Engineers at Rutgers, The State University of New Jersey, have invented a ‘4D printing’ method for a smart gel that could lead to the development of living’ structures in human organs and tissues, soft robots and targeted drug delivery.
The 4D printing approach involves printing a 3D object with a hydrogel (water-containing gel) that changes shape over time when temperatures change, according to Howon Lee, senior author of a new study.
The study, published in Scientific Reports, reportedly demonstrates fast, scalable, high-resolution 3D printing of hydrogels, which remain solid and retain their shape despite containing water.
Hydrogels are often found in everyday items like contact lenses and diapers, and even the human body.
The smart gel could provide structural rigidity in organs such as the lungs, and can contain small molecules like water or drugs to be transported in the body and released.
It could also create a new area of soft robotics, and enable new applications in flexible sensors and actuators, biomedical devices and platforms or scaffolds for cells to grow, Lee added.
Lee, who is assistant professor in the Department of Mechanical and Aerospace Engineering at Rutgers University–New Brunswick, said: “The full potential of this smart hydrogel has not been unleashed until now.
“We added another dimension to it, and this is the first time anybody has done it on this scale. They’re flexible, shape-morphing materials. I like to call them smart materials.”
Hydrogel plays important role in biomedical applications
Engineers at Rutgers–New Brunswick and the New Jersey Institute of Technology worked with a hydrogel that has been used for decades in devices that generate motion and biomedical applications such as scaffolds for cells to grow on.
But hydrogel manufacturing has previously relied heavily on conventional, two-dimensional methods such as moulding and lithography.
In their study, the engineers used a lithography-based technique that’s fast, inexpensive and can print a wide range of materials into a 3D shape.
It involves printing layers of a special resin to build a 3D object. The resin consists of the hydrogel, a chemical that acts as a binder, another chemical that facilitates bonding when light hits it and a dye that controls light penetration.
The engineers learned how to precisely control hydrogel growth and shrinkage. In temperatures below 32°C / 90°F, the hydrogel absorbs more water and swells in size.
When temperatures exceed 32°C, the hydrogel begins to expel water and shrinks. The objects they can create with the hydrogel range from the width of a human hair to several millimetres long.
The engineers also found that they can grow one area of a 3D-printed object – creating and programming motion – by changing temperatures.
Lee said: “If you have full control of the shape, then you can program its function. I think that’s the power of 3D printing of shape-shifting material. You can apply this principle almost everywhere.”
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