Bottom-up approaches to engineered living materials: Challenges and future directions

Abstract

Biomaterials made by living systems, while very diverse, generally share similar organization: different lineages of cells are precisely patterned within a matrix to create a hierarchically defined structure. This meticulous organization allows for their multifunctional properties, which often exceed those of traditional materials. For these reasons, there is growing interest in creating engineered living materials (ELMs) that will have capabilities similar to those of natural living materials yet with tailored functions. This review aims to highlight technologies still missing from the field of ELMs, which currently prevents more impactful applications. We briefly review the existing literature and identify challenges in designing novel protein-based and non-ribosomally synthesized matrix elements, producing and incorporating biominerals, and improving critical material properties such as lifespan, spatial patterning, and cell-cell communication. We also discuss the interplay between these challenges and the need for the development of new chassis and corresponding genetic toolboxes. By overcoming these obstacles, we come ever closer to unlocking the potential and versatility of biomaterials to create designer ELMs.Protein-based materials (PBMs) are ubiquitous in nature and have often been studied and explored for commercial applications-especially in the biomedical field.

A de novo matrix for macroscopic living materials from bacteria

“…By incorporating engineered cells into a biopolymer matrix, these materials can function as living sensors 5 , therapeutics 6 , biomanfacturing platforms 7 , electronics 8 , energy converters 9 , and structural materials 10 . While cells confer functionality to ELMs, the matrix assembles the material and controls the bulk material composition, structure, and function 11 .…”

“…Here we show genetic changes to a single engineered protein can yield dramatic changes in the ELM's composition and mechanical properties. The modularity of the BUD protein and the ease of engineering protein biopolymers offer much greater opportunities for introducing desirable properties into the matrix 11 . 16 Known polypeptides and proteins can exhibit desirable optical, electrical, mechanical, thermal, transport, and catalytic properties 32 .…”

“…Since the matrix plays such a key role over material properties, engineering macroscopic ELMs that grow from the bottom-up with a synthetic biomolecular matrix is a primary goal of the field. It is considered well beyond the current state-of-the art 11 because secreting recombinant biopolymers at concentrations that gelate is challenging 12 and because assembly of micrometersized cells into centimeter-scale materials requires self-organization across length scales spanning four orders of magnitude. Engineering principles to achieve this are unknown 11,12 , so most ELMs are microscopic [13][14][15][16][17] and must be processed into macroscopic materials.…”

“…It is considered well beyond the current state-of-the art 11 because secreting recombinant biopolymers at concentrations that gelate is challenging 12 and because assembly of micrometersized cells into centimeter-scale materials requires self-organization across length scales spanning four orders of magnitude. Engineering principles to achieve this are unknown 11,12 , so most ELMs are microscopic [13][14][15][16][17] and must be processed into macroscopic materials. The few macroscopic ELMs have been created by genetically modifying existing matrices 18 or genetically manipulating mineralization of inorganic matrices 19 .…”

Engineered Living Hydrogels

“…Several reviews have thoroughly described existing engineered living materials. [3,4,[33][34][35] Yet, the interplay between the hydrogel matrix and the microbial community in these materials has not been comprehensively discussed. We then review the ways that the engineered living hydrogels interact with the environment, focusing on the applications of sensing, treatment, and energy conversion that are enabled by engineered living hydrogels.…”