3D Printed Photoresponsive Sunflower Could Have Applications in Soft Robotics and Biomedical Devices

It’s no secret that receiving flowers from someone can brighten your day – it’s nice to know that the other person is thinking of you, most flowers have a lovely smell, and they’re not bad to look at either. However, flowers of the 3D printed variety are more than just a collection of pretty petals. While we’ve seen 3D printed flowers used as unique works of art and advertisements, they’ve also proved to be very helpful when used to study plant evolution, and they can even have applications in the field of soft robotics. This is what a team of scientists from Nanyang Technological University (NTU) in Singapore are currently studying, within the fascinating field of biomimetics. They’ve used shape memory composites to create a 3D printed, photoresponsive device: a synthetic flower that blooms on its own whenever it’s exposed to light.

By studying the blooming 3D printed flower and the material used to create it, chemists at the university, which recently opened a new 3D printing research center, believe that the unique material could be used to help create new opportunities for developing soft robotics and smart biomimetic devices. NTU materials scientist Xiaodong Chen is leading the team, which developed a modified polyurethane that shows shape memory, and, when it’s illuminated, can recover its original shape.

The research team published a paper in the Advanced Materials journal about their work, titled “3D Printed Photoresponsive Devices Based on Shape Memory Composites.” In addition to Chen, co-authors include Hui Yang, Wan Ru Leow, Ting Wang, Juan Wang, Jiancan Yu, Ke He, Dianpeng Qi, and Changjin Wan, all of whom work with the university’s Innovative Center for Flexible Devices.

The abstract of the paper reads, “Compared with traditional stimuli-responsive devices with simple planar or tubular geometries, 3D printed stimuli-responsive devices not only intimately meet the requirement of complicated shapes at macrolevel but also satisfy various conformation changes triggered by external stimuli at the microscopic scale. However, their development is limited by the lack of 3D printing functional materials. This paper demonstrates the 3D printing of photoresponsive shape memory devices through combining fused deposition modeling printing technology and photoresponsive shape memory composites based on shape memory polymers and carbon black with high photothermal conversion efficiency. External illumination triggers the shape recovery of 3D printed devices from the temporary shape to the original shape. The effect of materials thickness and light density on the shape memory behavior of 3D printed devices is quantified and calculated. Remarkably, sunlight also triggers the shape memory behavior of these 3D printed devices. This facile printing strategy would provide tremendous opportunities for the design and fabrication of biomimetic smart devices and soft robotics.”

The NTU researchers used polyurethane for their work, due to its abilities in shape recovery, and small amounts of carbon black were mixed in as well; this material generates heat when it’s illuminated, so it was used as the activator for the polymer’s shape recovery.

An FDM 3D printing method was utilized to create a 3D printed sunflower, which was able to mimic the plant family’s natural heliotropism (motion of plant parts in response to the sun’s direction) in order to demonstrate the new composite’s memory response.

“When materials comprising these photoresponsive groups are used to fabricate 3D printable photoresponsive devices through photopolymerization, the aforementioned transitions in the 3D printing process can lead to remarkable changes in the optical, mechanical, and chemical properties of the photoresponsive devices,” the researchers state in the paper.

The research team also used luminous triggers, because they can be accurately and easily focused, they’re fast, and they are able to be activated remotely. Once the photoresponsive, 3D printed sunflower was exposed to a xenon lamp or natural sunlight, it bloomed in less than five minutes.

According to the researchers, there aren’t too many stimuli-responsive 3D printed devices available, because there aren’t a lot of functional materials that are 3D printable. In addition, most of the existing devices only respond to temperature changes – not many react to other stimuli like chemical changes, humidity, and light. So, designing and creating 3D printable devices that are responsive to other types of stimuli could have a major impact in medical devices, soft robotics, and customized wearable sensors.

As the paper states, “these 3D printed stimuli-responsive devices may shape the future trends and opportunities of device development in various fields ranging from biomedical devices to soft robots.”

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