Artificial Support and Replacement of Human Organs - Biomimetics: Biologically Inspired Technologies - page 465

heart failure (Thompson et al., 2003). From the initial euphoria in 1990 to disappointment in 2004,
tissue engineering has been put to test; a number of products have not shown benefit in clinical
trials, that in turn is reflected in the lack of market interest in these products (Lysaght and Reyes,
2001; Lysaght and Hazlehurst, 2004).
Tissue engineering has the necessary potential of seeding appropriate scaffolding with cells of
interest as in the case of tubule cells used in artificial kidney (Fey-Lamprecht et al., 2003; Humes,
2000; Ozgen et al., 2004). As our understanding increases in terms of cell growth characteristics in
relation to biomaterials, we are likely to move towards bio-artificial organ replacement systems.
Normal organs, however, are composed of many different cell types with complex messaging and
interactions. Using a single cell type may not necessarily guarantee adequate functioning of such
systems. The importance of developing appropriate scaffolds for the blood vessels to grow can be
key to future development of solid organs (Kaihara et al., 2000; MacNeill et al., 2002). The current
systems use altered cancerous cells or cells from animal origin, which raises the likelihood of risk of
cancerous transformation and transmission of animal originated diseases (van de Kerkhove et al.,
2004). However, using adult stem cells from the patients' own bone marrow may be the solution
which will be more widely applied in the future.

18.15.1.2 Stem Cell Technology

Stem cells are the precursor cells from which any type of cell differentiation is possible (Jain,
2002). There are two types of stem cell sources that can be used, one from the embryonic stage
and another from the adult stem cells within the bone marrow. Stem cells from the embryonic stage
offer the characteristic of differentiating into any possible cell type (Kakinuma et al., 2003; Sukhikh
and Shtil, 2002); but recent findings, however, of increasing plasticity shown by the human
hematopoietic stem cells to differentiate into different cell types has led to interest in developing
them as a cell therapy for organ failure (Liu et al., 2004a-c; Schuster et al., 2004; Strom et al., 2004;
Yokoo et al., 2003).

18.15.1.3 Impact of Understanding the Human Genome

The human genome sequence now has been decoded (Venter et al., 2001). This offers the potential
of synthetic DNA which can create proteins of interest. Theoretically, this can be used to develop
synthetic organ systems and conceivably a complete organism. However, there are several limita-
tions to this concept since we still do not have the insight into the function and role of all the human
genes. Early indications suggest a possibility of tailor-made treatment based on the individual
patient's genomic characteristics; how this will apply to the treatment and replacement of organ
systems remains to be fully explored.

18.15.1.4 Microelectromechanical Systems

Microdevices have been applied for certain diagnostic, therapeutic, and selected surgical proced-
ures (Evans et al., 2003; Polla et al., 2000; Richards Grayson et al., 2004). Microelectromechanical
systems (MEMS) employ the same manufacturing methods as silicone chips for computer industry.
They can be a useful tool for rapid screening of diseases, measurement of blood levels of hormones
and drugs, targeted drug delivery, and novel micro-stimulators in neurosciences (Evans et al., 2003;
Huang et al., 2002; Liu et al., 2004a-c; Polla et al., 2000; Roy et al., 2001).
What makes MEMS more promising is the building of small rotors capable of running on
miniscule energy (Epstein and Senturia, 1997; Miki et al., 2003). These have enormous potential
to provide the energy source for organ replacement systems. In addition, they can provide the
capability to detect the minute changes in hormones and endorphins on which the response of the
organ support system can be tailored.