Spatial considerations during cryopreservation of a large volume sample

AbstractThere have been relatively few studies on the implications of the physical conditions experienced by cells during large volume (litres) cryopreservation – most studies have focused on the problem of cryopreservation of smaller volumes, typically up to 2 ml.This study explores the effects of ice growth by progressive solidification, generally seen during larger scale cryopreservation, on encapsulated liver hepatocyte spheroids, and it develops a method to reliably sample different regions across the frozen cores of samples experiencing progressive solidification.These issues are examined in the context of a Bioartificial Liver Device which requires cryopreservation of a 2 L volume in a strict cylindrical geometry for optimal clinical delivery. Progressive solidification cannot be avoided in this arrangement. In such a system optimal cryoprotectant concentrations and cooling rates are known. However, applying these parameters to a large volume is challenging due to the thermal mass and subsequent thermal lag. The specific impact of this to the cryopreservation outcome is required.Under conditions of progressive solidification, the spatial location of Encapsulated Liver Spheroids had a strong impact on post-thaw recovery. Cells in areas first and last to solidify demonstrated significantly impaired post-thaw function, whereas areas solidifying through the majority of the process exhibited higher post-thaw outcome. It was also found that samples where the ice thawed more rapidly had greater post-thaw viability 24 h post-thaw (75.7 ± 3.9% and 62.0 ± 7.2% respectively).These findings have implications for the cryopreservation of large volumes with a rigid shape and for the cryopreservation of a Bioartificial Liver Device

Evaluation of encapsulated liver cell spheroids in a fluidised-bed bioartificial liver for treatment of ischaemic acute liver failure in pigs in a translational setting

Liver failure is an increasing problem. Donor-organ shortage results in patients dying before receiving a transplant. Since the liver can regenerate, alternative therapies providing temporary liver-support are sought. A bioartificial-liver would temporarily substitute function in liver failure buying time for liver regeneration/organ-procurement. Our aim: to develop a prototype bioartificial-liver-machine (BAL) comprising a human liver-derived cell-line, cultured to phenotypic competence and deliverable in a clinical setting to sites distant from its preparation. The objective of this study was to determine whether its use would improve functional parameters of liver failure in pigs with acute liver failure, to provide proof-of-principle. HepG2cells encapsulated in alginate-beads, proliferated in a fluidised-bed-bioreactor providing a biomass of 4-6×10 10 cells, were transported from preparation-laboratory to point-of-use operating theatre (6000miles) under perfluorodecalin at ambient temperature. Irreversible ischaemic liver failure was induced in anaesthetised pigs, after portal-systemic-shunt, by hepatic-artery-ligation. Biochemical parameters, intracranial pressure, and functional-clotting were measured in animals connected in an extracorporeal bioartificial-liver circuit. Efficacy was demonstrated comparing outcomes between animals connected to a circuit containing alginate-encapsulated cells (Cell-bead BAL), and those connected to circuit containing alginate capsules without cells (Empty-bead BAL). Cells of the biomass met regulatory standards for sterility and provenance. All animals developed progressive liver-failure after ischaemia induction. Efficacy of BAL was demonstrated since animals connected to a functional biomass (+ cells) had significantly smaller rises in intracranial pressure, lower ammonia levels, more bilirubin conjugation, improved acidosis and clotting restoration compared to animals connected to the circuit without cells. In the +cell group, human proteins accumulated in pigs' plasma. Delivery of biomass using a short-term cold-chain enabled transport and use without loss of function over 3days. Thus, a fluidised-bed bioreactor containing alginate-encapsulated HepG2cell-spheroids improved important parameters of acute liver failure in pigs. The system can readily be up-scaled and transported to point-of-use justifying development at clinical scale

An academician's approach to the application of human factors standards: A case study on a liver support system

Until recently, academia typically did not engage with the development of medical technology but instead developed techniques, processes, and lab-evaluated studies that were picked up by industry. With the introduction of rapid prototyping and access to information via the internet, more and more medical technology is being developed within academia from conception to product. However, academia still suffers from siloed research groups, access to partial knowledge, and anticipating, at the outset, the requirements of a final product necessary to engage all the required multidisciplinary input. Support for the design and development of the technology can often be provided by other academic departments; however, the current environment of isolated research, often due to funding remit restrictions and limited resources, limits this. In this paper, we highlight lessons learnt within academia about using regulatory standards within a multidisciplinary research project to assess the usability of a novel medical device; specifically, the current guidance is not sufficient for new practitioners to apply regulatory processes straightforwardly. We report on the assessment of a novel medical device being evaluated to regulatory standards, using the system under ‘normal use’, and discuss how using ecological validity as a guide can help ensure that the device is effective, efficient, and most importantly safe

Cryopreservation and re-culture of a 2.3 litre biomass for use in a bioartificial liver device.

For large and complex tissue engineered constructs to be available on demand, long term storage using methods, such as cryopreservation, are essential. This study optimised parameters such as excess media concentration and warming rates and used the findings to enable the successful cryopreservation of 2.3 litres of alginate encapsulated liver cell spheroids. This volume of biomass is typical of those required for successful treatment of Acute Liver Failure using our Bioartificial Liver Device. Adding a buffer of medium above the biomass, as well as slow (0.6°C/min) warming rates was found to give the best results, so long as the warming through the equilibrium melting temperature was rapid. After 72 h post thaw-culture, viable cell number, glucose consumption, lactate production, and alpha-fetoprotein production had recovered to pre-freeze values in the 2.3 litre biomass (1.00 ± 0.05, 1.19 ± 0.10, 1.23 ± 0.18, 2.03 ± 0.04 per ml biomass of the pre-cryopreservation values respectively). It was also shown that further improvements in warming rates of the biomass could reduce recovery time to < 48 h. This is the first example of a biomass of this volume being successfully cryopreserved in a single cassette and re-cultured. It demonstrates that a bioartificial liver device can be cryopreserved, and has wider applications to scale-up large volume cryopreservation

Dimethyl sulfoxide for cryopreservation of alginate encapsulated liver cell spheroids in bioartificial liver support; assessments of cryoprotectant toxicity tolerance and dilution strategies

The Bioartificial Liver (BAL) is an extra-corporeal liver support designed to support the function of the Liver in patients with impaired liver function. The BAL biomass consists of alginate encapsulated liver spheroids (AELS). To facilitate rapid delivery of a BAL to patients the AELS are cryopreserved using a DMSO-containing cryoprotectant solution. This study assesses toxicity of DMSO in AELS at concentrations and temperatures relevant to the cryopreservation and recovery process of a cellular biomass. Additionally, it develops a process to remove DMSO from AELS before delivery of cell product to patients. Exposure of AELS to DMSO, at a concentration of 12% (v/v) for 10 min did not have a negative effect on the viability of the AELS up to 24 h after exposure, irrespective of the exposure temperature between 37 C and 0 C. Evidence of toxicity was only seen with exposure to 40% (v/v) DMSO, which was more notable at warm temperatures. Post-Thaw removal of DMSO was measured by determining the DMSO concentration of the post-thaw washes using refractometry. Washing AELS 3 times in tapering concentrations of Glucose supplemented DMEM at an AELS:wash ratio of 1:2 was sufficient to reduce DMSO to undetectable levels (<1%). The study demonstrated that the thawing method minimised DMSO toxicity to the BAL biomass, and the post-thaw washing protocol successfully removed all the DMSO present in the cryopreserved BAL. Thereby enabling effective cryopreservation of the BAL for future clinical translation

Cryopreservation and re-culture of a 2.3 litre biomass for use in a bioartificial liver device

<div><p>For large and complex tissue engineered constructs to be available on demand, long term storage using methods, such as cryopreservation, are essential. This study optimised parameters such as excess media concentration and warming rates and used the findings to enable the successful cryopreservation of 2.3 litres of alginate encapsulated liver cell spheroids. This volume of biomass is typical of those required for successful treatment of Acute Liver Failure using our Bioartificial Liver Device. Adding a buffer of medium above the biomass, as well as slow (0.6°C/min) warming rates was found to give the best results, so long as the warming through the equilibrium melting temperature was rapid. After 72 h post thaw-culture, viable cell number, glucose consumption, lactate production, and alpha-fetoprotein production had recovered to pre-freeze values in the 2.3 litre biomass (1.00 ± 0.05, 1.19 ± 0.10, 1.23 ± 0.18, 2.03 ± 0.04 per ml biomass of the pre-cryopreservation values respectively). It was also shown that further improvements in warming rates of the biomass could reduce recovery time to < 48 h. This is the first example of a biomass of this volume being successfully cryopreserved in a single cassette and re-cultured. It demonstrates that a bioartificial liver device can be cryopreserved, and has wider applications to scale-up large volume cryopreservation.</p></div

Glucose consumption (left) and lactate production (right) following cryopreservation.

<p>Top–glucose consumption and lactate production per ml ELS as a fraction of unfrozen control 72 h post-thaw, comparing the cryovial cryopreservation (light grey), scale-down process cryopreservation (dark grey), and large volume cryopreservation (black). No significant difference was observed in glucose consumption. Lactate production was significantly higher in both the cryovial and scale-down process samples over the large volume cryopreservation. Centre–production at various timepoints in the large volume cryopreservation per ml ELS over an unfrozen control. Base–Total glucose and lactate measured in the bioreactor at set timepoints post large volume thaw. N = 5 ± SD, significance over large volume cryopreservation (top) or unfrozen control (centre) defined as * = P<0.001, unpaired Student’s t-test.</p