Micropump with electrostrictive material actuation

Abstract

A micro-pump (µP) system comprises a flat capillary tube section with inner width (w) and height (h), where w > 5h. A plurality of separate actuation elements En are successively positioned along the length of the capillary tube section, each actuation element comprising inner and outer electrode segments on both wide sides of the capillary tube section and being addressable by a driving signal and an electrostrictive material layer arranged between the electrodes A control unit generates driving signals imposing electrical fields straining each actuation element and corresponding capillary tube section. The phase of driving signal for actuation element En is a function of time and relative position of E n to generate a wave travelling of amplitude S along the capillary tube section. The micro-pump can be configured to operate as a travelling wave micro-pump (TWµP) by adjusting the driving signal so that 2S < 0,2h or to operate as a peristaltic micro-pump (PµP) by adjusting the driving signal so that 2S = 0,5h.

Description

[0001] MICROPUMP WITH ELECTROSTRICTIVE MATERIAL ACTUATION

[0002] FIELD OF THE INVENTION

[0003] The present disclosure pertains to the field of pumps with a flow rate in the microliter-per- minute range.

[0004] BACKGROUND

[0005] A micropump is a very small pump with a flow rate (Q) in the microliter-per-minute range, i.e., Q e [1 pL / min ; 1000pL / min]. Micropumps are especially interesting for use in wearable drug delivery systems, such as in insulin delivery devices for the treatment of diabetes.

[0006] Micropumps for use in wearable drug delivery systems are often referred to as patch pumps since they are intended to be attached to the skin of the user in a bandage or patch.

[0007] Prominent key performance parameters for patch pumps are:

[0008] Size and wearability. Size and weight affect the user experience and, ultimately, the decision to adopt the treatment.

[0009] Drug delivery accuracy. A high accuracy ensures a high therapeutic efficacy, and a higher accuracy allows using more concentrated drugs which reduces liquid volumes and handling.

[0010] Power. Power consumption is important for the required battery capacity - and thus size and weight - as well as battery duration.

[0011] Patch pumps even hold the potential to be inserted under the skin, which would add further key performance parameters such as biocompability and non-toxicity. The best performing micropumps for current wearable drug delivery systems have a size around 10x10x1 mm3for a 400 pL / min flow rate with an accuracy of about 20% of the nominal value and a power consumption of around 1-2 kJ / L.

[0012] Mechanical micropumps are mostly Micro Electro Mechanical Systems (MEMS) with ceramic piezoelectric actuators as the most used actuators due to their generally high reliability, large actuation forces, low power consumption, and fast operation.

[0013] Piezoelectricity is an electromechanical property that only occurs in a particular class of dielectrics. Electrostriction is the mechanical deformation, or strain, of a dielectric in the presence of an external electric field and is caused by displacement of ions in the crystal lattice upon being exposed to the electric field. The strain resulting from a given electric field (typically measured in relative deformation in % at a field strength in million volts per meter - MV / m) varies widely for different materials. Piezoelectricity is a linear effect while electrostriction as such is a quadratic effect. The most widely used piezoelectric material for actuation is Pb(Mg1 / 3Nb2 / 3)O3 - PbTiO3 (PMN-PT), with a permittivity of ~ 20,000 and S«1 / (60 GPa).

[0014] An exemplary micropump is described in J. Ogawa et al. “Development of liquid pumping devices using vibrating microchannel walls”, Sensors and Actuators A 152 (2009) 211-218, doi:10.1016 / j.sna.2009.04.004.

[0015] SUMMARY

[0016] Accordingly, there is a need for a micro-pump and methods of using such, which may mitigate, alleviate, or address the shortcomings existing and may provide a biocompatible and non-toxic micropump solution.

[0017] A micro-pump (pP) is disclosed, the pP comprising a flat capillary tube section having length (L), inner width (w), and inner height (h); a number of Nact separate actuation elements En, where n = 1 , 2,... Nact > 3, positioned successively along the length of the capillary tube section and in continuous mechanical contact with the capillary tube section, each actuation element comprising:

[0018] - an inner electrode arranged on at least both wide sides of the capillary tube section;

[0019] - an electrostrictive material layer arranged on the inner electrode on at least both wide sides of the capillary tube section;

[0020] - an outer electrode segment arranged on the electrostrictive material layer on at least both wide sides of the capillary tube section, each outer electrode segment being individually addressable by a driving signal; and

[0021] The flat capillary tube section may be dimensioned with w e [0,5mm ; 10mm], h e [0.05mm ; 0.1 mm], L > 10w, and w > 5h. A capillary tube section with such or similar dimensions is herein referred to as having a microcapillary geometry in that it will be influenced or dominated (depending on the polarity of the liquid) by capillary action. The capillary tube section may be formed in a flexible material with both wide sides of the capillary tube section having wall-thickness (t) with t < 3h. The flexible material may be a polymeric material.

[0022] The electrostrictive material layer may be one or more electrostrictive layers of oxygendefective metal oxide.

[0023] A micro-pump (pP) system is disclosed the pP system comprising the pP and a control unit comprising an electronic processor and an electric signal generator with the control unit being configured and connected to generate and apply driving signals between the inner electrode and the outer electrode segment of the actuation elements to impose an electrical field on the electrostrictive material layer leading to a strain of the actuation element and part of the capillary tube section, the driving signals having voltage amplitude (A) and frequency (f), and a driving signal for actuation element Enhaving a phase (n) as a function of time (t) and relative position of actuation element Enfor the driving signals to generate a travelling wave of amplitude (S) in a longitudinal direction of the capillary tube section. The driving signal amplitude A may be selected so that 2S < 0,5h.

[0024] The micro-pump may be configured to operate in a partially-closed-channel regime corresponding to a travelling wave micro-pump (TWpP) system, in travelling wave pumping, there will be both forward-flow and back-flow relative to the direction of the wave travelling in the walls, but a net forward-flow. Hence, in the TWpP configuration, the driving signal amplitude A can be selected so that 2S < 0,2h.

[0025] The micro-pump may be configured to operate in a fully-closed-channel or almost-fully closed channel regime corresponding to a peristaltic micro-pump (PpP) system. In peristaltic pumping, there will be no or very little back-flow against the direction of the wave travelling in the walls, and thus a complete closure of the channel is not essential. Hence, in the Pp.P configuration, the driving signal amplitude A can be selected so that S « 0,5h.

[0026] Use of a micro-pump system as disclosed in a patch pump or a micro-dosing unit configured to be attached onto, or implanted in or under, the epidermis of a subject is disclosed.

[0027] A patch pump or a micro-dosing unit configured to be attached onto, or implanted in or under, the epidermis of a subject is disclosed, comprising a micro-pump system as disclosed; a power interface configured to provide electrical power from a power source to the control unit; a first interface configured to provide liquid communication between a first end of the capillary tube section and a receptacle holding a liquid to be delivered to the blood of a subject; and a second interface configured to provide liquid communication between a second end of the capillary tube section and a cannulated needle to be inserted in a blood vessel of the subject.

[0028] A method for delivering a predetermined volume of liquid to a subject is disclosed, the method comprising:

[0029] - providing a patch pump or a micro-dosing unit as disclosed and attaching the patch pump onto, or implanting the patch pump in or under, the epidermis of a subject;

[0030] - connecting a power source to the power interface;

[0031] - connecting a receptacle holding a liquid to the first interface;

[0032] - connecting a cannulated needle to the second interface;

[0033] - inserting a tip of the cannulated needle into a blood vessel of the subject; and

[0034] - programming the control unit to apply the driving signal for a predetermined amount of time to deliver a predetermined volume of liquid from the receptacle through the cannulated needle.

[0035] It is an advantage of the present disclosure that it provides a pP system with a lower form factor and thus increased compactness and wearability in comparison to prior art micropump systems. In prior art micropump systems, the pump typically occupies around 50% of the pump system size. This form factor is crucial as size and weight affect the user experience and, ultimately, the decision to adopt the treatment. This effect is achieved in part because no membrane chamber, valves, or other microfluidic circuitry are needed.

[0036] It is an advantage of the present disclosure that it utilizes a microcapillary geometry with almost no "dead volume". This is achieved since interfaces for delivering liquid to and receiving liquid from the pump can be connected directly to the capillary tube section holding the actuation elements. Thereby, no microfluidic circuit besides the capillary tube section holding the actuation elements is required.

[0037] Because low but controlled pump rates are possible with a microcapillary system there is an advantage of the present disclosure that it can provide an improved delivery accuracy, such as within ±5% of the nominal value, thereby ensuring a high therapeutic efficacy. This effect is made possible by the combination of the microcapillary geometry and the travelling wave or peristaltic pumping mechanism.

[0038] Typical functional materials for MEMS actuators perovskite ferroelectric materials such as PbZrTiO3 (PZT) or Pb(Mg1 / 3Nb2 / 3)O3-PbTiO3 (PMN-PT) ceramics and their composites with electrodes of various conducting materials. Despite the excellent performances, these compounds contain lead (Pb), a highly toxic element. It is an advantage of the present disclosure that it provides a micropump using non-toxic actuators based on oxygen-defective metal oxide.

[0039] As the electromechanical performances of piezoceramic materials strictly depend on crystallinity, their fabrication typically requires a high-temperature sintering step. Piezoceramic actuators can therefore not be formed on temperature-sensitive materials such as polymeric materials. Instead, the piezoceramic actuators must be transferred onto the temperature-sensitive material, resulting in a more complicated fabrication and bulkier devices. It is an advantage of the present disclosure that it provides a micropump using actuators based on oxygen-defective metal oxide that can be deposited at low temperatures such as room temperatures and that can therefore be formed on temperature-sensitive materials such as polymeric materials.

[0040] It is an advantage of the present disclosure that it can provide a micropump with a reduced power consumption. Using electrostrictive layers of oxygen-defective metal oxide for the actuation may provide a 50% power reduction compared to similar designs applying piezoelectric transducers for the actuation. This factor influences the size and battery lifetime, both important aspects that patients take into consideration before adopting patch pumps. This effect is made possible by the geometry and flexible material of the flat capillary tube section, the use of electrostrictive layers of oxygen-defective metal oxide for the actuation, and the use of the travelling wave or peristaltic pumping mechanism.

[0041] It is an advantage of the present disclosure that it provides a micropump where no passive valves to prevent backflow are necessary. The absence of passive valves during pump operation simplifies the design and greatly improves reliability. It also reduces the size and the dead volume of the pump.

[0042] It is an advantage of the present disclosure that it provides a micropump with improved reliability. When running in the partially-closed-channel mode, i.e. as a TWpP , the strain due to the deformation of all parts is < 1000 ppm, which minimizes material fatigue and implies high reliability and long operation time. This effect is made possible by the geometry of the flat capillary tube section and the use of the travelling wave or peristaltic pumping mechanism. When running in the peristaltic mode, i.e. the PpP configuration with S « 0,5h, the maximum strain is of the order 0.1 ppm which may increase the fatigue of the micropump.

[0043] It is an advantage of the present disclosure that it provides a micropump with reduced tendency to clogging and improved adaptability: The longitudinal actuation along the capillary tube section means that no corners, bends, valves, or other microfluidic obstacles are necessary which removes most potential clogging hazards. The disclosed pP system is highly adaptable as increasing the number of thin-film layers in, and / or the length of and / or the number of actuation elements or connection capillary tube sections in series increases the backpressure.

[0044] It is an advantage of the present disclosure that it provides a micropump with improved modularity. Multi-drug delivery can be addressed by providing individual capillary tube sections for each fluid in parallel. Mixing chambers (chambers with pre-design turbulence) can be easily integrated with the capillary.

[0045] BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The above and other features and advantages of the present disclosure will become readily apparent to those skilled in the art by the following detailed description of examples thereof with reference to the attached drawings, in which:

[0047] Fig. 1 is a block diagram illustrating an example TWpP system according to this disclosure,

[0048] Fig. 2 is a cross-sectional view of an illustration of a capillary tube section according to this disclosure,

[0049] Figs. 3A and B are top view (3A) and a perspective view (3B) of an illustration of a capillary tube section with actuation elements according to this disclosure,

[0050] Figs. 4A-C are cross-sectional views of an illustration of a capillary tube section with actuation elements according to this disclosure, with each element containing one or more thin-film layers,

[0051] Fig. 5 is an illustration of the travelling wave pumping principle,

[0052] Fig. 6 is an illustration of a pP according to this disclosure, and Fig. 7 is an illustration of a patch pump according to this disclosure.

[0053] The figures are schematic and simplified for clarity, and they merely show details which aid in understanding the disclosure, while other details have been left out. Throughout, the same reference numerals are used for identical or corresponding parts.

[0054] DETAILED DESCRIPTION

[0055] Various examples and details are described hereinafter, with reference to the figures when relevant. It should be noted that the figures may or may not be drawn to scale and that elements of similar structures or functions are represented like reference numerals throughout the figures. It should also be noted that the figures are only intended to facilitate the description of the examples. They are not intended as an exhaustive description of the disclosure or as a limitation on the scope of the disclosure. In addition, an illustrated example does not show all the aspects or advantages. An aspect or an advantage described in conjunction with a particular example is not necessarily limited to that example and can be practiced in any other examples even if not so illustrated, or if not so explicitly described.

[0056] Fig. 1 is a diagram showing a pP 108 and a pP system 100 comprising a pP 108 according to the disclosure. The pP 108 comprises flat capillary tube section 110 having Nact separate actuation elements, En, where n = 1 , 2, ... Nact > 3, positioned successively along the length of the capillary tube section and in continuous mechanical contact with the capillary tube section. The design of the capillary tube section 110 and actuation elements Enwill be described in more detail later in relation to Fig. 2.

[0057] The pP system 100 comprises a control unit 101 comprising an electronic processor 102 and an electric signal generator 103, with the control unit being configured and connected to generate and apply driving signals to each actuation element En. In an exemplary embodiment, the control unit 101 or the electric signal generator 103 is connected to the actuation elements Envia electrical interface 106. The driving signals are preferably generated by the electric signal generator 103 based on instructions from the electronic processor. The driving signals have voltage amplitude (A) and frequency (f), and a driving signal for actuation element Enhas a phase (n) as a function of time (t) and relative position of actuation element Enalong the capillary tube section 110. Thereby, the driving signals can generate a wave of amplitude (S) travelling in a longitudinal direction of the capillary tube section 110.

[0058] The control unit 101 may comprise a computer-readable medium 104, for example removable and non-removable storage devices. The computer-readable medium 104 may hold computer-executable instructions, such as program code, to be executed by the electronic processor 102 to control the signal generator 103 and other functions of the control unit 101 . The control unit 101 may comprise a data interface 105, such as a wired or a wireless interface, for communicating with the control unit 101 from an external device. For example, data interface 105 may comprise a wireless Bluetooth or WiFi connection, whereby a user can communicate with and / or control the control unit 101 via an external device such as a smartphone or a tablet.

[0059] Fig. 2 is a cross-sectional view of an illustration of the capillary tube section 110, and Fig. 3A is a side view of an illustration of the pP 108 with the capillary tube section 110 and actuation elements En. Figs. 2 and 3A illustrate the relevant dimensions of the capillary tube section 110 alone (2) and with the actuation elements En(3A). inner width (w), and inner height (h). The capillary tube section is formed in a flexible material with both wide sides 112 of the capillary tube section having wall-thickness (t). The capillary tube section under the actuation elements has a length (L). A center-to-center distance between adjacent actuation elements is c-c, a gap between adjacent actuation elements is g, and a length, ln, of an actuation element Enin a direction along the length of the capillary tube segment is ln. If all actuation elements are dimensioned and formed uniformly, c-c = ln+ g.

[0060] The capillary tube section 110 may be a pipe section, channel, pipette section, hypodermic needle section. In an exemplary embodiment, the capillary tube section 110 may be a tube of small internal diameter that holds liquid by capillary action. The flat capillary tube has an aspect ratio (width / height) of at least 5, w / h > 5. The capillary tube can have an overall rectangular or oval cross-sectional shape, such as a rectangle with rounded corners or an oval or ellipse, with the major axis being the width and the minor axis being the height. This means the capillary tube will generally have two larger wide or flat sides 112 - a top side and a bottom side - of width w, and two smaller sidewalls 114 of height h. The two smaller sidewalls will typically be more affected by the curvature at the corners separating the wide sides 112 sides from sidewalls 114. When the cross-sectional shape is not rectangular, the width w will be the largest inner width of the capillary tube, and the height h will be the largest inner height of the capillary tube.

[0061] The capillary tube section 110 provides the liquid conduit of the pP system 100, and is preferably dimensioned with w e [0,5mm ; 10mm] and h e [0.05mm ; 0.1 mm], and with L > 10w, w > 5h and t < 3h. In an exemplary embodiment, the capillary tube section 110 is dimensioned with w e [0,5mm ; 10mm] and h e [0.05mm ; 0.1mm], and with L > 10w, w > 5h and t < 3h. In exemplary embodiments, c-c e [1 mm ; 2 mm], g < 1 mm, and lne [0.8 mm ; 2 mm].

[0062] Fig. 3B is a perspective view of an illustration of the pP 108 with the capillary tube section 110 and actuation elements, and Figs. 4A-C are cross-sectional views of an illustration of the pP 108 with the capillary tube section 110 and actuation elements.

[0063] An actuation element refers to a part of the pP, according to the disclosure, which achieves physical movements by converting electrical voltage into mechanical strain that is transferred as a force to the capillary tube. Herein, an actuation element is a configuration of one or more electromechanically active materials with electrodes connected to an electrical power source applying an electric driving signal.

[0064] Each of the Nact separate actuation elements Enare positioned successively along the length of the capillary tube section 110. Each actuation element comprises: an inner electrode 116 arranged on at least both wide sides 112 of the capillary tube section 110, the inner electrode being addressable by a driving voltage signal; an electrostrictive material layer 118 arranged on the inner electrode 116 on at least both wide sides 112 of the capillary tube section 110, wherein the electrostrictive material layer is one or more electrostrictive layers of oxygen-defective metal oxide; and an outer electrode segment 120 arranged on the electrostrictive material layer 118 on at least both wide sides 112 of the capillary tube section 110, each outer electrode segment 120 being individually addressable by a driving voltage signal.

[0065] Hence, further relevant dimensions of the actuation elements are the thicknesses of the inner electrode 116, tie, the electrostrictive material layer 118, tes, and of the outer electrode segments, toe. These are illustrated in Fig. 4A.

[0066] In the present description, different tube walls, materials, electrodes, and layers - in this paragraph collectively referred to as “members” - form parts of a layered structure around the capillary tube segment 110. A first member may be “arranged on” a second member, in which case the first member lies above / below the second member with at least some overlap and where there may or may not be other members between the first and second members. A first member may be “formed directly on” a second member, in which case there are no other members between the first and second members. For example, the inner electrode may be formed directly on the capillary tube with no other layers in between. In another example, a stress-relaxation layer may be formed in between so that the inner electrode is arranged on the capillary tube but formed directly on the stress-relaxation layer. In a third example, the electrostrictive material may contain a stack of several thin-film layers separated by electrodes, where every second of these are connected to the outer electrode 120, and the rest of them to the inner electrode 116.

[0067] When a driving voltage signal is applied to an actuation element En, a voltage difference is applied between the inner electrode 116 and the outer electrode segment 120. This imposes an electrical field on the electrostrictive material layer 118, leading to a strain of the actuation element Enand a stress on or strain of the part of the capillary tube section on which the actuation element Enis positioned. When actuation element Enis driven by a voltage signal, the resulting height variation or bulging in the corresponding part of the capillary tube section can be described by an amplitude, S. Hence, amplitude S may be seen as the amplitude of a travelling wave propagating in a wall of a wide side of the capillary tube section 110. Since the actuator elements are arranged on both flat sides 112 of the capillary tube section 110, a travelling wave will preferably propagate in unison in both flat sides 112, and the amplitude of the variation in the height h of 112 will be 2S. In the PpP and TWpP system configurations, the driving voltage signal amplitude A is selected to achieve the preferred values of amplitude S.

[0068] The strain of the part of the capillary tube section under the driven actuation element Enis proportional to the driving signal amplitude, A. If the strain becomes very large, the wide sides of the capillary tube would be squeezed together to a degree where the tube partially or completely closes. This corresponds to the PpP configuration where the squeezing would hinder or reduce liquid flow, such as reverse flow, through the tube, and a wave of such partial or complete closing action would amount to peristaltic pumping. In the PpP configuration, the materials and geometries of the pP and the driving voltage signal amplitude A of actuation elements Enare selected so that S - 0,5h, such as S > 0,48h or S > 0,45h.

[0069] In the TWpP configuration, the materials and geometries of the TWpP are selected so that an amplitude, S, of the height variation or bulging in a part of the capillary tube section under the driven actuation element Enfulfills S < 0,2h such as S < 0.1 h. Thereby, it is avoided that the wide sides of the capillary tube are squeezed together to a degree where the tube almost or completely closes.

[0070] Fig. 5 is an illustration of the travelling wave pumping principle used in the TWpP configuration. Fig. 5 serves to illustrate of the travelling wave pumping principle and related concepts and nomenclature and is not a depiction of an embodiment of the invention. When, in the present description, a travelling wave is generated ‘in the capillary tube section’, it is understood that the wave is a bulging of the wall of the capillary tube section under the actuation element, leading to a reducing in the height h of the capillary tube section under the bulge. Hence, the travelling wave in the capillary tube section may also be described as a travelling wave in the inner height as: h(x, t) = 2S exp[ / '2n(x / - ft)].

[0071] The illustration in Fig. 5 shows one side of a tube wall 500 being pushed in by some actuation mechanism triggered by the electrodes 502. The electrodes 502 are addressed by sinusoidal driving signals 504 with voltage amplitude (A) and frequency (f). The phases are shifted between successive electrodes in steps of 2K / 3. Thereby, the driving signals can generate a travelling wave of in a longitudinal direction of the tube wall. One of the main differences between a pP configured to run as a travelling wave pump (TWpP) or a peristaltic pump (PpP) is that the TWpP pump is configured or designed so that the amplitude 2S of the height variations inside the tube will be less than the complete constriction of the tube, i.e. 2S < h. In the TWpP, the fluid runs with a back-and-forward oscillatory motion, as illustrated by the round arrow 506, with a net positive time-averaged flow in the direction of the large arrow 508, induced by the non-linear fluid dynamics. Due to the specific features, the pump requires a careful design regarding size, materials, actuation frequency and the number of segmented actuators. In Fig. 5, six electrodes are driven with phase shifts of 2K / 3, resulting in two full waves travelling in the tube wall at one time.

[0072] The number of actuation elements and the phase shift in the driving signals to successive elements relates to how many waves will be travelling along the capillary tube section at a given time. In other words, the number Nact of actuation elements is related to the number Nwave of waves to be travelling in the capillary tube section at one time by:

[0073] Nact = N wave X N phase, where NPhaSe indicates the number of actuation elements used to generate one wave, as determined by the phase shift between driving signals addressing successive actuation elements. In an exemplary embodiment, the phase (n) of the driving signal applied to actuation element Encentered at lengthwise position xn, and with wavelength 2 = L / NWave is:

[0074] <|)n(t) = 2K (nNwave / Nact- ft) =2a:( xn / x - ft), and the driving voltage signal Vn(t) for actuation element Enhas a form like:

[0075] Vn(0 = A exp ^ n t)].

[0076] The inventors have performed detailed numerical simulations of the focused on maximizing hydrodynamic transport through the capillary tube section of a micropump according to the disclosure. The hydrodynamic transport - or the pumping characteristics - was quantified by the maximum and oscillation-period-averaged flow rate, Q, and backpressure, P, of an aqueous solution pumped through the capillary tube section. These numerical simulations of a capillary tube section with actuation elements applied different values for parameters such as geometries and dimensions (see Figs. 2, 3A, and 4A), material characteristics, Nact, NPhaSe, and driving signals. That all these parameters influenced the pumping characteristics is evident, but the numerical simulations revealed combinations of parameter values with very good as well as very poor performance and thus served to identify designs of a capillary tube section with actuation elements combined with corresponding driving signals providing optimal performance.

[0077] Therefore, in an exemplary embodiment of the TWpP configuration, NPhase= 4 to optimize the flow rate, and NWaVeis any integer. Increasing NWaVeincreases the backpressure without affecting the flow rate.

[0078] If a lower value of NWaVeis preferred for a given TWpP, a selection of the actuation elements En- such as their upper electrodes - may be left with floating voltage (unbiased), in which case they merely represent an enlarged gap between active actuation elements or an enlarged load at before or after the active actuation elements.

[0079] In an exemplary embodiment, the driving signal amplitude A is selected so that the amplitude S of the bulging in the capillary tube section is 0,01 h < 2S < 0,2h, with higher amplitudes producing improved pumping characteristics. The period-averaged flow rate Q and backpressure P are both proportional to A2.

[0080] In an exemplary embodiment, the driving signal frequency f is f e [500 Hz; 1 ,5 KHz], While no simple dependency on the driving signal frequency was found, improved pumping characteristics for most combinations of NPhase and NWave were found in this range. In an exemplary embodiment, f e [600Hz; 800Hz],

[0081] Electrostrictive materials with low dielectric constant are preferred since they result in actuation elements with low capacitance, which reduces the electrical power needed to drive the actuation elements. A preferred electrostrictive material with low dielectric constant is doped ceria. Moreover, the electrostrictor can respond in a linear fashion to an applied AC field, as a piezoelectric, i.e. in induced piezo mode, by applying a DC signal simultaneously to the AC signal. The DC signal breaks the inversion symmetry, and the AC signal then results in a piezoelectric response. This approach has been revived recently by applying asymmetric electrodes on centrosymmetric samples, creating different Schottky barriers at the electrodes, see e.g., D.-S. Park et al., Induced giant piezoelectricity in centrosymmetric oxides. Science 375, 653-657 (2022). DOI:10.1126 / science.abm7497. This is especially advantageous for thin films below 1-2 pm in thickness, where the DC bias is limited to a few volts.

[0082] The capillary tube section is formed in a flexible material. The flexible material is one or more materials that can be elastically deformed (reversibly) by stresses at room and body temperature. In an exemplary embodiment, the flexible material has a Young's modulus below 10 GPa and a shear modulus below 1 GPa.

[0083] In an exemplary embodiment, the flexible material is a polymeric material. In an exemplary embodiment, the flexible material comprises one or more of, polymers, polyimide, polytetrafluoroethylene, polyethene, polypropylene, polymethyl methacrylate (PMMA), polyvinyl chloride, polyamide, acrylonitrile butadiene styrene (ABS), polycarbonate, thermoplastics, and other medical safe plastics.

[0084] In an exemplary embodiment, the flexible material is one or more of glasses such as borosilicate, metallic alloys, hybrids, or covalent ceramics with stiffness below 10 (106m2s'2) or a Young's modulus below 10 GPa.

[0085] If the wall-thickness (t) of the capillary tube becomes too large relative to the height and width of the capillary tube, it becomes difficult for the strain exerted by the electrostrictive material layer to make a bulge in the inner side of the wall and thus reduce the inner height in the tube. In general, the thinner and more flexible the capillary tube wall is, the smaller strain is required to generate a given pumping in terms of flow rate and backpressure. Therefore, it is preferred that the wall-thickness is t < 3h, or preferably t < 2h.

[0086] In exemplary embodiments, the capillary tube has a wall thickness in the range t e [10pm ; 100pm], such as preferably in the range t e [20pm ; 70pm], The inner electrode 116 is arranged on at least both wide sides 112 of the capillary tube section 110. In an exemplary embodiment, the inner electrode 116 is formed directly on an inner or an outer surface of the capillary tube section 110.

[0087] One of the inner or outer electrodes may serve as a common electrode for more or all of the actuation elements. This common electrode may be grounded or held a bias voltage common for alle actuation elements. In exemplary embodiments the inner electrodes 116 of two or more actuation elements, such as preferably of all actuation elements, are provided by a common inner electrode arranged lengthwise on the capillary tube section 110. This is advantageous since it reduces and simplifies the wiring or connectivity to separate inner electrodes.

[0088] Similarly, the electrostrictive material layers 118 of two or more actuation elements can be provided by a common electrostrictive material layer arranged lengthwise on the capillary tube section 110.

[0089] The cross-sectional views of Figs. 4A-C illustrate a selection of different embodiments of the pP 108 with the inner electrode 116 of a given actuation element.

[0090] In exemplary embodiments, the inner electrode 116 of at least one actuation element, such as preferably all actuation elements, forms a closed (4A) or an open (4B) band around the capillary tube section 110, the band covering at least both wide sides 112 of the capillary tube section. In another exemplary embodiment illustrated in Fig. 4C, the inner electrode 116 of at least one actuation element, such as preferably all actuation elements, is arranged only on both wide sides 112 of the capillary tube section, in which case these are preferably electrically connected to have the same electric potential.

[0091] In the present description:

[0092] - a thin film refers to a material layer of pm thickness, i.e. a material layer having a thickness of less than 3 pm.

[0093] - a thick film refers to a material layer in the micron thickness, i.e. a material layer having a thickness between 3 and 1000pm.

[0094] - a bulk material refers to a material with a three-dimensional shape above the pm ranges, i.e. with geometrical features in the mm scale and above.

[0095] As indicated in Fig. 4A, the inner electrode 116 has thickness tie. The inner electrode can be a thin-film electrode. This is advantageous since the thinner the inner electrode, the easier it is for the strain of the electrostrictive material layer to be transferred to the inner wall of the capillary tube section.

[0096] The inner electrode may be a ceramic, metallic, or carbon-based electrode. In exemplary embodiments, the inner electrode 116 provides a low lateral (in-plane) electrical resistance, such as a resistivity smaller than < 2 Q cm. The outer electrode segments 120 are arranged on the electrostrictive material layer 118 on at least both wide sides 112 of the capillary tube section 110. In an exemplary embodiment, the outer electrode segments 120 are formed directly on the electrostrictive material layer 118.

[0097] The cross-sectional views of Figs. 4A-C illustrate a selection of different embodiments of the pP 108 with the outer electrode segment 120 of a given actuation element.

[0098] In exemplary embodiments, the outer electrode segment 120 of at least one actuation element, such as preferably all actuation elements, forms a closed (4A) or an open (4B) band around the capillary tube section 110, the band covering at least both wide sides 112 of the capillary tube section. In another exemplary embodiment illustrated in Fig. 4C, the outer electrode segment 120 of at least one actuation element, such as preferably all actuation elements, is arranged only on both wide sides 112 of the capillary tube section.

[0099] In preferred embodiments such as illustrated in Fig. 3B, both the inner electrode 116 and the electrostrictive material layer 118 of two or more, such as all, actuation elements can be provided by a common inner electrode layer and electrostrictive material layer arranged lengthwise on the capillary tube section. This is advantageous since no patterning or of these layers are needed during fabrication. This again means fewer and less complex fabrication steps, as well as an increased stability of the pP. In such embodiments, only the outer electrode segments need to be specific to each actuation element for each actuation element to be individually addressable by the driving signal. Thereby, the nomenclature previously introduced for the layout of actuation elements can be applied to the outer electrode segments 120. Hence, a center-to-center distance between adjacent outer electrode segments is c-c, a gap between adjacent outer electrode segments is g, and a length, ln, of outer electrode segment n in a direction along the length of the capillary tube segment is ln. If all outer electrode segments are dimensioned and formed uniformly, c-c = ln+ g-

[0100] Optimal outer electrode segment dimensions are a function of parameters including wall material and thickness of the capillary tube 110, thickness of inner electrode 116 and electrostrictive material layer 118, frequency f of the driving signal. In exemplary embodiments, such as with a polyimide capillary tube with wall thickness t e [25pm ; 40pm], preferred outer electrode segment dimensions are c-c e [1 mm ; 2 mm], g e [0,05 mm ; 1 mm], and lne [0.8 mm ; 2 mm].

[0101] As indicated in Fig. 4A, the outer electrode segment 120 has thickness toe. The outer electrode segments can be thin-film electrodes. This is advantageous since it reduces the size and weight of the pP. Alternatively, the outer electrode segments are thick-film electrodes. This is advantageous since the having a stiffer outer layer means that the strain of the electrostrictive material layer will be directed inwards, towards the inner wall of the capillary tube section. The outer electrode segments may be a ceramic, metallic, or carbon-based electrode.

[0102] The electrostrictive material layer 118 is arranged on the inner electrode 116 on at least both wide sides 112 of the capillary tube section 110. In an exemplary embodiment, the electrostrictive material layer 118 is formed directly on the inner electrode 116. One common electrostrictive material layer 118 arranged lengthwise on the capillary tube section 110 may serve as an electrostrictive material layer 118 for more or all of the actuation elements.

[0103] The cross-sectional views of Figs. 4A-C illustrate a selection of different embodiments of the pP 108 with the electrostrictive material layer 118 of a given actuation element.

[0104] In exemplary embodiments, the electrostrictive material layer 118 of at least one actuation element, such as preferably all actuation elements, forms a closed (4A) or an open (4B) band around the capillary tube section 110, the band covering at least both wide sides 112 of the capillary tube section. In another exemplary embodiment illustrated in Fig. 4C, the electrostrictive material layer 118 of at least one actuation element, such as preferably all actuation elements, is arranged only on both wide sides 112 of the capillary tube section.

[0105] The different layouts of the inner electrode 116, the electrostrictive material layer 118, and the outer electrode segment 120 described in relation to Figs. 4A-C may be combined. In an exemplary embodiment, the inner electrode 116 and the electrostrictive material layer 118 are formed as closed (4A) or open (4B) bands around the capillary tube section 110, whereas the outer electrode segments 120 are arranged only on both wide sides 112 of the capillary tube section. This is particularly advantageous in the embodiments wherein the inner electrode 116 and the electrostrictive material layer 118 are common for all actuation elements since the fabrication of these layers can be continuous or can be fabricated in without the need for patterning to define the actuation element. In such embodiments, the outer electrode segments 120 define the geometry and dimensions of the actuation elements, and their fabrication may require patterning or application only at the positions of the actuation elements.

[0106] The electrostrictive material layer comprises one or more electrostrictive layers of oxygendefective metal oxide. In an exemplary embodiment, the electrostrictive material layer comprises an electrostrictive thin film of doped cerium oxide (Ceria). In an exemplary embodiment, the electrostrictive material layer comprises one or more of Ca-doped ceria electrostrictors (CaCeO), Mg-doped ceria (MgCeO), Yb-doped ceria electrostrictors (YbCeO), and Zr-doped ceria electrostrictors (ZrCeO).

[0107] Oxygen-defective metal oxides are advantageous in that they can be deposited using physical vapor deposition at low temperatures, such as at or near room temperature, while still maintaining their electromechanical properties. This is because their electromechanical properties are not critically dependent on the crystallinity. This means that the oxygendefective metal oxides can be formed, such as deposited, on temperature-sensitive or degradable materials such as polymeric materials. The use of an electrostrictive layer of oxygen defective metal oxide provides a more efficient and more precise actuation of the capillary tube section than would be possible with other ceramic of polymeric actuators. This is due to at least the following:

[0108] Oxygen defective metal oxide electrostrictors have a large stroke - measured e.g. as strain per electric field strength - in comparison to conventional PZT and other leadbased piezoelectric and relaxor ferroelectric.

[0109] Oxygen defective metal oxide electrostrictors have low intrinsic capacitance, often in the pF range. This allows the actuation elements to be driven low powers and voltages than electromechanically active materials with higher intrinsic capacitance.

[0110] Since oxygen defective metal oxide electrostrictors may be deposited on temperature sensitive structures, the actuation elements can be made considerably smaller than PZT- based actuators.

[0111] In exemplary embodiments, the electrostrictive material layer is formed directly on the inner electrode which is formed directly on the capillary tube. The inner electrode thereby mechanically connects the electrostrictive material layer to the capillary tube. In exemplary embodiments, the electrostrictive material layer is deposited directly on an outer surface of the capillary tube, with the inner electrode being formed on an inner surface of the capillary tube.

[0112] The strain in the electrostrictive material layer of an actuation element, and thereby the reduction in the height h of the capillary tube section under the actuation element, is determined by the composition and thickness of the electrostrictive material layer and the strength of the electrical field provided by the driving signal.

[0113] As indicated in Fig. 4A, the electrostrictive material layer 118 has a thickness tes. In exemplary embodiments, the electrostrictive material layer has a thickness tese [1 pm ; 50 pm]. The thickness of the electrostrictive material layer depends on the amount of the mechanical energy required for pumping. The required minimum thickness tesincreases with the stiffness of the capillary tube (which is determined by the geometry and the flexible material properties), the viscosity of the liquid to be pumped, and the maximum pumping rate required.

[0114] An actuation element Enmay comprise more actuation elements stacked on top each other so that the strain of the stack is a sum of the strain provided by each element in the stack. In such actuation element stack, another electrode segment of one element may serve as the inner electrode of the next element lying atop thereof. Hence, in an exemplary embodiment, each actuation element comprises two or more two electrostrictive material layers stacked on at least both wide sides of the capillary tube section with intercalated outer electrode segments. This is advantageous since the actuation can be amplified while keeping the voltage constant, i.e. the electric field is augmented in the thinner layers. In an exemplary embodiment, actuation element Encomprises a thick-film-based actuator comprising and inner electrode 116, and electrostrictive material layer 118, and an outer electrode segment 120. This thick-film-based actuator may have dimensions as specified previously for an actuation element or an outer electrode segment and may be formed on or glued onto each wide side 112 of the capillary tube segment 110.

[0115] In both the TWpP and the PpP configurations, the various design parameters of the pP system are preferably finely adjusted to each other for the pP to be able to provide advantages such as a high delivery accuracy, low power consumption, small form factor, small dead volume, improved reliability, and high pumping efficiency in terms of flow rate and backpressure. Such design parameters comprise at least:

[0116] - the flexible material composition and the wall-thickness t of the capillary tube section;

[0117] - the amplitude A of the driving signals;

[0118] - an elastic modulus and a (polarization) electrostriction strain coefficient of the electrostrictive material;

[0119] - the layer thickness of the electrostrictive material layer; and

[0120] - the geometry and size of the top electrodes of each actuation element as well the spacing between and the number of the actuation elements

[0121] In one or more embodiments of the TWpP configuration, the design parameters are selected in unison to achieve amplitude S of the height variation in the capillary tube section to be 2S < 0,2h, such as 2S < 0,15h, such as 2S < 0,1 h.

[0122] Similarly, in one or more embodiments of the PpP configuration, the design parameters are selected in unison to achieve amplitude S of the height variation in the capillary tube section to be 2S = 0,5h, such as 2S « 0,5h, such as 2S > 0,48h or 2S > 0,45h.

[0123] In particular, for the PpP configuration, the driving signals may comprise two different driving signals having different voltage amplitudes (Awiand Aw?) being applied between the inner and outer electrode at opposing wide sides of the capillary tube section. In one or more embodiments, the two different driving signals are configured to generate waves of different amplitude (Swiand Sw?) in the opposing wide sides of the capillary tube section, with the amplitudes Awiand AW2 selected so that Swi+ SW2 = h, such as Swi+ SW2 « h, such as Swi+ SW2 > 0,95h or Swi+ SW2 > 0,9h.

[0124] Several pP systems, pP s, or capillary tube sections can be provided in series which can augment the pressure capability proportional to the number of pP systems, pP s, or capillary tube sections, while leaving flowrate unaltered. This can also be achieved by augmenting Nwave in one given pP.

[0125] Several pP systems, pP s, or capillary tube sections can be provided in parallel to augment the flowrate capability proportional to the number of pP systems, pP s, or capillary tube sections, while leaving pressure capability unaltered. This can also be achieved by augmenting the capillary tube width, w, in one given P.

[0126] Figure 6 is an illustration of an exemplary pP 600 with interface 106 for connection to the control unit (not shown) for provision of the driving signals to the actuation elements. The pP 600 has several capillary tube sections 110, each with actuation elements Enand electrical interface 106. The which capillary tubes 110 may be operated in unison or separately (in which case separate electrical interfaces 106 are required).

[0127] The pP 600 can be mounted on a platform of silicon, glass, or polymer, which provides easy integration with the control unit and other parts, such as the printed circuit board (PCB) and the other electronics in the pump device. In this embodiment of the pP 600 have layers 601 and 602 defining one or more internal volumes 603 from which the capillary tube sections 110 can draw liquid. Internal volume(s) 603 may be part of a first liquid interface configured to provide liquid communication between a first end of the capillary tube section(s) 110 and a receptacle (not shown) holding liquid to be pumped. The first liquid interface may also comprise one or more tubes or canals 604. In exemplary embodiments, tubes, or canals 604 may connect to separate internal volumes 603 so that different liquids can be pumped separately by separate capillary tube sections 110. In an alternative embodiment, internal volume 603 can be a mixing chamber for mixing different liquids from tubes or canals 604.

[0128] Capillary tubes suitable for the capillary tube section are commercially available. For example, flat polyimide capillaries are available in the market with several sizes, crosssections, lengths and surface roughness, and wall thickness. Polyimide capillaries manufactured by extrusion generally show high quality and low surface roughness and are produced at desired length.

[0129] The inner electrode and the electrostrictive material layer may be formed directly on the capillary tube section by physical vapor deposition at low temperatures where the flexible material of the capillary tube section is not damaged or compromised. In exemplary embodiments, the inner electrode and the electrostrictive material layer can be deposited on the capillary tube section by radio frequency magnetron sputtering (RF-MS) at room temperature.

[0130] The outer electrode can be defined either using lithography, screen-printing, or vacuum deposition through a shadow mask. In either case the capillary and the contacts manifest a single unit. The unit can be straight to curved (circular, flat to 3D spiral) or consists of a few sequential or parallel pumping sections.

[0131] The pP and pP system of the disclosure may be applied in a variety of different applications.

[0132] The travelling wave micro-pump system 100 described above can be used in a patch pump configured to be attached onto, or implanted in or under, the epidermis of a subject. Fig. 7 is an illustration of an exemplary patch pump 700 according to the disclosure, comprising a pP system as described above. The patch pump 700 is configured to be attached onto the epidermis 705 of a subject, such as by using a patch 704, such as an adhesive patch or bandage. In an alternative embodiment, the patch pump 700 is configured to be implanted in or under the epidermis 705 of a subject. In exemplary embodiments it may comprise one or more of:

[0133] - A power interface 706 configured to provide electrical power to the control unit from a power source 707 such as a battery.

[0134] - A first liquid interface 708 configured to provide liquid communication between a first end of the capillary tube section and a receptacle 709 holding liquid to be delivered to a subject. For the patch pump to be as small as possible, the receptacle 709 may be small, such as having a volume of 1cm3or smaller. In an exemplary embodiment, first liquid interface 708 and receptacle 709 can be safely connected and disconnected by the user, so that the receptacle 709 can be exchanged regularly, allowing for a smaller required volume of the receptacle 709.

[0135] - A second liquid interface 710 configured to provide liquid communication between a second end of the capillary tube section and a cannulated needle 711. Cannulated needle 711 serves to inject the liquid into the subject, such as into the blood or interstitial fluid of the subject. Cannulated needle 711 may be a microneedle or an array of microneedles.

[0136] A method for delivering a predetermined volume of liquid to a subject is described and illustrated in Fig. 7. The method comprises:

[0137] - providing a patch pump 600 and attaching the patch pump onto, or implanting the patch pump in or under, the epidermis 705 of a subject;

[0138] - connecting a power source 707 to the power interface 706;

[0139] - connecting a receptacle 709 holding a liquid to the first interface 708;

[0140] - connecting a cannulated needle 711 to the second interface 710;

[0141] - inserting a tip of the cannulated needle 711 into the subject; and

[0142] - programming the control unit 101 to apply the driving signal for a predetermined amount of time to deliver a predetermined volume of liquid from the receptacle 709 through the cannulated needle 711.

[0143] In addition to medical applications, the pump described can be used for any microfluidic applications in which continuous compact units with very low but precise pumping rate are required: e.g. lab on a chip, capillary electrophoresis, PCR amplification, DNA analysis, separation, and manipulation of cells. In all these applications the flows are of the order of a few pL / min at most, but precision and continuous flow are required. The main advantage of a pP proposed that it can be used in portable devices with tight energy budget.

[0144] The use of the terms “first”, “second”, “third” and “fourth”, “primary”, “secondary”, “tertiary” etc. does not imply any particular order but are included to identify individual elements. Moreover, the use of the terms “first”, “second”, “third” and “fourth”, “primary”, “secondary”, “tertiary” etc. does not denote any order or importance, but rather the terms “first”, “second”, “third” and “fourth”, “primary”, “secondary”, “tertiary” etc. are used to distinguish one element from another. Note that the words “first”, “second”, “third” and “fourth”, “primary”, “secondary”, “tertiary” etc. are used here and elsewhere for labelling purposes only and are not intended to denote any specific spatial or temporal ordering. Furthermore, the labelling of a first element does not imply the presence of a second element and vice versa.

[0145] Certain features discussed above as separate implementations can also be implemented in combination as a single implementation. Conversely, features described as a single implementation can also be implemented in multiple implementations separately or in any suitable sub-combination. Moreover, although features may be described above as acting in certain combinations, one or more features from a claimed combination can, in some cases, be excised from the combination, and the combination may be claimed as any subcombination or variation of any sub-combination.

[0146] It is to be noted that the word "based on" may be seen as “as a function of’ and / or “derived from”. The terms “based on” and “as a function of” can be used interchangeably. For example, a parameter determined “based on” a data set can be seen as a parameter determined “as a function of” the data set. In other words, the parameter may be an output of one or more functions with the data set as an input.

[0147] It should further be noted that any reference signs do not limit the scope of the claims, that the examples may be implemented at least in part by means of both hardware and software, and that several "means", "units" or "devices" may be represented by the same item of hardware.

[0148] Language of degree used herein, such as the terms “approximately,” “about,” “generally,” and “substantially” as used herein represent a value, amount, or characteristic close to the stated value, amount, or characteristic that still performs a desired function or achieves a desired result. For example, the terms “approximately”, “about”, “generally,” and “substantially” may refer to a dimension or a flow amount that is within less than or equal to 10% of, within less than or equal to 5% of, within less than or equal to 1% of, within less than or equal to 0.1% of, and within less than or equal to 0.01% of the stated dimension or flow.

[0149] Although features have been shown and described, it will be understood that they are not intended to limit the claimed disclosure, and it will be made obvious to those skilled in the art that various changes and modifications may be made without departing from the scope of the claimed disclosure. The specification and drawings are, accordingly, to be regarded in an illustrative rather than restrictive sense.

Claims

CLAIMS1 . A micro-pump system comprising: a flat capillary tube section having length (L), inner width (w), and inner height (h), where w e [0,5mm ; 10mm], h e [0.05mm ; 0.1 mm], L > 10w, and w > 5h, the capillary tube section being formed in a flexible material with both wide sides of the capillary tube section having wall-thickness (t) with t < 3h;Nact separate actuation elements En, where n = 1 , 2, ... Nact > 3, positioned successively along the length of the capillary tube section and in continuous mechanical contact with the capillary tube section, each actuation element comprising:- an inner electrode arranged on at least both wide sides of the capillary tube section;- an electrostrictive material layer arranged on the inner electrode on at least both wide sides of the capillary tube section;- an outer electrode segment arranged on the electrostrictive material layer on at least both wide sides of the capillary tube section, each outer electrode segment being individually addressable by a driving signal; and a control unit comprising an electronic processor and an electric signal generator with the control unit being configured and connected to generate and apply driving signals between the inner electrode and the outer electrode segment of the actuation elements to impose an electrical field on the electrostrictive material layer leading to a strain of the actuation element and part of the capillary tube section, the driving signals having voltage amplitude (A) and frequency (f), and a driving signal for actuation element Enhaving a phase (n) as a function of time (t) and relative position of actuation element Enfor the driving signals to generate a wave of amplitude (S) travelling in a longitudinal direction of the capillary tube section; wherein the driving signal amplitude A is selected so that 2S < 0,5h; and wherein the electrostrictive material layer is one or more electrostrictive layers of oxygendefective metal oxide.

2. The micro-pump system according to claim 1 , wherein the flexible material is a polymeric material.

3. The micro-pump system according to claim 2, wherein the flexible material of the flat capillary tube comprises one or more of, polymers, polyimide, polytetrafluoroethylene,polyethene, polypropylene, polymethyl methacrylate, polyvinyl chloride, polyamide, acrylonitrile butadiene styrene (ABS), polycarbonate and other medical safe plastics.

4. The micro-pump system according to any of the preceding claims, wherein each actuation element comprises two or more two electrostrictive material layers stacked on at least both wide sides of the capillary tube section with intercalated outer electrode segments.

5. The micro-pump system according to any of the preceding claims, wherein:Nact is related to a number, NWaVe, of waves to be travelling in the capillary tube section at one time by:Nact = N wave X N phase, where NPhaSe indicates the number of actuation elements used to generate one wave; each actuation element is supplied with the driving voltage Vn(t)Vn(t) = A exp(l 2n(nNwave / Nact- ft)), where NPhaSe e (3, 4) and NWave is an integer.

6. The micro-pump system according to any of the preceding claims, wherein a center-to- center distance between outer electrode segments of adjacent actuation elements is xn- xn-i e [1 mm ; 2 mm] and a gap between the outer electrode segments of adjacent actuation elements is smaller than 1 mm.

7. The micro-pump system according to any of the preceding claims, wherein a length, / n, of an outer electrode segment of actuation element Enin a direction along the length of the capillary tube segment is lne [0.8 mm ; 2 mm],8. The micro-pump system according to any of the preceding claims, wherein the inner electrode of at least one actuation element forms a closed or an open band around the capillary tube section, the band covering at least both wide sides of the capillary tube section.

9. The micro-pump system according to any of the preceding claims, wherein the electrostrictive material layer of at least one actuation element forms a closed or an open band around the capillary tube section, the band covering at least both flat sides of the capillary tube section.

10. The micro-pump system according to any of the preceding claims, wherein the electrostrictive material is comprised in a thick-film-based actuator formed on or glued onto the capillary.11 . The micro-pump system according to any of the preceding claims, wherein the electrostrictive material layer is an electrostrictive thin-film of doped cerium oxide (Ceria), comprising one or more of Ca-doped ceria electrostrictors (CaCeO), Mg-doped ceria (MgCeO), Yb-doped ceria electrostrictors (YbCeO), and Zr-doped ceria electrostrictors (ZrCeO).

12. The micro-pump system according to any of the preceding claims configured to operate as a travelling wave micro-pump (TWpP) system, wherein the driving signal amplitude A is selected so that 2S < 0,2h13. The micro-pump system according to any of claims 1-11 configured to operate as a peristaltic micro-pump (PpP) system, wherein the driving signal amplitude A is selected so that S = 0,5h.

14. The micro-pump system according to any of claims 1-11 configured to operate as a peristaltic micro-pump (PpP) system, wherein the driving signals comprise two different driving signals having different voltage amplitudes (Awiand Aw?) being applied between the inner and outer electrode at opposing wide sides of the capillary tube section, the two different driving signals being configured to generate waves of different amplitude (Swiand Sw?) in the opposing wide sides of the capillary tube section; and wherein the amplitudes Awiand AW2 of the two driving signals are selected so that Swi+ SW2 = h.

15. A use of a micro-pump system according to any of claims 1 through 14 in a patch pump configured to be attached onto, or implanted in or under, the epidermis of a subject.

16. A patch pump configured to be attached onto, or implanted in or under, the epidermis of a subject, comprising:- a micro-pump system according to any of claims 1 through 14;- a power interface configured to provide electrical power from a power source to the control unit;- a first liquid interface configured to provide liquid communication between a first end of the capillary tube section and a receptacle holding a liquid to be delivered to a subject; and- a second liquid interface configured to provide liquid communication between a second end of the capillary tube section and a cannulated needle.

17. A method for delivering a predetermined volume of liquid to a subject, the method comprising:- providing a patch pump according to claim 16 and attaching the patch pump onto, or implanting the patch pump in or under, the epidermis of a subject;- connecting a power source to the power interface;- connecting a receptacle holding a liquid to the first liquid interface;- connecting a cannulated needle to the second liquid interface;- inserting a tip of the cannulated needle into the subject; and- programming the control unit to apply the driving signal for a predetermined amount of time to deliver a predetermined volume of liquid from the receptacle through the cannulated needle.

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