Dr. Bastian Rapp on 3D‑Printed Microfluidics: Advancing Biotech with NeptunLab

After earning his Ph.D. from the University of Karlsruhe in 2008, Dr. Bastian Rapp has become the world’s leading expert on using 3D printing for microfluidics and related technologies. As founder and director of NeptunLab at the Institute of Microstructure Technology (IMT) of the Karlsruhe Institute of Technology, he drives research that translates microfluidic concepts into practical biomedical and biotechnological solutions.

Below is an exclusive interview in which Dr. Rapp explains how additive manufacturing has reshaped his laboratory’s workflow, the challenges he faced, and the future directions of high‑resolution 3D printing.

Why 3D printing? How did you first encounter the technology?

Our lab focuses on microsystem engineering, advanced materials, and analytical diagnostics for biochemistry and medicine. We needed a rapid prototyping method that could bridge the gap between concept and test sample. Traditional microfabrication techniques offer incredible resolution but are time‑consuming and expensive. Additive manufacturing, particularly micro‑stereolithography, promised the speed and flexibility we required.

My interest began 12 years ago, driven by the need for sub‑50‑micron feature resolution and surface smoothness—qualities that standard 3D printers could not deliver. I started exploring how to push resolution limits while expanding material choices beyond the typical polymers used in commercial printers.

Implementation: In‑house vs. Outsourced?

Our early prints came from ProForm, a Swiss company pioneering micro‑stereolithography. While their resolution was impressive, the material set was unsuitable for our applications. Consequently, we began building our own instrumentation eight years ago, developing both hardware and compatible resins. This move mirrored the transition from proprietary ink cartridges to open‑platform systems, allowing us to print with any material we could formulate.

Our custom system achieves a resolution of 600 nm—well below the typical 50 µm of most stereolithography units. By stitching multiple DMD frames, we can also create larger lateral dimensions without sacrificing detail.

Early Challenges and Evolution

Initially, custom software was required to generate printable files. Today, designers can download STL models, process them with standard slicers, and print immediately. This evolution has dramatically lowered the barrier to entry.

Applications Realized

We’ve produced microfluidic biosensors, analytical devices, optical components (including laser‑based projectors), and chemistry‑on‑a‑chip platforms that miniaturize industrial processes. Optical devices are particularly promising as the field shifts toward photonic calculations.

Industry Adoption and Material Constraints

High resolution is a niche requirement; most commercial systems can’t meet our sub‑100‑nm needs. Consequently, adoption is slow, as it demands significant investment and setup time. Material selection remains a critical bottleneck—many printable polymers are chemically reactive and unsuitable for bio‑analytics.

We recently published a study on 3D‑printing glass, illustrating how established materials can be accessed via novel processes. This approach reframes additive manufacturing as a material‑process innovation rather than a material breakthrough.

Industrial stakeholders often cite two concerns: limited material options and insufficient resolution. While selective laser sintering (SLS) is robust, it requires extensive post‑processing. Stereolithography offers smoother surfaces but is chemistry‑dependent. By printing industrial thermoplastics like plexiglass at high resolution, we are narrowing these gaps.

Future Directions

Speed remains the primary hurdle. Technologies like CLIP have accelerated printing by ~100×, yet industrial scalability demands further gains. If 3D‑printed components can be produced within an order of magnitude of injection moulding speed, the cost‑benefit will shift dramatically—eliminating expensive moulds for low‑volume parts.

Key priorities moving forward are: 1) expanding the palette of printable materials—including metals and traditional polymers; 2) enhancing resolution and build volume; 3) reducing cycle times to match conventional manufacturing benchmarks.

By aligning material choice, resolution, and throughput, additive manufacturing can become the go‑to tool for rapid, cost‑effective prototyping and production across biotech, optics, and beyond.

For more on NeptunLab’s research, visit NeptunLab.

Images courtesy of NeptunLab