Periodic Reporting for period 1 - Liver Bioengineering (Ex vivo Re-vascularization in Porcine Liver Bioengineering - A Critical First Step Towards Effective Transplantation of Bioengineered Livers)
Reporting period: 2015-08-01 to 2017-07-31
to accomplish this, the impact of fluid flow pressure and the seeded cell number will be investigated in reendothelialization efficiency of an acellular porcine liver scaffold. Furthermore, bioreactor pre-conditioning with fluid flow pressure ramping and sequential cycles of vascular growth and maturation will be used to induce revascularization, maturation, and enhanced function to potentially increase vascular patency. Finally, revascularized liver scaffolds will be transplanted into 5-10Kg pigs and short and long-term vascular patency will be investigated. Hence, the long-term objective of this project is to create a functional re-vascularized porcine liver scaffold, a critical first step towards the effective transplantation of bioengineered livers.
From all the objectives proposed initially, we were able to address almost all of them throughout the period of the project. However, we have to recognize that the proposed objectives were a bit over-ambitious, considering the available time. In this regard, a third year would have been instrumental in concluding the outstanding work. Nevertheless, the completed goals are proving instrumental in the ongoing lab research.
One of the main points of this project was the evaluation of the revascularized liver scaffolds after transplantation into pigs. During the development of the animal model, we had several technical issues that led to high mortality and were only solved recently, in the past few months. Hence, only now we can proceed with the transplantation of these liver scaffolds and understand the effect of our in vitro manipulations on the outcome in vivo.
On a general note, I believe that the proposed goal of understanding the effects of flow pressure and cell number on scaffold revascularization was achieved with a great contribution to the efficiency which we generate revascularized organ scaffolds. Similarly, we now understand some of the mechanisms necessary to generate functional vessels in these matrices, by modulating cycles of cell growth and maturation. This might not be enough to completely fulfill our goal of generating transplantable liver scaffolds, but it is certainly a huge step towards it, since we are now capable of generating complex vascular networks in vitro.
We found that “near-physiological” higher fluid flow pressures in the portal vein (10-20mmHg) after cell seeding resulted in increased tissue growth and cell proliferation, while higher fluid flow pressures >50mmHg lead to cell death. Finally, we also found that within this range (10-20mmHg), there was a significant increase in the number of reendothelialized vascular structures, which was fluid flow pressure dependent, suggesting that precise mechanical stimulation is essential for efficient re-vascularization of acellular liver scaffolds ex vivo (Baptista et al. Tissue Engineering C - Methods, 2016). These results are in agreement with observations of small-for-size liver transplantations, where many have found that extreme hyperperfusion, indicative of high shear stress, leads to cell death and numerous other complications. Yet, mild elevations in flow rate are indispensible for liver regeneration following small-for-size transplantation, which we believe are correlated with fluid flow pressures within the 10-20mmHg range.
With this ultimate goal, we believe that this project will have a broad socio-economic impact, since it will help to generate some of the necessary technologies to create lab grown organs (with its own potential implications in intellectual property), adding more livers into the transplantation pool.