WO2015097659A1

WO2015097659A1 - System for determining the morphological characteristics and mechanical properties of living or reconstituted tissues, in particular cutaneous appendages, or structures associated therewith

Info

Publication number: WO2015097659A1
Application number: PCT/IB2014/067260
Authority: WO
Inventors: Giorgio MUSITELLI; Paola Perugini; Stefano SACCHI
Original assignee: Universita' Degli Studi Di Pavia
Priority date: 2013-12-23
Filing date: 2014-12-23
Publication date: 2015-07-02
Also published as: ITTO20131064A1

Abstract

A system is described for characterizing living or reconstituted tissues, in particular cutaneous appendages such as nails and the like or structures associated therewith, comprising: - a plurality of supports (12a- 12c) for a cutaneous appendage (N) under test, each of which is adapted to form at least one point of support of the cutaneous appendage (N) when this is subjected to application of a predetermined characterizing force; an image acquisition device (20) of the cutaneous appendage (N) under test, adapted to acquire a plurality of successive images over time representative of the geometric configuration of the cutaneous appendage (N); and a processing unit (30) coupled to the image acquisition device (20) and adapted to correlate the acquired images representative of the geometric configuration of the cutaneous appendage (N) with the characterizing forces applied.

Description

System for determining the morphological characteristics and mechanical properties of living or reconstituted tissues, in particular cutaneous appendages, or structures associated therewith The present invention relates to the qualitative and quantitative determination of morphological characteristics and mechanical properties of tissues, and more specifically a system for determining the morphological characteristics and mechanical properties of living or reconstituted tissues, in particular cutaneous appendages, more particularly nails, or structures associated therewith.

The cutaneous appendages are structures having an intimate functional link and common embryological origin with the skin. Among them, the nails are epidermal formations located at the ends of the digits with functions of protection, support, holding of foodstuffs, defence, and attack.

The nails mainly consist of hardened and compacted keratin and have the form of a roughly quadrangular, whitish-pink and semitransparent plate, in which it is possible to distinguish a free distal edge, a central portion or nail body that has a small, whitish sickle-shaped zone at the base, called the lunula or half-moon, two lateral edges inserted in a skin fold or nail groove, and a proximal portion called the root, deeply and firmly embedded in the rear portion of the nail groove.

The upper surface of the nail plate is free and in human society has always been a part of the body that is decorated and treated for ornamental purposes, by colouring using enamels, reconstruction or supeiposing of artificial structures (artificial nails).

In recent years, nail care products, which comprise enamels or masks intended for the wellbeing of the nail plate and of the adjacent parts, have become increasingly important in the cosmetics market.

The increasing market has also enhanced the value of properties of cosmetic products, not only with regard to the areas of application of the products themselves, but also with regard to the effects attributed to the cosmetic product and the aims pursued with their use. In this connection, a standard covering cosmetic products has been introduced at European level, (EC) regulation 1223/2009, which stipulates, among other things, verification of the veracity of properties not closely correlated with the actual nature of the cosmetic product.

For these purposes, it is fundamental to provide and have validated instrumental methods that are able to verify such effects. In particular, to verify the effectiveness and performance of a cosmetic formulation, it is essential to develop suitable experimental designs performing evaluations "in vivo", i.e. in the real conditions of use, which may take place over very different periods of time, from a few minutes to months, depending on the type of product and the functionalities to be ascertained.

The aim of the present invention is to make available suitable instrumentation to meet the need for qualitative and quantitative characterization of treated and untreated cutaneous appendages, and in particular of nails, whether they are nails that are living, reconstructed or structures associated therewith such as artificial nail plates or polymers for nail reconstruction or having decorative functions.

Another aim of the invention is to make an instrumentation available for carrying out measurements for qualitative and quantitative characterization of cutaneous appendages, and more particularly of nails, "in vivo" with non-invasive procedures, for carrying out characterization protocols of variable duration, in different conditions.

According to the present invention, this aim is achieved with a system for the characterization of living or reconstituted tissues, in particular cutaneous appendages such as nails and the like or structures associated therewith, having the features claimed in Claim 1.

Particular embodiments form the subject matter of the dependent claims, the contents of which are to be regarded as an integral part of the present description.

To summarize, the present invention is based on the principle of devising a comprehensive system for characterization, adapted to study cutaneous appendages, in particular nails, by employing conservative techniques associated with the acquisition of digital images allowing continuous monitoring of the analysis processes. The system comprises test sites (on the cutaneous appendages) including a plurality of supports adapted to work on at least one portion of nail or of the structures associated therewith undergoing tests, configured to form supporting and/or fulcrum surfaces for said nails with respect to a characterizing stress exerted on them. In a preferred embodiment, the system also includes a corresponding plurality of stressing members for applying and for measuring the intensity and duration of the stresses applied. The behaviour of a cutaneous appendage under test is monitored continuously by an image acquisition system, and the morphological and deformation data detected, representative of the mechanical parameters under observation, are acquired in real time throughout all the phases of a test protocol and are processed by software, also in relation to the related values of thickness and of morphology.

Further features and advantages of the invention will be presented in more detail in the following detailed description of one embodiment thereof, given as a non-limiting example, referring to the appended drawings, in which:

Fig. 1 shows schematically a system according to the invention;

Figs. 2 and 3 show examples of two embodiments of a support-holding structure of the system in Fig. 1 ;

Figs. 4 to 8 show examples of embodiments of the supports for cutaneous appendages used in the system of Fig. 1 and associated perspective enlargements of some parts thereof; and

Figs. 9, 10, 1 1 and 12 are diagrams representative of results of characterization of a cutaneous appendage under test.

Referring to Fig. 1 , this shows the essential elements of a system for characterization of living or reconstituted tissues, in particular cutaneous appendages such as nails and the like or structures associated therewith. The complete system, indicated with the numerical reference 10, comprises a plurality of supports 12, indicated individually with the references 12a, 12b, 12c, each of which is adapted to constitute at least one point of support of a cutaneous appendage N subjected to application of a predetermined force for characterizing the cutaneous appendage in a direction of application F by means of a stressing member B, for example in the form of a loading point or rod, to which an associated load cell T, for measuring the force applied, is coupled. Said characterizing force is predetermined in respect of its maximum value in order to avoid damaging the appendage, but its intensity is preferably progressive and gradual, and its speed of application can be predetermined and is controllable.

An image acquisition device 20, preferably for digital images, is arranged beforehand with its field of observation turned towards at least one support 12a- 12c and/or the cutaneous appendage temporarily associated therewith for acquiring a plurality of successive images over time, representative of the geometric configuration of a cutaneous appendage associated with the support, i.e. of its morphology and of the evolution of the strains. In the figure, the circumferential arrows between the supports indicate the possibility of arranging the supports selectively and alternately in a predetermined working position relative to the stressing device and to the image acquisition device. A data processing unit 30 is associated with said image acquisition device 20 and with a load cell T associated with a stressing member B, and is arranged beforehand (programmed) for synchronous correlation of said plurality of images representative of the strains of the cutaneous appendage with said characterizing forces applied. More specifically, the processing unit 30 is arranged beforehand for executing procedures of image recognition and to extract, from the images acquired, data on form (morphological characterization of the appendage), static dimensional data (values of thickness of the appendage) and dynamic strain data (values of displacement and/or strain of the appendage subjected to a load). The supports 12a- 12c are preferably mounted on a movable support-holding structure 40, adapted to expose each support alternately to a field of observation of the image acquisition device and to the stressing member, and each of these is preferably dedicated to one type of test.

The support-holding structure 40 comprises, for example, a structure that is movable by rotation or translation in a working plane W, such as a support 42 rotating about an axis orthogonal to the working plane W in at least one of two directions of rotation (shown in Fig. 2), bearing the supports 12a- 12c fixed stably at a predetermined mutual circumferential distance, or a belt running on the working plane W in at least one direction of translation, bearing the supports 12a- 12c fixed stably at a predetermined, adjustable mutual linear distance. In an alternative embodiment, shown in Fig. 3, the support-holding structure 40 comprises a drum structure 44 rotating about an axis parallel to the working plane W in at least one of two directions of rotation, bearing the supports 12a- 12c fixed on the lateral surface at a predetermined mutual circumferential distance, whose lateral surface emerges from the working plane W via a portion through a window 46 of the working plane W. A plurality of stressing members B of different forms, preferably held by a movable crosspiece surmounting the support-holding structure 40, to which a respective load cell is associated, is provided for applying different deforming forces at different points of application on the cutaneous appendage N depending on the nature of the characterizing tests to be performed on the cutaneous appendage N.

In a preferred embodiment, the image acquisition device 20 is arranged on the working plane W near the support-holding structure 40, in an arrangement such that it has its field of observation directed towards at least one position assumed by a support in which said support is visible, i.e. not obscured by other supports of the system.

Figs. 4-8 show different types of support and associated stressing members, arranged for carrying out specific tests for characterizing a cutaneous appendage N, such as a nail or a structure associated therewith. Fig. 4 shows a support 12a comprising a projecting flat fulcrum formation 52a adapted to build a support for the base of the distal edge of a nail N. The projecting formation has a curved top (visible in the perspective enlargement in Fig. 4a) in order to allow stable support, which does not alter the conformation of the nail plate during longitudinal bending.

This is or may be associated with a stressing member 54a, the end of which 56a in contact with the cutaneous appendage has a flat surface which is not pointed, but is chamfered or rounded, optionally shaped to match the curvature of the appendage, adapted to apply a force in a direction F substantially orthogonal to the nail plate at a preferably intermediate point of the distal edge of the nail, in such a way as not to damage the surface of the appendage.

The support 12a is preferably used for tests of longitudinal bending, i.e. for analysing the effects of a bending stress applied to a cutaneous appendage N that has a free end subjected to a deforming force orthogonal thereto. The test may be carried out both with monitoring of load and with monitoring of strain, and supplies a curve characteristic of the cutaneous appendage under examination. From such a curve it is possible to obtain the typical parameters of the static mechanical behaviour in bending of the cutaneous appendage (nail). The test is carried out by binding the nail to the projecting formation 52a of the support, leaving the distal edge thereof free, to which a load is applied.

During the test, the strain produced and the force applied to produce the aforesaid strain are recorded by means of the load cell T associated with the stressing member 54a and optionally also by means of the image acquisition device 20, and these data are supplied to the processing unit 30.

Fig. 5 shows a support 12b comprising a pair of projecting fulcrum formations 52b symmetrical relative to a sagittal plane∑ of a nail N, arranged at a variable mutual distance, adapted to build symmetrical points of support for the distal edge of the nail. The projecting formations are configured as cylindrical supports with ends cut with a flute tip of sufficient diameter to guarantee its rigidity in longitudinal bending, but small and smooth at the ends so that they can be inserted under the nail without causing damage or nuisance. These are shown in the perspective enlargement in Fig. 5a.

This is associated or is associable to a stressing member 54b whose end for contact 56b with the cutaneous appendage is preferably of spherical or hemispherical geometry, adapted to apply a force in a direction F substantially orthogonal to the nail plate at a preferably intermediate point of the distal edge of the nail. The nail portion stressed is defined by means of a system for adjustable fine travel. Fig. 6 shows the same support 12b, comprising a pair of projecting fulcrum formations 52b that are symmetrical relative to a sagittal plane∑ of a nail N, arranged at a controllable and variable mutual distance, adapted to build symmetrical points of support for the distal edge of the nail, similarly to the description with reference to the embodiment of Fig. 5. This is associated or associable with a stressing member 54b' whose end for contact 56b' with the cutaneous appendage has a double spherical or hemispherical head, adapted to apply a force in two parallel directions Fl , F2 substantially orthogonal to the nail plate in a pair of symmetrical points of the distal edge of the nail relative to a sagittal plane, internal to the fulcrum points constituted by the formations 52b.

The support 12b is preferably used for transverse bending tests, i.e. for characterizing the mechanical behaviour, and specifically for measuring the stiffness, rigidity and yield properties, of the material forming the cutaneous appendage stressed in the direction of application of a force.

The test protocol consists of subjecting the nail to a controlled deformation and measuring the force required to obtain the same, or, alternatively, quantifying the strain of the nail as a result of application of a predetermined force. The test may be carried out both with monitoring of load and with monitoring of strain and supplies a curve characteristic of the cutaneous appendage under examination. From such a curve it is possible to obtain the typical parameters of static mechanical behaviour in bending of the cutaneous appendage.

The transverse bending test may be carried out in variants with three points or with four points. In the variant with three points, provided by the configuration in Fig. 5, the bending action is exerted by a single stressing member applied at the mid-point between two supports or fulcrums. In the variant with four points, provided by the configuration in Fig. 6, the bending action is exerted by a double stressing member that is applied symmetrically relative to the mid-point between two supports or fulcrums. During the test, the strain produced and the force applied to produce the aforesaid strain are recorded by means of the load cell T associated with the stressing member 54b or 54b' and optionally also by means of the image acquisition device 20, and these data are supplied to the processing unit 30. Fig. 7 shows a support 12c comprising a substantially cylindrical formation 52c adapted to build a support for the distal edge of a nail N, smooth and with one end cut with a "flute tip" so that it can be inserted under the nail while maintaining substantial rigidity. This is shown in the perspective enlargement in Fig. 7a. This is associated or associable with a stressing member 54c whose end for contact 56c with the cutaneous appendage has a flat surface, chamfered or rounded (substantially hemispherical), adapted to apply a force in a direction F substantially orthogonal to the nail plate, preferably at an intermediate point of the distal edge of the nail, without effective penetration occurring, causing irreversible deformation and/or damage of the appendage (if the nail is damaged, one of the lateral edges may be used).

The support 12c is preferably used for tests of resistance to compressive force, i.e. for analysing the elasticity, i.e. the capacity of the material of the cutaneous appendage to return to its original form when a stress applied to a cutaneous appendage N that causes deformation of the latter is removed.

The test is earned out by supporting the distal edge of the nail plate on the flat formation 52c of the support, and by subjecting a previously defined area of the free upper surface of the distal edge to an increasing pressure, exerted by the stressing member 54c, keeping the lower surface of the distal edge supported on the surface of the support 52c. If the strain increases linearly with increase in the pressure applied on the cutaneous appendage by the stressing member 54c, the material is purely elastic. Some materials may, however, display viscoelastic behaviour, where the stress-strain relation is not linear and the response of the cutaneous appendage is highly dependent on the time and the speed of application of the stress, as well as on other factors such as state of hydration, particular treatments, etc. of the cutaneous appendage.

The test supplies a characteristic curve of the cutaneous appendage under examination, from which the typical parameters of the elastic behaviour of the cutaneous appendage (nail) may be obtained.

During the test, the strain produced and the force applied to produce the aforesaid strain are recorded by means of the load cell T associated with the stressing member 54c and optionally also by means of the image acquisition device 20, and these data are supplied to the processing unit 30.

Fig. 8 shows the same support 12c comprising a substantially cylindrical formation 52c adapted to constitute a support for the distal edge of a nail N, smooth and with an end cut as a "flute tip" so that it can be inserted under the nail while maintaining substantial rigidity.

This is associated or associable with a stressing member 54c' whose point end of contact 56c' with the cutaneous appendage has a head of truncated-cone or truncated-pyramid shape or else with a pointed tip or edge (some of the various possible forms are illustrated in the enlarged insert) and is adapted to apply a force of penetration in a direction F substantially orthogonal to the nail plate, preferably at an intermediate point of the distal edge of the nail (if the nail is damaged, one of the lateral edges may be used). The support 12c is used for instrumental evaluation in vivo of the hardness of the material of the cutaneous appendage, i.e. for measuring the resistance of the material to localized plastic deformation. The hardness is evaluated on the basis of the mark left (which may be visualized by analysis of the digital image acquired) by different heads of the stressing member, operating as a punch, to which the same force is applied, and by analysis of force/penetration curves associated with each punch at equal force of penetration exerted.

The test is carried out by supporting the distal edge of the nail plate on the flat formation 52c of the support, and submitting a previously defined area of the free upper surface of the distal edge to penetration of the stressing member 54c', keeping the lower surface of the distal edge supported on the flat surface of support 52c.

The test supplies force/penetration curves characteristic of the cutaneous appendage under examination, relative to different points of penetration of the stressing member, at equal force of penetration exerted, from which the typical parameters of hardness of the cutaneous appendage (nail) may be obtained.

During the test, the strain produced and the force applied to produce the aforesaid strain are recorded by means of the load cell T associated with the stressing member 54c' and optionally also by means of the image acquisition device 20, and these data are supplied to the processing unit 30.

Advantageously, in the context of the measurement in question, reference is not made to international hardness scales, but the effects of one and the same force of penetration exerted on the same cutaneous appendage submitted to various treatments, whether cosmetic and/or medical, are analysed and compared.

Referring to Figs. 9, 10 and 1 1 , some examples are presented for evaluation of the mechanical properties of the nails of healthy volunteers whose nails were first measured for thickness and conformation and were then submitted to tests with the system according to the invention, carried out by exerting stresses of up to 10 N of applied force, measuring deformation of the nail plate between 0 and 1 mm. The system was found to produce reproducible results on the same sample and in the various types of analysis. The data obtained can be converted to arbitrary units representative of the parameters investigated. Analysis of these data quantifies said variation optionally attributable to the effectiveness of the treatment that the substrate underwent.

Example 1

Fig. 9 shows two diagrams representative of the response of a cutaneous appendage to a transverse bending stress, in which the strain ΔΟ is shown on the abscissa and the applied force F is given on the ordinate. The top graph shows the response of the appendage as it is, while the bottom graph shows its behaviour after undergoing a treatment, which in this case consists of immersion in water for 10 minutes at 37°C.

The figures reveal elastic behaviour, in which the coefficient of linear regression of the curve is representative of the state of the nail. This interpretation is the result of repeated analyses on the same sample and on similar samples maintained in standardized environmental conditions (20°C, 60% RH) and analysed in the ranges of force given above. Since the elastic response to transverse bending stress depends on the geometry, in particular on the degree of curvature of the sample and on its thickness, it is not possible to extrapolate a scale of values that may be generalized.

However, analysis of the portions of the curves obtained before and after treatment proves extremely useful for evaluating the influence of said treatment on the sample. The results of the analyses given in Fig. 9, bottom graph, reveal the variation of elasticity induced by remaining in water with a reduction of the slope of the first portion of the curve up to a maximum of about 40%. This decrease in slope may be attributed to the decrease in elastic coefficient of the outemiost portions of the hydrated nail. The second portion of the curve tends to maintain a slope comparable to that obtained before treatment (Fig. 9, top graph) and therefore attributable to the more internal portion of said nail, less involved by the short duration of the hydration time ( 10 min).

Example 2 Fig. 10 shows a diagram representative of the response of a cutaneous appendage to a longitudinal bending stress, in which the strain Δϋ is shown on the abscissa and the applied force F is given on the ordinate. Since the elastic response to the longitudinal bending stress depends on the geometry, in particular on the degree of curvature of the sample and on its thickness, it is not possible to extrapolate a scale of values that may be generalized. However, analysis of the curves obtained, and in particular of the initial phase, which is found to be linear (in the bottom graph), is extremely useful for evaluating the elastic behaviour of the distal edge of the nail ^' and the influence of a possible treatment, such as hardening or dehydrating, on the sample.

Example 3

Fig. 1 1 shows a diagram representative of the response (resistance) of a cutaneous appendage to a compressive stress, in which the strain (displacement) in mm is shown on the abscissa and the force applied is given on the ordinate.

The curves and the associated data that may be extrapolated are useful for evaluating the elastic behaviour of the nail, bearing in mind that the values obtained are found to be independent of the morphology of the nail, but are only closely linked to the intrinsic structure of the material of which the appendage consists.

It is possible to evaluate the influence of possible treatments, taking into account that the profile of the curve of response to compression depends on said treatment. For example, after a hydration treatment, the curve has a two-phase course, an example of which is shown in Fig. 12. Point analysis of the compression curves is useful for identifying the effects of the treatment, whether it is pharmacological, cosmetic or aesthetic.

Moreover, it is possible to measure directly the thickness of the nail plate in the sampling area based on the difference between the predetermined total travel (theoretical idle travel) of the stressing member and the distance actually covered to reach the point of contact between the stressing member and the sample. In particular, with the system according to the invention it is possible, as an example, to determine simply and quickly:

- the elastic and viscoelastic behaviour of different portions of the nail plate as it is and following treatments, modifications and alterations;

- the behaviour and the resistance of the nail plate, as it . is and following treatments, modifications and alterations, to transverse and longitudinal deformation;

- determination of the hardness of the nail plate as it is and following treatments, modifications and alterations;

- evaluation of the morphology and thickness of the nail plate as it is and following treatments, modifications and alterations.

Advantageously, the system according to the present patent may be used in various settings, including analytical laboratories for verifying the effectiveness and safety of cosmetic products, beauty centres, research institutes in the clinical, forensic, pharmaceutical and in the biological field in general.

It is to be noted that the embodiment proposed for the present invention in the foregoing discussion is purely of the nature of an example and does not limit the present invention. A person skilled in the art will easily be able to implement the present invention in various embodiments, which do not, however, depart from the principles presented here, and are therefore included in the present patent.

This applies in particular with regard to the possibility of envisaging further supports, of different structure, or further stressing members.

Moreover, the digital acquisition system, in particular in morphological evaluation and in determination of plate thickness, may be different and separate from the equipment employed for direct monitoring of the mechanical testing, and the tests may be also be carried out at different times. The morphological parameters may be evaluated before, during and after application of the characterizing forces, if so required by the protocol, in order to evaluate possible modifications or alterations of the sample. Naturally, without prejudice to the principle of the invention, the embodiments and the details of execution can be varied widely relative to what has been described and illustrated purely as a non-limiting example, without departing from the scope of protection of the invention defined by the appended claims.

Claims

1. System for the characterization of living or reconstituted tissues, in particular cutaneous appendages such as nails and the like or structures associated therewith, comprising:

a plurality of supports (12a- 12c) for a cutaneous appendage (N) under test, each of which is adapted to determine at least one supporting point of the cutaneous appendage (N) when this is subject to the application of a predetermined characterizing force;

means (20) for the acquisition of images of said cutaneous appendage (N) under test, adapted to acquire a plurality of successive images over time representative of the geometric configuration of the cutaneous appendage (N), and

processing means (30) coupled to said image acquisition means (20) and adapted to correlate the acquired images representative of the geometric configuration of the cutaneous appendage (N) with said applied characterization forces.

2. System according to Claim 1 , comprising a support-holding structure (40) movable in a working plane (W), bearing the supports (12a- 12c) firmly fixed at a predetermined mutual distance, and adapted to alternately expose each support (12a- 12c) to a field of view of the image acquisition means (20).

3. System according to Claim 2, wherein the support-holding structure (40) comprises a support (42) rotating about an axis orthogonal to the working plane (W) in at least one of two directions of rotation, bearing said supports (12a- 12c) at a predetermined mutual circumferential distance.

4. System according to Claim 2, wherein the support-holding structure (40) comprises a belt on the working plane (W) moving in at least one direction of translation, bearing said supports (12a- 12c) at a predetermined mutual linear distance.

5. System according to Claim 2, wherein the support-holding structure (40) comprises a drum (44) rotating about an axis parallel to the working plane (W) in at least one of two directions of rotation, bearing laterally said supports (12a-12c) at a predetermined mutual circumferential distance, the lateral surface of said drum (44) emerging from the working plane ( W) for a portion through an opening (46) in said plane (W).

6. System according to any one of the preceding claims, including a plurality of stressing members (B) respectively associated with said plurality of supports (12a- 12c) and adapted to apply a force on a predetermined area of a cutaneous appendage (N) resting on a support.

7. System according to Claim 6, including a plurality of load cells (T), respectively associated with said stressing members (B).

8. System according to any one of the preceding claims, including a first support (12a) which includes a projecting flat fulcrum formation (52a) adapted to form a rest for the base of the distal edge of a nail (N).

9. System according to Claim 8, wherein a first stressing member (54a) having a contact end (56a) with a flat, chamfered or rounded surface, is associated or associable with said first support (12a) and arranged to apply a force along a direction orthogonal to the nail plate of said nail (N) at an intermediate point of the distal edge of the nail (N).

10. System according to any one of the preceding claims, including a second support (12b) that comprises a pair of projecting fulcrum formations (52b) adapted to form a rest for the distal edge of a nail (N), said support being symmetrically distributed with respect to a sagittal plane of the nail (N).

1 1. System according to Claim 10, wherein a second stressing member (54b) having a contact end (56b) with a spherical or hemispherical head is associated or associable with said second support (12b) and arranged to apply a force along a direction perpendicular to the nail plate of said nail (N) at a point of the distal edge of the nail (N).

12. System according to Claim 10, wherein a second stressing member (54b¹) having a double contact end (56b') with a spherical or hemi-splierical head is associated or associable with said second support (12b) and arranged to apply a force along two parallel directions which are perpendicular to the nail plate of said nail (N) at a pair of symmetrical points of the distal edge of the nail (N).

13. System according to Claim 10, wherein said pair of projecting fulcrum formations (52b) is disposed at a variable mutual distance.

14. System according to any one of the preceding claims, including a third support (12c) which comprises a substantially cylindrical formation (52c) adapted to form a rest for the distal edge of a nail (N).

15. System according to Claim 14, wherein a third stressing member (54c) having a contact end (56c) with a flat, chamfered or rounded surface is associated or associable with said third support (12c) and arranged to apply a force along a direction orthogonal to the nail plate of said nail (N) at a point of the distal edge of the nail.

16. System according to Claim 14, wherein a third stressing member (54c') having a contact end (56c) shaped substantially as a point or edge is associated or associable with said third support (12c) and arranged to apply a force of penetration along a direction orthogonal to the nail plate of said nail (N) at a point of the distal edge of the nail.