A METHOD OF FABRICATION OF FEMUR IMPLANT FOR ORTHOPEDIC APPLICATIONS

Abstract

TITLE: A METHOD OF FABRICATION OF FEMUR IMPLANT FOR ORTHOPEDIC APPLICATIONS APPLICANT: KARUNYA INSTITUTE OF TECHNOLOGY AND SCIENCES ABSTRACT The present invention discloses a method of fabrication of femur implant for orthopedic implants applications. The method of the present invention comprising of following steps; a. extracting 2D image of femur bone from computed tomography; b. feeding the extracted 2D image data into segmentation software to generate a 3D bone model; c. refining by importing the 3D bone model into Creo PTC software to obtain refined 3D bone implant model in which 3D bone model is analysed in ANSYS workbench to create the 3D bone implant model; d. meshing is done by importing the refined 3D implant model into ANSYS workbench comprising tetrahedral mesh element to obtain 3D meshed femur implant followed by adjustments in boundary conditions and applying required loading conditions to obtain 3D finite element model; e. fabricating multi-material implant of femur bone is carried out by transferring the 3D finite element model to 3D printing followed by printing with multi-materials to obtain unified multi-material femur implant.

Specification

Description:Form 2


THE PATENT ACT, 1970
(39 of 1970)
&
THE PATENT RULES, 2003
COMPLETE SPECIFICATION
(See section 10 and rule 13)






"A METHOD OF FABRICATION OF FEMUR IMPLANT FOR ORTHOPEDIC APPLICATIONS"






in the name of KARUNYA INSTITUTE OF TECHNOLOGY AND SCIENCES an Indian national having address at KARUNYA INSTITUTE OF TECHNOLOGY AND SCIENCES, KARUNYA NAGAR, COIMBATORE, COIMBATORE - 641114, TAMIL NADU, INDIA.



The following specification particularly describes the invention and the manner in which it is to be performed.
FIELD OF THE INVENTION:

The present invention generally relates to a method of fabrication of human bone implant. More particularly, the present invention relates to a method of fabrication of femur implant for orthopedic applications.

BACKGROUND OF THE INVENTION:

Bone tissue has a remarkable ability to regenerate and heal itself. However, large bone defects and complex fractures still present a significant challenge to the medical community. Current treatments centre on metal implants is for structural and mechanical support and auto-or allo-grafts to substitute long bone defects.

There are reports available in the state of art revealing the modelling methods for human bone.

EP1351628B1 discloses a structural and mechanical model and modelling methods for human bone based on bone's hierarchical structure and on its hierarchical mechanical behaviour. The model allows for the assessment of bone deformations, computation of strains and stresses due to the specific forces acting on bone during function, and contemplates forces that do or do not cause viscous effects and forces that cause either elastic or plastic bone deformations.

US7212958B2 discloses a method of preparing a model of the structural patterns of an osteon for use in determining mechanical response of bone to an external force, wherein the method comprises:identifying non-homogeneous structural patterns of the osteon;comparing the structural patterns with collagen bundle and hydroxyapatite orientation;comparing the structural patterns with lacunar and canalicular distributions;generating empirically-based data from the comparison of the structural patterns of the osteon with the collagen bundle and hydroxyapatite orientation and with the distributions of the lacunae and canaliculate;preparing a computer based model of the osteon using the empirically-based data; anddetermining mechanical response of the bone by applying parameters of the bone and parameters of force acting on the bone to the model;presenting mechanical response of the bone to a user using a computer.

US11260148B2 discloses an implant consists on coating of a supporting structure (1) with synthetic hydroxyapatite by immersing the supporting structure (1) in a suspension (3) and triggering of a cavitation in a portion of the suspension (3) being in contact with the supporting structure (1). The suspension (3) is formed by a liquid external phase, advantageously water, and internal phase, i.e. particles of synthetic hydroxyapatite having an average particle size not exceeding 100 nm and containing structural water in an amount from 2 to 6% by weight. The implant is coated with the above described hydroxyapatite subjected to cavitation and a thickness of 50 nm to 1000 nm, advantageously 50 nm to 300 nm.

US6183515B1 discloses a process for making bone implants from calcium phosphate powders. This process involves selectively fusing layers of calcium powders that have been coated or mixed with polymer binders. The calcium powder mixture may be formed into layers and the polymer fused with a laser. Complex three-dimensional geometrical shapes can be automatically replicated or modified using this approach.

US9675459B2 discloses a nanopowder of synthetic hydroxyapatite (Hap) is used having a hexagonal structure, average grain size in a range from 3 to 30 nm and the specific surface area greater than 200 m2/g. First the nanopowder is formed to the desired geometric shape, and then the shape is fixed. In the step of shape information the dried nanopowder is pressed in the mold under the pressure ranging from 50 Mpa to 2 GPa. In the step of fixing the pressed nanopowder at room temperature is subjected to the pressure rising from the ambient value to the peak value selected from a range of 1 to 8 GPa and to a temperature selected from a range of 100° C. to 600° C. for a period of time selected from a range from 30 seconds to 5 minutes. The density of thus produced implant, determined by helium method, is not less than 75% of the theoretical density.

WO2016176444A1 discloses a system comprising:(a) a photo-curable biomaterial ink; and(b) a 3D printing device for:(i) dispensing a layer of the photo-curable biomaterial ink in a partem according to encoded instructions,(ii) exposing the layer of the photo-curable biomaterial ink to light to cure the biomaterial ink and produce a solidified biomaterial layer, and(iii) repeating steps (i) and (ii), with each successive layer built upon the previous layer to produce a 3D structure of the solidified biomaterial.

However, the above disclosed methods have few disadvantages like the process is complicated and thus it increases cost of the product. Further, they lack accuracy and therefore, results in imprecise implant with less mechanical strength and less wear resistance.

Thus, there exists a need in the state of art for an alternative method that address the shortcomings.

Hence, an attempt has been made to develop a cost-effective method for fabrication of femur bone overcoming the above said drawbacks.


OBJECT OF THE INVENTION:

The main object of the present invention is to develop a cost-effective method of fabrication of femur implant for orthopaedic applications.

Another object of the present invention is to fabricate a multi-material implant of femur bone employing developed method.

Yet another object of the present invention is to analyse load capacity of the fabricated multi-material implant of femur bone.

Further object of the present invention is to utilize the developed method for fabrication of femur implant withhigh mechanical strength, high wear resistance and less bending for orthopaedic applications.

SUMMARY OF THE INVENTION:

The present invention discloses a method of fabrication of femur implantfor orthopedic implants applications. The method of the present invention comprising of following steps;

a. extracting 2D image of femur bone from computed tomography;
b. feeding the extracted 2D image data into segmentation software to generate a 3D bone model;
c. refining by importing the 3D bone model into Creo PTC software to obtain refined 3D bone implant model in which 3D bone model is analysed in ANSYS workbench to create the 3D bone implant model;

d. meshing is done by importingthe refined 3D implantmodel into ANSYS workbench comprising tetrahedral mesh element to obtain 3D meshed femur implant followed by adjustments in boundary conditions and applying required loading conditions to obtain 3D finite element model;
e. fabricating multi-material implant of femur bone is carried out by transferring the 3D finite element model to 3D printing followed by printing with multi-materials to obtain unified multi-material femur implant.

BRIEF DESCRIPTION OF THE DRAWINGS:

Figure 1 depicts
a. X-Ray of Femur bone(2D)
b. Dimensions of the femur bone in 2D
c. 3D model

Figure 2 depictsdifferent types of meshing.
a. Quadrilateral mesh
b. Polyhedral mesh
c. Hexahedra mesh
d. Tetrahedral mesh

Figure 3 depicts Meshed Femur Bone.

Figure 4 depicts Femur bone analysis with different loads.

Figure 5 depicts comparative results of various loads showing mechanical characteristics of Femur bone model of the present invention
Figure 6depicts the CAD model of the femur implant (a) and the 3D model created from ANSYS tools(b).

Figure 7 depicts meshing of femur implant.

Figure 8 depicts different parameters results for multi-materials.

Figure 9 depicts Total deformation of (a) Titanium (Ti-6Al-4v), (b) Stainless Steel 316L (c ) Cobalt Chrome

Figure 10 depicts schematic diagram of femur bone implant fabricated by method the present invention.

Figure 11a. Total Deformationof multi-material Femur implant:
a. Total Deformation
b. Equivalent Stress
c. Max Principal stress
d. Min Principal Stress
e. Max shear Stress
f. Equivalent Strain

DETAILED DESCRIPTION OF THE INVENTION:

The present invention discloses a method of fabrication of femur bone for orthopedic implants applications.

The method of the present invention: 2D image of femur bone is extracted from computed tomography. The extracted 2D image data is then fed into segmentation software to generate a 3D bone model. The 3D bone model is then imported into Creo PTC software to obtain refined 3D bone model.The refined 3D bone model is then incorporated into ANSYS workbench comprising tetrahedral mesh element for meshing to obtain 3D meshed femur bone and boundary conditions is adjusted and required loading conditions is applied to obtain 3D finite element model. The 3D finite element model is then transferred to 3D printing and printed with multi-materials to obtain unified multi-material implant of femur bone.

The developed method is then applied to fabricate a femur bone implant.

The X-ray image of the femur bone shown in Figure 1(a,b) has been taken to make a 3Dmodel (figure 1c). Dimensions taken from the X-ray image are shown in table 1.

Table 1: Dimension of the femur bone in 2D

Part number Length Width
A 32.0 cm 5.5 cm
B 36.7 cm 6.7 cm
C 36.0 cm 5.2 cm
D 39.3 cm 3.6 cm

Dimensions of the Creo model are validated with the original dimension of the 2D data. The model is created using the front view and built from bottom to top and constructed as a volumetric solid part.

Initially, different types of meshing such as Quadrilateral, Polyhedral, Hexahedral, and Tetrahedral mesh elements were applied to the refined 3D bone modelshown in Fig 2a, 2b, 2c, 2d. The number of nodes generated is shown in the table 2.
Table 2: Different types of meshing

S.no. Mesh Types Nodes Elements
1. Quadrilateral 14158 13941
2. Polyhedral 30311 9861
3. Hexahedral 15391 8454
4. Tetrahedral 77703 25579

From table 2, tetrahedral element is adopted for finite element analysis as it generated a greater number of nodes and elements compared to other meshing types. Meshed Femur Bone is shown in figure 3.

After meshing, mechanical characteristics of Meshed Femur Bone were analyzed. To study the loading capacity of bones, its mechanical characteristics were studied. Different types of loads such as Bending, Shear, Torsion, Tension, and Compression with different magnitudes of 10N, 50N, and 100N have been applied in the simulation. The resulting deformation from the simulationhas been compared to 3D model of structured bones to predict bone strength and stress distribution. From the simulation results, the minimum and maximum deformation values were determined. The results of the simulation show various deformation shapes indicated in Figure 4 shows the graphical remarks of the analysis of femur bone for deformation, maximum stress and shear stress, torsion, and compression during loading conditions. The values of deformation were tabulated in Table 3. The mechanical characteristics of the Femur bone shown for its simulation were shown in Figure 5.




Table 3: Parameters of femur bone Analysis

S.no. Loads Bending Shear Torsion Tension Compression
1. 100N Max(mm) 0.0022881 42.982 1990.9 30.32 25.869
Min(mm) 0 0.17428 8.9501 11.534 11.622
2. 50N Max(mm) 0.001144 21.491 995.45 15.16 12.934
Min(mm) 0 0.087141 4.475 5.7668 5.8112
3. 10N Max(mm) 0.00022894 4.2982 199.09 3.032 2.5869
Min(mm) 0 0.017428 0.895 1.1534 1.1622

The femur bone implant 2D graphic was obtain from the 3D meshed femur bone model and then transformed into a 3Dimension model employing ANSYS. Figure 6 indicates the CAD model of the femur implant and the 3D model created from ANSYS tools. Then, appropriate implant materials were chosen for the developed implant as it is important for biocompatibility.Precisely, the incorporation of implants made from different materials should capacitate the growth of body cells around the implants and not hinder them.

Materials and Properties: The following materials such as TI6AL4V(Titanium), SS316l(Stainless Steel), and Co-Cr(Cobalt Chrome), Zirconia, Nylon 6/6, Alumina AL2O3, and PMMA were employed for analysis in the method of the present invention to finalize the appropriate material for the implant by considering their material properties such as Young's modulus, Poisson ratio, Tensile strength, compressive strength, density, etc.





Table 4: Materials and their property

S.no. Prosthetic material Density
(Kg/m3) Young's
modulus
(GPa) Poisson's Ratio Ultimate
Tensile
strength (MPa) Ultimate
Compressive Strength
(GPa)
1. Ti-6Al-4V 4500 120 0.32 993 1086
2. SS316L 7750 193 0.31 485 570
3. Co-Cr 8360 210 0.29 145-270 200
4. Zirconia 6520 88 0.34 330 1200
5. Nylon6/6 3720 300 0.21 65-195 16-152
6. Alumina Al2O3 8500 240 0.31 210-290 1920-2750
7. PMMA 1180 220 0.2 47-79 83-124

The 3D femur implant is then subjected to meshingto obtain an accurate output given in Figure 7.For the 3D femur implant, 27053 nodes and 27159 elements were used in the meshingprocess.

Loading Analysis: The Femur implant was modeled with seven types of material and subjected to varying loads of 10N to 100 N. Their strain, strain, shear, and torsion strength were evaluated to determine the robust implant into the femur bone in humans. The applied loads and the deformation in various bending moments were given in figure 8.

To identify suitable material for femur bone implant, the mechanical load characteristics test is performed to evaluate the implant based on parameters such as Total deformation, Equivalentstress, Max principal stress, Min principal stress, and Equivalent strain. From the result, it wasinferred that the three materials TI6AL4V, SS316l, and Co-Cr show maximum resistance to deformation, fewer stress levels, and less torsion which show a high degree of mechanical strength compared with other materials. Hence these materials are preferred to build a novel multi-material implant.

In Figure 9, (a-c), each material has been analyzed for testing the mechanical strength. TI-6Al4v, SS316L, and Cobalt chrome show similar characteristic features and are hence identified for the multi-material implant as shown in the figure. This multi-material implant produces theadvantages of uniform stiffness, wear resistance, biodegradable, uniform contact pressure, elastic module, linear stiffness, etc. throughout its dimension and life span.

Figure 10 shows the schematic diagram of the multi-material with a head, neck, and stem builtwith three different materials forming a single implant. 3D printing, Additive manufacturing technic, and Selective laser melting technology are used for printing Hybrid femur implants.

Multi-material analysis: Figure 11 (a-f) shows an analysis of a single body with multi-materials developed for femur implant with head- (Co-Cr), neck - (SS316L), and body- (Ti6Al4V).

A comparison of a single body with multi-material was done with its load analysis. The performance of the implant was good, showing the deformation value is less, the strength level increased, and load withstands capacity was increased compared with the single body with a single element.


Table 7: Multi-material mechanical loading parameters

S. No Result MAX Value MIN Value
1. Total Deformation(mm) 0.0017004 0
2. Equivalent Stress (mm) 0.20283 0.00010684
3. Max Principal Stress (MPa) 0.21478 -0.0029068
4. Min Principal Stress (MPa) 0.0053685 -0.20317
5. Max Shear Stress (MPa) 0.10729 6.0549e-5
6. Equivalent Strain (MPa) 0.20283 0.00010684
7. Max Shear Elastic Strain (mm) 3.2676e-6 1.844e-9

In method of the present invention, a 2D X-Ray image has been converted into a 3D model. It has been imported into the ANSYS simulation tool and it has been analysed with different types of loading with a maximum load of 100 N. So that it is checked with Total deformation, Equivalent stress, Max principal stress, Min principal stress, Max shear stress, Equivalent Strain, and Max shear elastic strain. These seven types of loading analysis were used to check the bone condition and its performance during loading. A similar analysis was performed with different materials and multi-material for determining the overall performance of the femur implant.

A finite element model and simulation were carried out in the femur bone to determine the bending and shear studies. Analysis done with various materials indicate the best one for femur implant. Using the finite element program ANSYS, 77703 nodes and 25579 tetrahedral elements were used in the simulation. Different loading conditions were performed on the femur bone to contract. Seven different types of material were used in the simulation and three different types of load modes were applied. Ti-6Al-4V, SS316L, and Co-Cr were tested as suited implant materials since they possess high mechanical strength. Simulation of multi-material showed good performance compared with single-material combinations. Hence multi-material found to be the suited material for femur implant as it exhibits high mechanical strength and wears resistance and less bending.

Thus, from the above it is concluded that the developed method for fabrication of femur implant be a suitable method as it resulted in fabrication of femur implant exhibiting high mechanical strength and wears resistance and less bending which is lacking in the existing methods.

In one of the preferred embodiments, the present invention shall disclose a method of fabrication of femur bone for orthopedic implants applications. The method of the present invention comprises of following steps;

a. extracting 2D image of femur bone from computed tomography;
b. feeding the extracted 2D image data into segmentation software to generate a 3D bone model;
c. refining by importing the 3D bone model into Creo PTC software to obtain refined 3D bone implant model in which 3D bone model is analysed in ANSYS workbench to create the 3D bone implant model;
d. meshing is done by importingthe refined 3D implantmodel into ANSYS workbench comprising tetrahedral mesh element to obtain 3D meshed femur implant followed by adjustments in boundary conditions and applying required loading conditions to obtain 3D finite element model;

As per the invention, in the method of fabrication of femur implant of the present invention, the boundary condition is Static Structure


In accordance with the invention, in the method of fabrication of femur implant of the present invention, theloading condition is Structural loads.

In accordance with the invention, in the method of fabrication of femur bone of the present invention, theimplant materials selected from group comprising of TI6AL4V, SS316l, and Co-Cr.

Meshing process:

Creating a mesh using ANSYS Workbench, by the following steps:

1. Launch ANSYS Workbench and import your geometry.
2. Add the Mesh Module to your project and associate it with the geometry.
3. Access the Meshing Application by double-clicking on the mesh module.
4. Configure Global Mesh Settings for the entire model, including parameters like element size and relevance.
5. Set Local Mesh Controls (if necessary) for specific regions, such as faces, edges, or bodies.
6. Generate the Mesh by selecting the "Generate Mesh" option.
7. Examine and Improve the Mesh by evaluating element quality and making any necessary adjustments.
8. Confirm the Mesh Quality using mesh metrics to ensure it meets the requirements for your simulation.


The 3D finite element model then transferred to 3D printing and printed with multi-materials to obtain unified multi material implant of femur bone.

Steps in Fabrication process:

To create a unified multi-material implant of a femur bone using 3D printing, incorporating different materials like Co-Cr (Cobalt-Chromium) in the head, SS316L (Stainless Steel 316L) in the neck, and Ti6Al4V (Titanium alloy) in the stem, the process involves several key steps:

1. Design and Segmentation

Model Preparation:
• CAD Design: The 3D finite element model of the femur implant is designed using CAD software, ensuring that the geometry accurately reflects the intended implant shape and dimensions.
• Material Segmentation: The model is segmented into different regions where each material will be applied. This segmentation aligns with the functional requirements of each part of the implant:
o Co-Cr in the Head: For high wear resistance and strength.
o SS316L in the Neck: For corrosion resistance and moderate strength.
o Ti6Al4V in the Stem: For biocompatibility and high strength-to-weight ratio.



2. Material Assignment in the CAD Model

Multi-Material CAD File:

• Use advanced CAD software that supports multi-material design. Each region of the implant (head, neck, and stem) is assigned the specific material properties in the CAD file.

3. Preparation for 3D Printing

Multi-Material 3D Printing Setup:
• Slicing Software: Import the CAD model into slicing software that supports multi-material printing. The software divides the model into layers and assigns material extrusion instructions based on the segmented regions.
• Material Specification: Configure the printer with the required materials (Co-Cr, SS316L, and Ti6Al4V). Ensure the printer is capable of handling multiple materials and switching between them seamlessly.

4. 3D Printing Process

Printing Execution:
• Selective Laser Melting (SLM): These are common 3D printing technologies used for metal parts. SLM printers can handle multiple materials and are suitable for producing complex, high-strength components.
SLM Process: Uses a high-power laser to selectively melt and fuse powdered metal layer by layer. Multiple powder hoppers can supply different materials to the build area as needed.
• Material Transition: During the printing process, the printer transitions between materials according to the pre-defined regions. For instance, it starts with Ti6Al4V for the stem, then switches to SS316L for the neck, and finally to Co-Cr for the head.
• Quality Control: Continuous monitoring and quality control are crucial to ensure that the transitions between materials are seamless and the overall structural integrity of the implant is maintained.

5. Post-Processing

Finishing:
Laser welding :
Laser welding is preferred for joining the material, due to its precise control over heat, minimal distortion, and ability to produce high-quality welds in dissimilar metals, ensuring strong and reliable joints for critical applications.
• Heat Treatment: Post-printing heat treatment may be required to relieve internal stresses and enhance the mechanical properties of the metals.
• Surface Finishing: Machining, polishing, or other surface treatments are applied to meet the required surface finish and dimensional tolerances.
• Inspection and Testing: The final implant undergoes rigorous inspection and testing to ensure it meets all design specifications and regulatory standards.



6. Final Product

Unified Multi-Material Implant:
• The result is a single, integrated femur implant that combines the distinct advantages of Co-Cr in the head, SS316L in the neck, and Ti6Al4V in the stem, providing optimal performance and longevity.

Although the invention has now been described in terms of certain preferred embodiments and exemplified with respect thereto, one skilled in art can readily appreciate that various modifications, changes, omissions and substitutions may be made without departing from the scope of the following claim.

, Claims:WE CLAIM:

1. A method of fabrication of femur implantfor orthopedic implants applications, comprising of following steps;

a. extracting 2D image of femur bone from computed tomography;

b. feeding the extracted 2D image data into segmentation software to generate a 3D bone model;

c. refining by importing the said 3D bone model into Creo PTC software to obtain refined 3D bone model wherein 3D bone model is analysed in ANSYS workbench to create the 3D bone implant model;

d. meshing by importingthe said refined 3D bone implant modelinto ANSYS workbench comprising tetrahedral mesh element to obtain 3D meshed femur implant followed by adjustments in boundary conditions and applying required loading conditions to obtain 3D finite element model of femur implant;

e. fabricating multi-material femur implantby transferring the said 3D finite element model of femur implant to 3D printing followed by printing withmulti-materials to obtain unified multi material femur implant.

2. The method of fabrication of femur boneas claimed in claim 1 wherein the said boundary condition is Static Structure

3. The method of fabrication of femur bone as claimed in claim 1 wherein the said loading condition is Structural load

4. The method of fabrication of femur implant as claimed in claim 1 wherein the said implant materials selected from group comprising of TI6AL4V, SS316l, and Co-Cr.

Dated this 25th day of OCT 2024



For KARUNYA INSTITUTE OF TECHNOLOGY AND SCIENCES
By its Patent Agent

Dr.B.Deepa
IN/PA 1477

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