The subject of the invention is a pump for injecting a fluid, and can in particular relate to a micropump for injecting a determined dose of the fluid.
In a more detailed manner, it can relate to actuating devices for biology and health, in particular injector and microdosing devices, able to locally deliver volumes less than a microlitre with a resolution of a magnitude of the nanolitre of gaseous and liquid products of low viscosity by ultrasound means. The dose to be delivered is more preferably in the form of viscous liquid (gel) or highly fluid on the contrary, but can also be constituted of fine powder. The grains of the powder may be nanocapsules possibly imprisoned in a gel or a hydrogel. It can also be used for other applications, in particular, for depositing ink on surfaces or the nebulisation of essence, perfume, deodoriser or particular products in a closed enclosure or a room.
According to certain important particularities of the invention, the device for actuating does not have any mobile or deformable mechanical parts. The fluid can be injected continuously, with the dosage being obtained in an open loop by exploiting the duration and amplitude of activation or in a closed loop using a set value to be reached on the remaining level of the tank, with the level being deduced from the frequency offset of a characteristic resonance of the volume of the tank. The device can be used in particular for medical dosing devices inserted into the human body, in particular in the case of chronic dispensing of drugs at very low flow rates and over very long durations (typically more than 10 years).
The actuating of the micropumps can be carried out in different ways, for example by emission of ultrasonic waves as in the case of this invention, but also peristaltically, electrostatically, thermo-pneumatically, or even electromagnetically. A presentation of these different actuating devices can be found in the document of D. J. Laser and J. G. Santiago entitled “a review of micropumps”, J. Micromech. Microeng. 14(2004), R35-64. Peristaltic pumps are the most appreciated for pharmaceutical dosage because, on the one hand, they avoid any contact with the product to be delivered, on the other hand, they are compact and consume little current. However, they are reproached for the repeated flow of the pipe which allows for the displacement of the fluid, which can generate a fatigue and even abrasion of the material and the pulling off of matter.
The devices that are the most similar to this invention are ultrasound pumps.
In this field, the state of the art provides for example the following reference:
The main difference between the invention of G. Keilman and this invention is that in the latter, the structure constituting the chamber plays a fundamental role in the generation of the vibratory mode on the ejection nozzle, because in this invention the chamber is in fact a full solid cavity conveying bending waves. Its mechanical excitation is carried out at the resonance frequency of the full cavity. The resonator constituted as such furthermore produces a mechanical amplification of the ejection nozzle. And in this invention, the fluid absorbs much less energy than in that of G. Keilman. Moreover, the pumping is here obtained not through dissipation of energy in the fluid but through a lateral and centrifugation compression phenomenon generated by a particular movement of the ejection nozzle. Finally, in the case of the invention of G. Keilman, the broadband operation and the recourse to cavitation substantially reduce the energy efficiency of the acoustic pump, which therefore is not suitable to be miniaturised, implantable and usable with a limited source of energy. The increase in temperature is moreover not acceptable in a product intended to deliver pharmaceutical products.
Different non-ultrasound piezoelectric devices can also be encountered for carrying out an accurate dosage of drugs by micropump. This is in particular the case with patent FR 2650634 (A1) of Harald Van Lintel of 7 Aug. 1989. In this micropump, the pumping is obtained thanks to the deformation of a plate using a piezoelectric pellet. The periodic deformation of the piezoelectric plate causes a periodic volume variation of a pumping chamber delimited in a plate made of a material able to be machined by photolithographic methods. The outlet of the pump is sealed off selectively by a diaphragm valve which is in direct communication with another valve through the pumping chamber.
The flow rates reached are from 30 to 60 μl/min for differential pressures (output less input) of a magnitude of 60 cm for water height. This method is compact and adapted for the dosage of insulin, but it is not ultrasonic and its suction principle is different from the device according to the invention which uses an alternative centrifugation that may be combined with a projection effect. This method encounters moreover limitations linked to the possible backflow of the product.
In the field of implantable dosing devices, the patent of Thomas Lobl and al. WO2007133389 (A2) (filed by Neurosystec Corp.) sets the specifications of a dosing device administering a pharmaceutical agent in the inner ear using a flexible duct fixed to the entrance of the middle ear.
Patent WO 2011/109735 (A2) filed by Cornell University can also be mentioned and which describes a cannula for delivering a liquid drug that can be set into vibration by various piezoelectric transducers, of which certain ones act directly on it by being fixed to it. No particular vibration mode is mentioned, and it seems that the vibrations assist the flow of the liquid by the cavitation that they induce in front of the internal surface of the cannula, and that their effect sought is above all to transmit the vibrations to the tissues of the living organism receiving the drug, which are adjacent to the cannula in order to assist the diffusion of the drug.
In certain cases, a device for administering drugs includes an implantable osmotic pump connected to a housing containing a drug, with this housing connected to a needle, to a cochlear implant or to another type of component for the administration to the target tissue. In certain embodiments, a subcutaneous orifice receives a liquid from an external pump. Said orifice is connected to a needle or other component for the administration of one or several drugs to the target tissue. Solid and liquid drug formulas can be used. In embodiments that use solid drugs, a separated drug vehicle (such as physiological serum) can be used to dissolve a portion of the solid drug, with the drug-loaded vehicle then being administered to the target tissue. The utilisation of solid drugs combined with a separated drug vehicle is a way to resolve the insufficient autonomy of an osmotic pump. The non-rechargeable drug is stored in the form of solid pellets and will dissolve slowly in a neutral fluid which can be refilled via a standard access orifice.
However, these dosing devices are confronted with the following problems:
This type of problem can be resolved with this invention in the sense that the pump can also act as a mixer by centrifugation of the carrier fluid once the powder is introduced.
A problem to be resolved therefore relates to the micro-dosage (less than the microlitre, or 1 mm3) and more preferably the dosage of a volume with a resolution of a magnitude of the nanolitre of a product contained in a buffer tank of small size containing a typical total volume of a magnitude of the millilitre, but which can typically reach 10 ml. The tank can be housed in a supporting structure such as a case or the body of a stylus or for the medical field, in a biocompatible housing that can be implanted under the skin or even behind a bone wall. The tank can be refilled.
The product is more preferably a low viscous liquid or a liquid initially viscous but of which the viscosity decreases very locally on the ultrasound mechanical amplification following an increase in temperature caused by the viscous damping of the ultrasonic vibrations in contact with the product. The amplitude of the vibrations can be chosen in such a way that the heating of the fluid remains at a permissible degree, which is precious for delicate products such as drugs. The dosage is triggered either automatically and repeatedly if the device comprises an on-board source of energy that provides it with sufficient autonomy between two dosages, or punctually, by control, at the time when the device is subjected to ultrasound radiation that allows it to extract the energy that is sufficient to set it into operation. The energy recovery can be carried out remotely through a wall or transcutaneously by conventional inductive method or by ultrasound method.
In the case where the application requires, in particular for the nebulisation of flammable essence, the device according to the invention can accept high operating temperatures typically above 300° C. in the nebulisation zone. Finally, the ultrasound principle used does not make use of the electrostatic forces that can be found in the electro-fluid devices, and is not influenced by them. However, the dosing device can be covered by a hydrophilic layer in the tank and in the feed capillary to the ejection nozzle and hydrophobic in the zone of ejection or nebulisation orifice for a drop.
Another problem to resolve is more generally to make the pump compatible with biological applications, and in particular to allow it to be implanted without danger inside a living body with a stable operation, a sufficiently reduced volume, and during long operating times without replacement, which excludes any mechanism that can break down or that requires maintenance.
Another problem to resolve is to extract a dose from a tank designed so that no static leakage rate is possible and constitute drops rather quickly in order to prevent any evaporation in the ambient medium (this stands out as such from osmotic pumps). The tank is not necessarily under pressure or, in the case of implantation, necessarily hermetic in which case anti-bacteria or even anti-virus filters can protect the content. It is possible to use one or several one-way valves in such a way as to allow a flow only during the extraction of fluid and with the condition of inducing a pressure greater than a threshold (for example the Codman Hakim precision valves developed in the framework of hydrocephalus have pressure thresholds set as low as 10 mm H2O and which can be adjusted between 30 mm and 130 mm H2O (www.pedsneurosurgery.org/codman.pdf).
In the case of implanted systems another problem to be resolved is the robustness to the air bubbles in particular for a dispensing in the gaseous medium of the middle ear (37° C. saturated with moisture) while implantable pumps are in general designed to dilute an active substance in one of the body fluids (blood, lymph or other).
In order to resolve these problems, a dosing device is proposed that is able on the one hand to capture and convert a vibratory energy transmitted through a wall, for example the dermis and the bone, or (in other applications) a glass plate, a plastic, a concrete wall, a sheet metal in order to produce therefore its electrical power supply, on the other hand a high-efficiency injector capable of delivering a dose of the product contained in the tank using an ultrasonic vibration injector. In typical applications in biology, the tank contains a volume of approximately 1 ml in the form of a liquid, a gel, or a powder, able to provide 1000 to 1 million doses.
It is generally suitable to avoid the audible noises generated by the actuator regardless of its usage, as a dosing stylus, injector via centrifugation or nebulisation generated by the cavitation, or as an implantable device, able to be coupled to a bone wall. For this the dosing device operates in an ultrasound range between 20 kHz and 20 megahertz, making it possible moreover to resolve the problem of the miniaturisation in order to render the dosing device implantable and able to deliver small doses and finally to reduce the electrical consumption.
In the current microdosing systems, in particular for drugs, implantable pumps and dosing devices make it possible in general to refill the tank and supply via a transcutaneous operation inductively. And most of the pumps described in the state of the art do not provide an indication as to the means of electrical power other than the recourse to an on-board source of energy which may be rechargeable or a power supply via an inductive coupling. This method is not always suitable for the problem to be treated in particular in the case where the patient has to undergo an MRI (magnetic resonance imaging). Moreover, outside of applications for biology and health, it can be interesting to have a power supply other than inductive especially if the wall is metal. The acoustic pump described in this invention can include an acoustic means of piezoelectrically transforming a vibratory energy transmitted through the wall, skin or bone into electrical energy for supplying the pump. The piezoelectric convertor uses a piezoelectric layer that can operate in receiving mode in order to convert the vibratory energy. In an alternative embodiment, this layer deposited on the top portion of the tank opposite the ejection nozzle can also operate in transmitter mode in order to check the level of the tank and by difference the volume delivered. The measuring of the dose is carried out by analysis of the frequency shift of a frequency component characterising the volume of fluid available.
In the particular case of treating certain pathologies with active substances that are toxic for other parts of the organism, a local dispensing of the drugs is required. This is the case for certain substances that must be conveyed directly to the interior of the middle ear for the inner ear as some are toxic in particular for the brain and therefore cannot be administered by the other methods. The invention has a great importance for such applications.
In a general form, the invention relates to a pump for injecting a fluid, comprising a tank or fluid, a sleeve for the flow (or extraction) of the fluid outside of the tank and a device for controlling the flow, comprising a resonator arranged to apply flexural ultrasound oscillations to the sleeve, characterised in that the resonator comprises a piezoelectric transducer and a piezoelectrically deformable solid that is subjected to an oscillation under the effect of the transducer, said deformable solid thinning towards the sleeve.
The flow of the fluid outside of the tank is accomplished by progressing in a channel or a thin duct, often called a capillary in the rest of this description, which extends in the sleeve and opens to the exterior.
The dispensing of the fluid by oscillations of the sleeve that is always open by a piezoelectric resonator avoids any mobile parts in the pump and therefore makes it possible to use it favourably in a prosthesis for long durations. The absence of mobile mechanical parts also makes the pump perfectly reliable. The use of bending modes of the entire sleeve by a deformable solid of which the position, the shape and the behaviour are fully known makes it possible to determine the quantities of fluid delivered with high precision, contrary to the devices wherein the vibrations are applied randomly or unforeseeably by transducers placed without principle in the device. Despite the permanent opening of the sleeve, the finesse of the duct of the sleeve guarantees that no accidental dispensing of fluid will occur when idle. Finally, the pump can be adjusted by judiciously choosing its dimensions and control parameters, in particular the amplitude and the frequency of the vibrations, in such a way as to allow for very low dispensed flow rates. If required, a long duration of use of the pump is obtained even if it is of low capacity. An important advantage of the invention is in the use of a solid transmitter of vibrations from the transducer to the sleeve and which thins towards the sleeve, which results in that it concentrates the vibratory energy and amplifies the deformations of the sleeve without a large consumption of energy.
It will be shown that an important means for guaranteeing the presence of the flow of the fluid outside of the tank when the resonator is active consists in a sleeve that tapers without ceasing into sections from the tank to the free end.
Advantageously, the piezoelectrically deformable solid is a ring surrounding the sleeve and excited by a circular electrode divided into two sectors supplied by the same oscillating electric signal, but in phase opposition: this arrangement very conveniently generates the flexural oscillations of the sleeve.
The ring can be connected to the sleeve, by being distinct from the tank. In particular in this case, it can then be connected to the sleeve; moreover, the sleeve can taper towards the free end, likewise the ring can thin from a peripheral portion towards the sleeve; all of these arrangements facilitate the oscillations by increasing their amplitude.
The ring can also be part of a surface of the tank to which the sleeve is fixed, with the operation of the invention then being very different.
The sleeve can carry a flared nozzle at its free end in order to favour the delivery of the fluid by calibrated droplets.
The delivery of the fluid can also be guaranteed by a flexible tube surrounding the sleeve, wherein the sleeve opens, which comprises a free end that has an opening outside of the pump with reduced section in relation to a main portion of the flexible tube that contains the sleeve, and the resonator is arranged in order to apply flexural oscillations also to the flexible tube: the reduced orifice of the flexible tube, possibly obtained by a heat-shrink effect of the flexible tube made for example of polyethylene (PE) or polytetrafluorethylene (PTFE) or fluorinated ethylene propylene (FEP) or perfluoroalkoxy (PFA) with shrinkage ratios of 1.7/1 to 1.3/1 during its fastening to the sleeve by heating to a temperature of at least 210° C., then plays the same role as the tapering section of the capillary in other embodiments; the capillary can then be with uniform section without disadvantages.
The sleeve can be fixed to the tank rigidly, or it can be connected to it via a hose, in the case where it is supported by the resonator.
A particular embodiment of the invention authorises an inverse operation of the pump, i.e. an aspiration of ambient fluid then replaces the delivery of the fluid. Such an embodiment can be useful when a drug has to be applied temporarily, or when a sample of ambient fluid must follow or precede the delivery of the fluid contained in the tank. The sleeve then comprises two portions as a protruding extension on either side of the ring, dissymmetrical and the capillary passes through both of them. A system of valves can direct the fluid extracted towards a recipient other than the main tank.
The choice of the control frequency will preferentially control the oscillations of one of the two portions of the sleeve, and therefore the direction of flow of the fluid through the sleeve.
In an alternative embodiment, the sleeve comprises two portions as a protruding extension on either side of the ring, dissymmetrical and the capillary passes through both of them, and a middle portion joining said protruding portions, and the resonator also comprises two portions which are dissymmetrical and superimposed, respectively connected to said protruding portions, and between which the middle portion extends.
In the two cases, it is advantageous that the pump include a flexible tube surrounding each of the portions of the sleeve, which opens therein respectively, with each of the flexible tubes comprising a free end having an opening respectively outside of the pump and in the tank, with the opening having a reduced section in relation to a main portion of the flexible tube that contains the portion of the sleeve, and that the resonator be arranged in order to apply flexural oscillations also to the flexible tubes. As in a preceding embodiment, the flexible tubes favour the flow of the fluid in the desired direction.
According to another improvement, the pump can include a device for measuring the level of the fluid in the tank, which can include two sectors of the circular electrode, and a transducer located at a location of the tank opposite the resonator.
According to another type of improvement, wherein it is sought to prevent the inertia of the fluid from absorbing the vibratory energy of the resonator when the latter is part of the surface of the tank, the surface of the tank to which the sleeve is fixed is conical in such a way that the tank is convex, and a membrane extends in the tank by separating the fluid from said face. The membrane then isolates the fluid from the resonator.
The flow rate can also be regulated by a free valve between a piercing of the membrane facing the sleeve and an end of the sleeve opening into the tank.
Another possibility consists in providing the pump with a cover with an edge attached to the tank, covering the sleeve and provided with an orifice in front of the free end of the sleeve, which protects the sleeve. The orifice of the cover can then contain a free ball in a housing constituting the orifice, in order to correct the delivery of the fluid to the outside. Or again, the cover can delimit a housing forming a reserve of an additive to the fluid, which is delivered at the same time as the latter thanks to the vibrations, with a determined content of the mixture.
According to a very important operating mode, since it greatly facilitates the delivery of the fluid, the resonator is arranged to also apply axial oscillations to the sleeve. It has been observed that the superposition of the axial oscillations on the flexural oscillations, especially when the axial oscillations have a dual frequency of the flexural oscillations, favoured the flow of the fluid by the capillary.
Another manner to facilitate the transport of the fluid in the capillary consists in providing the pump with a needle fixed to the tank and extending in the capillary.
Finally, in a construction of the invention which is also important, the pump comprises a power transducer converting an electrical energy into pressure waves in an adjacent medium, a receiving transducer, also adjacent to said medium, converting the pressure waves into electrical energy is fixed to the tank, and connected to the resonator in order to control it.
The preceding notions shall now be developed while still describing in detail certain particular embodiments of the invention.
These modes are provided for the purposes of information on the various aspects of the invention, but it is manifest that the latter can be constructed in another manner, with different embodiments, obtained for example by combining elements of the embodiments effectively described. The following figures shall be referenced:
The ring 70 has a thinned central region 6 creating a mechanical amplification of the vibration. The central region 6 of the resonator 2 comprises a tubular section 7, in contact with the sleeve 3 tapered towards its free end of the sleeve, wherein is located an ejection nozzle 8, and not far from this free end. The movements of the centre of the ring 70 are therefore transmitted to the sleeve 3 by tubular section 7, which converts the especially vertical movement B into an especially horizontal movement C by leverage effect. This disposition also makes it possible to connect the resonator 2 to a more tapered location constituting a weaker mechanical load of the sleeve 3 and therefore to bend it more easily, while still transmitting oscillations that are more substantial than those of the central region 6, again thanks to the lever arm procured by the tubular section 7; the thinning of the central region 6 itself makes it possible to increase these oscillations thanks to the decrease in its rigidity.
The physical operating principle of the pump can be presented in two different ways. The first consists in saying that when the resonator 2 is in resonance flexing with the tipping of the assembly of the sleeve 3, with a swinging movement (B and C) corresponding to the first natural bending mode, the sleeve 3 stretches by curving and a portion of the fluid is driven towards the end. During the return movement, the sleeve 3 moves back through the vertical, the stretching is then minimal. The situation is such that after having easily progressed towards the free end, less loaded, towards the ejection nozzle 8, it is impossible for the fluid to rise to the base of the sleeve 3 which is much more loaded with fluid and therefore to rise towards the top portion of the tank 1 (with the liquid being by hypothesis incompressible in the absence of air bubbles in the sleeve 3). Indeed, the section of liquid that must be pushed in order to rise in the sleeve 3 is greater than that what must be displaced to go down it. This property is reinforced if the capillary channel inside the sleeve 3 is also tapered towards the free end. The small volume of liquid at the end subject to a substantial load, must descend towards the ejection nozzle 8 by triggering a squirt in the only direction possible which is towards the narrowest end where the load is the lowest, i.e. towards the exterior. Then, with the alternating of the swinging movements, another volume is driven towards the free end at each tipping, which will be in turn expulsed during a return to the vertical alignment of the end. There are therefore two squirts, i.e. two ejections, or two streams of liquid, per ultrasound period.
The second way to explain the operating principle of the pump is without a doubt as easy to understand and to model as it consists in saying that the sleeve 3 constitutes a rotation arm around an axis located at the base of the sleeve. For small swinging movements (of a few microns), the tipping of the sleeve 3 by a few millimetres in height, is similar to a rotation. The rotation of the sleeve 3 is inverted twice per ultrasound period. The masse of volume of liquid contained at the end of the sleeve 3 therefore undergoes an acceleration that is both tangential and centrifugal of which the force can be calculated and which, conveyed to the internal surface of the capillary channel, defines the intrinsic suction pressure of the pump. Knowing that the sleeve 3 carries out coming and goings at the resonance frequency of the resonator 2, the centrifugal and tangential acceleration is maximal at each time that the sleeve 3 passes through the vertical position. This explanation joins in its conclusions the preceding explanation, i.e. the production of a squirt twice per ultrasound period. Furthermore, it suggests that it is not necessary to provoke a strong dissipation of vibratory energy in the fluid in order to trigger the pumping. The process can have good energy efficiency. Finally, it makes it possible to think that a centrifugal acceleration threshold exists making it possible to overcome the hydrophilic or hydrophobic forces that result in a surface tension that could retain the liquid and allow it to progress. No cavitation of the fluid is required.
In a particular embodiment the tank 1 and the sleeve 3 are integrated, and the sleeve 3 is a conical tube inserted by force into the tubular section 7 of the resonator 2. The fluid located at the end of the sleeve 3 undergoes a lateral and centrifuge acceleration that propels it to the output of the ejection nozzle 8 with inner diameter 0.5 mm. The height of the acceleration arm is 21 mm between the average level of the resonator 2 and the ejection nozzle 8 (mark F). The resonator comprises a symmetrical thinning in its central region 6 that increases the amplitude of the vibration according to a bending mode. The internal electrodes in contact with the ring 70 are earthed. The piezoelectric ceramic of the transducers 4a, 4b and 5 is excited as a half bridge. Their internal electrode is earthed and their external electrode is excited by a symmetrical sinusoidal or square voltage. The piezoelectric ceramic can provide a second type of vibration in order to impress a movement according to the axis of the sleeve 3 and allow for the ejection of a single droplet which has formed at the end of the ejection nozzle 8 with tapered shape; there can then be two steps, a first wherein the droplet is formed slowly and increases in size at the end of the sleeve 3 to occupy the ejection nozzle 8 by means of transducers 4a and 4b, and a second step wherein the axisymmetric transducer generates an axial movement and propels the drop; this operation is more weakly obtained with flared ejection nozzles 8, forming a recipient and covered with a hydrophobic coating of which samples shall be seen further on.
The dimensions and the electrical power brought into play by this method of pumping makes this actuator compatible with all of the ultrasound pumps that apply this method. An alternative smaller in size and excitation power is described further on for an implantable use. It is possible to miniaturise further than in the exampled described.
The method of pumping via centrifugation lends itself well to the calculation of the pressure or of the vacuum of the pump. It is assumed that the fluid is initially inserted until the end of the conical tube forming the sleeve 3.
This first prototype is carried out with a resonator 2 with an outer diameter 50 mm and an internal radius of 2 mm of the ring 70 of which the tubular section 7 is pierced at 1.3 mm in diameter and at a height of 5.5 mm under the lower line of the ring 70 of the resonator 2 (mark G). It produces a resonance frequency of 26 kHz (period of 38 μs) and an amplitude of lateral vibration at the end of the sleeve 3 of 1.6 μm peak-to-peak, which is about 5 μm peak-to-peak at the end of the sleeve 3 of height 21 mm. The centrifugal acceleration is therefore maximal when the movement of tipping is at the vertical. If U0 is the amplitude of lateral deviation, f0 the resonance frequency of the resonator 2, ac the centrifugal acceleration, R the height between the base of the sleeve 3 and by considering the elementary volume of fluid located at the end of the ejection nozzle, there is:
with U0=2.5 μm,
f0=26 kHz,
R=21 mm,
or here: ac=2 m/s′. The centrifugal acceleration reaches about 20% of the acceleration of the gravity when the sleeve 3 passes through the vertical.
The lateral deviation also generates a tangential acceleration component (aT=R/U0 ac). This component is R/U times more powerful than the centrifuge component, which is approximately 8000 times more powerful. This acceleration is able in certain cases to generate a drop in pressure on lateral walls that is sufficient to create a cavitation phenomenon on the lateral wall of the side of the direction of tipping. But above all it generates an inertial flow of the fluid against the lateral walls of the sleeve 3, which flushes it in the axial direction. The reduction of the section of fluid towards the free end of the sleeve 3 is as such a condition that favours the progression of the fluid towards the end.
The strong acceleration undergone by the fluid is required in order to push it through a thin capillary. For a thin capillary, that does not authorise a flow of the fluid in static conditions, and which therefore can always remain open, without a valve of any type and which constitutes an advantageous embodiment of the invention, a simple acceleration of a few “g” is not enough to expulse a drop. The pump is therefore idle in a closed state, i.e. the content of the tank 1 does not flow although the sleeve 3 remains open. Thin capillary means a capillary wherein the fluid does not spontaneously flow by the effect of gravity, with the capillary forces therefore being predominant. In the absence of capillary bridges or capillary forces, for example due to a surface condition that is not perfectly smooth, so that there is a natural flow, the gravitational force (or if needed its projected value) must be greater than the surface force of which the amplitude and the angle with the wall of the tube depend on the wettability of the fluid and on the hydrophilic or hydrophobic surface treatment of the wall. In order for there to be spontaneous flow, it is therefore sufficient for the diameter to be sufficiently large so that the gravitational force finishes by exceeding the surface force. As such, the diameter of the capillary will be generally less than 1 mm, even less than 0.5 mm. It will typically be between 0.1 and 0.5 mm.
A valve can however be added, in particular in the case of a difference in gas pressure to be provided between the inside of the tank and the outside medium, in order to prevent any untimely flow (see an embodiment further on) and any leakage by simple capillarity and even any effect of evaporation.
In sum, an elementary volume of fluid at the end of the conical sleeve 3 undergoes a periodic pressure-vacuum of which the module reaches 16,000 Pa; this pressure is lateral and slightly downstream.
The pumping is continuous or intermittent. In the case of the prototype that is shown here, an excitation with a duty cycle of 10% makes it possible to expulse 100 μl of liquid in 20 seconds into a sleeve 3 with an inner diameter 0.7 mm at the thinnest. The same 100 μl are expulsed in 2 seconds for a continuous emission. The ceramics are of the Ferroperm PZ26 brand, of thickness 0.5 mm and excited by an excitation voltage of 80 Vcc.
An intermittent pumping can be constituted for example of 100 periods at 26 kHz, which is 3.87 ms with a duty cycle of 10% or an intermittent rate of fire of 1/38.7 ms=25.8 Hz. Each packet comprises 100 periods with flexing of the end and 150 periods at the frequency 2×26 kHz=52 kHz, with up and down movement (axial) of the end.
As indicated hereinabove, the bending mode is sufficient to trigger the pumping of the fluid. The axial mode can furthermore affect the ejection of the fluid at the end of the nozzle 8 and according to its geometry. For a drop-by-drop ejection, a bending mode to progressively constitute the drop at the end of the tapered nozzle 8 can be combined with an axial mode to expulse the drop after it has been formed.
If this actuator is miniaturised, it is possible to reach, for example, a working frequency of 600 kHz for a diameter of the resonator 2 of 7 mm (about 30 times higher in frequency). The following estimations can be made:
In sum, for the expulsion to be effective, the following conditions can be indicated:
1) a liquid contained in the tank 1, which is connected to a flexible tube (the sleeve 3) inserted by force into an orifice of the resonator 2;
2) a back and forth bending movement of the end of the sleeve 3 and of its ejection nozzle 8;
3) a conical or tapered shape of the end of the sleeve 3 or of the ejection nozzle 8, creating a situation of a reduction in the mechanical radiation impedance (product of the section of the tank×height over a half-period×density×velocity of sound in the fluid) along the axis;
4) a free end able to reach a large amplitude of lateral deviation.
Having in addition an axial vibration with the dual frequency of the bending mode triggers an elliptical vibration of the internal surfaces and can facilitate the flow.
The phase shift between the two axial tilting frequencies must be adjusted so that the two effects are added together and that the fluid is pushed in the correct direction i.e. towards the end of smaller section of the tank (for a lateral movement in U0 Sinus (2πf0t) there is an axial movement in Ut Sinus(2πf0t+φ) where Ut designates the maximum amplitude of the axial movement).
In the alternative embodiment shown in
The same effect can be obtained with the embodiment of
Another type of improvement, shown as an alternative of
Commentary will now be made on
Other embodiments shall be described by means of
The embodiment of
The embodiment of
Commentary will now be made on
The efficiency of the energy recovery depends substantially on the effectiveness of the piezoelectric conversion of the materials used and is then according to the dispersion of the acoustic energy during its propagation in a possibly heterogeneous semi-infinite medium. Through analogy with telecommunication transmission lines, mechanical impedance adaptation is evoked when two different acoustic propagation environments must be coupled. In certain cases, the difficulty of the coupling comes from the small coupling surface, while in other cases, the difficulty is due to the highly different nature of the two mediums, solid for one, liquid for the other. The problem that must be resolved has these two difficulties. They shall now be described somewhat more quantitatively.
The first notion is that of mechanical impedance. For an infinite medium, this rupture is characterised by the notion of intrinsic impedance of the mediums, Zi, a product of the density p and the velocity V of the acoustic waves that propagate therein: Zi=ρV is observed. The velocity V can be that VL of the longitudinal waves or VT of the transversal waves.
For a planar interface separating two non-viscous semi-infinite fluid mediums, characterised by their intrinsic impedances Z1 and Z2, the reflection coefficient of the acoustic power R of a planar sinusoidal acoustic wave in normal incidence at the interface is:
The transmission factor T of the acoustic intensity is:
If the mediums have impedances that are very different, the major portion of an incident wave emitted from the medium 1 is reflected at the interface without reaching the medium 2.
If the mediums are both solid and liquid, reflection, refraction and conversion coefficients appear according to the angle of incidence.
Moreover, the absorbing of the acoustic waves, linked to the viscosity of the propagation medium, is also a factor that is to be taken into consideration. The power of one acoustic wave P(z) propagating according to the direction z, in a medium with a loss by viscosity characterised by a coefficient of viscosity η (with
where T is the constraint and v the velocity of the particles) can be expressed according to the formula
α is often given in dB/cm. This coefficient increases with the square of the frequency f and is inversely proportional to the cube of the velocity of the waves. As the velocity of the longitudinal waves is practically twice that of the velocity of the transversal waves, the absorbing of transversal waves in a viscous medium is much greater than that of longitudinal waves. Soft plastics are part of this category.
The insertion rate shows the effectiveness of the piezoelectric transducer emitter thrust against the skin in converting the electrical energy into mechanical energy that propagates through the skin and the bone to a piezoelectric antenna provided on the dosing device.
As the transmitting and receiving transducers are excited at the same frequency, here a resonance frequency of these elements, and in a propagation medium with losses, the insertion rate characterises the capacity of the assembly to maintain the resonance at the terminals of the piezoelectric receiver at a high amplitude while the latter is charged under low electrical impedance. The highest insertion rate is sought.
The latter is measured according to the following assembly. A first piezoelectric transducer PZT1 is excited by an amplitude sinusoidal signal FEM=1 Vcc (peak-to-peak electromotive force) at a resonance frequency of the resonator. The output impedance Rs of the function generator is 50 Ohms. The transducer PZT1 converts a portion of the electrical signal into a mechanical wave which propagates to the transducer PZT2. The latter reciprocally converts the mechanical signal into an electrical signal VL that is measured via an oscilloscope probe at the terminals of a resistive load of 50 Ohms.
The entry/exit insertion rate is given by the ratio
When the mechanism of coupling with the receiving transducer PZT2 is optimal, in particular, the entry/exit insertion rate can be close to the conversion rate into energy K233 of a piezoelectric transducer, which is 46% and 49% for materials PZ26 and PZ27 respectively from the Ferroperm company.
In the case where the propagation medium is heterogeneous, such as skin, fat, bone, the acoustic wave has its wave front deformed and the input/output insertion rate is degraded. This is all the more so true when the working frequency is higher.
At 1 MHz, the wavelength of the acoustic waves in the body is of a magnitude of 1.5 mm. The thickness of tissues/bone to be passed through must be thin enough and the acoustic antenna rather extended laterally so that a sufficient proportion of the power emitted is recovered.
The transmission through the walls of an enclosure for more homogeneous materials such as glass and metals pose much less problems.
Furthermore, the working frequency and the shape of the receiving antenna must make it possible to prevent the untimely couplings with other sources of acoustic waves present in the environment.
Finally, supposing that a transducer emitter having good geometry and a shape adapted to the receiving antenna contained in the dosing device is applied against the skin, it can be imagined to introduce a modulation of the signal as an activation key. The source of the acoustic wave that has to put the doser into action would for example have to be emitted at a key rate (with the key able to be changed by the patient or solely by a physician) so that the dosing device delivers the dose.
In a medium with no loss with guided propagation, when the insertion rate is good, half of the electrical power can be converted into mechanical power piezoelectrically.
Interest here is given to a device of rather large dimensions located behind an artificial wall 53. In the power transducer 58, an unstable oscillator with a frequency of 19 kHz is used to create a high voltage of 90V by periodically opening and closing a transistor T1 which charges a self inductance of value 1 mH and series resistor 60 Ohms. The rising charge in current of the self lasts at least 40 μs (three times the time constant). During the closing of the transistor T1, a negative voltage appears and charges the tank capacitors in series arranged after the diode bridge. This high voltage is then used to excite the actuating transducer 56 at a frequency of 600 kHz by means of transistors NMOS and PMOS which switch in phase opposition, with one of them (Source), the PMOS, is used to bring the voltage of the transducer actuator to 90V while the other one, the NMOS (Sink), is used to empty the electrical charges. The two series capacitors have a combined capacity 10 to 100 times the value of the static capacity of the actuator which is approximately 100 nF. The burst at 600 kHz comprises N periods, with N between 1 and 60. The burst is re-emitted at a rate of 1 kHz in order to allow for the maintaining of the high voltage. The duty cycle for the excitation of the actuator does not exceed 10%. In the case of implantable devices, lower voltages will be used.
Particular points are:
The bending mode tips the sleeve 33. This tipping generates a movement of the fluid (liquid or gel or powder) towards the exterior of the doser. The fluid is as such expulsed by the tipping and the bending movement of the end of the sleeve 33. The fact that the end of the sleeve 33 is free is critical because it is because the end of the sleeve 33 is free in relation to its base that the fluid is sucked into the capillary and expulsed towards the outside. In the case of an implementation of the dosing stylus type, a protective part of the end of the dosing tube is provided.
The bending mode of the tube is typically associated with a resonance frequency of 600 kHz.
The excitation of the actuator lasts between 10 μs and 100 μs. It is carried out when the voltage at the terminals of the rectifier capacitor located at the entrance is sufficient to wake up the microcontroller. The latter then starts its real-time clock via a 32,768 Hz quartz. The microcontroller has a frequency generator (by FLL loop) that allows it to produce the excitation signal at 600 kHz of the transducer of the resonator 57. Once the excitation of the transducer of the resonator 57 has been carried out, the microcontroller switches to low consumption mode, with the sole obligation being to measure the time elapsed since the activation of the transducer of the resonator 57. The microcontroller records in a non-volatile memory, for example its flash memory, the time elapsed since the last excitation. This allows the microcontroller at each new emission to check the value of the register and verify that the safety delay has been complied with.
Commentary will now be made on
Here now are a few particular points relating to the application of the invention to the implantation in a living body, for example in a middle ear via a surgical operation, for example, a tympanostomy.
The receiving transducer 56 will transfer the energy to the resonator 57 via a wire covered with silicone. No magnet is used, with the advantage of not disturbing magnetic resonance imaging for clinical applications.
The excitation of the electrodes for the speaker mode, via an axial movement of the ring of the resonator, can allow the dosing device to also be used as a hearing aid, by reconstructing an analogue signal at the hearing frequencies inside the ear by a modulation of the beats of the ring of the resonator. The volume delivered can be determined in an open loop and therefore modified according to the needs at the time, in a therefore controlled and perfectly reliable manner. The increase in temperatures produced by the pump of the invention is greatly reduced. The pump can be implanted according to a cochlear implant technique in the middle ear; the use of the outlet hose of
The acceleration required for the flow and for the dosage of the product is of several thousands of “g”: the accelerations that are normally encountered, of a few “g” at most, cannot under any circumstances induce leakage.
The device, which is devoid of moving mechanical parts and materials that can degrade rapidly under mechanical stress, such as polymers, ages well.
It is possible to work with intermittent operation or on the contrary continuously or quasi-continuously, with a precise direction of the stream.
If an important application is the use as an implantable device for dispensing drugs (DDS category “Drug Delivery System”), others can also be considered just as easily, such as inking pens or deodorising devices or industrial dosage of 1 or 2 compounds or reagents on a float in particular.
Number | Date | Country | Kind |
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11 58458 | Sep 2011 | FR | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP12/68693 | 9/21/2012 | WO | 00 | 3/18/2014 |