Stem-cell technique may end need for heart donors

Growing human organs in the laboratory has moved a step closer with the development of a biodegradable material forming a non-living "scaffold" on which beating heart muscle can be grown from stem cells.

The aim is to make three-dimensional organs from scratch, although in the shorter-term scientists will be happy to be able to seed the scaffolding with stem cells in order to mend broken hearts in situ rather than relying on a transplant operation.

Scientists have attempted to grow live human tissue on synthetic scaffolds in the past, but this is the first time that one has been designed specifically to address the unusual demands of a flexible, pumping heart.

Researchers at the Massachusetts Institute of Technology said that growing living heart cells on such a scaffold could lead to the production of tailor-made patches of cardiac muscle that could be used to treat congenital heart defects in the young or chronic heart disease in the elderly.

They have already succeeded in growing layers of contracting heart muscle from the stem cells of rats which became embedded within the honeycomb structure of the scaffolding, where they matured into rhythmically-beating cardiac muscle.

The scaffolding – which degrades over a couple of months leaving no trace – could be adapted for growing a range of tissues for mending other organs such as the liver, kidney, skin or blood vessels, said Lisa Freed, a principal scientist at MIT and Harvard University.

"In the long term, we'd like to have a whole library of scaffolds for different tissues in need of repair. Each scaffold could be tailor-made with specific structural and mechanical properties. We're already on the way to a few other examples," Dr Freed said. "There are some challenges before human trials could take place. The implants are too thin to be of use at this time so we are trying to build them up to make the grafts thicker," she said.

In a study published in the journal Nature Materials, the scientists designed the honeycombed scaffolding to collapse like an accordion in one direction while remaining rigid in another, which could enable heart muscle to grow with the correct directional properties for proper contraction.

George Engelmayr, the lead author of the study, said that the scaffolding material is a synthetic polymer called poly(glycerol sebacate) which degrades within a few weeks to substances that are non-toxic to the body.

The honeycombed structure encourages the growth of stem cells in one direction, just as they would grow in the heart, which produces a tissue that closely matches the properties of the real organ, Dr Engelmayr said.

One application could be the growth of human heart tissue in the test tube for testing new drugs or treatments, which would reduce the number of animals used in medical research.

Eventually the scientists want to develop the scaffolding so that they can grow different components of the heart – such as valves and cardiac muscle patches – which may within a decade or so be combined together before being transplanted into a patient.

"It would theoretically allow us to make different scaffolds, and ultimately use them to make different components of the heart," Dr Engelmayr said. "We could grow individual components of the heart, but piecing them together is a considerable challenge."

Biotechnology: Growing a new heart

*A scaffold is built out of the non-toxic, biodegradable polymer poly(glycerol sebacate).

*The honeycomb structure of the scaffold is manipulated to the desired shape.

*The scaffold is seeded with stem cells, which embed into it.

*The stem cells develop to form living, healthy replacement tissue in the correct form.

*The scaffold biodegrades and it secreted harmlessly from the body.