Advancing 3D printed footwear beyond aesthetics and into performance

While a simple piece of responsive foam goes a long way, modern developments are pushing the threshold of footwear performance through supplemental components; embedded carbon-plates, airbags, and controversial tensile strands. In essence, the capacity of advancement is expanded with greater control over the midsole arrangement. This notion served as the foundation of our project examining ‘The enhancement of running performance through 3D printed midsole design’.

With a Formlabs SLA printer and elastic resin granted by the engineering department along with a license to nTopology’s previous software, Element, our team printed twenty different lattice models and measured each for their percentage of energy return.

The benefits of lattice structures to our study were 1) to provide three times the strength of foams at an equal density and 2) to distribute the energy transferred within each step more evenly and at a slower rate, offering greater stability and lower impact over time. Our team narrowed down the variables and manipulated a specific set of features of the unit cell; geometric base, length, thickness, arrangement, and height.

In reference to the graph on the left, the energy return is simply the amount of energy retained as the structure, after compressed, returns to its normal shape. This value, in turn, lowers the metabolic cost of running and pays significant dividends when cumulated over an entire marathon. While many performance metrics are improved through training and inherent to individual biology, the energy return is directly influenced, in part, by the behavior of the midsole; hence its obsessive mention by every running shoe company.

Apart from learning the intricacies of lattice geometries, this project served as a testament to the impact of additive manufacturing in transforming the overall design process. Companies no longer have to wait extended periods of time for mock-ups to be built overseas only to have large batches of finished products deemed unacceptable and money wasted. Now, production teams can create prototypes rapidly on-site for instant feedback, significantly streamlining the concept creation process. Products made through 3D printing would reduce both the time and cost of transporting parts, compress the length of supply chains, and offer immediate availability of past products just by pulling up its data file.

Personally, the most intriguing aspect is the ability to construct complex parts at a lower cost than traditional processes. Normally the concern of adopting additive methodologies is that the cost of producing an individual part is always the same, no matter if there are five or a thousand of it made, whereas for traditional methods the cost per unit decreases as the total number of units manufacturing increases. This isn’t the complete story, however, as the graph above shows that as the complexity of a part increases, there comes a point where the manufacturing cost actually becomes comparatively cheaper for additive manufacturing. So now, not only does design complexity open up new avenues for innovation, it could also come at a lower rate.

Top images: an outline of lattice generation from the unit cell to final render.
Bottom images: from distributed points or CAD body to the final midsole.

There have been impressive examples of lattice integration through the Adidas 4D Futurecraft and the New Balance Triple Cell, yet their purpose is bound within general functionality and casual runs. There has yet to be a development of printed running shoes that has been able to join the discussion of competition-made footwear. Our team’s project aimed to shed some insight into that empty space and had shown promising percentages of energy return, but failed to remain lightweight. With the advancement of algorithmic and parametric techniques, the potential of formulating footwear design more efficiently and even according to the athlete’s individual needs continues to reach exciting possibilities. While the model above was formed with a random distribution of points, force plate data taken from a runner’s landing can be imported to generate a lattice arrangement that varies the thickness and density in regions of higher load. The elusive goal of competitive performance in printed footwear requires continued breakthroughs in material science, biomechanics research, and innovative design.The potential of additive design to outperform conventional foams in the prospect of enhanced running performance surely exists but is yet to be realized.

This article is extracted from a study conducted by myself and two friends as part of a final year project at Boston University.  During the final year, a list of projects gathered from research professors and start-up companies is posted for undergraduate engineers to choose their senior capstone project. My two friends and I had found interest outside of that list in the field of printed footwear, specifically within the lack of literature approaching 3D midsoles in the context of running performance. We pitched a rough proposal to the department and professor of additive manufacturing, Dr. Anna Thornton, who served as our advisor.