culture systems was assessed by electron microscopic follow-up. Stable DNA-contents (52±2 μg) and low alanine-amino-transferase (ALAT) release were measured after early culture adaptation. Urea production under NH4CI, Albumin secretion, total bile acid synthesis (3.5 pmol/hr/μg DNA) and 7-ethoxicoumarin o-deethylase (ECOD) activity demonstrated functional activity and maintenance of Type IA1 cytochrome P450 (CYP450) dependent metabolism in cultured hepatocytes for at least 10 days. Compared to ex vivo isolation results in the literature, we could not see any disadvantages in the use of liver cells from slaughterhouse organs, but would like to point out four advantages. It saves animal lives, labor, costs, and time. Research groups especially with no animal housing and/ or surgical facilities should evaluate the presented technique for their own needs to make use of this unlimited cell source.

Effect of a Hybrid Liver Support System on Cardiopulmonary Function in Healthy Pigs

The aim of this study was to evaluate the effects of a hybrid liver support system (LSS) on cardiopulmonary function in nine healthy pigs. A hybrid LSS containing primary pig hepatocytes was connected to fully alert animals. The extracorporeal blood flow was maintained between 200-240 ml/min using a roller pump. Continuous plasma flow through the hybrid LSS was 50-60 ml/min. Hemodynamic and pulmonary gas exchange parameters were compared 1 hour before and 1 hour after connection to as well as 1 hour before and 1 hour after disconnection from the hybrid LSS. The hybrid LSS did not influence significantly hemodynamics and pulmonary gas exchange in this group of healthy and awake pigs. It can be concluded that the used LSS did not cause a cardiopulmonary effect per se and should be evaluated further concerning its function as a liver support system in an animal model of acute hepatic failure.

Consideration of Potential Immunological Problems in the Application of Xenogenic Hybrid Liver Support

Hybrid liver support systems (LSS) for the use of pig liver cells are under development for extracorporeal therapy of acute liver failure and for bridging to liver transplantation. A literature overview about possible immunological side effects of a clinical application is given. The data summarised from experimental studies and those clinical applications of porcine cells reported so far, suggest that clinical use of LSS utilising porcine cells and an immuno-isolation membrane should not be compromised by severe immunological complications. The reported data suggest that clinical application should be conducted in conjunction with carefully planned immunological monitoring. Only after such applications of LSS have been carried out and further data have been evaluated, might one be able to judge the immunological consequences of broader application of hybrid liver support.

Efficacy of Immunoadsorbent Devices for Maintaining Hepatic Function in Ex Vivo Direct Xenogenic Hemoperfusion

We have developed a new system for direct xenogenic hemoperfusion of a bioartificial liver support system adopting two types of immunoadsorbent devices. In this study, we compared the efficacy of each immunoadsorbent device in maintaining porcine hepatocyte function during 3 h perfusion treatment in a canine liver failure model. Suppression of humoral immunity by the immunoglobulin adsorber prevented immunogenic hepatocyte injury more effectively, and the system showed higher hepatic function when compared with suppression of cell-mediated immunity by the leukocyte adsorber. However, single use of immunoglobulin adsorber was less effective in reducing patients' systemic ammmonia levels and modulating the Fischer's ratio compared with the case of combined use of both immunoadsorbent devices. These results suggest that suppression of humoral immunity was of primary importance in preventing immunogenic hepatocyte injury, however the adsorption of leukocytes may have a synergic effect on maintaining hepatocyte function in direct xenogenic hemoperfusion.

Insertion of a Suicide Gene into an Immortalized Human Hepatocyte Cell Line

For developing a bioartificial liver (BAL) device, an attractive alternative to the primary human hepatocytes would be the use of highly differentiated immortalized human hepatocytes with a safeguard. To test the feasibility, the primary human hepatocytes were immortalized by a plasmid SV3neo encoding simian virus 40 large T antigen (SV40Tag) gene. A highly differentiated hepatocyte line OUMS-29 was established. A suicide gene of herpes simplex virus-thymidine kinase (HSV-TK) was retrovirally introduced into OUMS-29 cells as a safeguard for clinical application. One of the resulting HSV-TK-positive cell lines, OUMS-29/ tk, grew in chemically defined serum-free medium with the gene expression of differentiated liver functions. OUMS-29/tk cells were 100 times more sensitive to ganciclovir compared with unmodified OUMS-29 cells in in vitro experiments. We have established a tightly regulated immortalized human hepatocyte cell line. Essentially unlimited availability of OUMS-29/tk cells may be clinically useful for BAL therapy.

Rapidly Functional Immobilization of Immortalized Human Hepatocytes Using Cell Adhesive GRGDS Peptide-Carrying Cellulose Microspheres

With the development of biotechnology, hepatic support by a hybrid artificial liver (HAL) using hepatocytes has been given much attention. Because the availability of human livers is limited, we have established a tightly regulated immortal human hepatocyte cell line, NKNT-3, for developing HAL. Because high-density cell culture allows the compactness of the HAL device and its easy use under emergency circumstances, we have developed cell adhesive GRGDS peptide-containing cellulose microspheres (GRGDS/CMS). The GRGDS/CMS efficiently immobilized NKNT-3 cells within 24 h in a stirred suspension culture. Electron microscopic examinations demonstrated glycogen granules and well-developed endoplasmic reticulum and mitochondria in NKNT-3 cells attached to the GRGDS/CMS. The cells showed ammonia clearance activity, whereas HepG2-transformed human liver cells did not remove the loaded ammonia. An efficient adenoviral delivery of the lacZ reporter gene was performed in GRGDS/CMS-immobilized NKNT-3 cells. In this study we present rapid immobilization of NKNT-3 immortal human hepatocytes using cellulose microspheres carrying GRGDS peptides. These microspheres satisfied immediate preparation of NKNT-3 cells in sufficient quantity and of adequate quality.

Freezing Characteristics of Isolated Pig and Human Hepatocytes

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

Subnormothermic Preservation Maintains Viability and Function in a Porcine Hepatocyte Culture Model Simulating Bioreactor Transport

Bioartificial liver (BAL) systems have been developed to bridge patients with acute liver failure (ALF) to liver transplantation or liver regeneration. Clinical application of BAL systems is dependent on the supportive quality of cells used and direct availability of the whole system. Reliable transport of BAL systems from the laboratory to remote treatment centers is therefore inevitable. Subsequently, preservation conditions play a crucial role during transport of a BAL, with temperature being one of the most determining factors. In this study, we assessed the effect of subnormothermic preservation on freshly isolated porcine hepatocytes cultured in monolayer under oxygenation. Additionally, the effect of the University of Wisconsin (UW) preservation solution was compared with Williams' E (WE) culture medium at 4°C. The control group was cultured for 3 days at 37°C, whereas the transport groups were cultured at 4°C, 15°C, 21°C, or 28°C for 24 h at day 2. All groups were tested each day for cell damage and hepatic functions. Subnormothermic culture (i.e., 15°C to 28°C) for a period of 24 h did not reduce any hepatic function and did not increase cellular damage. In contrast, culture of hepatocytes in WE medium and preservation in UW solution at 4°C significantly reduced hepatic function. In conclusion, freshly isolated porcine hepatocytes can be preserved for 24 h at subnormothermic temperatures as low as 15°C. Future research will focus on the implementation of the AMC-BAL in an oxygenated culture medium perfusion system for transport between the laboratory and the hospital.

Use of Mammalian Liver Cells for Artificial Liver Support

Advances in orthotopic liver transplantation have improved the survival rate of both acute and chronic liver failure patients to nearly 70%. However, the success of this treatment modality has created an international organ shortage. Many patients die while awaiting transplantation in part due to the minimal capacity to store viable transplantable livers beyond 24 h. Additionally, for many areas of the world, routine use of whole liver transplantation to treat liver disease is impractical due to the demands on both financial and technical resources. Potentially, these issues may be alleviated, at least in part, by the use of liver cell transplantation or cellular-based liver assist devices. The well-documented regenerative capacity of the liver may obviate the need for whole organ transplantation in some instances of acute failure, if the patient may be provided temporary metabolic support. Although other patients ultimately may require transplantation, a longer period of time to find a suitable organ for transplantation may be gained by that supportive therapy. The field of liver cell transplantation may offer solutions to patients with inherited metabolic deficiencies or chronic liver disease. The potential to treat an hepatic disorder by using only a fraction of the whole liver would increase the number of whole organs available for orthotopic liver transplantation. Research in the fields of hepatocyte based intra- and extra-corporeal liver support is providing evidence that these therapeutic modalities may ultimately become routine in the treatment of severe liver disease. A historic overview of that technology along with its current status is discussed.

Improved survival of porcine acute liver failure by a bioartificial liver device implanted with induced human functional hepatocytes

Acute liver failure (ALF) is a life-threatening illness. The extracorporeal cell-based bioartificial liver (BAL) system could bridge liver transplantation and facilitate liver regeneration for ALF patients by providing metabolic detoxification and synthetic functions. Previous BAL systems, based on hepatoma cells and non-human hepatocytes, achieved limited clinical advances, largely due to poor hepatic functions, cumbersome preparation or safety concerns of these cells. We previously generated human functional hepatocytes by lineage conversion (hiHeps). Here, by improving functional maturity of hiHeps and producing hiHeps at clinical scales (3 billion cells), we developed a hiHep-based BAL system (hiHep-BAL). In a porcine ALF model, hiHep-BAL treatment restored liver functions, corrected blood levels of ammonia and bilirubin, and prolonged survival. Importantly, human albumin and α-1-antitrypsin were detectable in hiHep-BAL-treated ALF pigs. Moreover, hiHep-BAL treatment led to attenuated liver damage, resolved inflammation and enhanced liver regeneration. Our findings indicate a promising clinical application of the hiHep-BAL system.

In vitro culture of functionally active buffalo hepatocytes isolated by using a simplified manual perfusion method

Background

In farm animals, there is no suitable cell line available to understand liver-specific functions. This has limited our understanding of liver function and metabolism in farm animals. Culturing and maintenance of functionally active hepatocytes is difficult, since they survive no more than few days. Establishing primary culture of hepatocytes can help in studying cellular metabolism, drug toxicity, hepatocyte specific gene function and regulation. Here we provide a simple in vitro method for isolation and short-term culture of functionally active buffalo hepatocytes.

Results

Buffalo hepatocytes were isolated from caudate lobes by using manual enzymatic perfusion and mechanical disruption of liver tissue. Hepatocyte yield was (5.3±0.66)×10⁷ cells per gram of liver tissue with a viability of 82.3±3.5%. Freshly isolated hepatocytes were spherical with well contrasted border. After 24 hours of seeding onto fibroblast feeder layer and different extracellular matrices like dry collagen, matrigel and sandwich collagen coated plates, hepatocytes formed confluent monolayer with frequent clusters. Cultured hepatocytes exhibited typical cuboidal and polygonal shape with restored cellular polarity. Cells expressed hepatocyte-specific marker genes or proteins like albumin, hepatocyte nuclear factor 4α, glucose-6-phosphatase, tyrosine aminotransferase, cytochromes, cytokeratin and α1-antitrypsin. Hepatocytes could be immunostained with anti-cytokeratins, anti-albumin and anti α1-antitrypsin antibodies. Abundant lipid droplets were detected in the cytosol of hepatocytes using oil red stain. In vitro cultured hepatocytes could be grown for five days and maintained for up to nine days on buffalo skin fibroblast feeder layer. Cultured hepatocytes were viable for functional studies.

Conclusion

We developed a convenient and cost effective technique for hepatocytes isolation for short-term culture that exhibited morphological and functional characteristics of active hepatocytes for studying gene expression, regulation, hepatic genomics and proteomics in farm animals.

Bioreactor technologies to support liver function in vitro

Liver is a central nexus integrating metabolic and immunologic homeostasis in the human body, and the direct or indirect target of most molecular therapeutics. A wide spectrum of therapeutic and technological needs drives efforts to capture liver physiology and pathophysiology in vitro, ranging from prediction of metabolism and toxicity of small molecule drugs, to understanding off-target effects of proteins, nucleic acid therapies, and targeted therapeutics, to serving as disease models for drug development. Here we provide perspective on the evolving landscape of bioreactor-based models to meet old and new challenges in drug discovery and development, emphasizing design challenges in maintaining long-term liver-specific function and how emerging technologies in biomaterials and microdevices are providing new experimental models.

Whole-organ re-engineering: a regenerative medicine approach to digestive organ replacement

Recovery from end-stage organ failure presents a challenge for the medical community, considering the limitations of extracorporeal assist devices and the shortage of donors when organ replacement is needed. There is a need for new methods to promote recovery from organ failure and regenerative medicine is an option that should be considered. Recent progress in the field of tissue engineering has opened avenues for potential clinical applications, including the use of microfluidic devices for diagnostic purposes, and bioreactors or cell/tissue-based therapies for transplantation. Early attempts to engineer tissues produced thin, planar constructs; however, recent approaches using synthetic scaffolds and decellularized tissue have achieved a more complex level of tissue organization in organs such as the urinary bladder and trachea, with some success in clinical trials. In this context, the concept of decellularization technology has been applied to produce whole organ-derived scaffolds by removing cellular content while retaining all the necessary vascular and structural cues of the native organ. In this review, we focus on organ decellularization as a new regenerative medicine approach for whole organs, which may be applied in the field of digestive surgery.

Isolated hepatocytes in a bioartificial liver: A single group view and experience

Despite recent advances in medical supportive therapy, patients with severe fulminant hepatic failure (FHF) have mortality rate approaching 90%. Investigators have attempted to improve survival by using various extracorporeal liver support systems loaded with sorbents and liver tissue preparations. None of them succeeded in gaining clinical acceptance and orthotopic liver transplantation (OLT) remains a primary therapeutic option for patients with FHF. In this study, authors discuss the systems which utilize isolated hepatocytes. Most of these devices were tested in vitro and in animals with chemically and surgically induced liver failure. In some studies, signficant levels of detoxification and liver functions were achieved. The authors describe their own hepatocyte-based artificial liver (BAL). It is based on plasma perfusion through a hollow-fiber module seeded with matrix-anchored porcine hepatocytes. The BAL was used 14 times to treat 9 patients with acute liver failure. On 10 occasions, a charcoal column was included in the plasma circuit. Each treatment lasted 7 +/- 1 h. All procedures were tolerated well and 8 patients (including 6 patients with FHF) underwent OLT. Five patients with increased intracranial pressure (ICP) and evidence of decerebration had normalization of ICP and enjoyed full neurologic recovery after OLT. Laboratory data showed evidence for bilirubin conjugation, decrease in blood ammonia, maintenance of low lactic acid levels, and increase in the ration between the branched chain and aromatic amino acids. No allergic reactions to xenogeneic hepatocytes were observed. The authors conclude that BAL treatment with porcine hepatocytes appears to be safe and can help maintain patients alive and neurologically intact until a liver becomes available for transplantation. (c) 1994 John Wiley & Sons, Inc.

Review: Artificial liver support systems

Despite recent advances in medical therapy, patients with fulminant hepatic failure (FHF) have a mortality rate approaching 90%. Many patients die because of failure to arrest the progression of cerebral edema. Liver transplantation has improved survival to 65% to 75%. However, there is a shortage of donors and approximately one half of the patients with FHF will die while awaiting liver transplantation. There is thus a need to develop an extracorporeal liver assist system to help keep these patients alive and neurologically intact until either an organ becomes available for transplantation or the native liver recovers from injury. Such a system could also be used during the period of functional recovery from massive liver resection or to assist patients with decompensated chronic liver disease. Over the years, various methods utilizing charcoal and resin hemoperfusion, dialysis, plasma exchange, and other methods of blood detoxification have been developed and tested, but none have gained wide acceptance. This was due to: (i) incomplete understanding of the pathophysiology of liver failure; (ii) lack of accurate methods of assessment, quantitation, and stratification of the degree of liver dysfunction; and (iii) inadequate numbers of prospective controlled clinical trials examining the effects of specific therapeutic modalities. Liver support systems utilizing liver tissue preparations were developed in the 1950s, but it was not until recently that advances in hepatocyte isolation and culture, better understanding of hepatocyte-matrix interactions, and improved hollow-fiber technology have resulted in the development of a new generation of liver assist devices. Some of these devices are currently being tested in the clinical setting. In a preliminary clinical study, we have used a porcine hepatocyte-based liver support system to treat patients with acute liver failure as well as patients with acute exacerbation of chronic liver disease. Patients in the first group, who were candidates for transplantation, were successfully bridged to a transplant with excellent survival. No obvious benefit from bioartifical liver treatments was seen in the second group. It is possible that, in this group, patients will have to be treated earlier and for longer periods of time. Prospective controlled trials will be initiated as soon as the current phase I study is concluded to determine the efficacy of this system in both patients populations. (c) 1996 John Wiley & Sons, Inc.

A Macaca mulatta model of fulminant hepatic failure

AIM: To establish an appropriate primate model of fulminant hepatic failure (FHF).

METHODS: We have, for the first time, established a large animal model of FHF in Macaca mulatta by intraperitoneal infusion of amatoxin and endotoxin. Clinical features, biochemical indexes, histopathology and iconography were examined to dynamically investigate the progress and outcome of the animal model.

RESULTS: Our results showed that the enzymes and serum bilirubin were markedly increased and the enzyme-bilirubin segregation emerged 36 h after toxin administration. Coagulation activity was significantly decreased. Gradually deteriorated parenchymal abnormality was detected by magnetic resonance imaging (MRI) and ultrasonography at 48 h. The liver biopsy showed marked hepatocyte steatosis and massive parenchymal necrosis at 36 h and 49 h, respectively. The autopsy showed typical yellow atrophy of the liver. Hepatic encephalopathy of the models was also confirmed by hepatic coma, MRI and pathological changes of cerebral edema. The lethal effects of the extrahepatic organ dysfunction were ruled out by their biochemical indices, imaging and histopathology.

CONCLUSION: We have established an appropriate large primate model of FHF, which is closely similar to clinic cases, and can be used for investigation of the mechanism of FHF and for evaluation of potential medical therapies.

Acute liver failure: current practice and recent advances

ALF is an important cause of liver-related morbidity and mortality. Advances in the management of ICH and SIRS, and cardiorespiratory, metabolic, and renal support have improved the outlook of such patients. Early transfer to a liver transplant center is essential. Routine use of NAC is recommended for patients with early hepatic encephalopathy, irrespective of the etiology. The role of hypothermia remains to be determined. Liver transplantation plays a critical role, particularly for those with advanced encephalopathy. Several detoxification and BAL support systems have been developed to serve as a bridge to transplantation or to spontaneous recovery. However, such systems lack sufficient reliability and efficacy to be applied routinely in clinical practice. Hepatocyte and stem cell transplantation may provide valuable adjunctive therapy in the future.

A theoretical method to improve and optimize the design of bioartificial livers

Bioartificial livers (BALs) are a potentially effective countermeasure against liver failure, particularly in cases of acute or fulminant liver failure. It is hoped these devices can sustain a patient's liver function until recovery or transplant. However, no large-scale clinical trial has yet proven that BALs are particularly effective and evidently design issues remain to be addressed. One aspect of BAL design that must be considered is the mass transfer of adequate oxygen to the hepatocytes within the device. We present here a mathematical modeling approach to oxygen mass transport in a BAL. A mathematical model based upon Krogh cylinders is outlined to describe a diffusion-limited hollow fiber bioreactor. In addition, operating constraints are defined on the system--cells should not experience hypoxia and the cell population should be of adequate size. By combining modeling results with these operating constraints and presenting the results graphically, "operating region" charts can be constructed for the hollow fiber BAL (HF-BAL). The effects of varying various operating parameters on the BAL are then established. It is found that smaller radii and short, thin walled fibers are generally advantageous while cell populations in excess of 10 billion could be supported in the BAL with a plasma flow rate of 200 mL/min. For fibers of intermediate length and lumen radius, the minimum number of fibers required to produce a viable design ranges approximately from 7,000-10,000. In theory, this may be enough to support patients with failing livers.

A review of three-dimensional in vitro tissue models for drug discovery and transport studies

The use of animal models in drug discovery studies presents issues with feasibility and ethical concerns. To address these limitations, in vitro tissue models have been developed to provide a means for systematic, repetitive, and quantitative investigation of drugs. By eliminating or reducing the need for animal subjects, these models can serve as platforms for more tightly controlled, high-throughput screening of drugs and for pharmacokinetic and pharmacodynamic analyses of drugs. The focus of this review is three-dimensional (3D) tissue models that can capture cell-cell and cell-matrix interactions. Compared to the 2D culture of cell monolayers, 3D models more closely mimic native tissues since the cellular microenvironment established in the 3D models often plays a significant role in disease progression and cellular responses to drugs. A growing body of research has been published in the literature, which highlights the benefits of the 3D in vitro models of various tissues. This review provides an overview of some successful 3D in vitro models that have been developed to mimic liver, breast, cardiac, muscle, bone, and corneal tissues as well as malignant tissues in solid tumors.

Development of hepatic tissue engineering

Liver transplantation is still the only treatment for end-staged liver diseases in children. However, donor organ shortage and immunosuppression are major limitations. Thus, approaches of hepatocyte transplantation are under investigation. Using cells might permit mass expansion, cryopreservation, and the ex vivo genetic modification of cells. For the development of cell-transplantation techniques, the use of three-dimensional scaffolds as carrier was shown to be advantageous. Polymeric matrices permit the formation of a neo-tissue and stimulation by the modification of the matrix surface. Another important issue is to define the right cell type for transplantation. Adult hepatocytes have a limited growth and differentiation potential. In contrast, fetal liver cells (FLC) possess an enormous growth and a bipotential differentiation potential. Thus, these cells may be very attractive as a cell resource for developing cell-based liver replacement. A third major issue in this approach is the neo-vascularization. Therefore, the transplantation in a recently developed model using a microsurgically created arterioveno-venous (AV) loop as a central vessel for the neo-tissue was used for transplantation of FLC in a fibrin-matrix. Initial results indicated that the transplantation of FLC using the AV-loop transplantation model may be promising for the development of highly vascularized in vivo tissue-engineered liver support systems.

Extracorporeal treatment of acute liver failure

Acute liver failure (ALF) is a widespread problem with typically unfavorable prognosis. With the implementation of a liver support device in the clinical setting for treatment of patients with ALF, anticipated improvements include prolonging time available for spontaneous recovery and bridging to liver transplantation. Liver support could also serve to prevent systemic manifestations of ALF such as renal failure, pulmonary edema, systemic inflammatory response syndrome and cerebral edema evolving to brain death. Both non-cell based and cell based (bio-artificial) systems have been used in clinical trials. Systems with closed or open loop organization present different advantages and disadvantages; systems also differ in the membrane pore size for filtrate/dialysate exchange. Further optimization of liver assist devices is still required; when a system has proved to be successful in treating the debilitating results of ALF, the benefits will be enormous to liver failure patients.

Evaluation of a hybrid artificial liver module with liver lobule-like structure in rats with liver failure

We studied the recovery of rats with fulminant hepatic failure (FHF) by treating them with our original hybrid artificial liver support system (HALSS). We developed an original artificial liver module having a liver lobule-like structure (LLS). This module consists of many hollow fibers regularly arranged in close proximity and hepatocyte aggregates (organoids) induced into the extra capillary space of the module by centrifugal force. The LLS module can express some liver specific functions at high levels and maintain them for several months in vitro. In this study, we evaluated the efficacy of our LLS-HALSS by using rats with FHF induced by a method that combined partial hepatectomy with hepatic ischemia. In the animal experiments, blood ammonia levels rapidly increased in the control group (sham-HALSS group). These rats died during or immediately after application of the sham-HALLS. On the other hand, in the LLS module application group (LLS-control group), the increase in blood ammonia was completely suppressed and all rats recovered. Blood constituents at 4 weeks after application were at normal levels, and the weight of the liver was the same as that of a normal rat. These results indicate that HALSS may be useful for treating liver failure patients until liver transplantation can be performed or until regeneration of the native liver occurs.

Hepatic tissue engineering: from transplantation to customized cell-based liver directed therapies from the laboratory

Today, liver transplantation is still the only curative treatment for liver failure due to end-stages liver diseases. Donor organ shortage, high cost and the need of immunosuppressive medications are still the major limitations in the field of liver transplantation. Thus, alternative innovative cell-based liver directed therapies, e.g. liver tissue engineering, are under investigation with the aim, that in future an artificial liver tissue could be created and be used for the replacement of the liver function in patients. Using cells instead of organs in this setting should permit (i) expansion of cells in an in vitro phase, (ii) genetic or immunological manipulation of cells for transplantation, (iii) tissue typing and cryopreservation in a cell bank, and (iv) the ex vivo genetic modification of patient's own cells prior re-implantation. Function and differentiation of liver cells are influenced by the three-dimensional organ architecture. The use of polymeric matrices permits the three dimensional formation of a neo-tissue and specific stimulation by adequate modification of the matrix-surface which might be essential for appropriate differentiation of transplanted cells. Additionally, culturing hepatocytes on three dimensional matrices permits culture in a flow bioreactor system with increased function and survival of the cultured cells. Based on bioreactor technology, bioartificial liver devices (BAL) are developed for extracorporeal liver support. Although BALs improved clinical and metabolic conditions, increased patient survival rates have not been proven yet. For intra-corporeal liver replacement, a concept which combines Tissue Engineering using three-dimensional, highly porous matrices with cell transplantation could be useful. In such a concept, whole liver mass transplantation, long term engraftment and function as well as correction of a metabolic defect in animal models could be achieved with a principally reversible procedure. Future studies have to investigate, which environmental conditions and transplantation system would be most suitable for the development of artificial functional liver tissue including blood supply for a potential use in a clinical setting.

Patterned co-culture of primary hepatocytes and fibroblasts using polyelectrolyte multilayer templates

This paper describes the formation of patterned cell co-cultures using the layer-by-layer deposition of synthetic ionic polymers and without the aid of adhesive proteins/ligands such as collagen or fibronectin. In this study, we used synthetic polymers, namely poly(diallyldimethylammonium chloride) (PDAC) and sulfonated polystyrene (SPS) as the polycation and polyanion, respectively, to build the multilayer films. We formed SPS patterns on polyelectrolyte multilayer (PEM) surfaces either by microcontact printing PDAC onto SPS surfaces or vice-versa. To create patterned co-cultures on PEMs, we capitalize on the preferential attachment and spreading of primary hepatocytes on SPS as opposed to PDAC surfaces. In contrast, fibroblasts readily attached to both PDAC and SPS surfaces, and as a result, we were able to obtain patterned co-cultures of fibroblast and primary hepatocytes on synthetic PEM surfaces. We characterized the morphology and hepatic-specific functions of the patterned cell co-cultures with microscopy and biochemical assays. Our results suggest an alternative approach to fabricating controlled co-cultures with specified cell-cell and cell-surface interactions; this approach provides flexibility in designing cell-specific surfaces for tissue engineering applications.

Hybrid braided 3-D scaffold for bioartificial liver assist devices

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