New Smart Ink May Soon Transform 3D Printing

A team of researchers at Dartmouth College have created a smart ink that converts 3D-printed structures into objects that can change color and shape. The innovation is likely to add additional functionality to 3D printing and could make way for a new generation of printed material.

An example from the research shows how a 3D-printed object composed of hydrogel (G1) can change size after printing. While this example serves to demonstrate the result, other objects can be used as filters or storage devices. (Image credit: Chenfeng Ke)

The progress in the area of form-changing intelligent printing - also called 4D printing - provides an economical alternative to printing precision parts for uses in areas spanning from biomedicine to the energy sector.

This technique gives life to 3D-printed objects. While many 3D-printed structures are just shapes that don't reflect the molecular properties of the material, these inks bring functional molecules to the 3D printing world. We can now print smart objects for a variety of uses.

Chenfeng Ke, Assistant Professor of Chemistry - Dartmouth

A number of 3D printing protocols depend on photo-curing resins and result in hard plastic objects with stiff, but random molecular architectures. The new process enables designers to preserve specific molecular alignments and functions in a material and changes those structures for use in 3D printing.

By applying a combination of the new method in the pre-printing and post-printing processes, the team was able to decrease printed objects to 1% of their original sizes and with 10-times the resolution. Furthermore, the 3D printed objects could be animated to recurrently expand and contract in size due to the use of supramolecular pillars. Due to fluorescent trackers, the objects were able to change color in reaction to an external stimulus such as light.

The ability to decrease the size of an object after printing while keeping functional characteristics and increasing resolution allows low-cost printers to print high-resolution objects that were once only doable with much more hi-tech printers.

According to the research, which was chosen as a VIP paper by Angewandte Chemie, the journal of the German Chemical Society, the smart ink can print at a rough, 300-micron resolution, but the final product would possess a much finer line width of 30 µm.

"This process can use a $1,000 printer to print what used to require a $100,000 printer," said Ke. "This technique is scalable, widely adaptable and can dramatically reduce costs."

To develop the smart ink, the researchers used a polymer-based "vehicle" that combines intelligent molecular systems into printing gel and allows for the change of their functions from the nanoscale to the macroscale.

While a majority of materials are easily hardened during the 3D printing process, the new process adds a series of post-printing reactions which lock the active components together and retain the form of the molecular structure during the printing process.

The result is a printed object possessing a molecular design that is programmed to change itself: If one shines a light on it, it can change color. If one provides it with chemical fuel, it changes shape.

This is something we've never seen before. Not only can we 3D print objects, we can tell the molecules in those objects to rearrange themselves at a level that is viewable by the naked eye after printing. This development could unleash the great potential for the development of smart materials.

Chenfeng Ke, Assistant Professor of Chemistry - Dartmouth

While the researchers feel the technology is still far away from intelligent 3D systems that can dynamically alter their configuration, present uses for the technology could be to print storage devices and precision filters. Over time, the researchers anticipate that the process could result in a new group of macroscale 3D printed objects that can be used to create high-resolution bone replacements or to deliver medicine.

According to the research team involved in the study: "We believe this new approach will initiate the development of small molecule-based 3D printing materials and greatly accelerate the development of smart materials and devices beyond our current grasp that are capable of doing complex tasks in response to environmental stimuli."

In near future, the team expects the smart inks to be beneficial to 3D printing engineers, materials chemists, and others keen on adopting functional materials into 3D printing.

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