Optimisation of magnets positions on the knee joint using Comsol Multiphysics.
Laptoiu, Dan Constantin ; Antoniac, Iulian ; Cotrut, Cosmin 等
Abstract: The purpose of the project presented in this paper
consists in the development of a multifunctional knee device to be used
in the early stages of treatment of osteoarthritis. Magnetically
controlled vascosupplimentation therapy is a new concept of bioactive
treatment, which combines the advantages of intra-articular therapy
assisted by a more complex system of fixing and controlling joint
mobility. Several positions and dimensions of magnets on two different
knee positions (flexion/extension) were analysed and optimised using
finite elements analysis software, in order to create a magnetic field
able to localize and concentrate the nanoparticles for drugs delivery.
Key words: finite elements analysis, magnetic controlled therapy,
nanoparticles, magnetic field optimisation
1. INTRODUCTION
The main goals in treating degenerative knee joint disease (such as
arthritis) are minimizing the pain, maintaining or improving joint
mobility and minimizing functional deterioration. Infiltration of the
knee with steroids is in current medical practice for over 50 years and
vascosupplimentation for over 10 years. A newer approach is magnetically
controlled vascosupplimentation, which aims to restore the viscoelastic
qualities of the joint fluid, with concomitant improvement of rheology
as a result of endogenous synthesis and normalization of accelerated
degradation of hyaluronate into the joint. This therapy requires the use
of an orthosis with a specialized anatomic design, modified to allow
insertion of groups of permanent magnets for combined use with
application of infiltration of a composite viscoelastic
biopolymer--magnetic nanoparticles.
The research was focused on two main objectives:
1. Development of magnetic nanoparticles for correcting
osteoarthritic knees. Magnetite nanoparticles with 20-30mm dimensions,
coated with amine for controlling the aggregation during synthesis were
obtained, and tests with different concentration were performed.
2. Design and manufacturing a knee orthosis with magnets for
enhancing drags action time in the interest area. Several cases with
different magnets dimensions and placements were analysed using Comsol
Multiphysics simulation software for optimizing their position by taking
into account the influence on the magnetic field. The approach presented
in the current paper considers first the use of one magnet with
dimension of 10x2 mm, and then arrangements of 2, 3 and 4 magnets spread
on a surface of 10[mm.sup.2]--all magnets were neodymium iron boron,
1220-1250 mT and 287 kJ/[m.sup.3] maximal energy.
Analysis of the literature showed that magnetic orthoses currently
used are based on the effect of the magnetic field properties for pain
relief (Chen, 2008), (Mendel et al., 2010) and do not consider the
combined action of magnetic nanoparticles infiltrated in the interest
zone and the magnetic field created by magnets.
developing new technical solutions (Chen & Liao, 2009) and
(Nikitczuk et al., 2004) for improving existent designs.
2. MAGNETIC NANOPARTICLES FOR IMPROVING DRUGS DELIVERY
The magnetic assisted intra-articular therapy (hyaluronate covered
magnetic nanoparticles with viscoelastic properties) is focused on the
articular defect; the effect must be maintained for at least three
weeks. (Mitsuo et al., 2001) presented a similar solution based
therapeutics and cultures of chondrocytes atelocolagen. Nanoparticles
used in attempts to correct this deficiency, will be loaded into a
proposed concentration between 10 and 200 mg/ml to increase the
biomechanical properties. Also the concentration expressed in mg per mg
hyaluronic acid product will be different, ranging from 8 to 15 between
different preparations and the amount is about 5 ml.
Since the particles are scattered in the synovial liquid, the
recognition and elimination by phagocytes can take a long time. Unlike
inorganic magnetic particles, biodegradable polymers may release the
active absorbed ingredient in a controlled way by determining their rate
of degradation (Cinteza et al., 2006), (Gijs, 2010).
The use of magnetic core particles and biodegradable polymer shell
can take advantage of the properties of the two components. Thus, the
magnetic core particles can transport you directly to the target and
keep it there by applying an external magnetic field. Detailed studies
(Morega, 2006), (Lee&Shin, 2007), (Butoescu, 2010) have established
that magnetic carders must have the following properties: a near field
magnetic gradients and flow of the body's physiological system, the
ability to carry a larger amount. The active ingredient, not excessively
load the body with magnetic material, speed controllable release the
active compound in the target area, properties that provide maximum
surface biocompatibility, biodegradability and allowing easy elimination
of minimizing toxicity in the body.
3. MAGNETIC FIELD OPTIMISATION FOR A KNEE ORTHOSIS
COMSOL Multiphysics software was used for assessing the magnetic
field magnitude for nine cases obtained by varying the ratio between
magnet length and distance between magnets (d1/d2) and positions
matrices, as it can be seen in figures 2-3.
Figure 1 presents several results of the experiments for the case
in which the ratio d1/d2<l (for 1 magnet, 2x2 magnets, 3x3 magnets,
4x4 magnets), along an illustration of the directions in which the
ferrofluid placed in the intra-articular space will move when subjected
to the magnetic field action.
Similar analyses were performed for all cases; results comparison
allowed determining the best position of magnets on the analysed
patello-femural knee orthosis.
[FIGURE 1 OMITTED]
[FIGURE 2 OMITTED]
[FIGURE 3 OMITTED]
4. CONCLUSIONS
The main conclusion of the analysis performed was that in order to
obtain the best results in drugs delivery in the patello-femural
targeted area, an arrangement of 4x4 magnets on a square pattern close
to the rotula at distances which satisfy condition d1/d2<l for
ensuring a larger concentration of the magnetic nanoparticles.
These results are confirmed by the experiments performed in the
project and which will be presented in further articles.
5. ACKNOWLEDGEMENTS
This work was supported by CNCSIS, PNCDI2, Project 42-132,
ARTROMAG--Medical device for joint articular disease therapy using
nanomaterials and magnetic field effects.
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