Making Data Matter: Voxel-printing for the digital fabrication of data across scales and domains

While physical visualizations and representations of data are as old as prehistoric cave paintings, modern approaches still predominantly rely on the 2D display of 3D data sets on planar computer screens. Scientific visualizations account for a wide range of such virtual information displays, including volumetric rendering of patient data obtained from magnetic resonance imaging (MRI) or point-based rendering of geospatial data obtained from photogrammetry methods. Such visualizations map, process, and represent data and aim to allow a user to gather insights through perception and computer-aided interaction

Although conventional screen-based media visualizations are known to be effective, it has been argued that physical manifestations of data sets can leverage active as well as spatial perception skills, enabling a more comprehensive understanding of presented information in an inherently intuitive manner. Immersive visualization through virtual and augmented reality displays aim to improve the shortcomings of 2D information displays, but currently lack the tangible interaction offered by physical information displays. Advancements in the accessibility and affordability of digital fabrication workflows—such as additive manufacturing—enable a ‘resurrection’ of data in its physical manifestation. Consequently, the representation of data sets in a physical form through digital fabrication has emerged as a research area and practice. More broadly, the manifestation of data as a physical embodiment is often collected under the term data physicalization or physical visualization.

Furthermore, despite the availability and progression of 3D printing technology, fundamental 3D printing workflows have remained essentially unchanged for the past 30 years. These workflows are limited by the fact that shape specification is directly linked with material specification. This limitation is also reflected in the STL file format, which was introduced three decades ago for the first stereolithographic 3D printers and is still considered the standard file format for additive manufacturing. 

The STL file format represents objects through a closed regular surface, which is described by a list of triangles, defined through their vertices. During the 3D printing process each surface is considered a solid object, where space inside the triangle boundary representation is occupied by a single material. Unfortunately, these design and additive manufacturing workflows don’t think ‘beyond the shell’ of objects, despite the fact that commercially available 3D printers can print up to seven materials simultaneously. This means that, in order to 3D print any data set—especially those that are not naturally representable as surfaces—all data first must be converted into a boundary representation. Specifically for scientific data, this conversion process is problematic, as in many cases it introduces computational overhead, alteration of data, and even loss of information.

In our paper, and in contrast to the methods described above, we present an approach to physical data visualizationthrough voxel printing using multimaterial 3D printing to improve the current data physicalization workflows.

Multimaterial 3D printing with photopolymeric materials enables the simultaneous use of several different materials, and by utilizing dedicated cyan, magenta, yellow, black, white, and transparent resins, full-color models with variable transparency can be created. The ability to create objects with and inside transparent material enables the physical visualization of compact n-manifolds such as unconnected point cloud data, lines and curves, open surfaces, and volumetric data.

Multimaterial 3D printers operate by depositing droplets of several UV-curable resins in a layer-by-layer inkjet-like printing process to construct high-resolution 3D objects. High levels of spatial control in manufacturing can be achieved by generating a set of layers in a raster file format at the native resolution of the printer, where each pixel defines the material identity of a droplet and its placement in 3D space. The set of layers can be combined into a voxel matrix. A printer can then process these droplet deposition descriptions given as a voxel matrix to digitally fabricate heterogeneous and continuously varying material composites. This approach is often described as bitmap-based printing or voxel printing .

Commercially available multimaterial 3D printers can have a build envelope of 500 mm by 400 mm by 200 mm with a droplet deposition resolution of 600dpi and 300dpi, respectively, and a layer separation of down to 12μm, which results in 929 billion individually addressable material droplet positions, or voxels, through the approach described above. This high-resolution build space enables two key characteristics relevant for physical visualization:

• Volumetric color and opacity gradients, achieved by varying the spatial density of droplets of different materials.
• Preservation of detail, achieved through a clear enclosure volume, which allows the digital fabrication of highly detailed structures with fine features.

While multimaterial 3D printing is used in the sophisticated design processes of advanced products with complex geometries, it has only recently been used for the generation of data sculptures containing data-informed patterns.

Our approach to physical data visualization through voxel printing using multimaterial 3D printing presented herein enables direct digital manufacturing of numerous data sets commonly found in scientific visualizations through rasterization, without the need to create intermediate representations for 3D printing. As a result, the method and its various applications point towards the elimination of the digital/physical divide, bridging digital on-screen data and their physical manifestations.