Scientists produce 3D printed microscopic "life-like" creatures from smart polymer

Scientists at Heidelberg University could open up new opportunities in fields such as micro-robotics or biomedicine by using additive manufacturing.

Published in the Advanced Functional Materials on February 6, the printed microstructures are made from cutting-edge substances known as smart polymers, whose size and mechanical characteristics can be precisely and on-demand adjusted. 

"Manufacturing programmable materials whose mechanical properties can be adapted on demand is highly desired for many applications," states Junior Professor Dr. Eva Blasco, group leader at the Institute of Organic Chemistry and the Institute for Molecular Systems Engineering and Advanced Materials of Heidelberg University.

The concept of 4D printing

The term "4D printing" refers to this idea, and the "extra fourth dimension" describes how three-dimension printed items can change over time. Shape memory polymers, which are intelligent materials that can recover their original shape from a distorted condition in reaction to external stimuli like temperature, are a well-known example of materials for 4D printing.

One of the first examples of 3D printed shape memory polymers at the microscale was recently shown by the team under Prof. Blasco's guidance.

The researchers created a new shape memory material that can be 3D printed with a high resolution both at the macro and micro scales in collaboration with the working group of biophysicist Prof. Dr. Joachim Spatz, a researcher at Ruperto Carola and Director at the Max Planck Institute for Medical Research. The structures contain box-shaped microarchitectures with reopenable lids that close in reaction to heat.

"These tiny structures show unusual shape memory properties at low activation temperatures, which is extremely interesting for bioapplications," explains Christoph Spiegel, a doctoral researcher in the working group of Eva Blasco.

Alkoxyamines are well suited

The researchers used adaptive materials to create much more complex 3D microstructures with "life-like" properties, such as geckos, octopuses, and even sunflowers. According to Heidelberg researchers, alkoxyamines are particularly well suited for this purpose.

Following the printing process, these dynamic bonds allow the complex, micrometric structures to grow eight-fold in a matter of hours and harden while remaining in shape.

"Conventional inks do not have such features," Prof. Blasco emphasizes. "Adaptive materials with dynamic bonds have a promising future in 3D printing."

Researchers from the Karlsruhe Institute of Technology (KIT) who specialize in materials also took part in the study of adaptive materials with "life-like" properties. The investigation was also financed by the Carl Zeiss Foundation and the German Research Foundation.

Abstract:

A novel and versatile shape memory ink system allowing 4D printing with light at the macroscale as well as the microscale is presented. Digital light processing (DLP) and direct laser writing (DLW) are selected as suitable 3D printing technologies to cover both regimes. First, a system based on monofunctional isobornyl acrylate and two crosslinkers consisting of a soft and a hard diacrylate is identified and proven to be compatible with both printing techniques. Employing DLP, a large variety of structures exhibiting distinct complexity is printed. These structures range from simple frames to more demanding 3D geometries such as double platform structures, infinity rings, or cubic grids. The shape memory effect is demonstrated for all the 3D geometries. Excellent shape fixity as well as recovery and repeatability is shown. Furthermore, the formulation is adapted for fast 4D printing at the microscale using DLW. Importantly, the 4D printed microstructures display remarkable shape memory properties. The possibility of trapping and releasing microobjects, such as microspheres, is ultimately demonstrated by designing, smart box-like 4D microstructures that can be thermally actuated—evidencing the versatility and potential of the reported system.