The convergence of the fields of materials science and engineering biology is a nascent space. As such, researchers in these fields are just beginning to develop intersecting technologies and collaborative concepts. As the tools and technologies combine, there is a need to develop more common language between the fields. To that end, we have developed a glossary for the key terms and concepts in this roadmap. The glossary is specific to the context of this roadmap, but developed with input from the community in both fields.

Active Matter – States of matter that exist only because it is driven from equilibrium or that require a steady flow of energy through the system.

Architectured Materials – Architectured materials are those that derive a property based on the specific arrangement of the material, usually in the form of a scaffold or other structural component. This is in contrast to Engineered Materials that usually refers to the tuning of a material bulk property such as the composition and treatments of an alloy for a particular application. Many natural materials, such as bone or shells, can be considered architectured materials.

Biobased – Materials derived from biomass (in whole or in part), that may have undergone chemical, physical, or biological treatment. Note: the United States Department of Agriculture’s BioPreferred Program has a further definition of “biobased” that we find helpful, available at https://www.biopreferred.gov/BioPreferred/faces/pages/BiobasedProducts.xhtml

Biocomposite – A material consisting of two or more biotic components, or a combination of biotic and abiotic components. A biocomposite may be two- or three-dimensional and may be homogeneous or heterogeneous in composition and appearance. The subsequent performance or function of the biocomposite is improved over the function or performance of the components alone.

Biofabricated – Materials produced by living cells and microorganisms, such as bacteria, yeast, and mycelium. For further information, please see Understanding ‘Bio’ Material Innovation: a primer for the fashion industry (Biofabricate and Fashion for Good, 2020, available at https://www.biofabricate.co/resources)

Bioinspired – Typically referring to novel (usually abiotic/non-biological materials) materials based on or inspired by biology. The advancements described in this roadmap go beyond this classic definition to include (novel, adapted, or advanced) living, biotic materials and materials that incorporate(s) engineered biology (biocomposites).

Biomimicry – Material or material system built or designed to mimic a function or mechanism in biology. This is usually extending a biological design principle, biochemical reaction, or biological function to systems at very different length or time scales.

Biomaterial – The emerging definition of a biomaterial is any biological substance that has been engineered to interact with biological systems or derived from biological systems for non-biological use. Some have limited this definition as materials for medical purposes, either as a therapeutic (treat, augment, repair or replace bone or a tissue function in a body) or a diagnostic. The inclusion of materials from biology includes new small molecules (such as biofuels or enzymatic precursors), monomers, polymers/gels, mineralized composites, structured material systems, among many others, produced through engineering biology.

Biomolecule – A member of one of several major classes of biological molecules, including proteins, nucleic acids, lipids, and glycans.

Biosynthetic – Refers to molecules that can substitute for natural biochemicals in either biological processes or structure such as non-canonical lipids, nucleic acids, macro-molecules with protein-like function, biomineralization beyond carbon, calcium or silica (i.e., heavy metals).

Biotemplate – Biological components that act as the pattern or structure for the ordered or stepwise assembly of a material or material system.

Biotic and Abiotic Materials – Biotic material: Substance comprised of or produced by living cells or cell-free biological systems. Abiotic material: Substance comprised of non-living cells and not produced directly by living cells or cell-free biological systems. In this roadmap we consider tools and technology for the engineering of materials that are (entirely) biological (e.g., living materials or derived from living organisms) and composites of living or biology-based or -produced (biotic or organic) components and non-living (abiotic or inorganic) components, with particular focus for the latter on tools and technologies for the interactions and interface of the components.

Cell-free System – Typically produced by isolating subcellular fractions, a cell-free system is an engineering biology tool for more controlled study of cellular reactions; simplified production of desired chemicals, biomolecules, or materials; or production in extreme or non-natural environments or with non-natural precursors or components. Cell-free expression is the use of cell-free lysate harvested from living cells (bacterial or mammalian cells) that are translationally active. Cell-free expression is used for making proteins of interests outside of living cells.

Composite – A collection of materials or elements, either in an engineered or structured fashion, that has properties which are some superposition of the individual element’s properties.

Composition – The make-up or contents of a material or the result of the combination of components. This roadmap considers engineering of material composition through the design or control over the interactions between the components and how they function together, such as the biotic-abiotic interface and embedding of biomolecules, enzymes, and cells.

Engineered Materials – Material in which the bulk properties have been tuned for a particular application.

Engineering Biology – The design and construction of new biological entities such as enzymes, genetic circuits, and cells or the redesign of existing biological systems. Engineering biology builds on the advances in molecular, cell, and systems biology and seeks to transform biology in the same way that synthesis transformed chemistry and integrated circuit design transformed computing. The element that distinguishes engineering biology from traditional molecular and cellular biology is the focus on the design and construction of core components (e.g., parts of enzymes, genetic circuits, metabolic pathways) that can be modeled, understood, and tuned to meet specific performance criteria, and the assembly of these smaller parts and devices into larger integrated systems to solve specific problems. Unlike many other areas of engineering, biology is incredibly non-linear and less predictable, and there is less knowledge of the parts and how they interact. Hence, the overwhelming physical details of natural biology (gene sequences, protein properties, biological systems) must be organized and recast via a set of design rules that hide information and manage complexity, thereby enabling the engineering of many-component integrated biological systems. It is only when this is accomplished that designs of significant scale will be possible. EBRC (and thus, this roadmap) uses Engineering Biology synonymous with Synthetic Biology.

Living or Dynamic Material – A material in which the biological component enables change with time. Typically, though not always, it consists of whole cells incorporated into a host matrix that provides the persistence of the cells and the passing of bidirectional signals and output. Incorporating biocomponents into a material system introduces additional design consideration such as nutrient uptake and metabolite clearance, and concerns about genetic drift over time.

Multiscale Materials – Engineering biology can enable materials across scales: from atomic and nanoscale materials (such as nucleic acid based materials) to macroscale materials (such as biofilms). Furthermore, the biological component of a material can enable a dynamic material to cross scales over time. There is a unique challenge in producing and characterizing biocomposites or materials derived from biology because of the dynamic and inherently uncontrolled nature of biology. In particular, macro-level properties of biomaterials can’t necessarily be determined from micro-level measurements in the same way they can be from conventional materials. For example, the strength of a metal composite is going to be mostly consistent across scales (or civil engineering allows you to anticipate how the strength changes at scale), but biological materials will have emergent properties that can’t necessarily be predicted from small tests.

Material vs. Device – Enabling materials through engineering biology – particularly through leveraging biology’s ability to sense, integrate, and respond to local and environmental signals – can blur the lines between when the product is classified as a material or a device. For the purposes of this technical roadmap, we consider a material designed for a specific purpose or function to be a device, and focus (in the Technical Themes) on the development of materials with minimal emphasis on the discrete application of the material.

Material System – A system of multiple materials integrated in a designed way that combine the different physical properties and responses of the components into a higher functional whole. This concept extends the notion of materials toward a device.

Materials Science – The study and applications of matter and its properties, as determined by composition and structure, combining principles of physics, chemistry, and engineering.

Organic/Inorganic – See Biotic and Abiotic Materials

Orthogonal – In a cellular system, operating independently from those processes that support the cell; that is an orthogonal translation system operates independently of the cell-supporting translation machinery and can synthesize genetically-encoded polymers with fewer constraints imposed by the need to maintain cell viability.

Performance – The engineering of dynamic activities of materials, including sensing and response for computation, communication, and self-repair. This includes the engineering of materials to provide signals or store data through an engineered biological component.

Precursor vs. Material – Like the distinction between material and device, the difference between a precursor and material may be similarly subjective. We consider a material to be the product of combined precursors, but recognize that multiple materials can be combined to make another, different material.

Processing – The engineering of biology to conduct “unit operations” to build or destroy materials through polymerization and degradation, patterning and printing. This includes engineering the biological extrusion or secretion of materials, material deposition, and self-assembly and -disassembly. Processing also includes engineering biology-based technologies, tools and systems (e.g., cell-free systems) to manufacture, recover, and purify materials. Includes engineering biological materials to function in non-natural environments and extreme conditions.

Properties – The engineering of dynamic characteristics and activities of materials, including sensing and response for computation, communication, and self-repair. This includes the engineering of dynamic interactions between the biological and abiotic components of a material.

Scaffold – A structure, biologically-derived or synthesized that mimics the extracellular matrix and promotes cellular responses.

Segregation (Materials vs Biological phase segregation) – Aggregation of components based on characteristics, such as hydrophilicity/hydrophobicity or charge density. Surface segregation/presentation is a specific stratification that may take place at an interface, and result in graded composition in the material.

Self-assembly – The process in which a system’s components create an organized structure or pattern without external direction. Biomolecules readily self-assemble, both naturally and through engineered design, and can contribute significantly to ordering and patterning of materials. While self-assembly most often occurs at the molecular level, macromolecular- and cellular-level self-assembly can also facilitate material formation.

Self-healing/Self-repair – A critical functionality that may be imparted by incorporating biology into a material is the capacity to repeatedly self-heal or self-repair to reconstruct or replace damaged components or structures without external input/influence. Biocomposites can be engineered to sense damage and to elicit a reconstituting or repair response that, with the appropriate precursors and functional pathways, can be executed more than once.

Sensing/Detecting – This can refer to any mechanism that reacts to an external cue or stimulus and provides a signal (the response) denoting the reaction (either that it occurred or it occurred with a particular strength). Engineering biology can enable, tune, or modify this process by adapting the pathway from the target to the output measurement.

Stimuli-Responsive – In biological contexts, at the cellular level or larger where the agent (bacteria or animal) senses the environment around them (chemical, thermal, pressure, light, etc.) and responds to either avoid pain/death and/or seek reward/food. In a materials context, it generally refers to a designed interaction with an incident stimulus (e.g., light, heat, magnetic field oscillation) that can drive a change in property.

Structure – The architecture of a material. This roadmap considers engineering of the two- and three-dimensional space a material and its components occupies and the tools and technologies necessary to control and dictate the architecture, including engineering the physical and bulk characteristics of a material. Structure also includes the arrangement and templating of material components.

Synthesis – In the context of this roadmap, the generation of material components via engineered biology; primary production or creation of material components. Includes utilizing or exploiting engineered biology to produce monomers, polymers, biomolecules, and macromolecules that serve as components of a material (bulk or otherwise).

Synthetic Biology – See Engineering Biology

Synthetic (artificial) Cell – This roadmap considers synthetic cells as cell-like systems constructed from biological materials (proteins, nucleic acids, and lipids). One example is the encapsulation of cell-free expression systems expressing desired genetic circuits or proteins of interest in lipid bilayer vesicles. They can be engineered to respond to different external stimuli (e.g., light, mechanical forces, small molecules). The synthetic cells do not need to be patterned completely on naturally-evolved cells, for example, the lipid bilayer could be replaced by other organic or inorganic components.