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A recent paper by researchers at the Netherlands’ Technical University of Delft shows how novel micro-architected implant structures could further innovate the world of orthopedic additive manufacturing. The paper, titled “Multi-objective design optimization of 3D micro-architected implants,” addresses how mechanical components with “unprecedented geometric complexity” can be engineered to solve many objectives. In this case, the team focused on creating a structure that both eliminated bone loss as a consequence of receiving an implant and reduced tensile stress at the bone-implant interface.
The novel structure focuses on introducing a parametric micro-architecture, such that adjacent cell compatibility and smoothly varying geometric properties can be ensured. To be suitable for use with the team’s implant optimization formulation, the paper reads, the parametric micro-architecture must be able to produce a wide and smoothly varying range of mechanical properties. Additionally, it must possess adjacent cell connectivity and open-cell porosity and must be suited to additive manufacturing.
A figure from the paper shows generalized parametric cubic anti-chiral micro-architecture: (a) Sample unit cells exhibiting negative, neutral, and positive Poisson’s ratios; (b) Periodic arrays of unit cells (c) A functionally graded assembly of chiral micro-architectures exhibiting ideal interface connectivity. The left-hand side illustrations refer to the 2D version of the structure, while the right-hand side illustrations refer to the 3D version. Image courtesy of Eric Garner.
The paper states that the structure possesses the required attributes and can produce both positive and negative Poisson’s ratios, a rare feature that has been recently utilized in the design of hip implant stems.
A key motivator behind the project was the idea that a lot can be achieved with micro-architectural structures, said Amir Zadpoor, Ph.D., Professor of Biomaterials and Tissue Biomechanics, TU Delft. “How” those goals can be achieved, however, is not entirely clear. There’s still more research to be done in terms of optimizing the design and shape of implants while satisfying objectives simultaneously. However, he believes exploring ways to improve current designs has the potential to relieve ailments like pain or limited mobility for many.
“The gains to be made are not only in terms of the implants that are now being implanted but also in procedures that are currently not being done because we know that the outcomes are not very good,” Dr. Zadpoor said.
The idea of creating orthopedic implants with different mechanical properties throughout to achieve better integration with the body isn’t new, said Eric Garner, Ph.D. candidate, TU Delft. But the team’s research identified new progress. Garner’s previous work was focused on compatibility in microstructures. Through those efforts, he got the idea to start combining different structures to see how they would benefit hip implants.
A research team from TU Delft recently published a paper addressing how mechanical components with “unprecedented geometric complexity” can be engineered to solve many objectives. Pictured are authors Eric Garner, Jun Wu, Ph.D., and Amir Zadpoor, Ph.D. Photos courtesy of Garner and Zadpoor.
“We make use of a lot of developments from a field called ‘topology optimization’ for the actual analysis of this gradient information,” he said. “This lets us take these two conflicting objectives and handle them simultaneously without having to choose one over the other.”
While not currently working towards a clinical trial, Dr. Zadpoor said planning is underway. First, the structure must be physically realized. Then the team will pursue cadaveric experiments and clinical trials. A plus is that there is little that needs to be done before executing a clinical trial. The material being used in the manufacturing of these micro-architected implants is the same metallic alloy being used every day.
“We don’t require a different manufacturing technology. We don’t require any pharmaceutical agent to be added,” Dr. Zadpoor said.
Kaitlyn McGarvey is ORTHOWORLD’s Associate Editor.
