Microfabricated Fluidics Device Underpins Blood-Plasma Separation Method

Researchers at the University of the Basque Country (UPV/EHU) developed a microfluidics device to detect blood biomarkers. The researchers used a stereolithography (SLA) technique that enabled them to generate features as small as 10 µm — a capability that, along with the rapid printing times that the method demonstrated, could help establish 3D printing as a fabrication methodology with strong potential in the microfluidics field.

According to the researchers, the work also shows the potential for microfluidics technology to benefit the plasma separation biomedical devices market.

The researchers developed an ultraviolet (UV)-sensitive resin formulation and combined it with SLA, built and optimized a prototype of an operational microfluidic plasma separation module, and developed an iterative optimization process and evaluated the process with 17 different device designs with printing times ranging from 5 to 12 minutes.

Each device was tested individually, and the performance information was implemented in the next device configuration. This resulted in a final, operative device with many improved characteristics based on previous iterations.

The researchers experimented with three different resin formulations for device fabrication. Each resin was composed of a monomer, a UV absorber, and a photoinitiator. Although not all the formulations worked for the plasma separator, the results demonstrated the potential of customizing the device materials using resins with application-targeted properties, according to the researchers.

The team used a custom-made, high-resolution digital light processing-stereolithography (DLP-SLA) 3D printer to fabricate the microfluidic devices. The 3D printer used a 365-nm LED, and it provided a pixel size of 7.6 µm in the image plane and a layer thickness of 10 µm. Prototype devices were built on silanized glass microscope slides that were attached to the 3D printing platform before each print job. After printing, the researchers flushed isopropyl alcohol through the device channels to remove any remaining unpolymerized resin. The devices were cured under a 430-nm LED for 20 minutes.

During experiments with the device prototypes, the researchers took images with a 20 MP + 2 MP dual camera with f/1.8 aperture. They converted the original color images to 8-bit grayscale and then measured the black and white value of each image on a scale from 0 to 255. The whole blood input sample and the separated plasma were both measured, enabling the researchers to determine the quality of the plasma through image analysis.

Image analysis revealed that the amount of red blood cells in the separated plasma was reduced to half its value in the input sample. The analysis approach used in the plasma separation module is faster than traditional analysis methods. It is also less prone to errors because it requires less human intervention.

With only 12 µL of input sample required, the microfluidic device module could be applied at the point of need, with minimal invasiveness of the sample.

Fernando Benito-López, senior researcher in the UPV/EHU’s Microfluidics Cluster. Researchers at the UPV/EHU-University of the Basque Country developed a microfluidic plasma separator to optically detect blood biomarkers. Courtesy of Nuria González and UPV/EHU.

The optimized prototype highlights the potential improvements that microfluidics can bring to medical devices and analyses. In addition, it does so while working with very small sample sizes, according to the researchers.

“Imagine a channel measuring about 5 or 10 µm, whose surface is functionalized with receptors to capture a certain molecule, or biomarker, from the blood and analyze it using fluorescence,” said professor Fernando Benito-López.

In such a setup, red blood cells would prevent the fluorescence from being seen. Blood cells interfere with many biomarker determinations, leading to inaccurate concentration values.

“We have created a kind of hole in which the white and red blood cells are removed by gravity,” Benito-López said. “That way, only the plasma passes through the channel, and any interference that might occur in the integrated optical detection system is eliminated.”

According to Benito-López, the new system allows the entire analysis process to be integrated into a fluidic device. His team said that its work will facilitate the production of one-piece, 3D-printed devices fitted with integrated plasma separation components to detect biomarkers in the blood.

The microfluidic device produced to separate plasma from blood reliably demonstrated the potential of stereolithographic 3D printing technology for microfabrication. “An optimal fluidic structure can be achieved much faster than by using conventional methods, such as photolithography,” Benito-López said.

The research was published in the journal Polymers (www.doi.org/10.3390/polym14132537).