Parallelizable Microfluidic Platform to Model and Assess In Vitro Cellular Barriers: Technology and Application to Study the Interaction of 3D Tumor Spheroids with Cellular Barriers

Endothelial and epithelial cellular barriers play a vital role in the selective transport of solutes and other molecules. The properties and function of these barriers are often affected in case of inflammation and disease. Modelling cellular barriers in vitro can greatly facilitate studies of inflammation, disease mechanisms and progression, and in addition, can be exploited for drug screening and discovery. Here, we report on a parallelizable microfluidic platform in a multiwell plate format with ten independent cell culture chambers to support the modelling of cellular barriers co-cultured with 3D tumor spheroids. The microfluidic platform was fabricated by microinjection molding. Electrodes integrated into the chip in combination with a FT-impedance measurement system enabled transepithelial/transendothelial electrical resistance (TEER) measurements to rapidly assess real-time barrier tightness. The fluidic layout supports the tubeless and parallelized operation of up to ten distinct cultures under continuous unidirectional flow/perfusion. The capabilities of the system were demonstrated with a co-culture of 3D tumor spheroids and cellular barriers showing the growth and interaction of HT29 spheroids with a cellular barrier of MDCK cells.

Micro-Injection Molding of Polymer Nanocomposites Composition-Process-Properties Relationship

The mechanical, electrical, thermal, and rheological properties of micro injection molded nanocomposites comprising 2% and 5% carbon nanotubes (CNTs) incorporated in polycarbonate (PC), and polyamide 66 (PA) were studied. The design of experiments method was used to investigate the composition-process – properties relationship. Results indicated that the process variables significantly affected the flow patterns and resulting morphology during the filling stage of the microinjection molding (lIM) process, using 0.45 mm diameter lIM samples. Two distinct flow regimes have been identified in lIM using the low cross-section samples. The first was a conventional “fountain flow,” which resulted in a skin/core structure and reduced volume resistivity up to 10 X cm in the case of 5% CNTs and up to 100 X cm in 2% CNTs, in both polymers, respectively. In addition, inferior mechanical properties were obtained, attributed to polymer degradation under high shear rate conditions, when practicing high injection speeds, high mold temperatures, and high screw rotation velocities. The second was a “plug flow” due to wall slippage, obtained under low injection speeds, low mold temperatures, and low rotation velocities, leading to a substantial increase in modulus of elasticity (60%) with increased electrical resistivity up to 103 X cm for 5% CNTs and 105 X cm for 2% CNTs, respectively. The rheological percolation threshold was obtained at 2% CNTs while the electrical threshold was attained at 0.4% CNTs, in both polymers. It was concluded that in lIM, the process conditions should be closely monitored. In the case of high viscous heating, degradation of mechanical properties was obtained, while skin- core morphology formation enhanced electrical conductivity.

Moldability improvement in microinjection molding via film lamination

The purpose of this study is to integrate a polymeric film onto a mold to impede thermal heat transfer during resin infusion. A thin plastic plate was fabricated by using microinjection molding. A polyimide (PI) film was laminated onto a mold in an effort to produce a thin light guide plate (LGP). The film could decelerate the solidification of molten polymer in the cavity of mold and enhance the wall slip of resin on the mold. The insulation effect was modeled numerically. The surface roughness and pattern transfer characteristics of the LGP were evaluated. It was found that the fluidity of the resin increased due to the decreased skin layer during mold filling. The results showed that the strategy proposed in this study could help decrease the thickness of LGP effectively when manufacturing the part via injection molding.

Microinjection Molding of Out-of-Plane Bistable Mechanisms

We present a novel fabrication technique of a miniaturized out-of-plane compliant bistable mechanism (OBM) by microinjection molding (MM) and assembling. OBMs are mostly in-plane monolithic devices containing delicate elastic elements fabricated in metal, plastic, or by a microelectromechanical system (MEMS) process. The proposed technique is based on stacking two out-of-plane V-beam structures obtained by mold fabrication and MM of thermoplastic polyacetal resin (POM) and joining their centers and outer frames to construct a double V-beam structure. A copper alloy mold insert was machined with the sectional dimensions of the V-beam cavities. Next, the insert was re-machined to reduce dimensional errors caused by part shrinkage. The V-beam structure was injection-molded at a high temperature. Gradually elongated short-shots were obtained by increasing pressure, showing the symmetrical melt filling through the V-beam cavities. The as-molded structure was buckled elastically by an external-force load but showed a monostable behavior because of a higher unconstrained buckling mode. The double V-beam device assembled with two single-molded structures shows clear bistability. The experimental force-displacement curve of the molded structure is presented for examination. This work can potentially contribute to the fabrication of architected materials with periodic assembly of the plastic bistable mechanism for diverse functionalities, such as energy absorption and shape morphing.

Crystallization and Microstructure Evolution of Microinjection Molded Isotactic Polypropylene with the Assistance of Poly(Ethylene Terephthalate)

In this work, a series of isotactic polypropylene/poly(ethylene terephthalate) (iPP/PET) samples were prepared by microinjection molding (μIM) and mini-injection molding (IM). The properties of the samples were investigated in detail by differential scanning calorimetry (DSC), Wide-Angle X-ray Diffraction (WAXD), Polarized light microscope (PLM) and scanning electron microscopy (SEM). Results showed that the difference in thermomechanical history between both processing methods leads to the formation of different microstructures in corresponding iPP/PET moldings. For example, the dispersed spherical PET phase deforms and emerges into continuous in-situ microfibrils due to the intensive shearing flow field and temperature field in μIM. Additionally, the incorporation of PET facilitates both the laminar branching and the reservation of oriented molecular chains, thereby leading to forming a typical hybrid structure (i.e., fan-shaped β-crystals and transcrystalline). Furthermore, more compact and higher degrees of oriented structure can be obtained via increasing the content of PET. Such hybrid structure leads to a remarkable enhancement of mechanical property in terms of μIM samples.