Limitations of Standard Infill for TPE Objects

Soft artifacts with varying levels of “squishy” resistance could help stroke survivors to more easily release their grip while handling objects. While reliable foam 3D printing is still in the experimental phase (although we’re working on it!), there are thermoplastic elastomers (TPE’s) that can be printed using low-cost Fused Deposition Modeling (FDM) or Fused Filament Fabrication (FFF) printers (e.g. Makerbot). These materials flex and stretch without deforming the original shape, but they resist compression far more than tension or flexion. In order to get the desired effect, we propose using a geometrical approach in order to transfer compressive force into other movement.

The FDM/FFF printing process does not typically print solid parts. Instead, it relies on building scaffolding internally in order to increase strength and rigidity while minimizing material use. This is called “infill”. In addition, this allows parts with complex geometries to be printed without collapsing.

Traditional infill (usually honeycomb) is designed to resist compression and to be as strong as possible. It also creates areas that are less squishy than others, which is not really what we are looking for. A common infill type used with TPE is “moroccan star”. It collapses, thus allowing for greater flexibility of standard parts. Our ideas is to exploit this irregularity in the xy plane to purposefully create areas where some parts are firmer that others.