OCTAGONAL TRUSS UNIT CELL SCAFFOLD TO ENHANCE CELL PROLIFERATION RATE IN BONE REGENERATION

Abstract

A scaffold is designed for implantation into humans or animals for bone regeneration purposes. It consists of individual unit cells sequentially arranged to form a framework. The scaffold's load-bearing capacity is primarily determined by the strength of each unit cell, while tissue regrowth depends on factors such as porosity, biocompatibility, optimal surface area, and surface roughness. The proposed unit cell design integrates a combination of trusses to enhance structural strength, accounting for the mechanical stability. Once implanted, the scaffold facilitates angiogenesis, the formation of blood vessels throughout its structure. To optimize this development, the scaffold's pore size must be carefully controlled, which is achievable through modulation of the truss or strut diameter. Increasing the diameter reduces pore size and increases the surface area, which is crucial for cell growth, and vice versa. Thus, the scaffold unit cell design in the proposed invention effectively addresses these requirements by improving the mechanical strength of the scaffold as well as increasing the surface area required for cell proliferation.

Specification

Description:FIELD OF THE INVENTION
A scaffold is designed for implantation into humans or animals for bone regeneration purposes. This invention relates to the design of a scaffold unit cell structure employed in tissue regeneration. The scaffold structure is prepared to accommodate higher load-bearing capacity and facilitates cells to grow on the scaffold surface to regenerate the tissue. The scaffold unit cell invented design improves the scaffold's structural integrity by providing strength and cell proliferation rate due to its porosity and surface area, directly mimicking a natural cancellous bone structure.
BACKGROUND OF THE INVENTION
In tissue engineering, various aids are employed to rectify bone defects, with scaffolds being a significant option. When implementing scaffolds within a human or animal body, several factors must be carefully considered, including the scaffold's mechanical strength, manufacturing material, biocompatibility, and toxicity. Moreover, the long-term restoration of normal anatomical structure, shape, and function is clinically crucial following bone trauma, tumors, infections, and similar conditions. Therefore, designing and manufacturing scaffolds require meticulous attention to effectively blend these aspects. From the current state-of-the-art, it is evident that numerous unit cell structure designs are available in the market, yet only a few meet all the criteria. Many researchers have utilized titanium and its alloys due to their proven biocompatibility.
Biomedical engineering employs scaffolds to facilitate tissue regeneration in the human bone or cartilage by providing a framework within the damaged regions. This framework enables the body to initiate effective angiogenesis. Existing designs typically prioritize either mechanical strength or cell proliferation rate within the scaffold design. However, the proposed design effectively addresses both parameters, yielding optimal outcomes.
Existing state-of-the-art scaffold unit cell structures provide a stable framework to enhance mechanical strength. However, the cell regeneration rate in these designs is often lower due to an inappropriate combination of porosity levels, which are crucial for both mechanical and biological suitability. The primary innovation of the current design lies in achieving a balance of mechanical stability and cell proliferation within the unit cell. The design incorporates trusses to increase load-bearing capacity, enhancing mechanical strength by providing a robust framework. Additionally, the circular section of the trusses offers a larger surface area for cell growth and proliferation, ultimately improving the cell regeneration rate.
There are several prior arts related to the field of scaffold designs, 3D printed bone scaffolds, biocompatibility, etc. Some are -
DOI: 10.1016/j.msec.2017.09.004 discloses an optimization approach for the step-by-step construction and analysis of rhombicuboctahedron unit cells with different strut thicknesses and sizes has been suggested by researchers. According to their research, hexahedron unit cells function effectively at higher loads, but rhombicuboctahedron unit cells are best suited for medium to low-loading scenarios. To consider variables like production feasibility, material consumption, and mechanical performance all at once, the program incorporates a multi-objective optimization framework. It continuously improves the design space for rhombicuboctahedron unit cells through iterative refinement based on real-time performance data, guaranteeing adaptability to shift application requirements and environmental conditions.
Another DOI: 10.3390/ma11122402 document discloses that the researchers compared cubic and gyroid unit cell designs, each sized at 8 mm x 8 mm x 8 mm with a strut thickness of 0.2 mm. They varied the pore sizes and achieved a porosity range like natural bone. The study included a correlation between Finite Element Analysis (FEA) and experimental i.e., compression testing through which yield strength and Young's modulus were calculated. The results showed that the gyroid structure has higher mechanical strength because of the increased surface area for stress distribution and intricate structural parameters. Also, as the pore size increases beyond 0.3 mm, the yield strength of the scaffolds decreases. Hence, the 0.3 mm pore size of cubic and gyroid scaffold is best suitable for implantation applications manufactured using Ti-6Al-4V.
Another DOI: 10.1016/j.euromechflu.2019.09.015 discloses that the inventor tested why material transport, biocompatibility, and tissue engineering scaffolds' fluid flow dynamics are essential. Permeability and wall shear stress caused by fluid flow are examples of scaffold properties that affect biological behavior and have an impact on cell proliferation and differentiation. Triply periodic minimal surfaces (TPMS) and lattice-based structures were used to design eight bone scaffold models with 80% constant porosity. Computational Fluid Dynamics (CFD) analysis of these models showed that the design of the scaffold had a larger effect on permeability. Scaffold permeability varied by up to three times, with the highest permeability being found in architectures with minimal channel size variation. Remarkably, no association was discovered between the design of the scaffold and the statistics about the distribution of WSS on the scaffold walls. The design of scaffolds for tissue engineering that are more biologically effective could benefit from these findings.
Similarly, the US10695184B2 document discloses a porous unit cell design has been developed for constructing implant structures. The design features a centrally located square bipyramid-shaped node within a hexahedral volume, forming 8 faces. Special attention has been given to ensuring that the unit cell's biocompatibility is enhanced while maintaining its anisotropic properties. In the field of medical implantology, two critical factors are emphasized: the methods used to generate 3D lattice structures and the stress-shielding effect induced in the body. One method supports bone regeneration, while the other mitigates the stress shielding effect by providing mechanical spacing within the unit cell, promoting bone growth. Thus, the configurations of the bone repair scaffold, including pore size, interconnected porosity, shape, and modulus, can be adjusted by modifying the height of the faces or altering the angles between the faces and nodes.
Another US20110307073A1 document discloses an invention that relates to a 3D-printed multi-channel bone composite scaffold featuring 60-degree incremental rotations, where polycaprolactone (PCL) or PCL-composite material is arranged in 0/60/120-degree configurations. Additionally, the scaffolds contain centrally filled channels with bioactive agents to support the 3D matrix, allowing for slow degradation while preserving structural stability. The scaffold structures are designed to be both stiff and fracture-resistant, offering sufficient bending and compressive strength. In vivo testing was conducted on 6-week-old white rabbits, utilizing Human Cord Blood mesenchymal stem cells (MSC). To assess bone regeneration, radiographic X-ray analyses were performed at 4, 8, 12, and 16 weeks. The results indicated that bioresorbable scaffolds should have a porosity between 60 % and 80 %, with compressive strength ranging from 5 to 50 MPa. The conclusion drawn indicates that Polycaprolactone (PCL) material demonstrates superior biocompatibility and printability, making it well-suited for in-vivo implantations in scaffold applications.

OBJECTS OF THE INVENTION
The primary object of this invention is to develop a novel high-strength unit cell pattern comprising porosity variation in bone scaffolds for the replacement of diseased or damaged bones in the body.
Another object is to fabricate the bone scaffolds using a Stereolithography Apparatus (SLA) with BioMed Clear Resin.
Another object of the invention is to establish a method for manufacturing bone scaffolds, validated for maximum strength through Finite Element Analysis (FEA) and compression testing.
BRIEF DESCRIPTION OF THE DRAWINGS
The embodiments can be better understood with reference to the following drawings and descriptions. The articles in the figures are not necessarily to scale, the emphasis instead being placed upon illustrating the principles of the embodiments. Moreover, the figures, like reference numerals designate corresponding parts throughout the different views.
Reference will be made to embodiments of the invention, examples of which may be illustrated in the accompanying figures. These figures are intended to be illustrative, not limiting. Although the invention is generally described in the context of these embodiments, it is not intended to limit the scope of the invention to these embodiments.
The above and other objects, features, and advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:
[Figure 1] shows the circumscribed octagonal sketch.
[Figure 2] shows the octagonal sketch in all three planes.
[Figure 3] shows the solid truss elements created through a 2D sketch.
[Figure 4] shows the top view of the unit cell.
[Figure 5] shows the foundational layer of the scaffold in two directions.
[Figure 6] shows the isometric view of the scaffold.
[Figure 7] shows the porosity variation in the scaffold with 0.3 mm, 0.4 mm, and 0.5 mm strut diameter respectively.
[Figure 8] shows the static structural analysis results of the octagonal truss scaffolds.
[Figure 9] shows the compression testing results of the octagonal truss scaffolds.
It should be appreciated by those skilled in the art that any block diagrams herein represent conceptual views of illustrative systems embodying the principles of the present invention. Similarly, it will be appreciated that any flowcharts, flow diagrams, and the like represent various processes that may be substantially represented in a computer-readable medium and so executed by a machine such as a computer or a processor, regardless of whether such computer or processor is explicitly shown.
DETAILED DESCRIPTION OF THE INVENTION
The foregoing objects of the present invention are accomplished and the problems and shortcomings associated with the prior art, techniques, and approaches are overcome by the present invention as described below in the preferred embodiments.
The present invention provides a novel unit cell design for bone scaffolding, manufactured using 3D printing technology to enhance both mechanical and biocompatibility properties for clinical applications.
In the following description, for the purpose of explanation, specific details are set forth in order to provide an understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without these details. One skilled in the art will recognize that embodiments of the present invention, some of which are described below, may be incorporated into several systems.
Furthermore, connections between struts or pillars within the figures are not intended to be limited to exact dimensions. Rather, the unit cell size may be modified, reformatted, or otherwise changed by intermediary components and modules.
Throughout this application, with respect to all reasonable derivatives of such terms, and unless otherwise specified (and/or unless the particular context dictates otherwise), each usage of:
"a" or "an" is meant to read as "at least one." "the" is meant to be read as "the at least one."
References in the present invention to "one embodiment" or "an embodiment" mean that a particular feature, structure, characteristic, or function described in
connection with the embodiment is included in at least one embodiment of the invention. The appearances of the phrase "in one embodiment" in various places in the specification are not necessarily all referring to the same embodiment.
Embodiments of the present invention include various steps, which will be described below. The steps may be performed by hardware components and may be embodied in machine-executable instructions, which may be used to cause a general-purpose or special-purpose processor programmed with the instructions to perform the steps. Alternatively, steps may be performed by a combination of hardware, software, firmware, and/or human operators.
References in the present invention to "one embodiment" or "an embodiment" mean that a particular feature, structure, characteristic, or function described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of the phrase "in one embodiment" in various places in the specification are not necessarily all referring to the same embodiment.
If the specification states a component or feature "may' can", "could", or "might" be included or have a characteristic, that particular component or feature is not required to be included or have the characteristic.
As used in the description herein and throughout the claims that follow, the meaning of "a, an," and "the" includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of "in" includes "in" and "on" unless the context clearly dictates otherwise.
Exemplary embodiments will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. These embodiments are provided so that this invention will be thorough and complete and will fully convey the scope of the invention to those of ordinary skilled in the art. Moreover, all statements herein reciting embodiments of the invention, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents as well as equivalents developed in the future (i.e., any elements developed that perform the same function, regardless of structure).
While embodiments of the present invention have been illustrated and described, it will be clear that the invention is not limited to these embodiments only. Numerous modifications, changes, variations, substitutions, and equivalents will be apparent to those skilled in the art, without departing from the spirit and scope of the invention, as described in the claim.
The present invention is illustrated with reference to the accompanying drawings, throughout which reference numbers indicate corresponding parts in the various figures. These reference numbers are shown in brackets in the following description below.
In an implementation according to one of the embodiments, the present invention is a design of a novel unit cell, named an octagonal truss for bone scaffolding. The bone scaffold presented in the invention is manufactured using a liquid 3D printing technology to achieve precision printing as well as biocompatibility.
The present invention features a design that incorporates truss elements arranged to optimize strength within the unit cell structure. This unit cell, which is designed with specific strut thickness and pore size, is repeated linearly to create a porous beam. This beam is repeated to form a primary layer, which is then stacked perpendicularly to build the bone scaffold. The entire arrangement of the unit cells can be adjusted to suit the specific requirements and area of the defective zone in the patient. Additionally, the porosity level of the scaffold is crucial for achieving the optimal balance between mechanical strength and cell proliferation. This balance is maintained by varying the diameter of the truss elements (also referred to as strut diameter). Due to its modifiable unit cell size and strut diameter, this invention is particularly suitable for defects that vary from patient to patient.
The design of the unit cell begins with a circumscribed octagon, where all sides are of equal length. Each interior angle of the octagon measures 135° as illustrated in [Figure 1]. This octagonal sketch is then replicated in all three planes (X, Y, and Z), about the origin. An additional supporting member is added, passing through the center of all three axes to enhance the structural strength of the unit cell, as shown in [Figure 2].
The primary aim of the invention is to alter the truss or strut diameter to achieve the appropriate porosity level in the scaffold. To accomplish this, the two-dimensional sketch entities were converted into three-dimensional bodies using circular sections with a diameter of 0.4 mm, as shown in [Figure 3]. Hence, as the unit cell pertains to octagonal elements which results in a truss formation, it is named an Octagonal Truss unit cell. Additionally, to replicate the unit cell patterns in all directions and form a scaffold, the intersections of the trusses were smoothened out. After completing all the design steps, the unit cell structure has precise angles illustrated in [Figure 4].
This unit cell is then replicated in a linear pattern along the X and Y axes, creating a primary layer with linked pores and structural integrity. This foundational layer establishes the framework for the scaffold's architecture by repeating the designated unit cell, as shown in [Figure 5]. By replicating this layer along its perpendicular axis (Z axis), the scaffold is expanded into a three-dimensional structure in the required dimensions, as illustrated in [Figure 6]. This multi-layered structure, originating from accurate unit cell reproduction, features interconnected holes essential for tissue regeneration and cellular infiltration.
To test the current design with varying porosity levels ranging from 65 % to 85 %, the strut diameters were altered. [Figure 7] illustrates the scaffolds with different porosity levels: (a) 0.3 mm strut diameter with 85.5 % porosity, (b) 0.4 mm strut diameter with 76.3 % porosity, and (c) 0.5 mm strut diameter with 66 % porosity.
The scaffolds were manufactured using SLA 3D printing technology with BioMed Clear resin material, employing additional two conventional designs: A Face-Centered Cube and a Body-Centered Cube, for comparative analysis. SLA method was used to achieve precise micron-level accuracy for strut printing. Mechanical and biological tests were conducted to ensure successful potential implantation. Static structural analysis was performed using Finite Element Analysis (FEA) software under a loading condition of 2 mm displacement in the negative direction of the height. Compression testing was carried out to validate the mechanical properties using a Universal Testing Machine (UTM). [Figure 8] illustrates that the Von-Mises stress in the newly developed unit cell designs ranges from 373.7 MPa to 163.9 MPa, indicating a suitable compressive stress range for human bone. Additionally, [Figure 9] shows the load-bearing capacity of the octagonal scaffold, with a maximum load of 1621.4 N at a strut diameter of 0.5 mm.
ADVANTAGES OF THE INVENTION:
a) The unit cell design provides a simpler yet highly mechanically strong structure for bone scaffolds.
b) The unit cell design provides a highly efficient combination of strength and surface area for bone replacement.
c) The unit cell design provides maximum compressive and bending strength, validated through both software-based 3D models and physical testing using a UTM machine, with statistical analysis confirmation.
d) The unit cell design provides a higher rate of cell proliferation for bone regeneration compared to conventional designs.
e) The unit cell design provides a low-cost and affordable 3D-printed bone scaffold due to the use of SLA 3D printing technology and economical BioMed Clear Resin material.
The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the present invention to the precise forms disclosed, and obviously, many modifications and variations are possible considering the above description. The embodiments were chosen and described to best explain the principles of the present invention and its practical application, thereby enabling others skilled in the art to best utilize the present invention and various embodiments with various modifications as are suited to the particular use contemplated. It is understood that various omissions and substitutions of equivalents are contemplated as circumstance may suggest or render expedients, but such are intended to cover the application or implementation without departing from the spirit or the scope of the present invention. , C , Claims:An Octagonal Truss Unit Cell Scaffold to Enhance Cell Proliferation Rate in Bone Regeneration comprises:
1. An octagonal truss unit cell design for a bone scaffold is manufactured by the SLA 3D printing process using BioMed Clear Resin as printing material. The porosity variation ranges approximately from 65 % to 85 %.
2. An Octagonal Truss Unit Cell Scaffold to Enhance Cell Proliferation Rate in Bone Regeneration as claimed in Claim 1 wherein the scaffold porosity is in the range of 65 % to 85 %.
3. An Octagonal Truss Unit Cell Scaffold to Enhance Cell Proliferation Rate in Bone Regeneration as claimed in Claim 1 wherein the porosity of the 0.3 mm strut model is 85.5 %.
4. An Octagonal Truss Unit Cell Scaffold to Enhance Cell Proliferation Rate in Bone Regeneration as claimed in Claim 1 wherein the porosity of the 0.4 mm strut model is 76.3 %.
5. An Octagonal Truss Unit Cell Scaffold to Enhance Cell Proliferation Rate in Bone Regeneration as claimed in Claim 1 wherein the porosity of the 0.5 mm strut model is 66 %.
6. The method of manufacturing the octagonal unit cell scaffold for bone regeneration comprises the following steps-
a) Developing 3D printable scaffold models (STL file) with varying porosity.
b) Printing the scaffolds with 0.1 mm layer thickness and 100 % dense infill pattern.
7. The method of manufacturing the octagonal unit cell scaffold for bone regeneration as claimed in claim 6 wherein in step (b), the 3D printable bone scaffold models with varying porosity are created with strut diameters of 0.3 mm, 0.4 mm, and 0.5 mm.
8. The method of manufacturing the octagonal unit cell scaffold for bone regeneration, as claimed in claim 6, wherein in step (e), for each scaffold porosity, the von Mises stress plot generated in step (c) has been compared with the load versus displacement plot generated in step (d) for validation.
9. An Octagonal Truss Unit Cell Scaffold to Enhance Cell Proliferation Rate in Bone Regeneration as claimed in Claim 1 wherein the Octagonal Truss scaffold can withstand a load of 1300 N to 1600 N.

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