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Double-network Hydrogels for 3D Printing Ionic Skin
Table 1. Contents of DN hydrogel
Samples AAM GNPs MBAA 2959 NaCl solution (2M)
5% colloidal gel 0 mg 150 mg 0 mg 0 mg 3 ml
7.5% colloidal gel 0 mg 225 mg 0 mg 0 mg 3 ml
10% colloidal gel 0 mg 300 mg 0 mg 0 mg 3 ml
15% colloidal gel 0 mg 450 mg 0 mg 0 mg 3 ml
5% PAAm hydrogel 150 mg 0 mg 1.5 mg 15 mg 3 ml
10% PAAm hydrogel 300 mg 0 mg 3 mg 15 mg 3 ml
15% PAAm hydrogel 450 mg 0 mg 4.5 mg 15 mg 3 ml
10% PAAm composite hydrogel 300 mg 300 mg 3 mg 15 mg 3 ml
15% PAAm composite hydrogel 450 mg 300 mg 4.5 mg 15 mg 3 ml
PAAm: Polyacrylamide; DN: Double-network

such as light and mechanical signals. As an example, Acknowledgments
the ionic skin was mounted on the tester’s face, when
the tester smiled, the capacity of ionic skin increased, This work was supported by the National Key Research and
and correspondingly controlled the LED bulb on and off Development Program of China (No.2018YFA0703000),
(Figure 8B). Furthermore, by adhering the ionic skin National Natural Science Foundation of China
to the tester’s throat, we can control the inflation and (No. 31870957), and the Fundamental Research Funds for
deflation of a balloon by the inhalation and exhalation the Central Universities of China (No. DUT15RC(3)113).
of the tester. For patients with breathing difficulties and Conflict of interest
breathing disorders, we suggested that this design can
potentially test the inspiratory and expiratory volumes The authors declare no conflict of interest.
during breathing of the patients (Figure 8C). We further
put the ionic skin on the fingertips of the tester and used Author contributions
the finger to compress the substrate with different levels K.C. and H.W. designed the study. K.C., Q.Y., and X.H.
of forces, through which the ionic skin can generate performed the experiments and analyzed the results.
different degrees of deformation and capacitance values; K.C., Q.Y., and H.W. wrote the manuscript. All authors
this can be further converted to a readout signal. The commented on the manuscript.
increase of capacity signal can cause the LEDs to light up,
and the number of lit LEDs corresponded to the degree of References
the applied pressure (Figure 8D).
1. Wang X, Dong L, Zhang H, et al., 2015, Recent Progress in
4. Conclusion Electronic Skin. Adv Sci (Weinh), 2:1500169.

In summary, we hereby presented the development http://dx.doi.org/10.1002/advs.2015001691
of a novel class of DN hydrogels as printable skins 2. Chortos A, Liu J, Bao Z, 2016, Pursuing Prosthetic Electronic
for the fabrication of ions skin devices. The DN Skin. Nat Mater, 15:937–50.
hydrogels were based on reversible gelatin colloidal http://dx.doi.org/10.1038/nmat46712
network in combination with covalent PAAm network, 3. Jeon J, Lee HB, Bao Z, 2013, Flexible Wireless Temperature
which showed rapid, customized, and high-resolution Sensors Based on Ni Microparticle-filled Binary Polymer
fabrication of microscale constructs as ionic skins. The
DN hydrogel displayed significantly enhanced elasticity Composites. Adv Mater, 25:850–5.
and deformability which allow high adaptability of the http://dx.doi.org/10.1002/adma.2012040823
resulting ionic skin devices to the body’s movements. We 4. Chortos A, Bao Z, 2014, Skin-inspired Electronic Devices.
further used the DN hydrogel to print microarray-based Mater Today, 17:321–31.
capacitors as ionic skins with high elasticity, stretchability, http://dx.doi.org/10.1016/j.mattod.2014.05.0064
and sensitivity. The ionic skins exhibited high sensitivity 5. Sun JY, Keplinger C, Whitesides GM, et al., 2014, Ionic Skin.
to gentle finger-touch, body motion, and even wrist pulse- Adv Mater, 26:7608–14.
beating. We believe that this ionic skin can be potentially
applied in the fields of human/machine interactions and http://dx.doi.org/10.1002/adma.2014034415
wearable devices, and can promote the development of 6. Wen J, Tang J, Ning H, et al., 2021, Multifunctional Ionic
next-generation intelligent skin-mimicking sensors. Skin with Sensing, UV‐Filtering, Water‐Retaining, and Anti‐

106 International Journal of Bioprinting (2021)–Volume 7, Issue 3