The Complete Guide to Direct Ink Writing

Direct ink writing (DIW) is an extrusion-based additive manufacturing technique where ink is extruded through a fine nozzle that follows a digitally defined path to build a three-dimensional structure layer by layer. One of the key characteristics of this technique is its ability to print customizable inks at the meso- and microscale (essentially, not large-scale projects). The technology was first patented in 1997 by Joe Cesarano and Paul Calvert at the Sandia National Laboratory, where they developed it as a technique for printing complex ceramic structures. Since then, DIW has been applied broadly across a range of studies and fabrication processes beyond ceramics. It has mostly been used in research labs for small-scale fabrication and prototyping, but the technique has the potential to create efficient, industrial-grade parts. Here, we’ll take a closer look at the process, materials, and applications behind DIW, highlighting its advantages and limitations.

How Does Direct Ink Writing Work? Processes and Materials:

Typically, the fundamental process for DIW is the same as any 3D printing process. Users need a 3D model created via computer-aided design (CAD) and a movement path file from a slicing software. DIW can process almost any material, provided the ink exhibits the right rheological behavior, namely, the appropriate yield stress under shear and compression, along with suitable viscoelastic properties. As a result, DIW enables a wide range of inks to be printed into complex 3D structures with high-resolution patterning, architectural flexibility, and tailored material characteristics. This sets it apart from other AM technologies like FDM and SLA, which are constrained by material class. Additionally, DIW is versatile because of its ability to use multiple nozzles to create multi-material structures.

In DIW, applied pressure forces liquid inks through a nozzle, and this pressure can alter the ink’s viscosity. This is a key distinction of DIW: instead of using heat, DIW prints inks at room temperature, meaning the rheological properties of the ink are critical. After exiting the nozzle and before final deposition, the ink is not completely at rest. Rather, the material bends and stretches depending on the ratio between the extrusion rate and the speed of the printhead movements. Once deposited, the ink solidifies either naturally or through external processes like evaporation, phase changes, heat treatment, or gelation.

Researchers have experimented with many types of materials for DIW, including polymers, ceramics, cement, graphene, glass, waxes, hydrogels, alloys and pure metals, and even food. However, these materials must be processed into gel-based viscoelastic inks that possess shear-thinning behavior. A typical viscosity for a DIW ink is between 102 and 106 millipascal s range at a shear rate of about 0.1 s-1. This means that under shear strain, viscosity decreases, making the ink printable via DIW. Then, depending on the material and application, varying post-processing steps will follow.

Advantages and Disadvantages of DIW

As mentioned earlier, the process stands out for its ability to process a wide range of materials, as long as the correct rheology is achieved. However, this same characteristic means that any new material must be carefully formulated to meet strict rheological requirements, which can slow down the adoption of new systems.

Additionally, because the technology offers the possibility of extruding at room temperature, it is convenient for working with heat-sensitive compounds. It also helps to overcome the restrictions of other extrusion methods, which rely on high temperatures. Even so, printing remains relatively slow, and the quality of the interface between layers can be compromised when the speed is increased. As a result, it can be difficult to balance efficiency and structural performance.

DIW offers considerable freedom in terms of system configuration, as it can be modified with affordable components and easily adapted to different applications. This hardware flexibility is remarkable, but the technique remains limited mainly to small-scale manufacturing and research environments, as its production rate and resolution do not meet the standards required for high-volume industrial processes.

Another attractive feature of the process is its ability to generate complex geometries, from self-supporting structures to freeform shapes that do not require additional molds or supports. Yet, when seeking to grow vertically or produce long overhangs, the weight of the part itself can cause deformation or failure, especially in large structures.

Key Applications

Given the wide range of materials for DIW, the technique has a broad range of applications. Some of the most common are for energy storage, optics and photonics devices, and biomedical and tissue engineering.

For energy storage, DIW has been used to fabricate electrochemical energy storage (EES) devices, such as lithium-ion batteries and supercapacitors. DIW can create structures at the micro/nano-scale that offer exceptional electrochemical performance by permitting electrons and ions to move through the porous structure with more efficiency. The technology can be used to create devices with high conductivity and a highly specific surface area, which is especially desirable for electronic components and devices.

In the medical field, researchers have created biodegradable scaffolds, stretchable self-healing shape-memory elastomers, soft robotics, wearable devices, and more. One of the most promising DIW applications is the use of hydrogels to emulate biological tissues. Many hydrogels are biocompatible, which makes them suitable for interacting with living cells and tissues. Hydrogels can also contain bioactive molecules, growth factors, pharmaceuticals, or even living cells, making them capable of targeted drug delivery or tissue regeneration. Thanks to the precision that DIW ensures, the technology can also be used to create organ-on-a-chip devices and microfluidic systems. By replicating tissue microenvironments, these structures can facilitate the study of drug responses and the progression of diseases in a controlled and reproducible manner.

Beyond medical and electrical applications, DIW has been used for everything from soft robotics to food and structural engineering applications.

Manufacturers and Pricing

Unlike other established additive manufacturing technologies, the direct ink writing (DIW) ecosystem is characterized by a combination of startups and platforms created in academic environments. Among the most prominent manufacturers is Avay, an Indian company whose machines are geared toward the deposition of conductive inks and other insulating materials. The Polish company Sygnis offers systems for materials research and for flexible electronics and robotics. One of its most popular printers, the SYGNIS F-NIS, is priced between $10,759 and $13,350. Another notable brand is MakerPi. This Chinese company offers printers focused on multi-material printing with bioinks and gels for biomedical laboratories, priced at approximately $68,526.

Alongside these manufacturers, there are low-cost, open-source platforms such as Printess, designed to democratize DIW printing and use it in bioprinting, soft robotics, or educational projects. In turn, the Spanish startup PowerDIW, a spin-off of the CIM UPC technology center, has developed the PowerDIW platform, a hybrid system designed for ceramics, polymers, and functional materials within advanced R&D projects. Since there is no public price for this system, it is necessary to contact the manufacturer directly.

DIW printers are generally notable for their relatively low cost and the simplicity of their extrusion mechanisms compared to more complex 3D printing technologies. Beyond the manufacturers mentioned here, it’s important to recognize that most direct ink writing systems are tailored to specific applications. In other words, research centers and laboratories often develop or customize their platforms to meet their unique needs, which helps explain why there are fewer commercial brands than in other 3D printing sectors.

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*Cover Image Credit: Voltera