Galactosylated poly(vinylidene difluoride) hollow fiber bioreactor for hepatocyte culture

A review on the application of chitosan-based polymers in liver tissue engineering

Chitosan-based polymers have enormous structural tendencies to build bioactive materials with novel characteristics, functions, and various applications, mainly in liver tissue engineering (LTE). The specific physicochemical, biological, mechanical, and biodegradation properties give the effective ways to blend these biopolymers with synthetic and natural polymers to fabricate scaffolds matrixes, sponges, and complexes. A variety of natural and synthetic biomaterials, including chitosan (CS), alginate (Alg), collagen (CN), gelatin (GL), hyaluronic acid (HA), hydroxyapatite (HAp), polyethylene glycol (PEG), polycaprolactone (PCL), poly(lactic-co-glycolic) acid (PGLA), polylactic acid (PLA), and silk fibroin gained considerable attention due to their structure-properties relationship. The incorporation of CS within the polymer matrix results in increased mechanical strength and also imparts biological behavior to the designed PU formulations. The significant and growing interest in the LTE sector, this review aims to be a detailed exploration of CS-based polymers biomaterials for LTE. A brief explanation of the sources and extraction, properties, structure, and scope of CS is described in the introduction. After that, a full overview of the liver, its anatomy, issues, hepatocyte transplantation, LTE, and CS LTE applications are discussed.

Hollow Fiber and Nanofiber Membranes in Bioartificial Liver and Neuronal Tissue Engineering

To date, the creation of biomimetic devices for the regeneration and repair of injured or diseased tissues and organs remains a crucial challenge in tissue engineering. Membrane technology offers advanced approaches to realize multifunctional tools with permissive environments well-controlled at molecular level for the development of functional tissues and organs. Membranes in fiber configuration with precisely controlled, tunable topography, and physical, biochemical, and mechanical cues, can direct and control the function of different kinds of cells toward the recovery from disorders and injuries. At the same time, fiber tools also provide the potential to model diseases in vitro for investigating specific biological phenomena as well as for drug testing. The purpose of this review is to present an overview of the literature concerning the development of hollow fibers and electrospun fiber membranes used in bioartificial organs, tissue engineered constructs, and in vitro bioreactors. With the aim to highlight the main biomedical applications of fiber-based systems, the first part reviews the fibers for bioartificial liver and liver tissue engineering with special attention to their multifunctional role in the long-term maintenance of specific liver functions and in driving hepatocyte differentiation. The second part reports the fiber-based systems used for neuronal tissue applications including advanced approaches for the creation of novel nerve conduits and in vitro models of brain tissue. Besides presenting recent advances and achievements, this work also delineates existing limitations and highlights emerging possibilities and future prospects in this field.

Manipulation of cellular behaviour on surface-modified polyvinylidene difluoride using wet chemistry

The surface modification of polyvinylidene difluoride (PVDF) for various biomedical uses is notoriously hampered by the chemical inertness of the polymer. A wet chemical approach aiming at covalently grafting biomolecules was demonstrated by means of an elimination reaction of fluorine from the polymer backbone followed by subsequent modification steps. Exemplified as a possible biological application, the coupling of the peptide REDV rendered the material adhesive for endothelial cells while adhesion of thrombocytes was dramatically reduced.

Collagen modulates functional activity of hepatic cells inside alginate-galactosylated chitosan hydrogel microcapsules

To provide comparable hepatic tissue microenvironment and induce functional behavior for hepatocytes, galctosylated-chitosan (GC) as well as collagen (Col) was added to alginate microcapsule coated with extra layer of chitosan. Four different hydrogel groups of alginate/chitosan (AC); alginate-galactosylated chitosan/chitosan (AGC/C); alginate-collagen/chitosan (ACol/C); and alginate-galactosylated chitosan-collagen/chitosan (AGCCol/C) were prepared and characterized for physical properties such as porosity, swelling, degradation rate, and stiffness. Introduction of GC as well as Col to alginate regulated significantly the physical properties of the resultant hydrogels. GC addition decreased dramatically swelling, degradation, pore size and mechanical properties of the resultant hydrogel. However, the influence of GC on the physical properties in the presence of Col (AGCCol/A) was in a reverse manner, as compared to the AGC/C hydrogel. The AGCCol/C microenvironment also promoted proliferation of microencapsulated HepG2 cells, as a model of hepatocyte, compared to the control-matched groups. Biochemical analysis after 10 days revealed a superior effect of AGCCol/C on the secretion of albumin and urea compared to other groups (P < 0.05). These features were coincided with the mRNA up-regulation of P450 and albumin in the AGCCol/C groups compared to the AGC/C and ACol/C groups (P < 0.05). The study demonstrated that enrichment of alginate-based hydrogels with Col and GC could be touted as an appropriate 3D platform for modular hepatic tissue engineering.

Artificial liver research output and citations from 2004 to 2017: a bibliometric analysis

Background

Researches on artificial livers greatly contribute to the clinical treatments for liver failure. This study aimed to evaluate the research output of artificial livers and citations from 2004 to 2017 through a bibliometric analysis.

Methods

A list of included articles on artificial livers were generated after a comprehensive search of the Web of Science Core Collection (from 2004 to 2017) with the following basic information: number of publications, citations, publication year, country of origin, authors and authorship, funding source, journals, institutions, keywords, and research area.

Results

A total of 968 included articles ranged from 47 citations to 394 citations with a fluctuation. The publications were distributed in 12 countries, led by China (n = 212) and the US (n = 207). There were strong correlations of the number of citations with authors (r ² = 0.133, p < 0.001), and countries (r ² = 0.275, p < 0.001), while no correlations of the number of citations with the years since publication (r ² = 0.016, p = 0.216), and funding (r ² < 0.001, p = 0.770) were identified. Keyword analysis demonstrated that with the specific change of "acute liver failure," decrease in "bioartificial livers" and "hepatocyte," and increase in "tissue engineering" were identified. The top 53 cited keyword and keyword plus (including some duplicates counts) were identified, led by bioartificial liver (405 citations) and hepatocyte (248 citations). The top 50 cited keywords bursts were mainly "Blood" (2004-2008), "hepatocyte like cell" (2008-2015), and "tissue engineering" (2014-2017). All keywords could be classified into four categories: bioartificial livers (57.40%), blood purification (25.00%), clinical (14.81%), and other artificial organs (2.78%).

Discussion

This study shows the process and tendency of artificial liver research with a comprehensive analysis on artificial livers. However, although it seems that the future of artificial livers seems brighter for hepatocyte transplantation, the systems of artificial livers now are inclined on focusing on blood purification, plasma exchange, etc.

Bioengineering Organs for Blood Detoxification

For patients with severe kidney or liver failure the best solution is currently organ transplantation. However, not all patients are eligible for transplantation and due to limited organ availability, most patients are currently treated with therapies using artificial kidney and artificial liver devices. These therapies, despite their relative success in preserving the patients' life, have important limitations since they can only replace part of the natural kidney or liver functions. As blood detoxification (and other functions) in these highly perfused organs is achieved by specialized cells, it seems relevant to review the approaches leading to bioengineered organs fulfilling most of the native organ functions. There, the culture of cells of specific phenotypes on adapted scaffolds that can be perfused takes place. In this review paper, first the functions of kidney and liver organs are briefly described. Then artificial kidney/liver devices, bioartificial kidney devices, and bioartificial liver devices are focused on, as well as biohybrid constructs obtained by decellularization and recellularization of animal organs. For all organs, a thorough overview of the literature is given and the perspectives for their application in the clinic are discussed.

Optimising cell aggregate expansion in a perfused hollow fibre bioreactor via mathematical modelling

The need for efficient and controlled expansion of cell populations is paramount in tissue engineering. Hollow fibre bioreactors (HFBs) have the potential to meet this need, but only with improved understanding of how operating conditions and cell seeding strategy affect cell proliferation in the bioreactor. This study is designed to assess the effects of two key operating parameters (the flow rate of culture medium into the fibre lumen and the fluid pressure imposed at the lumen outlet), together with the cell seeding distribution, on cell population growth in a single-fibre HFB. This is achieved using mathematical modelling and numerical methods to simulate the growth of cell aggregates along the outer surface of the fibre in response to the local oxygen concentration and fluid shear stress. The oxygen delivery to the cell aggregates and the fluid shear stress increase as the flow rate and pressure imposed at the lumen outlet are increased. Although the increased oxygen delivery promotes growth, the higher fluid shear stress can lead to cell death. For a given cell type and initial aggregate distribution, the operating parameters that give the most rapid overall growth can be identified from simulations. For example, when aggregates of rat cardiomyocytes that can tolerate shear stresses of up to are evenly distributed along the fibre, the inlet flow rate and outlet pressure that maximise the overall growth rate are predicted to be in the ranges to (equivalent to to ) and to (or 15.6 psi to 15.7 psi) respectively. The combined effects of the seeding distribution and flow on the growth are also investigated and the optimal conditions for growth found to depend on the shear tolerance and oxygen demands of the cells.

Evaluation of a novel choanoid fluidized bed bioreactor for future bioartificial livers

AIM

To construct and evaluate the functionality of a choanoid-fluidized bed bioreactor (CFBB) based on microencapsulated immortalized human hepatocytes.

METHODS

Encapsulated hepatocytes were placed in the constructed CFBB and circulated through Dulbecco's Modified Eagle's Medium (DMEM) for 12 h, and then through exchanged plasma for 6 h, and compared with encapsulated cells cultivated under static conditions in a spinner flask. Levels of alanine aminotransferase (ALT) and albumin were used to evaluate the CFBB during media circulation, whereas levels of ALT, total bilirubin (TBil), and albumin were used to evaluate it during plasma circulation. Mass transfer and hepatocyte injury were evaluated by comparing the results from the two experimental conditions. In addition, the viability and microstructure of encapsulated cells were observed in the different environments.

RESULTS

The bioartificial liver model based on a CFBB was verified by in vitro experiments. The viability of encapsulated cells accounting for 84.6% ± 3.7% in CFBB plasma perfusion was higher than the 74.8% ± 3.1% in the static culture group (P < 0.05) after 6 h. ALT release from cells was 29 ± 3.5 U/L vs 40.6 ± 3.2 U/L at 12 h (P < 0.01) in the CFBB medium circulation and static medium culture groups, respectively. Albumin secretion from cells was 234.2 ± 27.8 μg/1 × 10(7) cells vs 167.8 ± 29.3 μg/1 × 10(7) cells at 6 h (P < 0.01), 274.4 ± 34.6 μg/1 × 10(7) cells vs 208.4 ± 49.3 μg/1 × 10(7) cells (P < 0.05) at 12 h, in the two medium circulation/culture groups, respectively. Furthermore, ALT and TBil levels were 172.3 ± 24.1 U/L vs 236.3 ± 21.5 U/L (P < 0.05), 240.1 ± 23.9 μmol/L vs 241.9 ± 31.4 μmol/L (P > 0.05) at 6 h in the CFBB plasma perfusion and static plasma culture groups, respectively. There was no significant difference in albumin concentration between the two experimental plasma groups at any time point. The microstructure of the encapsulated hepatocytes remained healthier in the CFBB group compared with the static culture group after 6 h of plasma perfusion.

CONCLUSION

The CFBB can function as a bioartificial liver based on a bioreactor. The efficacy of this novel bioreactor is promising for the study of liver failure.

Galactosylated reversible hydrogels as scaffold for HepG2 spheroid generation

Various galactosylated scaffolds have been developed for hepatocyte culture because galactose ligands help maintain cell viability, facilitate the formation of multicellular spheroids and help maintain a high level of liver-specific functions. However, it is difficult to harvest the cell spheroids generated inside the three-dimensional scaffolds for their further biological analysis and applications. Here we developed a new galactosylated hydrogel scaffold which solidifies in situ upon heating to physiological temperature, but liquefies again upon cooling back to room temperature. The new scaffold is composed of poly(N-isopropylacrylamide) (PNIPAM) microgel and poly(ethylene glycol) (PEG). Because of the thermosensitivity of PNIPAM microgel, the mixed dispersions gel upon heating and liquefy upon cooling. PEG was added to reduce the shrinkage of the gels. Part of the PNIPAM microgel was replaced with a galactosylated one to provide a series of blend gels with various galactose ligand contents. HepG2 cells, a human hepatocarcinoma cell line, were encapsulated in the in situ-formed gels. As expected, the cell viability increases with increasing content of galactose ligands. In addition, compact multicellular spheroids were obtained in gels containing galactose ligands, while loose spheroids formed in gel without galactose ligands. The cells cultured in galactose-containing gels also exhibit a higher level of liver-specific functions, in terms of both albumin secretion and urea synthesis, than those cultured in gel without these ligands. The new galactosylated scaffold not only promotes the formation of hepatocyte spheroids, but also allows for their harvest. By cooling back to room temperature to liquefy the gel, the hepatocyte spheroids can be facilely harvested from the scaffold. The reversible galactosylated scaffold developed here may be used for large scale fabrication of hepatocyte spheroids.

Novel in vitro and mathematical models for the prediction of chemical toxicity

The focus of much scientific and medical research is directed towards understanding the disease process and defining therapeutic intervention strategies. The scientific basis of drug safety is very complex and currently remains poorly understood, despite the fact that adverse drug reactions (ADRs) are a major health concern and a serious impediment to development of new medicines. Toxicity issues account for ∼21% drug attrition during drug development and safety testing strategies require considerable animal use. Mechanistic relationships between drug plasma levels and molecular/cellular events that culminate in whole organ toxicity underpins development of novel safety assessment strategies. Current in vitro test systems are poorly predictive of toxicity of chemicals entering the systemic circulation, particularly to the liver. Such systems fall short because of (1) the physiological gap between cells currently used and human hepatocytes existing in their native state, (2) the lack of physiological integration with other cells/systems within organs, required to amplify the initial toxicological lesion into overt toxicity, (3) the inability to assess how low level cell damage induced by chemicals may develop into overt organ toxicity in a minority of patients, (4) lack of consideration of systemic effects. Reproduction of centrilobular and periportal hepatocyte phenotypes in in vitro culture is crucial for sensitive detection of cellular stress. Hepatocyte metabolism/phenotype is dependent on cell position along the liver lobule, with corresponding differences in exposure to substrate, oxygen and hormone gradients. Application of bioartificial liver (BAL) technology can encompass in vitro predictive toxicity testing with enhanced sensitivity and improved mechanistic understanding. Combining this technology with mechanistic mathematical models describing intracellular metabolism, fluid-flow, substrate, hormone and nutrient distribution provides the opportunity to design the BAL specifically to mimic the in vivo scenario. Such mathematical models enable theoretical hypothesis testing, will inform the design of in vitro experiments, and will enable both refinement and reduction of in vivo animal trials. In this way, development of novel mathematical modelling tools will help to focus and direct in vitro and in vivo research, and can be used as a framework for other areas of drug safety science.

Bifunctional polyethersulfone hollow fiber with a porous, single-layer skin for use as a bioartificial liver bioreactor

A bioartificial liver bioreactor requires a bifunctional hollow fiber that is hemocompatible on one side and cytocompatible on the other side. In this study, we developed a single-layer skin polyethersulfone (PES) hollow fiber with smooth inner surface and rough/porous outer surface for an artificial liver bioreactor. The hemocompatibility of the inner surface was evaluated by hemolysis, complement activation and clotting time. The cytocompatibility of the outer surface with HepG2 cells was examined by morphology, proliferation and liver-specific functions. The inner surface of the PES hollow fiber exhibited lower hemolysis and complement activation than cellulose acetate (CA) hollow fiber and a prolonged blood coagulation time. HepG2 cells readily adhered to the outer surfaces of the PES hollow fibers, and proliferated to form multicellular aggregates with time. Furthermore, HepG2 cells cultured on the outer surface of the PES hollow fiber exhibited higher proliferation ability and liver-specific functions than those grown on the CA hollow fiber. These results suggest that the single-layer skin PES hollow fiber is a bifunctional hollow fiber with good hemocompatibility on the inner side and cytocompatibility on the outer side. Thus, porous and single-layer skin PES hollow fibers may have potential as materials for an artificial liver bioreactor.

Porous and single-skinned polyethersulfone membranes support the growth of HepG2 cells: A potential biomaterial for bioartificial liver systems

In this study, we evaluated a porous and single-layer skin polyethersulfone (PES) membrane as a material for use in hybrid bioartificial liver support systems. The PES membrane has been characterized as a single-layer skin structure, with a rough porous surface. Specifically, we studied the ability of the human hepatoblastoma cell lines (HepG2) to adhere, grow, and spread on the PES membrane. Furthermore, we examined albumin secretion, low-density lipoprotein uptake, and CYP450 activity of HepG2 cells that grew on the membrane. HepG2 cells readily adhered onto the outer surfaces of PES membranes. Over time, HepG2 cells proliferated actively, and confluent monolayer of cells covered the available surface area of the membrane, eventually forming cell clusters and three-dimensional aggregates. Furthermore, HepG2 cells grown on PES membranes maintained highly specific functions, including uptake capability, biosynthesis and biotransformation. These results indicate that PES membranes are potential substrates for the growth of human liver cells and may be useful in the construction of hollow fiber bioreactors. Porous and single-layer skin PES membranes and HepG2 cells may be potential biomaterials for the development of biohybrid liver devices.

Hepatocyte differentiation

Increasingly, research suggests that for certain systems, animal models are insufficient for human toxicology testing. The development of robust, in vitro models of human toxicity is required to decrease our dependence on potentially misleading in vivo animal studies. A critical development in human toxicology testing is the use of human primary hepatocytes to model processes that occur in the intact liver. However, in order to serve as an appropriate model, primary hepatocytes must be maintained in such a way that they persist in their differentiated state. While many hepatocyte culture methods exist, the two-dimensional collagen "sandwich" system combined with a serum-free medium, supplemented with physiological glucocorticoid concentrations, appears to robustly maintain hepatocyte character. Studies in rat and human hepatocytes have shown that when cultured under these conditions, hepatocytes maintain many markers of differentiation including morphology, expression of plasma proteins, hepatic nuclear factors, phase I and II metabolic enzymes. Functionally, these culture conditions also preserve hepatic stress response pathways, such as the SAPK and MAPK pathways, as well as prototypical xenobiotic induction responses. This chapter will briefly review culture methodologies but will primarily focus on hallmark hepatocyte structural, expression and functional markers that characterize the differentiation status of the hepatocyte.

Characterization of alveolar epithelial cells cultured in semipermeable hollow fibers

Cell culture methods commonly used to represent alveolar epithelial cells in vivo have lacked airflow, a 3-dimensional air-liquid interface, and dynamic stretching characteristics of native lung tissue--physiological parameters critical for normal phenotypic gene expression and cellular function. Here the authors report the development of a selectively semipermeable hollow fiber culture system that more accurately mimics the in vivo microenvironment experienced by mammalian distal airway cells than in conventional or standard air-liquid interface culture. Murine lung epithelial cells (MLE-15) were cultured within semipermeable polyurethane hollow fibers and introduced to controlled airflow through the microfiber interior. Under these conditions, MLE-15 cells formed confluent monolayers, demonstrated a cuboidal morphology, formed tight junctions, and produced and secreted surfactant proteins. Numerous lamellar bodies and microvilli were present in MLE-15 cells grown in hollow fiber culture. Conversely, these alveolar type II cell characteristics were reduced in MLE-15 cells cultured in conventional 2D static culture systems. These data support the hypothesis that MLE-15 cells grown within our microfiber culture system in the presence of airflow maintain the phenotypic characteristics of type II cells to a higher degree than those grown in standard in vitro cell culture models. Application of our novel model system may prove advantageous for future studies of specific gene and protein expression involving alveolar epithelial or bronchiolar epithelial cells.

The effect of nanofibrous galactosylated chitosan scaffolds on the formation of rat primary hepatocyte aggregates and the maintenance of liver function

Liver tissue engineering requires a perfect extracellular matrix (ECM) for primary hepatocytes culture to maintain high level of liver-specific functions and desirable mechanical stability. The aim of this study was to develop a novel natural nanofibrous scaffold with surface-galactose ligands to enhance the bioactivity and mechanical stability of primary hepatocytes in culture. The nanofibrous scaffold was fabricated by electrospinning a natural material, galactosylated chitosan (GC), into nanofibers with an average diameter of approximately 160 nm. The GC nanofibrous scaffolds displayed slow degradation and suitable mechanical properties as an ECM for hepatocytes according to the evaluation of disintegration and Young's modulus testing. The results of morphology characterization, double-staining fluorescence assay and function detection showed that hepatocytes cultured on GC nanofibrous scaffold formed stably immobilized 3D flat aggregates and exhibited superior cell bioactivity with higher levels of liver-specific function maintenance in terms of albumin secretion, urea synthesis and cytochrome P-450 enzyme than 3D spheroid aggregates formed on GC films. These spheroid aggregates could be detached easily during culture period from the flat GC films. We suggest such GC-based nanofibrous scaffolds could be useful for various applications such as bioartificial liver-assist devices and tissue engineering for liver regeneration as primary hepatocytes culture substrates.

Vitreous Cryopreservation of Cell–Biomaterial Constructs Involving Encapsulated Hepatocytes

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