Researchers at ETH Zurich have developed a new method for producing malleable microstructures, including vascular stents that are 40 times smaller than previously possible.

In the future, such stents could be used to widen life-threatening constrictions of the urinary tract.

The new method, called “indirect 4D printing,” produces highly detailed structures measuring less than 100 micrometers in diameter.

The technique uses a laser beam’s heat to cut a three-dimensional template into a dissolvable micromold layer.

The researchers filled the template, or “3D negative” with a shape-memory polymer and set the structure using UV light. Finally, the template was dissolved in a solvent bath, completing the three-dimensional stent.

The fourth dimension in the printing technique refers to the stent’s shape-memory properties. Even when deformed, the material “remembers” its original shape and returns to this shape when warm.

Approximately one in every thousand children develops a urethral stricture, sometimes even when they are still a fetus in the womb. In order to prevent life-threatening levels of urine from accumulating in the bladder, pediatric surgeons like Gaston De Bernardis at the Kantonsspital Aarau in Switzerland have to surgically remove the affected section of the urethra and sew the open ends of the tube back together again.

A stent that could widen the urethra, however, would cause less damage to the kidneys.

ETH Zurich’s shape-memory polymer is suitable for treating urethral strictures, according to pediatric surgeon Dr. De Bernadis, who approached the Multi-Scale Robotics Lab at ETH Zurich for a solution.

“When compressed, the stent can be pushed through the affected area,” said Dr. De Bernardis. “Then, once in place, it returns to its original shape and widens the constricted area of the urinary tract.”

Before human studies can be conducted to show whether they are suitable for helping children with congenital urinary tract defects, however, the stents must first be tested in animal models.

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Hydrogel helices produced by indirect 4D printing from ETH Zurich
Indirect 4D printing can also be used to create any number of other 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. (Image Credit: Carmela de Marco / ETH Zurich)