Mini human brains have become the latest body part to be grown from stem cells in the laboratory. Does this mean the age of regenerative medicine has arrived?
The concept of growing spare body parts in test tubes has long featured in science fiction, but research using stem cells is now allowing real organs and tissues to be created in laboratories.
This is part of a fast moving field known as regenerative medicine, which promises to provide patients with a catalogue of spare parts to repair and replace damaged or diseased bits of the body.
Already a number of tissues have been successfully created, but most have yet to be tested in the clinic.
So could growing human organs in the laboratory lead to the ability to renew parts of our bodies, or does their value lie elsewhere?
A lab-grown windpipe, created from stem cells that were grown on a scaffold, is the only rudimentary organ to have been successfully transplanted into a patient.
Stem cells taken from the patient’s bone marrow were implanted onto a scaffold that was created by striping a donated trachea of its cells.
The three inch long segment of windpipe was then transplanted into Claudia Castillo, who had suffered damage to her own trachea following a rare form of tuberculosis.
A two year old girl called Hannah Warren who received a windpipe transplant made from plastic fibres and her own stem cells sadly died three months after her operation.
However, replacing relatively simple structures like the trachea remains the most promising form of regenerative medicine at the moment.
Imagine being able to repair a broken bone, or even better replace smashed bones entirely.
A number of research groups around the world are developing techniques to grow human bones from stem cells in the laboratory.
Israeli biotechnology company Bonus BioGroup use three dimensional scans to build a gel-like scaffold of a bone before seeding it with stem cells taken from fat. They then developed into bone .
They have already transplanted the bones into animals.
A team at Keele University led by Professor Alicia El Haj are also working on technology to mend broken bones .
They have developed an injectable gel containing stem cells that have tiny magnetic particles attached to their surface.
By stimulating the area with a magnetic field, they can replicate the mechanical force that would normally be generated by walking around, which allows the bones to grow denser.
They hope to start trials in patients within the next five years.
There is currently no way to compensate for the loss of liver function, which plays an important role in metabolising drugs and removing harmful toxins from the blood stream.
Liver failure patients must rely upon waiting for a transplant and many die before receiving one.
However, tiny functioning human livers have been grown in the laboratory by Japanese researchers.
They announced earlier this year that these tiny organs, known as liver buds, were able to connect to the blood supply and function when transplanted in to mice.
While they are still some way from growing a fully formed human liver, the scientists believe transplanting thousands of these liver buds into patients with liver failure could help restore the function of their own organs.
However, scientists warn it could be sometime before stem cell using lab grown liver buds could be applied to patients.
Another crucial organ that once damaged cannot be easily replaced or repaired.Patients must rely upon dialysis treatment to filter the blood in their body instead.
Transplants are often in short supply and can be rejected by the recipient’s body, so using a patient’s own stem cells to grow a new one would be highly desirable.
In April, scientists reported that they had grown a kidney in the laboratory – making it one of the most complex organs to have been created.
They stripped an old rat kidney of its cells to leave a tangled web of proteins and blood vessels as a scaffold. They then pumped kidney and blood vessel cells through the scaffold and incubated it.
The resulting organ looked more like a sack of pink goo than a kidney, but when they were tested they produced urine at a rate of 23% of natural kidneys. These were then transplanted into rates.
However, the transplanted kidneys were far less effective, only operating at 5% of natural organs.
Another major hurdle is repeating this process with human cells and on something as large as a human kidney.
However, these lab grown organs could provide a more accurate model for testing new drugs and treatments in the laboratory before they are given to human patients.
A similar technique to the one above was used in 2008 to grow whole beating hearts. An old heart was stripped of its cells to leave a collagen structure behind.
This was then repopulated with heart muscle cells.
Earlier this year scientists reported they had produced beating heart tissue from stem cells.
Scientists at the University of Pittsburgh earlier this month announced they had created a beating mouse heart after rebuilding it with human stem cells .
These stem cells had been generated from human skin and “reset” to behave like embryonic stem cells, a type of cell that can grow into any other kind found in the body.
The scientists believe they could use a similar technique to create human heart tissue that can be used in drug testing or for grafts to repair damaged areas.
Scaling up this system to replace an entire human heart, however, will remain a major challenge.
Many researchers see more value in using beating human heart tissue in the laboratory as a tool for studying heart disease and as a way of safely testing new treatments.
This was probably the first organ to be grown in the laboratory and transplanted into patients. Essentially a hollow balloon, scientists at Wake Forest University in North Carolina grew new bladders from bladder cells taken from patients.
They seeded the cells onto a scaffold and grew them for seven weeks before surgically attaching the new bladders to the old bladders of seven patients in 2006.
In 2010 researchers revealed they had been able to grow bladders using stem cells taken from a patients own bone marrow.
The most recent development saw human stem cells derived from skin develop into brain tissue.
The researchers, from Institute of Molecular Biotechnology in Austria, created complex three dimensional brain tissue they described as “mini brains”.
They were found to survive for at least 10 months while kept in a bioreactor that supplied them with nutrients.
However, the main use for these will be to study neurological diseases and test the effects of new drugs on the brain.
It seems unlikely that anyone will seek to transplant an entire brain as without the learning and development that comes from the neurological connections that form over years of life experience, the new brains would be essentially infantile.
They would carry none of the memories nor necessarily have the same ability to control the body. This seems like the most far fetched possibility for a lab grown replacement organ.
But again, these lab grown organs could have far more value in allowing scientists to study neurological conditions like Alzheimer's Disease, potentially opening up new ways of treating and diagnosing the illness.
This tiny hormone-secreting organ is found at the base of the brain but can malfunction in some people, leading to a range of growth related diseases.
Japanese scientists have grown tiny pituitary glands in the laboratory from stem cells taken from a mouse embryo.
When these were transplanted into mice with pituitary gland defects, it raised levels of hormones in the animal's bodies.
The researchers are now working on using human stem cells to create pituitary tissue.
Probably one of the most complex organs in the human body, hopes of growing a whole human eye are still rather beyond the realms of possibility.
However, researchers have shown they can grow the light sensitive tissue at the back of the eye, known as the retina.
Last year, scientists in Japan grew a structure known as the optic cup – a precursor of a human eye.
Measuring just half a millimetre, it contained multiple layers of retinal cells including photoreceptors.
In the experiment, precursor retinal cells spontaneously formed a ball of tissue that bulged outwards to form a bubble called an eye vesicle.
This structure then folded pack on itself to form a pouch, creating the optic cup with an outer wall with a lining of retinal cells.