The use of natural materials in paper and textiles, and in support of tunable and mechanically robust systems for sensing toxic gases, removing pollutants from water, and constructing functional biodegradable scaffolds, is a topic of great scientific and practical importance. The social, environmental, and economic impact of using natural materials to functionalize integrated systems for new designs is imperative, as the need to reuse and recycle natural resources has increased in current manufacturing. The inclusion of sustainability in the design of new materials and processes is almost a common practice; concurrently, the usage of “being more sustainable” is becoming a more conjointly used term in urban conversations. That said, systems integration and natural materials are intrinsically related to produce novel materials that can function as sensors, switches, platforms, and building blocks in a sustainable fashion. The contributions in this issue of MRS Bulletin highlight the importance and benefits to society that systems integration of functional materials can provide.

“Bottom-up” assembly of fully functional cell-based materials has enormous potential for replicating endogenous tissues. Currently, most tissue-engineering strategies are based on incorporating dissociated cells into an artificial three-dimensional matrix of supportive structural elements that direct cellular migration, proliferation, and organization. The matrix provides “top-down” guidance cues that impose assembly directions on the cells; however, the matrix also competes for space and limits fully functional, cell-dense tissues. This article focuses on bottom-up fabrication of functional tissue by cell sheet engineering. Cell sheet engineering is based on the sequential stacking and adhesion of confluent and organized cell monolayers from two-dimensional cell culture without the need for artifical scaffolds or structural intermediates. The resulting functional cellular monolayers (either individually or as stacked sheets) can then be directly implanted into living systems. Clinical successes are highlighted as well as attempts to overcome the vascularization limit often observed in engineered tissues.

Paper is a material made from renewable resources, and it has been used intensively for almost 2000 years. It is a highly porous, bendable, and foldable flat structure of randomly arranged and connected fiber-like basic building blocks. The capability to transport fluids without pumps and sophisticated dosing systems is attractive. Paper microfluidics especially has gained increasing interest, particularly in the last decade. Although a number of interesting demonstration devices for easy-to-use diagnostic systems have been reported, only a limited number of these have found applications. This is mainly due to the geometric and chemical complexity of the material. While chemical functionalization (e.g., for defining hydrophobic barriers for spatially resolved fluid transport) is well advanced, understanding and controlling capillary-driven transport of a fluid within the complex porous matrix of paper. This article highlights recent advances and outlines design strategies for successful microfluidic paper-based applications.

The continued use of finite fossil fuel resources has shifted thinking toward a potential future bioeconomy, and the field of polymer science will play a critical role in valorization of bio-derived materials. Interest in renewable resources is constantly increasing, backed up by new environmental regulations and economic considerations. Biomass is abundant and diverse, and polymeric materials based on renewable feedstocks represent a viable alternative to fossil resources. Bio-oil—a dark brown, free-flowing organic liquid mixture—is a product of fast pyrolysis or liquefaction of biomass. Bio-oil generally comprises a large amount of water and hundreds of organic chemical compounds that can be further broken down into families of reactive structures, capable of producing new synthetic pathways to design and synthesize high-performance biopolymers and bioresins using lignocellulosic biomass. These new polymeric materials have demonstrated a unique combination of thermal resistance and low cost intrinsic of the biomass utilized, as well as superior mechanical performance of polymeric resins sufficient to compete with high-performance structural resins and coating materials.

Among the most abundant biopolymers in the biosphere, lignin represents an untapped opportunity to create novel bioproducts. In this article, we discuss possibilities to synthesize nano- and microparticles by harnessing lignin’s inherent tendency to associate and to develop new material compositions and functions by controlling its capacity to assemble into supramolecular structures. Because lignin is biodegradable, antimicrobial, antioxidative, and carbon neutral, inexpensive industrial lignin streams could generate value-added particulate materials that preserve the structure, composition, and colloidal features inherent to this macromolecule. We present available routes for synthesis or isolation of lignin particles, including antisolvent and aerosol processing. Metallic and polymeric lignin particle hybrids for magnetic, antibacterial, catalytic, photonic, and other applications are also discussed. Overall, the facile formation of nano- and microparticles from lignins is expected to open new pathways toward future material development.

Agricultural soils are among the depositories of engineered nanomaterials (ENMs). Soil exposure to ENMs occurs through the intentional use of nano-agrochemicals, as well as through incidental contamination from industrial-waste release, irrigation with wastewater or gray water, amendment with ENMs-loaded sludge (soil conditioning to stimulate plant growth), or atmospheric fallouts. Concerns about ENM interactions with plants raise two questions. (1) Are ENMs taken up from soil by plants? (2) If they are taken up, do they remain in the nanoform within plant tissues? Experiments with crop plants have demonstrated that some ENMs such as TiO2 are taken up by roots and translocated to aboveground tissues, including fruits, without biotransformation. CeO2 ENM is also taken up by the roots; however, although most of it remains as ENM, it releases cerium ions that are incorporated into organic compounds. CeO2 ENM has been shown to be translocated from roots to seeds in soybean grown in soil amended with such ENM. On the other hand, ZnO ENM is transformed at the soil/root interface, leading to tissue Zn enrichment. Overall, most ENMs are taken up by plants with either low or no transformation, and accumulate in tissues.

This article provides a personal guided tour of multiferroic materials, from their early days as a theoretical curiosity, to their position today as a focus of worldwide research activity poised to impact technology. The article begins with the history of, and the answer to, the question of why so few magnetic ferroelectric multiferroics exist, then gives a survey of the mechanisms and materials that support such multiferroicity. After discussing the tremendous progress that has been made in the magnetoelectric control of magnetic properties using an electric field, some unusual applications of multiferroics in high-energy physics and cosmology are outlined. Finally, the most interesting open questions and future research directions are addressed.