Periodic Reporting for period 1 - MagnetoSense (Haptic sensing skin for biomedical applications with soft magnetorheological elastomers)
Reporting period: 2022-10-01 to 2024-03-31
Sensorial and tactile information represent the base of all surgical procedures in medicine. The vision sense has been and continues to be developed extensively by use of micro-cameras, MRI, X-rays and many others. Nonetheless, in many cases, the vision is not enough. The touch sense is necessary to identify the stiffness of the underlying organ or tissue and press more or less to perform a cut, remove a tumor or even move a catheter inside a curved vain. This stiffness is transmitted to the finger of the surgeon as a “pressure-deformation” information. This haptic sense is present naturally in our fingertips. Nevertheless, with the recent development of non-invasive techniques, the surgeon operates robotic devices that deliver optical information via a screen but loses all haptic information since his/her fingers are not in direct contact with the organ. The present project aims at proposing a novel material, a magnetorheological elastomer (MRE) membrane as a haptic sensor. MREs are soft elastomeric materials comprising magnetic particles thus being able to deform significantly upon application of an external magnetic field. Recently, it was shown that by fabricating them in exotic or slender geometries one can exploit their resulting instabilities to shape surfaces, induce programmable swelling and deswelling, or even create swimming microrobots and externally controllable catheters. All those applications use MREs as actuators. By contrast, here, we plan to exploit the reverse operation that of sensing, i.e. induce magnetic field changes via deformation. The principle lies in using the inherent magneto-mechanical coupling to induce readable magnetic fields when the MRE deforms. The reading of the fields can then be translated back to a deformation and a force thus being able to sense soft or stiff objects. The very soft nature of MREs will allow for a very sensitive measurement of forces as low as those felt by touching a soft gel or baby-skin.
In simpler words, when the magnetic field is applied, the material will deform. But conversely, when it is deformed after being magnetized, it will act on the magnetic field that surrounds it. It is these properties and flexibility that will give it its haptic characteristics. "Let's say you're wearing a glove with this material. When you touch something, the material will deform, and the magnetic field will change around it. This change will be measurable. If you touch something that's stiff, the material will warp a lot. On the other hand, if you touch something very soft, the material won't deform, and the magnetic field won't change. We play with the alternations of magnetic fields following the deformation to measure touch," explains Kostas Danas. This type of technology, which is capable of measuring touch, is also called "haptic sensors".
The possible uses of these haptic sensors are diverse. "They have applications in all areas where there are robots. At the moment we don't have any robots that have this sense of touch, they only see with cameras," says Kostas Danas. The flexibility of the material created makes it possible to adapt to any form of robot. And adding meaning to robots can have multiple implications. For example, in the biomedical field, for minimally invasive surgeries1. This type of surgery consists of making very small incisions, and performing the surgery through this incision with the assistance of a video, either with long instruments or on robots equipped with small cameras. But 2D video limits the possibilities offered by these robots, so giving them extra meaning could greatly increase their capabilities and the amount of information they can return to the surgeon performing the operation. Thus, more surgeries would be eligible for this type of operation, yet the benefits of minimally invasive surgeries have been proven, including a reduction in recovery time after the operation and lower risks.
In simpler words, when the magnetic field is applied, the material will deform. But conversely, when it is deformed after being magnetized, it will act on the magnetic field that surrounds it. It is these properties and flexibility that will give it its haptic characteristics. "Let's say you're wearing a glove with this material. When you touch something, the material will deform, and the magnetic field will change around it. This change will be measurable. If you touch something that's stiff, the material will warp a lot. On the other hand, if you touch something very soft, the material won't deform, and the magnetic field won't change. We play with the alternations of magnetic fields following the deformation to measure touch," explains Kostas Danas. This type of technology, which is capable of measuring touch, is also called "haptic sensors".
The possible uses of these haptic sensors are diverse. "They have applications in all areas where there are robots. At the moment we don't have any robots that have this sense of touch, they only see with cameras," says Kostas Danas. The flexibility of the material created makes it possible to adapt to any form of robot. And adding meaning to robots can have multiple implications. For example, in the biomedical field, for minimally invasive surgeries1. This type of surgery consists of making very small incisions, and performing the surgery through this incision with the assistance of a video, either with long instruments or on robots equipped with small cameras. But 2D video limits the possibilities offered by these robots, so giving them extra meaning could greatly increase their capabilities and the amount of information they can return to the surgeon performing the operation. Thus, more surgeries would be eligible for this type of operation, yet the benefits of minimally invasive surgeries have been proven, including a reduction in recovery time after the operation and lower risks.
Currently, our project has led to the proposition of a novel material which allows to enhance magnetic field changes upon application of deformations. This was not initially possible with the existing magnetorheological elastomers (MREs) that were currently available in our laboratory and in the literature. The reason for that is related to the specific magneto-mechanical coupling in such materials. In a nutshell standard MREs may be actuated to deform by application of the magnetic field, but the opposite operation is not as strong. In other words, deforming a permanently magnetized MRE does not alter significantly (to be measurable with available magnetic sensors) its magnetization. This has been very recently explained theoretically and experimentally and by now we are able to understand the fundamental physics for such a behavior. Starting from this point, we were able to propose a new MRE material that allows changes in its magnetization when deformed.
The work performed so far involves fabrication and experimental testing of the new MRE material under combined magnetic and mechanical loads. The experimental part is supplemented by full field numerical simulations allowing to optimize further the setups and material fabrication. In the current system, we observe a measurable magnetization change upon application of various forms of deformation (in the order of tens of milli-Tesla) thus making the proposed material a promising candidate for sensing under large deformations.
The work performed so far involves fabrication and experimental testing of the new MRE material under combined magnetic and mechanical loads. The experimental part is supplemented by full field numerical simulations allowing to optimize further the setups and material fabrication. In the current system, we observe a measurable magnetization change upon application of various forms of deformation (in the order of tens of milli-Tesla) thus making the proposed material a promising candidate for sensing under large deformations.
The proposed MRE material is novel. It did not exist before the beginning of the project as such. It is therefore a result beyond the current state of the art on its own. The reason we were forced to create this new variant of MRE is simply related to the fact that the previous ones did not provide a measurable sensing capability. As a result, we are in the process of understanding and testing of this new magneto-mechanical composite. We believe that this new solid will allow to obtain in the future a mechanically soft sensor. This is a potential huge step towards sensors that can change form and adapt to more complex geometrical environments. Further uptake necessitates to embed electric grids or connected particles to allow a readable electric field at the exterior part of the material. This research is long term but with a high potential. It is necessary that we demonstrate the feasibility of such a sensor via an example case. While this is not trivial, the current MRE material is easily fabricated in a highly reproducible manner. Having a prototype device that is able to measure the applied deformation field is currently underway. This first prototype will allow to show the capabilities of such materials in measuring deformation fields indirectly via magnetic field changes.