Institute of Systems and Robotics, Department of Electrical Engineering, University of Coimbra, Coimbra, 3030-290, Portugal.
Soft Matter. 2022 Nov 16;18(44):8486-8503. doi: 10.1039/d2sm01103d.
Soft, conductive, and stretchable hydrogels offer a broad variety of applications, including skin-interfacing electrodes, biomonitoring patches, and electrostimulation. Despite rapid developments over the last decades, a combination of good electrical and mechanical properties, low-cost fabrication, and biocompatibility is yet to be demonstrated. Also, the current methods for deposition and patterning of these hydrogels are manual, and there is a need toward autonomous and digital fabrication techniques. In this work, we demonstrate a novel Gallium (Ga) embedded sodium-alginate-polyacrylamide-LAPONITE® (Ga-SA-PAAM-La) hydrogel, that is ultra-stretchable (Maximum strain tolerance of∼985%), tough (toughness ∼30 kJ m), bio-adhesive (adhesion energy ∼216 J m), conductive, and digitally printable. Ga nanoparticles are used as radical initiators. By adjusting the sonication parameters, we control the solution viscosity and curing time, thus allowing us to prepare pre-polymers with the desired properties for casting, or digital printing. These hydrogels benefit from a triple-network structure due to the role of Ga droplets as crosslinkers besides BIS (,'-methylene-bis-acrylamide) and LAPONITE®, thus resulting in tough composite hydrogels. The inclusion of LAPONITE® into the hydrogel network improved its electrical conductivity, adhesion, digital printability, and its mechanical properties, (>6× compared to the same hydrogel without LAPONITE®). As electrodes in the electrocardiogram, the signal-to-noise ratio was surprisingly higher than the medical-grade Ag/AgCl electrodes, which are applied for monitoring muscles, heart, respiration, and body joint angle through EMG, ECG, and bioimpedance measurements. The results obtained prove that such digitally printed conductive and tough hydrogels can be used as potential electrodes and sensors in practical applications in the next generation of printed wearable computing devices.
柔软、导电且可拉伸的水凝胶具有广泛的应用，包括皮肤接口电极、生物监测贴片和电刺激。尽管在过去几十年中取得了快速发展，但仍需要展示良好的电和机械性能、低成本制造和生物相容性的组合。此外，目前这些水凝胶的沉积和图案化方法是手动的，需要自主和数字化制造技术。在这项工作中，我们展示了一种新型的镓（Ga）嵌入的海藻酸钠-聚丙烯酰胺-LAPONITE®（Ga-SA-PAAM-La）水凝胶，它具有超拉伸性（最大应变容限约为 985%）、坚韧（韧性约为 30 kJ m）、生物粘附性（粘附能约为 216 J m）、导电性和数字可印刷性。Ga 纳米粒子用作自由基引发剂。通过调整超声参数，我们控制溶液的粘度和固化时间，从而可以制备具有所需性能的预聚物，用于浇铸或数字打印。这些水凝胶得益于三重网络结构，因为 Ga 液滴除了 BIS（'，-亚甲基双丙烯酰胺）和 LAPONITE®之外，还作为交联剂，从而产生坚韧的复合水凝胶。将 LAPONITE®纳入水凝胶网络提高了其导电性、粘附性、数字可印刷性和机械性能（与不含 LAPONITE®的相同水凝胶相比提高了 6 倍以上）。作为心电图中的电极，其信噪比出人意料地高于用于通过 EMG、ECG 和生物阻抗测量监测肌肉、心脏、呼吸和身体关节角度的医用级 Ag/AgCl 电极。所获得的结果证明，这种数字印刷的导电和坚韧的水凝胶可用作下一代印刷可穿戴计算设备中实际应用的潜在电极和传感器。
