The advances in 3D printing technology are creating a legal gray space for product liability. Generally, when a person is injured due to a defective product, or failure to warn, the manufacturer, designer, and/or the company that put the product into the marketplace can be found liable for the injury. But 3D printed objects don't exactly fit the current legal framework.
At first blush, one might think that the person who provides the design is going to be liable. However, the first question that arises is whether the design was compatible with the type of printer used. Then, it needs to be asked whether the printer caused the defect. Then, you need to find out whether it was the materials used in the printer that caused the defect.
Also, because 3D printed items require a user to print the design, you need to factor in user error and the ever elusive failure to warn on the part of designer, manufacturer, retailer, and component makers. Clearly, there are many considerations that make finding out who is liable much more difficult than one might initially think.