IN A SHOE

The present invention relates to a device for providing oxygen-enriched air, said device being incorporated into an object such as a shoe or sole of a shoe.

It has long been known that the feet need to breathe in order to avoid or minimize odor problems and health damages to the feet. Many systems embedded in shoes or soles of shoes for improving air circulation inside a shoe are already described in the prior art. Besides the simplest means of air circulation in shoes or soles of shoes, such as holes, perforations or vents that allow air to circulate freely, more complex systems have been developed.

For example, patent applications EP-Al-0 717 940 and FR-A1-2 597 308 describe a pumping and venting device that brings air from the ambient atmosphere to the interior of the shoe, and vice and versa.

A similar system is described in international application WO-A1-2007/011102, or in patent application FR-A1-2 558 044, in which the shoe is provided with a spring system which is acting as a pump, said pump being operated by the pressure of the foot on the ground during walking or running.

Patent Application FR-A1-2 789 481 describes a system of air circulation and temperature control in a shoe. Thermal control is provided by a compressor activated by the pressure of the foot forming a system with two pressure levels (compression and relaxation) that are used to generate a cold gas or a hot gas according to a Ranque tube open cycle.

The prior art existing to date teaches various ways to have air circulate inside a shoe. The basic principle is generally to take benefit of the pressure exerted by the weight of a person who walks or runs.

All these techniques correspond to systems that are integrated into a shoe or a sole of a shoe and are presented as techniques allowing the circulation of air only, at the foot level. However air is composed of approximately 21% oxygen, 78% nitrogen and 1% argon, as well as other gases in minor amounts. It is also known that oxygen itself has therapeutic effects, preventive and/or curative, that allow skin to better breathe, thus limiting the problems of odor, of skin crack and development of certain skin diseases on the foot. The techniques of the prior art provide air with relatively low oxygen content and high nitrogen content which is not satisfactory for foot hygiene.

There is thus a need for oxygen supply at the epidermis of feet, in order to further improve the prevention and/or treatment of odors, skin crack and other diseases of the skin when the feet are shod.

Thus, the present invention provides a device for delivery of oxygen-enriched air, that is to say air containing at least 21.5% oxygen, the maximum oxygen-enrichment of air possibly being up to 99% oxygen.

The device of the invention is advantageously integrated into a shoe or a sole of a shoe; this integration can be performed in addition to all air circulation systems described above or existing or that will later exist.

Devices for oxygen-enrichment of air are known and include for example devices comprising passing air containing about 21% oxygen on one or more adsorption units by Pressure Swing Adsorption process ("Pressure Swing Adsorption" or PSA in English). Many scientific articles and patents describe such units of oxygen concentration operating on this principle.

These adsorption units typically operate with molecular sieves, usually based on A or X type zeolites, with various Si/Al ratios of, or with activated alumina. The oxygen-enriched air can reach 95-96% oxygen purity with these adsorption processes. Treated flowrates may vary from few liters per minute to several cubic meters per minute.

These "oxygen concentrators" are generally used to treat people affected with breathing troubles or for whom the volume of air they can breathe is so low that it is necessary to enrich the air with oxygen so that the oxygen supply in vital organs is maintained.

However, the current minimum weight of such systems is around a few kilograms and they are composed of columns filled with molecular sieves, a compressor and a multitude of valves and connections. In addition, all current systems, even the most compact ones, require the use of a source of electrical power for operating said valves and said compressor. Because of these constraints, the integration of existing systems in a shoe or in a sole of a shoe is impossible.

Such apparatuses are therefore systems or devices of large size, complex and heavy enough to make them unfit to be embedded in objects as small as shoes or soles of shoes.

There is to date no such oxygen concentrators, or systems for oxygen-enrichment of air, which can be embedded in shoes or soles of shoes, that is to say, small enough and which may be used in the preventive and/or curative treatment of various problems related to foot hygiene, such as odor, cracking, and others.

As previously mentioned, an object of this invention is to provide a device for delivery of oxygen-enriched air that is both lightweight, about a few grams to a few tens of grams, and that does not necessarily requires a source of electrical power.

Another object of the invention is a shoe or a sole of a shoe integrating the above-described device for delivery of oxygen-enriched air cited above.

Thus, according to a first aspect, the device for delivery of oxygen-enriched air according to the invention comprises at least one system allowing to selectively separate nitrogen and oxygen out of one or more deformable air tanks embedded in a shoe or a sole of a shoe, said deformable tanks being successively pressurised and depressurised by pressure of the foot and body weight of a person on the ground during the normal physiological cycle of walking or running.

In the context of the present invention, description and claims, the term "sole" is used to define all kinds of soles that may be present in a shoe, and particularly the sole itself constituing the bottom part of a shoe which is directly in contact with Jhe^our L-as-wel-l- as any sole that can be introduced within the shoe so as to bring comfort or for orthopedic purposes, such as innersole, insole, chopine, platform, arch support, and the like.

More specifically, the device of the invention comprises:

one or more deformable tank(s) that can recover its or their original shape(s), that is(are) able to contain air and play the role of a compressor by pressure of the foot and body weight of a person, thus allowing the delivery of a compressed air to an adsorption or separation system, this(these) tank(s), once compressed; is(are) filled again with air through a connection with the outside of the shoe during the relaxation exerted when the foot leaves the ground;

at least one system for selectively separating nitrogen and oxygen coming from the deformable tank(s) and thus producing an oxygen-enriched air;

one or more exhaust ducts of the oxygen-enriched air into the interior of the shoe or into the shoe sole or between the sole and insole of the shoe, allowing diffusion of said oxygen-enriched air towards the epidermis of the foot, preferably the arch of the foot, and

one or more exhaust ducts of the oxygen-depleted air (nitrogen-enriched air) to the outside of the shoe, said oxygen-depleted air thus exhausted to the outside of the shoe not coming into contact with the epidermis of the foot.

According to an embodiment of the invention, the deformable tanks are generally made from flexible and deformable material, and are well known from those skilled in the art, for example and by way of non-limiting examples made of, or based on, flexible plastic such as polyolefins, silicones, elastomers, and others. By way of non-limiting examples, elastomers include natural rubbers, synthetic polyisoprenes, polybutadiene, polystyrene- butadiene, polyisobutylene, neoprene, nitrile rubber or polyurethane.

In addition, the flexible material is obviously chosen from flexible materials substantially tight to gases, including air, so that tanks can perform their function of air storage.

The shape of the tanks is not really important, but must be adapted to enable their integration into a shoe or a sole of a shoe.

The pressurization/depressurization system in the tank may be designed as a piston system with a sliding part that alternatively moves forwards and backwards into the resery.Qir--t.Q- compress the air under the action of the foot pressure on the soil and allows the air to escape when the pressure on the shoe sole by the foot is released.

According to a preferred embodiment of the invention, the inner volume of the the deformable tanks ranges from 0.1 mL to 10 mL, preferably from 0.2 mL to 7 mL, and more preferably from about 1 mL to 5 mL. As mentioned previously, the device of the invention includes at least one system of separation of oxygen and nitrogen contained in the air. Any system of oxygen/nitrogen separation working according to the principle of pressure variation may be suitable and are preferred systems comprising one or more adsorbents working according to the principle of Pressure Swing Adsorption (PSA). Systems for oxygen/nitrogen separation that can be used in the context of the present invention also include membrane-based systems operating according to the principle of diffusion rates of gases through a membrane, wherein the pressure of the inlet air supplied to the membrane based system is greater than the outlet pressure of the gases treated.

According to an embodiment of the invention, the system of separation of oxygen/nitrogen contained in the air is an ultra-compact system comprising one or more cartridges filled with one or more adsorbents.

According to a preferred embodiment of the invention, the cartridges of the system used for oxygen/nitrogen separation have a volume of between 0.1 mL and 10 mL, preferably between 0.2 mL and 2 mL. For instance and solely to illustrate this preferred embodiment, said cartridges may be in the form of cylinders with diameter of between 0.1 cm and 2 cm and length of between 0.5 cm and 5 cm. The skilled in the art will adapt, without undue burden, the global size and shape of the said cartridges, and more generally of the oxygen/nitrogen separation system, depending on the global shape, size, and overall aesthetic aspect of the shoe, sole, including insole, arch support, and the like.

Adsorbents for the separation of oxygen/nitrogen contained in the air according to the principle of PSA are well known to those skilled in the art and are preferably molecular sieves, among which A or X type zeolites are preferred, whatever the molar ratio Si/Al, which may range between about 1 and about 2. By way of non limiting examples, X type zeolites, with molecular ratio Si/Al generally between about 1.25 and about 2, and/or LSX

used.

The cationic form of X or LSX zeolites described above can be composed of one or more cations, preferably one or more cations selected from Na, Li, K, Ca, Mg, Ag, cations of rare earth, and the like. Without making any limitation to zeolitic adsorbents that can be used in the device of the present invention, may be mentionned the molecular sieves based on zeolites NaX, NaLSX, LiX, LiLSX or LiAgLSX.

The zeolites can be in the form of crystals, preferably of controlled size (monodisperse, that is to say calibrated or with a majority proportion of a single crystal size) or in agglomerates form, preferably of controlled size (monodisperse, that is to say calibrated or with a majority proportion of a single agglomerate size). Also preferred are zeolites agglomerated with a binder, wherein the binder may be a clay, e.g. kaolin, or more preferably a zeolitized binder, so that more than 90% of the agglomerates of zeolite present the sought properties of adsorption/desorption.

When the zeolites are in the form of crystals, they are advantageously, but not necessarily, supported for example in the form of films or zeolitic hollow tubes. The composition of such films or hollow tubes may be polymers, such as but not limited to polysulfones and PVDF, or aluminas, such as alpha alumina. Supported crystals of zeolites can be for example formed and then deposited on support(s), using techniques known to those skilled in the art. In one embodiment, the crystals of zeolites may be grown directly on said support(s), also using conventional techniques known to those skilled in the art.

Zeolitic adsorbents (molecular sieves) particularly suitable are, for example and without limitation, those commercialized by CECA SA under the tradenames Nitroxy ^® 5, Nitroxy ^® 51, Nitroxy ^® SXSDM or those commercialized by UOP under the tradenames Oxysiev ^® 5 and Oxysiev ^® 7. Of course, any other type of zeolitic adsorbent capable of producing an oxygen-enriched air with a reduced proportion of nitrogen may be used in the context of the present invention.

Furthermore preferred zeolites are X or LSX type zeolites with small crystals and/or whose agglomerates are in the form of very small beads, and especially_zeoJites_ -hQse_ciystals, size is between 1 micron and 10 microns, and/or agglomerates size is between 0.05 mm and 1 mm, preferably between 0.1 mm and 0.7 mm.

The above-described oxygen/nitrogen separation systems are advantageously contained in compartments, such as cartridges, adsorption/desorption columns, and the like. In one aspect of the invention, these cartridges, columns and the like are disposable so that they can be easily replaced or exchanged by the user. Advantageously, and according to a particularly preferred embodiment of the device of the invention, columns, cartridges and other adsorbent containers are integrated into the shoe or in the sole of the shoe.

At the end of the adsorption step, the zeolitic adsorbents are then regenerated by desorption by decreasing the pressure in the cartridges or columns of adsorbents, the decrease in pressure resulting from the release of the pressure from the foot on the ground when the shoe leaves the ground during the normal cycle of walking or running. When the foot hits the ground again, a new compression step is performed corresponding to an adsorption step, then a new decompression step when the foot again leaves the ground corresponding to a desorption step, and so on.

Alternatively, the system of oxygen enrichment of air (or oxygen/nitrogen separation) uses one or more membranes that allow the separation of nitrogen and oxygen. This technique, well known to those skilled in the art, is based on the fact that oxygen has a diffusion rate through the membrane faster than nitrogen. The membranes used in the context of the present invention can be of any type commonly used in the field and are made for example of materials such as polymers or polymer blends, such as for example and without any limitation, those selected from PVDF, polysulfones, polysiloxanes and perfluorinated polymers. Suitable polysiloxanes include for example polydimethylsiloxane. For example, Hisep ^® membranes that are polysulfone and polydimethylsiloxane based membranes may be used. Polymers are preferably extruded or spun, either in the form of flat films either in the form of hollow fibers. For example, spinning can be achieved by wet/dry-phase inversion spinning process. The membranes thus obtained have a thickness of 10 μιη to 500 μηι. For hollow fiber membranes, the diameter of the fiber can be of the order of 0.1 mm to 1 mm and the thickness between the inner and the outer surface of the fiber of about 10 μπι to 200 μηι. The membranes are then fed into a module or container ■constituting the nitrogen and oxygen separation container, Such a modiile-ox ontaiiier-may- contain one or several tens, or one or several hundreds, or one or several thousands, of membranes arranged/embedded in parallel in a resin based tip (e.g. epoxy), said tip being itself fitted in the module or container. The module or container is, in turn, preferably a hard material, resistant to pressure, such as stainless steel. In order to operate, the oxygen/nitrogen separation system using one or more membranes brings the air under pressure coming from the deformable tank(s) to one side of the module or container containing membranes. The difference of diffusion rates between oxygen and nitrogen allows for the separation of these gases. An output on the edges of the module or container allows to recover the permeate, for example, oxygen, and another output at the other side of the module or container allows to recover the other gas, e.g. nitrogen.

The separation system of oxygen/nitrogen from the air can of course combine the previously described molecular sieve(s) and membrane(s) system(s). The above-described separation systems (or enrichment systems) may furthermore include a desiccant, for example also in the form of a cartridge, for the removal of all or part of the water contained in the air, that could interfere with the correct operation of the oxygen/nitrogen separation system, especially when the system includes zeolite(s) and/or membrane(s).

Thus, and according to a preferred embodiment of the invention, the system for enriching oxygen in the air includes, in addition to the above-described adsorbents and/or membranes, one or more desiccant to dry the air and thus improving the production of oxygen-enriched air. Non limiting examples of such desiccants are silica gel and activated alumina, and among them may be mentionned those sold by Alcoa under the tradenames F200, DD420, HI 56, F2000, Selexsorb ^® CD, Selexsorb ^® CDX and Selexsorb ^® CDO-200. In one embodiment, the adsorption/desorption system that can be used in the device of the invention comprises one or more types of zeolitic adsorbents (molecular sieves) and/or one or more membrane device(s), in combination with one or more activated aluminas.

According to another embodiment of the invention, the device for delivering oxygen- enriched air in the shoe or in the shoe sole, includes, in addition to the above-described adsorbents and/or membranes separations systems, one or more desiccant systems to dry the oxygen-enriched air before delivery in the shoe or in the shoe sole. Such dessicant systems, designed for_the_removal of water (moisture), traces that are .present in gases,_such as air, oxygen, nitrogen, are well known to the skilled in the art and may be for example any known systems using zeolitic adsorbents, activated alumina, silica gel, gas separation membranes, and the like.

Said desiccant system(s) may be positioned before or after, or even before and after the nitrogen/oxygen separation system(s), specifically in order to remove water traces from the air before entering the nitrogen/oxygen separation system(s) and/or from the oxygen- enriched air after the nitrogen/oxygen separation system(s) and before being fed into the inner part of the shoe.

Alternatively, the driving force of the above-described air compressor presented as the result of the normal physiological cycle of walking or running, may be assisted or replaced by a compressor operated by hand or any other part of the body, or by an electrical battery and/or solar energy system(s).

The hereinbefore described separation systems of oxygen and nitrogen from the air that treat the compressed air coming from the deformables tanks allow to obtain an oxygen- enriched air which is then released within the shoe by any suitable system.

Generally, any device permitting the circulation of air through the action of the weight of a person in a system containing an adsorbent in order to enrich the air with oxygen is encompassed within this invention.

Generally, all techniques that helps the deformable tank(s) to recover faster its or their original shape(s) can be used in the device of the invention. For instance, one or more spring systems may be used to faster recover the original shape of a deformable tank.

The device of the invention can be incorporated into a shoe, but preferably in both shoes forming a pair. The adsorption step and the desorption step are involved alternately in the left shoe and right shoe during walking or running, depending on whether the shoe or the sole of the shoe is pressed onto the ground or is no longer in contact with the ground, following the normal physiological cycle of walking or running.

Alternatively, systems for the enrichment of air with oxygen can be multiple, removable, integrated in the shoe or in the sole of the shoe or be attached laterally on one side or both sides of the shoe and/or shoe sole, or positioned on the upper side of the shoe. One can for example consider incorporating deformable air tanks in the soles, and position the cartridge(s) of adsorbent(s) on the upper side of the shoe, the various elements being interconnected one to each others through pipes, hoses and other appropriate cannulas. In one embodiment, the different parts of the device of the invention, meaning deformable tanks, system for selectively separating nitrogen and oxygen and ducts can be directly molded in the shoe or in the sole of the shoe, on one side or both sides of the shoe and/or shoe sole, or on the upper side of the shoe. For instance and to illustrate this embodiment, the various ducts allowing circulation of air, oxygen-enriched air and nitrogen enriched air can be directly molded in the sole of the shoe by realizing channels in the mold that will serves to realize the sole.

According to a preferred embodiment of the invention, the ducts have an inner diameter ranging from 0.1 mm to 5 mm, preferably from 0.5 mm to 4 mm, more preferably from 1 mm to 3 mm.

The device for providing oxygen-enriched air according to the present invention can be incorporated into any type of footwear, and for example into walking shoes, hiking shoes, athletic footwear, running shoes, basketball shoes, soccer shoes , rugby shoes, tennis shoes, golf shoes, skiing shoes, roller shoes and the like.

The device for providing oxygen-enriched air is preferably removable in whole or in part, in order to maintain, repair and possibly replace some or all components of the device. In particular, the molecular sieve, the column containing the molecular sieve, the membrane, the membrane module, are advantageously provided in the form of one or more removable cartridges and easily disposable and replaceable.

Although the invention has been presented and described herein as embodiments now considered preferred, those skilled in the art may of course make various changes and / or variants, without departing from the present invention, the scope of which bieng defined in the following claims.

For an even better understanding, the present invention is now illustrated with ther.

following figures and non-limiting examples:

Example 1:

This example is illustrated in Figure 1 which shows a device for enriching air with oxygen according to the principle of Pressure Swing Adsorption, adaptable in a shoe or in a sole of a shoe. VI and V2 are two elastomer deformable tanks that can recover their original shapes, the volume of VI is 5 mL and that of V2 is 4 mL and are connected to an adsorption system comprising a column [1] made of hard material (stainless steel) filled with molecular sieves [2] of LiLSX type with Li content > 96%. The molecular sieve, for example LiLSX, Nitroxy ^® SXSDM from CECA is in the form of beads or pellets of 0.55 mm average diameter. The volume of the column [1] is 1.2 mL and the amount of molecular sieve is 0.75 g. A layer of molecular sieve of NaX type in the form of beads or pellets of 0.55 mm can also be used, or a mixture of NaX and LiLSX. A layer of alumina may be added in addition to the layer of molecular sieve in order to dry the air. One can also consider as an alternative a bi-layer consisting of 0.5 g of LiLSX molecular sieve and 0.25 g of silica gel. The check valve CI allows the passage of oxygen-enriched air (via the duct C) to the inside of the shoe when the pressure in the column is greater than 3 bar absolute. The check valve C2 allows the passage of air from the VI tank to the column [1] during the adsorption step. The check valve C3 allows the passage of air from the column

[1] to the V2 tank during the desorption step. The check valve C4 allows the passage of air from the outside of the shoe (via the duct A) to the tank VI. The check valve C5 allows the passage of air from the tank V2 to the outside of the shoe (via the duct B). Ducts Tl, T2 and T3 allow to establish connections between the different components of the device. When a person walks with shoes on a ground, he exerts alternately on each shoe a certain pressure. When the foot is no longer in contact with the ground, the pressure exerted decreases.

Assuming a normal walk, it is estimated that a same foot hits the ground every 2 seconds, which means that the weight of the person is distributed about every second from one foot to another. Of course, this period of time varies, depending on the speed of walking (or running) and is indicated here only to facilitate the understanding of the example. In this example, the cycle time, for one foot, is set at about 2 seconds.

When the person presses his foot in the shoe on the ground, the air in tanks VI and V2 is compressed to several bars absolute. This compressed air passes through C2, from VI to the column [1]. The pressure of the weight of the person can prevent the opening of the valve C3. The air compressed in V2 is simultaneously expelled to the outside of the shoe (B) by the valve C5. All compressed air coming from VI is thus directed to column [1] and passes through the molecular sieves [2]. The valve CI allows the passage of compressed air to the inside of the shoe only when the pressure in the column is greater than about 3 bars absolute, so that only part of the compressed air coming from VI will be expelled to inside the shoe (C). The pressure inside column [1] is thus maintained during this stage at 3 bars which allows a better adsorption of nitrogen on molecular sieve [2] and thus to obtain an oxygen-enriched air at the outlet of column [1]. The air expelled into the interior of the shoe has an oxygen purity above 40% in this example.

After this adsorption step, tanks VI and V2 contain almost no air and the pressure inside the column [1] is about 3 bars absolute.

When the foot leaves the ground, tanks VI and V2 are not compressed any longer so air from the outside fills VI through the valve C4. Similarly, column [1] is depressurized in reverse direction by pressure balance with V2. The air enriched with nitrogen at about 3 bars absolute in column [1] is discharged via the valve C3 and fills V2, this air will be expelled to the outside of the shoe (via the duct B) at the next foot pressure on V2. At the end of this desorption step, the pressure in column [1], in ducts T3 and T2, and in tank V2, is 1 bar absolute. The device is thus ready for a new cycle when the foot again hits the ground, and compresses simultaneously tanks VI and V2.

Example 2 :

This example is illustrated in Figure 2 which shows an alternative device for enriching air with oxygen according to the principle of Pressure Swing Adsorption, adaptable in a shoe or in a sole of a shoe. This device includes four elastomer deformable tanks that can recover their original shapes: VI (5 mL volume), V2 (4 mL volume), V4 (10 mL volume) and V5 (4 mL volume) and a non deformable tank V3 of 2 mL volume acting as buffer tank for the air coming from column [3]. The device in Figure 2 furthermore includes an adsorption system able to separate oxygen and nitrogen comprising a column [1] made of hard material (stainless steel) filled with molecular sieves [2] of LiLSX type with Li content higher than 96% (Nitroxy ^® SXSDM, sold by CECA) in the form of beads or pellets of 0.55 mm average diameter. The volume of column [1] is 0.8 mL and the amount of molecular sieve is 0.5 g. A layer of molecular sieve of NaX type in the form of beads or granules of 0.55 mm average diameter can also be used, or a mixture of molecular sieves of NaX and LiLSX type. The device in Figure 2 is provided with an adsorption system for drying air through a column [3] made of hard material (stainless steel) filled with silica gel or activated alumina [4]. The silica gel or activated alumina used is in the form of beads or granules of 0.3 mm average diameter. The volume of column [3] is 0.8 mL and the amount of silica gel or activated alumina is 0.5 g. A check valve CI allows the passage of the oxygen-enriched air to the inside of the shoe (C) when the pressure in the column is greater than about 2.5 bars absolute. A check valve C2 allows the passage of air from tank VI to column [1] during the adsorption step. A check valve C3 allows the passage of air from column [1] to tank V2 during the desorption step. A check valve C4 allows the passage of air from tank V3 to tank VI. A check valve C5 allows the passage of air from tank V2 to the outlet of the shoe (B2). A check valve C6 allows the passage of dried air to tank V3 as soon as the pressure in column [3] is above about 3 bars absolute. A check valve C7 allows the passage of air from tank V4 to column [3] during the adsorption step to realize the air drying. A check valve C8 allows the passage of air from column [3] to tank V5 during the desorption step. A check valve C9 allows the passage of air from the outside of the shoe (A) to tank V4. A check valve CIO allows the passage of air from tank V5 to the outside of the shoe (Bl). Ducts Tl, T2, T3, T4, T5 and T6 allow to establish connections between the different components of the device.

When a person of a certain weight walks on a ground with shoes each equipped with a device according to Figure 2, he exerts alternately on each shoe a certain pressure depending on the weight of the person. When the foot is no longer in contact with the ground, the exerted pressure decreases.

Assuming a normal walk, it is estimated that a same foot hits the ground every 2 seconds, which means that the weight of the person is distributed about every second from one foot to the other. Of course, this period of time varies depending on the speed of walking and is indicated here only to facilitate the understanding of the example. In this example, the cycle time is set at about 2 seconds.

When the person presses his foot in a shoe on the ground, the four tanks VI, V2, V4 and V5 are simultaneously compressed and the air contained in each of said tanks VI, V2, V4 and V5 is compressed to several bars absolute. The air thus compressed passes, through valve C7, from tank V4 to column [3]. The pressure of the weight of the person can prevent the opening of valve C8. The compressed air in V5 is then expelled to the outside of the shoe (Bl) through valve CIO. The previously dried and compressed air passes through valve C2 from tank VI to adsorption column [1]. The pressure of the weight of the person can prevent the opening of the valve C3. The compressed air in tank V2 is expelled to the outside of the shoe (B2) through valve C5. All compressed air coming from tank V4 is thus directed to the column [3] and passes through the silica gel or activated alumina [4] and all the compressed air coming from tank VI is directed to column [1] and passes through the molecular sieve [2]. Because the valve C6 allows the passage of compressed air to tank V3 only when the pressure in the column [3] is greater than about 3 bars absolute, only a portion of the compressed air coming from tank V4 will be expelled to tank V3. The pressure inside the column [3] is thus maintained during this step at about 3 bars absolute, which allows a better water adsorption on the silica gel or activated alumina

[4] and therefore to obtain a dried air at the outlet of the column [3]. Because the valve CI allows the passage of compressed air to the inside of the shoe only when the pressure in the column is greater than about 2.5 bars absolute, only a portion of the compressed air coming from VI will thus be expelled to the inside of the shoe. The pressure inside the column [1] is thus maintained during this step at about 2.5 bars, which allows a better adsorption of nitrogen on the molecular sieve [2] and therefore to obtain an oxygen-enriched air at the outlet of the column [1]. The air expelled into the inside of the shoe has an oxygen purity of above 45% in this example.

At the end of the adsorption step in column [3], tanks V4 and V5 almost contain no air and the pressure inside the column [3] is about 3 bars absolute.

When the foot is detached from the ground, outside air (A) fills V4 via valve C9 and column [3] is depressurized in reverse direction by pressure balance with tank V5. Undried air, at about 3 bars absolute, contained in column [3] is then directed to tank V5 through valve C8. At the end of this desorption step, the pressure in column [3], in ducts T6 and T5 and in tank V5, is 1 bar absolute.

When the foot is detached from the ground, dried air contained in tank V3 is aspirated, by pressure difference, in tank VI via the valve C4; column [1] is depressurized in reverse direction by pressure balance with tank V2. The nitrogen-enriched air at about 2.5 bars absolute contained in the column [1] thus flows to tank V2 through valve C3. At the end of this desorption step, the pressure in the column [1], in ducts T2 and T3 and in tank V2, is 1 bar absolute. The device is thus ready for a new cycle when the foot will again put pressure on the ground. Example 3 :

This example is illustrated in Figure 3 which shows another alternative device for enriching air with oxygen according to the principle of Pressure Swing Adsorption, adaptable in a shoe or in a sole of a shoe. This device includes three elastomer deformable tanks VI, V4 and V5that can recover their original shapes, of respective volumes 5 mL, 10 mL and 8 mL. A nondeformable tank V3 of 2 mL volume allows to get dried air from column [3]. The adsorption system for separating oxygen and nitrogen comprises a column [1] made of hard material (stainless steel) filled with molecular sieves [2] of LiLSX type with Li content higher than 96% (Nitroxy ^® SXSDM, marketed by CECA) in the form of beads or pellets of 0.55 mm average diameter. The volume of the column [1] is 0.8 mL and the amount of molecular sieve is 0.5 g. A layer of NaX type sieve in the form of beads or pellets of 0.55 mm can also be used, or a mixture of NaX and LiLSX.

An adsorption system for drying air includes a column [3] made of hard material (stainless steel) filled with silica gel or activated alumina [4]. The silica gel or activated alumina used is in the form of beads or granules of 0.3 mm average diameter. The volume of the column [1] is 0.8 mL and the amount of silica gel or activated alumina is 0.5 g. The check valve CI allows the passage of the oxygen-enriched air to the inside of the shoe (C) when the pressure in the column is greater than about 2.5 bars absolute. The check valve C2 allows the passage of the air from tank VI to the column [1] during the adsorption step. The check valve C3 allows the passage of the air from column [1] to column [3] during the desorption step. The check valve C4 allows the passage of the air from tank V3 to tank VI. The check valve C6 allows the passage of the dried air to tank V3 as soon as the pressure in the column [3] is greater than about 3 bars absolute. The check valve C7 allows the passage of the air from tank V4 to column [3] during the adsorption step to operate the drying of air. The check valve C8 allows the passage of the air from column [3] to tank V5 during the desorption step. The check valve C9 allows the passage of the air from the outside of the shoe (A) to tank V4. The check valve CIO allows the passage of the air from tank V5 to the outside of the shoe (B). The ducts Tl, T2, T3, T4, T5 and T6 allow to establish connections between the different components of the device.

When a person of a certain weight walks with shoes on a ground, he exerts alternately on each shoe a certain pressure depending on the weight of the person. When the foot is no longer in contact with the ground, the exerted pressure decreases. Assuming a normal walk, it is estimated that a same foot hits the ground every 2 seconds, which means that the weight of the person is distributed about every second from one foot to the other. Of course, this time varies depending on the speed of walking and is indicated here only to facilitate the understanding of the example. In this example, the cycle time is arbitrarily set at about 2 seconds.

When the person presses his foot in a shoe on the ground, the three tanks VI, V4 and V5 are simultaneously compressed and the air contained in said tanks VI, V4 and V5 is compressed to several bars absolute. This compressed air passes through the valve C7 from tank V4 to the column [3]. The pressure of the weight of the person can prevent the opening of the valve C8. The compressed air in tank V5 is expelled to the outside of the shoe (B) via the valve CIO. The air previously dried and compressed passes through the valve C2 from tank VI to column [1]. The pressure of the weight of the person can prevent the opening of the valve C3. All the compressed air coming from tank V4 is thus directed to the column [3] and passes over the silica gel or activated alumina [4]. All the compressed air coming from tank VI is thus directed to column [1] and passes over the molecular sieve [2]. Because valve C6 allows the passage of the compressed air to tank V3 only when the pressure in the column [3] is greater than about 3 bars absolute, only a portion of the compressed air coming from tank V4 will thus be expelled to tank V3. The pressure inside the column [3] is thus maintained during this step at about 3 bars, which allows a better water adsorption on the silica gel or activated alumina [4] and therefore to obtain a dried air at the outlet of the column [3]. Because the valve CI allows the passage of the compressed air to the inside of the shoe only when the pressure in the column is greater than about 2.5 bars absolute, only a portion of the compressed air coming from tank VI will be expelled inside the shoe. The pressure inside column [1] is thus maintained during this step at about 2.5 bars, which allows a better adsorption of nitrogen on the molecular sieve [2] and thus to obtain an oxygen-enriched air at the outlet of the column

[1], The air expelled into the inside of the shoe (C) has an oxygen purity above 45% in this example. At the end of this adsorption step in column [3], tanks V4 and V5 contain almost no air and the pressure inside column [3] is about 3 bars absolute.

When the foot is detached from the ground, outside air (A) fills V4 via valve C9 and column [3] and column [1] are depressurized in reverse direction by pressure balance with the tank V5. The dried air enriched in nitrogen at about 2.5 bars absolute contained in column [1] thus flows to column [3] via valve C3, and then flows to tank V5. The air enriched with water at about 3 bars absolute contained in column [3] also flows to tank V5 thtough valve C8. At the end of this desorption step, the pressure in column [3], in ducts T6 and T5 and in tank V5 is about 1 bar absolute. When the foot is detached from the ground, the dried air contained in tank V3 is aspirated into tank VI via valve C4. At the end of this desorption step, the pressure in column [1], in ducts T2 and T3 and in tank V2 is 1 bar absolute.

The device is thus ready for a new cycle when the foot hits again the ground. Example 4 ;

This example is illustrated in Figure 4 which shows another embodiment of the invention implementing a device for enrichment of air with oxygen working with membranes, and adaptable in a shoe or in the sole of a shoe.

The device includes an elastomer deformable tank VI in of 5 mL volume that can recover its original shape and an adsorption system comprising a column [1] made of hard material (stainless steel) filled with membranes capable of selectively separating oxygen and nitrogen, as for example, membranes used in membranes based oxygen concentrators commercialized by companies such as Inmatec or Dalian. The check valve CI allows the passage of the air from tank VI to column [1]. The check valve C2 allows the passage of the air from the outside of the shoe (A) to tank VI. The ducts Tl, T2 and T3 allow to establish connections between the different components of the device.

When a person of a certain weight walks with shoes on a ground, he alternately exerts on each shoe a certain pressure depending on the weight of the person. When the foot is no longer in contact with the ground, the exerted pressure decreases.

Assuming a normal walk, it is estimated that a same foot hits the ground every 2 seconds, which means that the weight of the person is distributed about every second from one foot to the other. Of course, this time varies depending on the speed of walking and is indicated here only to facilitate the understanding of the example. In this example, the cycle time is arbitrarily set at about 2 seconds.

When the person presses his foot in a shoe on the ground, the air contained in tank VI is compressed at several bars absolute. The air thus compressed passes through valve CI from tank VI to column [1]. All the compressed air coming from tank VI is thus directed to column [1] and passes over the membranes [2]. The air is thus separated and an oxygen- enriched air at 30% is thus produced and distributed through duct T2 to the inside of the shoe (C). The nitrogen enriched air is in turn expelled to the outside of the shoe (B) through duct Tl. At the end of this step, tank VI contains almost no air. When the foot is detached from the ground, outside air (A) refills tank VI via the valve C4. The device is thus ready for a new cycle when the foot hits the ground again.