Search for: All records

Abstract This work investigates the influence of dielectrophoretic forces on the structural features and the resulting aggregates of a chromogenic model system, peptide‐diacetylene (D₃GV‐DA) amphiphiles. Here, we systematically investigate how non‐uniform electric fields impact the (i) peptide‐directed supramolecular assembly stage and (ii) topochemical photopolymerization stage of polydiacetylenes (PDAs) in a quadrupole‐based dielectrophoresis (DEP) device, as well as the (iii) manipulation of D₃GV‐DA aggregates in a light‐induced DEP (LiDEP) platform. The conformation‐dependent chromatic phases of peptide‐PDAs are utilized to probe the chain‐level effect of DEP exposure after the supramolecular assembly or after the topochemical photopolymerization stage. Steady‐state spectroscopic and microscopy analyses show that structural features such as the chirality and morphologies of peptidic 1‐D nanostructures are mostly conserved upon DEP exposure, but applying mild, non‐uniform fields at the self‐assembly stage is sufficient for fine‐tuning the chromatic phase ratio in peptide‐PDAs and manipulating their aggregates via LiDEP. Overall, this work provides insights into how non‐uniform electric fields offer a controllable approach to fine‐tune or preserve the molecularly preset assembly order of DEP‐responsive supramolecular or biopolymeric assemblies, as well as manipulate their aggregates using light projections, which have future implications for the precision fabrication of macromolecular systems with hierarchical structure‐dependent function. 

Abstract Human mesenchymal stem cells (hMSCs) have gained traction in transplantation therapy due to their immunomodulatory, paracrine, immune‐evasive, and multipotent differentiation potential. The inherent heterogeneity of hMSCs poses a challenge for therapeutic treatments and necessitates the identification of robust biomarkers to ensure reproducibility in both in vivo and in vitro experiments. In this study, we utilized dielectrophoresis (DEP), a label‐free electrokinetic phenomenon, to investigate the heterogeneity of hMSCs derived from bone marrow (BM) and adipose tissue (AD). The electrical properties of BM‐hMSCs were compared to homogeneous mouse fibroblasts (NIH‐3T3), human fibroblasts (WS1), and human embryonic kidney cells (HEK‐293). The DEP profile of BM‐hMSCs differed most from HEK‐293 cells. We compared the DEP profiles of BM‐hMSCs and AD‐hMSCs and found that they have similar membrane capacitances, differing cytoplasm conductivity, and transient slopes. Inducing both populations to differentiate into adipocyte and osteoblast cells revealed that they behave differently in response to differentiation‐inducing cytokines. Histology and reverse transcription‐quantitative polymerase chain reaction (RT‐qPCR) analyses of the differentiation‐related genes revealed differences in heterogeneity between BM‐hMSCs and AD‐hMSCs. The differentiation profiles correlate well with the DEP profiles developed and indicate differences in the heterogeneity of BM‐hMSCs and AD‐hMSCs. Our results demonstrate that using DEP, membrane capacitance, cytoplasm conductivity, and transient slope can uniquely characterize the inherent heterogeneity of hMSCs to guide robust and reproducible stem cell transplantation therapies. 

We created an integrated microfluidic cell separation system that incorporates hydrophoresis and dielectrophoresis modules to facilitate high-throughput continuous cell separation. The hydrophoresis module consists of a serpentine channel with ridges and trenches to generate a diverging fluid flow that focuses cells into two streams along the channel edges. The dielectrophoresis module is composed of a chevron-shaped electrode array. Separation in the dielectrophoresis module is driven by inherent cell electrophysiological properties and does not require cell-type-specific labels. The chevron shape of the electrode array couples with fluid flow in the channel to enable continuous sorting of cells to increase throughput. We tested the new system with mouse neural stem cells since their electrophysiological properties reflect their differentiation capacity (e.g., whether they will differentiate into astrocytes or neurons). The goal of our experiments was to enrich astrocyte-biased cells. Sorting parameters were optimized for each batch of neural stem cells to ensure effective and consistent separations. The continuous sorting design of the device significantly improved sorting throughput and reproducibility. Sorting yielded two cell fractions, and we found that astrocyte-biased cells were enriched in one fraction and depleted from the other. This is an advantage of the new continuous sorting device over traditional dielectrophoresis-based sorting platforms that target a subset of cells for enrichment but do not provide a corresponding depleted population. The new microfluidic dielectrophoresis cell separation system improves label-free cell sorting by increasing throughput and delivering enriched and depleted cell subpopulations in a single sort.