Can you grow a human bone outside the human body?
Can you grow a human bone outside the human body?

The answer may soon be yes,
The answer may soon be yes,

but before we can understand how that's possible,
but before we can understand how that's possible,

we need to look at how bones grow naturally inside the body.
we need to look at how bones grow naturally inside the body.

Most bones start in a growing fetus as a soft, flexible cartilage.
Most bones start in a growing fetus as a soft, flexible cartilage.

Bone-forming cells replace the cartilage with a spongy mineral lattice
Bone-forming cells replace the cartilage with a spongy mineral lattice

made of elements like calcium and phosphate.
made of elements like calcium and phosphate.

This lattice gets harder, as osteoblasts,
This lattice gets harder, as osteoblasts,

which are specialized bone-forming cells,
which are specialized bone-forming cells,

deposit more mineral, giving bones their strength.
deposit more mineral, giving bones their strength.

While the lattice itself is not made of living cells,
While the lattice itself is not made of living cells,

networks of blood vessels, nerves and other living tissues
networks of blood vessels, nerves and other living tissues

grow through special channels and passages.
grow through special channels and passages.

And over the course of development,
And over the course of development,

a legion of osteoblasts reinforce the skeleton
a legion of osteoblasts reinforce the skeleton

that protects our organs, allows us to move,
that protects our organs, allows us to move,

produces blood cells and more.
produces blood cells and more.

But this initial building process alone
But this initial building process alone

is not enough to make bones strong and functional.
is not enough to make bones strong and functional.

If you took a bone built this way,
If you took a bone built this way,

attached muscles to it,
attached muscles to it,

and tried to use it to lift a heavy weight,
and tried to use it to lift a heavy weight,

the bone would probably snap under the strain.
the bone would probably snap under the strain.

This doesn't usually happen to us
This doesn't usually happen to us

because our cells are constantly reinforcing
because our cells are constantly reinforcing

and building bone wherever they're used,
and building bone wherever they're used,

a principle we refer to as Wolff's Law.
a principle we refer to as Wolff's Law.

However, bone materials are a limited resource
However, bone materials are a limited resource

and this new, reinforcing bone
and this new, reinforcing bone

can be formed only if there is enough material present.
can be formed only if there is enough material present.

Fortunately, osteoblasts, the builders,
Fortunately, osteoblasts, the builders,

have a counterpart called osteoclasts, the recyclers.
have a counterpart called osteoclasts, the recyclers.

Osteoclasts break down the unneeded mineral lattice using acids and enzymes
Osteoclasts break down the unneeded mineral lattice using acids and enzymes

so that osteoblasts can then add more material.
so that osteoblasts can then add more material.

One of the main reasons astronauts must exercise constantly in orbit
One of the main reasons astronauts must exercise constantly in orbit

is due to the lack of skeletal strain in free fall.
is due to the lack of skeletal strain in free fall.

As projected by Wolff's Law,
As projected by Wolff's Law,

that makes osteoclasts more active than osteoblasts,
that makes osteoclasts more active than osteoblasts,

resulting in a loss of bone mass and strength.
resulting in a loss of bone mass and strength.

When bones do break, your body has an amazing ability
When bones do break, your body has an amazing ability

to reconstruct the injured bone as if the break had never happened.
to reconstruct the injured bone as if the break had never happened.

Certain situations, like cancer removal,
Certain situations, like cancer removal,

traumatic accidents,
traumatic accidents,

and genetic defects exceed the body's natural ability for repair.
and genetic defects exceed the body's natural ability for repair.

Historical solutions have included filling in the resulting holes with metal,
Historical solutions have included filling in the resulting holes with metal,

animal bones,
animal bones,

or pieces of bone from human donors,
or pieces of bone from human donors,

but none of these are optimal as they can cause infections
but none of these are optimal as they can cause infections

or be rejected by the immune system,
or be rejected by the immune system,

and they can't carry out most of the functions of healthy bones.
and they can't carry out most of the functions of healthy bones.

An ideal solution would be to grow a bone made from the patient's own cells
An ideal solution would be to grow a bone made from the patient's own cells

that's customized to the exact shape of the hole,
that's customized to the exact shape of the hole,

and that's exactly what scientists are currently trying to do.
and that's exactly what scientists are currently trying to do.

Here's how it works.
Here's how it works.

First, doctors extract stem cells from a patient's fat tissue
First, doctors extract stem cells from a patient's fat tissue

and take CT scans to determine the exact dimensions of the missing bone.
and take CT scans to determine the exact dimensions of the missing bone.

They then model the exact shape of the hole,
They then model the exact shape of the hole,

either with 3D printers,
either with 3D printers,

or by carving decellularized cow bones.
or by carving decellularized cow bones.

Those are the bones where all of the cells have been stripped away,
Those are the bones where all of the cells have been stripped away,

leaving only the sponge-like mineral lattice.
leaving only the sponge-like mineral lattice.

They then add the patient's stem cells to this lattice
They then add the patient's stem cells to this lattice

and place it in a bioreactor,
and place it in a bioreactor,

a device that will simulate all of the conditions found inside the body.
a device that will simulate all of the conditions found inside the body.

Temperature, humidity, acidity and nutrient composition
Temperature, humidity, acidity and nutrient composition

all need to be just right for the stem cells to differentiate
all need to be just right for the stem cells to differentiate

into osteoblasts and other cells,
into osteoblasts and other cells,

colonize the mineral lattice,
colonize the mineral lattice,

and remodel it with living tissue.
and remodel it with living tissue.

But there's one thing missing.
But there's one thing missing.

Remember Wolff's Law?
Remember Wolff's Law?

An artificial bone needs to experience real stress,
An artificial bone needs to experience real stress,

or else it will come out weak and brittle,
or else it will come out weak and brittle,

so the bioreactor constantly pumps fluids around the bone,
so the bioreactor constantly pumps fluids around the bone,

and the pressure tells the osteoblasts to add bone density.
and the pressure tells the osteoblasts to add bone density.

Put all of this together, and within three weeks,
Put all of this together, and within three weeks,

the now living bone is ready to come out of the bioreactor
the now living bone is ready to come out of the bioreactor

and to be implanted into the patient's body.
and to be implanted into the patient's body.

While it isn't yet certain that this method will work for humans,
While it isn't yet certain that this method will work for humans,

lab grown bones have already been successfully implanted in pigs
lab grown bones have already been successfully implanted in pigs

and other animals,
and other animals,

and human trials may begin as early as 2016.
and human trials may begin as early as 2016.