A higher-strength hydrogel features a supportive scaffold made from an ingredient found in nature: seaweed.
The 3D-printable gels from North Carolina State University potentially enable new kinds of applications in biomedical materials and soft robotics.
Described in the journal Nature Communications , the water-based gels — called homocomposite hydrogels — are both strong and flexible. The 3D-printed jelly is composed of alginates — chemical compounds found in seaweed and algae that are commonly used as thickening agents and in wound dressings.
Merging different-size scale networks of the same alginate together eliminates the fragility that can sometimes occur when differing materials are merged together in a hydrogel, says Orlin Velev, Professor of Chemical and Biomolecular Engineering at NC State and corresponding author of the paper .
The homocomposite materials — a soft fibrillar alginate particles inside a medium of alginate — are really two hydrogels in one, according to the NC State researcher
"One is a particle hydrogel and one is a molecular hydrogel," said Prof. Velev. "Merged together they produce a jelly-like material that is better than the sum of its parts, and whose properties can be tuned precisely for shaping through a 3D printer for on-demand manufacturing."
Water-based gels are frequently soft, and even brittle. The N.C. State-developed product reinforces hydrogel with the alginate to improve the overall mechanical properties, expanding the possible applications.
"Alginates are used in wound dressings, so this material potentially could be used as a strengthened 3D-printed bandage or as a patch for wound healing or drug delivery," said Lilian Hsiao, an assistant professor of chemical and molecular engineering at NC State and a co-author of the paper.
Future work will attempt to fine-tune this method of merging of homocomposite materials to advance 3D printing for biomedical applications or biomedical injection materials, Velev said.
In a short Q&A with Tech Briefs below, Prof. Velev explains more about what's possible with a stronger hydrogel.
Tech Briefs: What is the exciting promise of hydrogels and how does your achievement advance what’s possible?
Prof. Orlin Velev: Hydrogels are one of the most basic classes of water-based "soft matter," with applications ranging from biomedical and pharmaceutical products to foods and soft robotics.
Tech Briefs: What does your hydrogel look and feel like?
Prof. Velev: Many, but not all, hydrogels look like the familiar clear "jelly," but in many cases they can be non-transparent paste-like materials. The most important feature of hydrogels is that they have high water content. They can be elastic, but are also commonly soft and fragile, a problem to which we provide one possible solution.
Tech Briefs: How simple is the manufacturing of the material? Is it a matter of just mixing it all together?
Prof. Velev: Common hydrogels are typically made just by cooling a hot solution of biopolymer, or mixing it with a cross-linking agent. However, our hydrogels require preliminary preparation of a class of special "sticky" fibrillar particles called soft dendritic colloids. They were discovered in my group and reported in an earlier publication . These particles, which are made of the same densified material as the hydrogels, interlock to create an internal reinforcement network.
Tech Briefs: How strong are these hydrogels once there’s an “internal reinforcement network?” How does the strength compare to standard hydrogels?
Prof. Velev: Our reinforced hydrogels have a 3 to 5 times larger Young's modulus and tensile strength at break than the "standard" molecular hydrogels. This is due to the synergistic reinforcement of the molecular network with a densified hierarchical network from the same material (alginate) made into the very adhesive soft dendritic colloid material.
Tech Briefs: What inspired the choice to use alginates?
Prof. Velev: Alginates are one of the most common types of hydrogel matrix, used in biomedical applications. They are well characterized, inexpensive, ubiquitous, and thus an ideal model system.
Tech Briefs: A few questions about tuning: How do you tune the properties? Would there be a menu of possibilities if, say, I wanted to 3D print a bandage versus thickening for soft robotics? Is it just the mechanical properties that you tune? If not, what else?
Prof. Velev: The ability to greatly improve and tune the properties of the "homocomposite" hydrogels is at the core of our work. It is achieved by mixing two hydrogel-forming components, made of the same alginate base and then combined together. The molecular alginate network makes the hydrogel soft and transparent, while the soft dendritic colloid network makes it sturdier and 3D-printable.
Tech Briefs: How “easy” (or challenging) is it to tune the material to have different strengths for different applications?
Prof. Velev: The tunability of the mechanical properties of the hydrogel is a key scientific goal of our work and the data on their rheology (non-Newtonian response) of the gels is presented in most of the figures. Basically, we can adjust the viscosity or stiffness of the material from near-water liquid to stiff and elastic gel. However, the more important and complex task is to design gels with "yield stress" — ones that could be extruded like a paste, but would then retain their shape once they come out of the printer nozzle. This is achieved by the addition of the soft dendritic colloids. Additionally, we can also control how quickly the extruded gels stiffen additionally to create a sturdy and resilient material.
Tech Briefs: What specific applications do you envision with this kind of stronger hydrogel? What is most exciting to you about this work?
Prof. Velev: The most exciting aspect from our perspective is the ability to design a new class of soft matter with improved and very well controlled properties. However, it has a number of applications in biomedical treatments, pharmaceuticals (e.g. injectable gels), soft robotic actuators, and even food products.
What do you think? Share your questions and comments below.
Transcript
00:00:12 ladies and gentlemen I have a question for you raise your hands if you've ever injured your knees while doing sports quite a bit looks like 40% of you have that's quite a lot well this guy has as well what you usually hurt actually the ligaments of your knees and if it's real bad that the ligaments are torn you need to replace
00:00:40 them with the new piece of ligament that you take from somewhere else in your body that sounds very complicated why don't we just make a new piece of synthetic ligament just like we do with the teeth implant any idea well the reality is we don't know how to make and it's really a question of material science I'm not talking to you about doing something as difficult as a heart
00:01:11 or lung no no it's really just a thread anchored on two bones and supposed to hold them together easy right well first in material science we classify ligaments as hydrogels so a warhol material ends the hydro and gel because it's a mixture of organic molecules so we would need such a hydrogel that is biocompatible but it's also as soft stretchy and tough as a real ligament
00:01:52 oh wait what is the toughness of a material whether it is its ability to resist fracture whether it breaks suddenly or not and that's the topic of my thesis a kg is about the toughness of hydrogels back to the lab I like to imagine myself a bit of a cook I just try out a bunch of recipes so I just take those organic molecules I mix them with some water for them in the
00:02:24 move quickly bake them every wallah I have my piece of hydrogen and then I do what any material scientists loves to do I pull on it until it breaks and that's exactly what you can see on the image on the right how the fracture went through my material and I try to better understand exactly what happened to be able to improve my recipe such that next time I need to pull even further before
00:02:57 my hydrogen braise and I hope like this that one day I would find the recipe of a hydrogen that is so tough that we can actually use it to make synthetic ligaments and that we can all even if you already injured your knees go back on the slopes and pull your craziest stunts as if nothing ever happened thank you [Applause]
