I'm limited to the materials that Shapeways offers, and titanium is not on the list. To the right of the picture of the ring is a group of small icons with different metallic patterns. If you hover the mouse over those pictures, you'll see the materials Shapeways offers.
I don't know much about silver allergies, but you may want to consider Rhodium Plated. Rhodium is shinier than silver, but has a completely different chemistry.