Elsevier

Biochemical Engineering Journal

Volume 48, Issue 3, 15 February 2010, Pages 348-361
Biochemical Engineering Journal

Review
Toward engineering of vascularized three-dimensional liver tissue equivalents possessing a clinically significant mass

https://doi.org/10.1016/j.bej.2009.10.010Get rights and content

Abstract

In this review, we focus on how to develop and rear liver tissue equivalents that can be finally used as liver tissues as a substitute for the original liver. The size should be over 500 cm3 and its per-volume-based functionalities should be those comparable to the in vivo liver. As can easily be imagined, it will necessitate continuous efforts and we cannot predict when it becomes feasible at present. However, we need to set up an appropriate road map based on the latest knowledge concerning various related areas and to make efficient and integrative efforts to address the issues. The efforts that are currently required include design and fabrication of scaffolds, procurement of large mass of mature hepatocytes, rearing of the liver tissue equivalents in vitro and proof-of-concept studies in large animals such as pigs. Through the establishment of fundamental methodologies in such preclinical studies, we will know whether we can proceed to human clinical trials of such tissue equivalents. According to the possible road map, we summarized latest related approaches, with consistently stressing the two important but sometimes conflicting standpoints, that is, optimization of oxygenation supply to the cells in both micro- and macro-scale and three-dimensional (3D) culture of hepatocyte progenitors or stem cells toward hepatic lineages. In addition, we tried to clear up the remaining issues and the clues to overcome them.

Section snippets

Hepatocyte-based therapies for liver failures

Liver is the center of the various metabolisms in humans. The functions are those such as metabolisms of sugars, proteins/amino acids and lipids, detoxification of exogenous chemicals, production of bile acids, and storing of various other essential chemicals such as vitamins or irons. Therefore, its failure often results in a fatal threat to our life. Even at present, the ultimate treatment for such fatal liver failure is orthotropic liver transplantation of donor livers, incurring the

Classification of the approaches

To design liver tissue equivalent from engineering point of view, we need to consider both the actual structure of the liver and the current feasibility of various technologies. Fig. 2 shows the schematic illustration of the macro- to micro-structure of the liver [22]. The 3D blood flow network is well arranged so that each hepatocyte can actively exhibit metabolic functions. The hepatic portal vein supplies various ingested nutrients or toxic chemicals from the small intestine and the hepatic

Advantages and drawbacks of 3D culture

As discussed above, 3D culture of hepatocyte are necessary in obtaining high cell density and are also advantageous in obtaining enhanced hepatic functions, on the condition that oxygen and nutrients are satisfactorily supplied to all the cells in the entire 3D structure. The possible mechanisms for the 3D effects from the biological point of view is categorized into the three as follows [52]: enhanced cell-to-cell contact that makes them recognize they are in in vivo mimicking cellular

Necessity of oxygen carriers for rearing large liver tissues

As far as we target at development of liver tissue equivalents possessing clinically significant mass, 500 cm3, we need to pay attention to the oxygen supply in such larger scale as well as in micro-scale. The first reason is the very low oxygen solubility in culture medium, 2 × 10−7 mol-O2/mL-culture medium under 21% O2 in the gas phase, which is about 1/70 that of blood. The second reason is that culture medium should be perfused at less than a certain flow rate that gives a physiological shear

Maximizing spontaneous tissue organization both in vitro and in vivo

A study in 1960 pointed out the fact that a confluent hepatocytes monolayer cultured in a usual static condition is usually put an extremely anaerobic condition [115]. This can easily be predicted from the Fick's First law, simple oxygen diffusion through the culture medium layers and the oxygen consumption of the hepatocyte monolayer beneath the culture medium. However, there has been almost no research that tried complete removal of this oxygen limitation and in vitro realization of aerobic

Conclusive remark and expected roles of biochemical engineers

Toward engineering of liver tissue equivalents possessing a clinically significant mass (500 cm3) and per-volume-based functionalities comparable to those of in vivo liver tissue, we proposed a possible road map showing the first proof-of-concept stage using pigs where the fundamental methodology for development of 3D vascularized tissue equivalents is to be established and the second human clinical stage based on the same methodology but using human liver cells (Fig. 1). Related important

Acknowledgement

The results introduced in this review as our works were partly supported by Grants-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology, Japan.

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  • Cited by (0)

    1

    Current address: Okami Chemical Industry Co. Ltd., Emba 78, Makishima-cho, Uji-shi, Kyoto 611-0041, Japan.

    2

    Current address: International Clinical Research Center, Research Institute, International Medical Center of Japan, Toyama 1-21-1, Shinjuku-ku, Tokyo 162-8655, Japan.

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