Elastomeric microparticles for acoustic mediated bioseparations.

BACKGROUND: Acoustophoresis has been utilized successfully in applications including cell trapping, focusing, and purification. One current limitation of acoustophoresis for cell sorting is the reliance on the inherent physical properties of cells (e.g., compressibility, density) instead of selecting cells based upon biologically relevant surface-presenting antigens. Introducing an acoustophoretic cell sorting approach that allows biochemical specificity may overcome this limitation, thus advancing the value of acoustophoresis approaches for both the basic research and clinical fields. RESULTS: The results presented herein demonstrate the ability for negative acoustic contrast particles (NACPs) to specifically capture and transport positive acoustic contrast particles (PACPs) to the antinode of an ultrasound standing wave. Emulsification and post curing of pre-polymers, either polydimethylsiloxane (PDMS) or polyvinylmethylsiloxane (PVMS), within aqueous surfactant solution results in the formation of stable NACPs that focus onto pressure antinodes. We used either photochemical reactions with biotin-tetrafluorophenyl azide (biotin-TFPA) or end-functionalization of Pluronic F108 surfactant to biofunctionalize NACPs. These biotinylated NACPs bind specifically to streptavidin polystyrene microparticles (as cell surrogates) and transport them to the pressure antinode within an acoustofluidic chip. CONCLUSION: To the best of our knowledge, this is the first demonstration of using NACPs as carriers for transport of PACPs in an ultrasound standing wave. By using different silicones (i.e., PDMS, PVMS) and curing chemistries, we demonstrate versatility of silicone materials for NACPs and advance the understanding of useful approaches for preparing NACPs. This bioseparation scheme holds potential for applications requiring rapid, continuous separations such as sorting and analysis of cells and biomolecules.

Magnetophoretic circuits: A review of device designs and implementation for precise single-cell manipulation.

Lab-on-a-chip tools have played a pivotal role in advancing modern biology and medicine. A key goal in this field is to precisely transport single particles and cells to specific locations on a chip for quantitative analysis. To address this large and growing need, magnetophoretic circuits have been developed in the last decade to manipulate a large number of single bioparticles in a parallel and highly controlled manner. Inspired by electrical circuits, magnetophoretic circuits are composed of passive and active circuit elements to offer commensurate levels of control and automation for transporting individual bioparticles. These specifications make them unique compared to other technologies in addressing crucial bioanalytical applications and answering fundamental questions buried in highly heterogeneous cell populations. In this comprehensive review, we describe key theoretical considerations for manufacturing and simulating magnetophoretic circuits. We provide a detailed tutorial for operating magnetophoretic devices containing different circuit elements (e.g., conductors, diodes, capacitors, and transistors). Finally, we provide a critical comparison of the utility of these devices to other microchip-based platforms for cellular manipulation, and discuss how they may address unmet needs in single-cell biology and medicine.

Magnetic Cellular Backpacks for Spatial Targeting, Imaging, and Immunotherapy.

Adoptive cell transfer (ACT) therapies are growing in popularity due to their ability to interact with diseased tissues in a specific manner. Disc-shaped particles, or "backpacks", that bind to cellular surfaces show promise for augmenting the therapeutic potential of adoptively transferred cells by resisting phagocytosis and locally releasing drugs to maintain cellular activity over time. However, many ACTs suffer from limited tumor infiltration and retention and lack a method for real-time spatial analysis. Therefore, we have designed biodegradable backpacks loaded with superparamagnetic iron oxide nanoparticles (SPIONs) to improve upon current ACT strategies by (i) controlling the localization of cell-backpack complexes using gradient magnetic fields and (ii) enabling magnetic particle imaging (MPI) to track complexes after injection. We show that magnetic backpacks bound to macrophages and loaded with a proinflammatory drug, resiquimod, maintain anticancer phenotypes of carrier macrophages for 5 days and create cytokine "factories" that continuously release IL-12. Furthermore, we establish that forces generated by gradient magnet fields are sufficient to displace cell-backpack complexes in physiological settings. Finally, we demonstrate that MPI can be used to visualize cell-backpack complexes in mouse tumors, enabling a potential strategy to track the biodistribution of ACTs in real time.

Tissue-adhesive hydrogel for multimodal drug release to immune cells in skin.

Both innate and adaptive immune systems play a crucial role in the pathology of skin diseases. To control these cells, there is a need for transdermal drug delivery systems that can target multiple cell populations at independently tunable rates. Herein, we describe a tissue-adhesive hydrogel system that contains particles capable of regulating the release of small molecule drugs at defined rates. Resiquimod (a macrophage-targeting drug) and palbociclib (a T cell-targeting drug) are encapsulated within two types of silicone particles embedded within the hydrogel. We demonstrate that drug release is mediated by the crosslink density of the particles, which is decoupled from the bulk properties of the hydrogel. We show that this system can be used to sustainably polarize macrophages toward an anti-tumor phenotype in vitro and ex vivo, and that the hydrogels can remain attached to skin explants for several days without generating toxicity. The hydrogel system is compatible with standard dermatological procedures and allows transdermal passage of drugs. The multimodal, tunable nature of this system has implications in treating a variety of skin disorders, managing infections, and delivering vaccines. STATEMENT OF SIGNIFICANCE: We describe a tissue-adhesive hydrogel that can regulate the release of drugs in a manner that is decoupled from its bulk properties. The mechanism of drug release is mediated by embedded microparticles with well-defined crosslink densities. The significance of this system is that, by encapsulating different drugs into the particles, it is possible to achieve multimodal drug release. We demonstrate this capability by releasing two immunomodulatory drugs at disparate rates. A drug that targets innate immune cells is released quickly, and a drug that targets adaptive immune cells is released slowly. This programmable system offers a direct means by which cellular responses can be enhanced through independent targeting for a variety of transdermal applications, including cancer treatment and vaccine delivery.

Magnetic separation of acoustically focused cancer cells from blood for magnetographic templating and analysis.

Liquid biopsies hold enormous promise for the next generation of medical diagnoses. At the forefront of this effort, many are seeking to capture, enumerate and analyze circulating tumor cells (CTCs) as a means to prognosticate and develop individualized treatments for cancer. Capturing these rare cells, however, represents a major engineering challenge due to their low abundance, morphology and heterogeneity. A variety of microfluidic tools have been developed to isolate CTCs from drawn blood samples; however, few of these approaches offer a means to separate and analyze cells in an integrated system. We have developed a microfluidic platform comprised of three modules that offers high throughput separation of cancer cells from blood and on-chip organization of those cells for streamlined analyses. The first module uses an acoustic standing wave to rapidly align cells in a contact-free manner. The second module then separates magnetically labeled cells from unlabeled cells, offering purities exceeding 85% for cells and 90% for binary mixtures of synthetic particles. Finally, the third module contains a spatially periodic array of microwells with underlying micromagnets to capture individual cells for on-chip analyses (e.g., staining, imaging and quantification). This array is capable of capturing with accuracies exceeding 80% for magnetically labeled cells and 95% for magnetic particles. Overall, by virtue of its holistic processing of complex biological samples, this system has promise for the isolation and evaluation of rare cancer cells and can be readily extended to address a variety of applications across single cell biology and immunology.