FR2955159A1 - Mechanical anchoring device for anchoring measurement or test units on connective tissue of skin of living subject, has maintaining units maintaining solicitation modifying viscosity of binder that is adhesion to support at contact surface - Google Patents

Abstract

The invention relates to anchoring devices on a soft or flexible support, such as a connective tissue, used to perform mechanical stress tests of said support. More particularly, the invention relates to an anchoring device on the epidermis of a living subject for the purpose of performing tests on the skin of said subject. According to a particular embodiment, the invention relates to mechanical coupling devices between an extensometry apparatus and the skin of a subject for the purpose of soliciting the skin of said subject in traction - compression.

Description

The invention relates to anchoring devices on a soft or flexible support such as a connective tissue. Such anchors are used to fix sufficiently mechanically and mechanically stable means for measuring or testing on said support, for example, in order to perform confocal measurements or mechanical stress tests of said support. More particularly, the invention relates to an anchoring device on the epidermis of a living subject for the purpose of performing tests on the skin of said subject. According to a particular embodiment, the invention relates to mechanical coupling devices between an extensometry apparatus and the skin of a subject, for the purpose of soliciting the skin of said subject in tension-compression. The applications to which these anchors are more particularly adapted are non-intrusive applications made on a living subject that do not lead to the rupture of the tissue, for example the skin. In general, all the properties relating to the skin mentioned below, such as its elastic modulus, refer to solicitation rates that do not lead to lesions or intrusions into the connective tissue, that is to say say, for deformation rates generally below 30%. Those skilled in the art will understand, however, that the invention may be advantageously used for ex vivo tests on tissues other than the skin, or on materials having comparable mechanical characteristics such as food preparations in pasty form. The carrying out of mechanical stress tests on a support such as the skin assumes a sufficiently strong and rigid mechanical coupling between the biasing device and said support so as, on the one hand, to transmit the entire mechanical stress test to the support, and secondly, according to the device, measure the response of the support to this solicitation directly by the displacement of the soliciting elements. The influence of the mechanical behavior of the connection on the measurement must remain in proportions compatible with the measurement accuracy sought.

The entire solicitation includes the spatial (direction), intensity and temporal characteristics of the said solicitation.

In addition, when the test is performed on a living subject, it is essential to break this mechanical coupling without any damage to the subject. It is known from the prior art, for example patent FR2858206 in the name of the applicant, devices adapted to the mechanical coupling between a traction device and the skin using a suction anchor. The effectiveness of such a device is based on a compromise between a sufficient depression to ensure good anchoring while remaining low enough to maintain a non-invasive character.

In practice, anchoring by depression is unpleasant for the subject and can lead to the appearance of petechiae. Moreover, in some cases (measurement zone, skin type), the mechanical link may be insufficient. This system is finally bulky and noisy due to the presence of a pneumatic pump.

Other devices of the prior art use double-sided adhesive adhesives. This technique, however, does not allow a strong adhesion, it is not reproducible and can hardly be controlled. These adhesives, called "PSA" for "pressure sensitive adhesives", are viscous systems and low stiffness because the tacky layer ensuring adhesion must be soft enough to match the irregularities of the bonding surface by simple pressure. Consequently, they deform during the solicitation and thus disturb the mechanical measurement, in particular by adding viscous components in the response to the test request. Furthermore, said adhesives being deformed under the effect of the test load, they must be changed before each test which forces to separate and replace the anchoring device and therefore adversely affects the repeatability of the measurements. The use of cyanoacrylate adhesives is not allowed for experiments on a living subject because of their toxicity. In addition, the detachment of the device, when it is used on an epidermis, is effected by tearing off the stratum corneum of said epidermis layer. Not to mention the trauma of the subject, the repeatability of the measurements can not be verified and the surface of the anchoring devices on which the adhesive is deposited must be cleaned before each new use. There is therefore a need for a non-invasive anchoring device which both - has a strong adhesion to the support and more specifically to the skin, - can be removed easily after the test, - is mechanically rigid so as not to disturb the measurement mechanical. To this end the invention proposes a temporary mechanical anchoring device to a soft or flexible support comprising: - a pad, - a binder interposed between said pad and the support and whose viscosity is a function of at least one bias; - A contact surface between the pad and the binder to which the mechanical adhesion of the binder is at least as strong as the support at the same level of stress; - Means adapted to solicit and maintain the stress modifying the viscosity of the binder. The support is advantageously a connective tissue and, in a particular embodiment, the epidermis of a living subject. The adhesion phenomenon is essentially mechanical and excludes any diffusion or solubility between the binder and the fabric. Without being bound by any theory, it is proposed that the coupling by mechanical adhesion of the anchors to the support is the result of two contradictory properties of the binder: the effective contact surface between the surface of the support and the binder; this surface will be all the more important and the adhesion all the stronger as the binder will be fluid and able to fill all surface irregularities; the rigidity of the binder, the mechanical coupling being all the stronger as the rigidity of the binder is high. In order to solve this contradiction, the invention consists in subjecting the binder to a load capable of modifying its viscosity so that the binder is more fluid when the anchor is applied to the support and more rigid during the application. mechanical stress test of said support. The viscosity-modifying solicitation may be the mechanical stress test itself, or additional stress of electrical or magnetic nature, for example using a binder with electro or magneto-rheological properties, mechanical such as vibration, thermal or radiation (UV). The additional stress to which the binder is subjected may alternatively increase the viscosity thereof or increase the fluidity. Thus the binder will be solicited by this additional solicitation at the time of application of the anchors on the support or at the time of the trial solicitation. It may be two additional solicitations of different natures or of the same type of stress at two different intensity levels applied during the hooking phase of the anchors and during the application of the test load.

According to an advantageous embodiment, the modification of the properties of the binder by the biasing is reversible so that said biasing or its absence makes it easy to remove the anchors from the support without damaging said support. In the opposite case, the anchors can however be detached from the support, for example by dissolving the binder by means of a suitable solvent. The invention also relates to a method for laying an anchor taking advantage of the characteristics of this device, comprising the steps of: - placing the pad in contact with the support via the binder which binds is at a level solicitation conferring a sufficiently low viscosity to fill the irregularities of the contact surface with the support. - Solicit the binder at a second level of stress so as to increase the viscosity to a value capable of allowing the transmission of all of the test load to the support. The method may advantageously comprise an additional step of soliciting the binder at the first level of stress after the application of the proofing test so as to separate the anchoring of the support. The anchoring of the anchors on the external surface of the support without intrusion in its sub-surface constitution, makes it possible to study the mechanical response of complex supports, in particular those whose mechanical behavior results from the composite response of several layers of properties and structures different. Connective tissues such as the skin are an example, but this situation also occurs in other areas. For example, the flexibility of a pasta may be a function of its cooking and the modification of its internal structure and crust during this cooking. It can also be a function of the interaction of said dough with the ingredients placed on it during the various preparation or cooking phases. In these various situations, the method which is the subject of the invention makes it possible to mechanically stress the support, in situ, without taking a sample, by anchoring on the surface without this anchoring interfering with the structure of the support in its thickness. According to an advantageous embodiment of the anchoring device, particularly adapted to mechanical tests carried out on the skin of a living subject, it comprises: a binder interposed between the pad and the epidermis and whose mechanical adhesion to said epidermis is a function of temperature; - A contact surface between the pad and the binder to which the adhesion of the binder is at least as strong as the epidermis at the same temperature; - Thermal control means capable of carrying and maintaining the binder at a temperature TO to which the mechanical adhesion of said binder to the epidermis is high. By changing the temperature, the adhesion of the pad on the epidermis is modified. Thus, it is sufficient to apply the pad and the binder to the skin at a temperature at which the adhesion of the binder to the skin is low, then to wear the pad at a temperature at which the adhesion of the binder to the skin is high. and to maintain the binder at that temperature during the mechanical test and the application of the proof test. Finally to break the anchor the binder is brought back to the temperature at which the adhesion is lower, the pad can then be removed without damage to the subject. According to this first embodiment, the thermal cycling of the binder is carried out between a temperature TO and the equilibrium temperature at ambient of the interface between the skin and the pad. This equilibrium temperature is between the ambient temperature and the body temperature of the subject.

TO may be higher or lower than this equilibrium temperature. For example, if the increased mechanical adhesion is caused by the condensation of a fluid or a gel, said fluid can be liquid at the equilibrium temperature and condensed at low temperature. TO will then be lower than the condensation or freezing temperature of said fluid and the thermal control means will be cooling means. By condensation, we mean an evolution from a more fluid state to a more viscous or rigid state. Alternatively, the fluid can be liquid at the equilibrium temperature and condense at a temperature higher than this, in this case TO will be greater than the equilibrium temperature and the thermal control means will be heating means. Advantageously, the thermal control means are capable of carrying the binder at a temperature Ti at which the mechanical adhesion of said binder to the epidermis is low. This configuration offers more choice in the nature of usable binders. Thus, Ti may be less than or greater than 0 and both may be lower or higher than the equilibrium interface temperature at room temperature. In all cases the mechanical stress test is applied to the temperature TO, the temperature at which the mechanical adhesion of the binder to the skin is the highest. The binder is chosen so that at this temperature its elastic modulus is greater than that of the skin. The elastic modulus of the skin is a function of the rate of deformation to which it is solicited. For tensile stresses resulting in a deformation of less than 30% its tensile elastic modulus is substantially between 0.05 and 1 MPa. Thus adhesives having an elastic modulus of the order of 0.1 MPa can be adapted for low tau deformation tests while adhesives having at the temperature TO an elastic modulus of the order of 1 MPa or greater will be adapted over the entire range of solicitation. According to a particular embodiment, the binder is water and TO is less than 0 ° C. The modulus of elasticity of the ice is more than 1000 times that of the skin. This embodiment of the anchoring allows a strong and rigid mechanical coupling and the absence of parasitic viscous component in the response. However, this embodiment has the risk of burning the subject during long exposure times, causing discomfort of the subject. In addition, it can modify locally the mechanical properties of the fabric. Alternatively, the binder may be a thermoreversible gel whose condensation temperature is of the order of 37 ° C. These gels are liquid at room temperature and condense at a higher temperature. In this case the pad is heated to this temperature after being applied to the skin at room temperature. This heating condenses the gel and increases the mechanical adhesion. These gels, generally made from poloxamers, have mechanical characteristics close to those of the skin. Their low elastic modulus, however, limits them to low tau deformation applications. According to a preferred embodiment, the binder is a PSA-type double-sided adhesive tape such that Ti is between 30 ° C and 40 ° C and TO is between 5 ° C and 10 ° C. By heating the adhesive to a temperature between 30 ° C and 40 ° C, the viscosity of the adhesive layers, preferably made of peg-based acrylic, is reduced which allows said pegging substance to better penetrate the surface irregularities of the skin and thus maximize the effective surface area of contact. By subsequently cooling the adhesive, the viscosity of the peelable layer and its elastic modulus increase which makes the mechanical adhesion stronger and reduces the deformability of the adhesive under the proofing stress. After the test, the adhesive is heated again to facilitate the removal of anchors from the subject's skin.

To implement this preferred embodiment, the anchors comprise heating means and cooling means. This heating and cooling can be obtained by the circulation in the anchor pads of a heat transfer fluid regulated at the desired temperature. Advantageously, these means can be electric, the heating being obtained by electrical resistance and cooling by Peltier effect. Even more advantageously heating and cooling of the pad can be achieved by a same Peltier effect module used both for heating and cooling by changing the polarity of the supply of said module. This latter solution allows a more compact embodiment of said pads. Advantageously, the anchors consist of a material having good thermal conductivity and good adhesion to the binder used. Typically the anchors may be made of an aluminum alloy which has such characteristics. The interface between the anchor and the binder can receive a particular coating or surface treatment to improve adhesion.

The invention will now be more specifically described in the context of preferred embodiments, which are in no way limiting, represented in FIGS. 1 to 7, in which: FIG. 1 is a diagrammatic representation in section of a device for the tensile stress of the skin using anchors according to an exemplary embodiment of the invention; - Figure 2 shows in section an embodiment of an anchor according to the invention; FIG. 3 shows in perspective a Peltier effect cell used in an embodiment of an anchoring device according to the invention; FIG. 4 is an example of a thermal cycle used when the binder used is water; FIG. 5 is an example of a thermal cycle used when the binder is a heat-reversible gel; FIG. 6 is an example of a thermal cycle used when the binder consists of a double-sided adhesive; - Figure 7 is an example of evolution of the storage module (7B) of the peel layer of a double-sided adhesive and the loss module (7A) with the temperature of the same peg layer. Figurel, according to an exemplary embodiment of a device (1) for the study of the skin (100) in extensometry and able to apply to said skin a stress in compression-traction, it comprises two sets (2, 3) movable in translation relative to each other and means (4) capable of producing a relative movement of said two sets. Each assembly is connected to the skin (100) via an anchor (10), this anchor comprises a shoe (11) fixed on one side to one of the movable assemblies (2,3) and glued to the other side to the skin (100) of the subject by a binder (12).

Figure 2, each anchor comprises a body (111) connected at one of its ends to one of the movable elements and which terminates at its other end by a pad (110) in contact with the binder (12). The body is surrounded by one or more Peltier cells (112), one side of which is in contact with the body (111) and the other with a radiator. Said radiator may be static, consisting of a ribbed plate of conductive material, or comprise a device (114) for circulating a heat transfer fluid. A temperature sensor (120) preferably in the form of a thermocouple is placed in the end of the pad anchor, as close as possible to the interface with the binder (12). Figure 3, the Peltier effect cells are known from the prior art, for example from US3635037 and available commercially. Such a cell acts as a heat pump and comprises two plates (1120, 1121), between which are arranged a series of pairs (1122) made of a semiconductor material. By circulating between these couples a direct current supplied by power connectors (1124, 1123), there is a thermoelectric effect called Peltier effect. The electrons circulating between the semiconductor couples act as a heat transfer fluid circulating between the plates (1120, 1121). One of the plates will then be cooled and the other heated. Inverting the polarity of the supply reverses the hot plate and the cold plate. 2, when the feed polarity of the Peltier cells is such that the cold plate is the one that is in contact with the body (111), the latter absorbs the heat of said body and transports it to the hot plate in contact with the body the radiator (113) or it is evacuated by the circulation of the coolant. The body temperature decreases, as does that of the pad (110) in contact with the binder (12). By reversing the polarity of the supply, the plate in contact with the radiator (13) becomes the cold plate and the plate in contact with the body (111) the hot plate. The thermoelectric effect acts as a heat pump and transfers heat from the coolant to the body (111). The temperature of the body increases as well as that of the pad (110) and that of the binder (12) in contact therewith. A temperature sensor (120), placed near the pad, measures the temperature thereof. This measurement is used to slave the Peltier cell supply device (112) so as to maintain a predetermined temperature on the pad. This control makes it possible to carry out controlled thermal cycles.

4, a first thermal cycle (250), corresponding to an evolution of the temperature (200) as a function of time (201), allows the implementation of the anchoring process using water as a binder. Starting from the ambient temperature (251), the pad is first cooled to a temperature (252), lower than TO and well below the freezing temperature, for example -10 ° C. A drop of water is then deposited on the skin at each location where an anchorage is to be made. Previously, the subject's skin is shaved, cleaned and degreased according to the rules of the art. The pads are brought into contact with the skin at the level of drops of water. The pads being initially worn at low temperature (252) freeze the film of water almost instantaneously. The control system, taking into account the body heat supply, maintains said film at a so-called temperature of adhesion or strong adhesion (TO, 253) between -4 ° C and -2 ° C, so that the film remains frozen but the fabric is not damaged by too low a temperature. The tensile test is then performed according to the specified instructions. When the latter is finished, the temperature controlled pad is heated to a temperature above 0 ° C, for example 20 ° C, in order to obtain the liquefaction of the water film and, consequently, the rupture of the membership. 5, the thermal cycle used when the binder is a thermoreversible gel uses the particular properties of these polymers which exhibit a phase transition between a liquid state at room temperature and a gel structure at a higher temperature. Therefore, obtaining a body temperature adhesion becomes possible.

The cycle (260) then consists in depositing the liquid polymer at a temperature of the order of 20 ° C (261) on the surface of the pads (110) which are then brought into contact with the skin.

The regulation system, taking into account the body heat supply, heats the polymer film to a so-called bonding temperature (262) close to 37 ° C. The film is then solid. The extensometry test can then be performed. At the end of the latter, the pads are cooled to room temperature (261) to allow the skates to take off from the skin. Advantageously used for this purpose a gel consisting of a mixture Hydroxylpropylmethylcellulose (HPMC) and Poloxamer 407. However the low elastic modulus thereof, of the order of 0.1 MPa, limits its use at low levels of stress.

Figure 6, according to a preferred embodiment, the anchoring is performed by a double-sided adhesive associated with a thermal cycle (270). Preferably, this double-sided adhesive consists of a PVC support coated on each side of acrylic peg. Such adhesives are available, for example, under the trade names Tesa 4970 or 3M 9087®. The double-sided adhesive, previously bonded to the pad at room temperature (271), is heated to a temperature Ti (273) such that 30 ° C <Ti <40 ° C. During this cycle, its rheological properties are modified, which results in a decrease in its viscosity. Thus, when the adhesive is brought into contact with the skin of the subject, the peelable layer easily fills all surface irregularities of the skin, thus increasing the effective contact surface between the adhesive and the skin. The pads (110) are then cooled to the temperature TO (272) (5 ° C <TO <10 ° C) which stiffens the adhesive and increases its elastic modulus.

The extension test is then performed. Then, the detachment of the assembly is obtained by a new heating of the Ti adhesive (273). 7, the suitable adhesive and the temperatures Ti and TO are selected according to the rheological properties of said adhesive as a function of temperature (300). More particularly according to the rheological characteristics defining its rigidity, such as its elastic storage modulus (301) and its viscosity, such as its elastic modulus of dissipation (302) or loss. The evolutions of the storage module (350) and the loss module (360) are given qualitatively with the temperature (300) along a logarithmic ordinate (301, 302). Examination of the evolution of these modules according to the temperature reveals 3 zones of behavior. A first zone (310) of vitreous behavior in which the polymer behaves like a rigid solid This behavior zone is observed below a glass transition temperature (3100). In contrast, beyond a so-called flow temperature (3130), a flow zone (313) where the polymer behaves like a fluid.

For temperatures below the flow temperature there is observed a so-called rubber behavior zone (312), during which the evolution of the storage module (350) describes a bearing as a function of temperature. A transition zone (311), in which the stiffness evolves very strongly, generally separates the zone of rubbery behavior from the zone of vitreous behavior. In this transition zone the storage and loss modules evolve by a factor of 100 or more. The temperature of use of an adhesive is clearly above its glass transition temperature (3100) and in practice at least 40 ° C higher than this temperature. Indeed, although the adhesive is very rigid in this area of behavior, its behavior is fragile. It is therefore easy to break the adhesive layer by peeling. The temperature TO is preferably chosen in the transition zone. In this zone (311) the adhesive is rigid, its elastic storage modulus is high but without reaching a fragile behavior. The adhesive is applied to the skin of the subject at a temperature Ti included in the rubber bearing, without going to the flow temperature so that the adhesive retains a certain hold when it is applied to the skin. Typically the module gap both storage (351) and loss (361) between Ti and TO is of the order of a factor 10. For an application on the skin of a living subject, Ti will be chosen moreover less than 50 ° C and TO greater than 0 ° C so as to avoid any risk of burning the subject.

The above description clearly illustrates that by its different characteristics and advantages, the present invention achieves the objectives it has set for itself. In particular, it allows a temporary anchoring for mechanical stressing purposes on the surface of a soft or flexible substrate without intrusion into said substrate.

Claims (10)

REVENDICATIONS1. Mechanical anchoring device (10) on a soft or flexible support (100) comprising: a shoe (11), a binder (12) interposed between said shoe (11) and the support (100) and whose viscosity is a function of at least one solicitation; a contact surface (110) between the pad and the binder (12) to which the adhesion of the binder is at least as strong as the mechanical adhesion of the binder to the support at the same level of stress; means (112) capable of soliciting and maintaining the micromechanical loading (II) to IV4AII II4 to I414A IVV IV4V 4AM II4AI I4. 2. Device according to claim 1 characterized in that the nature of the binder (12) is selected so that the change of its viscosity according to the at least one solicitation is reversible. 3. A method for laying a mechanical anchor (10) according to claim 1 for the purpose of subjecting a soft or flexible support to a mechanical stress test, characterized in that it comprises the steps of: Place the pad (11) in contact with the support (100) via the binder (12) which binds is at a stress level giving it a viscosity sufficiently low to fill the irregularities of the contact surface with the support ; - Solicit the binder (12) at a second level of stress (252, 262, 272, 253) so as to increase the viscosity to a value able to allow the transmission of the entire test load to 25 support. 4. Method according to claim 3 characterized in that it comprises a step of soliciting the binder (12) at the first level of stress (251, 261, 271) after the application of the test request so as to separate anchoring (10) the support (100) without damaging said support. 5. Device according to claim 2 adapted for temporary anchoring on the epidermis of a living subject characterized in that it comprises: - a binder (12) interposed between the pad and the epidermis and whose mechanical adhesion said epidermis (100) is a function of the temperature; - A contact surface between the pad and the binder (12) to which the adhesion of the binder is at least as strong as the epidermis at the same temperature; - Thermal control means (112, 114, 113) adapted to carry and maintain the binder at a temperature TO to which the mechanical adhesion of said binder to the epidermis is high. 6. Device according to claim 5 characterized in that the thermal control means are adapted to carry the binder at a temperature Ti (273) to which the mechanical adhesion of said binder to the epidermis is low. 7. Device according to claim 5 characterized in that the binder (12) has the temperature TO (253, 262, 272) an elastic modulus equal to or greater than that of the skin on which is anchored the device. 8. Device according to claim 5 characterized in that the binder is water and that TO is less than 0 ° C. 9. Device according to claims 5 or 6 characterized in that the binder is a thermo-reversible gel and that TO is close to 37 ° C. 10. Device according to claim 6 characterized in that the binder is a double-sided adhesive tape PSA type such that Ti is between30 ° C and 40 ° C and TO is between 5 ° C and 10 ° C.