The Bits of Nature

Abstract

In the vast domain of biomedical engineering, the challenge of developing synthetic materials that can replace damaged tissues has proved a daunting task. Millions of years of adaptation have provided natural tissues with multiple strategies that yield highly efficient mechanical properties that are not found in human-made materials. The first of these strategies relates to the material composition of living tissues. Natural materials tune their functionality thanks to the presence of multiple constituting phases with highly different properties (e.g., soft collagen and the hard mineral phase in the bone). The second strategy is manifested in the arrangement of these phases, where these constituents take a wealth of intricate geometries to strengthen and toughen their structures. For example, the hierarchical arrangement of different constituents at multiple length scales enables them to work in synergy to distribute the deformation energy within tissues, thereby delaying their critical failure. Yet another strategy is the use of functional gradients, where the volume fraction of one material changes across a relatively short interface, thereby attenuating the stress concentrations caused by the mismatch between the mechanical properties of the different constituents.

In recent years, replicating these exceedingly complex yet harmonious natural design paradigms has been a significant drive in the scientific community. Mainly achieved using multi-material additive manufacturing techniques, architected materials have been developed that implement some of the design strategies found in natural materials to achieve seemingly contradictory design objectives, such as simultaneously high strength and toughness. However, limitations in computational resources and standard processing methods hinder the complexity and multi-scale rationality of the design features that one can introduce within a construct. Bitmap multi-material 3D-printing techniques, however, offer the possibility to experiment with different design strategies at the level of individual microscale voxel, leading to the emergence of -by-es. In such approaches, the constituting material of each voxel can be individually selected, yielding unprecedented freedom to generate microarchitectures that seamlessly mimic the morphologies observed in natural tissues.