Bionic organs.

Abstract

When a lizard loses its tail, a new caudal appendage soon grows to replace the one that is missing. But when a human loses a kidney, severs a peripheral nerve or worse, the spinal cord, that organ is lost forever. Such at least is conventional thinking. But imagine that the victim of an industrial accident with a paralyzed hand could achieve new levels of function by inducing axonal regrowth through a synthetic nerve guidance channel; or that a Parkinsonian patient's symptoms could be relieved by implanting in his brain neural tissue encased in a selectively permeable polymer envelope; or that the inexorable progression of the vascular complications of juvenile diabetes could be stopped, even reversed, by a membrane-protected xenograft of insulin-producing tissue. This is the dream of bionic organ science. It is predicated on two lines of technological achievement: the availability of ultra-thin, biocompatible, selectively permeable polymer membranes which can protect a transplant against immune rejection while allowing solute exchange between the graft and its environment; and the synthesis of novel materials, some biostable, some bioresorbable, which can serve as scaffolding or anchor for tissue regrowth in the geometrically and chemically controlled environment of an implant. The fabrication, growth and survival of composites of living tissues with synthetic polymers, often enhanced by the incorporation of specific cell growth factors or inhibitors, has been demonstrated at the tissue culture level, and extended in vivo to experimental models of human endocrine deficiency or neurological defects. The key to progress with bioartificial organs is the confluence of knowledge ranging from materials science to cell and molecular biology to experimental surgery. Obstacles to clinical implementation of this new therapeutic concept include: large scale procurement of specific tissue structures or isolated postmitotic cells from animal sources; demonstration of safety and efficacy of spontaneously occurring, bioactive tumor cell lines; verification of long-term stability and bio-acceptance of polymer implants; and industrialization of the fabrication process to meet quality control, shelf-life and commercial distribution requirements.(ABSTRACT TRUNCATED AT 400 WORDS)