Guide wires are commonly used to assist surgeons during vascular surgery. Guide wires are usually the first to be placed, eventually allowing easy exchange of surgical tools to the target site. The surgeon has to manually control and manipulate the guide wire to the target region. This process is complicated by the tortuous nature of the vasculature and is made worse as the surgeon has limited vision (constant need to switch between overlay angiographs) and control over the guide wire tip (controlling the distal tip from the proximal end). For the first time towards minimally invasive Arteriovenous Fistula Angioplasty Procedures, we aim to improve the controllability of the in vivo guide wire via the attachment of a magnetic tip to the distal end of the guide wire, which under the control of external magnetic field generators can deflect the magnetic tip. This controlled deflection translates to the selection of entrance angle for the guide wire tip, affording distal control.
This is especially useful for navigating around stenosis which is common for patients with Arteriovenous(AV) Fistula. The repeated use of the fistula during dialysis has been claimed as a cause for the high occurrence of stenosis (due to tissue scaring from access). Fistulas and their grafts are however still preferred over other renal access in most situation due to its lower risk of infections. Our proposed system here can improve the controllability, safety and speed of current procedures and can enable AV-Fistula Angioplasty Procedures to be shifted to out-patient clinics.
Student: Bok Seng Yeow
Research fellow: Jinji Sun
Project Investigators: Hongliang Ren, Jackie Ho
Yeow, B. S.; Sun, J.; Ho, J. & Ren, H. Towards Magnetically Actuated Guide-wire Steering in Arteriovenous Fistula Angioplasty Procedures IEEE Conference on Real-time Computing and Robotics (RCAR), IEEE, 2016, best student paper.
The objectives of this project are to design and evaluate the performance of an electromagnetic actuated (EMA) drug delivery system and explore the related issues.
The EMA system consists of magneto-responsive microcapsules as drug carriers, a coil system with controlled currents flowing through, as well as a tracking algorithm for close loop feedback control.
The magneto-responsive and thermal sensitive microcapsules are prepared through an encapsulator. The properties can be further utilized for controlled drug release. The encapsulated microbubbles are prepared based on a gas foaming technique for enhancing the ultrasound imaging contrast.
The coil system consists of 2 Helmoholz coil pairs and 2 Maxwell coil pairs are fabricated with printed aluminum skeleton and copper wires. A current control system including 3 DC motor governors and a USB to RS485 converter are added to realize programmable current control. Hence, the magnetic fields generated by the coils are controlled by the signals sent by the computer. Figure 1 shows the principle of actuation over the microcapsules.
Fig. 1: Principle of Magnetic Actuation over the Microcapsules
Figure 2 shows the preliminary set up for actuation over microparticles within the region of interest.
Fig. 2 Setup for Microparticles Actuation
Microcapsules with evenly distributed magnetic stripes have been fabricated. The stripes make the spherical microcapsules asymmetric so that their locomotion control is directed. Alignment and movement of the microcapsules are observed in the EMA system under DC output, while rotation is observed under sinusoidal output current.
Fig. 3 Microcapsules with magnetic CI strips. Scale bar: 200μm.
Fig.4 Magnetic actuation with (A)small cylindrical magnet and (B)magnetic microcapsules
Staff: Shen Shen, Song Shuang and Zhu Jingling
PIs: Ren Hongliang and Li Jun
Presentations and Publications
1．Shen Shen, Shuang Song, Jingling Zhu, Max Q-H Meng, Jun Li and Hongliang Ren, Preliminary Design towards a Magnetic Actuated Drug Delivery System, 7th IEEE International Conference on Cybernetics and Intelligent Systems and the 7th IEEE International Conference on Robotics, Automation and Mechatronics, 2015.
Poster in BME Showcase 2015
Magnetic microbubbles which can be controlled by an external magnetic field have been explored as a method for precise and efficient drug delivery. In this paper, a technique for the fabrication of microbubble encapsulated magnetic spheres is presented. The resultant magnetic spheres were subsequently imaged using ultrasound and the encapsulated microbubbles proved to appear as bright spots and resulted in enhanced ultrasound image contrast, as compared to the solid magnetic spheres which appeared dull. A tracking algorithm was then developed for the tracking of the magnetic microbubbles based on optical flow tracking. Further development of the magnetic microbubbles and tracking algorithm can lead to future use of the tracking algorithm in the case of in vivo injection of the magnetic microbubbles.
1. Loh Kai Ting, Ren Hongliang and Li Jun, Tracking Magnetic Particles under Ultrasound Imaging using Contrast-Enhancing Microbubbles, The 11th Asian Conference on Computer Aided Surgery, 2015.
Poster in BME Showcase 2015