WO2017134614A1

WO2017134614A1 - Patient specific near-net shaped uniaxially pressed ceramic femoral head and acetabular socket, and fabrication method thereof

Info

Publication number: WO2017134614A1
Application number: PCT/IB2017/050590
Authority: WO
Inventors: Debasish Sarkar; Sambireddy BHIMAVARAPU; Sourav MANDAL; Bikramjit BASU
Original assignee: Indian Institute Of Science; National Institute of Technology
Priority date: 2016-02-05
Filing date: 2017-02-03
Publication date: 2017-08-10

Abstract

The present disclosure provides a method for fabricating biocompatible orthopedic prosthesis such as acetabular socket and femoral head with highest possible mechanical properties, wherein the method includes the steps of: a) providing a composite material powder, and placing the composite material powder into a mold cavity; b) applying uniform uniaxial pressure to the powder- filled mold cavity to cause the composite material powder to be compacted and formed into a green compact of acetabular socket or femoral head, and unloading the compact from the cavity; d) pre- sintering the green compact to bond the compacted powder, thereby forming a intermediate solid compact; e) machining the pre-sintered compact; f) sintering the machined compact; and g) polishing the machined compact to produce the acetabular socket or femoral head. The present disclosure further provides an apparatus for near net shape fabrication of acetabular socket and femoral head with patient-specific dimensions and a composite material for producing acetabular socket or femoral head for use in total hip prosthesis, wherein the composite material comprises: 60 to 95 % by weight of alumina; and 1 to 40 % by weight of zirconia. and preferably magnesium nitrate as sintering aid.

Description

PATIENT SPECIFIC NEAR-NET SHAPED UNIAXIALLY PRESSED CERAMIC FEMORAL HEAD AND ACETABULAR SOCKET, AND FABRICATION METHOD

THEREOF

FIELD OF THE INVENTION

[0001] The present disclosure pertains to implantable prosthesis adapted to be inserted into human body. In particular, the present disclosure pertains to fabrication method and fabrication apparatus for producing femoral head and acetabular socket with patient-specific dimensions for total hip replacement.

BACKGROUND OF THE INVENTION

[0002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.

[0003] The hip joint is one of the most important flexible articulating joints, allowing us to a greater range of motion, and such joints experience static/dynamic compressive stress. For example, slow walking, knee bending, walking down stairs, climbing up stairs, standing up from a chair and sitting down on a chair requires 3.3MPa, 3.7MPa, 3.8MPa, 5.7MPa, 8.8MPa and 9.4MPa compressive at articulating joints stress, respectively. From engineering perspective, the functioning of a joint can be better described as the round 'ball-bearing' mechanism and typically, a hip-joint bears body force of the strong hip and leg muscles. The round concave acetabulum cup and counterpart convex femoral head project the socket and bearing arrangement for total hip replacement (THR). This entire assembly is further supported by the neck of the femur, when spherical femoral head is placed upward to maintain the convexity of joint towards pelvic. The compressive stress, as mentioned above, can be distributed throughout THR/host bone contact area. Typically, the THR surface is smooth and coated with cartilage in healthy adults. Arthritis, injury, dislocation or irregular activity bring about wear and tear of the surrounding cartilage inside a hip joint and hence causes pain to patients. This leads to the friction between the bones as they rub against each other and the hip joint becomes severely damaged in this process. This unexpected damage demands the replacement of THR by a synthetic biomedical device assembly in a diseased patient. Such assembly contains acetabular socket with a conforming femoral head and a long stem, whose neck is closely fitted into the inner cavity of femoral head. Typically, individual component of a THR assembly is fabricated separately and then assembled together to obtain the entire device.

[0004] With the increasing life expectancy in many countries of the world, the demand for hip replacement surgery is on rise. For example, 3,00,000 patients undergo primary or revision arthroplasty in a year in India and around 1,00,000 patients for knee surgery. In India, the cemented hip replacement can cost between Rs 35,000 and Rs 40,000, whereas the price of an uncemented one could range between Rs 60,000 and Rs 1.5 lakh. The difference in the cost structure is because the materials used for uncemented hip prostheses are more expensive and also they are technically more challenging to manufacture.

[0005] The gradual change of hip prosthesis material from metal to a ceramic has resulted in an increased implant life with minimal wear. Most prostheses consist of a femoral head with polished male projection to accommodate in acetabular socket and blind hole female part maintains the dimensional conformity for femoral stem. In general, the outer surface of uncemented implants is designed to favour biologic bone in-growth and fixation of the prosthesis. The various prostheses available in Indian market are from foreign manufacturer Depuy, Zimmer, Stryker and Aesculap. Common cemented hip prostheses available are Charnley's, Exeter, C Stenprosthesis, while uncemented prostheses available are AML, Pinnacle, Zymuller, Corail and Proxima.

[0006] The demand for durable femoral head and acetabular socket has been the driver for new material development. While new materials in specific ceramic composites with better properties are being widely researched in the materials community, the attempts to make patient-specific prototypes are rather limited.

[0007] Among the several combination of THR, cobalt chrome alloy is considered as a popular choice for hip prostheses, although some studies have revealed that metal-on-metal implants can cause elevated levels of the metal ions in urine and bloodstream. This indicates that the wear debris particles, that enter the body, may have an adverse effect. At the same time, better properties of acetabulum cup material are also needed to account for the minimization of the fretting wear, chipping and ultimate failure. For a long time, biocompatible zirconia and alumina have been explored for developing femoral head and acetabular socket, but alumina or zirconia material alone does not pass the necessary mechanical properties for an orthopaedic implant. Researchers in Japan and Europe investigated alumina ceramic bearing materials due to their low friction, wetability, wear resistance, and biocompatibility. However, the first applications of alumina in orthopaedics were associated with high fracture rates.

[0008] In the 1980s, zirconia (Zr0₂) was introduced in orthopaedics because of its improved fracture toughness and mechanical strength, relative to alumina. Zirconia owes its higher fracture toughness to stress-induced phase transformation from its metastable tetragonal phase to its stable monoclinic phase at ambient temperatures. During the 1990s, stabilized zirconia was widely used as ceramic femoral heads in ceramic-on-polyethylene (COP) bearings, because of its higher toughness and strength relative to alumina. However, depending on the manufacturing conditions and hydrothermal effects in vivo, the pure tetragonal zirconia component may be unstable and can transform catastrophically into the monoclinic phase and hence failure of the component. Further, loosening of the implant, dislocation, and fractures of the implant severely affect the success rates of joint replacement surgeries.

[0009] There is thus a need in the art for a fabrication method and fabrication apparatus for producing orthopedic prosthesis such as, femoral head and acetabular socket with excellent biocompatibility, compressive strength, flexural strength, wear resistance, uniform microstructure, desired fracture strength under compressive mode and low average surface roughness for total hip replacement with patient-specific dimensions. Also, there is a need for improved composite material that facilitates simple and cost effective fabrication of patient specific femoral head and acetabular sockets with high dimension stability and polishing, and also eliminates the need of additional machining of the finished product.

[0010] The present invention satisfies the existing needs, as well as others, and generally overcomes the deficiencies found in the prior art.

OBJECTS OF THE INVENTION

[0011] It is an object of the present disclosure to provide a method for fabricating implantable prosthesis such as femoral head and acetabular sockets for total hip replacement with patient- specific dimensions.

[0012] It is a further object of the present disclosure to provide a method for producing femoral head and acetabular cup that exhibits high level of biocompatibility with surrounding tissues.

[0013] It is another object of the present disclosure to provide a method for producing femoral head and acetabular cup with highest possible mechanical properties, such as compressive strength, flexural strength, wear resistance properties, uniform microstructure, desired fracture strength under compressive mode and low average surface roughness for total hip replacement with patient-specific dimensions.

[0014] It is another object of the present disclosure to provide a method for producing femoral head and acetabular cup having extended functional lifetime.

[0015] It is another object of the present disclosure to provide a method for producing femoral head and acetabular cup that alleviates problems associated with aseptic loosening of implants and dislocation, and thus extend their useful working life.

[0016] It is another object of the present disclosure to provide a fabrication apparatus that facilitates simple and cost effective fabrication of patient specific femoral head and acetabular sockets with high dimension stability and polishing.

[0017] It is another object of the present disclosure to provide a fabrication apparatus that provides ready to use implantable prosthesis such as femoral head and acetabular sockets, and eliminates the need of additional machining of the finished product.

[0018] It is another object of the present disclosure to provide a method of fabricating implantable prosthesis such as femoral head and acetabular sockets for total hip replacement with improved mechanical properties.

[0019] It is another object of the present disclosure to provide a simple and economic method of fabricating femoral head and acetabular cup for use in total hip replacement.

[0020] It is another object of the present disclosure to provide a composite material for fabricating implantable prosthesis such as femoral head and acetabular sockets for total hip replacement with patient-specific dimensions.

SUMMARY OF THE INVENTION

[0021] The present disclosure provides a fabrication method and apparatus for producing biocompatible orthopedic prosthesis such as acetabular socket and femoral head with highest possible mechanical properties such as compressive strength, flexural strength, wear resistance properties, uniform microstructure, desired fracture strength under compressive mode and low average surface roughness for total hip replacement with patient-specific dimensions.

[0022] In one aspect, the present disclosure provides a method for fabricating an acetabular socket or femoral head for use in total hip prosthesis, wherein the method can include the steps of: a) placing the composite material powder into a mold cavity; b) applying uniform uniaxial pressure to the powder-filled mold cavity to cause the composite material powder to be compacted and formed into a green compact of acetabular socket or femoral head, and unloading the compact from the cavity; c) pre-sintering the green compact to bond the compacted powder, thereby forming an intermediate solid compact; d) machining the pre-sintered compact; e) sintering the machined compact; and f) polishing the machined compact to produce the acetabular socket or femoral head.

[0023] In an embodiment, the composite material powder that can be uniaxially pressed into a green compact of acetabular socket or femoral head can include 85 to 95 % by weight of alumina; 5 to 15 % by weight of zirconia; 0.05 to 10 % by weight of magnesium nitrate; and 1 to 5 % by weight of polyvinyl alcohol.

[0024] In an embodiment, the green compact of acetabular socket or femoral head can be pre- sintered at a temperature of 1200°C for a length of time preferaly ranging from 0.5 to 3 hours.

[0025] In an embodiment, the pre-sintered green compact of acetabular socket or femoral head can be machined with a computer numerically controlled (CNC) lathe.

[0026] In an embodiment, the pre-sintered and machined compact can be sintered at a temperature ranging from 1600 to 1650°C for a length of time preferaly ranging from 2 to 8 hours.

[0027] In another embodiment, the sintered compact can be polished using a diamond paste which can have a grit size ranging from 10 to 1 μιη.

[0028] In another aspect, the present disclosure provides an apparatus for near net shape forming of femoral head, the apparatus can include:

a die having at least two separable die parts that, in the assembled state, define a die cavity for receiving a powder to be compacted, wherein the die cavity defines the desired configuration of a femoral head;

a cylindrical-shaped plunger guide having a longitudinal axis, wherein the plunger guide having an opening in its longitudinal axis through which a powder to be compacted may be charged; and

a plunger configured for uniaxially pressing the powder material, which has been loaded into the die cavity and the opening of the plunger guide, wherein the plunger is being guided by the plunger guide. a specific ejection means configured to include four pin guide and circular cavity that together can accommodate and withhold the entire powder compressed assembly during slow ejection rate at lmm/min in the same uniaxial press

[0029] In another aspect, the present disclosure provides an apparatus for near net shape forming of acetabular socket, the apparatus can include:

a die having at least two separable die parts that, in the assembled state, define a die cavity for receiving a powder to be compacted; wherein the die cavity defines the desired configuration of an acetabular socket; a cylindrical-shaped plunger guide having a longitudinal axis, wherein the plunger guide having an opening in its longitudinal axis through which a powder to be compacted may be charged; and

a plunger configured for uniaxially pressing the powder, which has been loaded into the die cavity and the opening of the plunger guide, wherein the plunger is being guided by the plunger guide.

[0030] Various objects, features, aspects and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components.

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The accompanying drawings are included to provide a further understanding of the present disclosure, and are incorporated in and constitute a part of this specification.

[0032] FIG. 1A is a flow chart illustrting lab-scale to prototype development of femoral head (FH) and acetabular socket (AS) for ultimate hip joint replacement using the composite material (zirconia toughened alumina (ZTT), in accordance with embodiments of the present disclosure.

[0033] FIG. IB is a flow chart illustrating process for fabrication of femoral head and acetabular socket, in accordance with embodiments of the present disclosure.

[0034] FIG. 2A depicts computer aided design (CAD) originated orthogonal and isometric projection of targeted 26mm zirconia toughened alumina femoral head which consists of tapered cylindrical blind hole and fillet curvature, in accordance with embodiments of the present disclosure. [0035] FIG. 2B depicts 26.5mm inner diameter (ID) acetabular socket, in accordance with embodiments of the present disclosure.

[0036] FIG. 2C shows top view of polished surface of a developed femoral head during fused deposition method (FDM) in accordance with embodiments of the present disclosure.

[0037] FIG. 2D depicts 26.48mm inner diameter of articulating surface of an acetabular socket, in accordance with embodiments of the present disclosure.

[0038] FIG. 3A illustrates cross-sectional view of slicing of femoral head, in accordance with embodiments of the present disclosure.

[0039] FIG. 3B shows exemplary rapid prototype model made of acrylonitrile butadiene styrene (ABS) polymer for femoral head, in accordance with embodiments of the present disclosure.

[0040] FIG. 3C depicts exemplary dimensions fixed up with consideration of volume shrinkage of ceramic particles (alumina zirconia nanopowder mixture) during sintering and designing of femoral head, in accordance with embodiments of the present disclosure.

[0041] FIG. 4A illustrates an exemplary base support including side view of slicing of acetabular socket during FDM, in accordance with embodiments of the present disclosure.

[0042] FIG. 4B shows an exemplary rapid prototype model made of ABS polymer for acetabular socket, in accordance with embodiments of the present disclosure.

[0043] FIG. 4C depicts exemplary dimensions fixed up with consideration of volume shrinkage of ceramic particles (alumina zirconia nanopowder mixture) during sintering and designing of acetabular socket, in accordance with embodiments of the present disclosure.

[0044] FIGs. 5A-F show plan and perspective view of bottom die, top die, powder and plunger guide die, plunger cum mandrel with ejection pin guide, ejection head including base pins and ejection support plates and rods respectively, of an exemplary multi-piece steel die designed for fabricating femoral head, in accordance with embodiments of the present disclosure.

[0045] FIGs. 6A-C show plan and perspective view of bottom die, powder cum plunger guide die and plunger respectively, of an exemplary multi-piece integrated steel die designed for fabricating acetabular socket, in accordance with embodiments of the present disclosure.

[0046] FIG. 7A shows isometric view of green compact through uniaxial press in accordance with embodiments of the present disclosure.

[0047] FIGs. 7B-F show top view, side view, tapered entrance of femoral stem neck, thickness of wall at truncated zone, and blind hole depth, respectively, of an exemplary machined and sintered femoral head, wherein all dimensions are near to CAD generated model in accordance with embodiments of the present disclosure.

[0048] FIGs. 8A-D show top view, side view, wall thickness, and femoral head accommodate space respectively, of an exemplary machined and sintered acetabular socket, wherein all dimensions are near to CAD generated model in accordance with embodiments of the present disclosure.

[0049] FIG. 9 depicts optimized composite material composition and process parameters for small coupon specimen utilized to scaling up the zirconia toughened alumina (ZTA) based femoral head and acetabular socket prosthesis in accordance with embodiments of the present disclosure.

[0050] FIGs. 10A-B illustrate microstructure of sintered ZTA based femoral head, and acetabular socket respectively, wherein different contrast indicates the uniform distribution of zirconia particulate (white) in alumina (grey) matrix.

[0051] FIG. 11 illustrates dimension analysis of polished femoral head by co-ordinate measuring method (CMM) in accordance with embodiments of the present disclosure.

[0052] FIGs. 12A-B show cross sectional view of an acetabular socket and dimensional analysis of articulating surface, and outer shell diameter respectively, measured by co-ordinate measuring machine (CMM), in accordance with embodiments of the present disclosure.

[0053] FIG. 13 A is micro - CT image of a femoral head which shows isometric view of edge and convex surface including blind hole projection of same component without any cracks and defects in accordance with embodiments of the present disclosure.

[0054] FIG. 13B is micro - CT image of a femoral head which shows 3D distribution of zirconia grains along the matrix in accordance with embodiments of the present disclosure.

[0055] FIG. 14A is micro - CT image which shows perspective view of edge and concave surface of an acetabular socket in accordance with embodiments of the present disclosure.

[0056] FIG. 14B is micro - CT image of an acetabular socket which shows Zr0₂ particle distribution on one plane of AI2O3 matrix in accordance with embodiments of the present disclosure.

[0057] FIG. 15 is a graph showing MTT analysis of C2C12 myoblast cells cultured on 95A-5Z- 800 samples for the periods of 24, 48 and 72 h. Statistical difference from control: # significant at p<0.05; Statistical difference (intra group) from the 24 h of cell culture: *significant at p<0.05; ** significant at p<0.01using one way Anova followed by post hoc tukey test. Statistical difference (intra group) from the 48 h of cell culture:†† significant at p<0.01 using one way Anova followed by post hoc tukey test. Each value is represented as mean ± standard error.

[0058] FIGs. 16A-B are fluorescence microscopic images of C2C12 myoblast cells cultured on control, and 95A-5Z-800 for a time period of 24 h, in accordance with embodiments of the present disclosure.

[0059] FIGs. 16C-D are fluorescence microscopic images of C2C12 myoblast cells cultured on control, and 95A-5Z-800 for a time period of 72h, in accordance with embodiments of the present disclosure.

[0060] FIGs. 17A-B show average initial, and polished surface roughness profile, respectively of articulating surface of an acetabular cup in accordance with embodiments of the present disclosure.

[0061] FIG. 18 illustrates an exemplary in house fabricated assembly for burst test measurement of a developed femoral head; wherein a ZTA based femoral head and tapered dummy femoral stem is placed on copper ring according to ISO-7206-10, and the base dimension is maintained 100° cone, in accordance with embodiments of the present disclosure.

[0062] FIG. 19 shows different pieces of exposed fractured surface of a femoral head after performing the burst strength at the peak load of 15.3kNat the loading rate of lkN/sec, in accordance with embodiments of the present disclosure.

[0063] FIG. 20 shows force versus displacement plot during burst strength measurement of femoral head, in accordance with embodiments of the present disclosure.

[0064] FIG. 21 is fracto graph of a femoral head, wherein different contrast indicates the uniform distribution of zirconia particulate (white) in alumina (gray) matrix, in accordance with embodiments of the present disclosure.

[0065] FIG. 22 shows an exemplary assembly of ZTA based femoral head accommodate in ZTA based acetabular socket, in accordance with embodiments of the present disclosure.

[0066] FIGs. 23A-B illustrate plan and perspective view of an exemplary total hip replacement (THR) biomedical devices, wherein FIG. 23A illustrates an exposed ZTA acetabular socket and ABS femoral stem (135mm) inserted ZTA femoral head, and FIG. 23B illustrates complete assembly of ceramic socket - ceramic head including dummy femoral stem of ABS Plus (P430). DETAILED DESCRIPTION OF THE INVENTION

[0067] The following is a detailed description of embodiments of the disclosure depicted in the accompanying drawings. The embodiments are in such detail as to clearly communicate the disclosure. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.

[0068] Each of the appended claims defines a separate invention, which for infringement purposes is recognized as including equivalents to the various elements or limitations specified in the claims. Depending on the context, all references below to the "invention" may in some cases refer to certain specific embodiments only. In other cases it will be recognized that references to the "invention" will refer to subject matter recited in one or more, but not necessarily all, of the claims.

[0069] Unless the context requires otherwise, throughout the specification which follow, the word "comprise" and variations thereof, such as, "comprises" and "comprising" are to be construed in an open, inclusive sense that is as "including, but not limited to."

[0070] Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

[0071] As used in this specification and the appended claims, the singular forms "a," "an," and "the" include plural referents unless the content clearly dictates otherwise. It should also be noted that the term "or" is generally employed in its sense including "and/or" unless the content clearly dictates otherwise.

[0072] In some embodiments, the numbers expressing quantities of ingredients, properties such as concentration, reaction conditions, and so forth, used to describe and claim certain embodiments of the invention are to be understood as being modified in some instances by the term "about." Accordingly, in some embodiments, the numerical parameters set forth in the written description are approximations that can vary depending upon the desired properties sought to be obtained by a particular embodiment. In some embodiments, the numerical parameters should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of some embodiments of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as practicable.

[0073] The recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g. "such as") provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.

[0074] The headings and abstract of the invention provided herein are for convenience only and do not interpret the scope or meaning of the embodiments.

[0075] Reference will now be made in detail to the exemplary embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts.

[0076] The following discussion provides many example embodiments of the inventive subject matter. Although each embodiment represents a single combination of inventive elements, the inventive subject matter is considered to include all possible combinations of the disclosed elements. Thus if one embodiment comprises elements A, B, and C, and a second embodiment comprises elements B and D, then the inventive subject matter is also considered to include other remaining combinations of A, B, C, or D, even if not explicitly disclosed.

[0077] Various terms as used herein are shown below. To the extent a term used in a claim is not defined below, it should be given the broadest definition persons in the pertinent art have given that term as reflected in printed publications and issued patents at the time of filing.

[0078] In one aspect, the present disclosure provides a method for fabricating biocompatible orthopedic prosthesis such as acetabular socket and femoral head with highest possible mechanical properties such as compressive strength, flexural strength, wear resistance properties, uniform microstructure, desired fracture strength under compressive mode and low average surface roughness for total hip replacement with patient-specific dimensions.

[0079] According to embodiments of the present disclosure, the entire scheme of product development can include three major steps viz. a) thermoplastic polymer prototype development for total hip replacement (THR), b) specific mold assembly for manufacturing orthopedic prosthesis such as acetabular socket and femoral head, and c) fabrication of dimensional stable femoral head and acetabular socket. The flow chart as shown in FIG. 1A illustrtes lab-scale to prototype development of femoral head (FH) and acetabular socket (AS) for ultimate hip joint replacement using a composite material, in accordance with embodiments of the present disclosure. The flow chart in FIG. IB illustrates process for fabrication of femoral head and acetabular socket.

[0080] FIG. 2A depicts computer aided design (CAD) originated orthogonal and isometric projection of targeted 26mm zirconia toughened alumina femoral head which consists of tapered cylindrical blind hole and fillet curvature, in accordance with embodiments of the present disclosure. FIG. 2B depicts 26.5mm inner diameter (ID) acetabular socket, FIG. 2C shows top view of polished surface of a developed femoral head, and FIG. 2D depicts 26.48mm inner diameter of articulating surface of an acetabular socket, in accordance with embodiments of the present disclosure.

[0081] According to embodiments of the present disclosure, an acrylonitrile butadiene styrene (ABS) based polymer prototype can be prepared initially in consideration of volume shrinkage of ceramic particles during final stage of sintering, machining and polishing of sintered components, and then appropriate molds can be fabricated using hardened non-shrinkage steel.

[0082] In an embodiment, the present disclosure provides a method for fabricating an acetabular socket or femoral head for use in total hip prosthesis, wherein the method can include the steps of: a) providing a composite material powder and placing the composite material powder into a mold cavity; b) applying uniform uniaxial pressure to the powder-filled mold cavity to cause the composite material powder to be compacted and formed into a green compact of acetabular socket or femoral head, and unloading the compact from the cavity; c) pre-sintering the green compact to bond the compacted powder, thereby forming a intermediate solid compact; d) machining the pre-sintered compact; e) sintering the machined compact; and f) polishing the machined compact to produce the acetabular socket or femoral head. [0083] In an embodiment, the composite material powder that can be uniaxially pressed into a green compact of acetabular socket or femoral head can be zirconia toughened alumina (ZTA).

[0084] In one aspect, the present disclosure provides a composite material for fabricating acetabular socket and femoral head, wherein the composite material can include 60 to 95 % by weight of alumina; and 1 to 40 % by weight of zirconia. The composite material can further include a sintering aid such as magnesium nitrate, and a polymer binder such as polyvinyl alcohol.

[0085] In a more preferred embodiment, a composite material that can be used for producing acetabular socket or femoral head can include 85 to 95 % by weight of alumina; 5 to 15 % by weight of zirconia; 0.05 to 10 % by weight of magnesium nitrate; and 1 to 5 % by weight of polyvinyl alcohol.

[0086] The magnesium nitrate which is used as a sintering aid in the present composite material can present in the form of hydrate, for example in the form of hexahydrate (Mg(N0₃)2 6H₂0).

[0087] In an embodiment, uniform uniaxial pressure can be applied to a powder-filled mold to form a green compact of acetabular socket or femoral head, and then the green compact can be pre-sintered to bond the compacted powder and form a solid intermediate solid product. Pressures on the order of about 18 TSI (tons per square inch) to about 25 TSI, or higher, may be adequate to form the desired compact.

[0088] In an embodiment, the green compact of acetabular socket or femoral head can be pre- sintered at a temperature ranging from 800 to 1600°C for a length of time ranging from 0.5 to 3 hours. The pre-sintering step can improve the holding strength of the compact that allows smooth machining of the compacts to a desired extent.

[0089] In a more preferred embodiment, the green compact of acetabular socket or femoral head can be pre-sintered at a temperature of 1200°C for 2 hours with a slow heating and cooling rate

[0090] In an embodiment, the pre-sintered green compact of acetabular socket or femoral head can be machined with a computer numerically controlled (CNC) lathe to get final desired shape and size for acetabular socket and femoral head through appropriate M-code and G-code.

[0091] In an embodiment, the pre-sintered and machined compacts of acetabular socket and femoral head can be sintered at a temperature which can impart uniform density and hardness to the prosthesis from end to end with high density. [0092] In an embodiment, the the pre-sintered and machined compacts can be sintered at a temperature ranging from 1500 to 1650°C, preferably from 1600 to 1650°C, for a length of time preferaly ranging from 4 to 8 hours.

[0093] After achieving desired accurate shape and dimension for the acetabular socket and femoral head through machining and sintering, the prosthetic components can be polished in order to remove any excessive material and to get smooth surface finish, which in turn can reduce the interaction among the asperities between the convex femoral head (outer ID) and concave acetabular socket (inner ID).

[0094] In another embodiment, the sintered compacts of acetabular socket and femoral head can be polished using a diamond paste which can have a grit size ranging from 10 to 1 μιη. The polished acetabular socket and femoral head can exhibit surface finish maximum, R_a value in the range of 0.2μηι for articulating surface of femoral head and 0.01 μηι for acetabular socket (ID).

[0095] The fabrication methods of the present disclosure can be employed to fabricate acetabular sockets with patient specific dimensions. In an embodiment, the present methods can be used to fabricate an acetabular socket having a spherical inner diameter ranging from 26.5 to 35 mm, and a spherical outer diameter ranging from 37 to 48 mm.

[0096] Similarly, the fabrication methods of the present disclosure can be employed to fabricate femoral heads with any patient specific dimensions. In an embodiment, the present methods can be used to fabricate a femoral head having a spherical outer diameter ranging from 26 to 35 mm.

[0097] According to embodiments of the present disclosure, the methods of the present disclosure can be adopted to develop other ceramic implantable prosthesis, such as knee implant, elbow joint, ankle joint, shoulder joint and wrist joint, with patient-specific shape and size.

[0098] In an embodiment, the present disclosure provides an acetabular cup for use in a total hip joint prosthesis, the acetabular cup can have a spherical upper side having a size and shape configured to be received within an a patient's acetabulam, and a lower side having a part- spherical cavity having a size and shape for articulatory reception of a ball-shaped femoral head, wherein the acetabular cup can be formed from zirconia toughened alumina (ZTA) powder which can be uniaxially pressed into a green compact and subsequently sintered to produce the acetabular socket.

[0099] In another embodiment, the present disclosure provides a femoral head for use in a total hip joint prosthesis, the femoral head can have a spherical upper side having a size and shape adapted for articulatory reception within a cavity of an acetabular cup, and a lower side having a downwardly open cavity having a size and shape configured to receive a neck of a femoral stem, wherein the femoral head can be formed from zirconia toughened alumina (ZTA) powder which can be uniaxially pressed into a green compact and subsequently sintered to produce the femoral head.

[00100] In another aspect the present disclosure provides an implantable hip joint prosthetic assembly, wherein the prosthetic assembly can include: (a) an acetabular cup having a spherical upper side having a size and shape configured to be received within an a patient's acetabulam, and a lower side having a part-spherical cavity having a size and shape defining an articulation surface; (b) a femoral head having a spherical upper side having a size and shape adapted for articulatory reception within the part- spherical cavity of the acetabular cup, and a lower side having a downwardly open cavity having a size and shape configured to receive a neck of a femoral stem, wherein the acetabular cup and the femoral head are formed from zirconia toughened alumina (ZTA) powder which can be uniaxially pressed into a green compact and subsequently sintered to produce the acetabular socket and femoral head.

[00101] In another aspect, the present disclosure provides a multi-piece integrated fabrication apparatus for producing biocompatible orthopedic prosthesis such as acetabular socket and femoral head with highest possible mechanical properties such as compressive strength, flexural strength, wear resistance properties, uniform microstructure, desired fracture strength under compressive mode and low average surface roughness for total hip replacement with patient- specific dimensions.

[00102] In an embodiment, the present disclosure provides an apparatus for near net shape forming of femoral head, the apparatus can include:

a cylindrical-shaped plunger guide having a longitudinal axis, wherein the plunger guide having an opening in its longitudinal axis through which a powder to be compacted may be charged; and a plunger configured for uniaxially pressing the powder material, which has been loaded into the die cavity and the opening of the plunger guide, wherein the plunger is being guided by the plunger guide.

[00103] In an embodiment, the apparatus for near net shape forming of femoral head can further include a specific ejection means for releasing the plunger from the die cavity after uniaxial pressing. The ejection means can be configured to include four pin guide and circular cavity that together can accommodate and withhold the entire powder compressed assembly during slow ejection rate at lmm/min in the same uniaxial press.

[00104] In another embodiment, the present disclosure provides an apparatus for near net shape forming of acetabular socket, the apparatus can include:

a die having at least two separable die parts that, in the assembled state, define a die cavity for receiving a powder to be compacted; wherein the die cavity defines the desired configuration of an acetabular socket;

[00105] Referring to FIGs. 5A-F, there is shown various parts of a multi-piece integrated compression mold assembly designed for fabrication of ceramic femoral head, in accordance with embodiments of the present disclosure. The multi-piece integrated mold assembly can overcome the limitations imposed by conventional molds through various parting directions and surfaces. The fabrication mold can consist of more than one primary parting surfaces and contain more than two mold pieces or sub-assemblies with independent parting directions. Such a degree of freedom can be used to assemble and separate mold pieces as well as to apply compaction pressure to a green body from many different directions.

[00106] FIGs. 5A-F illustrate plan and perspective view of various parts of a femoral head fabrication mold such as, bottom die 100, top die 200, powder and plunger guide die 300, plunger cum mandrel with ejection pin guide 400, ejection head including base pins 500 and ejection support plates and rods 600, respectively. The multi-piece integrated compression mold can enable fabrication of ceramic femoral head by uniaxially pressing a composite material powder in the die cavity.

[00107] Referring to FIG. 5A, that shows exemplary configuration of a bottom die 100 which can include a top surface 102, parting surface 104, step portion for top die insertion 106, half part of femoral head cavity (acetabulum contact side) 108, M8 threaded holes 110, Ml 2 threaded holes 112, and bottom surface 114. FIG. 5B shows exemplary configuration of a top die 200 which can include bottom surface 202, parting surface 204, bottom protrusion 206, half part of femoral head cavity (truncated side) 208, M8 threaded holes 210, top surface 212, and M12 threaded holes 214.

[00108] The bottom and top dies 100 and 200 can be the female part of the mold and can hold on the lower parts of entire mold assembly. The dies 100 and 200 can be fabricated using conventional manual lathe for rough finish and semi-automatic CNC lathe for smooth finish operation. The component area of the mold can be polished to get an excellent surface finish on the component. FIG. 5A and 5B show the partitioned bottom and top cavity dies machined to accommodate an acrylonitrile butadiene styrene (ABS) based polymer prototype femoral head. The parting surfaces 104 and 204 can be maintained at zero draft, which in turn can minimize the powder penetration between the interactive surfaces during the powder compaction process. This cavity portion can create uniform pressure gradient during powder compaction. From the top surface of cavity, a step portion 106 can be maintained to provide room to insert the top die 200 and such arrangements can allow one to avoid powder insertion between the mating surfaces within top and bottom dies. The parting surfaces 104 and 204 of the bottom and top dies 100 and 200 can be fastened together by high tension Ml 2 bolts. Similarly, M8 thread hole can be produced at the bottom of the die and also in the vertical direction in order to hold the top die 200, as well as powder and plunger guide die 300. Similarly, the top die 200 can be partitioned into two symmetrical halves, which in turn can be used to separate the die along the parting direction. The bottom surface 202 of the top die 200 can consist of protrusion 206, which can be used to insert into the step portion 106 of the bottom die 100. Similarly, the bottom surface of the top die 202 can have another projection that can be inserted into the bottom surface 306 of the powder and the plunger guide die slot 300. The truncated side of a femoral head can be used as the top die because the plunger 400 can be allowed to move and compress the powder in the mould cavity to create the perfect blind hole within parallel positioned both of the fixed and moveable platforms. [00109] A powder and plunger guide 300, as shown in FIG. 5C, can be placed on the assembled cavity. The powder and plunger guide 300 can include a top surface 302, powder and plunger guide hole 304, and bottom surface 306. Heat treatment may be carried out for a cavity material to avoid bulging due to heavy load with a steel specification of EN-24, HRC-55.

[00110] Referring to FIG. 5D, that shows an exemplary configuration of a plunger cum mandrel with ejection pin guide 400, which can be the male part of the mold assembly and also can hold the upper parts of the entire assembly. During uniaxial pressing, the powder mix in the cavity of top and bottom dies 200 and 100 can be compressed from the upper side by the plunger rod 406. The plunger 400 can be fabricated using conventional manual lathe for rough finish and automatic CNC lathe for smooth finish operation. The component area of the mold can be polished to get good surface finish of the component. The plunger 400 can have four M8 threaded holes 404 around the periphery thereof, and the plunger can be constructed using the same material and material specifications as that of the bottom and top dies 100 and 200.

[00111] The plunger cum mandrel 400 can compact a composite material powder (e.g. alumina- zirconia mixed powder) in the pressure zone of mould cavity as well as to generate a blind hole in a femoral head. One end of the plunger 400 can consist of taper mandrel 408, which in turn can penetrate into a powder to create cylindrical blind hole on the truncated side of the femoral ball head. Another end of the plunger can consist of a head 402, which can guide the ejection pins which are shown in FIG. 5E.

[00112] Referring to FIG. 5E, that shows an exemplary configuration of ejection head including base pins assembly 500 that includes an ejector head 502 with four ejector pins 504. After uniaxial pressing, a green compact of femoral head can be ejected by introducing a unique ejection mechanism through ejection pin 504 and applied reverse direction of load. Four rod assembled ejection support 600 can be machined for the ejection purpose as shown in FIG. 5F. The ejection support 600 can include an ejector retaining plate 602 and ejector plate support 604, and ejector base plate 606. The total assembly including the ejection pin guide can be placed on the ejection support 600 and appropriate load can be applied to remove the plunger 400 from the assembly. This effort can release the plunger 400 very smoothly without any damage from the assembly and thereafter all the bolts can be loosened to get a green compact.

[00113] Referring to FIGs. 6A-C, there is shown various parts of a multi-piece integrated compression mold assembly designed for fabrication of ceramic acetabular socket, in accordance with embodiments of the present disclosure. The compression mold can include various parts such as, partitioned bottom die 700, powder and plunger guide die 800 and plunger 900. The multi-piece integrated compression mold can enable fabrication of ceramic acetabular socket by uniaxially pressing a composite material powder in the die cavity.

[00114] Referring to FIG. 6A, that shows exemplary configuration of a bottom die 700 which can include a top surface 702, parting surface 704, female step portion for insertion of plunger guide die 706, integrated cavity of acetabular socket 708, Ml 2 threaded hole 710, and M8 threaded hole 712. The bottom die 700 can consist of a partitioned configuration as shown in FIG. 6A, which in turn can be used to access one surface of an acetabular socket and to de-mould the green compact without any damage. The partitioned surface 704 can be formed with zero draft that can reduce the powder penetration and can produce uniform pressure while powder compaction. A female step portion 706 can be formed on the top surface 702 of bottom die to insert the powder cum plunger guide die 800 which has male step portion 806, such step arrangement can restrict powder penetration during compaction. FIG. 6B shows exemplary configuration of a powder cum plunger guide die 800 which can have a cylindrical body 802, core guide hole 804, and male step portion to insert on bottom die 806. The bottom die 700 can be fastened together by high-tension Ml 2 bolts. The bottom 700 and plunger guide die 800 can be fixed firmly by M8 bolts in vertical direction.

[00115] FIG. 6B shows exemplary configuration of a plunger 900 which can include hydraulic pressure applied surface 902, cylindrical elongated body 904, and mandrel 906. The plunger 900 can be lowered down through the core guide hole 804 of the powder cum plunger guide die 800 upon the powder-filled die cavity 708, to uniaxially press the powders in the die cavity 708 of the bottom die 700. The final green compacted can then be ejected from the die cavity 708 by raising the plunger 900.

[00116] FIGs. 5A-F and 6A-C are purely exemplary and the various components of the multi- piece integrated compression molds can take any desired size, shape and thickness to suite configuration of matching parts.

EXAMPLES

[00117] The present disclosure is further explained in the form of the following examples. However, it is to be understood that the foregoing examples are merely illustrative and are not to be taken as limitations upon the scope of the invention. Various changes and modifications to the disclosed embodiments will be apparent to those skilled in the art. Such changes and modifications may be made without departing from the scope of the invention.

[00118] Manufacturing of acrylonitrile butadiene styrene (ABS) Polymeric prototypes

A judicious selection of prototype design and their growth direction on base can reduce the effort and perfection of the final product. The entire process starting from CAD originated modeling to acrylonitrile butadiene styrene (ABS) polymer prototype development process is described in the following sections.

[00119] Pre-process and generation of standard triangularization language (STL) file

Pre-process is a technique which can make the 3D virtual model of standard triangularization language (STL) file ready for the development of components through fused deposition method (FDM). The pre-process in the rapid prototype method was accomplished in three steps, namely create a standard tessellated language file, build supports, and slice the STL file into layers. Using the 3D modelling software Pro/E, the 3D solid femoral head and acetabular socket were converted into an STL file in binary format with the help of deviation control units, chord height of 0.0057 mm, the distance between femoral head design surface to tessellated surfaces and angle control of 0.5°, which allowed the angular deviation between adjacent planar triangles. The smaller chord height ensured less deviation from the original surface to the tessellated surface. This format represented a 3-dimensional surface as a mesh of planar triangles. The file contained the coordinates of the planar triangle vertices and the direction of the outward normal of each triangle.

[00120] Slicing and base support build-up

Prior to prototype fabrication, an essential base support is necessary and hence preliminary support was prepared independently using polyphenylsulfone (PPSF). The deposition technique for base as well as components is governed by the thin layer slicing technique using catalyst EX software. The layer thickness during z-axis deposition movement was maintained around 0.254 mm for both the base and components. The base platform build time for head was lhr 05min. During the fabrication of base platform, the estimated volume of material was consumed 1.44cm³ for head. In the same way, estimated build time and consumed material volume for acetabular socket was lhr 30 min and 2.12 cm , respectively.

[00121] Materials and methods for Polymer rapid prototypes

Fused deposition modelling (FDM) technique was employed for the development of 3D prototype of desired shape. The FDM technique involves two types of materials- one is the support material that acts as a scaffolding to support the printed product as described earlier and the second one is modelling material of the same composition as the final product. A thermoplastic acrylonitrile butadiene styrene (ABS) wire filament of diameter 1.8mm was used for the fabrication of prototypes and thereafter steel mold from polymeric replicas. During the printing of the product, special care was taken to minimise the mechanical vibrations to prevent the floating layers to support the overhanging and twisted surfaces as well as to improve the stability of the system for the easy removal of the finished part from the working platform.

[00122] Fabrication process of Polymer femoral head and acetabular socket prototypes In order to reduce the contact between support material and developed components, convex zone was considered as the bottom for both the prototype, which allowed easy removal from base after completion of the fabrication (FIG. 3A and 4A). The slicing shows the cross-section area of the femoral head and acetabular socket in a particular orientation, where the material injection nozzle follows the stereo-lithography contour. In a typical FDM system, the extrusion nozzle moves over the build platform horizontally and vertically, thereby draws the cross-section of an object onto the platform. If the first layer was completed, the base platform moves downward, i.e. Z-direction, usually by about one layer height and makes it ready to place the next layer of material. During printing, these materials take the spools, where the spools were unwound and made it passing through a liquefier and then to an extrusion nozzle. The liquefiers melt the filaments and extrude them further onto a base, earlier designated as build platform or table. Numerical control machine was used to monitor the movements of extrusion nozzle and platform in X, Y and Z translational directions. The deposited prototypes, as demonstared in FIG. 3B and 4B were separated from the working platform and then the support material was removed by the peel off or snap technique, and used to design multi-piece integrated cavity mould. The detailed dimensions of both ABS prototype equivalent to green femoral head and acetabular socket are specified in FIG. 3C and 4C.

[00123] Formulation of composite material of the present disclosure

Femoral heads and acetabular sockets were fabricated using different compositions of the composite material and processing conditions which are summarized herein below. FIG. 9 illustrates optimized composition and process parameters for small coupon specimen utilized to scaling up the zirconia toughened alumina based femoral head and acetabular socket prosthesis.

[00124] Composition 1: Commercial pure alumina and zirconia were used in different ratio to fabricate the femoral head at a wide range of sintering temperature and time profile in air atmosphere. During this green compaction preparation, a variable amount of sintering aid Mg(N03)2.6H₂0, and constant amount of 3wt.% of polyvinyl alcohol (PVA) binder were used for different batches. In this example, 95wt% Alumina (A), 5wt% Zirconia (Z), 400ppm MgO (M) was mixed and sintered at 1600°C for the different time variation of 4-8 hrs.

[00125] Composition 2: In continuation of other parameters, a combination of 85 wt% Alumina (A), 15wt% Zirconia (Z), 400ppm MgO (M) was used and sintered at 1500 - 1650°C for a constant time schedule of 6 hrs.

[00126] Composition 3: In continuation of other parameters, a combination of 95 wt% Alumina (A), 5wt% Zirconia (Z), 800ppm MgO (M) was used and sintered at 1500 - 1650°C for a constant time schedule of 6 hrs.

[00127] Composition 4: In continuation of other parameters, a combination of 85 wt% Alumina (A), 15wt% Zirconia (Z), 800ppm MgO (M) was used and sintered at 1600°C for the different time variation of 4-8 hrs.

[00128] Composition 5: In continuation of other parameters, a combination of 90wt% Alumina (A), 10wt% Zirconia (Z) was used with different content of sintering aid 400 - 800ppm MgO (M), and sintered at 1600°C for the different time variation of 4-8 hrs.

[00129] Fabrication of femoral head and acetabular socket using the composite material:

The fabrication set up as shown in FIGs. 5 and 6 was used for fabricating femoral head and acetabular socket prototypes through uniaxial pressing of powder mixtures. Commercial grade alumina (Sumitomo, Japan, AKP - 5N, 120nm, 99.999% purity), Zirconia (Tosoh, Japan, 3Y-E, 25nm, >99.9%) and Mg(N0₃)2.6H₂0 (Sigma Aldrich, >99.9% trace metal basis) were used without any further modification. The composite material (also referred to as "ZTA", i.e. Zirconia toughened alumina) of around 80g was mixed with 3wt% polyvinyl Alcohol (PVA) organic binder for the two components and the powder mix was separately uniaxially pressed in respective assembled molds. The dried and free flowing powders were poured into the mould cavity, which was assembled multi-piece moulds together by high tension bolts along different directions. Before starting the compaction, steric acid was applied on the cavity and plunger walls that serves as a lubricant. Subsequently, heavy-duty silicone spray was applied to release a green body from the mould cavity walls without any distortion and breakage. The compaction force of 18 and 22 tons for equal dwell time of 120 sees was applied to transfer the load uniformly throughout the powder compact and to obtain sufficient strength in the green compact of femoral head and acetabular socket, respectively. After compaction, the plunger was removed and the multi - parts mold was carefully dismantled to get the perfect shape of femoral head and acetabular socket in commensurate with the ABS prototype model as shown in FIGs. 7 A to 7F and FIGs. 8A to 8D.

[00130] The de-moulded green femoral ball head and acetabular socket were further pre- sintered at 1200°C for 2 hr with a slow heating and cooling rate of 2°C/min. The pre-sintering condition was optimized from continuous sintering at different level of peak temperature starting from 800 - 1600°C with an interval of 100°C. The pre-sintering was mainly used to improve the holding strength of the prototypes that allow smooth machining to a limited extent. The pre- sintered ZTA femoral head and acetabular socket was machined by CNC lathe machine to get the final desired shape through appropriate M-code and G-code. Such a ceramic body allowed the machining operations at pre-sintered stage only, which provided the accurate dimension without critical effort after final stage of sintering.

[00131] The pre-sintered and machined femoral head and acetabular socket were finally sintered with a temperature range of 1500 - 1650°C for different time-scale to get highly dense compacts. The sintered ceramic femoral head and acetabular socket were polished in order to remove the excessive material and to get the mirror surface, which reduced the interaction among the asperities between the convex femoral head (outer ID) and concave acetabular socket (inner ID). Excellent geometrical smooth surface finish of the femoral head is a primary requirement, since it undergoes significant tribological interaction with the acetabular socket in THR assembly. After achieving accurate shape and dimension of the product through machining and sintering, further attempt was made in order to achieve a better surface finish maximum, Ra value in the range of 0.2μηι for articulating surface of femoral head and 0.01 μηι for acetabular socket (ID). Polishing was carried out with sequentially varying diamond paste of grit sizes (10 - 1 μηι) to obtain smooth outer surface of spherical dome-shaped object, like the femoral head. The component was mounted on the rotating spindle and pressed against a spring-loaded rotating attachment at a definite load. The spindle variation was maintained while polishing the component.

[00132] Characterization of microstructure, mechanical and biological properties

[00133] Microstructure

The density of sintered component was determined by Archimedes' principle. The specimen was cleaned by ethanol in ultrasonicator, followed by thermal etching for 30 minutes at a temperature below 50°C to peak sintering temperature. Microstructure was taken from different zone of the thermally etched specimen by scanning electron microscope (Jeol JSM 6480LV, Japan)at 15KV accelerating voltage in backscattered mode. The grain size was measured from the average of near to 500 numbers of grains from a different zone of microstructures. The femoral head and acetabular socket were compacted nearly to 99% density and the dense microstructure is characterized by 3-4 μηι alumina and 0.5-1 μηι zirconia grains. FIGs. 10A and B illustrate the microstructure of sintered femoral head and acetabular socket respectively, where different contrast indicates the uniform distribution of zirconia particulate (white) in alumina (grey) matrix.

[00134] CMM measurement:

The dimensional stability, including a targeted tolerance limit of ± 50μηι of 26mm diameter femoral head and articulating diameter of the acetabular socket were measured through coordinate measuring machine (CMM). Herein, the polished hip prostheses were placed on a fixed platform to restrict any degree of freedom during assessment. A measuring instrument probe was made to contact the object and to measure the circularity through X and Y axes movement only, whereas Z-axis movement was restricted during such operation. The profile data were plotted on a polar graph to determine the circularity within stipulated tolerance limit and the results are illustrated in FIGs. 11 and 12A-B. The entire process was repeated in several locations to identify the shape and size stability.

[00135] Micro - CT analysis:

The μCT imaging was carried out for 26mm (OD) femoral head and 26.5 mm acetabular socket with VersaXRM-500 (Xradia, Zeiss, Germany) instrument with X-Ray source energy of 80 kV and 7 W power (see Figuresl3& 14). A combination of 0.39 X object with 0.8 sec exposure time and HE2 filter used to 10 - 18% transmission range and intensity of 4500 - 8000 counts. 3201 images were collected at 29.028 μιη voxel size. 3D tomogram was reconstructed from the transmission images in XM-Reconstructor (Xradia, Zeiss) software using standard beam hardening correction and Gaussian smoothing with 0.5 kernel size. Image processing, analysis, and visualisation were done in Avizo Fire 8.1 (FEI, France). No filter was used as all the images had sufficient signal/noise ratio for further analysis. FIG.13A is Micro - CT image of the femoral head which shows isometric view of edge and convex surface including blind hole projection of same component without any cracks and defects, and FIG. 13B shows 3D distribution of zirconia grains along the matrix. FIG. 14A is Micro - CT image of acetabular socket which shows perspective view of edge and convex surface, and FIG. 14B shows Zr0₂ particle distribution on one plane of AI2O3 matrix.

[00136] Invitro Biocompatibility:

Mouse myoblast cells were cultured on dense ZTA following standard cell culture protocol. The cell viability was analysed using MTT (3(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, Sigma Aldrich) assay. A comparison was made using a 0.2% gelatin coated glass cover slip as control. 3000-4000 C2C12 cells/ well were seeded on each sterilized sample placed in 12 well plates and incubated for 24, 48 and 72 h in a C0₂incubator (37° C, 5% C0₂and 90% humidity). After the incubation period, the medium in the well plate was aspirated and samples were washed twice with IX PBS. This was followed by an addition of 15% reconstituted MTT reagent (Sigma Aldrich) prepared in DMEM (without phenol red) in each well and further incubation for 3 h to allow the formation of formazancrystals. MTT reagent is transformed into formazan by mitochondrial dehydrogenases of metabolic active cells proliferated on sample providing a measure of cell viability and activation. The medium was removed and replaced by dimethyl sulfoxide (DMSO, Merck) to solubilize the purple colour formazan crystals. The optical density was measured at 595 nm with a reference wavelength of 750 nm in a microplate reader (i-mark, BioRad laboratories, India). The cell viability (%) was calculated using the following formula: % Cell Viability = (Mean optical density of sample/ Mean optical density of control)* 100. The experimental results are shown in FIG. 15 and FIGs. 16A to 16D.

[00137] Surface Profile study:

To validate the efficiency of polishing, the surface roughness of acetabular socket was precisely measured before and after polishing using mechanical stylus type surface analyzer (Surftest SJ 400, Make: Mitutoyo) and the results are shown in FIG. 17. The average roughness of the concave surface of sintered ZTA acetabular socket was measured to be 0.49 μηι (FIG. 17A). The continuous radial force smoothens of the ceramic surface and average surface roughness was measured as minimum as Ο.ΟΙμηι, as represented in FIG. 17B. It was found that the present polishing technique reduced the average surface roughness up to 98% that assisted to enhance the lifespan of acetabular socket in the perspective of tribolocial behaviour against counterbody, say ceramic femoral head.

[00138] Burst Strength:

An attractive combination of Vickers hardness (H_vlo = 19GPa) and SENVB fracture toughness (~4.3MPa.m^1,z) were recorded for the optimized composition. A typical burst test was used to measure the uniaxial compressive strength of the femoral ball head in accordance with the ISO 7206-10 guideline and the results are shown in FIG. 18. The dummy femoral stem and metal cone were manufactured with mild steel. Prior to burst test, the femoral ball head was mounted on the dummy femoral stem neck and was loaded hydraulically against 100° metal female cone. In order to reduce the local stress and smooth transfer of load between the femoral head and 100°cone geometry, a metallic copper ring was also used. The cone support and copper ring fixture are assembled to mimic the invivo fracture behaviour (FIG. 19). Five sets of femoral ball heads were used to test the strength at a loading rate of lkN/sec using universal testing machine (InstronSatec 600 kN, USA). The fractured pieces after performing the burst strength at a maximum load of 15.3kN are represented in FIG. 20. The microstructure as shown in FIG. 21 depicts that the grains are supposed to follow intergranular fracture that is initiated from top of the femoral head under compression mode of loading.

[00139] Dimension stability to accommodate Femoral Head in Acetabular Socket:

In order to fit the ceramic (ZTA) femoral head within ceramic (ZTA) acetabular socket, a tolerance limit of 0.5 mm was maintained. FIG. 22 represents sintered ceramic prototypes in commensurate with the achieved near net shaped dimension as well as the geometrical conformation through a perfect assembly of 26mm (OD) femoral head, 26.5mm (ID) acetabular socket bearing. In order to demonstrate the product conformity in reference to dimensional stability and performance for total hip replacement, a set of ZTA ceramic femoral head and acetabular socket and ABS polymer stem prototype have been prepared. As shown in FIG. 23, the implant assembly elucidates the importance of the present invention in the perspective of bio- implant prototype development. An exposed concave surface of acetabular socket with 26.5 mm (ID) demonstrating the ease of accommodating the male part of 26 mm (OD) femoral head, together with geometrical conformity with a polymer prototype femoral stem (FIG. 23A). In continuation, a short 135 mm in total length of femoral stem was prepared, which consist of different neck geometry to accommodate the blind hole of 26 mm (OD) femoral head (FIG. 23B).

ADVANTAGES OF THE PRESENT INVENTION

[00140] The present disclosure provides a method for fabricating femoral head and acetabular cup with highest possible mechanical properties, such as compressive strength, flexural strength, wear resistance properties, uniform microstructure, desired fracture strength under compressive mode and low average surface roughness for total hip replacement with patient-specific dimensions.

[00141] The present disclosure provides a composite material and method for producing femoral head and acetabular cup with extended functional lifetime, thus minimizing the need for revision surgery.

[00142] The present disclosure provides a method for producing femoral head and acetabular socket that facilitates substantial reduction of friction and wears debris of articulating joint elements under dynamic load, and thereby reducing osteolysis and inflammatory reactions.

[00143] The present disclosure provides a fabrication method that enables fabrication of defect- free femoral head and acetabular socket and thereby eliminates the need of additional machining of the finished product.

[00144] The present disclosure provides near-net shaped implantable prosthesis such as femoral head and acetabular socket with patient specific dimensions.

[00145] The present disclosure provides near-net shaped implantable prosthesis such as femoral head and acetabular socket that exhibit high fracture toughness, excellent wear characteristics and low susceptibility to stress assisted degradation over commercially available implants.

[00146] The present disclosure provides a fabrication apparatus that facilitates reproducible, faster, and more economical production of implantable prosthesis such as femoral head and acetabular socket with patient specific dimensions.

[00147] The present polishing technique enables to obtain nanoscale average surface roughness that can assist in minimizing the squeaking noise and can enhance the lifespan of acetabular socket in the perspective of tribolocial behaviour against counter body, say ceramic femoral head.

[00148] The present disclosure provides a fabrication apparatus that facilitates simple and cost effective fabrication of patient specific femoral head and acetabular sockets with high dimension stability and polishing.

[00149] The present disclosure provides a composite material that significantly enhances the fracture toughness and compressive fracture strength of femoral head and acetabular socket prepared there from, and thus increases the life of the implant.

Claims

We Claim:

1. A method for fabricating an acetabular socket or femoral head for use in total hip prosthesis, the method comprising the steps of:

a) placing a composite material powder into a mold cavity;

b) applying uniform uniaxial pressure to the powder-filled mold cavity to cause the composite material powder to be compacted and formed into a green compact of acetabular socket or femoral head;

c) pre-sintering the green compact to bond the compacted powder, thereby forming an intermediate solid compact;

d) machining the pre-sintered compact;

e) sintering the machined compact; and

f) polishing the machined compact to produce the acetabular socket or femoral head.

2. The method according to claim 1, wherein the pre-sintering in step (c) is performed at a temperature of 800 to 1600°C.

3. The method according to claim 2, wherein the pre-sintering in step (c) is performed at a temperature of 800 to 1600°C with a heating and cooling rate of 2°C/min.

4. The method according to claim 2, wherein the pre-sintering in step (c) is performed at a temperature of 1200°C.

5. The method according to claim 1, wherein the pre-sintering in step (c) is performed for a length of time ranging from 0.5 to 3 hours.

6. The method according to claim 1, wherein machining of the pre-sintered compact in step (d) is done with a computer numerically controlled (CNC) lathe.

7. The method according to claim 1, wherein the sintering in step (e) is performed at a temperature of 1500 to 1650°C.

8. The method according to claim 7, wherein the sintering in step (e) is performed at a temperature of 1600 to 1650°C.

9. The method according to claim 1, wherein the sintering in step (e) is performed for a length of time ranging from 4 to 8 hours.

10. The method according to claim 1, wherein the polishing in step (f) is performed using a diamond paste.

11. The method according to claim 10, wherein the diamond paste has a grit size ranging from 10 to 1 μιη.

12. A composite material for producing acetabular socket or femoral head for use in total hip prosthesis, wherein the composite material comprising:

60 to 95 % by weight of alumina; and

1 to 40 % by weight of zirconia.

13. The composite material according to claim 12, further comprises an inorganic nitrate as sintering aid.

14. The composite material according to claim 13, wherein the inorganic nitrate is magnesium nitrate.

15. The composite material according to claim 12, further comprises a polymer binder.

16. The composite material according to claim 15, wherein the polymer binder is polyvinyl alcohol.

17. An acetabular cup for use in total hip prosthesis, comprising a composite material as claimed in claim 12.

18. A femoral head for use in total hip prosthesis, comprising a composite material as claimed in claim 12.

19. A composite material for producing acetabular socket or femoral head, comprising:

85 to 95 % by weight of alumina;

5 to 15 % by weight of zirconia;

0.05 to 10 % by weight of magnesium nitrate; and

1 to 5 % by weight of polyvinyl alcohol.

20. An acetabular cup for use in a total hip joint prosthesis, the acetabular cup having a spherical upper side having a size and shape configured to be received within an a patient's acetabulam, and a lower side having a part-spherical cavity having a size and shape for articulatory reception of a ball-shaped femoral head,

wherein the acetabular cup is formed from a composite material comprising 60 to 95 % by weight of alumina; and 1 to 40 % by weight of zirconia, and wherein the composite material is uniaxially pressed into a green compact and subsequently sintered to produce the acetabular socket.

21. The acetabular cup according to claim 20, wherein the acetabular cup has a spherical inner diameter ranging from 26.5 to 35 mm.

22. The acetabular cup according to claim 20, wherein the acetabular cup has a spherical outer diameter ranging from 37 to 48 mm.

23. A femoral head for use in a total hip joint prosthesis, the head having a spherical upper side having a size and shape adapted for articulatory reception within a cavity of an acetabular cup, and a lower side having a downwardly open cavity having a size and shape configured to receive a neck of a femoral stem,

wherein the femoral head is formed from a composite material comprising 60 to 95 % by weight of alumina; and 1 to 40 % by weight of zirconia, and wherein the composite material is uniaxially pressed into a green compact and subsequently sintered to produce the femoral head.

24. The femoral head according to claim 23, wherein the femoral head has a spherical outer diameter ranging from 26 to 35 mm.

25. An implantable hip joint prosthetic assembly, comprising:

an acetabular cup having a spherical upper side having a size and shape configured to be received within an a patient's acetabulam, and a lower side having a part-spherical cavity having a size and shape defining an articulation surface;

a femoral head having a spherical upper side having a size and shape adapted for articulatory reception within the part-spherical cavity of the acetabular cup, and a lower side having a downwardly open cavity having a size and shape configured to receive a neck of a femoral stem,

wherein the acetabular cup and the femoral head are formed from a composite material comprising 60 to 95 % by weight of alumina; and 1 to 40 % by weight of zirconia, wherein the composite material is uniaxially pressed into a green compact and subsequently sintered to produce the acetabular socket and femoral head.

26. An apparatus for near net shape forming of femoral head, the apparatus comprising:

a die having at least two separable die parts that, in the assembled state, define a die cavity for receiving a powder to be compacted, wherein the die cavity defines a desired configuration of a femoral head;

a plunger configured for uniaxially pressing the powder material, which has been loaded into the die cavity and the opening of the plunger guide, wherein the plunger is being guided by the plunger guide.

27. The apparatus according to claim 26, wherein the apparatus further comprises an ejection means for releasing the plunger from the die cavity after uniaxial pressing.

28. The apparatus according to claim 26, wherein the ejection means is being supported by an ejection support means.

29. An apparatus for near net shape forming of acetabular socket, the apparatus comprising: a die having at least two separable die parts that, in the assembled state, define a die cavity for receiving a powder to be compacted; wherein the die cavity defines a desired configuration of an acetabular socket;

30. A method for fabricating an implantable prosthesis, the method comprising the steps of: a) placing a composite material powder into a mold cavity, wherein the mold cavity defines a desired configuration of an implantable prosthesis;

b) applying uniform uniaxial pressure to the powder-filled mold cavity to cause the composite material powder to be compacted and formed into a green compact of implantable prosthesis;

d) machining the pre-sintered compact;

e) sintering the machined compact; and

f) polishing the machined compact to produce the implantable prosthesis.

31. The method according to claim 31, wherein the implantable prosthesis is selected from the group consisting of knee implant, elbow joint, ankle joint, shoulder joint and wrist joint.