WO2021105743A1

WO2021105743A1 - Container

Info

Publication number: WO2021105743A1
Application number: PCT/IB2019/060155
Authority: WO
Inventors: Germano Grandi
Original assignee: Plax S.R.L.
Priority date: 2019-11-26
Filing date: 2019-11-26
Publication date: 2021-06-03
Also published as: KR20200128648A; CN214804879U

Abstract

Described is biopsy container (C) comprising a body (1) equipped with a lower chamber (2a) filled with liquid designed to preserve at least one bioptic sample (B) and an upper chamber (2b). The container (C) also comprises a descender (6) equipped with a bottom wall (7) connected to the body (1) in such a way as to isolate the lower chamber (2a) from the upper chamber (2b). The descender (6) also comprises a tubular body (8) having a first end (9a) coupled to the bottom wall (7) and a second end (9b) opposite the first end (9a) in such a way as to define a containment space (V) open at the top designed to receive the at least one bioptic sample (B). The container (C) also comprises compliant connecting means, configured for connecting the bottom wall (7) to the body (1) in a disengageable fashion, and a lid (17) reversibly coupled to the body (1) and acting in conjunction with the lateral wall (8) of the descender (6). The container (C) also comprises a closing element (22) which can be engaged with the second end (9b) in such a way as to close the second end (9b).

Description

DESCRIPTION

CONTAINER

Technical field

This invention relates to a container, and in particular a container for organic material to be used, for example, for a biopsy. These containers are widely used in the medical field. Background art

As is known, in order to perform a biopsy, a bioptic sample is taken from the patient and transferred to an analysis centre where the biopsy or an histopathological examination is performed.

There are prior art containers designed for transporting bioptic samples wherein the samples are immersed in a solution containing formaldehyde, commonly known as formalin.

However, it is known that the formalin has cancerogenic properties and is therefore potentially harmful for the health of the person taking the bioptic samples and introducing them into the substance to store them. There are prior art containers which attempt to overcome this problem by providing solutions which make it possible to reduce to a minimum, ideally eliminate, any possible interaction of the operator with the formalin when the bioptic sample is stored for its transfer.

For example, there are prior art containers which have a zone for containing the formalin isolated from the rest of the container by means of a fluid-tight membrane. In this case, the bioptic sample is placed over the membrane, in the space of the container free from the formalin. The container is then closed with a lid equipped with a perforating element. When the container is closed, the element perforates the membrane in such a way that the formalin inundates the entire space of the container and, therefore, also the bioptic sample.

There are also prior art containers having a first sub-container in which the bioptic sample is introduced and a second sub-container containing the formalin. Both the sub-containers are provided with two holes mutually facing each other in such a way that the sub-containers can move between a closed position, wherein the holes are not in communication, preventing the formalin from passing in the first sub-container, and an open condition, wherein the holes are in communication allowing the passage of the formalin in the first sub-container in such a way as to immerse the sample.

There are also prior art containers for bioptic samples wherein a layer of oily substance is placed, above the formalin, to form a barrier which is able to inhibit the inhaling of formalin at the moment of opening the container for inserting/withdrawing the bioptic sample.

There are also prior art containers which have a lower chamber, containing formalin, and an upper chamber containing a descender, that is to say, a small vessel open at the top and designed for containing the bioptic sample. The descender is immersed, together with the sample, in the formalin following a screwing of a lid on the main body of the container. In this case, the two chambers are isolated at the moment of the insertion of the sample of the descender. When the lid is screwed onto the container, it acts in conjunction with the upper portion of the descender to cause its falling and the immersion of the sample in formalin. In this situation, the vessel is free to move between one chamber and the other in the case of tipping of the container.

However, these containers also have drawbacks in terms of practicality and safety.

Generally speaking, the bioptic samples are sticky and tend to adhere to the bottom of the container. This means that in the case of a tipping of the container, for example during transport, the liquid flows towards the lid leaving the sample, which remains stuck to the bottom, uncovered from the formalin.

Disadvantageously, therefore, the containers having the membrane must be transported vertically to prevent the samples contained therein from being damaged by an incorrect immersion in formalin. The containers provided with holes have the drawback of not being provided with a fluid tight seal between one sub-container and the other even in the closed configuration. This means that a minimum quantity of formalin can pass into the first sub-container also at the moment of opening the container for depositing the sample, making the operation not very safe for the operator.

A further drawback derives from the fact that the use of the sub-containers is difficult since the operator must make sure that the holes match well so as to allow the formalin to wet the bioptic sample.

A further drawback derives from the fact that the use of the sub-containers does not allow the sample to be kept immersed in the formalin if the container undergoes an overturning during transport.

The containers having the layer of oily substance are not safe and reliable. The containers having the descender are not reliable since, in the case of tipping of the container, the sample could be inserted in the space between the descender and the wall of the container, remaining stuck there. When the container is returned to the correct position, the formalin again flows towards the lower chamber together with the descender but the bioptic sample remains stuck and therefore no longer immersed.

Aim of the invention

The technical purpose of the invention is therefore to provide a container for samples to undergo a biopsy which is able to overcome the drawbacks of the prior art.

The aim of the invention is therefore to provide a biopsy container which is able to guarantee the correct storage of the sample taken whilst at the same time maintaining high standards of safety for the health of the operator.

The technical purpose indicated and the aims specified are substantially achieved by a biopsy container comprising the technical features described in one or more of the appended claims. The dependent claims correspond to possible embodiments of the invention. Brief description of the drawings

The description is set out below with reference to the accompanying drawings which are provided solely for purposes of illustration without restricting the scope of the invention and in which: - Figure 1 is an exploded view of the biopsy container according to the invention;

Figures 2A and 2B show, respectively, the container of Figure 1 closed by a lid and open;

Figures 3A and 3B show, respectively, cross section views of the container without and with the descender inserted inside it;

Figures 4A-4C are perspective views of the descender with and without the closing element;

Figure 5 is a perspective view of the closing element;

Figures 6A and 6B are perspective views, respectively, of the lid of the container without and with the closing element;

Figures 7A and 7B are cross section views of the container according to the invention in different configurations.

Detailed description of preferred embodiments of the invention

With reference to the accompanying drawings, the numeral “C” denotes a biopsy container comprising a body 1 extending along a main axis “X”. Preferably, the body 1 is made in the form of a cylindrical tubular element. The body 1 is equipped with a lower chamber 2a filled with liquid, preferably formalin, designed to preserve at least one bioptic sample “B” and an upper chamber 2b positioned above the lower chamber 2a. Preferably, the diameter of the upper chamber 2b is greater than the diameter of the lower chamber 2a.

Preferably, the space of the lower chamber 2a is greater than the space of the upper chamber 2b.

As shown in Figure 1 , the lower chamber 2a is delimited at the bottom by a base wall 3 and laterally by a lower lateral portion 4a of a lateral wall of the body 1. The upper chamber 2b is delimited laterally by an upper lateral portion 4b of the lateral wall of the body 1 and is open at the top.

The lower lateral portion 4a of the lateral wall of the body 1 is joined to the upper lateral portion 4b by a joining collar 5.

Preferably, the body 1 is made entirely of rigid plastic material.

Preferably, the body 1 is made in a single piece in such a way that there are no joints/attachments which can cause the escape of the formalin from the lower chamber 2a or which can cause the entry of air in the container “C” thus adversely affecting the correct storage of the bioptic sample “B”. The biopsy container “C” also comprises a descender 6 positioned, at least initially, in the upper chamber 2b in such a way that a bottom wall 7 of the descender 6 is connected to the body 1 for isolating the lower chamber 2a from the upper chamber 2b.

In other words, the bottom wall 7 defines an upper closure of the lower chamber 2a.

In this position the container “C”, and the descender 6 in particular, is in a storage configuration, that is to say, in a configuration in which the container “C” is new and ready to receive the bioptic sample “B”. Advantageously, the isolation between the chambers 2a, 2b due to the presence of the descender 6 prevents a medical operator, at the moment the container 1 is opened for depositing the bioptic sample “B”, from inhaling formalin vapours.

Preferably, the descender 6 is made in a single piece using a type of rigid plastic having a specific weight greater than the specific weight of the formalin or, more generally, of the liquid contained in the lower chamber 2a of the body 1.

As shown in Figures 4A and 4C, the descender 6 comprises the bottom wall 7 from which extends away a cylindrical tubular body 8 having a first end 9a coupled to the bottom wall 7 to define a closure of the first end 9a and a second end 9b opposite the first end 9a in such a way as to define a containment space “V” open at the top and designed to receive the bioptic sample “B”.

Preferably, the descender 6 has the circular bottom wall 7 having a diameter less than the diameter of the upper chamber 2b and that of the lower chamber 2a. Preferably, the tubular body 8 has a height just greater than the height of the upper chamber 2b in such a way that, in the storage configuration, the second end 9b of the descender 6 protrudes from an upper end 11 of the body 1.

According to the embodiment illustrated in the accompanying drawings, the descender 6, in the storage configuration, is connected in such a way that it can be uncoupled from the body 1 by compliant connecting means. The compliant connecting means comprise an annular groove 12 of weakness joining a peripheral portion 10 of the bottom wall 7 of the descender 6 to the body 1. The annular groove 12 is located inside the body 1 between the upper chamber 2b and the lower chamber 2a at the same height as the joining collar 5 in such a way as to form, between the annular groove 12 and the body 1 , a housing in the shape of a “U”.

An annular seal 13 is positioned across the housing. The annular seal 13 is coupled to the body 1 in such a way as to be interposed between the upper chamber 2b and the lower chamber 2a inside the body 1 and at the same height as the joining collar 5.

The annular seal 13 has at least one lip reversibly connected to the bottom wall 7 of the descender 6, more precisely to the peripheral portion 10 of the bottom wall 7, in such a way as to define a sealed connection such as to prevent the passage of the liquid from the lower chamber 2a to the upper chamber 2b.

Preferably, as illustrated in Figure 3A, the annular seal 13 comprises two lips 13a, 13b separated by a groove 14 in which the peripheral portion 10 of the bottom wall 7 is inserted in such a way as to be supported together with the entire descender 6 when the latter is in the storage configuration. In other words, in the storage configuration, the descender 6 is supported thanks to the insertion of the peripheral portion 10 of the bottom wall 7 inside the groove 14 interposed between the two lips 13a, 13b of the seal 13 and the second end 9b protrudes from the upper end 11 of the body 1. Therefore, in the storage configuration, the descender 6 is ready to receive the bioptic sample “B” inside the containment space “V”.

Due to its nature, the bioptic sample “B” is sticky and tends to adhere both to the walls of the tubular body 8 and to the bottom wall 7 of the descender 6, once the bioptic sample “B” has been inserted in it. The bioptic sample “B” also tends to stick to the medical instruments used for its handling, in particular during the insertion of the sample “B” in the containment space “V”.

For this reason, in order to favour the transfer of the bioptic sample “B” inside the container “C”, the descender 6 also comprises a protuberance 15 extending away from the bottom wall 7 of the descender 6 inside the containment space “V”.

The protuberance 15 is designed to favour a detachment of the bioptic sample “B” from the medical instrument during an insertion of the sample “B” in the containment space “V” of the descender 6.

In fact, the operator can slide the medical instrument, on which the bioptic sample “B” is positioned, along the protuberance 15 in order to detach the bioptic sample “B” from the instrument causing the falling in the containment space “V”.

As shown in Figure 4A, the descender 6 also comprises at least one series of holes 16 made on the tubular body 8 in such a way as to facilitate the entrance of the formalin in the containment space ‘V’ when the container ‘C’, in particular the descender 6 containing the bioptic sample ‘B’, is in a configuration of use, shown for example in Figure 7B.

According to the embodiment illustrated in the accompanying drawings, the descender 6 has two series of holes 16 positioned on diametrically opposite portions of the tubular body 8, preferably the holes being positioned according to a square matrix.

As shown in the accompanying drawings, the container “C” also comprises a lid 17 reversibly coupled with the body 1 and acting in conjunction with the tubular body 8 of the descender 6 in such a way as to apply a pressure on the descender 6 to disengage the connecting means and cause a falling of the descender 6 in the lower chamber 2a in such a way as to bring the descender 6 into the configuration of use shown in Figure 7B.

As shown in Figure 6A, the lid 17 comprises a lateral surface 17a equipped inside with a thread 18 designed to engage reversibly with a thread 19 made externally on the upper lateral portion 4b of the lateral surface of the body 1 , in such a way that the lid 17 can slide along the body 1 according to a screwing/unscrewing movement which allows the pressure on the descender 6 to be applied.

In other words, once the bioptic sample “B” has been inserted in the containment space “V”, the lid 17 is screwed onto the body 1 in such a way that, engaging with the second end 9b of the descender 6, its lowering causes a twisting moment on the descender 6 and, therefore, a failure of the compliant connecting means.

Following the failure of the compliant connecting means, the peripheral portion 10 of the bottom wall 7 is disengaged, by elastic deformation, from the annular seal 13 causing the falling of the descender 6 into the lower chamber 2a of the body 1.

To prevent the descender 6 from being brought from the storage configuration to the configuration of involuntary use, and therefore without the bioptic sample “B” having firstly been inserted in the descender 6, the container “C” comprises a removable locking element 20, for example a rubber seal, at least partly interposed between the lid 17 and the body 1 and configured to prevent the screwing/unscrewing movement of the lid 17.

The removable locking element 20 also acts as a seal if a buffer solution is contained in the upper chamber 2b. Advantageously, during any transport/tipping of the container “C”, the removable locking element 20 prevents the escape of the buffer solution of the upper chamber 2b.

In other words, in the storage configuration, the removable locking element 20 is positioned in such a way as to prevent a complete screwing of the lid 17 which would cause a falling of the descender 6 into the lower chamber 2a, and therefore into the formalin. Preferably, the removable locking element 20 is also configured to prevent the escape of the buffer solution from the upper chamber 2b.

When, on the other hand, the bioptic sample “B” has been placed in the containment space “V” of the descender 6, the removable locking element 20 is removed and the lid 17 can therefore be screwed completely on the body 1 in such a way as to make it fall into the lower chamber 2a and therefore into the formalin.

According to the embodiment illustrated in the accompanying drawings, the lid 17 also comprises an anti-tampering device designed to seal the lid 17 with the body 1 in such a way that it is simple to understand whether the container “C” has already been opened, and therefore used, or not.

The anti-tampering device is in effect automatically broken when the lid 17 is unscrewed for the first time from the body 1.

Preferably, the anti-tampering device is made in the form of a plastic disc 21a fixed in a compliant fashion to an annular rib 21b located below the thread 19 of the body 1. At the moment of the first unscrewing of the lid 17 on the body 1 , the plastic disc 21a yields and detaches from the annular rib 21b.

The container “C” also comprises a closing element 22 which can be engaged with the second end 9b of the descender 6 in such a way as to close the second end 9b and therefore the containment space “V” once the bioptic sample “B” has been placed inside it.

Advantageously, the closing of the containment space “V”, by the closing element 22, prevents the escape of the bioptic sample “B” from the descender 6 and therefore any trapping between the body 1 and the lateral body 8 of the descender 6 in the event of tipping of the container “C”.

Advantageously, in the case of tipping of the container “C”, the bioptic sample “B” is always retained inside the descender 6 thus remaining immersed in the formalin.

Advantageously, the closing element 22 allows the reliability of the container “C” to be increased.

As shown in Figure 5, the closing element 22 is made substantially in the form of a disc-shaped cap comprising a base wall 23, a lateral wall 24 extending away from the base wall 23 and an edge 25 protruding along an upper end 26 of the lateral wall 24, in such a way that, in a plane containing the main axis “X”, the closing element 22 has a step like profile (shown in Figure 3A, 3B, 7A and 7B).

The closing element 22 also comprises at least one shaped recess 27 extending between the base wall 23 and the edge 25 in such a way as to define an elastic tab 28. Preferably, the closing element 22 comprises three shaped recesses 27 each having a first radial stretch 27a extending along the edge 25, a second stretch 27b extending along the lateral wall 24 and a third stretch 27c extending along the line of intersection of the base wall 23 with the lateral wall 24.

When the container “C” is in the storage configuration the closing element 22 is engaged by the elastic tab 28 in a seat 30 shaped to match, positioned inside the lid 17.

As shown in detail in Figure 6B, the closing element 22 is therefore engaged with the seat 30 thanks to the elastic tabs 28 in such a way that the edge 25 is in contact with an inner surface 17b of the lid 17.

At the same time, as shown in Figure 7A, when the container “C” is in the storage configuration, the lid 17 is only partly screwed to the body 1 thanks to the action of the removable locking element 20 and the descender 6 is in the upper chamber 2b, in such a way that the second end 9b protrudes from the upper end 11 of the body 1. In this situation, between the closing element 22 and the second end 9b of the descender 6 there is space.

At the moment of the first use of the container “C”, the lid 17 is unscrewed from the body 1 causing the breakage of the anti-tampering device, that is to say, the detachment from the plastic disc 21 a of the annular rib 21 b. Once the lid 17 has been unscrewed, the removable locking element 20 is removed and the bioptic sample “B” is inserted in the containment space “V” of the descender 6.

Subsequently, the container “C” is brought to the operating configuration by screwing the lid 17 on the body 1 in such a way that the thread 18 of the lid 17 fully engages the thread 19 of the body 1. During the screwing, the closing element 22 is moved towards the descender 6 in such a way that the lateral wall 24 engages with the second end 9b of the descender. The screwing of the lid 17 causes a pressure on the descender 6 such as to determine the engaging of the second end 9b of the descender 6 with the tab 28 of the closing element 22 compressing it and uncoupling it from the shaped seat 30.

In fact, the shaped seat 30 has a diameter greater than the second end 9b of the descender 6. This causes an elastic compression of the tab 28 at the moment of engaging the lateral wall 24 with the second end 9b of the descender 6.

Following application of the pressure by the lid 17, the tab 28 is configured to apply an elastic return force such as to promote a retaining by interference of the closing element 22 in the second end 9b.

In other words, thanks to the screwing of the lid 17 on the body 1 , the closing element 22 is automatically uncoupled from the seat 30 and engaged by interference to the second end 9b of the descender 9 in such a way as to close the containment space “V”. During this step, the elastic tab 28 is elastically compressed since the diameter of the second end 9b is less than that of the seat 30. At the moment of inserting the lateral wall 24 of the closing element 22 in the tubular body 8 of the descender 6, the tab 28 is subjected to the elastic return force locking the closing element 22 on the descender 6, in particular locking the closing element 22 in such a way that the edge 25 comes into contact with the second end 9b of the descender 6.

In the use configuration, shown in Figure 7B, the closing element 22 closes the containment space “V” and then, during the screwing of the lid 17, the descender 6 together with the bioptic sample “B” falls into the formalin.

Advantageously, the fact of closing the containment space “V” using the closing element 22 prevents the escape of the bioptic sample “B” from the descender 6 if the container “C” is tipped. For this reason, the descender 6 and the bioptic sample “B” “follow” the flow of the formalin during any tipping of the container “C” in such a way that the bioptic sample “B” always remains immersed in the formalin.

Advantageously, the closing element 22 is applied to the descender 6 without the need for an operator to insert the hands into the container “C”. In order to extract the bioptic sample “B” from the containment space “V” in such a way as to perform the analyses, the closing element 22 also comprises a gripping portion 29 integrated with the base wall 23.

The gripping portion 29 is designed to be engaged by means of a medical instrument, such as, for example, a gripper, for removing the closing element 22 from the second end 9b of the descender 6 in such a way as to open the second end 9b and therefore the containment space “V” for extracting the bioptic sample “B”.

The presence of the gripping portion 29 prevents the medical operator from having to use the hands to remove the closing element 22. Advantageously, the invention achieves the above-mentioned aims, eliminating the drawbacks highlighted in the prior art.

In fact, the structure of the container “C” makes it possible not to expose a medical operator to the risk of contact and/or inhaling of formalin.

A further advantage is due to the fact that the closing element 22 prevents the escape of the bioptic sample “B” from the descender 6 if the container “C” is tipped.

This means that the bioptic sample “B” does not remain stuck to the container “C”, with the risk of no longer being immersed in the formalin following the return to a vertical position of the container “C”.

A further advantage derives from the fact that the closing element 22 is inserted automatically upon the activation of the descender 6 or removed by using a medical instrument at the opening of the descender 6 thanks to the presence of the gripping portion 29, in such a way as to not require the direct interaction with the operator.

Claims

1. A biopsy container (C) comprising:

- a body (1) equipped with a lower chamber (2a) filled with liquid designed to preserve at least one bioptic sample (B) and an upper chamber (2b) positioned above the lower chamber (2a), said body (1) extending along a main axis (X);

- a descender (6) positioned in said upper chamber (2b) and equipped with a bottom wall (7) connected to said body (1) in such a way as to isolate said lower chamber (2a) from said upper chamber (2b), said descender (6) also comprising a tubular body (8) having a first end (9a) coupled to the bottom wall (7) to define a closing of said first end (9a) and a second end (9b) opposite the first end (9a) in such a way as to define a containment space (V) open at the top designed to receive said at least one sample (B);

- compliant connecting means configured for connecting said bottom wall (7) to said body (1) in a disengageable fashion;

- a lid (17) reversibly coupled to said body (1) and acting in conjunction with said tubular body (8) of the descender (6) in such a way as to apply a pressure on said descender (6) to disengage said connecting means and cause a falling of the descender (6) in the lower chamber (2a); characterised in that it also comprises:

- a closing element (22) which can be engaged with the second end (9b) in such a way as to close said second end (9b).

2. The container (C) according to claim 1 , wherein said closing element (22) comprises a base wall (23), a lateral wall (24) extending away from said base wall (23) and an edge (25) protruding along an upper end (26) of said lateral wall (24), in such a way that, in a plane containing said main axis (X), said closing element (22) has a step-type profile.

3. The container (C) according to claim 2, wherein:

- the closing element (22) comprises at least one shaped recess (27) extending between said base wall (23) and said edge (25) in such a way as to define an elastic tab (28);

- the lid (17) comprises internally a seat (30) shaped to match said closing element (22) and designed to engage said elastic tab (28);

- the second end (9b) is configured to engage the lateral wall (24) of the closing element (22) in a configuration of use; said second end (9b) having a diameter less than the diameter of the seat (30), in such a way that during the application of the pressure on the descender (6) the second end (9b) engages the elastic tab (28) compressing it and uncoupling it from the seat (30).

4. The container (C) according to claim 3, wherein following application of the pressure the elastic tab (28) is configured to apply an elastic return force such as to promote a retaining by interference of the closing element (22) in the second end (9b).

5. The container (C) according to any one of claims 2 to 4, wherein said closing element (22) comprises a gripping portion (29) integrated with said base wall (23), said gripping portion (29) being designed to be engaged by a medical instrument to perform a removal of said closing element (22) from the second end (9b) in such a way as to open said second end (9b).

6. The container (C) according to any one of the preceding claims, wherein a space defined by said lower chamber (2a) is greater than a space defined by said upper chamber (2b).

7. The container (C) according to any one of the preceding claims, wherein said descender (6) comprises at least one series of holes (16) made on the tubular body (8), said series of holes (16) being designed to allow an entrance of said liquid in said containment space (V) when the descender (6) is immersed in said liquid.

8. The container (C) according to any one of the preceding claims, wherein said descender (6) comprises a protuberance (15) extending away from said bottom wall (7) inside said containment space (V), said protuberance (15) being designed to favour a detachment of the bioptic sample (B) from a medical instrument during an insertion of said bioptic sample (B) in said containment space (V) of the descender (6).

9. The container (C) according to any one of claims 2 to 8, wherein said lid (17) comprises a lateral surface (17a) equipped with a thread (18) designed to engage reversibly with a thread (19) made externally on the body (1) in such a way that said lid (17) can slide along said body (1) according to a screwing/unscrewing movement for applying said pressure on said descender (6).

10. The container (C) according to claim 9, comprising a removable locking element (20) at least partly interposed between the lid (17) and the body (1), in such a way as to prevent the screwing/unscrewing movement.

11. The container (C) according to any one of the preceding claims, wherein said lid (17) comprises an anti-tampering device (21a, 21b) designed to seal said lid (17) to said body (1), said anti-tampering device (21a, 21b) being configured to break following a unscrewing of said lid (17).

12. The container (C) according to any one of the preceding claims, wherein said compliant connecting means comprise an annular groove (12) of weakness joining a peripheral portion (10) of the base wall (7) of said descender (6) to the body (1), said annular groove (13) being configured to break when said lid (17) applies said pressure on the descender (6).

13. The container (C) according to any one of the preceding claims, wherein the compliant connecting means comprise an annular seal (13) coupled to the body in such a way as to be interposed between the upper chamber (2b) and the lower chamber (2a) and having at least one lip (13a/13b) reversibly connected to the bottom wall (7) in such a way as to define a sealed connection such as to prevent the passage of the liquid from the lower chamber (2a) to the upper chamber (2b).

14. The container (C) according to any one of the preceding claims, wherein said descender (6) is made of rigid plastic, said rigid plastic having a specific weight higher than the specific weight of said liquid.