Researchers have engineered artificial human ears that look and act like the real thing thanks to 3D printing, giving hope to patients missing all or part of their ears. The new ears, practically identical to human ones, could provide the solution long sought by reconstructive surgeons to treat thousands of children born with the congenital deformity microtia, along with those who suffered ear loss to cancer or in an accident. In a study published online in the PLOS ONE journal, Cornell biomedical engineers and Weill Cornell Medical College physicians said the flexible ears grew cartilage over three months to replace the collagen used to mold them. "This is such a win-win for both medicine and basic science, demonstrating what we can achieve when we work together," said co-lead author Lawrence Bonassar, associate professor of biomedical engineering at Cornell. Bonassar and his colleagues first constructed the ears with a digitized 3D image of a person's ear that served to build a mold of a solid ear using a 3D printer. A high-density, injectable gel made of living cells helped fill the mold. Once the mold removed, cartilage was grown on the collagen. And researchers praised the speed of the process, noting it takes half a day to build the mold, about a day to print it, 30 minutes to inject the gel and the ear can be removed just 15 minutes later. "We trim the ear and then let it culture for several days in nourishing cell culture media before it is implanted," Bonassar said in a statement. Microtia, when the external ear is not fully developed, occurs in about 1 to four per 10,000 births each year in the United States. Although children born with the deformity often have an intact inner ear, they lose hearing due to the missing external structure. Weill Cornell associate professor Jason Spector noted that physicians could reduce the chances of rejection by using human cells from the same patient to build the ear. The best time to implant a bioengineered ear on a child would be around the age of five or six, when ears are at about 80 percent of their adult size. Spector predicted that researchers could try the first human implant of a Cornell bioengineered ear in as little as three years. Replacement ears are usually built using materials with a foam-like consistency, or using a patient's harvest rib. But the process is often painful, especially for children, as the ears rarely look natural or perform well.