Increasing the break dc of Iron Chains?

[CWheezy]

I have a grappler character who likes to tie monsters up in chains. I was wondering if there is a way to up the break dc on them? I was thinking adamantine chains, but I don't think that actually changes the dc of the strength check

[Eridan]

Chains have the same break DC as manacles. Manacles have rules for masterwork and special material versions.

Base DC + Masterwork bonus + Material bonus

Manacles DC 26, hardness 10
Masterwork manacles DC+2 = 28
Mithral (always masterwork) manacles DC+2+2 = 30 , hardness 15

Adamantine is not supported by RAW but you can calculate it as a homerule.

By RAW Adamantine has hardness 20 so that is 5 more than Mithral and 10 more than iron. Base DC is 26 with +2 for every 5 hardness more than 10 and +2 for being masterwork.

Adamantine (always masterwork) manacles DC+2+4 = 32, hardness 20