This article describes a successful effort in Italy to convert full face scuba masks to full-face CPAP masks that can be used for CPAP therapy, using 3D printing. CPAP is a useful therapy for some COVID-19 patients, but is difficult to provide in hospitals because a standard CPAP mask generates a lot of aerosol spray. A full helmet-style mask solves this problem.
This is a great effort because a)it still works even if the hospital is out of ventilators (CPAP machines are cheap and plentiful in most western countries) and b)It uses a commercially available, manufactured item as the base, so only a few bits and bobs need to be 3D printed. Notice how fast they were able to ship 100 units to the local hospital!