- Open Access
Improving guidewire-mediated steerability of a magnetically actuated flexible microrobot
- Sungwoong Jeon†1, 2,
- Ali Kafash Hoshiar†2,
- Sangwon Kim3,
- Seungmin Lee1, 2,
- Eunhee Kim1, 2,
- Sunkey Lee1, 2,
- Kangho Kim1, 2,
- Jeonghun Lee1, 2,
- Jin-young Kim1, 2 and
- Hongsoo Choi1, 2Email authorView ORCID ID profile
© The Author(s) 2018
- Received: 24 October 2018
- Accepted: 10 December 2018
- Published: 13 December 2018
Here, we develop a flexible microrobot enhancing the steerability of a conventional guidewire. To improve steerability, a microrobot is attached to the tip of the guidewire and guided using an external magnetic field generated by an electromagnetic coil system. The flexible microrobot is fabricated via replica-molding and features a body made of polydimethylsiloxane (PDMS) and a single permanent magnet. As the robot is made of a deformable material, it can be steered using a low-intensity external magnetic field; the robot can potentially be guided into the coronary artery. To study steering performance, we employed mathematical modeling and a finite element model (FEM), and performed experiments under various magnetic fields. We found that a mathematical model using the Euler–Bernoulli beam could not precisely calculate the deformation angles. The FEM more accurately estimated those angles. The deformation angle can be controlled from 0 to 80° at a magnetic field intensity of 15 mT. The trackability at angles of 45 and 80° of the guidewire-based microrobot was confirmed in vitro using a two-dimensional blood vessel phantom.
- Flexible microrobot (robot)
- PCI surgery
- Magnetic actuation
Biomedical microrobots (here termed simply “robots”) will potentially revolutionize medicine. Many research groups have studied the biomedical applications of robots, including targeted drug delivery, biopsy-taking, hyperthermia control, radioactive therapy, scaffolding applications, in vivo ablation, stenting, sensing, and marking [1–7]. Most robots are controlled and operated in low Reynolds number fluids [8–10]. Therefore, the robots must be appropriately designed and fabricated; size, geometry, and material properties must be considered if they are to operate within the body [8, 11, 12]. More recently, tethered robots have been developed for diverse biomedical applications.
Especially, robots may play roles in minimally invasive vascular surgery. One treatment for chronic total occlusion (CTO), i.e., complete blockage of a coronary artery, is percutaneous coronary intervention (PCI) [13–17] employing guidewires and catheters. Some guidewires penetrate blood clots while others guide catheters. The guidewires are manually controlled by pushing them back-and-forth or rotating them about their axes. However, this is time-consuming and highly dependent on operator skill. Thus, to reduce operative time and increase success rates, many groups are seeking robotic solutions.
Several groups have performed distal shaping of catheters and guidewires to improve steerability and controllability [18–26]. Krings et al. and Lalande et al. developed magnetic microguidewires fitted with permanent magnets at the tips; an external magnetic field was used for steering [20, 21, 24]. However, a high-intensity magnetic field was required because the microguidewires were not very flexible and the steering system was composed of permanent magnets, which limits the real-time steering for a catheter.
Clogenson et al. developed a steerable guidewire compatible with magnetic resonance imaging (MRI) . Settecase et al. designed a steering catheter for use with MRI systems. A mathematical model was derived by exploiting the equilibrium between the magnetic and mechanical restorative torque; the equation was expressed in a linear form to simplify modeling. Thus, the model has certain limitations when used to estimate large nonlinear deformations . Thus, we here develop a novel magnetic robot attached to a guidewire that exhibited high-level steerability through multi-angled branches of a blood vessel phantom under the influence of a low-level magnetic field, improving real-time delivery performance. In this study, an electromagnetic steering system was used to improve the steering performance. Moreover, the proposed guidewire-based microrobot with flexible material is easier to control using external magnetic field compared with the previously reported magnetic catheter in Ref. .
Our robot was fabricated from polydimethylsiloxane (PDMS), which has a low elastic modulus and a high Poisson ratio. Because it is highly deformable, the robot can be readily steered through various vessel branches using a low-level magnetic field. A permanent magnet placed at the end of the PDMS beam is used for steering. To verify robot deformation and effective steering, we used a mathematical model based on the Euler–Bernoulli beam and a finite element model (FEM) to predict the deformation angles of the microrobot tip. We compared the results of the mathematical model, the FEM simulation, and the experimental values. To demonstrate its practical utility, we performed steering and tracking using a complex two-dimensional phantom. To demonstrate the potential of the robot, we performed biocompatibility testing using human colorectal cancer (HCT116) cells.
The mathematical model and the FEM
Material properties of flexible microrobots used in mathematical modeling and establishment of the FEM
Neodymium magnet (NdFeB, N52)
Young’s modulus (Pa)
750 × 103
160 × 109
Remanence flux density (T)
Geometric properties of flexible microrobots with guidewires PDMS, polydimethylsiloxane
Neodymium magnet (NdFeB, N52)
O.D 500, I.D 300
Experimental and simulated conditions used to evaluate steering of the flexible microrobot
Length of flexible microrobot (μm)
Direction of magnetic field (°)
Intensity of magnetic field (mT)
5, 10, 15
The microrobot without guidewire was sterilized twice with 70% ethanol and phosphate buffered saline (PBS, Welgene, Gyeongsan, South Korea) for sterilization and then dried for 20 min.
The microrobot was placed in each well of a 24-well plate except for the control groups.
One mL cell culture medium with HCT 116 cells (5 × 105 cells/mL) was dropped into each well plate.
- 4.Well plates were incubated for 3 days in an incubator (Fig. 10c) and then the cell viability test was performed according to the manufacturer’s instructions.
Cell viability was assessed using a LIVE/DEAD Cell Imaging Kit (excitation wavelength 488 nm, emission wavelength 570 nm; Molecular Probes, Life Technologies Corp., USA) to stain live (green fluorescent signal) and dead (red fluorescent signal) cells. Cells cultured without robots (control cells) are shown in Fig. 10a, and cells cultured with microrobots in Fig. 10b, c. Figure 10d shows the cell viabilities, which were similar between the two groups. Thus, the robot is non-toxic.
We designed and fabricated, via replica-molding, a guidewire-based robot for use during PCI. A low-level magnetic field affords actuation; the robot is highly flexible, smaller than a coronary artery, and connected to a conventional guidewire. The robot is steered and controlled using a low-intensity, external magnetic fields (5–15 mT). Robot deformation is controlled using geometric parameters (length and diameter), magnetic steering (extent and direction), and the material properties. We used Euler–Bernoulli theory and an FEM to predict robot deformation. The experimental results were in good agreement with the simulated values, but not the mathematical data. The robot moved within a two-dimensional blood phantom featuring many branches. The robot was guided to desired locations and steered into branches at angles of 45 and 80º. Furthermore, the robot was not toxic to human cells, and can thus be used in vivo.
SJ and AKH carried out the simulation, the experiment and wrote the manuscript. SK and SL guided analysis data and reviewed the manuscript. EK cultured HCT116 cells and conducted biocompatibility test of microrobot. SL and KK designed and fabricated microrobots. JL conducted the experiment. JK and HC conceived of the study and wrote the manuscript. All authors read and approved the final manuscript.
The authors are grateful to all members of DGIST-ETH Microrobot Research Center and Bio-Micro Robotics Lab. for their sincere help and comments.
The authors declare that they have no competing interests.
Funding for this research was provided by the Korea Evaluation Institute of Industrial Technology (KEIT) funded by the Ministry of Trade, Industry & Energy (No. 10052980) and the Global Research Laboratory from the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT (No. NRF 2017K1A1A2013237).
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- Kafash Hoshiar A, Le T, Amin F, Kim M, Yoon J (2017) A novel magnetic actuation scheme to disaggregate nanoparticles and enhance passage across the blood–brain barrier. Nanomaterials 8(1):3View ArticleGoogle Scholar
- Kafash Hoshiar A, Le T, Amin F, Kim M, Yoon J (2017) Studies of aggregated nanoparticles steering during magnetic-guided drug delivery in the blood vessels. J Magn Magn Mater 427:181–187View ArticleGoogle Scholar
- Amin F et al (2017) Osmotin-loaded magnetic nanoparticles with electromagnetic guidance for the treatment of Alzheimer’s disease. Nanoscale 9(30):10619–10632View ArticleGoogle Scholar
- Kim S, Qiu F, Kim S, Ghanbari A, Moon C, Zhang L et al (2013) Fabrication and characterization of magnetic microrobots for three-dimensional cell culture and targeted transportation. Adv Mater 25:5863–5868View ArticleGoogle Scholar
- Ullrich F, Bergeles C, Pokki J, Ergeneman O, Erni S, Chatzipirpiridis G et al (2013) Mobility experiments with microrobots for minimally invasive intraocular surgery: microrobot experiments for intraocular surgery. Invest Ophthalmol Vis Sci 54:2853–2863View ArticleGoogle Scholar
- Han J, Zhen J, Go G, Choi Y, Ko SY, Park JO, Park S (2016) Hybrid-actuating macrophage-based microrobots for active cancer therapy. Sci Rep 6:28717View ArticleGoogle Scholar
- Kim S, Lee S, Lee J, Nelson BJ, Zhang L, Choi H (2016) Fabrication and manipulation of ciliary microrobots with non-reciprocal magnetic actuation. Sci Rep 6:30713View ArticleGoogle Scholar
- Servant A, Qiu F, Mazza M, Kostarelos K, Nelson BJ (2015) Controlled in vivo swimming of a swarm of bacteria-like microrobotic flagella. Adv Mater 27(19):2981–2988View ArticleGoogle Scholar
- Zhang L, Abbott JJ, Dong L, Kratochvil BE, Bell D, Nelson BJ (2009) Artificial bacterial flagella: fabrication and magnetic control. Appl Phys Lett 94(6):064107View ArticleGoogle Scholar
- Abbott JJ, Peyer KE, Lagomarsino MC, Zhang L, Dong L, Kaliakatsos IK, Nelson BJ (2009) How should microrobots swim? Int J Robot Res 28(11–12):1434–1447View ArticleGoogle Scholar
- Nelson BJ, Kaliakatsos IK, Abbott JJ (2010) Microrobots for minimally invasive medicine. Annu Rev Biomed Eng 12:55–85View ArticleGoogle Scholar
- Peyer KE, Tottori S, Qiu F, Zhang L, Nelson BJ (2013) Magnetic helical micromachines. Chem Eur J 19(1):28–38View ArticleGoogle Scholar
- Fu Y, Liu H, Huang W, Wang S, Liang Z (2009) Steerable catheters in minimally invasive vascular surgery. Int J Med Robot Comput Assist Surg 5(4):381–391View ArticleGoogle Scholar
- Touma G, Ramsay D, Weaver J (2015) Chronic total occlusions—current techniques and future directions. IJC Heart Vasculature 7:28–39View ArticleGoogle Scholar
- Jeon S, Kafash Hoshiar A, Kim K, Lee S, Kim E, Lee S et al (2018) A magnetically controlled soft microrobot steering a guidewire in a three-dimensional phantom vascular network. soft robotics, On-line publishedGoogle Scholar
- Kafash Hoshiar A, Jeon S, Kim K, Lee S, Kim JY, Choi H (2018) Steering algorithm for a flexible microrobot to enhance guidewire control in a coronary angioplasty application. Micromachines 9(12):617View ArticleGoogle Scholar
- Lee S, Lee S, Kim S, Yoon CH, Park HJ, Kim JY, Choi H (2018) Fabrication and characterization of a magnetic drilling actuator for navigation in a three-dimensional phantom vascular network. Sci Rep 8(1):3691View ArticleGoogle Scholar
- Houser RA, Bourne T (1998) U.S. Patent No. 5,833,604. Washington, DC: U.S. Patent and Trademark OfficeGoogle Scholar
- Chatzipirpiridis G, Erne P, Ergeneman O, Pané S, Nelson BJ (2015). A magnetic force sensor on a catheter tip for minimally invasive surgery. In: Engineering in medicine and biology society (EMBC), 2015 37th annual international conference of the IEEE, pp 7970–7973Google Scholar
- Krings T, Finney J, Niggemann P, Reinacher P, Lück N, Drexler A et al (2006) Magnetic versus manual guidewire manipulation in neuroradiology: in vitro results. Neuroradiology 48(6):394–401View ArticleGoogle Scholar
- Schiemann M, Killmann R, Kleen M, Abolmaali N, Finney J, Vogl TJ (2004) Vascular guide wire navigation with a magnetic guidance system: experimental results in a phantom. Radiology 232(2):475–481View ArticleGoogle Scholar
- Petruska AJ, Ruetz F, Hong A, Regli L, Sürücü O, Zemmar A, Nelson BJ (2016). Magnetic needle guidance for neurosurgery: initial design and proof of concept. In: Robotics and automation (ICRA), 2016 IEEE international conference on, pp 4392–4397Google Scholar
- Muller L, Saeed M, Wilson MW, Hetts SW (2012) Remote control catheter navigation: options for guidance under MRI. J Cardiovasc Magn Reson 14(1):33View ArticleGoogle Scholar
- Lalande V, Gosselin FP, Vonthron M, Conan B, Tremblay C, Beaudoin G et al (2015) In vivo demonstration of magnetic guidewire steerability in a MRI system with additional gradient coils. Med Phys 42(2):969–976View ArticleGoogle Scholar
- Settecase F, Sussman MS, Wilson MW, Hetts S, Arenson RL, Malba V et al (2007) Magnetically-assisted remote control (MARC) steering of endovascular catheters for interventional MRI: a model for deflection and design implications. Med Phys 34(8):3135–3142View ArticleGoogle Scholar
- Haga Y, Esashi M (2000) Small diameter active catheter using shape memory alloy coils. IEEJ Trans Sens Micromachines 120(11):509–514View ArticleGoogle Scholar
- Clogenson HC, Dankelman J, van den Dobbelsteen JJ (2014) Steerable guidewire for magnetic resonance guided endovascular interventions. J Med Devices 8(2):021002View ArticleGoogle Scholar
- Zhang M, Wu J, Wang L, Xiao K, Wen W (2010) A simple method for fabricating multi-layer PDMS structures for 3D microfluidic chips. Lab Chip 10(9):1199–1203View ArticleGoogle Scholar
- Schuerle S, Erni S, Flink M, Kratochvil BE, Nelson BJ (2013) Three-dimensional magnetic manipulation of micro- and nanostructures for applications in life sciences. IEEE Trans Magn 49(1):321–330View ArticleGoogle Scholar
- Kratochvil BE, Kummer MP, Erni S, Borer R, Frutiger DR, Schürle S, Nelson BJ (2014). MiniMag: a hemispherical electromagnetic system for 5-DOF wireless micromanipulation. In: Experimental robotics. Springer, Berlin, pp 317–329Google Scholar
- Kummer MP, Abbott JJ, Kratochvil BE, Borer R, Sengul A, Nelson BJ (2010) OctoMag: an electromagnetic system for 5-DOF wireless micromanipulation. IEEE Trans Rob 26(6):1006–1017View ArticleGoogle Scholar
- Kim JY, Jeon S, Lee J, Lee S, Lee J, Jeon BO et al (2018) A simple and rapid fabrication method for biodegradable drug-encapsulating microrobots using laser micromachining, and characterization thereof. Sens Actuators B Chem 266:276–287View ArticleGoogle Scholar
- Lee S, Kim S, Kim S, Kim JY, Moon C, Nelson BJ, Choi H (2018) A capsule-type microrobot with pick-and-drop motion for targeted drug and cell delivery. Adv Healthc Mater 7(9):1700985View ArticleGoogle Scholar
- Kim E, Yoo SJ, Kwon TH, Zhang L, Moon C, Choi H (2016) Nano-patterned SU-8 surface using nanosphere-lithography for enhanced neuronal cell growth. Nanotechnology 27(17):175303View ArticleGoogle Scholar