Enabling New Medical Interventions through Medical Nanorobotics

By Sylvain Martel

- Nanorobotics

26 Jun, 2007 05:17 pm

comment(s) 3

Nearly 100,000 km of blood vessels inside the human body could provide the best routes for conducting new or improved medical interventions non-invasively. Modern interventional instruments such as catheters are constrained to larger blood vessels and as such, can only access a very small fraction of this blood circulatory network.

For instance, accessing remote locations beyond the reach of modern instruments to deliver therapeutic agents to a tumor through the human blood circulatory network can be done using known therapeutic methods such as chemotherapy. But many disadvantages of such approaches could potentially be avoided or at least reduced if drugs are administered and delivered to a target location using the most direct accessible routes. Such direct targeting would offer the potential to reduce dosage while minimizing systemic circulation of toxic compounds through healthy tissues. Hence, providing a technique capable of delivering therapeutic agents directly to a target location could be regard to as an important complementary tool to enhance the efficacy of many medical treatments.

A first demonstration with experimental results recently published in the scientific Journal Applied Physics Letters, March 12, 2007, suggests that such new therapeutic interventions may not be that far way. In fact, the experiment conducted by the research team led by Prof. Sylvain Martel of École Polytechnique de Montréal (EPM) in Canada demonstrated for the first time the feasibility of automatically navigate an untethered object in the blood vessels of a living animal. During the experiment, a 1.5 mm ferromagnetic bead was navigated without human intervention at an average speed of 10 cm/s in the carotid artery of a 25 kg living swine placed in a 1.5 T magnetic resonance imaging (MRI) system. From a special custom interface on a computer display, waypoints were plotted on top of an image of the carotid artery obtained with the MRI system. Once the bead was injected in the artery, its presence and location were automatically detected by the MRI system previously updated with specially developed software modules, and corrective actions were immediately performed automatically by the same system to bring the bead to its first waypoint. Determining the position of the bead and performing corrective actions to bring the object along a pre-planned trajectory following successive waypoints were executed 24 times per second by specially control software programs developed by the research team.

To propel the bead in a given direction, a propulsion force is induced in the ferromagnetic bead by varying the surrounding magnetic field or in another term, by applying magnetic gradients. The same three orthogonal coils used for slice selection during MR imaging were also used to track the object being navigated and to create the 3D magnetic gradients necessary to propel the bead at a speed and direction necessary to correct its trajectory within the artery.

This demonstration could be considered as a major technological breakthrough in modern interventional medicine and medical robotics considering that the researchers managed to integrate and synchronize at a sufficient speed, all the components necessary to efficiently navigate an object within the blood vessels. But more importantly, the fact that the experiments were done in the same type of clinical MRI platforms used for human and that an animal model relatively close to the human anatomy was used for the experiments, suggest that the same technique could also be used in human. In fact, the same research team also successfully navigated the same bead in laboratory settings reproducing precisely complex human blood vessels pathways.

Now that a functional platform is in place, the next step which has already begun is the miniaturization of the devices being navigated. To reach a tumor through the smallest capillaries, the overall diameter of each of these micro-devices or micro-carriers is estimated to be in the vicinity of 2 micrometers or approximately 1/40 the thickness of a human hair. Because the overall size of these micro-carriers will be smaller that a red blood cell, agglomeration of larger number of these micro-carriers will be steered between red cells. MRI-based magnetic gradients will be used to influence their paths at blood vessel bifurcations until the tumor being targeted is reached. Various drug release mechanisms are also under investigations as well as other medical applications that may benefit from this technology.

Reference:

Martel, Sylvain, et al. “Automatic navigation of an untethered device in the artery of a living animal using a conventional clinical magnetic resonance imaging system”, Applied Physics Letters , vol. 90, no. 11, March 12, 2007

Key words :

nanoscience,

medicine

nanotechnology

nanorobots

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3 comment(s)

[1]

Comment by Dr Hashim Uddin Ahmed

21 Jun, 2007 08:10 pm

Review status: ACCEPTED
The field of nanotechnology will have a tremendous impact in the field of medicine over the next decade or two. This short article summarises a report which takes us a step closer to targeted therapy using nanoparticles. If drugs or therapy can be delivered precisly to organs or parts of organs, morbidity from such therapy will be reduced as less damage is cause whilst theoretically efficacy may be improved by delivering a greater concentrated therapeutic effect where needed. The report should certainly be accepted for publication.

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[2]

Comment by Wolfgang Bacsa

27 Jun, 2007 01:15 pm

What is meant here with 'nanorobotics'?

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[3]

Comment by Sylvain Martel

3 Jul, 2007 05:17 pm

Although not obvious in the text, the term nanorobotics is used here because targeting in small blood vessels will be done with devices such as biodegradable polymer-based carriers relying on the properties of nano-components embedded in these carriers to enable them to perform the task. For instance, in the smallest capillaries, such carriers do not need to be smaller than approximately 2 micrometers (diameter) since approx. 42% of the blood vessel diameter would provide the best compromise between propulsion force versus drag force caused by blood vessel wall effect while maintaining efficient drug loading in the polymer. Within these micro-carriers, relatively large agglomeration of magnetic nanoparticles will replace a single larger magnetic particle for many reasons. For instance, nanoparticles are in the single magnetic domain and do not cause MR imaging distortions as other larger particles do, enabling better tracking and imaging registration. The size of nanoparticles also allows us to perform hyperthermia deep in the human body enabling us to increase the temperature locally under computer control and hence improving treatment efficacy or as a trigger mechanism for releasing drug. Hence, the fact that these carriers are under computer closed-loop control and rely on the properties defined in nanotechnology suggests that such approach may be defined within the field of nanorobotics.

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