Wearable biosensor technology has attracted intensive research interests since it provides accurate monitoring of physiological samples for diagnosing, managing and treating disease and monitoring individual physical health without extracting blood sample. The most common detection technique depends on frequently correcting blood samples for measurement or continuous monitoring devices, which are expensive, painful and inconvenient. Thus, extensive efforts have been devoted to develop noninvasive sensors that rely on electrical and electrochemical techniques. Mechanical properties are important to wearable devices since they directly contact with human skin, which should need the Young’s modulus around 130–657 kPa [1, 2]. To meet this requirement, electrode materials should hold high viscosity at low-shear rates (103 to 105 Pa s) with shear thinning and viscoelastic behavior with high extensional relaxation times (>1 s), limiting their processing using common electrode fabrication technology. 3D printing technologies typically can process the materials with high concentration as well as high viscosity and shear-thinning behavior; utilize stretchable polymer composites with conductive compounds and have ability to construct complex, customized 3D geometries [3-4]. It can easily employ thin conductive films on stretchable substrates.
In our study, our micro additive manufacturing of wearable glucose/lactase biosensor shows the advantage over conventional methods, including: (1) feasible design of objects with higher levels of integrate enzyme/electrode co-production (layer by layer), and (2) appropriate for modifications due to fine resolution and significant materials saving. This will enable us to achieve high conductivity and physiochemical stability of electrode on flexible substrates as well as thinner, higher aspect ratio structures with ideal three-dimensional stacking. We found that the sensitivity of our wearable sensor was much higher than that of traditional printed biosensor (~ 3 folds) due to the extreme fine and less defected surface area printed by DIW technique, which resulting in uniform surface carbon nanoparticle distribution. Besides, our wearable sensors show excellent reproducibility and long-time stability.
Reference
(1) Guo S Z, Qiu K, Meng F, et al. 3D Printed Stretchable Tactile Sensors[J]. Advanced Materials, 2017.
(2) Muth J T, Vogt D M, Truby R L, et al. Embedded 3D printing of strain sensors within highly stretchable elastomers[J]. Advanced Materials, 2014, 26(36): 6307-6312.
(3) Nesaei S, Rock M, Wang Y, et al. Additive Manufacturing With Conductive, Viscoelastic Polymer Composites: Direct-Ink-Writing of Electrolytic and Anodic Poly (Ethylene Oxide) Composites[J]. Journal of Manufacturing Science and Engineering, 2017, 139(11): 111004.
(4) Truby R L, Lewis J A. Printing soft matter in three dimensions[J]. Nature, 2016, 540(7633): 371-378.