Biomimetic differently structured and multi-branched hydrogel tubes inspired by bud-growth of plants

Multi-branched hydrogel tubes have promising applications in various fields. However, it remains a great challenge to prepare such structures using a convenient method. Herein, an innovative method inspired by the bud-growth of plants (bud-notching and bud-picking) was proposed to prepare multi-branched hydrogel tubes based on sodium alginate/copper ions (Na-Alg/Cu²⁺). The bud-notching technique refers to the selective decrosslinking of Na-Alg/Cu²⁺ gels by controlled ethanolamine treatment, resulting in an "opening" in the tube wall. By adjusting the location and number of bud-notching on the primary tube and combining the apical growth technique, branched hydrogel tubes with diverse dimensions (two and three-dimensional) and structures ("zigzag"-shaped and "helical"-shaped) could be prepared on demand, without the need for templates and expensive equipment. Furthermore, biomimetic multi-segment hydrogel tubes were fabricated as simplified models to investigate the stability at the connection sites. The results demonstrated that the secondary hydrogel tubes prepared through multi-step growth retained approximately 70% of the elongation at break and 90% of the fracture force compared to the directly formed monolithic hydrogel tubes. Furthermore, the perfusion experiments showed that connections between branches were stable, which made the developed multi-branched hydrogel tubes have promising applications in some in vitro models and fluidic transport application areas. This kind of biomimetic method will also be meaningful for broadening the preparation of multi-branched materials.