Magnetoactive elastomers (MAEs) on the basis of a silicone matrix filled with carbonyl iron microparticles are developed for an envisaged application in eye surgery for treatment of complicated retinal detachments. The proposed magnetic fixator of an eye retina consists of an MAE seal placed inside an eye in the area of a retinal break, and an external silicone sponge with embedded permanent magnets which can be sutured to the sclera to provide magnetic field acting on the internal MAE seal. For MAE seal development, MAEs of various compositions (containing 52-76 mass% of ferromagnetic iron microparticles) are synthesized and their surface, magnetic, mechanical, and rheological properties are investigated in external magnetic fields. To demonstrate MAEs efficacy as an element of the retina magnetic fixator, magnetic forces acting between MAE samples and systems of permanent magnets were measured in the curved configuration corresponding to the human eye geometry. It has been demonstrated that the pressure produced within the fixator can be varied in a wide range by tuning the MAE composition and MAE seal dimensions as well as by optimizing the size and configuration of permanent magnets within the external silicone sponge.A high magnetic response of MAEs makes them very promising for numerous practical applications. Being a solid analogue to magnetic fluids 20 MAEs can be explored in the areas where magnetic fluids are usually used, in particular, as sealing elements, vibration absorbers, and so forth. Moreover, MAEs have some advantages in comparison with magnetic fluids, in particular, Additional Supporting Information may be found in the online version of this article.
We explore the possibility of creating an effective retinal fixator on the basis of magnetoactive elastomers (MAEs) and systems of permanent magnets. MAEs consist of silicone elastomer matrix with embedded magnetic iron microparticles. We study theoretically and experimentally magnetic forces acting between MAE samples and permanent magnets in various configurations. The theoretical model is based around classical magnetostatics and Maxwell equations with different parameters accounting for peculiarities of the material and the setup. Approximation of the experimentally measured magnetization curves for MAE samples was used to find input parameters for the theoretical model. To test the model, we conducted a series of experimental measurements of magnetic forces accompanied by model predictions for the system of one cylindrical magnet and a cuboid MAE sample. Calculated dependences of the average pressure arising from magnetic interactions on the distance between the closest faces of MAE samples and a permanent magnet are in a good agreement with the experimental data. The proof on concept for smaller magnetic systems required for eye surgery includes data for 10 magnets configuration and a thin MAE band. This research demonstrates high prospects of using MAE as an element of a magnetic fixator for treatment of complicated retinal detachments.
Abstract.We study the effects the geometric configuration has on magnetic interactions between a magnetoactive elastomer (MAE) sample and various systems of permanent magnets for problems with both flat and curved geometry. MAEs consist of a silicone polymer matrix and iron filler microparticles embedded in it. Permanent magnets are cylindrical neodymium magnets arranged in a line on a flat or curved solid surfaces. We use computer simulations, namely the finite element method, in order to study the interaction force and magnetic pressure in a system with an MAE sample and permanent magnets. The model is based on classical Maxwell magnetostatics and two factors taking into account field dependence of MAE's magnetic properties and inhomogeneities caused by local demagnetization. We calculate magnetic pressure dependences on various geometric parameters of the system, namely, the diameter and the height of permanent magnets, the distance between the magnets and dimensions of MAE samples. This research aims to create a set of guidelines for choosing the geometric configuration of a retina fixator based on MAE seals to be used in eye surgery for retinal detachment treatment.
Scleral buckling (SB) has been regaining its popularity in the treatment of retinal detachments. On large clinical material, it has been proved to be the technique of choice in phakic patients with retinal detachment of moderate severity. A combined procedure that incorporates features of episcleral as well as intravitreal surgeries has also become widely used. Aim - to investigate the prospects for increasing technical potential of SB, particularly, to investigate the possibility of additional atraumatic mechanical fixation of the retina from within the vitreous cavity. The proposed device consists of an episcleral magnetic buckle and endovitreal magnetic buckles (endobuckles). The episcleral magnetic buckle is made of medical grade silicone and cannot be distinguished from common buckles, except that it contains one or more permanent magnets on the basis of neodymium-iron-boron powders. Endobuckles are small flat elastic elements made of silicone elastomer filled with magnetic particles. Еndobuckles are implanted into the vitreous cavity through a small pars plana incision and placed on the retina at the projection of the scleral magnetic buckle. Thus, in experiments with cadaver eyes, the authors have showed the principle feasibility of retinal fixation by the force of magnetic interaction between the magnetic scleral buckle and endobuckles. The described technique of additional mechanical fixation of the retina provides wider surgical opportunities in the management of retinal detachments.
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