Material Characterization of 3D-Printed Energy-Absorbent Polymers Inspired by Nature

In nature there is a wealth of mineral-based and protein-based bio-composites spe- cially designed to resist impact and crushing. Some examples are enamel, dentin, horn, hoof and bone among others which are exhibiting unique reinforcing and toughening mechanisms that allow them to withstand large impact- and compressive loads [1]. Such bio-composites feature complex multi-scale and hierarchical struc- tures with several levels and types of reinforcements, density/stiffness gradients and porous phases that act in synergy to efficiently absorb the impact energy [70]. These multiscale architectures/concepts will be utilized to aid the designing of lighter, safer and tailored helmet liners for cyclists, motorcyclists and athletes. This means moving from the conventional EPS foams used nowadays as liner material, to a customized architecture with a liner based on the rider’s skull. But also the head morphology/physiology and impact resistance/absorption requirements mimicking architectures found in nature. The effectiveness of such structures is an example of concepts inspired by nature that can be used to realize more customized/purpose-built and energy absorbing architectures, a process called biomimicry. For centuries, designers and architects have been looking to nature for inspiration for the best source of inspiration with its 3.85 billion years of evolution [42]. Today, the tailored density gradient, nature’s ability to rearrange its structure as well as the self-healing property found in e.g. bones is not achievable using any conventional manufacturing, therefore additive manufacturing is the way forward for solving the tailored density gradient problem. In additive manufacturing or 3D-printing, three-dimensional objects/components are manufactured by deposition of materials in a layer-by-layer fashion. The layer thickness and path are controlled by computer models. Such a manufacturing ap- proach has received rather large global attention the last few years. The reason is that very complex objects can be built which are difficult or impossible to create using conventional, subtractive manufacturing methods. This new way of manufac- turing can produce highly customizable components with minimal material waste. Considering the high complexity of the aforementioned bio-composite structures and the vast capabilities of additive manufacturing, it is foreseen that the combina- tion would enable the realization of complicated 3D-printed architectures capable of withstanding impact and crushing inspired by the long-proven strategies found in living organisms and animals.