EP2352530A2

EP2352530A2 - Auxetic material

Info

Publication number: EP2352530A2
Application number: EP09740093A
Authority: EP
Inventors: Carolin KÖRNER; Peter Heinl; Robert Friedrich Singer
Original assignee: Friedrich Alexander Univeritaet Erlangen Nuernberg FAU
Current assignee: Friedrich Alexander Univeritaet Erlangen Nuernberg FAU
Priority date: 2008-11-10
Filing date: 2009-10-14
Publication date: 2011-08-10
Also published as: WO2010052101A3; US20110282452A1; DE102008043623A1; WO2010052101A2

Abstract

The invention relates to an auxetic material that is composed of a periodic arrangement of three-dimensional structural elements (G, G1, G2, G3) connected to each other, wherein each of the structural elements (G) comprises a first (3) and at least three second supporting elements (4), wherein the first (3) and the second supporting elements (4) are connected at a common node (1) with their one ends, and wherein a first angle (a) between the first supporting element (3) and the second supporting elements (4) is less than 90°.

Description

Auxetic material

The invention relates to an auxetic material.

An auxetic material is understood as meaning a material having a negative transverse contraction number v. Auxetic materials behave abnormally, unlike materials with a positive transverse contraction index v. Ie. under compressive stress, they contract in a direction perpendicular to the direction of compression, whereas against it they expand in a direction perpendicular to the tensile direction under tensile stress.

From the prior art, auxetic materials made of a compressed polymer foam are known. For example, reference is made to US 4,668,557, WO 99/25530, US 5,035,713 and WO 2007/052054 A1.

E.A. Friis, R.S. Lakes, J.B. Park: Negative Poisson's Ratio polymeric and metallic forms, Journal of Materials Science, 23, 1998, 4406-4414 discloses an auxetic material made from a highly ductile copper foam. The auxetic properties are also imparted to the copper foam by a suitable plastic deformation.

For the production of the known auxetic materials by a plastic deformation of foams, only thermoplastic polymers and highly ductile metals are suitable. The randomly formed three-dimensional structures are not periodic and have only partially an auxetic structure. The auxetic properties of these materials can not be adjusted exactly.

The object of the invention is to eliminate the disadvantages of the prior art. In particular, an auxetic material is to be specified, which consists of a large number of different materials can be produced. According to a further object of the invention, the auxetic properties should also be adjustable.

This object is solved by the features of claims 1 and 16 to 18. Advantageous embodiments of the invention will become apparent from the features of claims 2 to 15.

According to the invention, an auxetic material is proposed, which is formed from a periodic arrangement of three-dimensional framework elements, wherein each of the framework elements comprises a first and at least three second support elements, wherein the first and the second support elements with their one ends in a common node are connected, and wherein a first angle between the first support member and the second support elements is smaller than 90 °. The proposed material comprises a framework structure which, because of its particular design of the three-dimensional framework elements forming it, has auxetic properties. The framework structure results from a periodic arrangement of the interconnected framework elements. In a framework level, the periodicity is expediently equal to 1, d. H. Each scaffolding element is directly connected to another scaffolding element. The periodicity can be given in three linearly independent spatial directions. The free ends of the support elements are expediently connected to each other. The framework elements are connected to one another in such a way that their nodes and supporting elements do not touch each other during a deformation of the grid. The term "deformation" is understood to mean a reversible deformation of the grid.

In the context of the present invention, the framework elements can be varied by, for example, the number of the second support elements and / or the first angle and / or a Length of the first and / or second support elements to be changed. The first and / or second support elements may be configured straight, curved or wavy. By changing the framework element, it is possible to set desired auxetic properties. The scaffolding elements can be made of any suitable material, especially ceramic, all metals or polymers. This can significantly expand the class of auxetic materials. In particular, the combination of auxetic materials and non-auxetic materials opens up completely new options for adjusting material and component properties.

With regard to the configuration of the three-dimensional scaffolding element, it has proved to be advantageous that a second angle between two adjacent second support elements is in each case the same size. Ie. all second angles have the same value. Furthermore, the second support elements may have the same length. A length of the first support element may differ from the length of the second support elements. However, it can also be that the first support element and the second support elements have the same length.

Advantageously, the interconnected scaffold elements form a scaffold layer in which the nodes lie in a scaffold plane and the first support elements extend perpendicularly in the same direction from the scaffold plane. In the framework layer, the framework elements are thus connected to one another by the ends of the second support elements.

In the connection of three scaffolding elements with their second support elements results in a scaffold layer with a honeycomb-like structure. A three-dimensional framework structure formed by the framework elements is formed by skeleton layers arranged one above the other. The framework layers can expediently be arranged one above the other such that their framework levels run essentially parallel. The framework layers are supported in this case by the first support elements from each other.

According to a further embodiment, the framework layers are arranged periodically in 2 or 3 stacks one above the other. A periodicity in a z-direction is thus here preferably equal to 2 or 3. By the different periodic arrangement of the framework layers, framework structures with different properties can be produced.

The framework layers are advantageously connected to one another via the first support elements. In this case, the connection points formed for connecting the framework layers can lie in a connection point plane which is essentially parallel to the framework plane. In a connection point, at least three second support elements of a framework layer and a first support element of a further framework layer arranged above are advantageously connected to one another.

The framework elements may be made of metal, preferably titanium, a titanium, cobalt chrome or nickel-based alloy, steel, magnesium, shape memory alloys, in particular NiTi. Likewise, it is possible, the scaffolding elements made of plastic, preferably polyamide, polyetheretherketone or the like. to manufacture. Furthermore, it is possible to produce the framework elements made of ceramic, preferably SiC, Al ₂ O ₃ , hydroxyapatite or the like. According to an expedient embodiment, the framework elements are coated with a coating material. It may be, for example, hydroxyapatite, tantalum, TiN, TiC or diamond. It can also be that the surface of the framework elements, for example, by etching or the like. is modified.

The proposed auxetic material can be used in many areas. It has proven particularly expedient to use the auxetic material as a bone substitute or as a component of a bone substitute or implant. In that regard, it is expected that, due to the auxetic properties during loading and unloading, there will be a pumping effect which assists the supply of the biological tissue. The auxetic material may in particular also consist of a resorbable material, for. As magnesium, Hydroxylap- tit, are produced. The proposed auxetic material is also particularly suitable for the production of disc replacement materials, for the back-feeding, for example of a knee joint implant or as a replacement for bone marrow.

Apart from that, the proposed auxetic material for the production of sound absorbing materials, the

Manufacture of materials for the protection of an impact or an impact as well as for the production of adaptive filters with variable pore size can be used.

In addition, the auxetic material can serve as a scaffold for

Production of composite materials, eg. B. by infiltration with polymers, metals or ceramic materials.

For the preparation of the proposed auxetic material are common rapid manufacturing or additive manufacturing processes, such as selective laser or electron beam melting. However, it is also possible to produce the proposed auxetic material in a casting process, preferably in precision casting. In addition, it is conceivable other suitable manufacturing processes, such as lithography, electroforming, impression and micro-machining techniques to use. For coating an auxetic framework structure according to the invention, conventional processes are suitable, for example physical or chemical gas phase deposition, galvanic coating processes, powder coating processes and the like.

Embodiments of the invention will be explained in more detail with reference to the drawings. Show it:

1 shows the derivation of a scaffold element,

2 shows the formation of a framework layer from the framework element according to FIG. 1, FIG.

FIG. 3 shows a first framework structure using the framework layer according to FIG. 2 and FIG

4 shows a second framework structure using the framework layer according to FIG. 2.

The left-hand view of FIG. 1 shows a tetrahedral structure, as realized, for example, in the diamond lattice. In this case, four arms 2 of the same length extend from a node 1 under the known tetrahedral angle of 109.5 °. From such a tetrahedral structure, a framework element G according to the invention can be derived by mirroring three arms on a plane of symmetry running perpendicularly to the fourth arm and through the node 1. Such a framework element G is shown in the right-hand illustration of FIG. It is formed from a first supporting element 3 and three second supporting elements 4. The first 3 and the second supporting elements 4 are connected at the junction 1. The support elements are preferably rod-like or rod-like educated. They expediently have a circular cross section. A first angle α between the first 3 and each of the second support elements 4 is identical. The angle α is less than 90 °. It is expediently in the range from 85 to 30 °, preferably in the range from 85 to 60 ° or from 85 to 70 °. A formed between two adjacent support elements 4 second angle ß is also the same. It is in the embodiment shown in Fig. 1 109.5 °. The size of the second angle β is dependent on the size of the first angle α. In the framework element G shown in FIG. 1, the first 3 and the second support elements 4 have the same length. However, it is also conceivable that the first support element 3 are formed longer or shorter than the second support elements 4. Furthermore, it is conceivable to also execute the second support elements 4 in different lengths. In this case, it may be necessary to deviate from the angle equality provided between the second support elements 4, ie, second angles β of different sizes can then also be realized between the second support elements 4.

FIG. 2 shows the formation of a framework layer GS using the framework element G shown in FIG. 1. In this case, three framework elements G1, G2, G3 are connected to the free ends of respectively two second support elements 4 in such a way that in the projection on the xy plane creates a honeycomb-like structure. The first support elements 3 are each perpendicular to a frame plane GE formed by the nodes 1.

FIG. 3 shows the formation of a first framework structure A by stacking a plurality of the framework layers GS shown in FIG. 2. In this case, a second framework layer GS2 is supported on a first framework layer GS1 with its first support elements 3 in connection points 5. In each of the Connecting points 5 are each at least three second support elements 4 of the first framework layer GSl and a first support member 3 of the overlying second framework layer GS2 connected to each other. The connection points 5 form a connection point plane VE, which runs approximately parallel to the framework plane GE. The second framework layer GS2 is rotated by 60 ° with respect to the first framework layer GS1, wherein the axis of rotation is perpendicular to the framework layer GS. The framework layer sequence comprising the first framework layer GS1 and the second framework layer GS2 is periodically stacked to form the first framework structure A. The result is the first framework structure A shown in the right-hand illustration of FIG. 3.

In the second framework structure B shown in FIG. 4, a framework layer sequence comprises a first framework layer GS1, a second framework layer GS2 and a third framework layer GS3, each without rotation, but with a translation in the framework plane GE in the direction of the projection of a second framework element 4 are arranged on the framework level GE. The second framework structure B is formed by periodically stacking the framework layer sequence formed from the three framework layers GS1, GS2 and GS3.

The proposed framework structures A, B can, for example, by means of rapid prototyping method, casting method or the like. be made of a variety of different materials. By varying the geometry, in particular the length or the width of the support elements 3, 4 and the provided between the support members 3, 4 angle α, ß can be adjusted to the auxetic and other properties of the proposed material.

Auxetic frameworks can also be made using other framework elements G. Suitable scaffolding For example, elements G can also have four second support elements 4 and a first support element 3.

The proposed auxetic material is particularly suitable for the production of bone substitutes. In this case, a length of the support elements 3.4 is preferably 0.5 to 3 mm. The diameter of the cross-section preferably round support members 3, 4 is between 0.1 and 1 mm and can be variably adjusted in the structure.

Reference sign list

1 node

2 arm 3 first support element

4 second support element

5 connection point

α first angle ß second angle

A, B framework structure

G, Gl, G2, G3 Scaffolding

GE scaffolding level

GS, GSl, GS2, GS3 framework layer VE connection point level

Claims

claims

1. Auxetic material formed from a periodic arrangement of interconnected three-dimensional framework elements (G, Gl, G2, G3), wherein each of the framework elements (G, Gl, G2, G3) has a first (3) and at least three second support elements (4 ), wherein the first (3) and the second support elements (4) are connected with their one ends in a common node (1), and wherein a first angle (α) between the first support element (3) and the second support elements ( 4) is less than 90 °.

2. Auxetic material according to claim 1, wherein a second angle (ß) between two adjacent second support elements (4) is equal in size.

3. Auxetic material according to one of the preceding claims, wherein the second support elements (4) have the same length.

4. Auxetic material according to one of the preceding claims, wherein the first support element (3) and the second support elements (4) have the same length.

5. Auxetic material according to one of the preceding claims, wherein the interconnected scaffolding elements (G, Gl, G2, G3) form a framework layer (GS, GS1, GS2, GS3), in which the node points (1) in a framework level (GE) lie and the first support elements (3) extend perpendicularly in the same direction from the framework level (GE).

6. Auxetic material according to one of the preceding claims, wherein a three-dimensional framework structure (A, B) formed by the framework elements (G, G, G2, G3) is replaced by each other arranged scaffold layers (GS, GSl, GS2, GS3) is formed.

7. Auxetic material according to one of the preceding claims, wherein the framework layers (GS, GS1, GS2, GS3) are arranged one above the other so that their framework levels (GE) are substantially parallel.

8. Auxetic material according to one of the preceding claims, wherein the framework layers (GS, GS1, GS2, GS3) are arranged periodically in 2 or 3 stacks one above the other.

9. Auxetic material according to one of the preceding claims, wherein the framework layers (GS, GS1, GS2, GS3) are connected to one another via the first support elements (3).

10. Auxetic material according to one of the preceding claims, wherein connection points (3) formed for connecting the framework layers (GS, GS1, GS2, GS3) lie in a connection point plane (VE) which is substantially parallel to the framework plane (GE).

11. Auxetic material according to one of the preceding claims, wherein in a connection point (5) at least three second support elements (4) of a framework layer (GS, GS1, GS2,

GS3) and a first support element (3) of a further scaffold layer (GS, GS1, GS2, GS3) arranged above it are connected to one another.

12. Auxetic material according to one of the preceding claims, wherein the scaffold elements (G, Gl, G2, G3) of metal, preferably titanium, a titanium, cobalt chrome or nickel-based alloy, Mg, steel, shape memory alloys, in particular NiTi, are prepared.

13. Auxetic material according to one of the preceding claims, wherein the scaffold elements (G, Gl, G2, G3) made of plastic, preferably polyamide, polyetheretherketone, are prepared.

14. Auxetic material according to one of the preceding claims, wherein the framework elements (G, Gl, G2, G3) of ceramic, preferably SiC, Al ₂ O ₃ , hydroxyapatite, are prepared.

15. Auxetic material according to one of the preceding claims, wherein the framework elements (G, Gl, G2, G3) are coated with a coating material, preferably hydroxylapatite, tantalum, TiN, TiC or diamond.

A bone substitute comprising the auxetic material of any one of the preceding claims.

17. An implant comprising the auxetic material according to any one of claims 1 to 15.

18. A composite material comprising the auxetic material according to any one of claims 1 to 15.