# Template-Free Wet-Spinning of Multifunctional Sodium Alginate Hollow Hydrogels

## TL;DR

A new method for making hollow hydrogels without templates is developed, enabling flexible electronics and bioengineering applications.

## Contribution

A template-free wet-spinning method for creating multifunctional sodium alginate hollow hydrogels is introduced.

## Key findings

- Hollow hydrogels self-form through ionic cross-linking and CO2 generation during wet-spinning.
- The hydrogels show excellent sensing performance for detecting limb motions and muscle activity.
- They exhibit good biocompatibility and can be fabricated with diverse geometries.

## Abstract

Hollow hydrogels are promising for flexible electronics and bioengineering, yet their fabrication is limited by sacrificial templates, specialized equipment, and complex engineering processes. Herein, a facile wet-spinning strategy is developed to fabricate sodium alginate (SA) hollow hydrogels. Extruding SA/CaCO3 precursor suspension into an acidic coagulation bath induces simultaneous ionic cross-linking and in situ CO2 generation, driving the self-formation of hollow tubular architectures with tunable morphologies, mechanical performance, macroscopic architecture, and functional properties. Moreover, the introduction of secondary cross-linking enhances the SA hydrogels’ water retention and resistance to freezing conditions. Utilizing their intrinsic ionic conductivity, the hollow hydrogels demonstrate outstanding sensing performance, enabling reliable detection of both large-amplitude limb motions and subtle muscle activity in the human body. Furthermore, hollow hydrogel tubes with diverse geometries can be readily fabricated by simply modifying the spinning mold, thereby broadening their potential applications. In vitro cytotoxicity assessments further confirm that the SA hollow hydrogels exhibit excellent biocompatibility with minimal cytotoxicity, satisfying the fundamental criteria for bioengineering applications. The combination of a simple yet controllable fabrication strategy with the intrinsic multifunctionality of the SA hollow tubes confers substantial potential for their deployment in bioengineering and flexible electronic applications.