Porous materials and methods

Abstract

A porous material suitable for implantation is disclosed that contains a large number of substantially spherical intercalated cavities in a polymer. The cavities are formed by combining the polymer with a dissipative material under heat and pressure, followed by removing the dissipative material to expose the cavities. Intercalation can be increased by subjecting the dissipative material to a consolidation molding process before combining it with the polymer. The porous material can be combined with solid materials, such as solid polymers, to produce complex implantable materials with a variety of characteristics.

Description

Technical Field

[0001] The present invention relates to porous materials and methods for producing them. In particular, the present invention relates to porous polymers suitable for implants and methods for producing them.

Background Art

[0002] There are various methods in the art for forming porous microplastic materials. In particular, the prior art discloses mixing a salt-type pore-forming agent such as sodium chloride into a resin to form a molding material, subjecting the molding material to a molding process to produce a molded part, and then washing the product to elute or leach out the salt-type pore-forming agent, thereby forming pores to produce a porous product. The prior art also teaches methods for producing porous structures etc. using spherical or circular salt particles. However, due to their spherical nature, these spherical salt particles only contact each other at their diameter edges, resulting in weak interconnectivity of the pores of the porous material.

Summary of the Invention

[0003] To address the foregoing and other drawbacks, there is provided a material suitable for an implant comprising a strong biocompatible polymer containing a plurality of interconnected hollows, substantially all of which are spherical, substantially all of which have a diameter of 180 μm to 600 μm, and further less than 50% of the volume contains this biocompatible polymer.

[0004] There is also provided a material suitable for an implant comprising a solid portion containing a solid biocompatible polymer, the porous portion comprising a strong biocompatible polymer containing a plurality of interconnected hollows, substantially all of which are spherical, substantially all of which have a diameter of 180 μm to 600 μm in terms of volume, and further less than 50% of the volume of this porous portion contains this biocompatible polymer.

[0005] Furthermore, this provides intermediate materials for manufacturing implants containing a robust biocompatible polymer and dissipative material that essentially consists of partially flattened spherical particles suspended in this polymer.

[0006] A method for manufacturing a porous implant is also provided. The method includes placing a quantity of inelastic particles of a dissipative material into a mold; heating the mold to a first temperature while applying a first mechanical pressure to the partially flattened inelastic particles; placing a biocompatible polymer together with the partially flattened particles into the mold; heating the mold to a second temperature while applying a second mechanical pressure to form a mixture of the biocompatible polymer and the partially flattened particles; and removing the partially flattened particles from the mixture. The quantity of the partially flattened particles relative to the polymer is such that, upon removal of the partially flattened particles from the mixture, a porous material is left, which includes the polymer and a plurality of interconnected hollows.

[0007] Furthermore, the present invention provides an intermediate material for subsequent use in the manufacture of porous materials suitable for implants. The intermediate material essentially consists of a mass of substantially spherical, coalesced particles. [Brief explanation of the drawing]

[0008] [Figure 1A] Figures 1A and 1B provide a plan view of a porous material according to an exemplary embodiment of the present invention and a CT scan image of a porous material according to an exemplary embodiment of the present invention, respectively. [Figure 1B] Same as above. [Figure 2] Figure 2 provides a perspective view of a porous biocompatible material combined with a solid biocompatible material according to an exemplary embodiment of the present invention. [Figure 3] Figure 3 provides a plan view of a dissipative material according to an exemplary embodiment of the present invention. [Figure 4A] Figures 4A and 4B provide cross-sectional views of a mold filled with dissipative material and a molded assembly compressing dissipative material according to exemplary embodiments of the present invention, respectively. [Figure 4B]Same as above. [Figure 5A] Figures 5A, 5B, and 5C provide cross-sectional views of a mold filled with compressed dissipative material and PEEK according to an exemplary embodiment of the present invention, a molded assembly compressing the compressed dissipative material and PEEK, and the molded assembly after compression of the compressed dissipative material and PEEK, respectively. [Figure 5B] Same as above. [Figure 5C] Same as above. [Modes for carrying out the invention]

[0009] Referring to Figures 1A and 1B, a material suitable for implants, generally indicated by reference no. 10, is described. Material 10 comprises a porous biocompatible polymer 12 containing numerous spherical hollows 14. The hollows 14 have substantially similar diameters, for example, 300 μm to 415 μm, and are interconnected with each of several other hollows 14 by openings 16. Each opening 16 is of similar size and substantially circular in shape. Furthermore, the spacing between the hollows 14 is such that the biocompatible polymer 12 occupies at most 15% to 50%, with the remainder being the material 10.

[0010] Referring to Figure 2, in a particular embodiment, the porous biocompatible material 10 can be combined with a solid biocompatible material 18 to form a composite blank 20. The composite blank 20 can be machined, for example using a CNC milling machine (not shown), to provide an implant 22 that exposes the porous surface 24 of the porous material 12 and can introduce various features such as a perforation 26 for receiving a positioning pin (not shown), a hole 28 that may contain a screw thread 30 for receiving a fastener, such as a screw (not shown), an opening 32, a beveled edge 34, and a contoured surface 36.

[0011] Returning to Figure 1A in addition to Figure 2, in certain embodiments, the hollow 14 can be filled with a material that promotes bone endografting, such as bioglass (not shown), through the porous surface 24 that is exposed during or after the production of the porous biocompatible polymer 12. In another embodiment, the hollow can be filled with a bioactive agent such as bioglass, which can be replaced after implantation by a biological process.

[0012] Referring to Figure 3 in addition to Figure 1A, in one embodiment, the porous material 12 is manufactured from a polymer such as polyetheretherketone (PEEK) and a dissipative material 34, which is substantially entirely spherical with few non-spherical particles. In exemplary embodiments, the polymer described herein comprises a polyaryletherketone such as PEEK, the dissipative material comprises a sodium chloride salt, and in a given embodiment, other suitable materials may be used. The method comprises four main steps: spherization of the dissipative material; molding the spherical dissipative material together with the polymer to produce an intermediate portion; processing the intermediate portion to expose the porous surface and introduce features; and removing the dissipative material from the processed portion to form an implant.

[0013] Referring to Figure 3, the dissipative material is exemplary composed of a number of spherical particles 34, each having a similar diameter D. In exemplary embodiments, preferred diameters D are in the range of 300 μm to 600 μm, particularly at least about one-third of the spherical particles are between 300 μm and 400 μm, and the remainder outside these ranges are at least about one-third of the particles between 400 μm and 600 μm. In particular embodiments, about 5% to about 20% of the spherical particles are outside the 300 μm to 600 μm range. Other ranges or combinations of ranges may be used in a given embodiment, in particular to help achieve specific porosity (i.e., the ratio of the resulting hollow space to the polymer when the dissipative material is removed) or insertion, as will be detailed below.

[0014] Referring to Figure 3, as described above, in the exemplary embodiment, the dissipative material is NaCl salt. Irregularly shaped NaCl salt particles are sieved into groups containing salt particles of different sizes. Exemplarily, a four-stage sieve can be used to separate the salt into a range of sizes. In one embodiment, the sieving apparatus can sort into four size ranges. Exemplarily, the first sieve allows for the recovery of salt particles between 716 μm and 583 μm, the second sieve allows for the recovery of salt particles between 582 μm and 471 μm, the third sieve allows for the recovery of salt particles between 470 μm and 311 μm, and the fourth sieve allows for the recovery of salt particles smaller than 310 μm.

[0015] Referring to Figure 3, in the next step, a spheroidizing assembly (not shown) is used to subject a selected range of salt particles to a spheroidizing process to produce a quantity of spherical salt particles. The spheroidizing assembly assists in the process of physically transforming the salt particles from an irregular shape to a spherical shape.

[0016] Referring to Figure 3, a selected range of salt particles 38 are stirred, drawn along a conduit (not shown) by compressed air, and passed through an oven (also not shown) to heat the salt particles 38. The air ensures good separation of the flow of salt particles 38 to form spheres. Once the heated salt particles 38 exit the conduit, they are further heated in a flame (also not shown), for example, from a torch lamp, to form a substantially spherical dissipative material 34. The spherical dissipative material 34 is substantially cooled and recovered.

[0017] Referring to Figure 3, the desired dissipative material 34 is obtained by combining heating, stirring, and subsequent cooling of the salt particles 38. The spherical dissipative material 34 is recovered and, exemplary, subjected to additional sieving by a sieving apparatus (not shown) and then sorted into various ranges. Exemplarily, the spherical dissipative material 34 is sorted into the following size ranges: 180 μm to 300 μm, 300 μm to 425 μm, 425 μm to 500 μm, 500 μm to 600 μm, and >600 μm.

[0018] Referring to Figures 4A and 4B, after spheroidization, the spherical dissipative material 34 is placed in a mold 40 defining a cavity 42, and subsequently closed with a tight-fitting molding cap 44. A piston (not shown) drives the upper plate 46 to the lower plate 48 and drives the molding cap 44 into the mold cavity 42. Controlled heating of the mold cavity 42 and the molding cap 44 is provided, for example, by a plurality of electric heating elements 50. Furthermore, controlled cooling of the mold cavity 42 and the molding cap 44 is provided to both the upper plate 46 and the lower plate 48, to which a cooling fluid such as water can be circulated, for example, by a cavity (not shown). The temperature of the mold cavity 42 is detected by a thermocouple (also not shown) installed close to the lower end of the mold cavity 42. Furthermore, the actual mechanical pressure exerted between the upper plate 46 and the lower plate 48 by the piston can be detected by means of a load cell (also not shown). By including an independent heating element 50, the cooling cavity, as well as the multiple thermocouples, the upper plate 46, and the molding cap 44, can be heated and cooled independently of the lower plate 48 and the mold cavity 42, ensuring precise control of the temperature of the material in the mold cavity 42. The piston is preferably driven by an electric actuator (not shown), but other types of actuators, such as hydraulic air or compressed air, may be suitable for specific applications. Furthermore, heating and cooling of the upper plate 46 and the lower plate 48 are exemplified by electric heating and water cooling, respectively, but other means of heating and cooling the mold 40, such as a Peltier effect device (not shown), may provide appropriate modifications to the assembly.

[0019] Referring to FIGS. 4A - 4B, in particular, to increase the hollow interconnectivity of the porous material, the spherical dissipative material 34 placed in the cavity 42 is first subjected to a compression and heating process. In this regard, with the spherical dissipative material 34 in the cavity 42, the piston is driven so that the upper plate 46 moves lower towards the lower plate 48, and the forming cap 44 is driven into the cavity 42. It should be noted that the forming cap 44 and the cavity 42 can take on several simple or complex shapes, thereby enabling the material formed for subsequent processing or parts with various formed shapes. While this compression is being carried out, a current is applied to the electric heating element 50 to heat the mold 40 and the spherical dissipative material 34, illustratively to 280°C. When the desired temperature is reached, additional pressure is applied, illustratively up to a maximum of 1.37 Mpa.

[0020] Referring to FIGS. 4A - 4B, after applying pressure while heating, the spherical dissipative material 34 is illustratively partially flat and mostly coalesced. Usually, when the mold is opened at this stage, the partially flat coalesced spherical dissipative material 34 can be removed in one piece or in a few large pieces, each containing a number of partially flat spherical dissipative materials 34. In any case, when the mold 40 is opened, the partially flat coalesced spherical dissipative material 34 does not disintegrate when subjected to the next process step and retains its structure.

[0021] Referring to Figures 5A-5C, in an exemplary embodiment, after compression, the mold 40 is opened and a layer of PEEK 52 is placed on a partially flat, unified spherical dissipative material 34. The mold opening 42 is closed again by a molding cap 44, and heat is applied by a heating element 50 to heat the mold 40 to an exemplary 400°C, compressing the PEEK 52 into the partially flat dissipative material 34 while forming an intermediate material 54 containing a mixture of PEEK 52 and the partially flat dissipative material 34. The duration of the molten phase depends on several factors, including the amount and depth of the intermediate material 54 in the mold 40. Once the desired temperature is reached, additional pressure, exemplary about 3.45 MPa, is applied and the intermediate material containing the mixture of PEEK 52 and dissipative material 34 hardens. At the end of the heating and hardening phases, the heating element 50 is stopped and the cooling phase begins. During the cooling phase, high pressure, exemplified by about 6.9 MPa, is applied to the intermediate material by a piston through the molding cap 44, and a cooling fluid such as water circulates within the cavity, thereby cooling the mold 40 and the intermediate material 54. Once the intermediate material 54 has solidified sufficiently, the piston moves, retracting the molding cap 44 from the mold hole 42, thereby allowing the molded intermediate material 54 to be removed from the mold hole 42.

[0022] As mentioned above, and referring back to Figure 2, the porous structure can be subsequently processed. In some cases, processing is optional, and in some embodiments, the embeddable portion can be reached without any processing. Furthermore, processing can be performed before or after the removal of the dissipative material 34. Those skilled in the art will understand that a desired structure of the portion containing the porous structure can be obtained using various processing techniques. PEEK is easy to process, and the porous PEEK portion manufactured according to the present invention can be shaped using various cutting tools.

[0023] To remove the fugitive material in the form of spherical particles 34, the solidified molding mixture 54 is placed in an ultrasonic bath (not shown) containing a solvent such as heated distilled water. Exemplarily, the water is heated to 70 °C. The solidified molding mixture 54 is immersed in the bath until the salt dissolves from the mixture 54, thereby exposing the porous material having the inserted hollow. The solidified molding mixture 54 is held in the bath for a time corresponding to its volume. Thereafter, the porous material is taken out of the bath and dried, for example, overnight at 100 °C in a dryer (not shown). Finally, the final porous material is taken out of the dryer. The resulting porous PEEK material has interconnected hollows that promote bone ingrowth and is suitable for implants.

[0024] To improve the strength of the resulting porous part, annealing techniques can be used. Usually, the annealing techniques used are supplied by the manufacturer of the raw material.

[0025] Referring to FIGS. 5A - 5C in addition to FIG. 2, in an alternative embodiment, to form a solid PEEK / porous PEEK composite, an additional layer of PEEK 52 can be placed under the mold 40 or over the PEEK / salt mixture 54. In this regard, the solid layer acts as a barrier between the porous layer and other parts and can be used, for example, to limit bone ingrowth in the resulting molded part. Further, as described above, PEEK is excellent in processing and, as a result, the solid layer can be processed to interconnect with other parts made of, for example, PEEK or other materials such as titanium, tantalum, etc. Alternatively, other PEEK composite materials such as PEEK reinforced with carbon (e.g., PEEK carbon prepreg or pre - impregnated fibers) or other fibers can be molded together with the PEEK / salt mixture to provide a composite structure having various different characteristics regarding strength, rigidity, flexibility, etc., thereby resulting in a composite suitable for a wide variety of applications. Further, by alternating the layers of PEEK or PEEK composite and the PEEK / salt mixture, a multi - layer solid / porous composite can be formed.

[0026] In another alternative exemplary embodiment, the method of the present invention can be more generally applied using materials other than PEEK and table salt. Indeed, as will be understood by those skilled in the art, the present invention can be substantially applied to any first material that is in liquid or fluid form at a temperature lower than the melting point of the second specific material and can subsequently harden to form a solid composite. Of course, the second specific material can also be removed from the solid composite, leaving the porous structure of the hardened first material.

[0027] In yet another alternative exemplary embodiment, the method of the present invention can be applied more generally to a first material in liquid form at room temperature, such as epoxy or other polymers, which is then cured after mixing with a second solid specific material by introducing a catalytic curing agent or the like. Similar results can be obtained with a first material that can be heat-set or cured by applying heat and pressure.

[0028] The present invention can be modified by certain embodiments without departing from the spirit and essence of the invention as set forth in the appended claims, as described above. [Explanation of Symbols]

[0029] 10 materials 12 Biocompatible polymers 14 Hollow 16 Opening 18. Biocompatible materials 20 Composite Blanks 22 Implants 24 Porous surface 26 perforation 28 holes 30 screw threads 32 openings 34. Dissipative materials 36 Contour surface 38 Salt particles 40-inch 42 Cavity 44 Molded caps 46 Top plate 48 Lower plate 50 Electric heating element 52 PEEK 54 Intermediate materials

Claims

1. Solid biocompatible polymers, The polymer contains a dissipative material essentially consisting of partially flat, spherical particles that are suspended and coalesced. Substantially all of the aforementioned spherical particles have a diameter of 180 μm to 600 μm. The aforementioned partially flat spherical particles are inelastic particles, The aforementioned dissipative material is NaCl, an intermediate material for manufacturing implants.

2. The intermediate material according to claim 1, wherein substantially all of the spherical particles have a diameter of 315 μm to 425 μm.

3. The intermediate material according to claim 1, wherein the volume of the dissipative material based on the volume of the intermediate material is 50% to 85%.

4. The intermediate material according to claim 1, wherein the dissipative material can be decomposed in water.

5. A method for manufacturing porous implants, Placing inelastic particles of a dissipative material into a mold, Heating the mold to a first temperature while applying a first mechanical pressure to the partially flattened inelastic particles, To place the biocompatible polymer in the mold together with the aforementioned partially flat particles, The mold is heated to a second temperature while applying a second mechanical pressure to form a mixture of the biocompatible polymer and the partially flat particles. This includes removing the partially flat particles from the mixture, By removing the partially flat particles from the mixture, the partially flat particles remain in such an amount relative to the polymer that the polymer and a porous material containing a plurality of interconnected hollows are left. The method involves the inelastic particles being table salt.

6. The method according to claim 5, wherein the particles of the dissipative material are substantially spherical.

7. The method according to claim 5, further comprising cooling the mold under a third mechanical pressure until the mixture hardens.

8. The method according to claim 5, wherein the polymer is a polyaryl ether ketone.

9. The method according to claim 8, wherein the polyaryl ether ketone is polyether ether ketone (PEEK).

10. The method according to claim 5, wherein the inelastic particles can be decomposed into a solvent that does not react with the polymer, and the removal step comprises washing the mixture in a bath of the solvent.

11. The method according to claim 10, wherein the solvent is water.

12. The method according to claim 5, wherein the second pressure is greater than the first pressure.

13. The method according to claim 5, further comprising cooling the mixture while applying a third pressure greater than the second pressure.

14. The method according to claim 5, further comprising annealing the porous material.

15. Essentially consisting of a mass of unified particles that is practically spherical, The aforementioned spherical, coalesced particles are partially flat. Substantially all of the aforementioned spherical, unified particles have a diameter of 180 μm to 600 μm. The aforementioned spherical, coalesced particles are inelastic particles. The aforementioned spherical, coalesced particles are an intermediate material to be used in the subsequent production of porous materials for implants, manufactured from NaCl.

16. The material according to claim 15, wherein the spherical coalesced particles can be decomposed in water.

17. The material according to claim 15, wherein substantially all of the spherical coalesced particles have a diameter of 315 μm to 425 μm.

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