A Feature-Specific Local Cooling System to Control Tensile Strength and Dimensional Accuracy in Fused Filament Fabrication.

There is in-depth understanding of the effects and interactions of various process parameters on the mechanical properties and dimensional accuracy of parts produced through fused filament fabrication (FFF). Surprisingly, local cooling in FFF has been largely overlooked and is only rudimentarily implemented. It is, however, a decisive element of the thermal conditions governing the FFF process and of particular importance when processing high-temperature polymers such as polyether ether ketone (PEEK). This study, therefore, proposes an innovative local cooling strategy, which allows for feature-specific local cooling (FLoC). This is enabled by a newly developed hardware in combination with a G-code postprocessing script. The system was implemented on a commercially available FFF printer and its potential was demonstrated by addressing typical drawbacks of the FFF process. Specifically, with FLoC, the conflicting requirements for optimal tensile strength versus optimal dimensional accuracy could be balanced. Indeed, feature-specific (i.e., perimeter vs. infill) control of thermal conditions resulted in a significant increase in ultimate tensile strength and in strain at failure in upright printed PEEK tensile bars compared with those manufactured with constant local cooling-without sacrificing the dimensional accuracy. Furthermore, to improve the surface quality of downward-facing structures the controlled introduction of predetermined breaking points at feature-specific part/support interfaces was demonstrated. The findings of this study prove the importance and capabilities of the new advanced local cooling system in high-temperature FFF and provide further directions on the process development of FFF in general.

Additive-manufactured microporous polymer membranes for biomedical in vitro applications.

Microscale porous membranes are used in a wide range of technical and medical applications such as water treatment, dialysis and in vitro test systems. A promising approach to control membrane properties and overcome limitations of conventional fabrication techniques is given by additive manufacturing (AM). In this study, we designed and printed a microporous membrane via digital light processing and validated its use for biomedical in vitro applications based on the example of a cell culture insert. A multi-layer technique was developed, resulting in an eight-layer membrane with an average pore diameter of 25 µm. Image analyses proved the printing accuracy to be high with small deviations for an increasing number of layers. Permeability tests with brilliant blue FCF (E133, triarylmethane dye) and growth factors comparing the printed to track-etched membranes showed similar transfer dynamics and confirmed sufficient separation properties. Overall, the results showed that printing microporous polymer membranes is possible and highlight the potential of AM for biomedical in vitro applications such as cell culture inserts, scaffolds for tissue engineering or bioreactors.

In Vivo-Like Culture Conditions in a Bioreactor Facilitate Improved Tissue Quality in Corneal Storage.

The cornea is the most-transplanted tissue worldwide. However, the availability and quality of grafts are limited due to the current methods of corneal storage. In this study, a dynamic bioreactor system is employed to enable the control of intraocular pressure and the culture at the air-liquid interface. Thereby, in vivo-like storage conditions are achieved. Different media combinations for endothelium and epithelium are tested in standard and dynamic conditions to enhance the viability of the tissue. In contrast to culture conditions used in eye banks, the combination of the bioreactor and biochrom medium 1 allows to preserve the corneal endothelium and the epithelium. Assessment of transparency, swelling, and the trans-epithelial-electrical-resistance (TEER) strengthens the impact of the in vivo-like tissue culture. For example, compared to corneas stored under static conditions, significantly lower optical densities and significantly higher TEER values were measured (p-value <0.05). Furthermore, healing of epithelial defects is enabled in the bioreactor, characterized by re-epithelialization and initiated stromal regeneration. Based on the obtained results, an easy-to-use 3D-printed bioreactor composed of only two parts was derived to translate the technology from the laboratory to the eye banks. This optimized bioreactor facilitates noninvasive microscopic monitoring. The improved storage conditions ameliorate the quality of corneal grafts and the storage time in the eye banks to increase availability and reduce re-grafting.

Embedded Disposable Functionalized Electrochemical Biosensor with a 3D-Printed Flow Cell for Detection of Hepatic Oval Cells (HOCs).

Hepatic oval cells (HOCs) are considered the progeny of the intrahepatic stem cells that are found in a small population in the liver after hepatocyte proliferation is inhibited. Due to their small number, isolation and capture of these cells constitute a challenging task for immunosensor technology. This work describes the development of a 3D-printed continuous flow system and exploits disposable screen-printed electrodes for the rapid detection of HOCs that over-express the OV6 marker on their membrane. Multiwall carbon nanotube (MWCNT) electrodes have a chitosan film that serves as a scaffold for the immobilization of oval cell marker antibodies (anti-OV6-Ab), which enhance the sensitivity of the biomarker and makes the designed sensor specific for oval cells. The developed sensor can be easily embedded into the 3D-printed flow cell to allow cells to be exposed continuously to the functionalized surface. The continuous flow is intended to increase capture of most of the target cells in the specimen. Contact angle measurements were performed to characterize the nature and quality of the modified sensor surface, and electrochemical measurements (cyclic voltammetry (CV) and square wave voltammetry (SWV)) were performed to confirm the efficiency and selectivity of the fabricated sensor to detect HOCs. The proposed method is valuable for capturing rare cells and could provide an effective tool for cancer diagnosis and detection.