RESUMEN
Hydrogel-based flexible electronics have been widely investigated in electronic skin and wearable sensors. However, the challenge of matching the modulus between the hydrogel and the electrode underscores the critical importance of flexibility of the electrode. Gallium-based liquid metals (GaLMs) are ideal electrode materials for flexible substrates due to their high conductivity and stretchability. However, the ease of aggregation and lack of adhesion happen when patterning GaLMs on hydrogel surfaces. This work proposes a direct ink writing (DIW) of highly oxidized EGaIn (hoEGaIn) on an acrylamide (AAm) hydrogel. The interface is modulated by increasing the oxide content to improve the printability. Compared to EGaIn with an oxide layer, hoEGaIn displays a lower surface tension dropped by about 28.5%, higher adhesion (an increase of about 24.4%), and lower contact angles. These optimized interface properties significantly improve its wettability and DIW stability on AAm hydrogel substrates. A minimum line width of 65 µm is obtained by regulating DIW parameters. Meanwhile, hoEGaIn exhibits impressive multisubstrate printability and conductivity of up to 2.22 × 106 S·m-1. Furthermore, a cantilever beam strain sensor is manufactured by DIW hoEGaIn on an AAm hydrogel, which exhibits fast response and recovery, excellent dynamic response, and stability. This study demonstrates a potential method for the DIW of GaLMs on hydrogels.
RESUMEN
Hydrogels are extensively explored as biomaterials for tissue scaffolds, and their controlled fabrication has been the subject of wide investigation. However, the tedious mechanical property adjusting process through formula control hindered their application for diverse tissue scaffolds. To overcome this limitation, we proposed a two-step process to realize simple adjustment of mechanical modulus over a broad range, by combining digital light processing (DLP) and post-processing steps. UV-curable hydrogels (polyacrylamide-alginate) are 3D printed via DLP, with the ability to create complex 3D patterns. Subsequent post-processing with Fe3+ ions bath induces secondary crosslinking of hydrogel scaffolds, tuning the modulus as required through soaking in solutions with different Fe3+ concentrations. This innovative two-step process offers high-precision (10 µm) and broad modulus adjusting capability (15.8-345 kPa), covering a broad range of tissues in the human body. As a practical demonstration, hydrogel scaffolds with tissue-mimicking patterns were printed for cultivating cardiac tissue and vascular scaffolds, which can effectively support tissue growth and induce tissue morphologies.