Multiple Myeloma Cell Drug Responses Differ in Thermoplastic vs PDMS Microfluidic Devices

Poly­(dimethylsiloxane) (PDMS) is a commonly used elastomer for fabricating microfluidic devices, but it has previously been shown to absorb hydrophobic molecules. Although this has been demonstrated for molecules such as estrogen and Nile Red, the absorption of small hydrophobic molecules in PDMS specifically used to treat cancer and its subsequent impact on cytotoxicity measurements and assays have not been investigated. This is critical for the development of microfluidic chemosensitivity and resistance assay (CSRA) platforms that have shown potential to help guide clinical therapy selection and which rely on the accuracy of the readout involving interactions between patient-derived cells and cancer drugs. It is thus important to address the issue of drug absorption into device material. We investigated drug absorption into microfluidic devices by treating multiple myeloma (MM) tumor cells with two MM drugs (bortezomib (BTZ) and carfilzomib (CFZ)) in devices fabricated using three different materials (polystyrene (PS), cyclo-olefin polymer (COP), and PDMS). Half-maximal inhibitory concentrations (IC₅₀) were obtained for each drug–material combination, and an increase in IC₅₀ of ∼4.3× was observed in PDMS devices compared to both thermoplastic devices. Additionally, each MM drug was exposed to polymer samples, and samples were analyzed using time-of-flight secondary ion mass spectrometry (ToF-SIMS) to characterize adsorption and absorption of the drugs into each material. ToF-SIMS data showed the bias observed in IC₅₀ values found in PDMS devices was directly related to the absorption of drug during dose–response experiments. Specifically, BTZ and CFZ absorption in both PS and COP were all in the range of ∼100–300 nm, whereas BTZ and CFZ absorption in PDMS was ∼5.0 and ∼3.5 μm, respectively. These results highlight the biases that exist in PDMS devices and the importance of material selection in microfluidic device design, especially in applications involving drug cytotoxicity and hydrophobic molecules

Fluorescence-Based Assessment of Plasma-Induced Hydrophilicity in Microfluidic Devices via Nile Red Adsorption and Depletion

We present a simple method, called fluorescence-based assessment of plasma-induced hydrophilicity (FAPH), that enables spatial mapping of the local hydrophilicity of surfaces normally inaccessible by traditional contact angle measurement techniques. The method leverages the change in fluorescence of a dye, Nile Red, which is adsorbed on an oxygen plasma-treated surface, and its correlation with the contact angle of water. Using FAPH, we explored the effect of microchannel geometries on the penetration distance of oxygen plasma into a microchannel and found that entrance effects prevent uniform treatment. We showed that these variations have a significant impact on cell culture, and thus the design of cell-based microfluidic assays must consider this phenomenon to obtain repeatable and homogeneous results

Microfluidic Multiculture Assay to Analyze Biomolecular Signaling in Angiogenesis

Angiogenesis (the formation of blood vessels from existing blood vessels) plays a critical role in many diseases such as cancer, benign tumors, and macular degeneration. There is a need for cell culture methods capable of dissecting the intricate regulation of angiogenesis within the microenvironment of the vasculature. We have developed a microscale cell-based assay that responds to complex pro- and antiangiogenic soluble factors with an <i>in vitro</i> readout for vessel formation. The power of this system over traditional techniques is that we can incorporate the whole milieu of soluble factors produced by cells <i>in situ</i> into one biological readout (vessel formation), even if the identity of the factors is unknown. We have currently incorporated macrophages, endothelial cells, and fibroblasts into the assay, with the potential to include additional cell types in the future. Importantly, the microfluidic platform is simple to operate and multiplex to test drugs targeting angiogenesis in a more physiologically relevant context. As a proof of concept, we tested the effect of an enzyme inhibitor (targeting matrix metalloproteinase 12) on vessel formation; the triculture microfluidic assay enabled us to capture a dose-dependent effect entirely missed in a simplified coculture assay (<i>p</i> < 0.0001). This result underscores the importance of cell-based assays that capture chemical cross-talk occurring between cell types. The microscale dimensions significantly reduce cell consumption compared to conventional well plate platforms, enabling the use of limited primary cells from patients in future investigations and offering the potential to screen therapeutic approaches for individual patients <i>in vitro</i>