Development of high-fidelity 3D models to recapitulate the tumor microenvironment is essential for studying tumor biology and discovering anticancer drugs. Here we report a method to engineer the 3D microenvironment of human tumor, by encapsulating cancer cells in the core of microcapsules with a hydrogel shell for miniaturized 3D culture to obtain avascular microtumors first. The microtumors are then used as the building blocks for assembling with endothelial cells and other stromal cells to create macroscale 3D vascularized tumor. Cells in the engineered 3D microenvironment can yield significantly larger tumors in vivo than 2D-cultured cancer cells. Furthermore, the 3D vascularized tumors are 4.7 and 139.5 times more resistant to doxorubicin hydrochloride (a commonly used chemotherapy drug) than avascular microtumors and 2D-cultured cancer cells, respectively. Moreover, this high drug resistance of the 3D vascularized tumors can be overcome by using nanoparticle-mediated drug delivery. The high-fidelity 3D tumor model may be valuable for studying the effect of microenvironment on tumor progression, invasion, and metastasis, and for developing effective therapeutic strategy to fight against cancer.

Dielectrophoresis (DEP) has been widely explored to separate cells for various applications. However, existing DEP devices are limited by the high cost associated with the use of noble metal electrodes, the need of high-voltage electric field, and/or discontinuous separation (particularly for devices without metal electrodes). We developed a DEP device with liquid electrodes, which can be used to continuously separate different types of cells or particles based on positive DEP. The device is made of polydimethylsiloxane (PDMS) and ionic liquid is used to form the liquid electrodes, which has the advantages of low cost and easy fabrication. Moreover, the conductivity gradient is utilized to achieve the DEP-based on-chip cell separation. The device was used to separate polystyrene microbeads and PC-3 human prostate cancer cells with 94.7 and 1.2% of the cells and microbeads being deflected, respectively. This device is also capable of separating live and dead PC-3 cancer cells with 89.8 and 13.2% of the live and dead cells being deflected, respectively. Moreover, MDA-MB-231 human breast cancer cells could be separated from human adipose-derived stem cells (ADSCs) using this device with high purity (81.8 and 82.5% for the ADSC and MDA-MB-231 cells, respectively). Our data suggest the great potential of cell separation based on conductivity-induced DEP using affordable microfluidic devices with easy operation.

A dielectrophoresis (DEP)-based method is reported to achieve highly efficient on-chip extraction of cell-laden microcapsules of any stiffness from oil into aqueous solution. The hydrogel microcapsules can be extracted into the aqueous solution by DEP and interfacial tension (IFT) forces with no trapped oil while the encapsulated cells are free from the electrical damages due to the Faraday cage effect.

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Manipulation of microscale bioparticles including living cells is of great significance to the broad bioengineering and biotechnology fields. Dielectrophoresis (DEP), which is defined as the interactions between dielectric particles and the electric field, is one of the most widely used techniques for the manipulation of bioparticles including cell separation, sorting, and trapping. Bioparticles experience a DEP force if they have a different polarization from the surrounding media in an electric field that is nonuniform in terms of the intensity and/or phase of the electric field. A comprehensive literature survey shows that the DEP-based microfluidic devices for manipulating bioparticles can be categorized according to the methods of creating the nonuniformity via patterned microchannels, electrodes, and media to generate the DEP force. These methods together with the theory of DEP force generation are described in this review, to provide a summary of the methods and materials that have been used to manipulate various bioparticles for various specific biological outcomes. Further developments of DEP-based technologies include identifying materials that better integrate with electrodes than current popular materials (silicone/glass) and improving the performance of DEP manipulation of bioparticles by combining it with other methods of handling bioparticles. Collectively, DEP-based microfluidic manipulation of bioparticles holds great potential for various biomedical applications.

Abstract:Polymers with advanced topological architectures are promising materials for wide applications due to their structure-generated unique properties different from that of the linear analogues. The elegant integration of stimuli-responsive polymers with such advanced architectures can create novel materials with virtues from both moieties, are thus a hot subject of research for both fundamental and practical investigations. To fabricate cyclic brush polymer-based intelligent materials for biomedical applications, herein, we designed and synthesized thermo-sensitive cyclic brush polymers with poly(N-isopropylacrylamide) (PNIPAAm) brushes by controlled living radical polymerization using cyclic multimacroinitiator. The thermo-induced phase transition behaviors of the resultant cyclic brush polymers with different compositions were investigated in detail by temperature-dependent optical transmittance measurements, and compared with the properties of bottlebrush and linear counterparts. Interestingly, the cloud point transition temperature (T cp ) of cyclic brush PNIPAAm could be regulated by the chain length of PNIPAAm brush. Although the bottlebrush polymers with the same composition exhibited similarly structurally dependent T cp s behaviors to the cyclic brush polymers, the cyclic brush PNIPAAm did show higher critical aggregation concentration (CAC) and enhanced stability against dilution than the bottlebrush counterpart. The readily tailorable T cp s together with the ability to form highly stable nanoparticles makes thermo-sensitive cyclic brush PNIPAAm a promising candidate for controlled drug delivery.

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Efficient capture of rare circulating tumor cells (CTCs) from blood samples is valuable for early cancer detection to improve the management of cancer. In this work, we developed a highly efficient microfluidics-based method for detecting CTCs in human blood. This is achieved by creating separate capture and flow zones in the microfluidic device (ZonesChip) and using patterned dielectrophoretic force to direct cells from the flow zone into the capture zone. This separation of the capture and flow zones minimizes the negative impact of high flow speed (and thus high throughput) and force in the flow zone on the capture efficiency, overcoming a major bottleneck of contemporary microfluidic approaches using overlapping flow and capture zones for CTC detection. When the flow speed is high (≥ 0.58 mm/s) in the flow zone, the separation of capture and flow zones in our ZonesChip could improve the capture efficiency from ~0% (for conventional device without separating the two zones) to ~100%. Our ZonesChip shows great *