[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:06.67,0:00:10.17,Default,,0000,0000,0000,,Can you grow a human bone\Noutside the human body?
Dialogue: 0,0:00:10.17,0:00:12.44,Default,,0000,0000,0000,,The answer may soon be yes,
Dialogue: 0,0:00:12.44,0:00:15.33,Default,,0000,0000,0000,,but before we can understand\Nhow that's possible,
Dialogue: 0,0:00:15.33,0:00:19.48,Default,,0000,0000,0000,,we need to look at \Nhow bones grow naturally inside the body.
Dialogue: 0,0:00:19.48,0:00:24.04,Default,,0000,0000,0000,,Most bones start in a growing fetus\Nas a soft, flexible cartilage.
Dialogue: 0,0:00:24.04,0:00:27.91,Default,,0000,0000,0000,,Bone-forming cells replace the cartilage\Nwith a spongy mineral lattice
Dialogue: 0,0:00:27.91,0:00:30.100,Default,,0000,0000,0000,,made of elements like calcium\Nand phosphate.
Dialogue: 0,0:00:30.100,0:00:33.32,Default,,0000,0000,0000,,This lattice gets harder,\Nas osteoblasts,
Dialogue: 0,0:00:33.32,0:00:35.78,Default,,0000,0000,0000,,which are specialized bone-forming cells,
Dialogue: 0,0:00:35.78,0:00:39.28,Default,,0000,0000,0000,,deposit more mineral,\Ngiving bones their strength.
Dialogue: 0,0:00:39.28,0:00:41.85,Default,,0000,0000,0000,,While the lattice itself\Nis not made of living cells,
Dialogue: 0,0:00:41.85,0:00:45.19,Default,,0000,0000,0000,,networks of blood vessels, nerves\Nand other living tissues
Dialogue: 0,0:00:45.19,0:00:47.88,Default,,0000,0000,0000,,grow through special channels\Nand passages.
Dialogue: 0,0:00:47.88,0:00:49.46,Default,,0000,0000,0000,,And over the course of development,
Dialogue: 0,0:00:49.46,0:00:52.42,Default,,0000,0000,0000,,a legion of osteoblasts\Nreinforce the skeleton
Dialogue: 0,0:00:52.42,0:00:54.75,Default,,0000,0000,0000,,that protects our organs, \Nallows us to move,
Dialogue: 0,0:00:54.75,0:00:57.34,Default,,0000,0000,0000,,produces blood cells and more.
Dialogue: 0,0:00:57.34,0:00:59.60,Default,,0000,0000,0000,,But this initial building process alone
Dialogue: 0,0:00:59.60,0:01:03.16,Default,,0000,0000,0000,,is not enough to make bones \Nstrong and functional.
Dialogue: 0,0:01:03.16,0:01:04.77,Default,,0000,0000,0000,,If you took a bone built this way,
Dialogue: 0,0:01:04.77,0:01:06.73,Default,,0000,0000,0000,,attached muscles to it,
Dialogue: 0,0:01:06.73,0:01:09.27,Default,,0000,0000,0000,,and tried to use it \Nto lift a heavy weight,
Dialogue: 0,0:01:09.27,0:01:13.02,Default,,0000,0000,0000,,the bone would probably snap\Nunder the strain.
Dialogue: 0,0:01:13.02,0:01:14.82,Default,,0000,0000,0000,,This doesn't usually happen to us
Dialogue: 0,0:01:14.82,0:01:17.23,Default,,0000,0000,0000,,because our cells \Nare constantly reinforcing
Dialogue: 0,0:01:17.23,0:01:19.82,Default,,0000,0000,0000,,and building bone wherever they're used,
Dialogue: 0,0:01:19.82,0:01:23.24,Default,,0000,0000,0000,,a principle we refer to as Wolff's Law.
Dialogue: 0,0:01:23.24,0:01:26.28,Default,,0000,0000,0000,,However, bone materials \Nare a limited resource
Dialogue: 0,0:01:26.28,0:01:28.37,Default,,0000,0000,0000,,and this new, reinforcing bone
Dialogue: 0,0:01:28.37,0:01:32.54,Default,,0000,0000,0000,,can be formed only if \Nthere is enough material present.
Dialogue: 0,0:01:32.54,0:01:35.85,Default,,0000,0000,0000,,Fortunately, osteoblasts, the builders,
Dialogue: 0,0:01:35.85,0:01:40.35,Default,,0000,0000,0000,,have a counterpart \Ncalled osteoclasts, the recyclers.
Dialogue: 0,0:01:40.35,0:01:44.62,Default,,0000,0000,0000,,Osteoclasts break down the unneeded\Nmineral lattice using acids and enzymes
Dialogue: 0,0:01:44.62,0:01:48.47,Default,,0000,0000,0000,,so that osteoblasts can then \Nadd more material.
Dialogue: 0,0:01:48.47,0:01:52.33,Default,,0000,0000,0000,,One of the main reasons astronauts\Nmust exercise constantly in orbit
Dialogue: 0,0:01:52.33,0:01:56.85,Default,,0000,0000,0000,,is due to the lack of skeletal strain\Nin free fall.
Dialogue: 0,0:01:56.85,0:01:58.91,Default,,0000,0000,0000,,As projected by Wolff's Law,
Dialogue: 0,0:01:58.91,0:02:02.55,Default,,0000,0000,0000,,that makes osteoclasts more active\Nthan osteoblasts,
Dialogue: 0,0:02:02.55,0:02:06.15,Default,,0000,0000,0000,,resulting in a loss \Nof bone mass and strength.
Dialogue: 0,0:02:06.15,0:02:09.26,Default,,0000,0000,0000,,When bones do break, your body\Nhas an amazing ability
Dialogue: 0,0:02:09.26,0:02:13.85,Default,,0000,0000,0000,,to reconstruct the injured bone\Nas if the break had never happened.
Dialogue: 0,0:02:13.85,0:02:16.52,Default,,0000,0000,0000,,Certain situations, like cancer removal,
Dialogue: 0,0:02:16.52,0:02:18.21,Default,,0000,0000,0000,,traumatic accidents,
Dialogue: 0,0:02:18.21,0:02:23.28,Default,,0000,0000,0000,,and genetic defects exceed the body's \Nnatural ability for repair.
Dialogue: 0,0:02:23.28,0:02:27.49,Default,,0000,0000,0000,,Historical solutions have included\Nfilling in the resulting holes with metal,
Dialogue: 0,0:02:27.49,0:02:29.09,Default,,0000,0000,0000,,animal bones,
Dialogue: 0,0:02:29.09,0:02:31.63,Default,,0000,0000,0000,,or pieces of bone from human donors,
Dialogue: 0,0:02:31.63,0:02:35.03,Default,,0000,0000,0000,,but none of these are optimal\Nas they can cause infections
Dialogue: 0,0:02:35.03,0:02:37.63,Default,,0000,0000,0000,,or be rejected by the immune system,
Dialogue: 0,0:02:37.63,0:02:41.45,Default,,0000,0000,0000,,and they can't carry out most \Nof the functions of healthy bones.
Dialogue: 0,0:02:41.45,0:02:46.36,Default,,0000,0000,0000,,An ideal solution would be to grow a bone\Nmade from the patient's own cells
Dialogue: 0,0:02:46.36,0:02:49.71,Default,,0000,0000,0000,,that's customized to \Nthe exact shape of the hole,
Dialogue: 0,0:02:49.71,0:02:53.98,Default,,0000,0000,0000,,and that's exactly what scientists \Nare currently trying to do.
Dialogue: 0,0:02:53.98,0:02:55.87,Default,,0000,0000,0000,,Here's how it works.
Dialogue: 0,0:02:55.87,0:02:59.86,Default,,0000,0000,0000,,First, doctors extract stem cells from\Na patient's fat tissue
Dialogue: 0,0:02:59.86,0:03:05.18,Default,,0000,0000,0000,,and take CT scans to determine\Nthe exact dimensions of the missing bone.
Dialogue: 0,0:03:05.18,0:03:07.60,Default,,0000,0000,0000,,They then model the exact \Nshape of the hole,
Dialogue: 0,0:03:07.60,0:03:08.92,Default,,0000,0000,0000,,either with 3D printers,
Dialogue: 0,0:03:08.92,0:03:12.13,Default,,0000,0000,0000,,or by carving decellularized cow bones.
Dialogue: 0,0:03:12.13,0:03:14.80,Default,,0000,0000,0000,,Those are the bones where all of the cells\Nhave been stripped away,
Dialogue: 0,0:03:14.80,0:03:18.22,Default,,0000,0000,0000,,leaving only the sponge-like \Nmineral lattice.
Dialogue: 0,0:03:18.22,0:03:21.11,Default,,0000,0000,0000,,They then add the patient's stem cells\Nto this lattice
Dialogue: 0,0:03:21.11,0:03:23.10,Default,,0000,0000,0000,,and place it in a bioreactor,
Dialogue: 0,0:03:23.10,0:03:27.88,Default,,0000,0000,0000,,a device that will simulate all \Nof the conditions found inside the body.
Dialogue: 0,0:03:27.88,0:03:31.02,Default,,0000,0000,0000,,Temperature, humidity, acidity\Nand nutrient composition
Dialogue: 0,0:03:31.02,0:03:34.56,Default,,0000,0000,0000,,all need to be just right for\Nthe stem cells to differentiate
Dialogue: 0,0:03:34.56,0:03:36.93,Default,,0000,0000,0000,,into osteoblasts and other cells,
Dialogue: 0,0:03:36.93,0:03:38.73,Default,,0000,0000,0000,,colonize the mineral lattice,
Dialogue: 0,0:03:38.73,0:03:41.87,Default,,0000,0000,0000,,and remodel it with living tissue.
Dialogue: 0,0:03:41.87,0:03:43.64,Default,,0000,0000,0000,,But there's one thing missing.
Dialogue: 0,0:03:43.64,0:03:45.31,Default,,0000,0000,0000,,Remember Wolff's Law?
Dialogue: 0,0:03:45.31,0:03:48.14,Default,,0000,0000,0000,,An artificial bone needs \Nto experience real stress,
Dialogue: 0,0:03:48.14,0:03:51.09,Default,,0000,0000,0000,,or else it will come out weak and brittle,
Dialogue: 0,0:03:51.09,0:03:54.66,Default,,0000,0000,0000,,so the bioreactor constantly pumps\Nfluids around the bone,
Dialogue: 0,0:03:54.66,0:03:59.50,Default,,0000,0000,0000,,and the pressure tells the osteoblasts\Nto add bone density.
Dialogue: 0,0:03:59.50,0:04:02.11,Default,,0000,0000,0000,,Put all of this together,\Nand within three weeks,
Dialogue: 0,0:04:02.11,0:04:04.99,Default,,0000,0000,0000,,the now living bone is ready \Nto come out of the bioreactor
Dialogue: 0,0:04:04.99,0:04:08.02,Default,,0000,0000,0000,,and to be implanted \Ninto the patient's body.
Dialogue: 0,0:04:08.02,0:04:11.58,Default,,0000,0000,0000,,While it isn't yet certain that \Nthis method will work for humans,
Dialogue: 0,0:04:11.58,0:04:15.46,Default,,0000,0000,0000,,lab grown bones have already been\Nsuccessfully implanted in pigs
Dialogue: 0,0:04:15.46,0:04:17.13,Default,,0000,0000,0000,,and other animals,
Dialogue: 0,0:04:17.13,0:04:20.66,Default,,0000,0000,0000,,and human trials may begin\Nas early as 2016.