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Biological Materials in Engineering Mechanisms 377

demonstrated in vitro (Makino et al., 1999). The cultured cells beat spontaneously, expressed
cardiomyocyte-specific genes, and exhibited electrophysiological characteristics similar to in vivo
cardiomyocytes. Another progenitor cell that exhibits developmental plasticity is the hematopoietic
stem cell. Transplanted hematopoietic stem cells have been shown to be involved in skeletal muscle
repair and regeneration (Camargo et al., 2003). However, it is still unclear whether the hemato-
poietic stem cells switches to a myogenic cell fate in response to microenvironmental cues as in the
case of bone marrow derived mesenchymal stem cells or the generation of myogenic cells result
from the fusion of hemopoietic stem cells with the muscle myofibers. In the later case, it is believed
muscle nuclear factors may play a role in activating a myogenic program in the fused hemopoietic
stem cells. A variety of specialized bioreactors have been used to optimize tissue outcomes (Kim
et al., 1998; Carrier et al., 1999; Radisic et al., 2004).

14.3 CONCLUSIONS

The examples provided from Nature illustrate the diverse and functional (high performance)
materials that are available as blueprints for exploitation in the broader field of materials science
and engineering. The gap between synthetic and natural polymers in terms of diverse yet controlled
sequence chemistry, coupled with control of regioselective and stereoselective chemical features,
suggests that a significant hurdle will remain for some time for synthetic systems to fully emulate
the novel features of natural materials. As control of synthetic processes for polymers continues to
improve, and as models from biology continue to be understood via reverse engineering, more
crossover among these systems will be realized. The marriage of both biological and synthetic
approaches may provide a useful bridge toward the future such that new materials, new processing
paradigms, and new assembly controls can be studied and technologically exploited.

ACKNOWLEDGMENTS

We thank various agencies for funding various background aspects used in this chapter, including
the NIH, NSF and NASA. We also wish to acknowledge the opportunity to organize this
chapter as a class project — Biotechnology Engineering Seminar. We also greatly appreciate
the input and comments from the reviewers that helped the class improve the focus and refine the
details.

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