3D printing: An emerging opportunity for soil science

The soil, at the interface between geosphere, biosphere, and atmosphere, is a particularly challenging object to study. The ecological and environmental impacts of soil functioning encourage soil scientists to exploit new technologies to generate new data or develop new research protocols. Among these technologies, 3D printing is a promising technology for improving the understanding of soils. The general principle of 3D printing is to build parts by adding materials layer by layer following a three-dimensional solid model. The 3D printing technology makes it possible to produce almost any geometrically complex shape or feature in a wide range of materials. Its interest lies in its ability to produce customized objects easily and rapidly in an endlessly reproducible 3D-arrangement. A large number of techniques and materials are available, which differ in their principles, advantages, and shortcomings. In this article, we present the main challenges and opportunities of using 3D printing in soil science. To this end, we present a review of the literature from 2000 to 2019 to identify and understand recent applications of 3D printing in this field. We first describe applications such as the manufacturing of agricultural equipment and laboratory devices in soil science, the development of new construction materials, or the geotechnical characterization of soil as a construction base. However, none of these applications requires replication of the soil functional properties as opposed to applications that would be dedicated to improving the understanding of soil functioning. We detail here the challenges and opportunities of building soil models that reproduce its physical, chemical, biological properties, and its dynamics in contact with living organisms. Despite the remarkable and rapid progress made in the development of 3D printing in recent years, this technology is still underused in the field of soil science. In particular, very few applications focus on the functioning of the soil itself as an ecological compartment. Indeed, several technical limitations have still to be overcome. 3D printed objects must be biocompatible, chemically and mechanically stable, and must be spatially resolved on the microscale. Many efforts are being made by the 3D printing community to push these boundaries. This paves the way for the wider use of 3D printing in soil science. In the near future, the availability of additive manufactured soil models, with strict and controlled composition and structure, will provide researchers with an irreplaceable opportunity to conduct reproducible experiments and better understand soil functioning factors.