The researchers at TU Delft in the Netherlands have combined origami techniques and 3D printing to create flat structures that self-fold according to a pre-planned sequence.
“If the goal is to create complex shapes, and it is, some parts should fold sooner than others”, said lead researcher Prof Amir Zadpoor. “Therefore, we needed to programme time delays into the material. This is called sequential shape-shifting.”
According to TU Delft, Prof Zadpoor’s team accomplished this by simultaneously printing and stretching the material in certain places.
“The stretching is stored inside the material as a memory”, said PhD researcher Teunis van Manen. “When heated up, the memory is released and the material wants to go back to its original state.”
By alternating the thickness and the alignment of the filaments in the material, the researchers succeeded in creating 2D-structures that shape-shift sequentially in the way described by Prof Zadpoor.
This combined approach of origami and 3D printing is said to be an important step in the development of better bone implants because the technique makes it possible to create prosthetics with a porous interior.
This will allow a patient’s own stem cells to move into the structure of the implant and attach themselves to the interior surface area, instead of just coating the exterior. The end result will be a stronger, more durable implant.
Secondly, with this technique, nanopatterns that guide cell growth can be crafted on the surface of the implant.
“We call these 'instructive surfaces' because they apply certain forces to the stem cells, prompting them to develop into the cells we want them to be,” said PhD researcher Shahram Janbaz. “A pillar shape, for instance, may encourage stem cells to become bone cells.”
It is impossible to create such instructive surfaces on the inside of a 3D structure. “This is why we decided we needed to start from a flat surface,” said Prof Zadpoor.
For the current research, Zadpoor’s team used an Ultimaker 3D printer that is popular with hobbyists, and PLA, the most common printing material available.
“At about €17 per kilo, its dirt cheap”, said Prof Zadpoor. “Nevertheless, we created some of the most complex shape-shifting ever reported with it.”
A paper - Programming 2D/3D shape-shifting with hobbyist 3D printers – has been published in Materials Horizons.
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