Materialists - developed - method of 4D-printing, which allows creating objects from materials with shape memory. It is based on the curing of photosensitive materials with the help of projector light - the authors called the technique a projection microstereolithography. High resolution printing provides a higher rate of reaction of materials to temperature changes.
One of the most famous materials with shape memory is nitinol - an alloy of nickel and titanium. If you temper the spring from such a material, and then, in a cold form, straighten it, then under the influence of heating it again curls into a spring. This effect is due to the fact that the alloy consists of elongated needle-like grains - martensites. After hardening, the grains are in a normal, relaxed state. The deformation of the material leads to mechanical strains in the grains, which, when heated, relax, restoring the original shape.
Source "The Eiffel Tower model restores the shape after deformation."
Memory of the form is found not only in alloys - polymeric materials with such properties are well known. Typically, such materials consist of two components, flexible and rigid - for example, a long polymer chain can consist of a flexible fragment (polyethylene glycol) connected to a rigid (polyethylene terephthalate). The temperature dependence of the mechanical properties of these components should differ - the violation of the crystal structure (vitrification) of the rigid component should occur at higher temperatures than the loss of the crystal structure (or even melting) of the first component.
It is the rigid component of the polymer material that is responsible for the restoration of the mold. When the polymer is deformed, stresses arise in it, from which it can not escape due to the small mobility of the surrounding molecules. However, at sufficiently high temperatures, the mobility of the flexible component increases and the material restores the shape.
Unlike alloys, polymers can recover their shape not only under the action of heat - materials are known in which the transition is triggered by light, electricity or chemical reaction. Another advantage of polymers over alloys is ease of processing - such materials can be printed even on 3D printers.
The higher the print resolution, the faster the shape is restored. Modern methods allow the creation of elements a few millimeters in size, which greatly slows down the response of objects. In order to cope with this circumstance, we developed a new printing technique capable of creating elements thick in human hair.
Source "Principle of printing".
The method is similar to liquid 3D printing with light curing, but as a light source, a projector with ultraviolet light-emitting diodes was used here. The photosensitive polymer was poured into the printer's capacity and the layers of the object were created. Each new layer was cured at the previous one, resulting in a three-dimensional object. Changing the type of polymer can achieve printing from several different materials. The printer asks not only the form of the object, but also its behavior over time - the ability to recover after deformations.
To test the functionality of the technology, materials scientists printed a soft polymer manipulator - a gripper, which is closed in a deformable state. With its help, scientists were able to successfully capture small objects (for example, bolts). To do this, the manipulator was brought to the object and heated the air around it to a temperature above 40 degrees. The temperature of recovery of the material form lies in the range from 40 to 180 degrees Celsius, and the process itself took only a few seconds.
According to scientists, technology can have medical applications. For example, it is possible to create capsules that can release antipyretic substances when the body temperature rises. To do this, the authors are looking for materials that will have a slightly lower temperature for starting the recovery of the form than those used in the work.
3D printing from soft materials is a complex technological task. Due to the fact that curing takes some time, the material may be in time to shift, which will violate the required shape. One solution to this problem is the use of hydrogels. Thanks to the use of a chemical "hardener", fed through a thin needle into the cells of the hydrogel, the engineers managed to print an object resembling a jellyfish and other mobile structures.