The use of 3D printers is spreading in medical research and development: "researchers have used a 3D printer to create a bone-like material and structure that can be used in orthopedic procedures, dental work, and to deliver medicine for treating osteoporosis. Paired with actual bone, it acts as a scaffold for new bone to grow on and ultimately dissolves with no apparent ill effects. The authors [say] they're already seeing promising results with in vivo tests on rats and rabbits. It's possible that doctors will be able to custom order replacement bone tissue in a few years ... If a doctor has a CT scan of a defect, we can convert it to a CAD file and make the scaffold according to the defect ... The material grows out of a four-year interdisciplinary effort involving chemistry, materials science, biology and manufacturing. A main finding of the paper is that the addition of silicon and zinc more than doubled the strength of the main material, calcium phosphate. The researchers also spent a year optimizing a commercially available ProMetal 3D printer designed to make metal objects. The printer works by having an inkjet spray a plastic binder over a bed of powder in layers of 20 microns, about half the width of a human hair. Following a computer's directions, it creates a channeled cylinder the size of a pencil eraser. After just a week in a medium with immature human bone cells, the scaffold was supporting a network of new bone cells."