Patent Publication Number: US-2021161381-A1

Title: Medical implant, assembly for implanting the medical implant and assembly for detecting an intracorporeal movement pattern with the medical implant

Description:
TECHNICAL FIELD 
     The invention relates to a medical implant with a structure which is made of at least one biocompatible material, an assembly for implanting the medical implant, and an assembly for detecting an intracorporeal movement pattern with the medical implant. More particularly, the aim is to detect at least one physiological parameter, preferably the human or animal blood pressure, by means of the medical implant. 
     PRIOR ART 
     The metrological detection of physiological parameters is usual and commonly practised in medical technology. An example of such detection of a physiological parameter is the continuous measurement of arterial blood pressure. A device of this type and corresponding detection method, which without the known inflatable arm cuff manages with the pressure sensor functioning in accordance with the Riva-Rocci principle, are, for example, described in U.S. Pat. No. 5,241,964. Here, two non-invasive ultrasonic Doppler sensors are applied extracorporeally via a larger artery. The blood flow signals measured therewith are then used to parametrically characterise a simplified mathematical empirical model of the artery. The thereby determined so-called resonance frequency of the model correlates with the blood pressure. A conventional cuff measurement calibrates the system at irregular intervals to the blood pressure. 
     DE 198 29 544 C1 also describes an assembly for non-invasive blood pressure measurement. By means of ultrasound or laser Doppler technology, a parameter linked to the blood flow or blood flow rate is measured, for example. Signal processing downstream of measurement recording includes filtering in order to remove artefacts and other interfering factors. 
     On the one hand, problematic for recording blood pressure by means of optical or ultrasound-based pulse wave sensors as precisely as possible, is the sensitivity with regard to correct spatial extracorporeal application and orientation of the relevant sensors relative to the blood-conveying vascular regions. Even slight losses of adjustment in the sensor orientation relative to a blood vessel can make it impossible to reliably record the blood pressure. On the other hand, the detectable signal levels, which are of relevance for recording blood pressure, are only very low and therefore require laborious amplification, filtering and signal evaluation. Costly system-related work is required for this. 
     DESCRIPTION OF THE INVENTION 
     The object of the invention is to largely eliminate the aforementioned drawbacks in the detection of medically relevant physiological parameters, such as, in particular, in the measurement of the blood pressure of a person or an animal through the transcutaneous transmission of ultrasonic waves as well as the detection of intracorporeally reflected ultrasonic wave portions. Firstly, the robustness of the measurement to be carried out against loss of alignment of the components required for emitting and receiving ultrasonic waves must be significantly improved, and secondly, measures must be taken to reduce the metrological complexity and as well as the effort associated with signal evaluation. 
     An assembly according to the invention is the subject matter of claim  1 , which relates to a medical implant which can be applied intracorporeally by means of an assembly according to claim  18 . The subject matter of claim  21  is an assembly for detecting an intracorporeal movement pattern using the medical implant, through which it is possible to record medically relevant physiological parameters. Features that advantageously further develop the inventive concept are the subject matter of the sub-claims and can also be found in the further description, more particularly with reference the examples of embodiment. 
     The idea forming the basis of the invention relates to a structure, made of biocompatible material, which, preferably, by means of a cannula assembly, is intracorporeally implantable in a transcutaneous manner, preferably in the immediate vicinity of a blood vessel, and which within the body is able to expand by itself and, if necessary, through the application of external force or energy fields, or through fluid mechanical support, in such a way that the structure forms a so-called effective operating surface on which the ultrasonic waves are reflected. The structure made of biocompatible material also has an inherent elasticity, which is comparable with the inherent elasticity of organ vascular walls, in particular that of the wall of the blood vessel relative to which the implanted structure is arranged. Through the choice of material of the biocompatible structure as well as its geometric shape and intracorporeal positioning with regard to a blood vessel, the biocompatible structure, and, in particular, its effective operating surface, undergoes spatial deformations which are caused by natural pulse waves, which in turn are transmitted, through the pulsatile blood pressure in the blood vessel and the vascular wall expanding and contracting in a pulsatile manner, into parts of the body that are directly extravasally adjacent to the vascular wall. Through the macroscopically selected size of the effective operating surface, the latter is able to reflect a quite considerable portion of the ultrasonic waves subcutaneously transmitted by means of an extracorporeally positioned sonographic device. Through this, the requirements relating to precise spatial positioning of the sonographic device relative to the blood vessel are considerably reduced in contrast to the known methods which require direct recording of the blood vessel. In addition, the ultrasonic waves reflected on the effective operating surface create ultrasonic signals with a much higher signal level in the sonographic device, through which the S/N ratio is improved and the amount of subsequent signal processing and evaluation work can be reduced. 
     The medical implant according to the solution, with a structure made of at least one biocompatible material, is therefore characterised by the combination of the following features: The structure made of biocompatible material can be converted from a first spatially compact state into a second spatially deployed, flexibly deformable state in which the deployed structure has an effective operating surface which is flexibly deformable and can at least partially reflect ultrasonic waves. The biocompatible material of the structure has a modulus of elasticity that corresponds to that of a blood vessel and is in an order of magnitude of between 10 5  Nm −2  and 10 7  Nm −2 . Additionally, at least in one region the structure has an acoustic impedance of more than 1.63×10 6  kg/m 2 s/. In the second state, in which the structure made of biocompatible material assumes a spatially deployed shape, the structure has an effective operating surface which is flexibly deformable and can at least partially reflect ultrasonic waves. 
     Preferably the structure is configured in the form of a film, a mesh, a sponge or tangled structure and due to its materially elastic properties assumes a ball or capsule-shaped spatial form in the first state, which allows introduction and passing through by means of a medical hollow cannula which has a cannula size of between 10 G and 30 G, preferably 17 G and 25 G. This means that the structure, compacted in the first state, has a diameter dimension corresponding to the internal diameter of the hollow cannula. In an appropriate manner, in the first state the structure assumes an elongated, ellipsoidal or cylindrical spatial shape, the cylinder diameter of which corresponds to the inner diameter of the respectively selected hollow cannula and in this form can be distally pushed or moved through the hollow cannula by means of a stylet or a means on which pressure can be exerted. Instead of using a stylet, it is conceivable to proximally apply a pressurised fluid, e.g. saline solution, to the hollow cannula in order to convey the compacted structure within the hollow cannula through the distal opening. 
     Preferably the structure expands by itself from its compacted or compressed first state into the second due to elastic restoring forces inherent in the material. The process of expansion or enlargement into the expanded or unfolded state can be supported by additional external influences. The process of enlargement from the first into the second state takes place within the intracorporeal, moist environment which is able to support the “unfolding process”. In a preferred example of embodiment, the biocompatible material has hygroscopic properties and through the absorption of water is able to effectively support the unfolding or expansion of the structure. Alternatively, or in combination with the measures described above, through the the application of an external force or energy field which can be generated by means of an extracorporeally arranged force field generator, an effect is achieved which supports the conversion process from the first into the second state. For this, in a preferred example of embodiment, the structure made of biocompatible material has at least one means and/or a material property, through which the structure directly or indirectly comes to interact with the extracorporeally applied force field so that a force moment can be generated that changes the spatial shape and/or spatial position of the structure, can support the transformation process from the first into the second state, and/or allows positioning of the structure that has been intracorporeally applied and converted into the second state. 
     The means to be applied to or integrated into the structure must be suitably selected depending on the nature of the force field, for example in the form of a magnetic field, electrical field, acoustic field or a caloric field, i.e. a temperature field. In the case of a magnetic field, magnetic or magnetisable sections that are applied in or on the structure are suitable. In the case of an electrical field, electrically conducting material sections within the structure are used, which interact with an electrodynamic or electrostatic field. In the case of an acoustic force field, means that are locally applied to the structure and preferably absorb or reflect sound waves are deployed in order to be able to functionally utilise a force moment acting on the structure through sound impulse transmission. Suitable in the case of an extracorporeally applied caloric force field are, for example, bimetallic or bimetallically-acting materials or material combinations which, integrated into or applied to the structure, can result in local structural deformations. 
     Conversion materials or so-called smart materials, for example materials with shape memory, are also suitable for integration into or application on the structure in order to generate deformation forces with the aid of an externally applied force field. 
     Other suitable materials for implementing an implant according to the solution are, for example, metamaterials or hybrid material combinations of metamaterial and biological tissue material and/or biocompatible polymers. Also suitable are film-like substrates made of or at least with superficially provided nanostructures, e.g. in the form of nanotubes or nanograss. Such nano-structures, usually made of carbon or titanium alloys (e.g. Ti6Al4V, TiO2) have specially conditionable physical properties which can be influenced in an appropriate manner in the presence of energy fields. 
     All materials added to or integrated into the structure, must meet the selection criterion of biocompatibility that is applicable for medical implants. 
     Typically, the structure is initially present in the second state, i.e. in a spatially deployed, non-compressed state or in a non-compacted form. Starting from this state, the structure is preferably converted into the first state through folding, compressing and/or rolling, and placed in a hollow cannula for implantation. 
     After corresponding separation of the structure from the hollow cannula, the structure unfolds or expands and forms the effective operating surface on which the ultrasonic waves are reflected. The effective operating surface has a surface area of at least 0.2 mm 2  and a maximum of 500 mm 2 . In the implanted state, the effective operating surface, which is preferably planar, in one piece and continuous, is orientated relative to a blood vessel so that the pulse waves coming from the blood vessels are transmitted through the effective operating surface as orthogonally as possible, i.e. the direction of propagation of the pulse waves preferably forms an angle α of 90°±30° with the effective operating surface. In this way the effective operating surface of the implanted structure is dynamically deformed as a function of the pulse waves. 
     If diagnostic ultrasonic waves, which are transmitted via the skin, i.e. subcutaneously, by means of a known sonography device, strike the effective operating surface, at least one portion of the ultrasonic waves striking the effective operating surface is reflected and received by the sonography device. The ultrasonic waves received by the sonography device contain information about the respective state of deformation of the effective operating surface of the implanted structure which changes over time and is correlated with the blood pressure prevailing in the blood vessel. In the context of measurement calibration, carried out, for example, using a known inflatable arm cuff with a pressure sensor operating in accordance with the Riva-Rocci principle, the ultrasonic signals received by means of the sonography device can be assigned to quantitative blood pressure values. 
     In contrast to an aforementioned planar, film-like substrate, in a further preferred form, the structure made of biocompatible material is in the form of a mesh, a sponge or a tangled structure, which in the spatially expanded second state has an effective operating surface that is in projection along a spatial direction, ideally coinciding with the direction of propagation of the ultrasonic waves, on the expanded structure in the second state. For example, in the case of a spherical tangled structure, the effective operating surface is a circular area with a diameter that corresponds to the diameter of the spatial tangled structure. 
     Advantageously, however, the effective operating surface is not necessarily structured and is preferably formed in an undulating or zig-zag manner, wherein the predetermined structuring remains essentially intact despite the deformation caused by the pulse waves and thereby imprints the ultrasonic waves reflected on the effective operating surface with a typical signature, through which largely fault-free signal detection is made possible and fault signal portions arising from possible intracorporeal interfering reflexes and which do not have a characteristic signature of this type can be recognised and invalidated when evaluating the signal. 
     In order to ensure that in the second state after appropriate unfolding and spatial positioning, the implanted structure remains in situ largely unchanged and does not begin to rove around, a preferred example of embodiment envisages at least one anchoring element on the structure which can anchor itself mechanically in immediately surrounding tissue. For example, the anchoring element is formed in the manner a barb-shaped section directly or indirectly on the structure. 
     Another preferred embodiment envisages additional material areas on the structure which reflect electromagnetic waves, preferably in the form of radar waves. Through this the function of the structure as a pure ultrasonic wave reflector is supplemented by a further function which is based on the interaction with electromagnetic waves. 
     In combination with or alternatively to the aforementioned advantageous forms of embodiment, the structure has at least one structural area with an RFID, interdigital electrode and/or electrical coil structure, via which electrical energy as well as signal-based information can be transmitted in a contactless manner between the implanted structure and an extracorporeal transmitting and receiving unit. 
     In a further preferred form of embodiment, the implantable structure also serves as a support for at least one functional material which can be applied to or integrated into the structure made of biocompatible material. The functional material is preferably a pharmaceutical active substance, which in the implanted state of the structure, can be locally released, preferably in accordance with a determined dosing pattern. The release of the active substance can be predefined by time and/or individually influenced by means of extracorporeally applicable force fields. 
     Alternatively, or in combination with a pharmaceutical active substance, in a further form of embodiment, a biocompatible adhesive acts as a functional substance to immobilise the structure and permanently position it at a particular intracorporeal point with a defined, predetermined spatial position. The biocompatible adhesive is applied to the structure in such a way that in the spatially expanded state of the structure the adhesive superficially comes into contact with adjacent tissue surfaces, on which a durable joint connection is formed. 
     As has already been mentioned, hygroscopic material acts as a functional substance introduced into the structure made of biocompatible material as a means to support unfolding or expansion through the absorption of tissue fluid. 
     To implant the medical implant a hollow cannula is used, which is adapted and designed to be suitable for the subcutaneous implantation of the medical implant in such a way that the structure, present in the first state, can be introduced into or accommodated within the hollow cannula, in order to then distally apply it intracorporeally through the skin from the hollow cannula. Preferably, a pushing means configured as a stylet is used, with which the structure positioned within the hollow cannula can be distally precisely pushed out of the hollow cannula and positioned by an operator. As an alternative to the use of a stylet, a pressurisable fluid reservoir can be connected proximally to the hollow cannula, by means of which a biocompatible fluid, for example a saline solution, conveys the structure placed in the hollow cannula in the distal direction under the effect of pressure, in order to ultimately apply it intracorporeally. The quantity of fluid additionally releasable intracorporeally in a dosed manner via the hollow cannular, can support the intracorporeal unfolding or expansion of the compressed structure and is then resorbed by the surrounding tissue. 
     If the structure in an aforementioned, preferred form of embodiment has a means that can interact with an externally or extracorporeally applied force field, an extracorporeally arranged generator is required, which can generate a force field of the following type: magnetic field, electrical field, caloric field and/or acoustic field. Preferably the generator is able to generate the force field variably in relation to the field strength and/or spatial field distribution. 
     The medical implant designed in accordance with the solution is a partial component of an assembly for detecting an intracorporeal movement pattern, which also envisages a sonography device, which is known per se, that is positioned extracorporeally in such a way that the ultrasonic waves generated by the sonography device strike the effective operating surface of the intracorporeally applied medical implant and are at least partially reflected thereon. By detecting the ultrasonic waves reflected on the effective operating surface, changes in the spatial between the effective operating surface and the sonography device can be recorded which can be used to determine an intracorporeal movement pattern. In particular, in this way, after appropriate calibration of the measurements obtained with the sonography device, it is possible to record the blood pressure and metrologically monitor its change over time. The assembly according to the solution thus makes long-term recording and monitoring of the blood pressure possible without any additional components which have an unpleasant effect on the patients, for example arm pressure cuffs. 
     Advantageously, the assembly for detecting the intracorporeal movement pattern also envisages an extracorporeally arranged transmitting and receiving unit for a electromagnetic field, the electromagnetic field of which interacts with an RFID, interdigital electrode and/or electrical coil structure applied on the implanted structure. 
    
    
     
       BRIEF DESCRIPTION OF THE INVENTION 
       As an example, the invention will be described below, without restricting the general inventive concept, by way of examples of embodiment with reference to the drawings. Here: 
         FIGS. 1   a, b, c  show a structure made of biocompatible material for a medical implant, 
         FIG. 2  shows an assembly for implanting the medical implant, 
         FIGS. 3 a, b    show variants of embodiments for unfolding the medical implant, 
         FIG. 4  shows a medical implant with integrated fluid channels and 
         FIG. 5  shows an assembly for detecting an intracorporeal movement pattern 
     
    
    
     WAYS OF IMPLEMENTING THE INVENTION, INDUSTRIAL APPLICABILITY 
       FIG. 1 a    shows a medical implant  1  in a spatially compressed spatial form which is suitable for applying the medical implant  1  by way of a hollow cannula  2 , see  FIG. 2 , for the purpose of intracorporeal positioning.  FIG. 2  shows a pointed device for introducing the medical implant  1  by way of a cannula  2  into a human or animal body (not shown). The introduction of the medical implant  1  can take place using a carrier fluid, for example, saline, or in dry form. As part of the implantation procedure, the hollow cannula  2  should be orientated close to a large, arterial blood vessel, as parallel as possible to this vessel, for the purpose of injecting the implant  1  according to the solution. 
     As shown in  FIG. 1 a   , the compressed medical implant  1  comprises a support rod  3 , preferably in the form of a polysaccharide rod, along which a planar, film-like structure  4  can be applied which can be configured in one part or in several parts. By retracting the cannula  2  and pushing out the medical implant  1 , the planar, film-like structure  4  unfolds radially in a fan-like manner from the support rod  3  in accordance with  FIG. 1   b.    
     The planar, film-like structure  4  of the medical implant  1  preferably comprises a flexible polymer film, on the surface of which a coating  5  of ultrasound-reflecting material is applied. The ultrasound-reflecting material can also have additional electromagnetic wave-reflecting properties. Preferably nanostructure material in the form of nanotubes or nanograss, for example in the form of carbon nanotubes or titanium oxide nanograss, is suitable for this, see also  FIG. 1   c.    
     For improved unfolding of the planar medical implant  1  from the compressed stated into the unfolded state, a form of embodiment illustrated in  FIG. 3 a, b    envisages a film-like structure  4  of the medical implant  1  which is interspersed with at least one fluid channel  6 , preferably oil channel. The preferably oil-filled channel  6  generates a mechanical pre-tensioning, which is held in the compressed form of the medical implant  1  with additional threads  7 , which connect the planar, film-like structures  4  of the medical implant  1  with the support rod  3 , see  FIG. 3 a   . As soon as the medical implant  1  is located within the body, the holding threads  7  are resorbed, so that the fluid channels  6  are able to unfold the planar substrate of the medical implant  1 , see  FIG. 3   b.    
     The planar substrate  4  of the medical implant  1  can comprise individual surface areas  4 ′, which are all, or in pairs, connected with a fluid channel  6 . In this way it is possible for the individual surface areas  4 ′ to expand in a skewed manner independently of each other which benefits the orientation of the surface areas in the form of reflector surfaces and ultimately the reflected signal. Through a preferred filling of the channels  6 , preferably with oil, disruptive influences on the ultrasonic wave reflection behaviour of the medical implant  1  can be avoided, particularly as oil is acoustically transparent for ultrasound. 
     In addition, it can be assumed that through the intracorporeally moist environment, on the basis of an osmotic pressure effect on the medical implant  1 , water can penetrate into and through the polymer-based surface substrate  4  of the medical implant  1 , so that water enters into the channels  6  thereby increasing the tensioning force of the surface structure of the medical implant  1 . 
     It is also desirable that the individual surface areas  4 ′ of the medical implant  1  vary their spatial orientation and/or shape as a function of the intracorporeally occurring pulse waves  11 . The spatial variation can be supported and brought about in that the individual surfaces areas  4 ′ of the medical implant  1  are arranged movably with regard to each other. This is ensured through constrictions  8  between surface areas  4 ′ connected at least in pairs, along which at least one fluid channel  6  runs in each case, see  FIG. 4 . The constrictions  8  act in the form of a “natural joint”  9 , which can predetermine the mechanical movability of the individual surface areas  4 ′ relative to each other. In the case of the state shown in  FIG. 4 , the support rod  3  is already resorbed. 
       FIG. 5  illustrates an intracorporeal blood vessel  10 , from which blood pressure waves  11  emanate and interact with the medical implant  1  according to the solution so that the planar, expanded medical implant  1  is spatially deformed by the pressure waves  11 . By means of an extracorporeally arranged ultrasonic head  12 , ultrasonic waves  13  are subcutaneously transmitted into the region of the medical implant  1 . Through the spatial deformations on the medical implant  1  caused by the blood pressure waves  11 , the ultrasonic waves  13  are reflected and modulated on the medical implant  1 . This modulation in the reflected ultrasonic waves represents a function of the extent of the deformation or deflection of the medical implant  1  and, in connection therewith, a strength of the blood pressure waves  11 , which can be detected and precisely measured. 
     REFERENCE LIST 
     
         
         
           
               1  Medical implant 
               2  Hollow cannula 
               3  Support rod 
               4  Film-like substrate 
               4 ′ Surface areas of the medical implant 
               5  Nanostructure 
               6  Hollow channel 
               7  Resorbable holding threads 
               8  Constriction 
               9  Joint 
               10  Blood vessel 
               11  Blood pressure waves 
               12  Ultrasonic coupler 
               13  Ultrasonic waves