Mimicking the locomotive abilities of living organisms on the microscale, where the downsizing of rigid parts and circuitry presents inherent problems, is a complex feat. In nature, many soft-bodied organisms (inchworm, leech) have evolved simple, yet efficient locomotion strategies in which reciprocal actuation cycles synchronize with spatiotemporal modulation of friction between their bodies and environment. We developed microscopic (∼100 μm) hydrogel crawlers that move in aqueous environment through spatiotemporal modulation of the friction between their bodies and the substrate. Thermo-responsive poly-n-isopropyl acrylamide hydrogels loaded with gold nanoparticles shrink locally and reversibly when heated photothermally with laser light. The out-of-equilibrium collapse and reswelling of the hydrogel is responsible for asymmetric changes in the friction between the actuating section of the crawler and the substrate. This friction hysteresis, together with off-centered irradiation, results in directional motion of the crawler. We developed a model that predicts the order of magnitude of the crawler motion (within 50%) and agrees with the observed experimental trends. Crawler trajectories can be controlled enabling applications of the crawler as micromanipulator that can push small cargo along a surface.
Get full access to this article
View all access options for this article.
References
1.
SittiM, CeylanH, HuW, et al.Biomedical applications of untethered mobile milli/microrobots. Proc IEEE, 2015; 103:205–224.
2.
CianchettiM, LaschiC, MenciassiA, et al.Biomedical applications of soft robotics. Nat Rev Mater, 2018; 3:143–153.
SittiM. Miniature soft robots—road to the clinic. Nat Rev Mater, 2018; 3:74–75.
5.
TasogluS, DillerE, GuvenS, et al.Untethered micro-robotic coding of three-dimensional material composition. Nat Commun, 2014; 5:3124.
6.
FloydS, PawasheC, SittiM. An untethered magnetically actuated micro-robot capable of motion on arbitrary surfaces. In: 2008 IEEE International Conference on Robotics and Automation, Pasadena, CA, May 19–23, 2008, pp. 419–424. IEEE.
7.
ShenT, FontMG, JungS, et al.Remotely triggered locomotion of hydrogel mag-bots in confined spaces. Sci Rep, 2017; 7:16178.
8.
LogetG, KuhnA. Electric field-induced chemical locomotion of conducting objects. Nat Commun, 2011; 2:1–6.
9.
ChenX-Z, JangB, AhmedD, et al.Small-scale machines driven by external power sources. Adv Mater, 2018; 30:1705061.
10.
LeeH, XiaC, FangNX. First jump of microgel; Actuation speed enhancement by elastic instability. Soft Matter, 2010; 6:4342–4345.
RogóżM, ZengH, XuanC, et al.Light-driven soft robot mimics caterpillar locomotion in natural scale. Adv Opt Mater, 2016; 4:1689–1694.
13.
MoralesD, PalleauE, DickeyMD, et al.Electro-actuated hydrogel walkers with dual responsive legs. Soft Matter, 2014; 10:1337–1348.
14.
MaedaS, HaraY, SakaiT, et al.Self-walking gel. Adv Mater, 2007; 19:3480–3484.
15.
HuW, LumGZ, MastrangeliM, et al.Small-scale soft-bodied robot with multimodal locomotion. Nature, 2018; 554:81–85.
16.
PalagiS, MarkAG, ReighSY, et al.Structured light enables biomimetic swimming and versatile locomotion of photoresponsive soft microrobots. Nat Mater, 2016; 15:647–653.
17.
AydinO, ZhangX, NuethongS, et al.Neuromuscular actuation of biohybrid motile bots. Proc Natl Acad Sci, 2019; 116:19841–19847.
18.
MenciassiA, AccotoD, GoriniS, et al.Development of a biomimetic miniature robotic crawler. Auton Robots, 2006; 21:155–163.
19.
ZengH, WasylczykP, WiersmaDS, et al.Light robots: bridging the gap between microrobotics and photomechanics in soft materials. Adv Mater, 2017; 30:1703554.
20.
Camacho-LopezM, FinkelmannH, Palffy-MuhorayP, et al.Fast liquid-crystal elastomer swims into the dark. Nat Mater, 2004; 3:307–310.
21.
KuoJ-C, HuangH-W, TungS-W, et al.A hydrogel-based intravascular microgripper manipulated using magnetic fields. Sens Actuators Phys, 2014; 211:121–130.
22.
GauthierM, GibeauE, HeribanD. Submerged robotic micromanipulation and dielectrophoretic micro-object release. In: 2006 9th International Conference on Control, Automation, Robotics and Vision, Singapore, December 5–8, 2006, pp. 1–6. IEEE.
23.
AlapanY, YasaO, YigitB, et al.Microrobotics and microorganisms: biohybrid autonomous cellular robots. Annu Rev Control Robot Auton Syst, 2019; 2:205–230.
24.
ParkS-J, GazzolaM, ParkKS, et al.Phototactic guidance of a tissue-engineered soft-robotic ray. Science, 2016; 353:158–162.
RamanR, CvetkovicC, BashirR. A modular approach to the design, fabrication, and characterization of muscle-powered biological machines. Nat Protoc, 2017; 12:519–533.
27.
MourranA, ZhangH, VinokurR, et al.Soft microrobots employing nonequilibrium actuation via plasmonic heating. Adv Mater, 2017; 29:1604825.
28.
ZhangH, KoensL, LaugaE, et al.Microgel rotors: a light-driven microgel rotor (small 46/2019). Small, 2019; 15:1970246.
29.
HauserAW, EvansAA, NaJ-H, et al.Photothermally reprogrammable buckling of nanocomposite gel sheets. Angew Chem Int Ed, 2015; 54:5434–5437.
30.
SershenSR, MensingGA, NgM, et al.Independent optical control of microfluidic valves formed from optomechanically responsive nanocomposite hydrogels. Adv Mater, 2005; 17:1366–1368.
31.
ZhuZ, SensesE, AkcoraP, et al.Programmable light-controlled shape changes in layered polymer nanocomposites. ACS Nano, 2012; 6:3152–3162.
32.
YoonJ, BianP, KimJ, et al.Local switching of chemical patterns through light-triggered unfolding of creased hydrogel surfaces. Angew Chem, 2012; 124:7258–7261.
33.
LiuD, BastiaansenCWM, den ToonderJMJ, et al.(Photo-)thermally induced formation of dynamic surface topographies in polymer hydrogel networks. Langmuir, 2013; 29:5622–5629.
34.
DeSimoneA, TatoneA. Crawling motility through the analysis of model locomotors: two case studies. Eur Phys J E, 2012; 35:85.
35.
ElderingJ, JacobsHO. The role of symmetry and dissipation in biolocomotion. SIAM J Appl Dyn Syst, 2016; 15:24–59.
36.
TungHW, MaffioliM, FrutigerDR, et al.Polymer-based wireless resonant magnetic microrobots. IEEE Trans Robot, 2014; 30:26–32.
37.
SulOJ, FalvoMR, TaylorRM, et al.Thermally actuated untethered impact-driven locomotive microdevices. Appl Phys Lett, 2006; 89:203512.
38.
PurcellEM. Life at low reynolds number. Am J Phys, 1977; 45:3–11.
39.
YangC, WangW, YaoC, et al.Hydrogel walkers with electro-driven motility for cargo transport. Sci Rep, 2015; 5:13622.
40.
FairbanksBD, SchwartzMP, BowmanCN, et al.Photoinitiated polymerization of PEG-diacrylate with lithium phenyl-2,4,6-trimethylbenzoylphosphinate: polymerization rate and cytocompatibility. Biomaterials, 2009; 30:6702–6707.
41.
DendukuriD, GuSS, PregibonDC, et al.Stop-flow lithography in a microfluidic device. Lab Chip, 2007; 7:818–828.
42.
PlautRH. Mathematical model of inchworm locomotion. Int J Non-Linear Mech, 2015; 76:56–63.
KreerT. Polymer-brush lubrication: a review of recent theoretical advances. Soft Matter, 2016; 12:3479–3501.
45.
NalamPC, RamakrishnaSN, Espinosa-MarzalRM, et al.Exploring lubrication regimes at the nanoscale: nanotribological characterization of silica and polymer brushes in viscous solvents. Langmuir, 2013; 29:10149–10158.
46.
KanekoY, YoshidaR, SakaiK, et al.Temperature-responsive shrinking kinetics of poly (N-isopropylacrylamide) copolymer gels with hydrophilic and hydrophobic comonomers. J Membr Sci, 1995; 101:13–22.
47.
MorimotoN, OhkiT, KuritaK, et al.Thermo-responsive hydrogels with nanodomains: rapid shrinking of a nanogel-crosslinking hydrogel of poly(N-isopropyl acrylamide). Macromol Rapid Commun, 2008; 29:672–676.
48.
LiuG, ZhangG. Collapse and swelling of thermally sensitive poly(N-isopropylacrylamide) brushes monitored with a quartz crystal microbalance. J Phys Chem B, 2005; 109:743–747.
49.
ChengH, LiuG, WangC, et al.Collapse and swelling of poly(N-isopropylacrylamide-co-sodium acrylate) copolymer brushes grafted on a flat SiO2 surface. J Polym Sci Part B Polym Phys, 2006; 44:770–778.
50.
ChengH, ShenL, WuC. LLS and FTIR studies on the hysteresis in association and dissociation of poly(N-isopropylacrylamide) chains in water. Macromolecules, 2006; 39:2325–2329.
51.
LuY, ZhouK, DingY, et al.Origin of hysteresis observed in association and dissociation of polymer chains in water. Phys Chem Chem Phys, 2010; 12:3188.
52.
VarmaS, BureauL, DébarreD. The conformation of thermoresponsive polymer brushes probed by optical reflectivity. Langmuir, 2016; 32:3152–3163.
53.
SuiX, ChenQ, HempeniusMA, et al.Probing the collapse dynamics of poly(N-isopropylacrylamide) brushes by AFM: effects of co-nonsolvency and grafting densities. Small, 2011; 7:1440–1447.
54.
JunkMJN, LiW, SchlüterAD, et al.Formation of a mesoscopic skin barrier in mesoglobules of thermoresponsive polymers. J Am Chem Soc, 2011; 133:10832–10838.
LeeS, ItenR, MüllerM, et al.Influence of molecular architecture on the adsorption of poly(ethylene oxide)−poly(propylene oxide)−poly(ethylene oxide) on PDMS surfaces and implications for aqueous lubrication. Macromolecules, 2004; 37:8349–8356.
Supplementary Material
Please find the following supplemental material available below.
For Open Access articles published under a Creative Commons License, all supplemental material carries the same license as the article it is associated with.
For non-Open Access articles published, all supplemental material carries a non-exclusive license, and permission requests for re-use of supplemental material or any part of supplemental material shall be sent directly to the copyright owner as specified in the copyright notice associated with the article.
