Monday November 3 2008
Heart donors may no longer be needed because of advances in stem cell techniques, according to a news story in The Independent. The story suggests scientists are closer to growing replacement organs in a lab after the development of a man-made material that has enabled the growth of beating rat heart tissue from stem cells.
While this technology offers exciting possibilities it will be some time before heart donors are no longer needed, as the article might suggest. Research into growing usable human tissue is still at an early stage and the study in question was actually concerned with the development of a synthetic structure that might allow the successful growth of heart tissue, rather than growing transplantable tissue itself.
The structure tested does have physical properties that might allow beating human heart tissue to be grown, and will feature in further research. Whether or not this technology will allow the growth of usable human tissue and organs will only become apparent several years from now.
Where did the story come from?
Dr George Engelmayr and colleagues from Massachusetts Institute of Technology and the Charles Stark Draper Laboratory carried out this research. The study was funded by the National Institutes of Health and NASA. It was published in the science and engineering journal Nature Materials.
What kind of scientific study was this?
This was a laboratory study
in which researchers were furthering the development of a man-made structure that might be used as a framework for heart cells. Using a biodegradable polyester material called poly(glycerol sebacate) and complex fabrication techniques, researchers created a microscopic scaffold structure to support the growth of stem cells into heart tissue.
The researchers aimed to create a structure that was “biomimetic”, meaning its structure mimicked nature. The researchers created “accordion-like honeycomb scaffolds” which would mimic the structure and stretching properties of heart cells.
The specific quality the researchers were concerned with was ‘anisotropy’ which describes a substance that has different properties, such as stiffness or stretch, depending on the direction in which they’re measured. They reasoned that an anisotopic, accordion-like honeycomb structure would have similar properties to normal heart muscle and would also provide a structure to guide heart muscle fibres.
Once a scaffold had been created, it was assessed for stiffness, its anisotropic qualities and what degree of force would cause it to fail. They repeated these experiments with the scaffold under different conditions compared the results to cells from rat hearts. They also “seeded” the scaffolds with cardiac fibroblasts (connective tissue cells) followed by neonatal rat heart cells and cultured them for one week.
What were the results of the study?
The researchers found that the accordion-like honeycomb structure had properties that resembled native rat hearts in terms of anisotropy. The stiffness of the structure was similar to that seen in an adult rat right ventricule heart muscle. When rat heart muscle cells were grafted on to the scaffolds and cultured, the growing cells organised themselves and aligned in the “preferred direction” along the scaffold, much as they would in a real rat heart.
Following more intensive seeding (distribution of cells onto the structure) with connective tissue cells and heart cells from young mice, most of the honeycomb cells in the structure were filled with rat heart cells after one week and spontaneous contractions of the tissue was seen as early as four days after culturing began.
What interpretations did the researchers draw from these results?
The researchers say that to the best of their knowledge, this is the first study to report development of a scaffold with an accordion-like honeycomb microstructure. They say that the structure can thus overcome “principal structural-mechanical limitations of previous scaffolds, promoting the formation of grafts with aligned heart cells and mechanical properties more closely resembling native myocardium.”
What does the NHS Knowledge Service make of this study?
The study has further progressed investigations that may one day be used as a basis to culture heart structures such as valves and blood vessels. The findings that an ‘accordion-like honeycomb structure’ had similar stiffness to right ventricular heart tissue from rats and that heart cells are able to beat while growing on it suggest the techniques developed could potentially be used in growing human tissues.
This laboratory study also illustrates how a combination of sub-disciplines in science can combine to forward potentially useful research. This being research into materials, stem cell and biomedical techniques allowing the synthesis and testing of new materials with potential practical use in human disease.
Given the early stage of these investigations it will still be some time before we see laboratory-grown organs such as hearts replace the need for organ donors, but this exciting technology will undoubtedly play a role in future research.
Sir Muir Gray adds...
Don’t tear up your donor card just yet.