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±3.2U/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±27.8μg/1×107cells vs 167.8±29.3μg/1×107 cells at 6 h(P<0.01),274.4±34.6μg/1×107 cells vs 208.4±49.3μg/1×107 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±23.9μmol/L vs 241.9±31.4μmol/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.

Hydrodynamics characterization of a choanoid fluidized bed bioreactor used in the bioartificial liver system： Fully resolved simulation with a fctitious domain method

Choanoid fluidized bed bioreactors （CFBBs） are newly developed core devices used in bioartificial liver- support systems to detoxify blood plasma of patients with microencapsulated liver cells. Direct numerical simulations （DNS） with a direct-forcing/fictitious domain （DF/FD） method were conducted to study the hydrodynamic performance of a CFBB. The effects of particle-fluid density ratio, particle number, and fil- ter screens preventing particles flowing out of the reactor were investigated. Depending on density ratio, two flow patterns are evident： the circulation mode in which the suspension rises along one sidewall and descends along the other sidewall, and the non-circulation mode in which the whole suspension roughly flows upward. The circulation mode takes place under non-neutral-buoyancy where the particle sedimentation dominates, whereas the non-circulation mode occurs under pure or near-neutral buoy- ancy with particle-fluid density ratios of unity or near unity. With particle-fluid density ratio of 1.01, the bioartificial liver reactor performs optimally as the significant particle accumulation existing in the non-circulation mode and the large shear forces on particles in the circulation mode are avoided. At higher particle volume fractions, more particles accumulate at the filter screens and a secondary counter circulation to the primary flow is observed at the top of the bed. Modelled as porous media, the filter screens play a negative role on particle fluidization velocities; without screens, particles are fluidized faster because of the higher fluid velocities in the jet center region. This work extends the DF/FD-based DNS to a fluidized bed and accounts for effects from inclined side walls and porous media, providing some hydrodynamics insight that is important for CFBB design and operation optimization.