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

  • The answer may soon be yes,

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

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

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

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

  • made of elements like calcium and phosphate.

  • This lattice gets harder, as osteoblasts,

  • which are specialized bone-forming cells,

  • deposit more mineral, giving bones their strength.

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

  • networks of blood vessels, nerves and other living tissues

  • grow through special channels and passages.

  • And over the course of development,

  • a legion of osteoblasts reinforce the skeleton

  • that protects our organs, allows us to move,

  • produces blood cells and more.

  • But this initial building process alone

  • is not enough to make bones strong and functional.

  • If you took a bone built this way,

  • attached muscles to it,

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

  • the bone would probably snap under the strain.

  • This doesn't usually happen to us

  • because our cells are constantly reinforcing and building bone

  • wherever they're used,

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

  • However, bone materials are a limited resource

  • and this new, reinforcing bone

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

  • Fortunately, osteoblasts, the builders,

  • have a counterpart called osteoclasts, the recyclers.

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

  • so that osteoblasts can then add more material.

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

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

  • As projected by Wolff's Law,

  • that makes osteoclasts more active than osteoblasts,

  • resulting in a loss of bone mass and strength.

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

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

  • Certain situations, like cancer removal, traumatic accidents,

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

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

  • animal bones, or pieces of bone from human donors,

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

  • or be rejected by the immune system,

  • 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

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

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

  • Here's how it works.

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

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

  • They then model the exact shape of the hole,

  • either with 3D printers,

  • or by carving decellularized cow bones.

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

  • leaving only the sponge-like mineral lattice.

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

  • and place it in a bioreactor,

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

  • Temperature, humidity, acidity and nutrient composition all need to be just right

  • for the stem cells to differentiate into osteoblasts and other cells,

  • colonize the mineral lattice,

  • and remodel it with living tissue.

  • But there's one thing missing.

  • Remember Wolff's Law?

  • An artificial bone needs to experience real stress,

  • or else it will come out weak and brittle,

  • so the bioreactor constantly pumps fluids around the bone,

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

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

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

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

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

  • lab grown bones have already been successfully implanted in pigs and other animals,

  • and human trials may begin as early as 2016.

Can you grow a human bone outside the human body?

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B2 US TED-Ed bone lattice mineral wolff patient

【TED-Ed】How to grow a bone - Nina Tandon

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    Ann posted on 2015/07/12
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