i'd like to spend some time abroad in a foreign country like an American/Canadan or Asian uni while doing my phd. is this possible and how would i go about doing it? would it have to be with a uni which my uk uni already has a collaboration with? i

my field is bio-nanotechnology

It's unlikly (but not impossible) that you will find a PhD position that will offer this... if your supervisor (not the university) has a collaboration with a lab in one America/Asia then ask during the interview if this will be possible.

I am going to be doing a stint abroad for my upcoming phd – ask your dept whether they have links with other unis – certainly they should have some with some European unis at least. Obviously the study abroad will have to be relevant to ur research ie how will an Asian/American dimension fit into your study? You might want to ask whether you have to justify your time abroad – and how this will add to your whole phd. Good luck!