My second design project of the year was centered around designing a hip implant (as seen to the right) for Diane Chambers, a fictional patient with post menopausal osteoporosis. In order to confront this challenge, my team needed to determine a way to replace her hip without compromising her fragile bones. After careful consideration, we decided to take the standard hip implant design and incorporate a series of ridges on the femoral stem to house bone grafts. We decided to take this route in the hopes that the bone grafts would promote osseointegration and strengthen the bone, preventing it from fracturing. Additionally, we decided to use a titanium-niobium alloy to further encourage bone growth and increase the stability of the implant by mimicking the physical characteristics of bone.
| Strengths | Learning Opportunities |
|---|---|
| CAD modelling in Inventor | Exporting stl files from Inventor |
| Technical communication | Adding supports in Prusaslicer |
| 3D printing knowledge | Be more vocal about ideas |
| Materials research | |
| Creative design ideation |
As a part of the CAD sub-team, I was responsible for producing a 3D model of our implant along with my partner. I contributed by modelling the acetabular head and liner, as well as the femoral head (three topmost components). I accomplished this by using the revolve, loft, and circular pattern tools in conjunction with other techniques. To make the model more accurate, my partner and I also added textures to represent the materials each component was made of. I found that I was quite comfortable with modelling, as I was able to draw on some of my prior experience with Autodesk’s Fusion 360 and apply it to Inventor. So, I used my skills to help my partner when he encountered issues. Whenever he ran into an obstacle we would work it out over a video call, and throughout the course of the project I found my technical communication skills had grown stronger as a result.
In addition to modelling the implant, we were also tasked with producing a 3D printed prototype of our design. Since I own a 3D printer and had prior experience, I took the lead on this part of the project. I knew that we would be displaying our prototype as a part of our final presentation, so I wanted to ensure that it was of exceptional quality. This meant printing a full scale model that would feel more substantial than a smaller version. However, with limited time in the design studio, I knew I had to print some of the components at home to have everything ready on time. Therefore, I split the workload between the design studio’s printer and my own by printing the stem at the university and the other components at my house. Since my printer differs from the one in the design studio, I had to use two slicing softwares - Ultimaker Cura and Prusaslicer - to convert the stl files into G-code. Below to the left is the femoral stem, which I printed in the design studio, and to the right is the acetabular cup, which I printed at my home.
Learning from my last design project, I decided to be more thorough when researching materials for the femoral head and acetabular liner. I began by reading some review articles on the efficacy of different combinations of materials, like metal on polymer, or metal on metal for example. After determining that a combination of a ceramic head and a polymer liner was ideal, I began investigating specific materials. After looking into various polymers like PEEK and polyethylene, I found that the best option was crosslinked polyethylene due to its extremely low wear rate.
Source: https://www.quora.com/What-is-an-XLPE
Later on, I discovered that yttria doped zirconia was the ideal ceramic because it was compatible with cross linked polyethylene and only produces inert debris.
After experimenting unsuccessfully with scaling and resolution of the models for some time, I went to the design studio and consulted with the supervisor there to get some advice. I quickly learned that I had exported the stl file incorrectly from Inventor. Once I fixed this, I found that the printer was able to produce a one-to-one prototype from the CAD model. Below are some of the failed attempts I produced during this process:
