Soft conductive nanocomposites for recording biosignals on skin

Abstract

Soft conductive nanocomposites have introduced significant breakthroughs in bio-integrated electronics by mitigating the mechanical mismatch between the body and the device. Compared with conventional wearable sensors based on rigid electronic materials, the wearable sensors based on soft nanocomposites are advantageous to long-term and high-quality biosignal recordings. Materials used for the synthesis of the nanocomposites, especially nanofillers, are critical for determining the quality of recorded biosignals and the performance of the nanocomposites. In this review, we focus on recent advances in soft conductive nanocomposites, mainly on their electrical and mechanical properties according to the types of nanofillers, and present their applications to wearable biosignal recording devices. We have classified the nanofillers into four categories: carbon-based nanomaterials, conducting polymers, metal-based nanomaterials, and liquid metals. We then introduce the applications of nanocomposites as wearable sensors that record various biosignals, including electrophysiological, strain, pressure, and biochemical information. In conclusion, a brief outlook on the remaining challenges for future nanomaterial-based bioelectronics is provided.

Keywords

Nanocomposites / nanomaterials / soft materials / wearable sensors / bio-integrated electronics

References

[1] Cho KW,Kim BS.Sensors in heart-on-a-chip: a review on recent progress.Talanta2020;219:121269

[2] Sunwoo S,Joo H.Advances in soft bioelectronics for brain research and clinical neuroengineering.Matter2020;3:1923-47

[3] Squair JW,Mahe L.Neuroprosthetic baroreflex controls haemodynamics after spinal cord injury.Nature2021;590:308-14

[4] Hong YJ,Kim J.Multifunctional wearable system that integrates sweat-based sensing and vital-sign monitoring to estimate pre-/post-exercise glucose levels.Adv Funct Mater2018;28:1805754

[5] Song J,Kim J.Wearable force touch sensor array using a flexible and transparent electrode.Adv Funct Mater2017;27:1605286

[6] Hua Q,Liu H.Skin-inspired highly stretchable and conformable matrix networks for multifunctional sensing.Nat Commun2018;9:244 PMCID:PMC5770430

[7] Konstantinidis D,Tatakis F.Wearable blood pressure measurement devices and new approaches in hypertension management: the digital era.J Hum Hypertens2022;36:945-51 PMCID:PMC8942176

[8] Choi MK,Choi C.Cephalopod-inspired miniaturized suction cups for smart medical skin.Adv Healthc Mater2016;5:80-7

[9] Sunwoo SH,Han SI.Ventricular tachyarrhythmia treatment and prevention by subthreshold stimulation with stretchable epicardial multichannel electrode array.Sci Adv2023;9:eadf6856 PMCID:PMC10065438

[10] Kim HJ,Sunwoo S,Koo JH.Integration of conductive nanocomposites and nanomembranes for high‐performance stretchable conductors.Adv Nanobiomed Res2023;3:2200153

[11] Hong YJ,Cho KW,Kim D.Wearable and implantable devices for cardiovascular healthcare: from monitoring to therapy based on flexible and stretchable electronics.Adv Funct Mater2019;29:1808247

[12] Kim SJ,Cho HR.Stretchable and transparent biointerface using cell-sheet-graphene hybrid for electrophysiology and therapy of skeletal muscle.Adv Funct Mater2016;26:3207-17

[13] Joo H,Kim J.Soft implantable drug delivery device integrated wirelessly with wearable devices to treat fatal seizures.Sci Adv2021;7:eabd4639 PMCID:PMC7775752

[14] Lee H,Lee YB.A graphene-based electrochemical device with thermoresponsive microneedles for diabetes monitoring and therapy.Nat Nanotechnol2016;11:566-72

[15] Lee H,Hong YS.Wearable/disposable sweat-based glucose monitoring device with multistage transdermal drug delivery module.Sci Adv2017;3:e1601314 PMCID:PMC5342654

[16] Park C,Kim HH.Stretchable conductive nanocomposites and their applications in wearable devices.Appl Phys Rev2022;9:021312

[17] Kim H,Joo H.Wide-range robust wireless power transfer using heterogeneously coupled and flippable neutrals in parity-time symmetry.Sci Adv2022;8:eabo4610 PMCID:PMC9200287

[18] Lee M,Choi C.Soft high-resolution neural interfacing probes: materials and design approaches.Nano Lett2019;19:2741-9

[19] Yoo S,Joo H,Kim S.Wireless power transfer and telemetry for implantable bioelectronics.Adv Healthc Mater2021;10:e2100614

[20] Sunwoo SH,Lee S,Kim DH.Wearable and implantable soft bioelectronics: device designs and material strategies.Annu Rev Chem Biomol Eng2021;12:359-91

[21] Zhang H,Shen X.Catechol/polyethyleneimine conversion coating with enhanced corrosion protection of magnesium alloys: potential applications for vascular implants.J Mater Chem B2018;6:6936-49

[22] Morais LS,Muller CA.Titanium alloy mini-implants for orthodontic anchorage: immediate loading and metal ion release.Acta Biomater2007;3:331-9

[23] Kaltenbrunner M,Reeder J.An ultra-lightweight design for imperceptible plastic electronics.Nature2013;499:458-63

[24] Shim HJ,Kim Y,Kim DH.Functionalized elastomers for intrinsically soft and biointegrated electronics.Adv Healthc Mater2021;10:e2002105

[25] Zhou Y,Yang Y.Highly stretchable, elastic, and ionic conductive hydrogel for artificial soft electronics.Adv Funct Mater2019;29:1806220

[26] Kang T,Park OK.Penetrative and sustained drug delivery using injectable hydrogel nanocomposites for postsurgical brain tumor treatment.ACS Nano2023;17:5435-47

[27] Lim C,Jung J.Tissue-like skin-device interface for wearable bioelectronics by using ultrasoft, mass-permeable, and low-impedance hydrogels.Sci Adv2021;7:eabd3716 PMCID:PMC8104866

[28] Cha GD,Sunwoo SH.Multifunctional injectable hydrogel for in vivo diagnostic and therapeutic applications.ACS Nano2022;16:554-67

[29] Lim C,Jung J,Lee S.Stretchable conductive nanocomposite based on alginate hydrogel and silver nanowires for wearable electronics.APL Mater2019;7:031502

[30] Yuk H,Zhao X.Hydrogel bioelectronics.Chem Soc Rev2019;48:1642-67

[31] Koo JH,Lee S.A vacuum-deposited polymer dielectric for wafer-scale stretchable electronics.Nat Electron2023;6:137-45

[32] Song JK,Yoon J.Stretchable colour-sensitive quantum dot nanocomposites for shape-tunable multiplexed phototransistor arrays.Nat Nanotechnol2022;17:849-56

[33] Cho KW,Hong YJ.Soft bioelectronics based on nanomaterials.Chem Rev2022;122:5068-143

[34] Jung D,Park C.Adaptive self-organization of nanomaterials enables strain-insensitive resistance of stretchable metallic nanocomposites.Adv Mater2022;34:e2200980

[35] Park J,Janardhan AH.Electromechanical cardioplasty using a wrapped elasto-conductive epicardial mesh.Sci Transl Med2016;8:344ra86

[36] Lee W,Song J,Kim D.Nanoscale materials and deformable device designs for bioinspired and biointegrated electronics.Acc Mater Res2021;2:266-81

[37] Sunwoo SH,Jung D.Stretchable low-impedance conductor with Ag-Au-Pt core-shell-shell nanowires and in situ formed Pt nanoparticles for wearable and implantable device.ACS Nano2023;17:7550-61

[38] Sunwoo S,Kang H.Stretchable low-impedance nanocomposite comprised of Ag-Au core-shell nanowires and Pt black for epicardial recording and stimulation.Adv Mater Technol2020;5:1900768

[39] Cha GD,Lim C,Kim DH.Materials engineering, processing, and device application of hydrogel nanocomposites.Nanoscale2020;12:10456-73

[40] Choi S,Kim D,Kim DH.High-performance stretchable conductive nanocomposites: materials, processes, and device applications.Chem Soc Rev2019;48:1566-95

[41] Joo H,Sunwoo SH,Kim DH.Material design and fabrication strategies for stretchable metallic nanocomposites.Small2020;16:1906270

[42] Kim DC,Lee W,Kim DH.Material-based approaches for the fabrication of stretchable electronics.Adv Mater2020;32:e1902743

[43] Hong S,Do K.Stretchable electrode based on laterally combed carbon nanotubes for wearable energy harvesting and storage devices.Adv Funct Mater2017;27:1704353

[44] Jung D,Shim HJ.Highly conductive and elastic nanomembrane for skin electronics.Science2021;373:1022-6

[45] Niu X,Liu L,Sheng P.Characterizing and patterning of PDMS-based conducting composites.Adv Mater2007;19:2682-6

[46] Lv R,Na B.Insight into the role of filler network in the viscoelasticity of a carbon black filled thermoplastic elastomer: a strain dependent electrical conductivity study.J Macromol Sci2008;47:774-82

[47] Kong J,Kim S.Simple and rapid micropatterning of conductive carbon composites and its application to elastic strain sensors.Carbon2014;77:199-207

[48] Chen Z,Gao L,Pei S.Three-dimensional flexible and conductive interconnected graphene networks grown by chemical vapour deposition.Nat Mater2011;10:424-8

[49] Boland CS,Ryan G.Sensitive electromechanical sensors using viscoelastic graphene-polymer nanocomposites.Science2016;354:1257-60

[50] Kabiri Ameri S,Jang H.Graphene electronic tattoo sensors.ACS Nano2017;11:7634-41

[51] Lee WH,Lee J.Simultaneous transfer and doping of CVD-grown graphene by fluoropolymer for transparent conductive films on plastic.ACS Nano2012;6:1284-90

[52] Sekitani T,Maeda H.Stretchable active-matrix organic light-emitting diode display using printable elastic conductors.Nat Mater2009;8:494-9

[53] Han L,Wang M.Mussel-inspired adhesive and conductive hydrogel with long-lasting moisture and extreme temperature tolerance.Adv Funct Mater2018;28:1704195

[54] Lipomi DJ,Tee BC.Skin-like pressure and strain sensors based on transparent elastic films of carbon nanotubes.Nat Nanotechnol2011;6:788-92

[55] Ray TR,Bandodkar AJ.Bio-integrated wearable systems: a comprehensive review.Chem Rev2019;119:5461-533

[56] Wang C,Wang H,Yin Z.Advanced carbon for flexible and wearable electronics.Adv Mater2019;31:e1801072

[57] Hu L,Mantia FL.Stretchable, porous, and conductive energy textiles.Nano Lett2010;10:708-14

[58] Qiu L,Wang Y.Mechanically robust, electrically conductive and stimuli-responsive binary network hydrogels enabled by superelastic graphene aerogels.Adv Mater2014;26:3333-7

[59] Tringides CM,de Lázaro I.Viscoelastic surface electrode arrays to interface with viscoelastic tissues.Nat Nanotechnol2021;16:1019-29 PMCID:PMC9233755

[60] Polat EO,Kakenov N,Kocabas C.Synthesis of large area graphene for high performance in flexible optoelectronic devices.Sci Rep2015;5:16744 PMCID:PMC4649757

[61] Gan D,Wang X.Graphene oxide-templated conductive and redox-active nanosheets incorporated hydrogels for adhesive bioelectronics.Adv Funct Mater2020;30:1907678

[62] Xia S,Jia F.A flexible, adhesive and self-healable hydrogel-based wearable strain sensor for human motion and physiological signal monitoring.J Mater Chem B2019;7:4638-48

[63] Ojha S,Raghavendra G.Mechanical properties of natural carbon black reinforced polymer composites.J Appl Polym Sci2015;132

[64] Kim KS,Jang H.Large-scale pattern growth of graphene films for stretchable transparent electrodes.Nature2009;457:706-10

[65] Nair RR,Grigorenko AN.Fine structure constant defines visual transparency of graphene.Science2008;320:1308

[66] Lee H,Song C.An endoscope with integrated transparent bioelectronics and theranostic nanoparticles for colon cancer treatment.Nat Commun2015;6:10059 PMCID:PMC4674684

[67] Liu N,Lei T.Ultratransparent and stretchable graphene electrodes.Sci Adv2017;3:e1700159 PMCID:PMC5590784

[68] Shi G,Teo AJ.A versatile PDMS submicrobead/graphene oxide nanocomposite ink for the direct ink writing of wearable micron-scale tactile sensors.Appl Mater Today2019;16:482-92

[69] Sun Y,Kim JU.Carbon aerogel reinforced PDMS nanocomposites with controllable and hierarchical microstructures for multifunctional wearable devices.Carbon2021;171:758-67

[70] Wu J,Su Z.Highly flexible and sensitive wearable e-skin based on graphite nanoplatelet and polyurethane nanocomposite films in mass industry production available.ACS Appl Mater Interfaces2017;9:38745-54

[71] Amjadi M,Clementson CP.Parallel microcracks-based ultrasensitive and highly stretchable strain sensors.ACS Appl Mater Interfaces2016;8:5618-26

[72] Sekitani T,Hata K,Aida T.A rubberlike stretchable active matrix using elastic conductors.Science2008;321:1468-72

[73] Gu X,Xiao Y.Exposure to black carbon is associated with dermographism: a population-based study in college students.Australas J Dermatol2022;63:e86-8

[74] Serup J.How to diagnose and classify tattoo complications in the clinic: a system of distinctive patterns. In: Serup J, Bäumler W, editors. Diagnosis and Therapy of Tattoo Complications. S. Karger AG; 2017. p. 58-73.

[75] Fusco L,Martín C.Skin irritation potential of graphene-based materials using a non-animal test.Nanoscale2020;12:610-22

[76] Ema M,Kobayashi N,Nakanishi J.Evaluation of dermal and eye irritation and skin sensitization due to carbon nanotubes.Regul Toxicol Pharmacol2011;61:276-81

[77] Liu Y,Bao Z.Conjugated polymer for implantable electronics toward clinical application.Adv Healthc Mater2021;10:e2001916

[78] Green RA,Poole-Warren LA.Conducting polymer-hydrogels for medical electrode applications.Sci Technol Adv Mater2010;11:014107 PMCID:PMC5090549

[79] Wang S,Wang W.Skin electronics from scalable fabrication of an intrinsically stretchable transistor array.Nature2018;555:83-8

[80] Nezakati T,Tan A.Conductive polymers: opportunities and challenges in biomedical applications.Chem Rev2018;118:6766-843

[81] Wang Y,Pfattner R.A highly stretchable, transparent, and conductive polymer.Sci Adv2017;3:e1602076 PMCID:PMC5345924

[82] Deslouis C,Musiani M.Mixed ionic-electronic conduction of a conducting polymer film. Ac impedance study of polypyrrole.Electrochimica Acta1996;41:1343-9

[83] Tan P,Xiao F.Solution-processable, soft, self-adhesive, and conductive polymer composites for soft electronics.Nat Commun2022;13:358 PMCID:PMC8766561

[84] Fang B,Chang D.Scalable production of ultrafine polyaniline fibres for tactile organic electrochemical transistors.Nat Commun2022;13:2101 PMCID:PMC9018749

[85] Feig VR,Lee M.Mechanically tunable conductive interpenetrating network hydrogels that mimic the elastic moduli of biological tissue.Nat Commun2018;9:2740 PMCID:PMC6048132

[86] Liu Y,Chen S.Soft and elastic hydrogel-based microelectronics for localized low-voltage neuromodulation.Nat Biomed Eng2019;3:58-68

[87] Jiang Y,Wang YX.Topological supramolecular network enabled high-conductivity, stretchable organic bioelectronics.Science2022;375:1411-7

[88] Pomfret SJ,Comfort NP.Inherently electrically conductive fibers wet spun from a sulfonic acid-doped polyaniline solution.Adv Mater1998;10:1351-3

[89] Cho S,Joo H.Recent developments of the solution-processable and highly conductive polyaniline composites for optical and electrochemical applications.Polymers2019;11:1965 PMCID:PMC6960645

[90] Wang Y,Pan L.Dopant-enabled supramolecular approach for controlled synthesis of nanostructured conductive polymer hydrogels.Nano Lett2015;15:7736-41

[91] Humpolicek P,Saha P.Biocompatibility of polyaniline.Synthetic Metals2012;162:722-7

[92] Lalegül-ülker Ö,Elçin YM.Intrinsically conductive polymer nanocomposites for cellular applications. In: Chun HJ, Park CH, Kwon IK, Khang G, editors. Cutting-Edge Enabling Technologies for Regenerative Medicine. Singapore: Springer; 2018. p. 135-53.

[93] Choi S,Hyun W.Stretchable heater using ligand-exchanged silver nanowire nanocomposite for wearable articular thermotherapy.ACS Nano2015;9:6626-33

[94] Ma R,Cho S,Baik S.Extraordinarily high conductivity of stretchable fibers of polyurethane and silver nanoflowers.ACS Nano2015;9:10876-86

[95] Miyamoto A,Cooray NF.Inflammation-free, gas-permeable, lightweight, stretchable on-skin electronics with nanomeshes.Nat Nanotechnol2017;12:907-13

[96] Zhang A,Lieber CM.Nanowire-enabled bioelectronics.Nano Today2021;38:101135 PMCID:PMC10038126

[97] Kim Y,Yeom B.Stretchable nanoparticle conductors with self-organized conductive pathways.Nature2013;500:59-63

[98] Hyun DC,Park C.Ordered zigzag stripes of polymer gel/metal nanoparticle composites for highly stretchable conductive electrodes.Adv Mater2011;23:2946-50

[99] Ma R,Choi D,Baik S.Knitted fabrics made from highly conductive stretchable fibers.Nano Lett2014;14:1944-51

[100] Liang J,Pei Q.A water-based silver-nanowire screen-print ink for the fabrication of stretchable conductors and wearable thin-film transistors.Adv Mater2016;28:5986-96

[101] Jiang Z,Fukuda K.Highly stretchable metallic nanowire networks reinforced by the underlying randomly distributed elastic polymer nanofibers via interfacial adhesion improvement.Adv Mater2019;31:e1903446

[102] McShan D,Yu H.Molecular toxicity mechanism of nanosilver.J Food Drug Anal2014;22:116-27 PMCID:PMC4281024

[103] Lim G,Kwon N.Fully stretchable and highly durable triboelectric nanogenerators based on gold-nanosheet electrodes for self-powered human-motion detection.Nano Energy2017;42:300-6

[104] Gong S,Wang Y.A wearable and highly sensitive pressure sensor with ultrathin gold nanowires.Nat Commun2014;5:3132

[105] Yang M,Yang X,Xia Y.Facile synthesis of Ag@Au core-sheath nanowires with greatly improved stability against oxidation.Chem Commun2017;53:1965-8

[106] Lim C,Sunwoo SH.Facile and scalable synthesis of whiskered gold nanosheets for stretchable, conductive, and biocompatible nanocomposites.ACS Nano2022;16:10431-42

[107] Choi S,Jung D.Highly conductive, stretchable and biocompatible Ag-Au core-sheath nanowire composite for wearable and implantable bioelectronics.Nat Nanotechnol2018;13:1048-56

[108] Paladini F,Pollini M.In vivo testing of silver treated fibers for the evaluation of skin irritation effect and hypoallergenicity.J Biomed Mater Res B Appl Biomater2014;102:1031-7

[109] Hadrup N,Loeschner K.Toxicity of silver ions, metallic silver, and silver nanoparticle materials after in vivo dermal and mucosal surface exposure: a review.Regul Toxicol Pharmacol2018;98:257-67

[110] Bomhard EM.The toxicology of indium oxide.Environ Toxicol Pharmacol2018;58:250-8

[111] Roach KA,Stefaniak AB,Boyce GR.Evaluation of the skin-sensitizing potential of gold nanoparticles and the impact of established dermal sensitivity on the pulmonary immune response to various forms of gold.Nanotoxicology2020;14:1096-117 PMCID:PMC7945003

[112] Gupta R.Penetration of gold nanoparticles through human skin: unraveling its mechanisms at the molecular scale.J Phys Chem B2016;120:7133-42

[113] Daeneke T,Mahmood N.Liquid metals: fundamentals and applications in chemistry.Chem Soc Rev2018;47:4073-111

[114] Wang H,Chen S,Dickey MD.Liquid metal composites with enhanced thermal conductivity and stability using molecular thermal linker.Adv Mater2021;33:e2103104

[115] Yan J,Chen G,Gu Z.Advances in liquid metals for biomedical applications.Chem Soc Rev2018;47:2518-33

[116] Dickey MD.Stretchable and soft electronics using liquid metals.Adv Mater2017;29:1606425

[117] Li Y,Cao S,Kong D.Printable liquid metal microparticle ink for ultrastretchable electronics.ACS Appl Mater Interfaces2020;12:50852-9

[118] Veerapandian S,Seol JB.Hydrogen-doped viscoplastic liquid metal microparticles for stretchable printed metal lines.Nat Mater2021;20:533-40

[119] Guymon GG.Multifunctional liquid metal polymer composites.J Polym Sci2022;60:1300-27

[120] Hoang TT,Thai MT.Magnetically engineered conductivity of soft liquid metal composites for robotic, wearable electronic, and medical applications.Adv Intell Syst2022;4:2200282

[121] Fassler A.Liquid-phase metal inclusions for a conductive polymer composite.Adv Mater2015;27:1928-32

[122] Clarkson TW,Myers GJ.The toxicology of mercury - current exposures and clinical manifestations.N Engl J Med2003;349:1731-7

[123] Kalantar-zadeh K,Tang J.Low melting temperature liquid metals and their impacts on physical chemistry.Acc Mater Res2021;2:577-80

[124] Song H,Kang S,Lee K.Ga-based liquid metal micro/nanoparticles: recent advances and applications.Small2020;16:1903391

[125] Malakooti MH,Matyjaszewski K.Liquid metal nanocomposites.Nanoscale Adv2020;2:2668-77 PMCID:PMC9419082

[126] Lin Y,Wang M,Genzer J.Handwritten, soft circuit boards and antennas using liquid metal nanoparticles.Small2015;11:6397-403

[127] Boley JW,Kramer RK.Mechanically sintered gallium-indium nanoparticles.Adv Mater2015;27:2355-60

[128] Liu S,White EL.Laser sintering of liquid metal nanoparticles for scalable manufacturing of soft and flexible electronics.ACS Appl Mater Interfaces2018;10:28232-41

[129] Deng B.Pulsed laser modulated shock transition from liquid metal nanoparticles to mechanically and thermally robust solid-liquid patterns.Adv Mater2019;31:e1807811

[130] Xu Y,Rajavel K.Tailorable, lightweight and superelastic liquid metal monoliths for multifunctional electromagnetic interference shielding.Nanomicro Lett2021;14:29 PMCID:PMC8669089

[131] Markvicka EJ,Huang X.An autonomously electrically self-healing liquid metal-elastomer composite for robust soft-matter robotics and electronics.Nat Mater2018;17:618-24

[132] Mou L,Tang L.Highly stretchable and biocompatible liquid metal-elastomer conductors for self-healing electronics.Small2020;16:e2005336

[133] Liu S,Kramer-Bottiglio R.Highly stretchable multilayer electronic circuits using biphasic gallium-indium.Nat Mater2021;20:851-8

[134] Zhao Y.Mechanisms and materials of flexible and stretchable skin sensors.Micromachines2017;8:69 PMCID:PMC6190259

[135] Xu Y,Zhou S.Bioinspired perspiration-wicking electronic skins for comfortable and reliable multimodal health monitoring.Adv Funct Materials2022;32:2200961

[136] Liu S,Jang H,Lu N.Strategies for body-conformable electronics.Matter2022;5:1104-36

[137] Ma Z,Xu Q.Permeable superelastic liquid-metal fibre mat enables biocompatible and monolithic stretchable electronics.Nat Mater2021;20:859-68

[138] Park JE,Baek J.Rewritable, printable conducting liquid metal hydrogel.ACS Nano2019;13:9122-30

[139] Jiang Y,Sun J.A universal interface for plug-and-play assembly of stretchable devices.Nature2023;614:456-62

[140] Kim JJ,Wang H,Yokota T.Skin electronics: next-generation device platform for virtual and augmented reality.Adv Funct Mater2021;31:2009602

[141] Choi C,Hyeon T.Nanomaterial-based soft electronics for healthcare applications.ChemNanoMat2016;2:1006-17

[142] Zheng Z,Wang B.Hierarchically designed nanocomposites for triboelectric nanogenerator toward biomechanical energy harvester and smart home system.Nano Energy2022;95:107047

[143] Lee Y,Joo H,Ghaffari R.Wearable sensing systems with mechanically soft assemblies of nanoscale materials.Adv Mater Technol2017;2:1700053

[144] Wang C,Li J.Conformal electrodes for on-skin digitalization.SmartMat2021;2:252-62

[145] Kwak SS,Avila R.Skin-integrated devices with soft, holey architectures for wireless physiological monitoring, with applications in the neonatal intensive care unit.Adv Mater2021;33:e2103974

[146] Xiang L,Xia F,Liu Y.Recent advances in flexible and stretchable sensing systems: from the perspective of system integration.ACS Nano2020;14:6449-69

[147] Tang L,Qu J,Tang J.A review of conductive hydrogel used in flexible strain sensor.Materials2020;13:3947 PMCID:PMC7560041

[148] Ge J,Zhang FR.A stretchable electronic fabric artificial skin with pressure-, lateral strain-, and flexion-sensitive properties.Adv Mater2016;28:722-8

[149] Ha KH,Jang H.Highly sensitive capacitive pressure sensors over a wide pressure range enabled by the hybrid responses of a highly porous nanocomposite.Adv Mater2021;33:e2103320

[150] Choi J,Baker LB.Skin-interfaced systems for sweat collection and analytics.Sci Adv2018;4:eaar3921 PMCID:PMC5817925

[151] Jang H,Kim E.Graphene e-tattoos for unobstructive ambulatory electrodermal activity sensing on the palm enabled by heterogeneous serpentine ribbons.Nat Commun2022;13:6604 PMCID:PMC9633646

[152] Zhang L,He H.Fully organic compliant dry electrodes self-adhesive to skin for long-term motion-robust epidermal biopotential monitoring.Nat Commun2020;11:4683 PMCID:PMC7499260

[153] Kim D.Stretchable electronics: materials strategies and devices.Adv Mater2008;20:4887-92

[154] Lee GH,Yoon C.A personalized electronic tattoo for healthcare realized by on-the-spot assembly of an intrinsically conductive and durable liquid-metal composite.Adv Mater2022;34:2270236

[155] Yao S,Hinson R.Ultrasoft porous 3D conductive dry electrodes for electrophysiological sensing and myoelectric control.Adv Mater Technol2022;7:2101637 PMCID:PMC9581336

[156] Li Y,Wu Z.Self-adhesive, self-healing, biocompatible and conductive polyacrylamide nanocomposite hydrogels for reliable strain and pressure sensors.Nano Energy2023;109:108324

[157] Huang F,Fan Q,Zhao M.Super-stretchable and adhesive cellulose nanofiber-reinforced conductive nanocomposite hydrogel for wearable motion-monitoring sensor.J Colloid Interface Sci2022;615:215-26

[158] Lee JH,Zhu J.Flexible conductive composite integrated with personal earphone for wireless, real-time monitoring of electrophysiological signs.ACS Appl Mater Interfaces2018;10:21184-90

[159] Bayoumy K,Elshafeey A.Smart wearable devices in cardiovascular care: where we are and how to move forward.Nat Rev Cardiol2021;18:581-99 PMCID:PMC7931503

[160] Ershad F,Yue J.Ultra-conformal drawn-on-skin electronics for multifunctional motion artifact-free sensing and point-of-care treatment.Nat Commun2020;11:3823 PMCID:PMC7393123

[161] Zu W,Carneiro MR,Tavakoli M.A comparative study of silver microflakes in digitally printable liquid metal embedded elastomer inks for stretchable electronics.Adv Mater Technol2022;7:2200534

[162] Namkoong M,Rahman MS.Moldable and transferrable conductive nanocomposites for epidermal electronics.Npj Flex Electron2022;6:41 PMCID:PMC9393028

[163] Roberts P,Majidi C.Soft tactile sensing skins for robotics.Curr Robot Rep2021;2:343-54

[164] Feng Y,Sun D,Shao C.Solvent-induced in-situ self-assembly lignin nanoparticles to reinforce conductive nanocomposite organogels as anti-freezing and anti-dehydration flexible strain sensors.Chem Eng J2022;433:133202

[165] Li S,Hu J.Recent advances of carbon-based flexible strain sensors in physiological signal monitoring.ACS Appl Electron Mater2020;2:2282-300

[166] Zhou Y,Li Z.Crack engineering boosts the performance of flexible sensors.VIEW2022;3:20220025

[167] Sun H,Fang Z.An ultrasensitive and stretchable strain sensor based on a microcrack structure for motion monitoring.Microsyst Nanoeng2022;8:111 PMCID:PMC9522852

[168] Wang S,Liang Y.Network cracks-based wearable strain sensors for subtle and large strain detection of human motions.J Mater Chem C2018;6:5140-7

[169] Amjadi M,Lee S,Park I.Highly stretchable and sensitive strain sensor based on silver nanowire-elastomer nanocomposite.ACS Nano2014;8:5154-63

[170] Stoyanov H,Risse S,Kofod G.Soft conductive elastomer materials for stretchable electronics and voltage controlled artificial muscles.Adv Mater2013;25:578-83

[171] Lee H,Cho H,Kim J.Soft nanocomposite based multi-point, multi-directional strain mapping sensor using anisotropic electrical impedance tomography.Sci Rep2017;7:39837 PMCID:PMC5264388

[172] Araromi OA,Dorsey KL.Ultra-sensitive and resilient compliant strain gauges for soft machines.Nature2020;587:219-24

[173] Yun T,Ji X.Waterproof and ultrasensitive paper-based wearable strain/pressure sensor from carbon black/multilayer graphene/carboxymethyl cellulose composite.Carbohydr Polym2023;313:120898

[174] Hasan MR,Suleman S.Papertronics: marriage between paper and electronics becoming a real scenario in resource-limited settings.ACS Appl Bio Mater2023;6:1368-79

[175] Solak İ,Yıldırım B,Hah D.Respiration monitoring using a paper-based wearable humidity sensor, a step forward to clinical tests.Sens Actuator A Phys2023;355:114316

[176] Li T,Qian Z.Ultrasensitive capacitive sensor composed of nanostructured electrodes for human-machine interface.Adv Mater Technol2022;7:2101704

[177] Zhang J,Wise HG,Chung J.Electromechanical coupling of isotropic fibrous networks with tailored auxetic behavior induced by water-printing under tension.J Mater Chem C2021;9:4544-53

[178] Lee J,Seo J.Conductive fiber-based ultrasensitive textile pressure sensor for wearable electronics.Adv Mater2015;27:2433-9

[179] Su X,Chen S.A highly conducting polymer for self-healable, printable, and stretchable organic electrochemical transistor arrays and near hysteresis-free soft tactile sensors.Adv Mater2022;34:2200682

[180] Yang T,Chu X.Hierarchically microstructure-bioinspired flexible piezoresistive bioelectronics.ACS Nano2021;15:11555-63

[181] Yin T,Hou Y.3D porous structure in MXene/PANI foam for a high-performance flexible pressure sensor.Small2022;18:e2204806

[182] Yang C,Zhao J.Highly sensitive wearable pressure sensors based on three-scale nested wrinkling microstructures of polypyrrole films.ACS Appl Mater Interfaces2018;10:25811-8

[183] Wang D,Song R.Freestanding silver/polypyrrole composite film for multifunctional sensor with biomimetic micropattern for physiological signals monitoring.Chem Eng J2021;404:126940

[184] Kwon K,Won SM.A battery-less wireless implant for the continuous monitoring of vascular pressure, flow rate and temperature.Nat Biomed Eng2023;

[185] Li AL,Hu ZH,Fang X.The distribution and epidemic characteristics of cerebrovascular disease in followed-up hypertension patients.Sci Rep2021;11:9366 PMCID:PMC8087808

[186] Jaffey JA,Leach SB,Girens RE.Pulmonary hypertension secondary to respiratory disease and/or hypoxia in dogs: clinical features, diagnostic testing and survival.Vet J2019;251:105347

[187] Luo N,Li C.Flexible piezoresistive sensor patch enabling ultralow power cuffless blood pressure measurement.Adv Funct Mater2016;26:1178-87

[188] Lou Y,Zhang J.Liquid metals in plastics for super-toughness and high-performance force sensors.Chem Eng J2020;399:125732

[189] Ning C,Cheng R.Flexible and stretchable fiber-shaped triboelectric nanogenerators for biomechanical monitoring and human-interactive sensing.Adv Funct Mater2021;31:2006679

[190] Liu Y,Luo X,Cui Y.Continuous monitoring of diabetes with an integrated microneedle biosensing device through 3D printing.Microsyst Nanoeng2021;7:75 PMCID:PMC8481261

[191] Bakker J,Jansen TC.Clinical use of lactate monitoring in critically ill patients.Ann Intensive Care2013;3:12 PMCID:PMC3654944

[192] Pirovano P,Shinde A.A wearable sensor for the detection of sodium and potassium in human sweat during exercise.Talanta2020;219:121145

[193] Lee H,Baik S,Kim DH.Enzyme-based glucose sensor: from invasive to wearable device.Adv Healthc Mater2018;7:e1701150

[194] Zhai Q,Wang R.Vertically aligned gold nanowires as stretchable and wearable epidermal ion-selective electrode for noninvasive multiplexed sweat analysis.Anal Chem2020;92:4647-55

[195] Oh SY,Jeong YR.Skin-attachable, stretchable electrochemical sweat sensor for glucose and pH detection.ACS Appl Mater Interfaces2018;10:13729-40

[196] Garg V,Rani S.A hierarchically designed nanocomposite hydrogel with multisensory capabilities towards wearable devices for human-body motion and glucose concentration detection.Compos Sci Technol2021;213:108894

[197] Shu Y,Lu Q,Xu Q.Highly stretchable wearable electrochemical sensor based on Ni-Co MOF nanosheet-decorated Ag/rGO/PU fiber for continuous sweat glucose detection.Anal Chem2021;93:16222-30

[198] Chandran N,Bayal M,Nair SS.Development of a paper printed colorimetric sensor based on Cu-Curcumin nanoparticles for evolving point-of-care clinical diagnosis of sodium.Sci Rep2022;12:6247 PMCID:PMC9012761

[199] Lim H,Jones KA.All-in-one, wireless, fully flexible sodium sensor system with integrated Au/CNT/Au nanocomposites.Sens Actuators B Chem2021;331:129416

[200] Khalid MAU.Flexible strain sensors for wearable applications fabricated using novel functional nanocomposites: a review.Compos Struct2022;284:115214

[201] Said RAM,Abdelzaher AM.Review - insights into the developments of nanocomposites for its processing and application as sensing materials.J Electrochem Soc2020;167:037549

[202] Shameem M, Sasikanth S, Annamalai R, Ganapathi Raman R. A brief review on polymer nanocomposites and its applications.Mater Today2021;45:2536-9

[203] Guo L,Zhang N,Anderson DG.Stretchable polymeric multielectrode array for conformal neural interfacing.Adv Mater2014;26:1427-33 PMCID:PMC4047984

[204] Li Y,Lan L.Ultrastretchable and wearable conductive multifilament enabled by buckled polypyrrole structure in parallel.npj Flex Electron2022;6:42

[205] Guan YS,Tang Y,Ren S.Kirigami-inspired nanoconfined polymer conducting nanosheets with 2000% stretchability.Adv Mater2018;30:1706390