Taxonomy for engineered living materials

Engineered living materials (ELMs) are the most relevant contemporary revolution in materials science and engineering and aim to outperform current examples of "smart," active, or multifunctional materials, enabling countless industrial and societal applications. The "living" materials facilitate unique properties, including autonomy, intelligent responses, self-repair, and even self-replication. Within this dawning field, current literature has classified ELMs mainly into biological ELMs (bio-ELMs), which are solely made of cells, and hybrid living materials (HLMs), consisting of abiotic scaffold and living cells. Considering that the most relevant feature of ELMs is the living cell colonies or micro-organisms, we consider that ELMs should be classified and presented differently, more related to life taxonomies than to materials science disciplines. Toward solving the current need for the classification of ELMs, this study presents the first complete proposal of taxonomy for these ELMs. Here, life taxonomies and materials classifications are hybridized hierarchically. Once the proposed taxonomy is explained, its applicability is illustrated by classifying several examples of bio-ELMs and HLMs, and its utility for guiding research in this field is analyzed. Finally, possible modifications and improvements are discussed, and a call for collaboration is launched for progressing in this complex and multidisciplinary field.