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

Comprehensive Evaluation of Organotypic and Microphysiological Liver Models for Prediction of Drug-Induced Liver Injury

Drug-induced liver injury (DILI) is a major concern for the pharmaceutical industry and constitutes one of the most important reasons for the termination of promising drug development projects. Reliable prediction of DILI liability in preclinical stages is difficult, as current experimental model systems do not accurately reflect the molecular phenotype and functionality of the human liver. As a result, multiple drugs that passed preclinical safety evaluations failed due to liver toxicity in clinical trials or postmarketing stages in recent years. To improve the selection of molecules that are taken forward into the clinics, the development of more predictive in vitro systems that enable high-throughput screening of hepatotoxic liabilities and allow for investigative studies into DILI mechanisms has gained growing interest. Specifically, it became increasingly clear that the choice of cell types and culture method both constitute important parameters that affect the predictive power of test systems. In this review, we present current 3D culture paradigms for hepatotoxicity tests and critically evaluate their utility and performance for DILI prediction. In addition, we highlight possibilities of these emerging platforms for mechanistic evaluations of selected drug candidates and present current research directions towards the further improvement of preclinical liver safety tests. We conclude that organotypic and microphysiological liver systems have provided an important step towards more reliable DILI prediction. Furthermore, we expect that the increasing availability of comprehensive benchmarking studies will facilitate model dissemination that might eventually result in their regulatory acceptance.

A multiphase model for chemically- and mechanically- induced cell differentiation in a hollow fibre membrane bioreactor: minimising growth factor consumption

We present a simplified two-dimensional model of fluid flow, solute transport, and cell distribution in a hollow fibre membrane bioreactor. We consider two cell populations, one undifferentiated and one differentiated, with differentiation stimulated either by growth factor alone, or by both growth factor and fluid shear stress. Two experimental configurations are considered, a 3-layer model in which the cells are seeded in a scaffold throughout the extracapillary space (ECS), and a 4-layer model in which the cell-scaffold construct occupies a layer surrounding the outside of the hollow fibre, only partially filling the ECS. Above this is a region of free-flowing fluid, referred to as the upper fluid layer. Following previous models by the authors (Pearson et al. in Math Med Biol, 2013, Biomech Model Mechanbiol 1-16, 2014a, we employ porous mixture theory to model the dynamics of, and interactions between, the cells, scaffold, and fluid in the cell-scaffold construct. We use this model to determine operating conditions (experiment end time, growth factor inlet concentration, and inlet fluid fluxes) which result in a required percentage of differentiated cells, as well as maximising the differentiated cell yield and minimising the consumption of expensive growth factor.

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.

Effect of plasma components on the stability and permeability of microcapsule

Immobilization of hepatocytes in microcapsules has been a potentially alternative methodology for bioartificial livers (BALs). Moreover, the stability and permeability are the key parameters of these microcapsules. However, these alginate-based microcapsules are unstable if the surrounding medium disrupts the ionic interactions between alginate and the polycation. As hundreds of components are included in human plasma, the stability and permeability in plasma of microcapsules need to be sufficiently investigated. In the present study, the stability of three kinds of alginate-based microcapsules was evaluated when they were immersed in plasma. Our results showed that stability of alginate-α-poly (L-lysine)-alginate (α-APA) microcapsules was well maintained, better than those of alginate-ε-poly (L-lysine)-alginate (ε-APA) and alginate-chitosan-alginate (ACA) microcapsules. Also, factors affecting the stability of microcapsules in plasma were analyzed and it showed that heparin was the key factor that affected the stability of α-APA microcapsules, whereas heparin and low molecular electrolytes such as HCO3(-) and H2 PO4(-)/HPO4(2-) were the factors to ε-APA and ACA microcapsules. In addition, the permeability evaluation showed no decrease in permeability of microcapsules after incubation in plasma. Our study might provide a foundation for the selection and modification of materials for microcapsule-based BAL devices.

Modifying three-dimensional scaffolds from novel nanocomposite materials using dissolvable porogen particles for use in liver tissue engineering

Background:

Although hepatocytes have a remarkable regenerative power, the rapidity of acute liver failure makes liver transplantation the only definitive treatment. Attempts to incorporate engineered three-dimensional liver tissue in bioartificial liver devices or in implantable tissue constructs, to treat or bridge patients to self-recovery, were met with many challenges, amongst which is to find suitable polymeric matrices. We studied the feasibility of utilising nanocomposite polymers in three-dimensional scaffolds for hepatocytes.

Materials and methods:

Hepatocytes (HepG2) were seeded on a flat sheet and in three-dimensional scaffolds made of a nanocomposite polymer (Polyhedral Oligomeric Silsesquioxane [POSS]-modified polycaprolactone urea urethane) alone as well as with porogen particles, i.e. glucose, sodium bicarbonate and sodium chloride. The scaffold architecture, cell attachment and morphology were studied with scanning electron microscopy, and we assessed cell viability and functionality.

Results:

Cell attachment to the scaffolds was demonstrated. The scaffold made with glucose particles as porogen showed a narrower range of pore size with higher porosity and better inter-pore communications and seemed to encourage near normal cell morphology. There was a steady increase of albumin secretion throughout the experiment while the control (monolayer cell culture) showed a steep decrease after day 7. At the end of the experiment, there was no significant difference in viability and functionality between the scaffolds and the control.

Conclusion:

In this initial study, porogen particles were used to modify the scaffolds produced from the novel polymer. Although there was no significance against the control in functionality and viability, the demonstrable attachment on scanning electron microscopy suggest potential roles for this polymer and in particular for scaffolds made with glucose particles in liver tissue engineering.

Future of bioartificial liver support

Many different artificial liver support systems (biological and non-biological) have been developed, tested pre-clinically and some have been applied in clinical trials. Based on theoretical considerations a biological artificial liver (BAL) should be preferred above the non-biological ones. However, clinical application of the BAL is still experimental. Here we try to analyze which hurdles have to be taken before the BAL will become standard equipment in the intensive care unit for patients with acute liver failure or acute deterioration of chronic liver disease.

Engineering imaging: using particle image velocimetry to see physiology in a new light

1. Despite the array of sophisticated imaging techniques available for biological applications, none of the standard biomedical techniques adequately provides the capability to measure motion and flow. Those techniques currently in use are particularly lacking in spatial and temporal resolution. 2. Herein, we introduce the technique of particle image velocimetry. This technique is a well-established tool in engineering research and industry. Particle image velocimetry is continuing to develop and has an increasing number of variants. 3. Three case studies are presented: (i) the use of microparticle image velocimetry to study flow generated by high-frequency oscillatory ventilation in a human airway model; (ii) the use of stereoparticle image velocimetry to study stirred cell and tissue culture devices; and (iii) a three-dimensional X-ray particle image velocimetry technique used to measure flow in an in vitro vascular flow model. 4. The case studies highlight the vast potential of applying the engineering technique of particle image velocimetry and its many variants to current research problems in physiology.

Effects of common sterilization methods on the structure and properties of poly(D,L lactic-co-glycolic acid) scaffolds

While methods for the production of scaffolds with the appropriate mechanical properties and architecture for tissue engineering are attracting much attention, the effects of subsequent sterilization processes on the scaffold properties have often been overlooked. This study sought to determine the effects of sterilization with ethanol, peracetic acid, ultraviolet irradiation, and antibiotic solution on the structure of 50:50 (mol:mol) 65:35, and 85:15 poly(D,L-lactic-co-glycolic acid [PLGA]) flat-sheet and hollow-fiber scaffolds. All methods resulted in scaffold sterilization, but scanning electron microscopy revealed deformations to the scaffold surface for all treatments. The extent of surface damage increased with treatment duration. This was further investigated by measurement of pore sizes, water flux, breaking strain, and Young's modulus. External pore size and water flux was found to be increased by all treatments in the following order: ethanol (largest), antibiotics, ultraviolet light, and peracetic acid. Pore sizes were 0.25 to 0.17 microm and water flux ranged from 0.01 kg x m(-2) x s(-1) to 3.34 kg x m(-2) x s(-1). For all samples, the Young's modulus was 1.0 to 31.1 MPa and breaking strain was 1.2 to 2.4 MPa. The results of this study suggest that antibiotic treatment shows the most potential to sterilize PLGA hollow fibers for tissue engineering.

Adhesion contact dynamics of primary hepatocytes on poly(ethylene terephthalate) surface

The design of bioartificial liver assist device requires an effective attachment of primary hepatocytes on polymeric biomaterials. A better understanding of this cell-surface interaction would aid the optimal choice of biomaterials. In this study, the adhesion contact dynamics of primary hepatocytes on poly(ethylene terephthalate) (PET) surface with grafted poly(acrylic acid) (PAA) and coated collagen is probed with confocal reflectance interference contrast microscopy (C-RICM) in conjunction with phase contrast microscopy. An increase of acrylic acid density from 0 to 12 nmole/cm2 raises both the root-mean-square surface roughness and amount of adsorbed collagen of PET surface. C-RICM demonstrates that hepatocytes form tight adhesion contacts upon seeding on both plain PET and PAA-grafted PET (both with collagen coating) despite the insignificant two-dimensional cell spreading. At two hours after cell seeding, the normalized contact area and adhesion energy of hepatocytes on 12 nmole/cm2 PAA-grafted-PET (with collagen coating) is 27% and 114% higher, respectively, than that on collagen coated plain PET. Interestingly, the growth kinetics of adhesion patch for hepatocyte on PAA-grafted PET with collagen coating is best fitted by R proportional to t0.5 and is significantly different from that on collagen coated plain PET, which is best fitted by R proportional to t0.25. Overall, this study demonstrates the modulation of biophysical response of adherent hepatocytes through the control of the biomaterial surface properties.

Gd-BOPTA Transport Into Rat Hepatocytes: Pharmacokinetic Analysis of Dynamic Magnetic Resonance Images Using a Hollow-Fiber Bioreactor

RATIONALE AND OBJECTIVES

To investigate the transport of the hepatobiliary magnetic resonance (MR) imaging contrast agent Gd-BOPTA into rat hepatocytes.

MATERIALS AND METHODS

In a MR-compatible hollow-fiber bioreactor containing hepatocytes, MR signal intensity was measured over time during the perfusion of Gd-BOPTA. For comparison, the perfusion of an extracellular contrast agent (Gd-DTPA) was also studied. A compartmental pharmacokinetic model was developed to describe dynamic signal intensity-time curves.

RESULTS

The dynamic signal intensity-time curves of the hepatocyte hollow-fiber bioreactor during Gd-BOPTA perfusion were adequately fitted by 2 compartmental models. Modeling permitted to discriminate between the behaviors of the extracellular contrast agent (Gd-DTPA) and the hepatobiliary contrast agent (Gd-BOPTA). It allowed the successfully quantification of the parameters involved in such differences. Gd-BOPTA uptake was saturable at high substrate concentrations.

CONCLUSIONS

The transport of Gd-BOPTA into rat hepatocytes was successfully described by compartmental analysis of the signal intensity recorded over time and supported the hypothesis of a transporter-mediated uptake.