The Liver is Super The Liver is Super Super AwesomeSuper Awesome

Olga Filippova, Munir Nahri, Akash Patel

BMES 471

- Most metabolically complex organ- 2 main, 2 smaller lobe

- Eight segments- Functional unit – lobule

- Dual blood supply - Portal vein (75%)- Hepatic artery (25%)

- Hepatocyte plates- Endothelial, Kupffer’s, Fat-storing, Pit

Anatomy of the LiverAnatomy of the Liver11

Lobule, the functional unit of the liver, and its circulatory system

http://education.vetmed.vt.edu/curriculum/vm8054/labs/Lab20/LAB20.HTM

- Metabolism - carbohydrate, protein, fat- Glucose regulation - glucogenesis, glucogenolysis- Amino acid catabolism- Drug neutralization

- Bile synthesis- digestion and absorption of fat- Cholesterol catabolism- Stored in gallbladder- Released by CCK from SI

Functions of the LiverFunctions of the Liver11

- Multicellular Aggregates

• number of improvements to the homotypic aggregation– Abu-Absi et al. (2002) have demonstrated that homotypic aggregations formed in a stirred

suspension culture can form functional bile canaliculi.– Currently, there is a lot of activity in the design of heterotypic aggregates in which other cell types of

the liver are combined with hepatocytes.– This co-culture concept replacing of generic fibroblast lines with non-parenchymal liver cells which

include sinusoidal endothelial, and Stellate cells

- Scaffolds are another primary topic of research• From an engineering perspective there are clear advantages in intervening in the

process of spheroid formation and providing an improved architectural template– As of today, Alginate scaffolds have been widely investigated in liver tissue engineering.– Alginate material was used to fully encapsulate a hepatocyte cell line (HepG2). In this experiment,

cells maintained significantly higher expression of differentiated functions.– Furthermore, enhancing hepatocyte adhesion to scaffolds has been achieved by including various

biological molecules and signals within scaffolds.

Current State of Liver TE2

Current State of Liver TE2

- Bioreactor• The liver lobule is a highly perfused tissue structure precise zonal structure and directional blood flow. The

use of multicellular aggregates and/or scaffolds does not address the need to recreate perfusion conditions.– Bioreactor can serve at least four functions in liver tissue engineering:

• enhanced delivery of oxygen and nutrients• improved viability and functionality of hepatocytes if transportation is required• miniaturisation of engineered tissue for higher throughput assay• zonation of hepatocyte functioning.

– Gerlacher and colleagues developed a new bioreactor that promotes the reorganisation of hepatocytes and non-parenchymal cells into histotypic structures • Both bile canaliculi and sinusoidal-like structures developed spontaneously.• Gerlach's work elegantly demonstrates that the self-assembly of complex tissue structures can be promoted by perfusion of the cells

with medium and direct access to oxygen.

- Microtechnology and Cell Patterning– most intriguing aspects of liver tissue engineering is the need to replicate the architecture of the liver lobule to fully replicate function– now focusing on methods of building microscale architecture into their liver models.– Ho et al. (2006) have demonstrated a heterogeneous liver cell on-chip system in which hepatocyte cell livers and endothelial cells are focussed into radial

patterns that mimic the liver lobule structure.– Fukuda et al. (2006) combined microfabrication and microcontact printing to form 300 m cavities in which spheroids formed with tight control of diameter.– Finally, full 3D systems require the formation of a network that replicates the sinusoids of the liver with surrounding hepatocytes. Microfluidic structures offer

the potential to expose small populations of cells to flowing medium with precise control of the location of multiple chemicals and the potential to recreate the relationships between fluid flow and liver architecture.• These patterns have been used in vitro to maintain hepatocyte functionality but the greatest promise of these devices is as

implantable 3D organs in which a large mass of hepatocytes can be implanted with an in-built vascular network.

-At Drexel, work by Dr. Wei Sun and colleagues is proceeding towards an automated process of the cell printing in 3D scaffolds via hydrogels. The goal is to print 3-D micro-organs that are reproducible and useful for experimental and drug metabolic studies.

Current State of Liver TE2

- In situ regeneration– aim is restore functional liver tissue in vivo. enhanced delivery of oxygen and

• Simple functions of the liver may be maintained in current tissue-engineered liver systems, more complex functions are always lost

• Display zonal liver functions that mimic anatomical structure of liver

• Recreating complex spatial and flow relationships

• Development of predictive animal models to evaluate live therapies

• Limited supply of primary human cells– Primary human cells are preferred source of cellular therapies

Room for Improvement

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Room for Improvement

Future of Liver TE2

- Development of complex 3D Liver models- Artificial or Bioartificial Liver (BAL)

- Vascular network capable of providing oxygen and nutrients to tissue [3]- Ability to restore liver natural function and able to maintain hemostasis- Capable of bidirectional mass transport

- Optimal results- Mimic natural liver

- Size of BAL - Spatial arrangement

- Viable cell source- Progenitor stem cells Promote phenotypic stability and tissue

morphogenesis [4]- Key success:

- Ability to control differentiation and proliferation of stem cells- Proper signaling to introduce other key cells in liver regeneration

- Ultimate goal fully functional tissue engineered implantable liver

- Extracorporeal bioartificial liver Devices- Bidirectional mass transport- Stable microenviornment

- Hepatocytes require specific environment to maintain function4

- Scale Up- Examples:

- Hollow fiber devices, Flat plate systems, perfusion bed/ scaffolds, suspension and encapsulation4

Future of Liver TE2

1. Hilsden, R.J., Shaffer, E.A. Chapter 14: The Liver, 1. Liver Structure and Function. First Principles of Gastroenterology: the basis of Disease and an Approach to Management. Canadian Association Pf Gastroenterology. 1994.

2. Gerlach, J.C., Zeilinger, K., Patzer, J.F. II. Bioartificial Liver Systems: Why, What, Whither? Regenerative Medicine. 3, 575, 2008.

3. Behnia, K., Bhatia, S., Jastromb, N., Balis, U., Sullivan, S., Yarmush, M., Toner, M. Xenobiotic Metabolism by Cultured Primary Porcine Hepatocytes. Tissue Engineering. 6, 467, 2000.

4. Allen, J.W., Bhatia S. N. Engineering Liver Therapies for the Future. Tissue Engineering. 8, 725, 2002.

References

Questions?Questions?

Olga Filippova, Munir Nahri, Akash Patel

BMES 471