Time was, all medical devices were treated as medicines under the law. That changed in 1976, when Congress finally allowed the Food and Drug Administration to draw a bright line between drugs, which worked by "chemical action," and medical devices that were often mechanical in nature.

The line between drugs and devices has become blurry again — a fact on display this week at the Minneapolis Convention Center, where 1,100 scientists, doctors and biotech business people converged for the annual conference of the Society for ­Biomaterials, which concludes Saturday.

"Where Materials Become Medicine" was the tagline for the four-day conference. Under that banner, speakers talked about using chemical reactions and clever new materials to cut down on infections, build personalized body parts, do research on human tissue "printed" by a machine and many other applications.

In the latter example, representatives with the year-old Swedish company Cellink chatted up curious university researchers on the expo floor while a machine called the Inkredible+ Bioprinter quietly manufactured a nose.

It wasn't really a nose, of course. It was smaller than an adult nose would be, and was composed only of the special gel that Cellink's "bioprinters" are designed to extrude, layer by layer, just like an ordinary 3-D printer. But in research labs, scientists use "bioink" gels that contain living cells. The company has gels that mix well with bone cells, brain cells and other tissues commonly used in pharmaceutical and medical-device research. Stem cells can also be used.

"The whole industry is moving toward using animals less and human tissue more," in preclinical medical experiments, said Cellink CEO Erik Gatenholm, delivering his sales pitch. "You want to work with human tissue as much as you can, and the only way to do that is to print it."

Nearby, Minnesota's own Mayo Clinic was exhibiting the work of its Biomaterials and Histomorphometry Core lab, which works on a large swath of projects that blend the macroscopic functionality of medical devices with molecular-level reactions to improve patient care.

The Mayo table included a goat jaw impregnated with a chunk of titanium next to a similar-looking mandible that was treated with a novel biomaterial instead of metal. On its own, the whitish biomaterial is light and is filled with symmetrical holes through which bone grows. Once implanted, the material dissolves to leave behind more or less "natural" bone.

In the main hall, Boston Scientific's Barbara Huibregtse said the well-known story of stent medicine is essentially a ­biomaterials story.

In the 1970s, doctors typically opened clogged arteries by threading a small balloon into the blood vessel and inflating it. But many patients' vessels had ­"elastic recoil" that caused them to narrow again over time. The 1980s saw the development of small metal-mesh tubes called stents that were intended to permanently hold a vessel open.

But for various reasons those stents can also close over time, so scientists developed the "drug-eluting" stent, which is coated in a special polymer that slowly releases a drug that is supposed to ­prevent vascular re-closure. "We really have improved patient care through biomaterials," Huibregtse said Friday.

The next wave of stents may be made of materials that are absorbed into the vessel wall and eventually dissolve completely. In July, the FDA approved the nation's first fully absorbable coronary stent, which was Abbott Laboratories' Absorb GT1 device. (The agency announced last month that it was investigating an increased rate of major adverse cardiac events in patients who got an Absorb GT1 device, though that didn't come up in Huibregtse's talk.)

Although Minnesota is known for its cluster of traditional medical-technology companies, the annual biomaterials conference landed in Minneapolis this year because of the state's strong presence in many different areas of health technology.

A Chaska-based company called Lifecore Biomedical manufactures a naturally occurring chemical called sodium hyaluronate, which is widely used in research for orthopedic and ophthalmological products, a company business-development manager explained over a table of free pens displaying the company name.

Next to the Lifecore booth was Shakopee-based ­TestResources, which manufactures machines that can be used to test biomaterials. On the other side of the exhibit hall was Eden Prairie's MTS Systems Corp., a firm that also sells machines that can be used to measure the resiliency of novel materials.

"The discoveries that are reported here at this meeting are some of the most basic ones with human health," said Society for Biomaterials President Liisa Kuhn, who also works at the University of Connecticut. "This is where biomaterials are impacting human health."