Researchers have developed a novel 3D printing technique that grows dense, complex, and exceptionally strong objects made of metal and ceramic from within a water-based hydrogel. The new method, pioneered by a team at the Swiss Federal Institute of Technology in Lausanne (EPFL), bypasses critical flaws in existing additive manufacturing processes. By building a preliminary scaffold and then infusing it with material, the scientists have created intricate structures that are significantly stronger and more reliable than those produced by other techniques.
This innovative approach successfully addresses long-standing challenges in the 3D printing of high-performance materials. For years, attempts to print metals and ceramics have been hampered by issues of porosity, which compromises the strength and integrity of the final product. Furthermore, previous methods resulted in dramatic shrinkage and warping of the printed object during its final processing stage. This new hydrogel-based growth method dramatically reduces these defects, producing parts with unprecedented density and structural stability, paving the way for advanced applications in fields ranging from biomedical implants to next-generation electronics and energy systems.
A Step-by-Step Growth Method
The new fabrication technique fundamentally reimagines how 3D printing can be used to create non-polymer objects. Instead of directly printing with a material-infused resin, the process begins by creating a template, or scaffold, in the desired final shape. This is accomplished using a common 3D printing method known as vat photopolymerization, where a light-sensitive polymer is selectively hardened by a laser or UV light to form an intricate structure. The key difference is that the initial material is a simple, water-based hydrogel.
The Hydrogel Scaffold
The process starts with the creation of a blank 3D object made entirely of this hydrogel. This scaffold serves as a stable, high-resolution template. Because it is created without any embedded precursor materials, the initial printing step is simple and reliable. This hydrogel structure is porous on a molecular level, allowing it to act like a sponge in the subsequent stages of the process.
Infusion and Conversion Cycles
Once the hydrogel scaffold is printed, it is submerged in a solution containing precursor metal salts. The scaffold absorbs this solution, which permeates its entire structure. A chemical process is then used to convert these salts into metal-containing nanoparticles that become trapped within the hydrogel matrix. This infusion-and-conversion step is repeated multiple times, in what the researchers term “growth cycles.” With each cycle, the concentration of nanoparticles within the gel increases. According to the research, 5 to 10 of these cycles are typically performed to achieve a very high density of the desired material packed into the scaffold.
Final Sintering
The final step involves heating the infused hydrogel to a high temperature. This heating process, known as sintering, achieves two goals simultaneously. First, it burns away the hydrogel polymer, leaving behind only the metal or ceramic nanoparticles. Second, the heat fuses these nanoparticles together into a solid, dense, and continuous object that perfectly retains the intricate shape of the original scaffold. The result is a fully formed metal or ceramic part with fine details and a robust internal structure.
Overcoming Previous Limitations
The primary advantage of this new technique is its ability to solve the critical problems of porosity and shrinkage that have long hindered the 3D printing of strong materials. In more conventional methods, metal or ceramic precursors are mixed into the light-sensitive resin before the printing begins. When the resin is burned away in the final heating stage, it leaves behind significant gaps between the material particles, resulting in a porous and therefore mechanically weak structure.
This porosity has been a major barrier to using 3D-printed parts in demanding applications where reliability is essential. The EPFL team’s method avoids this by growing the material within the scaffold, ensuring a much higher packing density of nanoparticles before the final heating step. The result is a final object that is unprecedentedly dense and solid. The researchers also report a massive reduction in shrinkage. While previous methods saw printed parts shrink by 60% to 90% of their original volume during heating, causing severe warping and loss of precision, the new technique limits shrinkage to only 20%. This drastic improvement in dimensional stability allows for the reliable production of complex and precise components.
Demonstrated Strength and Complexity
To showcase the capabilities of their method, the research team fabricated a series of intricate objects with complex internal geometries known as gyroids. These mathematically defined, lattice-like shapes are known for their high surface area and strength but are difficult to produce with traditional manufacturing. The team successfully created gyroids from iron, silver, and copper, demonstrating the method’s versatility.
The mechanical properties of these objects were then rigorously tested. Using a universal testing machine to apply increasing amounts of pressure, the researchers found their materials to be exceptionally robust. The 3D-printed gyroids could withstand 20 times more pressure than comparable structures made using earlier 3D printing techniques. This leap in strength confirms that the high density achieved through the hydrogel growth process translates directly into superior mechanical performance.
Expanding Material Possibilities
Another significant advantage of the hydrogel-based process is its material flexibility. Because the initial scaffold is a “blank” template, a single printed hydrogel can be used to create an object from a wide variety of different materials. The choice of metal or ceramic is determined by the specific precursor salt solution used during the infusion cycles. This separates the shaping process from the material-selection process, which is a major departure from traditional methods where the material is locked in at the pre-printing resin stage.
This versatility could accelerate research and development, allowing engineers to rapidly prototype a component using different metals or ceramics from a single, easily produced hydrogel master. The team has already demonstrated the technique with several metals and is exploring its use for a wider range of materials, further broadening its potential applications.
Future Engineering Applications
The combination of high strength, high density, low shrinkage, and the ability to create complex shapes opens the door for this technology to be used in numerous advanced fields. The researchers suggest that it could be applied to create next-generation energy technologies, such as more efficient catalysts or compact heat exchangers that benefit from intricate internal channel designs. In the biomedical field, the process could be used to manufacture custom implants or medical devices with precisely controlled geometries that are both strong and biocompatible.
Other potential areas include the fabrication of specialized sensors and electronic components that require complex 3D architectures at a small scale. The work, published in the journal Advanced Materials, was led by Daryl Yee, head of EPFL’s Laboratory for the Chemistry of Materials and Manufacturing, with doctoral student Yiming Ji serving as the study’s first author. The team’s breakthrough represents a significant step toward making 3D printing a viable and reliable method for manufacturing high-performance functional parts.