Porous Interbody Spacer Structure for Bone Ingrowth and Load Transfer
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Solution Overview
Problem
Current orthopedic implants, particularly interbody spacers, face challenges in providing optimal pore size and stiffness that are conducive to bone growth, as they often have stiffness that shields bone from mechanical stimulus, leading to minimal or improper bone ingrowth.
Innovation Solution
The development of orthopedic implants, specifically interbody spacers, with a combination of appropriate pore size (150-600 microns) and stiffness (400-1200 MPa) using osteoconductive materials like titanium and tantalum alloys, manufactured via additive manufacturing to create a nested coil spring construction that allows interconnected pores for bone growth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If implants are made with high stiffness to provide structural support, then mechanical strength is improved, but bone growth is inhibited due to shielding from mechanical stimulus
Solution Approach 1:
The implant incorporates a porous structure with controlled porosity (30-70%) that allows bone ingrowth while maintaining structural integrity. The porous configuration enables mechanical stimulus transmission to bone cells while providing the necessary structural support, resolving the contradiction between strength and bone growth promotion.
Solution Approach 2:
The patent optimizes the stiffness parameter by selecting specific materials (PEEK with 4 GPa, titanium alloys with 110-120 GPa) and controlling pore size (150-650 microns) to achieve a balance where the implant provides support while allowing bone growth. This parameter optimization enables simultaneous achievement of structural strength and bone integration.
2Reliability
If pore size is reduced to enhance bone growth, then bone ingrowth is improved, but structural strength deteriorates
Solution Approach 1:
The implant utilizes a porous structure with optimized pore size (150-650 microns) that is large enough to maintain structural strength but small enough to promote bone ingrowth. The specific porosity range (30-70%) is designed to simultaneously satisfy both structural and biological requirements, resolving the contradiction between pore size and strength.
Solution Approach 2:
The patent employs composite material strategies by combining different materials (PEEK polymer with titanium reinforcement, or titanium alloys with varying porosity) to achieve a structure that simultaneously provides structural strength and promotes bone growth. This composite approach allows independent optimization of mechanical and biological properties.
3Ease of manufacture
If traditional manufacturing methods are used, then manufacturing simplicity is maintained, but manufacturing precision of pore structure is insufficient
Solution Approach 1:
The patent replaces traditional mechanical manufacturing methods with additive manufacturing technology that enables precise control of pore structure at the micro-scale. This substitution allows for accurate fabrication of complex porous geometries with controlled porosity (30-70%) and pore size (150-650 microns), achieving high manufacturing precision while maintaining ease of production through digital modeling.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The implants facilitate proper bone bridging and loading, stimulating bone growth throughout the device according to Wolff's law, enhancing bone integration and fusion.
Implementation Method 1
The cells responsible for bone growth, including osteocytes and osteoblasts, work together to form bone as needed within the body
Implementation Method 2
Many orthopedic implants are provided with a porous surface at the bone-implant interface, with the expectation that bone will grow into the porous surface of the implant
Implementation Method 3
When the implants have the proper pore size and stiffness, osteocytes are able to properly bridge the pores of the implant and then experience a proper compressive load to stimulate the bone cells to form bone within the pores throughout the implants according to Wolff's law
Data Source
AI summary
Orthopedic implants, particularly interbody spacers, have a combination of correct pore size and stiffness/flexibility. When the implants have the proper pore size and stiffness, osteocytes are able to properly bridge the pores of the implant and then experience a proper compressive load to stimulate the bone cells to form bone within the pores. An implant includes a body formed of an osteoconductive material and having a stiffness of between 400 megapascals (MPa) and 1,200 MPa. Additionally, the body includes a plurality of pores having an average size of between 150 microns and 600 microns. The pores permit the growth of bone therein. The body is formed of packs of coils which may be formed using an additive manufacturing process and using traditional orthopedic implant materials such as titanium and titanium alloys while still achieving desired stiffness and pore sizes of the implants. Other implementations are described.