Spinal Implant

At the University of Virginia I spent three years conducting research with Dr. Ji Ma in his metal additive manufacturing lab. One of the projects I undertook was the creation of a spinal implant that matches the stiffness of the bone around it to promote longevity.

The challenge was to create a 5mm tall spring that could be printed out of titanium without warping or requiring support, displace evenly along the top surface, and withstand the force of a human spine. This traditional spring failed on all metrics.

I designed this novel spring to combat the problems faced. It can be manufactured without support, will not warp, and under compression the top surface deforms straight down. By altering the diameter of the curves, the spring stiffness can be precisely defined.

I then determined the effect of the number of curves and the diameter of the curves on stiffness and stress. Using FEA, I found five curves to be the optimal layout to minimize stress within the desired 100-400N/mm stiffness range. Analyzing the spring with different curve sizes, I established a mathematical model for the direct relationship between curve circumference and spring stiffness.

Individual springs were printed out to confirm manufacturability and test the accuracy of their stiffness

Next I created a full implant model with the springs. I set up the model so that with the input of desired stiffness at each point, the necessary geometry will be calculated and created automatically.

The model was perfected and made to be double-sided

It was then printed out for cadaver testing. It has proved extremely successful across all the stated metrics.

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