Implantable access device and method for preparing thereof

Abstract

The present invention concerns an implantable access device and a method for preparing the device. According to the invention the device comprises a shape memory base structure with a biological substructure suitable for cell adhesion, cell engraftment and proliferation for use in transferring and transporting fluid mixtures (blood, suspensions, drug formulations, emulsions, cell suspensions) in/into/out of a human or animal body.

Claims

1. An implantable vascular access device comprising a shape memory base structure having openings, a substructure having openings, the substructure thereby being suitable for cell adhesion, cell engraftment and proliferation for use in transferring fluid into/out of a human or animal body, the shape memory base structure and the substructure permitting three-dimensional fixation and integration of cells on and within the access device, the shape memory base structure and the substructure together comprising a generally conical body having the shape memory base structure as a base of the generally conical body and adapted to receive a needle and a positioning end forming an apex of the generally conical body and adapted to position the end of said needle.

2. A device according to claim 1 wherein said substructure has filaments that are at least one of monofilaments and multifilaments.

3. A device according to claim 1, wherein said substructure is at least one of a biological polymeric substructure and a synthetic polymeric substructure.

4. A device according to claim 3, wherein said polymeric substructure comprises at least one of fibrin, plasma, platelet rich plasma, collagen, serum components, polyelectrolytes, hyaluronic acid, glycosaminoglycan, polyglucose, chitosan, alginate, polylactic acid, polyglycolic acid, polygluconic acid or mixtures thereof.

5. A device according to claim 1 wherein said shape memory base structure comprises at least one of a shape memory material and an elastic material.

6. A device according to claim 5, wherein said material is chosen from the group consisting of shape memory metallic alloy material, stainless steel, polymeric shape memory material, polygluconic acid, polyglycolic acid, polylactic acid, and collagen.

7. A device according to claim 1 wherein said base structure is at least one of braided, woven, foamed, and knitted.

8. A device according to claim 1 further comprising a mechanism for opening and closing to control fluid flow through the device.

9. A device according to claim 8, wherein said opening and closing mechanism is adapted to open when a needle is introduced into and bears upon said body portion positioning end.

10. A device according to claim 8, wherein said opening and closing mechanism is a valve.

11. A device according to claim 1 connected in the positioning end to a graft.

12. A device according to claim 1 connected in the positioning end to a stent.

13. A device according to claim 1 connected in the positioning end with a permanent catheter.

Description

BRIEF DESCRIPTION OF THE DRAWING(S)

(1) FIG. 1 shows the number of adhered normal human dermal fibroblasts on different coated nitinol plates measured as metabolic activity.

(2) FIG. 2 shows the adherence of Normal Human Dermal Fibroblasts (NHDF) on different coated and non-coated Nitinol meshes measured as metabolic activity.

(3) FIG. 3 shows the access device according to the invention implanted with two different techniques in the hypodermis.

(4) FIG. 4 shows one embodiment of the access device according to the invention integrated and fixed to the outer surface of a graft.

(5) FIG. 5 shows one embodiment of the access device according to the invention integrated and fixed to a stent in a blood vessel.

(6) FIG. 6 shows one embodiment of the access device according to the invention with a permanent catheter, which enters the blood vessel directly.

(7) FIG. 7 shows that cells on Nitinol meshes proliferate well on fibrin coated Nitinol meshes analyzed by confocal laser scanning microscopy (Nitinol black, fibroblasts grey). This picture also depicts the cell integrating biofunctional 3-dimensional structure of the disclosed structures.

DETAILED DESCRIPTION OF THE INVENTION

(8) The access device according to the invention consists of a shape memory base structure with a substructure suitable for cell adhesion, cell engraftment and proliferation for use in transferring fluid into/out of a human or animal body or transporting fluids in the body.

(9) The base structure with the shape memory or elastic structure allows an inbuilt mechanism that after the puncturing process, which is after removal of a needle, the skin construct is automatically moved back to the initial structure. By this the skin function and wound healing is enhanced, the bleeding after removal of the needle is reduced and with respect to therapeutic application or requirements of a vascular access system a reduced risk for invasion of bacteria and fibrous scar tissue formation can be achieved. Furthermore, there is support of the skin by the shape memory base material, which increases the resistance of the tissue against manipulations and movement in daily life as well as during application.

(10) The material in the base structure could be a shape memory material, an elastic shape memory material or an elastic material. It should allow introduction of a needle therein, but most important is that the base material has the feature of having a driving force or ability to regain the geometry shape of the access device after removal of a needle. By this driving force or ability to regain the geometry shape, the base structure takes over the mechanical integrity of the tissue during reconstruction in tissue healing and revascularisation phase, i.e. closing openings, channels formed during puncture.

(11) On the base structure a substructure is to be formed. This substructure provides basically two functions, 1) tailored distance between openings in a network, and 2) allowing anchoring, cell supporting and intrusion of cells and formation of multiple pseudopodia to get a 3-dimensional (3-D) fixation or integration of cells on and within the access device according to the invention.

(12) Accordingly, the access device according to the invention has a base structure and a substructure which allows in-growth of cells into the whole access device in order to let the access device become filled with tissue material. In this way the puncturing is made with a needles which is guided through the tissue within the access device to a positioning end for blood access, after removal of the needle the shape memory base structure helps the skin tissue to regain the original geometric shape to thereby close the channels formed in the tissue during puncture.

(13) The access device according to the invention should be subcutaneously implanted as a permanent device. The device (1) is preferably implanted in the hypodermis layer and arranged to enter the vessel system (2), see e.g. FIGS. 3 and 4. As stated above, said device (1) has a body portion with a receptor end (3) adapted to receive a needle (4) and a positioning end (5) adapted to position the end of said needle (4).

(14) In one embodiment of the access device according to the invention the receptor end (3) is adapted to receive needles (4) from a number of discrete puncture points (6). In even an additional embodiment this is provided by having an entry member (11) containing a plurality of apertures (6), wherein each aperture (6) is adapted to receive a needle (4) that has passed through overlaying skin. In one embodiment this entry member is a sheet (11) having a plurality of apertures (6).

(15) Said positioning end (5) could be arranged to enter into the vessel system (2) in different ways. In one embodiment the positioning end (5) of the device is integrated with a kind of fixation mesh (7), which is fixated on the outer surface of a graft (8), see FIG. 4. In another embodiment the positioning end (5) is integrated with a fixation mesh in form of a stent (9) in a blood vessel (2), see FIG. 5. The guided pathway in the device according to the invention in combination with such fixation meshes guarantees that the needle will always find its right way for puncturing the graft or the vessel. In another access device according to the invention the positioning end (5) of the access device is connected with a permanent catheter (10), see FIG. 6 and FIG. 3 (left). Of course other combinations could be done with the access device according to the invention, a permanent catheter, a stent, and a graft.

(16) The opening/closing mechanism in the access device according to the invention could in the simplest version be that the puncturing force opens the access and then closes the access when the force disappears, i.e. when the puncturing needle is removed, and then it could also include a valve.

(17) The puncturing could take place with specific needles that allow bending, whereby access to the vascular system is achieved over a tube or funnel type of connection ridging to the vascular system. In one embodiment the puncturing needles have blunt end to find or to get through the guided pathway without problems and not to damage the skeletal structure of the access system and not to cause too much injury/stress for the skin cells and small vessels. Below you find test methods and results in which we have verified and evaluated adhesion and proliferation of cell adhesion and growth on an access material which could be used in the access device according to the invention, the results of these tests are shown in FIG. 1 and FIG. 2.

Test Methods and Results

(18) Verification and Evaluation of Adhesion and Proliferation

(19) Description of AlamarBlue Test

(20) AlamarBlue can be used as a proliferation and cytotoxicity indicator. The application of AlamarBlue requires the adjustment of different parameters to the scope of the test method. These parameters are AlamarBlue concentration, cell concentration, and time of incubation. For the definition of the measuring method several experiments were conducted and the time courses/kinetics of the reduction of AlamarBlue were evaluated.

(21) Due to different experiments and microscopic controls of the cell population, the execution of the proliferation test method by means of AlamarBlue was specified, concerning the cell concentration as well as incubation periods and AlamarBlue concentrations, as follows:

(22) TABLE-US-00001 TABLE 1 Parameter for proliferation verification of NHDF by means of AlamarBlue. Conc. Volume of Volume of Tissue culture [Cells/well Culture- Incubation AlamarBlue- Incubation- plate [Number Area per resp. Cells/ medium per period for Cell Solution per period with of wells] well [cm.sup.2] Test-substrate] well [ml] Suspension [h] well [ml] AlamarBlue [h] Petri-dish 20 50 000 6 24 6 24 6 10 40 000-60 000 3 24 3 24 24 3.6 10 000-20 000 1 24 1 24 96 0.32 1 000-2 000 0.1 24 0.1 24
Description of the MTT-Test

(23) The MTT Test is a rapid and sensitive colorimetric assay based on the formation of a coloured insoluble formazan salt. The amount of formazan produced is directly proportional to the cell number and therefore can be used to measure cell viability and proliferation. The assay is based on the capacity of the mitochondrial dehydrogenase enzymes to convert a yellow water-soluble tetrazolium salt (=MTT) into purple insoluble formazan product by a reduction reaction. This allows photometric analysis.

(24) First different cell concentrations as well as different incubation periods of fibroblasts were examined to evaluate, in which scopes the settlement of the cells of surfaces can be determined.

(25) The results of the colorimetric measurements are listed in Table 2.

(26) TABLE-US-00002 TABLE 2 Proof of proliferation of NHDF by means of MTT, MTT added after 24, 48 and 72 hours. Incubation period 24 48 72 Mean Mean Mean value value value Concentration OD STD OD STD OD STD n 1000 0.012 0.002 0.006 0.003 0.022 0.003 8 2000 0.027 0.005 0.026 0.006 0.042 0.008 8 4000 0.052 0.015 0.053 0.009 0.091 0.004 8 6000 0.075 0.014 0.080 0.010 0.139 0.007 8 8000 0.108 0.018 0.095 0.013 0.160 0.010 8 15000 0.128 0.034 0.131 0.021 0.178 0.015 8

(27) The measured values show, that the optical density is increasing with an ascending cell concentration. The cell cycle of fibroblast is around 20-24 h, in which the cells under optimal conditions should have been divided. Between the incubation periods of 24 h as well as 48 h are no significant changes of the measured values. After an incubation period of 72 h the cells have increased in number and proliferation signal. The reason therefore is, that the cells need an adaptation period after sowing before they accommodate to their regular cell cycle. For further proliferation examinations by means of MTT cell concentrations between 4000 and 6000 cells/100 l will be sowed. In that scope it comes to clear signals, which are in the linear area of the OD (optical density)-courses.

(28) Growth of fibroblasts on Nitinol (Results from Experiments)

(29) Due to the mechanical properties and highly biocompatibility Nitinol was a primary choice for the first test for the base structure of the access device according to the invention. For further characterization of the materials biocompatibility examinations concerning cell adhesion and proliferation were carried out. Further, two functional elements need to be combined, mechanical and super elasticity, but still a sufficient and functional integration in the tissue environment must be achieved. The following experiments indicate possible solutions to the problem.

(30) The material was coated with different human plasma components to get information about the influence of these coatings to cell adhesion and proliferation. One possibility of coating is to bring up fibrin nets on the base structure for simulating the wound healing process. The formation of fibrin is stimulated through the activation of coagulation in human platelet rich plasma (PRP). This goes on during a dynamic process, which has to be optimised concerning temperature, coagulation time, presence of calcium and platelet concentration of the plasma. Execution of the examined coatings are described in the following:

(31) Platelet Rich Plasma (PRP):

(32) Platelet count of the PRP is diluted with plasma to a total count of 100 000 platelets. The Nitinol samples are incubated in the adjusted PRP for 1 hour at 37 C./7% CO.sub.2.

(33) Plasma:

(34) The Nitinol samples are incubated in plasma for 1 hour at 37 C./7% CO.sub.2.

(35) Fibrin Net Coating:

(36) Adjusted PRP with a platelet count of 100 000 was added to the Nitinol samples and incubated for 30 min at 37 C./7% CO.sub.2. Then the coagulation was started by addition of calcium chloride. 4 to 10 min after the coagulation process was started the formation of a 3-dimensional fibrin structure occurred and was then be stopped with sodium citrate at different levels.

(37) Serum Coating:

(38) Serum contains no coagulation factors. Therefore human whole blood is transferred in tubes, which are containing sterile glass beads. The glass beads known as initiators coagulation offer a great surface to the blood, which starts the coagulation procedure. The tubes with the whole blood were incubated for 1 hour at room temperature and 1 hour on ice. After centrifugation the supernatant, i.e. serum, were transferred into fresh tubes for storage or used directly for coating.

(39) Collagen Coating:

(40) Collagen is only soluble in an acid solution and polymerised at a neutral pH value. The collagen solution was added to the Nitinol samples, neutralised with sodium hydroxide and incubated for 1 hour at 37 C./7% CO.sub.2.

(41) For the adhesion and proliferation test methods, the coated and uncoated Nitinol meshes were transferred in test devices e.g. tubes or multi-dwell plates. All Nitinol samples were cleaned and steam sterilised before they were coated. There was given the cell concentration of fibroblast into the test device with the Nitinol samples. As positive controls for high proliferation rates fibroblasts in tissue culture plates were used.

(42) The indicator solution containing AlamarBlue as non-toxic metabolic probe was brought on the test samples e.g. 24 hours and 48 hours after bringing the fibroblasts on the Nitinol samples and incubated for another 24 hours.

(43) In FIG. 1 it is shown that the number of adhered fibroblasts on the substrate could be significantly increased through the coating with human plasma compound on the Nitinol material. This is shown by the higher reduction rates of AlamarBlue. The best results were determined at Nitinol plates with a fibrin coating.

(44) In FIG. 2 the proliferation of NHDF on Nitinol meshes are shown. After 15 days of proliferation, there are high reduction rates for cells on Nitinol meshes. That means that it is possible to proliferate/integrate normal human dermal fibroblast cells (NHDF), i.e. normal human skin cells, on the devices when a substructure is present on the device before introducing the NHDF cells.

(45) However, after an incubation period of 15 days the reduction rate of Alamar Blue is nearly the same for Nitinol meshes as for Nitinol plates (except meshes without coating). That means that it is possible to proliferate/integrate human skin cells on the 3D-Nitinol device and the substructure can develop by different preparation methods.

(46) It is also evident that the coating of the device is very important to get high proliferation rates of the fibroblasts on the implantation device, which is very important to achieve a total integration of the access device into the human body.

(47) Identification and Visualization of Fibroblast Cell Growth on Nitinol Meshes

(48) In order to more clearly identify and visualize the growth of fibroblasts on Nitinol meshes and to get a 3D-layout from the samples, specific immuno-staining procedure was performed and evaluated under the fluorescence microscope before confocal laser scanning microscopy (CLSM) was performed.

(49) FIG. 7 shows that cells on Nitinol meshes proliferate well on fibrin coated Nitinol meshes (Nitinol black, fibroblasts grey)

(50) It should be understood that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the present invention and without diminishing its attendant advantages. It is therefore intended that such changes and modifications be covered by the appended claims.