CA2176707A1

CA2176707A1 - Composite materials using bone bioactive glass and ceramic fibers

Info

Publication number: CA2176707A1
Application number: CA 2176707
Authority: CA
Inventors: Michele S. Marcolongo; Paul Ducheyne; Frank Ko; William Lacourse
Original assignee: Individual
Current assignee: University of Pennsylvania Penn
Priority date: 1993-11-15
Filing date: 1994-11-14
Publication date: 1995-05-26
Also published as: US5645934A; IL111446A; IL111446A0; JPH11506948A; CA2218086A1; DE69431254D1; EP0730681A4; AU700443B2; EP0871504A4; AU701236B2; ATE226098T1; ES2181762T3; WO1996036368A2; DE69624376D1; ES2186780T3; EP0871504A2; JPH09505345A; DE69624376T2; EP0730681B1; WO1996036368A3

Abstract

Composite materials formed from bone bioactive glass or ceramic fibers and structural fibers are disclosed. In pre-ferred embodiments, a braid or mesh of interwoven bone bioactive glass or ceramic fibers and structural fibers is im-pregnated with a polymeric material to provide a composite of suitable biocompatibility and structural integrity. Most preferably, the mesh or braid is designed so that the bioac-tive fibers are concentrated at the surface of the implant (200) to create a surface comprised of at lest 30 % bioactive material, thereby providing enhanced bone ingrowth. The interweaving between the bone bioactive glass or ceramic fibers and the core of structural fibers overcomes the prob-lems found in prior composite systems where the bioactive material delaminates from the polymer. Preferred bioactive materials include calcium phosphate ceramics and preferred structural fibers include carbon fibers. Improved prosthetic implants (200) and methods of affixing an implant (200, are thus also disclosed

Description

2 1 7 6 7 ~ 7 COMPOSITE M~TPDT~T..~ USING BONE
BIOACTIVE GLASS AND CERAMIC FIBERS
The present invention relates to composites made from fibers comprised of bioactive glass and the use of such 5 composites to form implantable surfaces. In particular, the present invention relates to composites comprised of bone bioactive glass or ceramic fibers intermingled with structural f ibers such as carbon f ibers in a matrix of a polymeric material.
0 BA~ UNU OF THE INVENTION
Low modulus composite materials have been employed as femoral components of hip implants to reduce stress shielding of the bone and consequently reduce bone tissue resorption. Currently, composite implants are stabilized in 15 their bony bed by a press ~it. With this method of stabilization, however, optimum stress distribution effects are not fully realized.
Several attempts have been made to improve the fixation of composite femoral implants to bone. These 20 include porous polymer coatings and particulate bioactive coatings. Implants using porous polymer coatings seek to achieve f ixation through mechanical interlocking between the implant and surrounding bone tissue, while the bioactive coatings are designed to attain fixation through a chemical 25 bond between the implant and bone.
Implant surfaces coated with polysulfone particles in an etfort to create a porous coating which would behave similarly to a porous metal coating are disclo~ed in M.
Spector, et al., "Porous Polymers for Biological Fixation, "
.. . ., . , . , . , _ _ _ _ , 2~ 76707 Wo 95/14127 PcrluS94113152--Clin. Ortho. Rel. Res., 235:207-218 (1988) . Although it is disclosed that some bone growth was evident, the majority of the tissue about the implant surface was fibrous. The porous polymer did not enhance the bone tissue growth in any way.
Composite system of calcium phosphate ceramic powder pressed onto a polymer surface and then cured are also known. See P. Boone, et al., ~Bone Attarl t of HA coated Polymers, " J. Biomed. Mater. Res. 23, No. A2:183-199 (1989);
and M. Zimmerman, et al., "The At~ ~nt of Hydroxyapatite Coated Polysulfone to Bone," J. Appl. Biomat., 1:29~-305 (1990). These systems are provided in two fashions. First, the ceramic is flush with the polymer surface, hence, only bonding occurs. Second, the calcium phosphate particles extend from the polymer surface. When interfacial bonding is 15 tested, the failure is between the polymer and the calcium phosphate particles . Hence, the interf ace between the calciulrl phosphate particles and the polymer is the weak link in the system. These referellces disclose the use of polyurethane thermoset and polysulfone thermoplastic 20 polymers, a number of other polymers are similarly used as a matrix for a filler of calcium phosphate ceramic powder in U.S. Patent No. 4,202,055--Reiner et al. The ceramic particles at the surface of t~is implant resorb and are replaced by bone tissue . There are no structural f ibers and 25 the polymer alone is i ntPn-l~d to bear the load . This limits the load-bearing applications of this material to those of:
the polymer. An implantable bone f ixation device comprised of an absorbable polymer and a calcium phosphate ceramic powder filler material is disclosed in U.S. Patent No.
30 4,781,183--Casey et al. The device disclosed is a temporary load bearing device which reso-rbs upon implantation. The calcium phosphate particles are added for strength and also resorb, therefore this device is not fixed to bone tissue through the chemical bonding of bioactive materlal or porous 35 ingrowth.
Structural fibers will improve certain mechanical properties of composite materials. For example, U.S. Patent ~-- Wo 95/14127 2 1 7 6 7 0 7 Pcrluss4ll3ls2 No. 4,239,113--Gross et al. discloses a composition of methylmethacrylate polymers and a bioactive ceramic powder combined with vitreous mineral fibers less than 20 millimeter3 long. This device is used as a grouting material 5 to bond implants to bone tissue . The chopped f ibers are not Gpecifically tailored or designed for mechanical property optimization. A similar composition is disclosed in U.S.
Patent 4,131,597--Bluethgen et al., which mentions the use of glasH or carbon f ibers to add strength to the composite .
10 This patent, however, does not spe~;f;~ y discuss placing fibers to achieve bone bonding regionally. Also, no method of optimization of material properties through arrangement of the structural fibers is suggested. Finally, the method of f ixation to be achieved by the disclosed material is not 15 explained.
A 3imilar approach using a textured device of carbon fiber/triazin, coated or non-coated with calcium phosphate particles is discussed in G . Maistrelli , et al ., "Hydr u~Lyd~ati~e Coating on Carbon Composite Hip Implants in Dogs, " J. Bone ~t. Surg., 74-B:452-456 (1992) . The results reported show a higher degree of bone contact f or the coated devices after six months. However, longer studies are needed to evaluate the long term fatigue effects on the triazin/calcium phosphate interface.
In all these prior art systems, however, it has been found that although a bond between the substrate polymer and bone may be achieved through the use of a bioactive material at the interface, the resulting implant is still unsatisfactory. As discussed above, the significant 30 limitation remains the i~terfacial bond between the bioactive material and the polymer.
Much of the prior art discussed immediately above utilized calcium phosphate ceramic powders as the bioactive component of the composite. Bioactive glass materials were 35 developed by Hench in 1969. See L. Hench, et al., "Bonding Mechanisms at the Interface of Ceramic Prosthetic Materials, ~. ~iomed. Mater. Res., 2:117-141 (1971). More recently, ~ ~ 767a7 Wo 95/14127 ; ~ Pcr~ss4/l3l~2--elongated, c~ntin~ bioactive glass fibers have been fabricated See U. Pazzaglia, et al., "Study of the Oeteoconductive Properties of Bioactive Glass Fibers, " J.
Biomed. Mater. Res., 23:1289-1297 (1989); and H. Tagai, et 5 al., "Preparation of Apatite Glass Fiber for Application as Biomaterials, " Ceramics in Surgery, Vincenzini, P. (Ed. ), Amsterdam, ~sevier Sci. Pub. Co. (1983), p. 387-393. The latter reference discloses bioactive glass fibers in resorbable bone plates.
As seen from the foregoing, it would be desirable to provide a composite mater~al f or use as a prosthetic device that could be designed to provide a structural modulus that closely matched bone . It is thus an obj ect of the present invention to provide composite structures that 15 incorporate a bioactive material in a polymer matrix along with a structural fiber to provide adequate strength.
Additionally, it is a further object of the present invention to provide three dimensional and hybrid composite materials that overcome the deficiencies of the pri~r art, and in 20 particular that provide an adequate interfacial bond between the bioactive material and the polymer.
6~ARY OF l~E lNV~l`lLl--~N
It has now been found that bone bioactive glass or ceramic fibers are useful as a chemical bonding vehicle in 25 combination with a structural three-r~; - c;~-n:il braided fiber substrate . The bioactive f ibers enhance bone growth and bond to surrounding bone tissue. These bone bioactive glass or ceramic f ibers are interwoven in the three dimensional braid with carbon fibers and infiltrated with a thermoplastic 30 polymer to form a three-dimensional bioactive composite material. The glass fibers are preferably concentrated on the outer surface of the composite so as to be exposed to physiological fluids upon implantation. This leaves the carbon fibers concentrated in the center region of the 35 implant material to bear the majority of the load.

o95/14127 ~1 76707 Pcr/uss4/13152 The stress transfer achieved by interfacial bonding between the implant and bone, combir~ed with the "matched modulus ~ of the composite Implant, provides near optimal stress distribution in the bone, thereby improving long term 5 stability and fixation. In addition, with adequate fixation, there is decreased micromotion between the implant and bone, hence the potential for abrasion of the composite material surface is greatly reduced. Consequently, the chances of particulate debris from the implant causing an inflammatory lO response, which often leads to 1088 of implant stability, are also greatly reduced.
BRIEF DESU~l~LluN OF THE DRl~T~
FIG. l is an illustration of the apparatus used to draw bone bioactive glass or ceramic fibers used in the 15 present invention.
FIG. 2 is a photomicrograph of a section of bone showing ingrowth achieved in an implant.
FIG. 3 is a photomicrograph of a section of bone similar to FIG . 2, but taken at higher magnif ication .
FIG. 4 is a cross-section of a composite fiber braid made in accordance with the present invention.
FIG. 5 is a schematic illustrating the orientation and placement of ~ibers in a textile woven from bone bioactive glass or ceramic fibers and structural fibers in 25 accordance with the pre~ent invention.
FIG. 6 is an elevation view of a hip prosthesis made in accordance: with the present invention.
DETAILED DESUKl~LlUN OF THE P~i~ EMBODIMEN-TS
The uniquely constructed composite material of the 30 present invention is able to maintain continuity from the interface of the structural substrate and the carbon fiber~polymer interface, and to the interface between the bioactive surface and the bioactive glass fiber/polymer interface. As explained below, the bioactive section of the 35 implant material is integrally incorporated into the . . - 21 767~7 ~
Wo 9S114127 PCT/US94/13152 substrate through a braided interf ace . Because of this construction there 18 an increased bond surface between the bioactive material and the polymer that imparts a higher degree of integrity to the bioactive composite material as 5 compared to a particulate coating on the surface of a polymeric composite, such as that found in the prior art.
Thus, the likelihood of delamination of the bioactive material from the polymer is greatly reduced. Thus, the present invention provides interfacial bonding between the lO polymer and bioactive coating, overcoming the main limitation of the prior art.
The configuration of the fiber architecture results in the load being applied to a central portion of the composite, which is preferably comprised of strong, inert 15 fibers such as carbon fibers or other biocompatible fibers integrated with the bioactive fiber surface. Stress is therefore transferred from the inert structural fibers to the bioactive fibers at the implant surface. The integration also serves to increase the mechanical integrity of the 20 material system and prevent r~Pl ;~Tn; ni~tion within the composite structure .
In the local environment of the bioactive gla3s fiber, a partial degradation occurs. A9 the bioactive glass f iber i8 resorbed it is replaced by bone tissue; the bone 25 tissue is chemically bonded to the glass fiber and also interlocked with these fibers. Furthermore, the bioactivity reactions occurring at the glass surf ace lead to a precipitation layer on the polymer. This layer, in turn, promotes bone tissue formation and bonding. The triple means 30 of interfaclal bonding leads to an interface which stabilizes the implant in its bony bed and provides stress transfer from the implant across the bonded interface into bone tissue.
The bone is stressed, thus limiting bone tissue resorption due to stress shielding. This significant occurrence~ will 35 increase the life of an implant because fixation and stability will not be lost due to bone tissue resorption, 2~ 7~7G7 Wo 95114127 PCTIU5941131~2 which is an initiator in the cascade of events leading to prosthesis loosening.
In the present invention, a composition of bone bioactive glass or ceramic fibers is preferred. In the case 5 of class the preferred composition leads to a slowly reacting glass while maintaining the ability to be fabricated. A slow reaction rate i8 desired because a large surface area of glass is exposed to physiological solutions during implantation with glass in a fibrous configuration. A
l0 bioactive glass that quickly degrades may lead to an adverse inf lammatory response, impeding bone growth and bonding . The tradeoff is that since the glass must be drawn into continuous fibers it cannot be too viscous or too fluid, or the f ibers would break upon drawing . Describing the 15 compositional range for materials capable of being drawn into ~ioactive glass or ceramic fibers thus involves bioactivity versus manufacturability. A most preferred composition that can be successfully drawn into fibers while nlA;ntA;n;n~
bioactivity is: 52~ sio2; 30% Na20; l~9~ CaO; 3g6 P20s. In 20 developing this range, experimental trials showed that a composition of 5296 SiO2; 32~ CaO; 3~6 P20s; l356 Na20 would be bioactive, however, it is rl;ff;~ lt to draw this composition of glass into f ibers . This is because the CaO and the P2Os work against fiberization, while the Na2O and SiO2 work for 25 it. It was also found that a composition of 52~ SiO2; 2796 CaO; 29~ P20s; l9~ Na20 led to the same difficulties relating to fiberization. The following trends were seen among experimental batches:
Fiberization Bioactivity sio2 increases 40-609~ give bioactivity, decreased bioactivity with higher SiO2 CaO decreases increases P2Os decreases increases, but not required to achieve bioactivity Na2O increases decreases ;~ ; 2~ 767G7 W09~14127 PCrlU594113152--Thus, in preferred embodiments, glass compositions used with the present invention wili be comprised of 40-6096 SiO2; 10-2136 CaO; 0-491~ P20s; and 19-30~ NaO. A more preferred range will be comprised of 45-5596 sio2 15-20~ CaO; 25-35 5 Na20; and 0-396 P20s by mole. As noted above, the most preferred composition on the criteria of slow reaction rate and the ability to be manufactured is 52~ SiO21 30%- Na20~ 15 CaO, and 35~ P20s by mole. Modifiers which may be added to the base composition (by mole) include: 0~3~ K20; 0-25o MgO;
10 0-.296 Al203; and 0-350 F2. As known in the art, such modifiers may be added in small quantities to vary the properties and process parameters without severely affecting the bioactivity or ability of the material to be manufactured.
The following Examples will discuss and explain the 15 formation of a continuous fiber of a bioactive glass for use in a braided fiber and a woven fabric, both of which are impregnated with a polymeric.material such as polysulfone to create a three dimensional composite material.
EXAMPLE I
The most preferred glass fiber composition disclosed immediately above (5296 SiO2~ 305O Na20~ 1596 CaO, and 3% P20s (in mole ~) ) was prepared from powders. The powders were weighed, mixed, and melted at 1350C for two hours in a silica crucible. The glass drawing apparatus used for this 25 Example is shown in FIG. l and includes a resistance heated platinum crucible 50 with an orif ice at the bottom. Glass shards were placed into the crucible 50 and melted at approximately 1150C. The viscous melt formed a meniscus at the crucible orifice 52 To form the fiber lOO, the glass 30 meniscus was gently touched with a glass rod and the glass rod was quickly, yet smoothly, pulled from the crucible orifice 52 to form a glass fiber lOO from the melt. The fiber lOO was manually pulled and attached to the take-up wheel 60 spinning at 300~500 rpm, as determined by the speed 35 control 72 attached tot he motor 70 that rotates the take-up ,. ,,, 21767a7 Wo 95114127 PCTIUS94/131S2 g wheel 60. A smooth, continuous glass fiber 10-13 microns in diameter was obtained.
Polymer ~lates were manufactured using a closed die and a hot press. The polymer (polysulfone) was weighed and 5 dried in an oven at 163C for two hours to drive out excess moisture. The mold was cleaned with ethanol and sprayed with tef lon mold release . The thermoplastic powder was poured into the mold and the mold was placed in the hot press. The press was heated to 260C and pressure was then applied to 10 14, 000 lbs and released. This was repeated twice. The mold was then heated to 300C and a pressure of 620 psi was maintained for thirty minutes. At this time the pressure was released and the mold was air cooled.
The same processing parameters were followed to 15 make plates of a composite material . The polymer was f irst mixed with chopped glass fibers and then processed with the closed die in the hot press, as described above.
Plugs 4 mm in diameter and 3 mm thick, were machined out of both the polymer plates and the plates that included the chopped bioactive fibers using a core drill tip.
The samples were then cleaned with soap and water to remove cutting fluids, and ultrasonically cleaned in ethanol and deionized water, being dried after each cleaning. The implants were sterilized with ethylene oxide.
One bioactive glass fiber/polysulfone and one control polysulfone plug were implanted bilaterally in the medial proximal aspect of the tibia using aseptic techniques.
Each rabbit served as its own control. Five rabbits were euthanized at three weeks and f ive at six weeks .
The retrieved tibiae were immersed in formalin fixative for two weeks. They were rinsed in deionized water and gross sectioned with a low speed blade saw using 7096 ethanol as cutting f luid. The sections were dehydrated according to a graded alcohol immersion plan from 709~ ethanol 35 to 100~ absolute ethanol over a two week period. Following dehydratlon, the specimens were sectioned perpendicular to the implant long axis into approximately 1 mm thick sections.

- `-; ` 21 76707 Wo 95114127 PCT/US94/13152 The sections were infiltrated with Spurr's embedding media according to a graded infiltration sequence in a vacuum desiccator using polyethylene ~h~; n~ molds . The Spurr' s infiltration cycle was as follows:
5 2596 Spurr' 9*/75~ ethanol 2 days (change day 2) 50~6 Spurr's*/509~ ethanol 2 days (change day 2) 75~ Spurr' s*/25~ ethanol 2 days l o 0 ~ Spurr ' 8 * l day 10096 Spurr' s ( . 04 DMAE) l day lO * No DMAE (n,n-dimethylaminoethanol) added The specimens were then cured for 2 days in an oven at 21C.
Following embedding, the specimens were sectioned to approximately 0 . 5 mm thick sections using a low speed diamond wafered rotating blade saw. These sections were ground and 15 polished using 800 and 1200 grit paper to a final section thickness of about 50 ~Lm. The sections were stained using Villanueva Mineralized bone Stain (Polyscientific, New York).
As seen in FIG. 2, taken at 400X. The composite material shows very close apposition to bone in areas of high 20 fiber concentration. In these areas, bone bioactive glass or ceramic fibers are partially resorbed, more clearly seen in FIG. 3, taken at lOOOX. In addition, in regions where fibers are close together and bone apposition is achieved, there is also bone apposition to the adjacent polysulfone matrix. In 25 contrast, the polysulfone implants show bone tissue ~u,, .,u.lding the plug, but with an interposing layer between the implant and bone tissue.
* * *
Thus, the foregoing Example shows that the 30 bioactive glass fiber/polysulfone plugs made in accordance with the present invention achieve a bond between surrounding bone tissue and the glass fibers at the implant surface. The bonded f ibers are partially resorbed with bone tissue replacing the glass. Consequently, the method of glass fiber 35 fixation to bone is not only by rh~m; r~l bonding, but also by mic~ h~n; cal interlocking. Additionally, there appears to be a bond between the adj acent polymer and surrounding bone Wo 95114127 PCrlUS94/13152 tissue . This would lead to increased areas of f ixation between the composite and bone beyond that of the fiber itself.
The bond between polysulfone- and bone may be due to 5 a calcium phosphate layer being precipitated onto the adjacent polymer surface as it was being precipitated onto the glass fiber. Once this calcium phosphate layer is formed, the polymer itself may act as a substrate for bone growth. Similar findings after implantation of a titanium l0 fiber/bioactive glass composite in dogs will be recently reported. ~. Van Hove, E. Schepers and P. Ducheyne, "Titanium Fiber Reinforced Bioactive Glass composite Implants, " Bioceramics, Vol. 6; (P. Ducheyne and D.
Christiansen, Eds. ), Butterworth-TTPin~-~nn ~td. (in press) .
15 This study shows bone growth over a titanium f iber which was between two islands of bioactive glass. If the separation between the glass was less than 50 microns, the titanium was covered with bone, but if it was greater than lO0 microns (two fiber diameters) there was incomplete bone coverage. An 2 0 in vi tro study has concluded that when a polymer is f aced l mm or less away from a bioactive glass in simulated body fluid, a calcium phosphate layer is precipitated onto the polymer surface. See T. Kokubo, et al, "International Symposium on Ceramics in Medicine, " Butterworth-T~P;n^-~nn 25 ~td., ~ondon (l99l).
The histological observations of the foregoing Example indicate that bone bioactive glass or ceramic f ibers in combination with polysulfone polymer will bond to bone tissue . This f inding indicates that bone bioactive glass or 30 ceramic fibers on the surface region of low modulus composite implants, such as hip stems and bone :plates will achieve improved results.
Another aspect of the present invention is the optimization of the amount of ~iber used in the composite.
35 As explained above, previous bioactive polymeric composites had used ~ nt;n~ us particle coatings on the surface of polymers or polymeric composites with a bioactive powder ~ i 2 1 76707 Wo 95114127 PCTiU594/13152 dispersed through the polymer matrix. It has been determined having surface area partially covered by bioactive glase in a composite form leads to bone bonding in vivo. A calcium phosphate layer is the substrate~ for bone growth. As 5 explained above, the desirable development of a calcium phosphate layer on a non-bioactive material is possible if the material is in close apposition to the bioactive glass.
Consequently, it has been found that a composite with only a partial bioactive surface would still achieve bonding.
lO Preferably, the proportion of bioactive surface area exposed should be greater than 30~ of the total surface area and the bioactive material should be homogeneously distributed over the surface of the composite~to maintain the 30~ surface area of bioactive material over the entire surface desired for 15 fixation.
Based upon the foregoing, it has also been discovered that f ibers made in accordance with Example I and similar f ibere can be advantageously used in composite materials that incorporate a structural fiber along with the 2 0 polymer and the bioactive f iber . Thus, the present invention also relates to composite materials formed of woven, intermingled or juxtaposed elongated fibers of both a bioactive material and another material chosen for its structural properties . These two f ibers are .:~ ' ,1 nf~d in a 25 polymeric matrix. The following Examples will illustrate embodiments of this aspect of the present invention.
E~MPLE II
One manner by which the location and density of fibers within a composite can be controlled is by forming a 3 0 braid of one or more types of f ibers and impregnating the braid with a filler material, such as a polymer. In preferred embodiments of the present invention, continuous bone bioactive glass or ceramic fibers are grouped into 5000 filament fiber bundles. The ~fiber bundles (or "tow") are 35 interwoven with carbon fibers into a braided textile preform.
Most preferably, the bone bioactive glass or ceramic fibers ~ . ~ 2 1 76707 are made in accordance with the composition formulation set f orth above . A9 seen in FI~ . 4, a pref erred construction has glass fibers 100 woven into a three dimensional tube about a central, but separate, carbon f iber core 110 . The two braids 5 are woven simultaneously while the carbon fibers in the core 110 and glass fibers 100 at the carbon/glass interface are interwoven, overlaid or otherwise intermingled. This results in structural interlocking and brings continuity to the structure, even before the polymer is infiltrated.
To create a composite in accordance with this embodiment of the invention, the carbon fibers in the core 110 are commingled with polymer and unidirectional thick polymer fibers are intPrm;ngled with the glass fibers 100 in the outer region of the preform. The hybrid preform is then 15 processed in a closed die using a hot press, as described above . The amount of polymer is calculated to give the f inal total volume fraction desired, thus no additional polymer is added before processing. Also, the resulting composite does not need to be inj ection molded due to the placement of the 20 polymer fibers 80 as to achieve uniform polymer distribution throughout the fibrous preform. The final composite is machined to expose bioactive glass 100 fibers at the surface.
The present invention is also directed to the 25 integration of a bioactive phase in fibrous form into a carbon fiber, three dimensional structural reinforcement network. This results in a ~PlAminAtion resistant, interpenetrating f ibrous network which allows bone tissue ingrowth .
3 o EXAMPLE III
To facilitate composite processing, a thermoplastic matrix in filAmPntous form is co-mingled with the reinforcement fibers. A8 a result, the thermoplastic fibers are uniformly distributed through out the structure. A
35 composite can be formed with bioactive fibers and by the 2~ 76707 Wo 95/14127 PCT/USs~113152 application of heat and pressure to melt the thermoplastic according to well-estAhl 1 chl~d regimens known in the art.
By proper selection of f iber architecture and textile processing techni~ue, the quantity and distribution 5 of the bioactive phase can be controlled so that a pref erred concentration of the bioactive f ibers it disposed near the surface of the structure. The thermal and mechanical properties of the composite system can be further tailored by chan~ing the fiber volume fraction and fiber orientation lO distribution. Depending on the type of implant, two or three dimensional f iber architectures can be selected and fabricated into net shape or near-net shape fibrous assemblies by weaving, knitting or braiding techniques, such as those disclosed in F.K. Ko, "Preform Fiber Architecture 15 for Ceramic Matrix Composites, " Bull . Am. Cer. Soc. (Feb.
1989) .
For illustrational purposes, a three dimensional hybrid mesh will be provided as a specific example. It should be noted, however, that the same principles can be 20 applied to cylindrical shapes and other complex structural shapes as seen in the three ~; c; t~l'lAl braiding loom design diagram illustrated in FIG. 5.
In FIG. 5, the X' s represent the bone bioactive glass or ceramic f ibers, the number and distribution of which 25 can vary, and the O' s are a structural fiber, preferably carbon fibers, which also may be provided in large and small bundles. The vertical rows of the loom are called ~tracks"
whereas the horizontal rows of the loom are "columns. " As known in the art, a three dimensional braided structure ~s 30 fabricated on the alternate motions of tracks and columns of bundles of fibers attached to a~ carrier based on the movement instructions indicated in the track and column direction in an alternate manner An " 0 " means no movement, and a " l means moving in the positive direction by one carrier 35 position and a "-l" means moving the carrier in the opposite direction of the other half of the carrier in the same 2 t 767~7 Wo 95/14127 PCr/13S94113152 direction. Naturally, a "2" means moving two carrier positions .
In a preferred ~mhn~ t, the integration of the bone bioactive glass or ceramic ibers into the carbon fiber 5 in an interfacial region is accommodate by the position of the carrier ln track/column coordinates 6/6, 6/7; 7/7, 7/8;
8/6, 8/7; 9/7, 9/8; 10/6, 1-0/7; 11/7, 11~8; 12/6, 12/7; 13/7, 13/8 being exchanged after each cycle of track/column movement From the foregoing, it can be seen that for a given yarn bundle size, the fiber orientation and fiber volume fraction can be designed. Knowing the fiber and matrix material properties, the elastic properties in the form of a 15 stiffness matrix [C] can be established for the composite.
Finite element analysis can also be performed to assess the stress - strain response of the implant under a set of boundary conditions. This preform design, micromechanics analysis and structural mechanics analysis can be performed in an 20 iterative manner to optimize the design of the implant and predict the performance ~:3ri~h; 1; ty of the structure.
Additional aspects of the present invention will best be understood with reference to FIG. 6, which illustrates a hip implant prosthesis 200 as an example of a 25 composite structure that can be constructed using the present invention. First, it will be understood by those of skill in the art that the surface, or part of the surface of the prosthesis 200 can be covered with grooves 210 or other surface irregularities. For example, as seen in FIG. 6, it 30 is preferred that the proximal circumferential third of the prosthesis 220 have grooves. These features aid in the macroscopic aspects of bone f ixation and have been shown to be beneficial. In accordance with the present invention, the grooves 21~ are most preferably formed by molding the preform 35 to the desired texture, rather than machining a smooth surf ace .

~ 21 767G7 Wo 95/14127 PCTIUS94113152 --Additionally, the present invention also permits bioactive and structural fibers to be localized to ~chieve a local fixation using a bioactive surface. In other words, the f ibers can be varied so that the bioactivity is 5 concentrated at a particular~ section or portion of an implant, device or prosthesis. Referring still to FIG. 6, the hip prosthesis 200 would most preferably have the bioactive fibers concentrated in the proximal one third 22Q
of the implant device. It has been shown that proximal lO stress transfer in a total hip arthroplasty is better achieved by using a material with fixation to bone in this region .
Thus, it will be appreciated that the present invention is very versatile in many of its parameters. The 15 bone bioactive glass or ceramic fiber can be~selected from bioactive glass or glass-ceramic materials, including calcium phosphate ceramic f ibers . The polymer system used may be any polymer which bonds to the bone bioactive glass or ceramic fibers, is biocompatible, and does not inhibit the 20 bioactivity of the fibers in vivo. Examples of such polymer systems are polysulfone, polyetheretherketone (PEEK), and polyetherketoneketone (PEKK). The structural fiber can be any inert fiber that fits the constraints of biocompatibility and exhibits the ability to bond to the chosen polymer. In 25 addition to the carbon fibers disclosed above, such fibers include inert high strength glass, aramid f ibers, and inert ceramic f ibers, such as alumina . The f iber orientation and type of weave may be varied for different applications and can be pre-selected and optimized using well known analysis 30 techniques. Moreover, the disclosed hybrid woven bioactive composite can be constructed not only as the three dimensional braided textile~structure discussed above, but any woven textile structure such as a two-dimensional braid, f iber interlock weave, or laminated composite, among others .
35 Finally, those of skill in the art will understand that the present invention may be adapted to many applications where material shape, strength, stiffness, and fixation to bone are ~ - 2t76707 Wo 95114127 PCr/Uss4/131~2 among the desigr. parameters. In accordance with the present invention fibrous composites o~ biocompatible materials can be made into bioactive composites by incorporating bone bioactive glass or ceramic fibers into the weave at the bone 5 contact surface.
Based upon the foregoing, it will be realized that a number of emb~ ir- tR of the present invention beyond tho3e discussed in detail above are possible. Such embodiments, however, will still employ the spirit of the present lO invention and, accordingly, reference should be made to the appended claims in order to determine the full scope of the present invention

Claims

What is claimed:

1. A biocompatible composite of tows of bone bioactive fibers comprising at least 19% Na2O by mole intermingled with tows of structural fibers in a non-bioabsorbable polymeric matrix.

2. The composite of claim 1, wherein the bone bioactive fibers are arranged in a predetermined distribution and a section of a surface of the composite to be affixed to bone is comprised of about 30% or more bone bioactive fibers.

3 [CANCELLED]

4. The composite of claim 2 wherein the composite comprises:
(a) biocompatible structural fibers disposed within the interior of the composite, (b) biocompatible structural fibers interwoven with the bone bioactive glass or ceramic fibers, and (c) a surface section defining a section to be affixed to bone comprising the bone bioactive fibers.

5. [CANCELLED]

6. The composite of claim 1 wherein the structural fiber is a carbon fiber.

7. The composite of claim 1 wherein the non-bioabsorbable polymeric material is chosen from the group consisting of: polysulfone; PEEK; and PEKK.

8. The composite of claim 1, wherein the bone bioactive fibers comprise 40-60% SiO2, 19-30% Na2O, 10-21%
CaO and 0-49% P2O5 by mole.

9. The composite of claim 1, wherein the bone bioactive fibers comprise 45-55% SiO2, 19-30% Na2O, 15-20%
CaO and 0-3% P2O5 by mole.

10. The composite of claim 9, wherein the bone bioactive fibers comprise 52% SiO2, 30% Na2O, 15% CaO and 3%
P2O5 by mole

11. The composite of claim 9 wherein the bone bioactive fiber has a diameter of about 5-25 microns.

12. A mesh comprised of bone bioactive fibers interwoven with structural fibers.

13. The mesh of claim 12 wherein the bone bioactive fibers are interwoven to produce a surface wherein a substantial percentage of the surface consists of the bone bioactive fibers.

14. The mesh of claim 13 wherein the surface consists of about 30% bone bioactive fibers.

15. The mesh of claim 11 further comprising a polymeric material.

16. The mesh of claim 14 wherein the bone bioactive fibers and the structural fibers are impregnated with a polymerized resin.

17. The mesh of claim 11 wherein the structural fibers are comprised of a material chosen from the group consisting of: carbon; aramid; and non-bioactive glass and ceramic materials.

18. The mesh of claim 11, wherein the bone bioactive fibers comprise 40-60% SiO2, 19-30% Na2O, 10-21%
CaO and 0-496 P2O5 by mole.

19. The mesh of claim 18, wherein the bone bioactive fibers comprise 45-55% SiO2, 19-30% Na2O, 15-20%
CaO and 0-3% P2O5 by mole.

20. The mesh of claim 19, wherein the bone bioactive fibers comprise 52% SiO2, 30% Na2O, 15% CaO and 3%
P2O5 by mole

21. A method of affixing an implant to bone tissue comprising the steps of: placing an implant comprising a fixation section for receiving bone ingrowth, wherein at least 30% of one or more of said fixation section comprises bone bioactive fibers.

22. A prosthesis for total hip arthroplasty comprising a distal end and a proximal end, the prosthesis comprised of a woven mesh of bioactive fibers and structural fibers impregnated with a polymer.

23. A prosthesis in accordance with claim 22, wherein the proximal end further comprises circumferential grooves.

24. A prosthesis in accordance with claim 22, wherein the bioactive fibers are selectively woven within the structural fibers to be concentrated at the proximal end.

25. The composite of claim 8 further comprising at least one modifier.

26. The composite of claim 25, wherein the modifier is chosen from the group consisting of: K2O; MgO;
Al2O3; and F2.

27. The mesh of claim 18 further comprising at least one modifier.

28. The mesh of claim 27, wherein the modifier is chosen from the group consisting of: K2O; MgO; Al2O3; and F2.

29. The composite of claim 11, wherein the bone bioactive fiber has a diameter between 10-13 microns.