NL2021860B1

NL2021860B1 - Self-supporting metal open cell foam structure for use in cranial surgery

Info

Publication number: NL2021860B1
Application number: NL2021860A
Authority: NL
Inventors: Leerkamp Peter
Original assignee: 2Move Implants B V
Priority date: 2018-10-23
Filing date: 2018-10-23
Publication date: 2020-05-13
Also published as: WO2020085905A1

Abstract

The invention pertains to a self-supporting three-dimensional metal open cell foam structure, the structure having cells with openings having a diameter of between 200 pm 5 to 750 pm, for use as a bone prosthesis in cranial surgery, wherein the structure has a porosity of 50% to 95% and a thickness between 0.5 mm and 5 mm. The invention also pertains to the self-supporting structure as such, methods for producing such a structure and

Description

SELF-SUPPORTING METAL OPEN CELL FOAM STRUCTURE FOR USE IN

CRANIAL SURGERY

GENERAL FIELD OF THE INVENTION

The invention pertains to a bone prosthesis for use in cranial surgery, in particular to a prosthesis for use in cranioplasty such as in maxillo facial surgery or cleft palate surgery.

BACKGROUND ART

Cranioplasty is the surgical intervention to repair cranial defects in both cosmetic and functional ways. It is performed mostly after traumatic injuries. With children younger than 3 years old, growing skull fractures and congenital anomalies are common causes. In all age groups, tumor removal or decompressive craniectomies are mostly the cause of cranial defects. The aim of cranioplasty is not only a cosmetic issue. Also, the repair of cranial defects gives relief to psychological drawbacks and increases the social performances. Many different types of materials were used throughout the history of cranioplasty. With the evolving new biomedical technology, new materials are now available to be used by the surgeons. An ideal cranioplasty material should fit the cranial defect and achieve complete closure, is resistant to infections, radiolucent, strong to (bio)mechanical processes, easy to shape, inexpensive, and ready to use.

Traditionally use has been made of autograph (such as tibia, rib, scapula, fascia, sternum and ilium), allografts (cadaveric cartilage or cranial bones) and xenografts (animal bones). After World War II non-metal allografts were developed, such as celluloids, methylmethacrylate, hydroxypatite, polyethylene, silicon, chorale, ceramics or reactive composites such as Cortoss™.

Metal allografts have also been used but their heat conduction, difficulty to shape, and radio-opacity limited their use as a proper cranioplasty material. Gold and silver have been used in the past but although gold gave good results as a cranioplasty material with low complication rates and ease to shape, the main problem with gold is that it is a very expensive metal. Silver materials are too soft and oxidization of silver causes color changes in the overlying skin. Tantalum was widely used in World War II, but abandoned due to its high price, difficulty to obtain, and the main complication of headache, probably because of high heat conduction ability. Steel is also used but the flexibility of steel and deformities in the material seen after minor traumas has prevented its use in large defects. Titanium on its turn is hard to shape, but relatively cheaper, bioacceptable, and radiolucent after mixing with other metals. It also shows good resistance to infection. However, it is not a good option in cases with bad skin viability. Recently, titanium meshes were used as a support to cement materials. In this way, the strong resistance against mechanical stress of the titanium and the ability to remodeling of the cement materials were combined. Lead was used for the first time as a cranioplasty material at the beginning of 20th century. However, due to its toxicity, the use of lead was abandoned. Platinum shows good biocompatibility with no tissue reaction. However, its use is not widespread due to its high price. Various alloy such as Titanium-Aluminium-Vanadium and Cobalt-Molybdenum-Chrome are also used in cranioplasty. Still, there is no perfect material to fit all criteria for a cranial bone prosthesis.

OBJECT OF THE INVENTION

It is an object of the invention to provide a new type of bone prosthesis for use in cranial surgery that meets the most relevant criteria for such surgery, in particular a prosthesis that can be used for complete closure, is strong to (bio)mechanical processes, easy to shape, inexpensive, and ready to use. It is a further object to provide the bone prosthesis as such, and one or more methods for producing such a prosthesis.

SUMMARY OF THE INVENTION

In order to meet the object of the invention a self-supporting three-dimensional metal open cell foam structure has been devised, wherein the structure has cells with openings having a diameter of between 200 pm to 800 pm, a porosity of between 50% and 95% and a thickness between 0.5 mm and 5 mm.

It was found that this new structure is ideally suitable for use as a bone prosthesis in cranial surgery. The metal base can give the structure its needed strength in (bio)mechanical processes, even when being formed as an open cell foam structure, i.e. a structure wherein the individual cells of the metal foam are interconnected via joint openings that connect the open space in one cell with the open space of a neighboring cell. When the cells have openings having a diameter of between 200 pm to 800 pm, the open cell structure allows surrounding bone tissue to infiltrate the foam and anchor it into position. When the structure is used “as is”, thus not as a coating on a solid material, but as a self-supporting material, and at the same time the porosity is over 50% while the thickness of the structure is less than 5 mm, it was found that the flexibility of the structure is sufficient to allow in situ shaping by a surgeon (typically the elongation before failure of a self-supporting structure according to the invention is 550%, whereas 20-40% would suffice for most types of cranial surgery).This means that the prosthesis does not need to be pre-formed using complex scanning and shaping processes, but can be produced as a ready-to-use metal sheet that is formed in situ during (trauma) surgery (the invention not excluding however that the prosthesis is preformed, for example using a 3D printing technique). Moreover, for example by adjusting the thickness and porosity, a flexibility can be obtained that meets the flexibility ofthe bone material around the defect. This may prevent reduction in bone density (also known as stress shielding) as a result of the removal of typical stress from the bone by the prosthesis (which is typical when using rigid implants connected to the bone). Another advantage of the present structure is that since there is no practical length and width restriction for this structure, a structure according to this invention is able to completely close any cranial bone defect.

Although in the art metal open cell foam structures are known for their use in orthopaedics implants, their use is restricted as coatings of supporting structures since it is generally believed that they do not readily have the required mechanical properties that would allow them to be used as bulk structural materials for implants, bone augmentation, or substitutes for bone graft. (Balia VK et al, “Porous tantalum structures for bone implants: fabrication, mechanical and in vitrobiological properties”, in Acta Biomater. 2010 Aug;6(8):3349-59). Moreover, even porous coated titanium (alloy) implants show 50 to 75% lower fatigue strength compared to their equivalent fully dense materials, which arises due to highly stress concentrated regions at particle substrate neck regions acting as crack initiation sites. Therefore, it came as a surprise that a metal open cell foam that meets the current restrictions, is suitable as a stand-alone bone graft for cranial surgery.

DEFINITIONS

Self-supporting means to be able and keep its dimensions without being supported by a secondary structure.

Porosity is the ratio of the volume of interstices of (i.e. “open cells in”) a material to the volume of its mass.

A metal open cell foam is a porous metal wherein individual cells are interconnected.

Cranial surgery is any surgery relating to the skull.

FURTHER EMBODIMENTS OF THE INVENTION

In a further embodiment of the self-supporting structure for use according to the invention, the metal comprises Ti (titanium) and/or Mg (magnesium). Both metals have been found to be useful as such, or in a mixture, as a basis for a metal foam in line with the invention. Titanium, even when the structure is made using titanium as the only metal, may provide ideal flexibility properties to the structure. The same is true for magnesium, although to arrive at a structure of very high strength (for example to fix a jaw), porosity restrictions are more demanding. Magnesium has the advantage over titanium that over time it will solve in the body. Advantageously, the metal of the selfsupporting structure consists in essence of Ti and/or Mg (i.e. the metal consists for at least 90% of Ti and/or Mg). Although any level of titanium and/or magnesium between 0 and 100% can be used (including all integer values between 0 and 100, i.e. the values of 1, 2, 3, 4, 5......48, 49, 50, 51, 52 ...... 95, 96, 97, 98 and 99%), particular good working examples have been based on a metal that consists of either 100% Ti, 94-97%

Mg (3-6% other pharmaceutical acceptable metals such as Ti, Al, V, Nd, Co, Mb, Cr, Y etc.; such as for example WE43 High Strength Magnesium Alloy which mainly contains yttrium and neodymium next to Mg) or a mixture of 50% Ti and 50% Mg.

Although the structure may have any thickness between 0.5 and 5 mm, for example 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1,2.2, 2.3, 2.4, 2.5, 2.6,

2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 4.1,4.2, 4.3, 4.4, 4.5, 4.6,

4.7, 4.8 and 4.9 mm, in a next embodiment the self-supporting structure according has a thickness between 1.0 and 2.0 mm. Such a thickness was found to be suitable for almost all cranial surgery, while obtaining very good flexibility properties for easy in situ shaping that does not depend on (expensive) tooling.

Although the structure may have any porosity between 50 and 95%, for example 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61,62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 90, 91, 92, 93 and 94%, in another embodiment of the self-supporting structure for use according to the invention, the porosity is between 60 and 90%. Such a porosity was found to be particularly suitable for maxillo facial and cleft palate surgery.

In yet another embodiment, although any diameter between 200 pm to 800 pm for the openings of the cells can be used according to the invention, such as for example, 210, 220, 230, 240, 250, 260, 270, 280, 290, 300, 310, 320, 330, 340, 350, 360, 370, 380

390, 400, 410, 420, 430, 440, 450, 460, 470, 480, 490, 500, 510, 520, 530, 540, 550,

560, 570, 580, 590, 600, 610, 620, 630, 640, 650, 660, 670, 680, 690, 700, 710, 720,

730, 740, 750, 760, 770, 780 and 790 pm, the cells have openings having a diameter between 250pm and 500pm, preferably between 300pm and 400 pm. Such a diameter was found to meet the structure of cranial bone tissue in an optimal way.

In still another embodiment, the self-supporting structure for use according to the invention is provided with a hydrophilic coating. Such a coating may lead to a better blood absorption and hence a quicker stem cell formation, and thus a quicker growth of the bone into the structure. Advantageously, the coating is chosen from metal oxide, bone morphogenic protein-2 (BMP-2; see Jun et al. in J Mater Sci Mater Med. 2013 Mar; 24(3):773-82.) and calcium phosphate.

Advantageously it was found that a structure that meets the most critical demands in cranial surgery can be made when formed as a regular polyhedron, such as a regular dodecahedron. Regular in this sense means that it is not completely ad random. The individual cells may for example differ in size. This can be advantageous to direct bone growth in a particular direction within the structure.

An embodiment of the invention is also directed to the structure itself, i.e. a selfsupporting three-dimensional metal open cell foam structure, with cells having openings having a diameter of between 200 pm to 800 pm, wherein the structure has a porosity of more than 50% and a thickness between 0.5 mm and 5 mm. This structure can have the further features as outlined here above in any of the structures for use in cranial surgery.

The invention is also embodied in several production methods to arrive at a structure for use according to the present invention. In a first method, which method has found to be ideally suitable when the metal consist for 50% -100% out of titanium, the structure is produced by 3D laser sintering metal beads having a diameter of between 10 pm and 50 pm, typically between 15 and 30 pm, such as 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28 and 29 pm. In a second production method for producing the self-supporting three-dimensional metal open cell foam structure of the invention, the structure is made by depositing the metal by chemical vapour deposition on a supporting framework. The framework may later be removed to arrive at the self-supporting metal structure.

The invention is also embodied in a method for cranial surgery on a patient comprising uncovering a defect in the cranial bone such that the defect and bone surrounding the defect is exposed to the environment, for example by taking away overlying tissue and/or skin, positioning the self-supporting structure of the invention over the defect so as to from a prosthesis for the cranial defect, spatially fixating the self-supporting structure relative to the cranial bone, for example by mechanically connecting the structure to the bone, and ultimately covering the self-supporting structure with tissue of the patient or artificial tissue (which is any tissue having an origin other than the patient itself, may be as simple as surgical cloth).

The invention will be further explained using the following non-limiting figures and examples.

EXAMPLES

Figure 1 schematically depicts a self-supporting structure according to the invention. Figure 2 schematically depicts one dodecahedron unit ofthe structure of figure 1.

Example 1: description of 3D printing of titanium dodecahedron.

Example 2: description of alternative production techniques for a metal open cell foam structure.

Example 3: description of cheek bone surgery.

Example 4: description of cleft palate surgery.

Figure 1

Figure 1 schematically depicts a self-supporting structure 1 according to the invention. In this embodiment the structure is a sheet made of titanium having width, length and thickness dimensions of 50, 50 and 1.5 mm respectively. The titanium sheet is made using a 3D printing method as described in example 1, starting from a bulk material that consists of 10-20 pm titanium beads. The beads are sintered to from a regular structure of open dodecahedrons (see figure 2) having cells with openings having a diameter of about 350 pm and struts of about 100pm, leading to a porosity of about 80%. The resulting sheet is flexible but mechanically strong, and can be elongated up to 50% before rupture. This means that the sheet can be easily shaped to resemble any part of the cranial bone. The material can be cut easily using a pair of metal cutting scissors.

Figure 2

Figure 2 schematically depicts one dodecahedron unit of the structure of figure 1, having a diameter of about 350pm. The unit is formed from titanium beads having a diameter of 10-20 pm. These beads are sintered as described here below and form the walls ofthe dodecahedron. Contiguous dodecahedrons are in fluid connection.

Example 1

Several self-supporting three-dimensional metal open cell foam structures consisting of pure titanium (although the surface of titanium will oxidize of course, leading to a product that also comprises titanium oxides at its surface) were produced using a direct metal printing technology (DMP, ProX DMP 320, 3D Systems Layerwise, Leuven, Belgium). In this technology pure titanium powder conforming to ASTM Grade 1 was used. File preparation was performed in the Magics software (Materialise, Leuven, Belgium) and DMP control software (3D Systems Layerwise, Leuven, Belgium). All structures were squares with a height of either 1.5 mm (for use as a skull prosthesis), 1.0 mm (for maxillofacial use) and 0.5 mm (for cleft palate use), an length and width dimensions of 50 mm x 50mm. The porous architecture is based on a dodecahedron unit cell. The DMP machine used for fabrication of the implants enables controlling the oxygen level in the building atmosphere to under 50 ppm and is therefore very suitable for production of structures from titanium. The samples were built on a so called CP-Ti build plate and cut from the plate by wire electrical discharge machining.

Example 2

This example provides a description of alternative production techniques for a metal open cell foam structure. In a first alternative, the open cell forma structure is made via vapour deposition. This is suitable for example for producing a structure made from pure magnesium (notwithstanding the magnesium oxides at the surface). Such a structure was provided on a polyurethane porous substrate that is cleaned and then fastened into a vacuum chamber; a magnesium thin layer formed by using radio frequency (RF) magnetron sputtering to deposit a first sputtering layer on the polyurethane substrate, wherein the first sputtering target is a magnesium target and a second magnesium target, and the sputtering gas is argon. As a result, when detecting hydrogen gas, the detection sensitivity is optimal when the temperature is 30°C, the hydrogen concentration is 1000 ppm, the deposition time is 80 minutes, and the magnesium film thickness is 1mm. A post treatment is performed to remove the polyurethane in a vacuum oven at a temperature of 600°C at a pressure of 200mbar during 30 min. The hydrogen content is lOOOmbar.

Yet another alternative technique is based on a sintering process. An open cell foam structure of pure titanium for the application in clinic orthopaedics field was manufactured by powder metallurgy technique using a space holder under different sintering conditions. The final morphological features and mechanical properties were as follows: titanium powder, with a mean particle size of 150 pm. TiH2 with mean particle sizes of 45-53 pm and 53-75 pm, respectively, were used as the space holder. It is observed that the TiH2 powder has an irregular shape. The powders were poured into a stainless steel die with a 5 mm inner diameter. Titanium powder was mechanically mixed with the space holder powder. The amount of space holder powder was in the range 0-20 % by weight. After mixing, the mixed powders were then compacted in the die by using uniaxial pressures of 77 MPa and 102 MPa at ambient temperature. The compacted specimens were then sintered at temperatures of 1173, 1373 and 1573 K for 2 hours under an argon gas atmosphere. A heating/cooling rate used in the sintering process was 5°C/min.

The results show that the increase of sintering temperature and time leads to improved grain size of porous titanium ligament and decreased pore size, with a concomitant increase of tensile strength and elastic modulus. The microstructure and mechanical properties of solid titanium depend more on the sintering temperature and time than those of porous titanium. The relative contributions of these mechanisms of porous titanium vary with the initial microstructure and oxygen content.

This way a WE43 like magnesium open cell foam structure could be made. This magnesium based structure has relative high corrosion speed making sure the metal foam is relatively quickly metabolised which makes the structure ideally suitable for non-load bearing cranio prosthesis applications.

Example 3

This example describes actual cheek bone surgery performed on a man, aged 47 years, having a broken cheek bone (fracture of the left zygomatic bone with displacement).

Status localis of patient

The configuration of the face is changed due to the retraction of soft tissues in the right infraorbital region, with palpation determined by the characteristic step. Palpation of the left infraorbital region is sharply painful. Presence of a hematoma with a diameter of about 3 cm, shallow abrasions. Opening the mouth is limited. Mobility of the alveolar process of the upper jaw in the area 22-28, contused wound of the upper eyelid. Presence of enophthalmos. On the presented X-ray photographs of the facial skull in the frontal and lateral projections a marked displacement of the fragment of the right zygomatic bone is visible.

Final diagnosis

Based on complaints, history, general Information, examination, data on systems and status localis, as confirmed by X-ray, the following diagnosis was made: right fracture zygomatic bone with displacement.

Plan of treatment

The patient underwent reconstructive surgery with the introduction of an endoprosthesis, in this case a self-supporting three-dimensional metal open cell foam structure of titanium made according to example 1 (1.0 mm thick), in order to replace the zygomatic bone defect.

Operation

The operation started with endotracheal anesthesia, followed by the dissection of the soft tissues of the infraorbital incision, the exposure of defects of the orbital floor and the zygomatic bone, measurement of the size of the bone defect and osteosynthesis of the upper jaw and zygomatic bone. After that, the zygomatic endoprosthesis was made in accordance with the configuration of the bone defect by forming a small structure out of the plate of open cell foam. With the help of scissors, an endoprosthesis was cut that exceeded the size of the bone defect by 4 mm, was bend to the required shape, corresponding to the configuration of the bone bed. Then, the zygomatic endoprosthesis was introduced into the tissue and fixed with screws inserted into the holes made in advance. The wound was sutured in layers with non-absorbable suture material. Finally, a traction test was performed. The postoperative period was stable. On the control radiograph, the position of the left zygomatic bone is anatomical. The endoprosthesis is tight to the bone defect. The patient was discharged on the 14th day. At the time of discharge and control inspection no complaints were presented. The cosmetic and functional effect is good.

Conclusion

Osteosynthesis of the titanium cell foam structure has allowed restoring the bone architecture of the cheek area, and bone defects were eliminated. A background for the successful functional and aesthetic treatment was created using the open cell foam structure of the present invention.

Example 4

This example describes cleft palate surgery. Bone grafting in congenital clefts of the upper palate is one of the most important stages in the medical rehabilitation of patients. The results of the osteoplasty of the alveolar process of the upper jaw formation depends on the formation of the correct form of dental arches of the upper jaw, stabilization of the segments of the upper jaw, which determines success of later orthodontic treatment, normalization of speech, breathing and etc. The technique, which is used today in the plastics of the alveolar process, was proposed by Boyne and Sands in 1972. By conducting this intervention, the vestibular-nasal, oro-nasal are simultaneously closed fistula and eliminate the bone defect of the upper jaw, through transplantation spongy autocapacity, which is taken from the iliac crest bones. The optimal age for bone plastics according to some ranges from 9 to 11 years, according to others it is 11 -13 years. The question of the time of the intervention remains open to this day. The main reason for the often poor efficacy of bone grafting is a high degree of resorption of transplanted spongy bone tissue in recipient bed (up to 50% of the initial volume of the transplant taken) in the process of its revascularization. With the elimination of bilateral clefts of the alveolar process up to 70% of the initial volume of the graft is subjected to resorption. The reasons for this are as follows. First, the graft represents small particles of autocapacity, which the organism does not recognize as bone tissue and resorbs them. It happens on stage revascularization. Secondly, this kind of graft cannot be reliably fixed in relation to the bone fragments of the upper jaw. At the same time, one of the principles of successful performing bone grafting with a predictable result is adequate fixation.

The purpose of this experiment is to increase the efficiency of the treatment of patients with congenital cleft palate, through the use of the open cell foam structure and the improvement of surgical treatment methods in complex medical rehabilitation of patients with this pathology. Objectives of the study are to give a comparative morphological assessment of reparative processes, to develop a method of plastics of the alveolar process of the upper jaws with the new open cell foam structure and to establish the optimal age of patients to perform plasty with the new structure in congenital crevices of the upper jaw.

Materials and research methods

The study includes 1 patient, aged 9 years, with congenital cleft of the alveolar process ofthe upper jaw. The child corresponds to the following criteria. The child is satisfactory fed, on the time of admission does not have colds and various kinds of infectious diseases, does not have severe somatic pathology, and the oral cavity is sanitized. The algorithm for examining patients with alveolar clefts to process the maxilla includes a complete blood count, urinalysis, biochemical analysis of blood, clotting time and duration of bleeding, blood group and Rh factor, and electrocardiography. The patient consults a pediatrician and an anesthesiologist. The size of the defect of the alveolar process of the upper jaw is visually assessed, as is the state of the oral mucosa in the area of the cleft. X-ray and computed tomography of the region crevices is performed. The listed research methods allowed to evaluate the conditions for surgery to eliminate crevices of the alveolar process of the maxilla using the open cell foam structure of the invention, to determine the surgical tactics, and to objectify the results of treatment.

Operation procedure

Step 1- General anesthesia

Step 2-Based on anthropometric facial analysis and computer modeling, we create a model of the open cell foam structure, also called the flexible titanium bone. The titanium bone is customized in the shape and size of the defect so that it enters into it with some effort, where after it is fixed with small titanium screws. The plate has a length of 50mm and 70mm. The thickness is 0.55-1.0 mm. Holes are located along the edges of the plate have an elongated shape. Through these holes screws are provided for fixing the upper jaw fragments. Thanks to the elongated shape ofthe holes, it is possible to expand the upper jaw with orthodontic treatment in the early postoperative period. Screws of two types are used, 5.0 mm and 7.0 mm long, with a diameter of 1mm. Maximum depth threads with a 45 degree thread angle are 0.1mm. This way, the screw is designed having an outer diameter of 1.0mm, an internal diameter of 0.8mm, and thread pitch of 0.4-0.5mm. Then we proceed to the final stage ofthe operation. The flexible titanium bone is covered with the vestibular mucoperiosteal flap and the wound is sutured.

Step 3- In the postoperative period the patient is prescribed a sparing diet, antibacterial, anesthetic treatment, physiotherapy. In the oral cavity sutures are removed on the 12th 14th day.

Conclusions

The flexible titanium bone is easy to model and has a high stability. It rapidly integrates with the surrounding tissues. It has appeared to be resistant to microbial infections. Overall, the structure allows in case of nonunion ofthe upper palate to obtain more stable results of osteoplastic operations and reduce the likelihood of recurrence of deformity.

Claims

A self-supporting three-dimensional metal open cell foam structure, the structure having cells with apertures between 200 µm and 800 µm in diameter, for use as a bone prosthesis in skull surgery, the structure having a porosity has from 50% to 95% and a thickness between 0.5 and 5 mm.

A self-supporting structure for use according to claim 1, characterized in that the metal comprises Ti and / or Mg.

A self-supporting structure for use according to claim 2, characterized in that the metal mainly consists of Ti and / or Mg.

A self-supporting structure for use according to claim 3, characterized in that the metal consists of 100% Ti, 94-97 %% Mg in combination with 3-6% other pharmaceutically acceptable metals or a mixture of 50% Ti and 50% Mg.

A self-supporting structure for use according to any one of the preceding claims, characterized in that the thickness of the structure is between 1.0 and 2.0 mm.

A self-supporting structure for use according to any one of the preceding claims, characterized in that the porosity is between 60 and 90%.

A self-supporting structure for use according to any one of the preceding claims, characterized in that the cells have openings with a diameter between 250pm and 500pm.

A self-supporting structure for use according to claim 7, characterized in that the cells have openings with a diameter between 300pm and 400pm.

A self-supporting structure for use according to any one of the preceding claims, characterized in that the structure is provided with a hydrophilic coating.

A self-supporting structure for use according to claim 9, characterized in that the coating is selected from metal oxide, bone morphogenic protein-2 (BMP-2) and calcium phosphate.

A self-supporting structure for use according to any one of the preceding claims, characterized in that the structure is a regular vein angle.

A self-supporting structure for use according to any one of the preceding claims, characterized in that the surgery is maxillo facial surgery, in particular cleft palate surgery.

13. A self-supporting three-dimensional metal open cell foam structure, with cells having openings between 200 µm and 800 µm in diameter, which structure has a porosity greater than 50% and a thickness between 0.5 and 5 mm.

A method of producing a self-supporting three-dimensional metal open cell foam structure according to claim 13, characterized in that the structure is made by 3D laser sintern of metal beads having a diameter between 10pm and 50pm.

A method of producing a self-supporting three-dimensional metal open cell foam structure according to claim 13, characterized in that the structure is made by depositing the metal by chemical vapor deposition on a supporting framework.

A method of surgery for a patient's skull comprising:

- exposing a defect in the skull so that the defect and the leg surrounding the defect is exposed to the environment;

- positioning the self-supporting structure according to claim 13 over the defect;

- spatially fixing the self-supporting structure relative to the skull;

- covering the self-supporting structure with the patient's tissue or artificial tissue.