Engineered living materials (ELMs) are created by embedding living cells into a non-living scaffold, or matrix. This integration results in a hybrid material with biological functions like the ability to grow, adapt, and heal. Imagine a building material that can mend its own cracks or a medical bandage that can sense an infection. The embedded microorganisms allow the material to respond to its environment in ways purely synthetic materials cannot.
Composition of Engineered Living Materials
An engineered living material has two primary components: the living organisms and the non-living matrix that houses them. The living portion consists of microorganisms chosen for specific traits. Bacteria like Escherichia coli and Bacillus subtilis, along with yeast, fungi, and microalgae, are common choices due to their rapid growth and the ease with which their genetics can be modified.
This living component is integrated into a non-living scaffold, or matrix, which provides the material’s structure and protects the cells. These matrices are often made from hydrogels, which are water-retaining polymer networks, or other polymers and textiles. The scaffold must provide a suitable microenvironment that supports cell life by supplying nutrients and shielding them from external stresses.
Programming Life into Materials
The “engineered” aspect of these materials comes from modifying the genetic code of the living cells to perform specific tasks. Scientists use tools from synthetic biology to program cells to produce specific molecules or react to environmental signals in a predetermined way. The goal is to create a predictable and controllable biological function within the structure.
This genetic programming is highly specific. For instance, a bacterial cell can be engineered to produce a fluorescent protein, causing it to glow when it detects a particular pollutant. In another scenario, cells might be programmed to synthesize an adhesive protein when the material is damaged. The instructions for these actions are written into the cell’s DNA, triggered by a stimulus like light, a chemical, or physical stress.
Unique Functional Properties
The fusion of living cells and structural scaffolds gives rise to materials with unique capabilities. One of the most studied properties is self-healing, where the material can autonomously repair damage. When a crack forms, the stress can trigger the embedded microorganisms to produce and secrete substances like calcium carbonate or biopolymers that fill the void and restore structural integrity.
These materials can also be designed for environmental sensing and response. By incorporating cells engineered to detect specific substances, an ELM can act as a living sensor that changes color or degrades a targeted toxin upon exposure. Another function is the on-demand production of valuable substances, where materials can be triggered to synthesize pharmaceuticals or fuels directly at the site of need.
Applications Across Industries
The properties of engineered living materials are paving the way for innovations in numerous fields. Potential applications include:
- Construction materials like self-healing concrete, which uses bacteria to produce limestone and seal cracks as they appear.
- Living bricks that are grown and solidified with microorganisms, reducing the energy needed for traditional manufacturing.
- Smart medical bandages that can sense the signs of an infection and respond by releasing antimicrobial agents into the wound.
- Implantable devices made from ELMs that produce therapeutic drugs, offering a targeted and sustained release of medicine.
- Environmental filters containing microbes engineered to capture and neutralize pollutants in contaminated water or soil.
Containment and Biosecurity
A primary consideration in developing ELMs is ensuring the genetically engineered organisms remain contained and do not pose a risk to the external environment. To address this, scientists are designing multiple layers of biocontainment controls directly into the cells’ genetic makeup. These safety measures are meant to prevent the survival of microorganisms if they escape their intended matrix.
One strategy is a “kill switch,” a genetic circuit that causes the cell to self-destruct under specific conditions. This can be triggered by the absence of a chemical signal present only within the material or after a predetermined amount of time has passed. Another approach is auxotrophy, where cells are engineered to be dependent on a specific nutrient supplied within the ELM. Without this nutrient, the cells cannot synthesize essential compounds and are unable to survive or reproduce in the natural environment.