Can you grow a human bone outside the human body?
你可以在人体外长一根骨头吗？
The answer may soon be yes, but before we can understand how that's possible,
答案在不久的将来会变成是的，但在了解这件事是如何达成之前，
we need to look at how bones grow naturally inside the body.
我们首先要知道骨头在身体里是如何自然生长的。
Most bones start in a growing fetus as a soft, flexible cartilage.
多数的骨头从胎儿长起，以柔韧的软骨组织存在。
Bone-forming cells replace the cartilage with a spongy mineral lattice made of elements like calcium and phosphate.
骨形成细胞会和一种海绵状矿物晶格取代这种软骨组织，这种物体是由钙和磷酸盐组成的。
This lattice gets harder, as osteoblasts,
晶格会越变越硬，并成为造骨细胞，
which are specialized bone-forming cells, deposit more mineral, giving bones their strength.
这是一种专用的骨生长细胞，它会产生更多的矿物质，提高骨头的强度。
While the lattice itself is not made of living cells,
晶格并非由活细胞、
networks of blood vessels, nerves and other living tissues grow through special channels and passages.
血管网、神经或其它在特殊的管道中生长的活的组织组成。
And over the course of development, a legion of osteoblasts reinforce the skeleton that protects our organs,
在发展过程中，大量的成骨细胞加固了骨架，骨架可以保护器官，
allows us to move, produces blood cells and more.
让我们移动，也能产生血细胞的骨架等等。
But this initial building process alone is not enough to make bones strong and functional.
但单单这个最初的建造过程不足以让我们的骨头变得强壮及有功能。
If you took a bone built this way, attached muscles to it,
如果你拿着一根这样子的骨头，附上肌肉，
and tried to use it to lift a heavy weight, the bone would probably snap under the strain.
试着用它去举起一个较重的物体，这根骨头很有可能会在强压下折断。
This doesn't usually happen to us because our cells are constantly reinforcing and building bone wherever they're used,
这一般不会在我们身上发生，因为我们的细胞会持续地在身体各处需要用到骨头的地方加固并建造骨头，
a principle we refer to as Wolff's Law.
这种理论来自于沃尔夫定律。
However, bone materials are a limited resource
但是，形成骨头的物质是一种有限的资源，
and this new, reinforcing bone can be formed only if there is enough material present.
这种新加固的骨头只有在物质足够的情况下才能产生。
Fortunately, osteoblasts, the builders, have a counterpart called osteoclasts, the recyclers.
幸运的是，成骨细胞，这个建造者，拥有一个相对的细胞，称为破骨细胞，即循环者。
Osteoclasts break down the unneeded mineral lattice using acids and enzymes so that osteoblasts can then add more material.
破骨细胞会用酸与酶降解不需要的矿物晶格，从而使得成骨细胞可以制造更多的物质。
One of the main reasons astronauts must exercise constantly in orbit is due to the lack of skeletal strain in free fall.
宇航员在太空轨道上必须时常运动的重要原因之一是失重导致的骨骼张力缺失。

As projected by Wolff's Law, that makes osteoclasts more active than osteoblasts, resulting in a loss of bone mass and strength.
根据沃尔夫定律中所提到的，这使得破骨细胞变得比成骨细胞更活跃，导致骨骼质量和力量的减少。
When bones do break, your body has an amazing ability to reconstruct the injured bone as if the break had never happened.
当骨头断掉后，你的身体有一项惊人的能力来重新建造断骨，恢复成未断之前的状态。
Certain situations, like cancer removal, traumatic accidents, and genetic defects exceed the body's natural ability for repair.
但有些情况，例如去除癌细胞，外伤事故和基因缺陷则超出了了身体自己恢复的能力。
Historical solutions have included filling in the resulting holes with metal,
历史上的一些填充由此引发的孔洞的方法有：用金属填充，
animal bones, or pieces of bone from human donors,
用动物的骨头来代替，或采用他人捐献的骨头，
but none of these are optimal as they can cause infections or be rejected by the immune system,
但是这些都不是理想的方法，因为他们都有可能会引起感染或是被人体的免疫系统排斥，
and they can't carry out most of the functions of healthy bones.
而且它们的功能并不像健康的骨头那样齐全。
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,
一个理想的解决方法便是根据孔洞的形状，用伤者自身的细胞重新制造一根。
and that's exactly what scientists are currently trying to do. Here's how it works.
这其实也是科学家正在尝试做的事。他们是这么做的。
First, doctors extract stem cells from a patient's fat tissue
首先，医生会从伤者的脂肪组织中提取出干细胞，
and take CT scans to determine the exact dimensions of the missing bone.
然后做CT扫描来确定缺骨的具体尺寸。
They then model the exact shape of the hole, either with 3D printers, or by carving decellularized cow bones.
他们然后做出这个空洞形状的精准模型，可以用3D打印，也可以在脱细胞牛骨上挖刻出这个形状。
Those are the bones where all of the cells have been stripped away, leaving only the sponge-like mineral lattice.
这些骨头上的细胞全都被剔除出去，只剩下类似海绵一样的矿物晶格。
They then add the patient's stem cells to this lattice and place it in a bioreactor,
科学家接着会把伤者的干细胞填入这些晶格之中，然后放入生物反应器，
a device that will simulate all of the conditions found inside the body.
这是一个可以模仿身体内部环境的仪器。
Temperature, humidity, acidity and nutrient composition all need to be just right for the stem cells
温度，湿度，酸度和营养成分，这些都需要调到合适的程度，
to differentiate into osteoblasts and other cells, colonize the mineral lattice, and remodel it with living tissue.
促使干细胞分裂成为成骨细胞和其他细胞，在矿物晶阁上增殖，然后用活组织来重塑。
But there's one thing missing. Remember Wolff's Law?
但是还缺了一件事情。记得沃尔夫定律吗？
An artificial bone needs to experience real stress, or else it will come out weak and brittle,
人造的骨头需要承受真实的压力，不然的话，它会轻易地断掉或碎裂，
so the bioreactor constantly pumps fluids around the bone, and the pressure tells the osteoblasts to add bone density.
生物反应器会持续地在骨头周围泵入液体，形成压力会让成骨细胞增强骨密度。
Put all of this together, and within three weeks,
一切就绪，在三个星期后，
the now living bone is ready to come out of the bioreactor and to be implanted into the patient's body.
一根活骨便可以从生物反应器中取出，并被移植到伤者的身体里。
While it isn't yet certain that this method will work for humans,
虽然这个方法是否适用于人体还未确定，
lab grown bones have already been successfully implanted in pigs and other animals, and human trials may begin as early as 2016.
但实验室培养的骨头已经成功移植到猪与其他动物的体中，而人体试验最早可能会在2016年开始。