Printing enters the 4th dimension

Experimental 4D printing, in which objects can change their shapes independently, holds promise for medicine, infrastructure and other fields.

Imagine a tube, a pipe, a cube or even a building. Now watch it move, change its shape, and adjust to its environment on its own.

That is the magic of 4D printing, a promising technology that is under development in several major laboratories, including at the Massachusetts Institute for Technology and Harvard University.

University of Michigan scientists have already developed 4D printed biomedical splints that are implanted in infants who cannot breathe on their own.

One recipient is Garrett Peterson, a Utah infant who suffered from bronchomalacia, or weak cartilage in the sides of his bronchial tubes, which caused his airways to collapse. The boy clung to life on a ventilator for the first 16 months of his life.

Splint adapts to body

Peterson received a 4D splint developed by Scott Hollister, a medical engineer at the University of Michigan. The splint can change its shape as the infant’s body develops and will last several years while the child’s bronchial cartilage repairs itself.

“4D printing” refers both to objects that use “smart materials” that can self-assemble as well as objects like the splints that can change shape and conform to their environment over time.

The term was popularized in a 2013 TED talk by Skylar Tibbits, a computational architect and researcher at MIT’s Self-Assembly Lab, who said the fourth dimension in 4D printing is time.

Applications for infrastructure

Tibbits said that the emerging technology will enable the printing of objects that can reshape themselves or self-assemble themselves over time, such as buildings that can repair themselves or pipes that are able to sense when to expand or contract.

Tibbits sees the emerging technology as a path to lighter, more resilient objects and structures that will be more energy efficient.

Tibbits technique fabricates prints that are composed of a rigid polymer and a soft, activated component. The materials are arranged in segments that transform when they come into water or another source of energy, bending or expanding. The objects he has created include self-folding strands and self-folding cubes.

Tibbits sees a future when infrastructure can repair itself and adapt to new conditions.

“All of these future programmable products will not just be thrown away when they fail; rather, they will error-correct and self-repair to meet new demands,” Tibbits said.

Objects mimic plants

At Harvard’s Wyss Institute for Biologically Inspired Engineering, meanwhile, scientists are creating flat gel objects that expand to three dimensions and change their shape, mimicking plant movements, when they are put into water.

The Harvard team uses microfibers derived from wood in an attempt to emulate the nature structure of plants in that they are bendable. The objects look like flowers and when they enter the water, the petals expand, curl and fold in towards the center.

The University of Michigan team made its splints by printing layers of polycaprolactone, a biomaterial. The splints have been implanted in four babies, and each was able to go home within weeks of their surgeries.

The process of making a customized splint is precise but it can be completed in one day, according to Hollister, who said as many as 200 splints can be printed at one time.

Medical use will expand

They must be compatible with a patient’s immune system and able to resist external compression from surrounding tissue, be able to expand with growth of the body and last at least two years. Then, the splint will dissolve and be excreted from the body.

Hollister and Dr. Robert Morrison, a resident otolaryngology-head and neck surgeon at the University of Michigan, see other 4D implants in the future and they are researching their use to correct skeletal problems.

The researchers believe that the 4D biomedical printing field will grow rapidly as new uses evolve.

“I think in the next five years, we will see an explosion of clinicians coming to table with new ideas for the use of this,” Morrison said.