I saw a talk a few years ago by a German company that was essentially trying to do the same thing. I forgot the name of the company, but I remembered they said

I saw a talk a few years ago by a German company that was essentially trying to do the same thing. I forgot the name of the company, but I remembered they said that expressing the proteins is the easy part. Spinning the proteins into a thread was the tough part. Apparently spiders have special excretion structures/organs that can anneal the proteins to the right conformation extremely quickly as they are ejected. This is why a spider can basically just jump off of anything and shoot out his "bungee cord" while falling which is incredibly fast if you think about it. When the researchers tried to replicate this by simply shooting the concentrated protein solution through a tiny capillary they weren't able to achieve the same molecular structure for their thread nor at the same speed. They noted that their thread was strong, but nevertheless significantly weaker than a spider's. I'm very interested to know if these other companies managed to overcome these challenges and how exactly.