A 0.05mm x 0.50mm microstent.
PHOTO: CARMELA DE MARCO / ETH ZURICH

Swiss researchers have developed a new method for producing malleable microstructures – enabling vascular stents that are 40x smaller than previously possible. Such stents could be used to help widen life-threatening constrictions of the urinary tract of gestating fetuses.

Approximately 1 in every 1,000 children develop a urethral stricture, sometimes when they are still in the womb. To prevent life-threatening levels of urine from accumulating in the bladder, pediatric surgeons have to surgically remove the affected section of the urethra and sew the open ends of the tube back together. A stent inserted to widen the constriction would be less damaging to the kidneys while the fetus is still in utero.

Stents successfully treat blocked coronary vessels, but a fetus’ urinary tract is much narrower in comparison. Conventional methods couldn’t produce stents with small enough dimensions, which is why Kantonsspital Aarau pediatric surgeon Gaston De Bernardis approached the Multi-Scale Robotics Lab at ETH Zurich. The lab’s researchers have developed a method that produces highly detailed structures measuring less than 100µm in diameter.

Indirect 4D printing can also be used to create any number of structures. De Marco and her colleagues have also used the method to produce helices made of hydrogel that is filled with magnetic nanoparticles. In a rotating magnetic field, these microstructures start to swim – like artificial bacterial flagella.
PHOTO: CARMELA DE MARCO / ETH ZURICH

Indirect 4D printing

“We’ve printed the world’s smallest stent with features 40x smaller than any produced to date,” says Carmela De Marco, lead author of the study and Marie Sklodowska-Curie fellow in Bradley Nelson’s research group.

The researchers use heat from a laser beam to cut a three-dimensional template – 3D negative – into a micro-mold layer that can be dissolved with a solvent. They then fill the negative with a shape-memory polymer and set the structure using ultraviolet (UV) light. Finally, they dissolve the template in a solvent bath and the three-dimensional stent is finished.

It’s the stent’s shape-memory properties that give it its fourth dimension. Even if the material is deformed, it remembers its original shape and returns to this shape when warm. The extra dimension generated the process’ name – indirect 4D printing.

“The shape-memory polymer is suitable for treating urethral strictures. When compressed, the stent can be pushed through the affected area. Once in place, it returns to its original shape and widens the constricted area of the urinary tract,” De Bernardis explains.

These stents are still a long way from finding real-world application. Before human studies can be conducted, the stents must first be tested in animal models.

Initial findings are promising, “We firmly believe that our results can open the door to the development of new tools for minimally invasive surgery,” De Marco concludes.

ETH Zurich
https://ethz.ch