The present invention resides in the field of mechanical engineering, in particular precision engineering, and relates to rotors for fluid pumps.

Rotary pumps are common knowledge but these are constantly being improved, in particular for special applications. Thus axial pumps have become known which have a rotor conveying fluid in the axial direction in a housing, rotor and housing being deformable, advantageously compressible, in order to bring these before operation to a desired place of use which is difficult to access and in order to decompress and operate them there.

Such pumps are used for example in medicine in microconstruction form in order to be introduced into the body of a patient, for example via the bloodstream, and to be operated there either in a blood vessel or in a ventricle.

The pumps can be compressed such that they can be pushed through the blood vessel and then possibly decompressed in a larger body cavity in order to bring the rotor to unfold and to achieve a high conveying power.

A compressible rotor is known for example from U.S. Pat. No. 6,860,713.

Another rotor is known from U.S. Pat. No. 7,393,181 B2. The known solutions are based either on the elasticity and deformability of the material of the rotor or on mechanical constructions, such as the provision of bent places or joints for folding and unfolding the individual components.

Such constructions often have the disadvantage that the compressibility is limited since for example the hub of a rotor remains unchanged, that complex joints must be provided which are stabilised during operation and that partially super-elastic materials are used, such as memory alloys which change their shape as a function of the ambient temperature.

These constructions often make the use of composite materials necessary, and it is difficult, during construction of support constructions, not to impede the flow of the fluid to be conveyed and possibly to preclude as far as possible also damage to the fluid. This is important in particular when conveying blood which contains highly functional and also mechanically susceptible components.

The object underlying the invention against the background of the state of the art is to produce a rotor in the simplest possible manner, which has a constructionally simple structure, is compressible reversibly to a high degree and is reliable in operation.

The object is achieved according to the invention by the features of patent claim1.

The rotor according to the invention for a fluid pump has at least one blade and at least one deformable cavity which is filled or can be filled with a fluid.

As a result, a volume compressibility of the rotor is produced, which leads per se, during compression, already to a reduction in the rotor volume and possibly the rotor diameter. In addition, the various components of the rotor, such as for example blades, can still be bent and pressed in the direction of the rotor axis in order to reduce the diameter further.

The rotor is hence distinguished by a material mixture or a material which can be converted by compression from a first, lower density or from a first, lower specific weight to a second, higher density or a higher specific weight. The cavities can thereby be closed and filled with a gas, such as for example air or nitrogen, or a noble gas or another bioinert gas which can be compressed easily in volume by pressure.

Such closed cavities tend to expand again in the absence of an external pressure force due to the gas elasticity so that the rotor, as soon as it is brought to the place of use, can unfold again automatically. At least the unfolding movement is assisted however by the gas elasticity.

In addition, also gas lines to the rotor can however by provided, which gas lines end in one or more cavities and actively allow the cavities to be pumped up. The gas for the compression can possibly also be suctioned out via the same lines.

Likewise, the operation can take place with a liquid if this is introduced into the cavities. If a liquid is situated in the cavities, then this is normally very much less compressible but, due to suitable choice of the viscosity in cooperation with the remaining constructional parts of the rotor, it can enable high moveability and hence compressibility and nevertheless support a certain rotor stability during operation due to the incompressibility after unfolding of the rotor.

The cavities can also have an open design, hence high compressibility likewise being provided. The material which delimits the cavities must then have a corresponding elastic configuration. This can be provided for example with an open-pore foam.

The invention can also be implemented advantageously by the cavity/cavities being at least partially delimited by a partially permeable membrane.

For this purpose, a body consisting of an open-pore foam can be sealed at the outside thereof at least partially by a semipermeable membrane or a closed-pore foam can consist of a partially permeable material. Through the membranes, a material transport can be respectively effected specifically, which material transport fills or empties the cavity/cavities and hence effects or assists expansion, compression of the body.

A cavity can be filled with a liquid which, together with the membrane used and as a function of the liquid in which the pump can be inserted, in particular human blood, allows diffusion into the cavity/cavities as a result of osmosis, which leads to an increase in pressure and to pumping-up of the rotor.

Likewise, also materials can be used as cavity-delimiting material or as a filler of the cavities, which, after coming in contact with the liquid to be conveyed, lead to swelling processes as a result of absorption of the liquid and hence assist decompression of the rotor via an increase in volume.

As partially permeable membrane for delimiting cavities, there can be used, according to the used filling materials for the cavities and the materials which are intended to be allowed through or held back, membranes of microfiltration (0.5-0.1 μm particle size), ultrafiltration (0.1-0.01 μm particle size) and nanofiltration (1-10 nm). Independently of the particle size, basically biological or synthetic membrane materials can be used (as biological materials, for example Cuprophan, Hemophan or cellulose triacetate, as synthetic membrane, for example Teflon or Goretex.

Synthetic materials in general have a higher water permeability and are themselves often hydrophobic. There can be used as synthetic materials, polysylphone, polyamide, polyacrylonitrile and also copolymers thereof and also polymethylmethacrylates, polytetrafluoroethylene and derivatives thereof.

High-flux membranes are advantageously used, which allow through molecules up to a molecular weight of 50,000 Dalton and which ensure rapid material transport.

Advantageously, the material is chosen such that it retains germs/bacteria/microorganisms preventing contamination or infection.

In the case of an osmosis process, filling the cavities with a salt or a salt solution, the salt concentration of which is higher than that of the liquids to be conveyed, is possible.

Advantageously, it can also be provided that at least the predominant part of the cavities is/are surrounded by solid material of the rotor and connected to each other via openings. In this case, during compression, a fluid transport can take place via the cavities and possibly also out of the rotor so that the corresponding cavities can be easily compressed entirely.

The rotor can consist for example partially of a porous material, such as foam, in particular polyurethane. Such a foam can be open- or closed-pore. In the case of an open-pore foam, the elasticity is based on the supporting material which surrounds the pores and moves after compression by itself back into its original form, the gas or fluid being able to flow back into the pores, and/or based on the elasticity of a filler gas if the open-pore foam body is surrounded entirely by an impermeable or partially permeable outer layer. Due to the limited flow cross-sections of the connections of the cavities/pores to each other, a time constant in the compression/decompression can be chosen within specific limits. This can ensure, during operation of the pump, that sudden deformations of the rotor due to irregular mechanical loading are counteracted.

The invention can advantageously also provide that the rotor has at least one cavity which has a greater extension in a first direction than in the directions essentially perpendicular thereto.

Provision of such anisotropic cavities, with correct positioning, also permits production of anisotropic mechanical properties of the rotor. As a result, it is possible to design the latter to be compressible radially in a simple manner and with low force expenditure without the same slight deformability occurring during operation due to the dynamic resistance of the fluid to be conveyed.

During operation, the rotor is hence stabilised relative to the forces acting axially and in the circumferential direction whilst it offers relatively low resistances to radial compression.

The corresponding cavities can be configured, in cross-section, to be for example round, hexagonal, triangular or square and have for example a strand shape so that their cross-section is essentially the same overall along it length. As a result, symmetry which serves for stability of the rotor is produced.

Corresponding cavities can be provided for example particularly advantageously in at least one blade since said cavities carry the largest proportion of the diameter reduction of the rotor, on the one hand, and, on the other hand, are subjected to the highest dynamic forces during operation.

However, the blade can have such a stable configuration that it is self-supporting and a hub can even be dispensed with. Such a blade can be configured for example as a flat body, which is bent in a spiral about an axis, in particular made of foam. For example, for production thereof, a polyurethane foam plate can be cut, as desired, in a flat shape, thereafter rotated about an axis and then hardened or stiffened. The shape of the blade is hence stabilised but an elastic compressibility is provided furthermore.

However it can also be provided to produce such a blade or an entire rotor by spraying a foam into a pre-manufactured mould.

The invention can also be used with rotors provided with hubs and, in this case, the hub body in particular can have the cavities according to the invention or be produced at least partially from a foam.

If anisotropic cavities are provided in the rotor, then it is advantageous to align these in the direction of their greatest stability along the force/stress extension lines which arise within the rotor during operation.

For example, the longitudinal axes of strand-shaped cavities, such as for example honeycomb bodies, can be orientated perpendicular to the blade surface in order to support forces acting in this direction or circumferential direction.

The object of producing a rotor which has as simple a construction as possible, which is compressible to a high degree (in particular reversibly) and is reliable in operation is achieved in addition by a compressible rotor for a fluid pump having at least one blade, the rotor being constructed such that it can adopt a compressed and a decompressed state and the average change in density of the rotor material between compressed and decompressed state is at least 10%.

It is hereby important, as a delimitation from the state of the art, that the volume change occurs above all also by changes in the density of the rotor material. What is involved here therefore is not merely elastic deformation processes in which the average density of the rotor material is essentially constant. The mentioned change in density is “temperature-adjusted”, i.e. it is the change in density with a warm rotor at e.g. 36° C. which is the basis for the compressed and decompressed state.

In order to produce this change in density, the approaches mentioned in this application can be chosen. Both reversible and irreversible methods are hereby considered. These are e.g. osmotic processes, however also processes in which open-pore or closed-pore foam is used.

The change in density of the rotor need not be uniform at all places, for example it is possible that, in the region of a hub or of the blade, a smaller change in density is achieved because of the possibly desired higher rigidity there and, in the region of a virtual “joint” between huh and blade, a stronger compression takes place.

The average change in density of the entire rotor can preferably also be even greater, for example at least 15%, alternatively at least 20%. With respect to a plastic material, starting values, by way of example, for the density are 0.01 . . . 2 g/cm3in the decompressed state and 0.05 . . . 3 g/cm3in the compressed state.

The invention relates, apart from to a rotor of the described type, also to a fluid pump having such a rotor, in which a compressible housing surrounding the rotor is provided.

According to the invention, the housing can consist at least partially also of a material which has cavities, in particular a foam, for example polyurethane. In this way, the housing can be compressed and decompressed simply together with the rotor.

