Scientists from North Carolina State University report that 3D-printable gels with improved and highly controlled properties can be created by merging micro- and nano-sized networks of the same materials harnessed from seaweed. The findings could have applications in biomedical material such as biological scaffolds for growing cells, according to the researchers.

The study (“Printable homocomposite hydrogels with synergistically reinforced molecular-colloidal networks“), which appears in Nature Communications, shows that these water-based homocomposite hydrogels are both strong and flexible. They are composed of alginates, which chemical compounds found in seaweed and algae that are commonly used as thickening agents and in wound dressings.

“The design of hydrogels where multiple interpenetrating networks enable enhanced mechanical properties can broaden their field of application in biomedical materials, 3D printing, and soft robotics. We report a class of self-reinforced homocomposite hydrogels (HHGs) comprised of interpenetrating networks of multiscale hierarchy,” write the investigators.

“A molecular alginate gel is reinforced by a colloidal network of hierarchically branched alginate soft dendritic colloids (SDCs). The reinforcement of the molecular gel with the nanofibrillar SDC network of the same biopolymer results in a remarkable increase of the HHG’s mechanical properties. The viscoelastic HHGs show >3× larger storage modulus and >4× larger Young’s modulus than either constitutive network at the same concentration.

“Such synergistically enforced colloidal-molecular HHGs open up numerous opportunities for formulation of biocompatible gels with robust structure-property relationships. Balance of the ratio of their precursors facilitates precise control of the yield stress and rate of self-reinforcement, enabling efficient extrusion 3D printing of HHGs.”

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, PhD, S. Frank and Doris Culberson Distinguished Professor of Chemical and Biomolecular Engineering at NC State and corresponding author of the paper.

“Water-based materials can be soft and brittle,” he said. “But these homocomposite materials are really two hydrogels in one: one is a particle hydrogel and one is a molecular hydrogel. 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.”

“We are reinforcing a hydrogel material with the same material, which is remarkable because it uses just one material to improve the overall mechanical properties,” added Lilian Hsiao, PhD, an assistant professor of chemical and molecular engineering at NC State and a co-author of the paper. “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.”

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.