A groundbreaking advancement in 3D printing technology has been achieved by a team of scientists led by Dr. Jose Marques-Hueso from the Institute of Sensors, Signals & Systems at Heriot-Watt University in Edinburgh. Their innovative approach utilizes near-infrared (NIR) light to enable the creation of complex 3D structures consisting of multiple materials and colors.
The researchers modified a well-established 3D printing method called stereolithography to push the boundaries of multi-material integration. Conventionally, a 3D printer uses a blue or UV laser to selectively solidify a liquid resin layer by layer, building the desired object. However, this technique has limitations when it comes to mixing materials.
What sets this project apart is the use of NIR light, which allows for printing at much greater depths into the resin vat without the need for layering. The NIR light source employed by the scientists has the capability to penetrate the resin vat beyond 5 cm, compared to the typical limit of around 0.1 mm in conventional technology. This breakthrough enables the printing of one material and the subsequent addition of a second material at any position within the 3D space, not just on the outer surfaces.
For instance, the researchers can print a mostly sealed hollow cube and then later introduce an object made from a completely different material inside the cube. The NIR laser effectively passes through the previously printed material as if it were transparent, solidifying the new material within.
Dr. Adilet Zhakeyev, a Ph.D. researcher who worked on the project, explains that while Fused Deposition Modeling (FDM) technology could already mix materials, it has lower resolution with visible layers. In contrast, light-based technologies like stereolithography can produce smoother samples with resolutions under five micrometers.
The key aspect of the project involves the development of engineered resins containing nanoparticles that exhibit optical upconversion. These nanoparticles absorb NIR photons and convert them into blue photons, which then solidify the resin. The phenomenon of optical upconversion is nonlinear, which means it mainly produces blue photons at the laser’s focus, allowing the NIR light to penetrate deep into the material and selectively solidify only the desired areas.
The new 3D printing technique enables the printing of multiple materials with distinct properties within the same object. For example, flexible elastomers and rigid acrylic can be combined in a single printed sample, making it useful for industries like shoe production. This method unlocks a wide range of possibilities, including 3D printing objects inside cavities, repairing broken objects, and even in-situ bioprinting through the skin.
Dr. Marques-Hueso further mentions that in a previous phase of their research, they developed a resin that can be selectively copper-plated. By combining both technologies, they can now 3D print with two different resins and selectively coat one of them with copper using a simple plating solution bath. This breakthrough allows the creation of integrated circuitry in 3D, which is highly beneficial for the electronics industry.
Surprisingly, despite its groundbreaking capabilities, the cost of this technology is remarkably low. Dr. Marques-Hueso highlights that the entire machine can be built for less than £400. In contrast, other advanced laser-based technologies like Two-Photon Polymerization (2PP) require expensive ultrafast lasers that cost tens of thousands of pounds. However, the use of cost-effective lasers is made possible by the specialist materials developed by the team.
With the results supporting their claims, the researchers now hope to collaborate with businesses to further develop this transformative technology. The findings have been published in the journal Advanced Engineering Materials.
Source: Heriot-Watt University