FR2607252A1 - Stress, temperature and shape sensors, for biomedical and industrial uses, using cholesteric polymers - Google Patents

Abstract

The invention relates to the production of stress, temperature and shape sensors integrated into various industrial products such as, for example, those intended for the biomedical sector. The sensor includes a layer of cholesteric polymer whose colour, related to the properties of selective reflection of light by the material, is initially uniform and varies under the effect of a change in stress, temperature, etc. The spatial distribution of these parameters is thus visually displayed by a network of isochromatic curves. The method of obtaining the sensor includes the preparation of a cholesteric layer of calibrated thickness which is freed from defects by vacuum homogenisation of the solution and shaping, then encapsulation thereof. In the event that this device forms part, for example, of the statokinesimeter, the print is obtained by digitising the optical densities at a given wavelength. The iso-density curves (Figure below) give the distribution of the plantar pressures.

Description

SENSORS OF CONSTRAINTS, TEMPERATURES AND SHAPES, FOR USE
BIOMEDICAL AND INDUSTRIAL, USING CHOLESTERIC POLYMERS
The present invention relates to the production of stress sensors using crolesteric polymers and their applications in the biomedical and industrial fields. These devices make it possible to define the spatial reparzition of the stresses exerted on the sensor, including contours and bearing surfaces. These maps, visualized by a network of isochromatic courses corresponding to the applied isostress curves, can be representative of static or dynamic to transcriptions can be, depending on the case, visual, photographic, video or digitalized images. They can be made in direct or delayed reading (using a modular remanence).

 The technical sector of this invention is that of construction.

constraint sensor instruments of a different model from those currently known. The latter systems, which define the spatial distribution of constraints, are based on a distributior.

discontinuous collection of information elements, such as, for example, a piezo-optical transducer associated with sequential analysis (Patent
ANVAR, No. 74 13383, 14/11/1975), or a filled rubber (ANVAR Patent No. 74 18944, 21/06/1974).

 The present device allows, by its intrinsic properties, an extremely fine or even almost continuous theoretical resolution. The sensor consists of a homogeneous layer of cholesteric polymer trapped in an envelope, one of whose faces is a homogeneous elastic tension film which provides the transfer function of the stress exerted. The other side is the reference surface, it may be elastic or not, rigid or flexible and adapted in a rigid shell. One of the surfaces of the envelope: the reference surface or the elastic film, is transparent while the other surface, black in color, has the effect of absorbing the light transmitted by the sample and increasing the contrast of the reflected colors. The liquid crystal polymer can also be encapsulated and the support film can be a transparent elastic film.

 One of the possible configurations of the sensor is shematized in FIG. 1. The plane, rigid and transparent reference support, FIG. 1.1, is for example a plexiglass plate. The spacer, fig. 1.2, also in plexiglass, determines the thickness of the cholesteric layer, fig. 14 The elements, fig. 1.1 and Fig. 1.2 can be combined into a single container made for example by molding a transparent material. The elastic membrane, fig. 1.3, is a black rubber film. It must be chemically inert with respect to the solution, in particular with respect to the solvents used in the case where the cholesteric material is a lyotropic solution. This may be a preferably chlorinated butyl rubber film. not containing a mineral filler but loaded with black carbon with fine particles. The tightness that must also ensure this film (in the case where the solvents are volatile and therefore likely to diffuse through the membrane) can be increased either by the deposition of a thin film of Hypalon type varnish on the elastic membrane. or by the interposition between the polymeric layer and the elastic membrane of a film of hydrophobic material or screen and thus allowing the retention of the solvent. The thickness of the elastic membrane is optimized according to the range of constraints. the viscosity of the solution is explored in order to limit the flow of the latter under the effect of pressure.

The tightness between the membrane, fis. 1.3 and the support fig. 1.2> is ensured by gluing using a suitable adhesive, such polyurethane type.

 The choice of the cholesteric pepper is dictated by the fact that it simultaneously exhibits the advantages of the polymeric character and the remarkable optical properties of the cholesteric liquid crystals. In particular, the property of selective reflection of light by a cholesteric layer is determined by the pitch Po of the structure (Po is the period of the helical organization in pseudo-birefringent layers whose principal axes undergo, between successive planes, a rotation a small angle) and the angle 0 defined by the axis of the helix and the direction of propagation of the (white) incident light.Wavelength X, corresponding to the maximum of the spectrum of the reflected light (circularly polarized) varies with the angle of incidence according to the Bragg condition at = P cos e, n is here the average index of the sample. Thus, a planar-oriented cholesteric layer presupposes a well-defined homogeneous color.

 This color varies with certain parameters such as pressure, temperature and the application of external fields such as: flow, electrical, magnetic.

 Due to the polymeric nature of the material, the viscoelastic and rheo-optical properties required for sensor applications can be adjusted in a very wide range. In particular, the parameters such as the value of the pitch of the cholesteric structure, its variation under the effect of a stress and the viscosity of the material, which condition the range of the stresses explored and the sensitivity of the system are controllable simultaneously by the choice variants such as the specific characteristics of the polymer chemical structures of the monomer and substituents, degrees of polymerization and substitution, the physical nature of the solution: thermotropic and lyotropic and in the latter case the concentration of the solution and the chemical nature of the solvents.

The cholesteric solutions used for producing the present stress sensor may be isotropic solutions of cellulosic derivatives such as those mentioned in the Maeno patent (N579> 511, 02/1975). We preferentially use non-volatile solvents, such as ethylene- and diethylene glycol, dibutyl phthalate ... so as to reduce the diffusion problems through the elastic membrane and to increase the life of the sensor. It may also be other solutions of these same cellulosic derivatives in complex solvents such as a saline solution of an organic solvent (or water) or a mixture of organic solvents (or water). the addition of an inorganic salt or one or more other solvents in the solution modifies the properties of the cholesteric phase, such as phase diagram and cholesteric pitch. The two examples reported in Table 1 relate to solutions of hydroxypropyl cellulose (t4w = 105)
We note the interest of using polysaccharide solutions in sensors for biomedical use: they are in fact bio compatible substances, harmless for humans, sterilizable ... In some cases> for example, when using of an aqueous solvent, fungicides and bactericides may be added to the solution without altering its properties Other families of cholesteric polymers may be used and we will cite in a nonlimiting manner: polyglutamates, polyesters, comb polymers. .

 For each of these solutions, a judicious choice of physicochemical parameters makes it possible to obtain a layer of desired color material.

The narrow spectrum of light diffused by such a film depends on the quality of the planar organization (the cholesteric planes are parallel to the reference surface) of the sample. This organization can either be induced by inking with the walls of the physical or chemical type, or be reached spontaneously as shown in FIG. 2 in the case of an aqueous solution of hydroxypropylcellulose HPC after a time which is a function of the nature of the solution.

 The spectral response of the sample under the effect of the application of a stress is specific to each solution; a blue shift of the maximum wavelength of the Bragg reflection peak is systematically observed. A solution-induced (shear) flow of the solution can produce, as in the case of small molecule liquid crystals, a partial tilting of the cholesteric helix for not too high velocity gradients and, at high shear, a tendency to align the molecules in the direction of flow.A decrease in the distance between pseudo molecular planes related to the elastic reaction of the sample and a local variation in concentration, related to polymeric interactions. solvent that can lead to translational diffusion coefficients different from each of the constituents, can induce the same spectral shift.

 In order to obtain the widest possible color dynamics, it is advantageous to have solutions having, at equilibrium, a wavelength of the reflected light # 0 lying in the red. We cite here some examples of HPC solutions lw = 6 x 104i for which X, = 730 mm: HPC / H2O at 59% g / g, HPPC / Ethanol at 68.8% / g, HPC / acetic acid at 71 5% g / g, HPC / Dimethyl acetamide 68% g / g, HPC / Diethylene glycol 57% g / g, HPC / (acetic acid 75% / H2O 25%) 63.8%.

 In the particular case of an aqueous solution of HPC 59% ç. / Ç. a variation at a pressure of 10 g / cm to 60 g / cm 2 causes a change from red to blue (# = 664 nm) to blue (\ = 525 nm): fig. 3.

 The present device also makes it possible, by the judicious choice of the parameters of the cholesteric solution, to have a stress sensor such that the wavelength of the reflected light, located at equilibrium in the IR range, moves, when applying a constraint, either in the IR range or again to wavelengths corresponding to the visible range.

 It should be noted that the spectral response curve of the P (#) sensor is characteristic of the pair: polymeric layer - elastic membrane, at a given temperature. The stress sensor, which is the subject of the present invention can also be used to establish maps of the pressures exerted by an object brought to a temperature T different from the ambient temperature. ## is enough to choose the new physicochemical parameters of the solution such that at this temperature is in the red. A solution of HPC in dimethylacetamide - DMAC - concentration 72% g / g may for example be used as a pressure sensor at 45 C.

 Conversely, the sensor currently described can also be used as a temperature sensor # working at constant pressure, the temperature can be chosen as the main parameter. In this case, the sensor becomes a temperature indicator defining, by the chromatic spatial distribution, the corresponding distributions of temperatures. A judicious choice of the composition of the solution makes it possible to fix the law of variation of the wavelength as a function of the temperature.

Thus, in the previous example, the 72% g / g HPC / DMAC solution changes from blue (\ = 500 nm) to red (\ = 800 nm) from 20 to J3XC with ## / T = - 8.5 nm / ° C. It is also possible to realize a digital or analog display of thermal values by using a panel of elements adapted to the temperatures by the color
In the case where the analysis of the pressure mapping can not be carried out in situ, it is always possible to use the present sensor, in deferred time, by exploiting the effect of the colorimetric remanence of the sample. characteristic of this remanence is in particular a function of the viscosity of the solution and the tension of the plastic membrane. it can vary from a few seconds to several hours. We show an example of this property in the case of a HPC sample (Mw = 6 x 104) / H2O at 59% g / g in Figure 4.

 The quality of the sensor - in particular the width of the spectral response of the reflected light - is conditioned, on the one hand, by the quality of the polymeric layer which must be one, formally distributed on the reference surface and free of of air bubble and secondly, by the quality of the elastic membrane and by the tightness of the system.

The described production method allows the manufacture of sensors of fine thickness (up to a few tens of microns) and sorted rani dimension, it comprises four steps:
I) Preparation of the polymeric solution under vacuum. In the case of a lyotropic solution, the constituents are - preferably - degassed and transferred to a kneader under vacuum. The mixture is then homogenized under vacuum, at a temperature which may be greater than ambient temperature (so as to reduce the viscosity of the medium).

2) Deposition of the solution on the reference support according to the following operations (Fig. 5):
- The volume to be spread, fig. 5. 1, corresponds to the volume of the receptacle fig. 5.2. The latter can be of any form and shape - including alveolar -.

 - The solution is deposited in mass on the receiver.

 - It is covered with a transparent sheet, fig. 5.3, inert vis-à-vis the solution (cellulose acetate, mylar ...). A transparent support block placed on the interlayer sheet - for example in plexiglass - serves as a pressure transmitter P, FIG. 5B, so as to produce a compression and spreading of the solution until the complete filling of the receptacle and to obtain a spreading-flow E, fig. 5B, homogeneous product without trapping air bubbles. The transparency of the intermediate sheets makes it possible to control the quality of the layer: flatness, constant thickness, absence of air bubbles and inhomogeneity.

 3) Separation of the intermediate sheet of the polymer product by lowering the temperature until freezing of the solution. Depending on the nature of the solution, temperatures ranging from 0 to 80 may be necessary. They allow to easily detach the interface - transparent filn - of the solution, without altering the surface state of the sensor.

 4) Application and sizing of the elastic membrane previously uniformly stretched on the rigid support containing the polymeric solution. This operation can be performed under vacuum so as to avoid trapping air.

 In the initial calculation, account is taken of the relative proportions by weight of the solvent / solution of the possible evaporation of the solvent which corresponds to operations i and 4 carried out under vacuum.

 The sensors thus produced can be integrated into different structures making it possible to define the distributions and the values of the stresses exerted during static or dynamic supports, impacts, mechanical deformations, etc.

 - In the biomedical field, can be studied the plantar supports, the structural deformations (lordosis, kyphosis ...), the breathing dynamics, the contact surfaces of an external environment with the body surfaces (mattress alterning, helmet of protection, seat, orthopedic and ondotological prostheses ...), functional, muscular, bony and respiratory reeducations ...

 - In the field of ergonomics, sensors can be used for the adaptation of seats and workstations as well as vehicle seats.

 - When analyzing the impact of projectiles or moving objects, these sensors can be used.

 - In shape recognition problems.

Three examples will be more particularly described:
1) The statokinesimometer.

2) Odontology
3) Industrial.

THE STATOKINESIMOMETER
The stress sensor, the manufacturing method of which has been previously described, is associated with two parts: a stand and a system for memorizing the associated isochrome curves corresponding to the pressure distributions.

 The nature of the polymeric layer, its thickness as well as the characteristics of the elastic membrane will be chosen from the solutions described above, so as to make it possible to analyze applied stresses varying from a few tens of g / cm to a few kg / cm 2.

This apparatus 2 for the purpose of defining the distributions of the supports
Plantar and other body supports, efforts exerted by a muscular or articular group, studies relating to equilibrium disorders.

The stand, fig.6, comprises the optical system, fig. 6.1 and fig.7, carrying out the transfer of the image of the sensor, fig. 6.2, on visual, photographic or other receivers (camera, video recorder,
digitization ...) and the device for defining the position of the patient, fig. 6.

 Depending on the desired use, an image of the reduced ratio or I / I colonimetric imprint can be obtained.

In verse simple, fig. 7, the optical system is reduced to a set of mirrors, the scree, fig. 7.!, 4 'of the plane defined by the sensor, fig. 7.3, allows the photographic recording, the second, fic. 7.2> substantially parallel to the plane of the latter allows the direct vision of the plate
A photographic system with instantaneous development fig. 7.6, sleeps optics, fig. 74, is adjusted for the optimization of the field of view is coupled - to the mirror - In some cases, the image can be conveyed by optical fiber (with a Hopkins or other type of input optics).

 A system of illumination in white light and with almost uniform field, fig. 7.5a and fig. 7.5b, is associated with direct vision through the mirror.

 With regard to the receivers, the illumination can be of the flash, strobe or continuous type. A digitization of the image with a sampling frequency adapted to the dynamics of the sensor responses can be associated.

 The position of the patient's body, either at rest or during a movement can be determined simultaneously using a device comprising either a camera system associated with a computer treatment or a game of Sou N cells ultra its receivers, fig. 6. 3,4,5, ie 2 or N coiled frames in enamelled copper wire coupled perpendicularly, FIG. 6.6, 7, 8, 9, or both.

The operation of the ultrasonic cells is as follows: the emission is pulsed every 5 ms, the reception comprises a time discriminator between the instant of departure of the emission, FIG. 8A, and the return of the reflected wave, fig. 8B, a flip-flop JK, fig. 8C, a logical product, fig. 8E, between the duration of the return of the wave reflecting on the patient and a clock H, fic. SE. A memory M, fig. 8F, stores the results of this logical product, fig. SE, N cells at different addresses. One or more analog digital converters coupled to the contents of these memories
will give a record of the different positions of the patient.The accuracy on the
defined tone of the position is of the order of mm.

In parallel, one or N electromagnetic emitters -solenoids
frequency> fig. 6. 6, /, 8.9, can be fixed on the body of the patient
which in their displacement induce a fem, in the wound frames, of
the form e = N dB (#i) / dt cos α where N is the number of turns of the coil.

the variation of the induction created by the emitter and the angle that the
solenoid with the normal to the frame.

The method of manufacturing the sensors previously described,
allowing the realization of large devices, an extension
I can see the previous one can be done to allow the analysis Or
unwinding of the foot during an ormaie or pathological walk. The study of 3
or 4 steps requires a sensor area of the order of 60 cm x 240 cm.

APPLICATION IN ODONTOLOGY
The present invention may be useful in defining the optimization of
prosthetic points of support, whether in full dentures or in points
occlusal support.

In the first case, fig.9 and fic. 10, a molding of the palace and its
mucous coating allows this to realize a prosthesis comprising a face
transparent classic (impression or molding of the palate), fig. 9.3 and 10.3, and
an elastic face, fig. 9.4 and 10.4, in contact with the palace. Between these two
faces, a cholesteric polymer film, fig. 9.2 and 10.2, memorize the
different pressure zones and thus allows to better adapt the prosthesis
to achieve by the necessary corrections. The same is true of
This procedure allows, moreover, to define
the elastic properties of the prosthesis and its importance in the
distribution of the stresses on its support (stomatognatic system) with
the repercussion on the salivation.

Regarding the deformations of the bone texture of the
mandible by positioning prosthetic elements, hooks and supports
occlusal, the present innovation also allows to analyze, fig. 11, the
distribution of forces between the abutment teeth and the ridges as well as in the bone
alveolar. The cholesteric film, fig. 11.1, is trapped between a mold
plexiglass, fig. 11.2, and the tooth itself, fig. 11.6.

The pressures and constraints exerted on the reference plane,
bitten static or bite-bite convenience are easily established
in colorimetric recovery of the sensor constituted for example, fig. 12, by
superposition of two modules with a solution layer
cholesteric, fig. 12.1A and fig. 12.1B, trapped between a black plastic membrane, fig. 12. 2A and Fig. 12.5 and a transparent film, fig. 12.3A and fig. 12.3b
III.APPLICATION IN THE INDUSTRIAL FIELD
The present innovation can be used in the problems of this recognition of shape of objects by means of their support on the sensor. This one makes it possible to discriminate shapes in three dimensions, for example a plano-convex object can be differentiated. of a plane object by the chromatic analysis of the concentric rings of the image, fig. 13.

COMMENTARY FIGURES
Fig. . P. pressure exerted on the sensor
Sensor illumination
1, 2, 3, 4: cf. text
Fig. 2 # wavelength in nm of the maximum of the spectrum t? r.

reflected light on the sensor
the intensity of the reflected light, in arbitrary unit
Spectra are recorded every minute
A1 t2mm; Al = t = (2 + i) mn; B: t = 48 hours
Fig. 3 p pressure exerted on the sensor in g.cm-2
# wavelength of reflected light in nm
Curve A: HPC solution (Mw = 6 x 104) / H2O, C # 59% g / g
Curve 5: HPC solution (Mw = 6 x 10) / DEG, CS 57% g / g
Fig 4. 1: Intensity of reflected light
T: time
E: excitement
D: exponential relaxation
Fig. 5 AH: shim
1 to 4: cf. text
Fig. E. P: Pressure exerted
E: spreading - flow
1 to 4: cf. text
Fig. 6. 1 to 9: cf. text
Fig. 7. 0: observer
1 to 6: cf. text
Fig. 8. A to F: cf. text
Fig. 9. Profile view
1
Fig. 10. View from above
1 r 14 cf. text
Fig. 11 D: displacement
F: strength
3: sealing cover
4: elastic seal
5: incident light
Fig. 12. 1A, 1B, 2A, 2B, 3A, 3B: cf. text
Fig. 13. 1. cholesteric polymer layer
2: black elastic membrane
3: reference area
4: cup
5. stress gradient
6. # isochronous lines
F. constraint
E illumination
TABLE 1

<SEP> HPC (105) <SEP>% LiCl <SEP> TTr <SEP># 0 <SEP><SEP> HPC <SEP> (105) <SEP>% H2O <SEP> TTr <SEP># 0
<tb><SEP> / KNMA +
<tb><SEP> / H2O <SEP> C <SEP> (nm) <SEP> DMP) + <SEP> (C) <SEP> (nm)
<tb><SEP> H2O]
<tb><SEP> (a) <SEP> (b) <SEP> (c) <SEP> (d) <SEP> (e) <SEP> (f)
<tb><SEP> 50% <SEP> 0% <SEP> 55 <SEP> 1162 <SEP> 66% <SEP> 0% <SEP> 116 <SEP> 700
<tb><SEP> 1.4% <SEP> 38 <SEP> 856 <SEP> 9% <SEP> 122 <SEP> 600
<tb><SEP> 2.6% <SEP> - <SEP> 550 <SEP> 39% <SEP> 162 <SEP> 525
<tb> (a) The concentration is expressed by weight of polymer
relative to the total weight of the solution.

(b)% LiCl is the weight of LiCl relative to
total weight of the solution.

(c) TT is the temperature of the transition
anisotropic phase - anisotropic gel.

(d) The concentration is expressed in weight of polymer
Relative to the total weight of the solution.

The ratio by relative weight of NMA (N Methyl Acéta
mide) relative to the weight of DMF (dimethyl forma
mide) is 56/44.

(e)% H2O is expressed by weight of H20 by weight
of the solvent.

(f) TTr corresponds to the aniso transition temperature
trope - isotropic.

Claims (5)

1. Sensor device for defining the spatial distribution of stresses and temperatures, characterized in that it comprises a layer of cholesteric polymer trapped in an envelope of which at least one of the faces is elastic and the opposite face must form a couple such that if one is transparent, the other is black. The said sensor is integrable into different structures for defining these spatial distributions in the biomedical field, in the field of ergonomics and in the industrial field. It has a double function and makes it possible to define, either at constant temperature, the spatial distribution of pressures, or at constant pressure, the spatial distribution of temperatures.  2) Device according to claim 1, characterized in that the properties of the solution such as the viscosity and the properties of the envelope such as elasticity, are adjusted according to the range of pressure and temperature to be measured.  3) Device according to claim 1, characterized in that, in one variant, the cholesteric polymer is encapsulated.  4) Device according to claim 1, characterized in that the cholesteric material is selected from lyotropic or thermotropic polymer groups, the polymer may belong to all families of cellulose derivatives of polyesters, polyglutamates, comb polymers ... and the associated solvents are chosen from organic solvents (or water), pure, in admixture or associated with inorganic salts, the characteristics of 1. solution being determined so as to have the spectral dynamic of the light reflected by the sensor, corresponding to the range of constraint and temperature explored, the widest possible.  5i Device according to claim 1 characterized with respect to its method of manufacture comprising 6 operations: the preparation of the vacuum homogenized polymeric solution, the deposit in misse define the solution in sor receptacle, its recovery by an intermediate sheet and a block pressure transmitter, its spreading by compression, the separation of the intermediate sheet by lowering temperature and the realization of the sealing of the device by vacuum bonding.  c> Device according to claim 1, characterized in that the spatial distribution of stresses and temperatures is analyzable in real time and delayed by the use of colorimetric remanence properties of the polymeric solution  7) Device according to claim 1! characterized in that! in its use in the biomedical field, it constitutes the sensor of the statokinesimometre system, intended to analyze the distribution of the plantar supports, which comprises a stand and an optical system coupled or disassociated from the stand, carrying out the transfer of the colorimetric image of the sensor, in static and dynamic cases, in visual, photographic or digitized forms.  8) Device according to claims 1 and 7, characterized in that in a variant of its use in the biomedical field, it fits into the system defining simultaneously the distribution of the plantar supports and the spatial positioning of the patient. For this, are associated, isolation or jointly, a set of ultrasound cells coupled to an electronic discrimination of the time of travel of these waves, a set of couples wound frames to electromagnetic emitters fixed on the body of the patient.  9) Device according to claim 1, characterized in that, in its use in the biomedical field, it allows to define the optimization of prosthetic support points. In dentistry, it applies to total dentures and occlusal support points.