Dec 6, 2017 | By Benedict

Researchers at Princeton University have developed a hydrogel that forms when fibers slide against each other as they are forced through a syringe. The chemical-free shearing method could be used in wound treatment and other areas.

A new hydrogel developed at Princeton University could help treat wounds

Because of their physical properties—porosity, water content, and squishiness—hydrogels are an important substance in many scientific disciplines. Not least in the rapidly growing field of 3D bioprinting, in which hydrogels are used to keep individually unprintable living cells in a solid and printable form.

Creating an effective hydrogel is difficult, generally requiring chemical reactions and material interactions, but researchers at Princeton have developed a hydrogel that requires no such chemicals. Rather, the hydrogel simply forms via the shearing effect of fibers sliding against each other when forced through a syringe.

The researchers are understandably pretty excited about their new creation, and think it could be used to plug and treat wounds, even opening up an entire new class of injectable hydrogels for biomedicine and other fields.

“Studying the flow of matter in suspensions containing such highly flexible fibers had never really been attempted before,” claims Antonio Perazzo, co-lead author of a research paper documenting the study. “Pursuing novel research has given us this unprecedented result of flow-induced gelation with flexible fibers.”

The hydrogel could someday be used in a 3D bioprinter

The scientific explanation for the behavior of the soft, extensible gel is the phenomenon of shear thickening, which causes fibers to firm up and gel under stress. Generally, however, a mixture of fibers and water will produce the opposite effect: shear thinning.

So what makes the hydrogel thicken instead of thin? The answer, the scientists say, can be most easily understood by watching YouTube videos of people walking across swimming pools filled with corn starch.

These people aren’t godlike: they’re just walking on a mixture of ingredients that result in shear thickening when subject to stress.

A detailed study was organized to see how this kind of shear thickening occurred with microfibers made of poly(ethylene glycol) diacrylate (PEG-DA), a flexible and biocompatible plastic that is entirely non-toxic.

The effect of shear thickening, the process used to make the hydrogel, can be seen in cornstarch-filled water

Measuring 35 micrometers in diameter and about 12 millimeters long, these ultra-fine fibers initially exist in a free-flowing, unentangled state when placed in water. However, when placed into a rheometer with a rotating top plate (applying pressure to the mixture by swirling the fibers around), the fibers bend, interlock, and tangle.

Eventually, the tangled-up, spaghett-like mass of fibers separate from the water, though some water remains trapped within them. This produces a water-filled fiber network with distinctly hydrogel-like properties. The properties of the gel can even be controlled by adjusting the length and diameter of the microfibers.

The Princeton researchers now plan to refine the process by optimizing the gelation of the material as it goes through a syringe, as well as incorporating useful substances like antibiotics, nutrients, and biomolecules.

The hydrogels could eventually be used in wound treatment, and syringes could eventually be replaced with 3D bioprinters.

The study, “Flow-induced gelation of microfiber suspensions,” has been published in Proceedings of the National Academy of Sciences. Its authors were Perazzo, Janine K. Nunes, Stefano Guido, and Howard A. Stone.

 

 

Posted in 3D Printing Materials

 

 

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