Researchers have developed a system for producing high-resolution, customised polymer microstructures economically using a technique known as photo-crosslinking.
The system is a new type of 3D printer that combines fast two-dimensional exposure (scrolling digital light processing, DLP) with a high-resolution laser process (multiphoton polymerisation, MPP), to produce microcomponents from photopolymers.
The work has been done within the ‘HoPro-3D’ project (High productivity and detail accuracy in additive manufacturing by combining UV polymerization and multiphoton polymerization) between Fraunhofer ILT, LightFab GmbH, Bartels Mikrotechnik GmbH and Miltenyi Biotec GmbH.
The HoPro-3D printer has two selectable exposure systems, for either high build rates (scrolling DLP) or high precision (MPP). The DLP module, which emits at a wavelength of 365nm, exposes the basic structures of a microcomponent with a pixel resolution of 10μm. To complement this, a femtosecond laser and the MPP module can be used to write contour lines with a resolution of about 2μm.
The layer-by-layer approach makes it possible to build the finest MPP structures on top of already printed DLP structures, thus quickly creating extended components with a complex structure and high-resolution details. The built-up laboratory pattern allows the production of components with a footprint of up to 60 x 100mm².
The control software of the HoPro-3D system enables users to smoothly switch between the two exposure modules. Moreover, they can use CAD data to decide when it makes sense to switch between the printing processes. During the layer-by-layer build-up of a component, it is possible to switch between the two processes several times.
“The concept is in place and the corresponding machine has been built and already extensively tested,” reports Dr Martin Wehner, Head of the Biofabrication Group at Fraunhofer ILT. After its completion in Spring, the laboratory prototype could already be tested and optimised in an application-oriented manner as part of the Fraunhofer SiCellNet network. The SiCellNet cluster forms a central point of contact for research into new tools and manufacturing techniques for the analysis, sorting and provision of living cells. The performance of the combination plant and the control of the process could thus be optimally expanded.
A sample component produced on the HoPro-3D printer. (Image: Fraunhofer ILT)
In the follow-up project PANDA (Precise assembly by high resolution seamless 3D printing), the Fraunhofer ILT team has been expanding the performance of DLP-based processes. The knowledge gained there will later be applied in the HoPro-3D system to continuously improve the economic efficiency of the 3D printing process.
Applications in biomedical analytics
The Fraunhofer ILT is able to build microchannel structures to develop customer-specific applications in a time- and cost-saving manner. Since there is no need to switch between different machines, smaller functional elements can be integrated directly into larger components. In addition, thanks to increased precision of the MPP process, a high local functional density of microscopic structures can be integrated into compo-nents during production.
The potential applications are numerous: Microfluidic chips for laboratory diagnostics and rapid tests, micromechanical components and complete microfluidic systems for efficient point-of-care diagnostics provide on-site diagnostics close to the patient without need further laboratory testing.