3-​​D printing method for creating patient-​​specific medical devices

We’ve all seen pic­tures of pre­ma­ture babies in neonatal care units: tiny beings, some weighing just a bit over a pound, with plastic tubes snaking through their nose or mouth, or dis­ap­pearing into veins or other parts of the body. Those tubes, or “catheters,” are how the babies get the nec­es­sary oxygen, nutri­ents, fluid, and med­ica­tions to stay alive. In the United States alone, nearly 500,000 pre­ma­ture babies are born each year.

The problem is, today’s catheters only come in stan­dard sizes and shapes, which means they cannot accom­mo­date the needs of all pre­ma­ture babies. “With neonatal care, each baby is a dif­ferent size, each baby has a dif­ferent set of prob­lems,” says Ran­dall Erb, assis­tant pro­fessor in the Depart­ment of Mechan­ical and Indus­trial Engi­neering. “If you can print a catheter whose geom­etry is spe­cific to the indi­vidual patient, you can insert it up to a cer­tain crit­ical spot, you can avoid punc­turing veins, and you can expe­dite delivery of the contents.”

Erb’s team has devel­oped an inno­v­a­tive 3-​​D printing tech­nology that uses mag­netic fields to shape com­posite materials—mixes of plas­tics and ceramics—into patient-​​specific prod­ucts. The bio­med­ical devices they are devel­oping, which include catheters, will be both stronger and lighter than cur­rent models and, with their cus­tomized design, ensure an appro­priate fit. Their paper on the new tech­nology appears in the Oct. 23 issue of Nature Com­mu­ni­ca­tions.

Back to nature

Others have used com­posite mate­rials in 3-​​D printing, says Joshua Martin, the doc­toral can­di­date who helped design and run many of the exper­i­ments for the paper. What sets their tech­nology apart, say Erb and Martin, is that it enables them to con­trol how the ceramic fibers are arranged—and hence con­trol the mechan­ical prop­er­ties of the mate­rial itself.

That con­trol is crit­ical if you’re crafting devices with com­plex archi­tec­tures, such as cus­tomized minia­ture bio­med­ical devices. Within a single patient-​​specific device, the cor­ners, the curves, and the holes must all be rein­forced by ceramic fibers arranged in just the right con­fig­u­ra­tion to make the device durable. This is the strategy taken by many nat­ural com­pos­ites from bones to trees.

Con­sider the struc­ture of human bone. Fibers of cal­cium phos­phate, the min­eral com­po­nent of bone, are nat­u­rally ori­ented just so around the holes for blood ves­sels in order to ensure the bone’s strength and sta­bility, enabling, say, your femur to with­stand a daily jog.

“We are fol­lowing nature’s lead,” explains Martin, PhD’17, “by taking really simple building blocks but orga­nizing them in a fashion that results in really impres­sive mechan­ical prop­er­ties.” Using mag­nets, Erb and Martin’s 3-​​D printing method aligns each minus­cule fiber in the direc­tion that con­forms pre­cisely to the geom­etry of the item  being printed.

“These are the sorts of archi­tec­tures that we are now pro­ducing syn­thet­i­cally,” says Erb, who has received a $225,000 Small Busi­ness Tech­nology Transfer grant from the National Insti­tutes of Health to develop the neonatal catheters with a local com­pany. “Another of our goals is to use cal­cium phos­phate fibers and bio­com­pat­ible plas­tics to design sur­gical implants.”

Mag­netic attraction

The mag­nets are the defining ingre­dient in their 3-​​D printing tech­nology. Erb ini­tially described their role in the composite-​​making process in a 2012 paper in the journal Sci­ence.

First the researchers “mag­ne­tize” the ceramic fibers by dusting them very lightly with iron oxide, which, Martin notes, has already been FDA approved for drug-​​delivery appli­ca­tions. They then apply ultralow mag­netic fields to indi­vidual sec­tions of the com­posite material—the ceramic fibers immersed in liquid plastic—to align the fibers according to the exacting spec­i­fi­ca­tions dic­tated by the product they are printing.

In a video accom­pa­nying the Sci­ence article, you can see the fibers spring to atten­tion when the mag­netic field is turned on. “Mag­netic fields are very easy to apply,” says Erb. “They’re safe, and they pen­e­trate not only our bodies—think of CT scans—but many other materials.”

Finally, in a process called “stere­olith­o­g­raphy,” they build the product, layer by layer, using a computer-​​controlled laser beam that hardens the plastic. Each six-​​by-​​six inch layer takes a mere minute to complete.

“I believe our research is opening a new fron­tier in materials-​​science research,” says Martin. “For a long time, researchers have been trying to design better mate­rials, but there’s always been a gap between theory and exper­i­ment. With this tech­nology, we’re finally scratching the sur­face where we can the­o­ret­i­cally deter­mine that a par­tic­ular fiber archi­tec­ture leads to improved mechan­ical prop­er­ties and we can also pro­duce those com­pli­cated architectures.”