Introduction to special issue

If I Only Had a ...

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Science  08 Feb 2002:
Vol. 295, Issue 5557, pp. 995
DOI: 10.1126/science.295.5557.995

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I could stay young and chipper and I'd lock it with a zipper, if I only had a heart,” sang the Tin Man to his companions in the 1939 movie The Wizard of Oz. There is hope yet for the Tin Man and for the many thousands of patients with diseased hearts, damaged livers, or injured tissues. Spurred on by a severe shortage of donor organs for transplantation, bioengineers, cell biologists, and clinicians are combining their talents to design off-the-shelf replacement parts for the human body. This dream is not new, as our historical timeline on the next two pages reveals.


A daring goal that has captured the public imagination is the implantation of a totally artificial heart into patients with end-stage heart failure (p. 1000), a remarkable achievement despite recent setbacks. Of simpler design, ventricular assist devices, which support the left ventricle until the heart repairs itself, may benefit the majority of patients with heart disease (p. 998). Similarly, a bioartificial liver device, composed of liver cells nurtured in a bioreactor, is undergoing clinical testing as a bridge to support the failing liver until it can regenerate (p. 1005). Meanwhile, despite numerous regulatory hurdles (p. 1003), researchers are developing artificial blood substitutes (p. 1002) for use instead of donor blood during lengthy surgeries or at disaster sites.

CREDIT: From Boing-Boing the Bionic Cat™. Illustrated by Ruth Denise Lear. Copyright the American Ceramic Society. All rights reserved.

From tendons (p. 1011) to bladders, bioengineers are manufacturing “ready-to-wear” designer tissues in the laboratory (p. 1009). They are coaxing cells to assemble into three-dimensional structures on biodegradable scaffolds that can be implanted in patients at sites of tissue injury. Challenges to be addressed before engineered tissues enter the clinic include identifying sources of suitable cells, developing new scaffolding biomaterials (p. 1014), and scaling up production, not to mention discovering ways to preserve the tissue product (p. 1015) and to prevent immune rejection. Animal models of spinal cord injury are being used to test different bioengineering and molecular strategies for their ability to induce the injured spinal cord to regenerate (p. 1029).

Sophisticated microelectronics for signal processing are bringing the dream of merging man and machine closer to reality. A brain-computer interface that enables patients to control artificial limbs through brain neural pathways is under development (p. 1018). The success of cochlear implants, which enable some profoundly deaf patients to hear (p. 1025), has accelerated engineering of the next generation of electrode implants for brainstem auditory centers. Researchers facing the enormous challenge of trying to restore vision to the blind are developing electrode arrays that activate the retina, optic nerve, or even the visual cortex itself (pp. 1022 and 1026).

Designing bionic devices that enhance human capabilities (cybernetics) is raising a host of ethical questions (p. 1020), as is the transplant of xenogeneic tissues from other species into human patients (p. 1008). Even older than the science of replacing body parts is the art of staying young, and antidotes to aging are becoming big business as millions of baby boomers hit their 50s (p. 1032).

The next 38 pages reveal how far we have come in our dream of engineering designer parts for the human body to replace those lost through injury or disease. However, this special section also highlights the many hurdles yet to be overcome before these fascinating technologies enter routine clinical use.

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