Christoph Jurischka, Brandenburg University of Technology Cottbus-Senftenberg, Germany

BACKGROUND: 3D printing is becoming increasingly relevant as manufacturing technology of functional models for bioanalytical applications. Modern 3D printing systems achieve high print quality and accuracy and are used to produce devices for sample preparation and point-of-care testing.

OBJECTIVE: In addition to the printing parameters, the material properties melting behavior and autofluorescence are decisive for the optimal printing process and the applicability of the product. These are influenced by additives and vary considerably depending on the manufacturer. There is little information in the literature on how this affects the development of bioanalytical devices for functional assays.

METHODS: We have produced chips for bioanalytical applications from commercially available white, black and colored thermoplastic polymers (polylactic acid (PLA), polyethylene terephthalate glycol (PETG), acrylonitrile-butadiene-styrene (ABS), thermoplastic polyurethane elastomers (TPU)) using a melt-layer process. All of the materials have an unknown chemical composition. The materials were characterized by differential scanning calorimetry, fluorescence spectroscopy and functional assays with a DNA capture assay, a model for cell adhesion (human), a bacterial adhesion and biofilm formation test.

RESULTS: PLA and ABS materials had a high autofluorescence between 350 nm and 650 nm depending on their color. Colored TPU and PETG had a strong autofluorescence even in the red range (~710 nm). Black PLA and ABS materials had the lowest autofluorescence and was useable in the red and near-infrared range. White and natural PLA had a strong autofluorescence in the range of 350-600 nm. Detection of fluorescent DNA probes and cell adhesion to the materials was possible. For fluorescence-based methods, untreated, deep black filaments (PLA, ABS) was preferred, which showed low autofluorescence only in the short-wave range of 300-400 nm. When used in temperature ranges below 40 °C, PLA materials were more suitable than PETG, ABS or TPU. PLA was suitable for bioanalytical purposes due to its temperature profile, a glass transition temperature of almost 60 °C, resistance to common laboratory chemicals and easy handling during printing. For temperature-critical methods, such as hybridization reactions up to 90 °C, ABS was better suited due to a glass transition temperature of approximately 100 °C.

CONCLUSIONS: While 3D printing can be used to create custom and cost-effective prototypes, a variety of material properties must be considered if functional assays are to be developed. From the 14 tested material we found only black ABS and some black PLA useable for fluorescence-based assays. Autofluorescence was not a disadvantage per se, but can also be used as a reference signal in the assay. The rapid development of individual protocols for sample processing and analysis required the availability of a material with consistent quality over time. The use of commercial standard materials did not seem to fulfill this requirement.