Living materials, which are fabricated by encapsulating living biological cells within a non-living matrix, have gained increasing attention in recent years. Their fabrication in spatially defined patterns that are mechanically robust is essential for their optimal functional performance but is difficult to achieve. Here, a bioprinting technique employing environmentally friendly chemistry to encapsulate microalgae within an alginate hydrogel matrix is reported. The bioprinted photosynthetic structures adopt pre-designed geometries at millimeter-scale resolution. A bacterial cellulose substrate confers exceptional advantages to this living material, including strength, toughness, flexibility, robustness, and retention of physical integrity against extreme physical distortions. The bioprinted materials possess sufficient mechanical strength to be self-standing, and can be detached and reattached onto different surfaces. Bioprinted materials can survive stably for a period of at least 3 days without nutrients, and their life can be further extended by transferring them to a fresh source of nutrients within this timeframe. These bioprints are regenerative, that is, they can be reused and expanded to print additional living materials. The fabrication of the bioprinted living materials can be readily up-scaled (up to ≥70 cm × 20 cm), highlighting their potential product applications including artificial leaves, photosynthetic bio-garments, and adhesive labels.

Biofilms are three-dimensional (3D) bacterial communities that exhibit a highly self-organized nature in terms of their composition and complex architecture. Bacteria in biofilms display emergent biological properties, such as resistance to antimicrobials and disinfectants that the individual planktonic cells lack. Bacterial biofilms possess specialized architectural features including unique extracellular matrix compositions and a distinct spatially patterned arrangement of cells and matrix components within the biofilm. It is unclear which of these architectural elements of bacterial biofilms lead to the development of their emergent biological properties. Here, we report a 3D printing-based technique for studying the emergent resistance behaviors of Escherichia coli biofilms as a function of their architecture. Cellulose and curli are the major extracellular-matrix components in E. coli biofilms. We show that 3D-printed biofilms expressing either curli alone or both curli and cellulose in their extracellular matrices show higher resistance to exposure against disinfectants than 3D prints expressing either cellulose alone or no biofilm-matrix components. The 3D-printed biofilms expressing cellulose and/or curli also show thicker anaerobic zones than nonbiofilm-forming E. coli 3D prints. Thus, the matrix composition plays a crucial role in the emergent spatial patterning and biological endurance of 3D-printed biofilms. In contrast, initial spatial distribution of bacterial density or curli-producing cells does not have an effect on biofilm resistance phenotypes. Further, these 3D-printed biofilms could be reversibly attached to different surfaces (bacterial cellulose, glass, and polystyrene) and display resistance to physical distortions by retaining their shape and structure. This physical robustness highlights their potential in applications including bioremediation, protective coatings against pathogens on medical devices, or wastewater treatment, among many others. This new understanding of the emergent behavior of bacterial biofilms could aid in the development of novel engineered living materials using synthetic biology and materials science approaches.

Sustainable structural materials with excellent impact-resistance properties are urgently needed but challenging to produce, especially in a scalable fashion and with control over 3D shape. Here, we show that bacterial cellulose (BC) and bacterially precipitated calcium carbonate self-assemble into a layered structure reminiscent of tough biomineralized materials in nature (nacre, bone, dentin). The fabrication method consists of biomineralizing BC to form an organic/inorganic mixed slurry, in which calcium carbonate crystal size is controlled with bacterial poly(γ-glutamic acid) and magnesium ions. This slurry self-assembles into a layered material that combines high toughness and high impact and fire resistance. The rapid fabrication is readily scalable, without involving toxic chemicals. Notably, the biomineralized BC can be repeatedly recycled and molded into any desired 3D shape and size using a simple kitchen blender and sieve. This fully biodegradable composite is well suited for use as a component in daily life, including furniture, helmets, and protective garments.

Graphene oxide (GO) has immense potential for widespread use in diverse in vitro and in vivo biomedical applications owing to its thermal and chemical resistance, excellent electrical properties and solubility, and high surface-to-volume ratio. However, development of GO-based biological nanocomposites and biosensors has been hampered by its poor intrinsic biocompatibility and difficult covalent biofunctionalization across its lattice. Many studies exploit the strategy of chemically modifying GO by noncovalent and reversible attachment of (bio)molecules or sole covalent biofunctionalization of residual moieties at the lattice edges, resulting in a low coating coverage and a largely bioincompatible composite. Here, we address these problems and present a facile yet powerful method for the covalent biofunctionalization of GO using colamine (CA) and the poly(ethylene glycol) cross-linker that results in a vast improvement in the biomolecular coating density and heterogeneity across the entire GO lattice. We further demonstrate that our biofunctionalized GO with CA as the cross-linker provides superior nonspecific biomolecule adhesion suppression with increased biomarker detection sensitivity in a DNA-biosensing assay compared to the (3-aminopropyl)triethoxysilane cross-linker. Our optimized biofunctionalization method will aid the development of GO-based in situ applications including biosensors, tissue nanocomposites, and drug carriers.

Graphene oxide (GO) has recently been highlighted as a promising multipurpose two-dimensional material. However, free-standing graphene oxide films suffer from poor strength and flexibility, which limits scaling-up of production and lifetime structural robustness in applications. Inspired by the relationship between the organic and inorganic components of the hierarchical structure of nacre found in mollusk shells, we have fabricated self-assembled, layered graphene-based composite films. The organic phase of our composite is produced via environmentally friendly and economical methods based on bacterial production of γ-poly(glutamic acid) (PGA). Composite films made of GO, PGA, and divalent cations (Ca2+) were prepared through a slow solvent evaporation method at ambient temperature, resulting in a nacre-like layered structure. These biobased nanocomposite films showed impressive mechanical properties, which resulted from a synergistic combination of hydrogen bonding with the bacterially produced PGA and ionic bonding with calcium ions (Ca2+). The GO/PGA/Ca2+ composite films possessed a high strength of 150 ± 51.9 MPa and a high Young's modulus of 21.4 ± 8.7 GPa, which represents an increase of 120% and over 70% with respect to pure GO films. We provide rational design strategies for the production of graphene-based films with improved mechanical performance, which can be applied in filtration purification of wastewater in the paper, food, beverage, pigment, and pharmaceuticals industries, as well as for manufacturing of functional membranes and surface coatings.

Transporting materials from Earth to Mars is a significant logistical constraint on mission design. Thus, a sustained settlement will be enhanced if it can perform elemental extraction and utilization in situ. In this study, all requirements to test a novel, biological approach for in situ resource utilization (ISRU) are conceptualized. We present designs for two bioreactor systems to be incorporated in a Mars habitat. The first system is a standard algae bioreactor which produces oxygen and biomass. The second bioreactor is capable of taking in Martian regolith and extracting enhanced iron ores from it via biological processes. Additionally, we propose the use of the leftover iron-poor but biomass rich material in a plant compartment. The multiple, different compartments feed into each other, creating an interconnected process enhancing self-sufficiency. In this paper, computational fluid dynamics of mixing behavior under reduced gravity, a breakdown of the process flow for a biological ISRU approach and exploratory in silico evaluation of the feasibility are presented.

The impressive mechanical properties of natural composites, such as nacre, arise from their multiscale hierarchical structures, which span from nano- to macroscale and lead to effective energy dissipation. While some synthetic bioinspired materials have achieved the toughness of natural nacre, current production methods are complex and typically involve toxic chemicals, extreme temperatures, and/or high pressures. Here, the exclusive use of bacteria to produce nacre-inspired layered calcium carbonate-polyglutamate composite materials that reach and exceed the toughness of natural nacre, while additionally exhibiting high extensibility and maintaining high stiffness, is introduced. The extensive diversity of bacterial metabolic abilities and the possibility of genetic engineering allows for the creation of a library of bacterially produced, cost-effective, and eco-friendly composite materials.

Nature is based on complex self-assembling systems that span from the nanoscale to the macroscale. We have already begun to design biomimetic systems with properties that have not evolved in nature, based on designed molecular interactions and regulation of biological systems. Synthetic biology is based on the principle of modularity, repurposing diverse building modules to design new types of molecular and cellular assemblies. While we are currently able to use techniques from synthetic biology to design self-assembling molecules and re-engineer functional cells, we still need to use guided assembly to construct biological assemblies at the macroscale. We review the recent strategies for designing biological systems ranging from molecular assemblies based on self-assembly of (poly)peptides to the guided assembly of patterned bacteria, spanning 7 orders of magnitude.

Bacterial biofilms are three-dimensional networks of cells entangled in a self-generated extracellular polymeric matrix composed of proteins, lipids, polysaccharides, and nucleic acids. Biofilms can establish themselves on virtually any accessible surface and lead to varying impacts ranging from infectious diseases to degradation of toxic chemicals. Biofilms exhibit high mechanical stiffness and are inherently tolerant to adverse conditions including the presence of antibiotics, pollutants, detergents, high temperature, changes in pH, etc. These features make biofilms resilient, which is beneficial for applications in dynamic environments such as bioleaching, bioremediation, materials production, and wastewater purification. We have recently described an easy and cost-effective method for 3D printing of bacteria and have extended this technology for 3D printing of genetically engineered Escherichia coli biofilms. Our 3D printing platform exploits simple alginate chemistry for printing of a bacteria-alginate bioink mixture onto calcium-containing agar surfaces, resulting in the formation of bacteria-encapsulating hydrogels with varying geometries. Bacteria in these hydrogels remain intact, spatially patterned, and viable for several days. Printing of engineered bacteria to produce inducible biofilms leads to formation of multilayered three-dimensional structures that can tolerate harsh chemical treatments. Synthetic biology and material science approaches provide the opportunity to append a wide range of useful functionalities to these 3D-printed biofilms. In this article, we describe the wide range of future applications possible for applying functional 3D-printed biofilms to the construction of living biofilm-derived materials in a large-scale and environmentally stable manner.

In situ resource utilization (ISRU) increasingly features as an element of human long-term exploration and settlement missions to the lunar surface. In this study, all requirements to test a novel, biological approach for ISRU are validated, and an end-to-end mission architecture is proposed. The general mission consists of a lander with a fully autonomous bioreactor able to process lunar regolith and extract elemental iron. The elemental iron could either be stored or directly utilized to generate iron wires or construction material. To maximize the success rate of this mission, potential landing sites for future missions are studied, and technical details (thermal radiation, shielding, power-supply) are analyzed. The final section will assess the potential mission architecture (orbit, rocket, lander, timeframe). This design might not only be one step further towards an international “Moon Village”, but may also enable similar missions to ultimately colonize Mars and further explore our solar system.

Graphene's maximized surface-to-volume ratio, high conductance, mechanical strength, and flexibility make it a promising nanomaterial. However, large-scale graphene production is typically cost-intensive. This manuscript describes a microbial reduction approach for producing graphene that utilizes the bacterium Shewanella oneidensis in combination with modern nanotechnology to enable a low-cost, large-scale production method. The bacterial reduction approach presented in this paper increases the conductance of single graphene oxide flakes as well as bulk graphene oxide sheets by 2.1 to 2.7 orders of magnitude respectively while simultaneously retaining a high surface-area-to-thickness ratio. Shewanella-mediated reduction was employed in conjunction with electron-beam lithography to reduce one surface of individual graphene oxide flakes. This methodology yielded conducting flakes with differing functionalization on the top and bottom faces. Therefore, microbial reduction of graphene oxide enables the development and up-scaling of new types of graphene-based materials and devices with a variety of applications including nano-composites, conductive inks, and biosensors, while avoiding usage of hazardous, environmentally-unfriendly chemicals.