Not sure about oxygen respirators, but some civil organizations in Hong Kong have been 3D-printing filter cans for 3M 6200 face-piece respirators since mid-Febr

Not sure about oxygen respirators, but some civil organizations in Hong Kong have been 3D-printing filter cans for 3M 6200 face-piece respirators since mid-February, amid shortage of surgical face masks. The designs of the filter cans are modified so that, instead of using 3M's particulate filters, one cuts a surgical face mask into many smaller pieces and inserts only one piece of them into the filter can in each use.