'The magic of this field is that it means we
will eventually be able to make body parts
that are as good as, or even better than, the
original,' said Professor Yos Morsi.
Illustration by Justin Garnsworthy

Like an intricate pink flower, a three-leaved valve is gradually forming from human body cells, which are growing around, and within, an elegant polymer framework.

This small, biological construction is part of Swinburne University of Technology’s pioneering research into a new way to mend broken hearts using the revolutionary approach of growing body parts from a combination of natural human cells and a soluble synthetic scaffold that helps them to achieve the desired shape and performance.

The research is being undertaken by Swinburne’s Tissue Engineering group, and team leader Professor Yos Morsi says the ultimate goal is to grow a fully functional human heart, replacing the need for donated organs. While this outcome is still a long way off, the team is applying itself to perfecting one of the heart’s most important and hard-working components, the aortic valve, which enables freshly oxygenated blood to pulse through the body.

Every year, an estimated 300 000 human heart valves are surgically replaced with ones made from synthetic materials or animal tissues. However, such is the wear-and-tear involved in flexing 30 to 40 million times a year as they help pump blood around the body, many of these replacement valves will themselves fail or else harden and need to be replaced, confronting the patient with a second or third round of traumatic surgery.

The answer, Professor Morsi says, is to grow a new valve that is, for all practical purposes, indistinguishable from the original healthy item, and which will become a living part of the patient’s body.

However, the challenge is even greater than it may sound. Although they appear simple, heart valves have a complex, triple-layered structure that is impossible to emulate with a single artificial material. The answer requires the design of a scaffold that enables the body’s cells themselves to do this.

Not only must this scaffold encourage the cells to grow in exactly the right shape, thickness and triple layering devised by nature, it must also quietly dissolve away when its work is done, leaving a fully functioning valve made of the patient’s own tissue that comes with a lifetime guarantee of reliable service.

All this involves a delicate fusion of sciences and engineering – cellular biochemistry, polymer nanochemistry, flow dynamics and computer modelling – in the design of totally novel materials and the subtle manipulation of cell growth patterns.

The Tissue Engineering lab has made steady progress towards this goal, to the point of placing its first engineered ‘natural’ valves in the hearts of experimental animals.

Starting with basic structural materials, such as polyurethane and bovine pericardium (the sac that covers a cow’s heart, currently used to make replacement valves), the team has developed a novel polymer material that is biocompatible – that is, easy to implant without risk of rejection – thin, flexible and hardy enough to bear the physiological stress of 70 beats to the minute, non-stop.

"It must be strong – but not too strong. Thin, but not too thin. Flexible, but not weak," Professor Morsi says. "Above all, cells must be able to attach to it.

"We have already done some in vivo work and we know that our theory works. We can control the rate and direction of the cell growth and match the attributes of a natural valve."

Furthermore, the new polymer is porous, allowing human or animal stem cells to be seeded into it in a defined way that sets them up to align themselves into the natural layers present in a normal heart valve.

The first step is to mould the polymer scaffold into the shape of a human heart valve and then to seed it with vein cells from the patient. The ‘infant’ valves are then cultured for a week or so in a bioreactor while the cells grow. Here they are carefully nurtured on special ‘foods’ that encourage the right sort of development. They are then subjected to pulses of fluid that imitate the heartbeat to influence the structures and layers they form.

Remarkable though it may seem, growing human body parts is now a well-established field, with research progressing globally for producing natural replacements for bone, skin, teeth and nerves, as well as heart valves.

"The magic of this field is that it means we will eventually be able to make body parts that are as good as, or even better than, the original," Professor Morsi says. "This is not only important for the many recipients of replacements today, but also for the growing number of people born with defective organs, whose quality of life will be affected if they are not replaced.

"Tissue-engineered body parts are not only as good as the original but, unlike mechanical or bio-prosthetic parts, they can continue to grow along with the person who receives them. This is especially important for child recipients."

At present, he adds, there are many technical hurdles to be overcome before tissue-engineered heart valves are feasible for human implantation. Understanding risks, evaluating their acceptability, taking adequate steps to reduce the risks and evaluating overall safety considerations must be addressed as tissue-engineered constructs undergo product development. This process is likely to take at least 10 years.

As well as helping to mend many broken hearts the Swinburne project will help create prosperity, injecting a revolutionary product into a global market already worth well over a billion dollars a year, and further cementing Australia’s reputation in the hotly competitive medical biotechology industry.

The research is being carried out in conjunction with Monash University’s Department of Surgery at the Alfred Hospital, where heart specialist Professor Frank Rosenfeldt describes it as extremely promising work.

"The production of a reliable replacement heart valve is a challenge that forward-looking cardiac surgeons have dreamed of for years," Professor Rosenfeldt says. "Yos Morsi has developed a very novel scaffold and succeeded in getting cells to grow on it. The next step is to implant it in animals and see how it performs.

"The progress at Swinburne is very encouraging. It’s an extremely tough nut to crack and a lot of people around the world are trying to do so. Yos’s great strength is his understanding of computational fluid dynamics, which is vital to achieving performance in the valve."