The object of the invention is a prosthesis for the non-invasive treatment of aneurysms, and a method for filling the aneurysm with the inventive prosthesis. Technical field Blood vessel dilations (aneurysms) are circumscribed dilations of arteries. According to the most widely accepted definition, an aneurysm is a blood vessel section with a diameter at least 50% greater than the diameter of a normal blood vessel section. Measurements carried out on a large number of adult persons show that the diameter of the normal abdominal aorta is 2 ± 0.3 cm. Thus, according to the above definition, in case the diameter of the abdominal aorta exceeds 3-4 cm, an aneurysm is diagnosed. This section is the most frequent place of occurrence of aneurysms (on the average 3% of the adult population suffers from this type of disorder). Other types of aneurysm (e.g. aneurysms of the thoracic aorta, the carotid artery, etc.) are also common. Background art

Aneurysms are dangerous because the continually dilating blood vessel may eventually rupture and cause internal haemorrhage (e.g. in the abdominal cavity), in which case the mortality rate is very high.

Thus, aneurysms need to be repaired by surgery before a rupture would occur.

Two main types of methods are known for aneurysm treatment. The first of these is conventional artificial blood vessel implantation, which is carried out by clamping off the artery below and above the affected section and making a longitudinal incision on the aneurysm. Then a biocompatible artificial blood vessel is implanted to provide a replacement for the incised

section, the implanted prosthesis being secured (by anastomosis) to the extremities of the vessel sections below and above the aneurysm. The main disadvantage of this method is that suturing the bleeding vessel branches and making the anastomosis are lengthy procedures that require great concentration and sophistication on the part of the operator, meaning that even an experienced surgeon may need as much as 40-50 minutes to complete the procedure. During this period of time the closed-off areas suffer from ischemia, which results in vital organs (e.g. liver, intestines, kidneys, spinal cord) being ischemic and may potentially lead to permanent damage to these organs.

Additionally, it may also be dangerous that as the clamping is removed and the vessel abruptly becomes under pressure, the sclerotic vessel wall may be ruptured, causing haemorrhage, which may in turn result in haemorrhagic shock. Because of these reasons 75% of all patients undergoing such an operation need to receive blood replacement during and after the operation.

The other widely known method is the so-called endoluminal method, which was developed with the intention to alleviate the patent's operative strain. Major advantages of this method are that the time during which the blood vessel is excluded can be decreased, and it is not necessary to make a cut on the aneurysm. The procedure involves a so-called stent-prosthesis being utilized for excluding the aneurysm from circulation. The stent- prosthesis is deployed through an opening made at a site that is easily accessible for surgery (usually the loins), with the device being worked to the aneurysm under constant x-ray supervision.

A stent-prosthesis is a thin-walled artificial blood vessel made of biocompatible plastic, which is pressed against the wall of the blood vessel at the upper and bottom attachment points by inbuilt stents.

The main disadvantages of this method are that it can be applied only in a restricted subset of anatomical situations, and that the attachment stents

may become loose, which causes the aneurysm to become under pressure again and may result in rupture and haemorrhage Oust as it would happen without surgery). Prosthesis loosening and displacement happen frequently (10-20% of the cases), so patients will have to undergo CT control regularly for the whole of their life.

Numerous plastic materials have been developed for application with the above methods. Such a material is described in US 6,096,525 which discloses a modified polytetrafluoroethylene material. US 4,642,242, US 4,973,493 and US 4,987,181 disclose materials that can be applied for similar purposes.

TW 553951 describes the application of modified polysaccharides. HU 216066 discloses an improved biocompatible polymer where the polypeptides built into the material effectively prevent platelet agglomeration. Disclosure of Invention The aim of the present invention is to eliminate the disadvantages of known methods and to provide a device suitable for that purpose.

The invention is based on the recognition that the aneurysm can be completely filled utilizing a customised casting-like vessel prosthesis made of biocompatible material, the prosthesis protecting at the same time the wall of the aneurysm against expansive forces and thereby preventing rupture. The prosthesis is firmly held in place by the aneurysm wall, so the implanted prosthesis will not get displaced. The prosthesis is advantageously configured that the wall thereof gradually becomes thinner towards the upper and bottom "necks" of the aneurysm and fits tightly against the normal vessel portions. The prosthesis comprises a central passage that is necessary for maintaining normal blood flow. Also, in case there are important vessel branches originating from the aneurysm, branch passages are provided to connect the main passage to these branches.

The inventive objective is realised by providing a method for manufacturing a cast prosthesis for the non-invasive treatment of aneurysms

that is characterised by taking, with the application of computer tomography known per se, the two- or three-dimensional image of the aneurysm and determining - by means of a three-dimensional CAD application - the thickness and location of the main passage of the prosthesis responsible for sustaining blood flow and, if necessary, the thickness and location of side passages; producing, preferably by means of computer aided manufacturing (CAM) technology and expediently with a 4-axis milling macine, the 1 :1 scale negative shape of the aneurysm and the core pieces providing for the formation of passages; casting to the negative shape (with the core pieces inserted) a biocompatible polymer or polymers; surface treating the outer and inner surfaces of the prosthesis and marking the prosthesis with direction marks; then, depending on the size of the prosthesis either leaving it integral or cutting it into multiple pieces that can be assembled to restore the original shape of the prosthesis; and finally sterilizing and packaging the completed prosthesis.

According to a preferred solution of the invention the biocompatible material of the prosthesis is selected from the group consisting of: polytetrafluoroethylene, polysilanes, hydrophilic polysiloxanes, polycarbonates, polyacrylates-metacrylates, polyaminoacids, polyethers, modified polyethylenes, aliphatic polyesters, segmented polyurethanes, and hydrophilic polyethylene oxides.

The inventive objective is further realised by providing a prosthesis for the non-invasive treatment of aneurysms that is characterised by being cast from customised biocompatible polymer, having an outer shape conforming to the shape of the aneurysm such that the prosthesis fits tightly against the wall of the aneurysm, with the wall of the prosthesis gradually becoming thinner towards the upper and bottom extremities of the aneurysm and the prosthesis fitting tightly against the normal section of the blood vessel, with the prosthesis comprising an internal passage portion ensuring the normal

flow of blood, and in specific cases further comprising internal branch passages connected to the branches of the aneurysm.

A preferred embodiment of the inventive prosthesis comprises a polysiloxane coating on its outer surface. Brief description of the drawings

A preferred embodiment and the method of implanting the inventive prosthesis is explained on basis of the attached drawings, where

Fig. 1 shows the schematic view of an aneurysm having no originating blood vessel branches that are to be preserved, Fig. 2 shows the inventive prosthesis adapted for being implanted into the aneurysm of Fig. 1 ,

Fig. 3 shows the prosthesis according to Fig. 2 implanted in the aneurysm shown in Fig. 1 ,

Fig. 4 is the schematic view of an aneurysm having branches to be preserved after the implantation,

Fig. 5 shows an embodiment of the inventive prosthesis adapted for being implanted into the aneurysm of Fig. 4, and

Fig. 6 shows the prosthesis according to Fig. 5 implanted into the aneurysm shown in Fig. 4. Best Mode of Carrying out the Invention

The procedure of producing and implanting the inventive prosthesis is different depending on the characteristics of the aneurysm to be treated.

Fig. 1 shows an aneurysm with no preservable vessel branches. The direction of blood flow in blood vessel 2 is indicated by the arrow 1. The blood vessel 2 has a diameter of D ₂ . The diameter of the aneurysm increases to D ₃ and then again decreases to D ₂ .

Fig. 2 shows a prosthesis 4 adapted for the treatment of the aneursysm shown in Fig. 1. The prosthesis 4 has an outer shape conforming to the shape of aneurysm 3, with a passage portion 5 being disposed in the

prosthesis 4. The passage portion 5 is essentially a channel which constitutes the continuation of the blood vessel 2.

The inventive prosthesis 4 is prepared according to the procedure described below. As the location and shape of the aneurysm may differ from patient to patient, prosthesis 4 should be customized to match the needs of the patient.

First, high-resolution 2- and 3-D images of the aneurysm are taken using high-definition computer tomography, and a 3-D design software is applied to establish the outer shape of the prosthesis 4 and the path and location of the internal main and side passages, responsible for sustaining blood flow, of prosthesis 4.

Then the negative shape of the aneurysm is produced together with elongated core pieces being inserted into the negative shape to ensure the formation of internal passages of prosthesis 4, and a cross-linkable poymer material is cast into the thus produced mould. The prosthesis 4 then undergoes surface treatment to prevent blood coagulation on the surfaces exposed to blood flow. Finally, direction marks are applied to prosthesis 4 which is sterilized and implanted at the appropriate location.

Implantation is carried out by first clamping off the artery above and below the aneurysm, and making an incision at the frontal surface thereof, at the portion with the greatest diameter, the incision having a length allowing the insertion of prosthesis 4 into the internal cavity of aneurysm 3. The prosthesis 4 is then inserted, paying attention to the correct orientation indicated by the direction marks, into the internal cavity of the aneurysm 3 through the opening produced in the previous step. Finally, the opening is sutured and the clamping is removed.

The central cavity of the aneurysm 3 is completely filled by prosthesis 4, with passage portion 5 thereof being connected to portions of blood vessel 2 to maintain the continuous flow of blood through the prosthesis 4 (see Fig. 3).

Fig. 4 shows aneurysm 3 with blood vessel branches 6, 7 to be preserved. The direction of blood flow in blood vessel 2, having a diameter

D ₂ , is indicated by the arrow 1. The diameter D ₂ of the vessel increases to D ₃ in the dilated vessel portion constituting aneurysm 3. The aneurysm 3 according to Fig. 4 is repaired by utilizing a prosthesis

8 shown in Fig. 5. The prosthesis 8 comprises, in addition to passage portion

9 attached to blood vessel 2, branch passages 10, 11 attachable to vessel branches 6, 7.

The prosthesis 8 according to Fig. 5 is prepared and implanted in the manner described above. Once prosthesis 8 has been implanted, passage portion 9 thereof forms the continuation of blood vessel 2, while blood flow through branch passages 10, 11 into vessel branches 6, 7 is also sustained

(see Fig. 6).

Any biocompatible polymer material can be utilized as the material of the prosthesis 4, 8 and for the surface treatment material thereof. Solely for the purposes of exemplification the materials most expediently applicable are listed below:

- polytetrafluoroethylene,

- polysilanes, - hydrophilic polysiloxanes,

- polycarbonates,

- polyacrylates-metacrylates,

- polyaminoacids,

- polyethers, - modified polyethylenes,

- aliphatic polyesters

- segmented polyurethanes,

- hydrophilic polyethylene oxides.

Apart from those listed above, any other commercially available partially or fully hardening biocompatible polymer can be utilized for the manufacture of the prosthesis 4, 8.

It may be advantageous if the outer surface of the prosthesis 4, 8 is coated with a not fully cross-linked, "sticky" biocompatible polymer, for instance polysiloxane, while the inner surface is coated with antithrombogenic coating. As a result prosthesis 4, 8, once in place, practically "sticks" to the wall of the blood vessel, and thus displacing of the implanted prosthesis becomes virtually . An advantageous feature of the inventive prosthesis is that no time- consuming vascular suture is needed during the implantation, and so thus, the length of the implantation procedure is reduced from 40-50 minutes to 4-5 minutes.

Since no suture bleeding should occur, and there is no bleeding from blood vessel branches originating from the aneurysm (as these branches are shut off from inside by the implanted prosthesis), blood loss during the operation is kept at a minimum. The relatively simple operative technique required by the implantation makes it possible that a larger number of professionals can carry out the operation, reducing thereby the time spent on waiting lists by patients and increasing the total number of performed operations.

List of reference numerals

1 arrow

2 blood vessel

3 aneurysm

4 prosthesis

5 passage portion

6 branch

7 branch

8 prosthesis

9 passage portion

10 branch passage

11 branch passage

D ₂ diameter of blood vessel

D ₃ diameter of aneurysm