and all of them working for a little while and then failing.

虽不是无用功但所有改进都以失败而告终
You can imagine it's a hard engineering problem,

可以想象这是一个很难的工程学问题
a difficult engineering problem,

非常难的工程问题
because you need to make this material strong enough

因为你需要让这种作为血管的材料
that it serves as a vessel.

足够坚固
It's got to withstand blood pressure, not burst.

它要能维持血压不会破裂
It's got to be strong enough to put a stitch into

它还得能受得住针扎
because you've got to sew this into the natural artery.

因为你要将它缝到人体动脉当中
It's got to have good mechanical properties on its own

这种材料自身要具有良好的机械性能
but still allow the formation of a natural tissue around it.

还要让天然组织能够包覆住它
All those criteria turn out to be difficult to meet.

结果表明这些标准很难达到
I want to talk in detail about an advance

我想仔细讲讲