A benchtop capillary flow layer-by-layer (CF-LbL) platform for rapid assembly and screening of biodegradable nanolayered films

Direct monitoring of protease activity using an integrated microchip coated with multilayered fluorogenic nanofilms

Proteases play an essential role in the four sequential but overlapping phases of wound healing: hemostasis, inflammation, proliferation, and remodeling. In chronic wounds, excessive protease secretion damages the newly formed extracellular matrix, thereby delaying or preventing the normal healing process. Peptide-based fluorogenic sensors provide a visual platform to sense and analyze protease activity through changes in the fluorescence intensity. Here, we have developed an integrated microfluidic chip coated with multilayered fluorogenic nanofilms that can directly monitor protease activity. Fluorogenic protease sensors were chemically conjugated to polymer films coated on the surface of parallel microfluidic channels. Capillary flow layer-by-layer (CF-LbL) was used for film assembly and combined with subsequent sensor modification to establish a novel platform sensing technology. The benefits of our platform include facile fabrication and processing, controllable film nanostructure, small sample volume, and high sensitivity. We observed increased fluorescence of the LbL nanofilms when they were exposed to model recombinant proteases, confirming their responsiveness to protease activity. Increases in the nanofilms' fluorescence intensity were also observed during incubation with liquid extracted from murine infected wounds, demonstrating the potential of these films to provide real-time, in situ information about protease activity levels.

Nanoparticle modification of microfluidic cell separation for cancer cell detection and isolation

We present a nanoparticle surface modification approach to improve the microfluidic performance in detecting cancer cells. Multiple cancer cell lines were included in this work, and the capture ability of the chip with surface modification reached a significant increase.

Effective reduction of non-specific binding of blood cells in a microfluidic chip for isolation of rare cancer cells

The high purity of target cells enriched from blood samples plays an important role in the clinical detection of diseases. However, non-specific binding of blood cells in the isolated cell samples can complicate downstream molecular and genetic analysis. In this work, we report a simple solution to non-specific binding of blood cells by modifying the surface of microchips with a multilayer nanofilm, with the outmost layer containing both PEG brushes for reducing blood cell adhesion and antibodies for enriching target cells. This layer-by-layer (LbL) polysaccharide nanofilm was modified with neutravindin and then conjugated with a mixture of biotinylated PEG molecules and biotinylated antibodies. Using EpCAM-expressing and HER2-expressing cancer cells in blood as model platforms, we were able to dramatically reduce the non-specific binding of blood cells to approximately 1 cell per mm2 without sacrificing the high capture efficiency of the microchip. To support the rational extension of this approach to other applications for cell isolation and blood cell resistance, we conducted extensive characterization on the nanofilm formation and degradation, antifouling with PEG brushes and introducing functional antibodies. This simple, yet effective, approach can be applied to a variety of microchip applications that require high purity of sample cells containing minimal contamination from blood cells.

Microfluidic preparation, shrinkage, and surface modification of monodispersed alginate microbeads for 3D cell culture

Functionalized alginate microbeads (MB) have been widely used for three-dimensional (3D) culture of cells and creating biomimetic tissue models. However, conventional methods for preparing these MB suffer from poor polydispersity, due to coalescence of droplets during the gelation process and post-aggregation. It remains an immense challenge to prepare alginate MB with narrow size distribution and uniform shape, especially when their diameters are similar to the size of cells. In this work, we developed a simple method to produce monodispersed, cell-size alginate MB through microfluidic emulsification, followed by a controlled shrinkage process and gelation in mineral oil with low concentration of calcium ion (Ca²⁺). During the gelation process caused by the diffusion of Ca²⁺ from the oil to water phase, a large amount of satellite droplets with sub-micrometer sizes was formed at the water/oil interface. As a result, each original droplet was transformed to one shrunken-MB with much smaller size and numerous submicron-size satellites. To explore the feasibility of the shrunken-MB for culturing with cells, we have successfully modified a variety of polymer nanofilms on MB surfaces using a layer-by-layer assembly approach. Finally, the nanofilm-modified MB was applied to a 3D culture of GFP-expressing fibroblast cells and demonstrated good biocompatibility.

Cell-size alginate microbeads for 3D cell culture were prepared by microfluidic emulsification and controlled shrinkage, followed by nanofilm modification.

Layer-by-layer assembly of nanofilms to control cell functions

Control of cell functions by layer-by-layer assembly has a great challenge in tissue engineering and biomedical applications. We summarize current hot approaches in this review.

Enhanced capture and release of circulating tumor cells using hollow glass microspheres with a nanostructured surface

Self-floating hollow glass microspheres (HGMS) modified with tumor-specific antibodies have been developed for the capture of circulating tumor cells (CTCs), and have demonstrated effective cell isolation and good viability of isolated cancer cells. However, the capture efficiency decreases dramatically if the spiked cell concentration is low, possibly due to insufficient interactions between cancer cells and the HGMS surface. In order to apply HGMS-based CTC isolation to clinically relevant samples, it is desirable to create nanostructures on the surface of HGMS to enhance cell-surface interactions. Nevertheless, current microfabrication methods cannot generate nanostructured-surfaces on microspheres. The authors have developed a new HGMS with a controlled nanotopographical surface structure (NSHGMS), and demonstrated isolation and recovery of rare cancer cells. NSHGMS are achieved by applying layer-by-layer (LbL) assembly of negatively charged SiO2 nanoparticles and positively charged poly-l-arginine molecules, then sheathing the surface with an enzymatically degradable LbL film made from biotinylated alginate and poly-l-arginine, and capping with anti-EpCAM antibodies and anti-fouling PEG molecules. Compared to smooth-surfaced HGMS, NSHGMS showed shorter isolation time (20 min), enhanced capture efficiency (93.6 ± 4.9%) and lower detection limit (30 cells per mL) for commonly used cancer cell lines (MCF7, SK-BR-3, PC-3, A549 and CCRF-CEM). This NSHGMS-based CTC isolation method does not require specialized lab equipment or an external power source, and thus, can be used for the separation of targeted cells from blood or other body fluids in a resource-limited environment.

In vitro blood cell viability profiling of polymers used in molecular assembly

Biocompatible polymers have been extensively applied to molecular assembly techniques on a micro- and nanoscale to miniaturize functional devices for biomedical uses. However, cytotoxic assessments of developed devices are prone to partially focus on non-specific cells or cells associated with the specific applications. Thereby, since toxicity is dependent on the type of cells and protocols, we do not fully understand the relative toxicities of polymers. Additionally, we need to ensure the blood cell biocompatibility of developed devices prior to that of targeted cells because most of the devices contact the blood before reaching the targeted regions. Motivated by this issue, we focused on screening cytotoxicity of polymers widely used for the layer-by-layer assembly technique using human blood cells. Cytotoxicity at the early stage was investigated on twenty types of polymers (positively charged, negatively charged, or neutral) and ten combination forms via hemolysis, cell viability, and AnnexinV-FITC/PI staining assays. We determined their effects on the cell membrane depending on their surface chemistry by molecular dynamics simulations. Furthermore, the toxicity of LbL-assembled nanofilms was assessed by measuring cell viability. Based on this report, researchers can produce nanofilms that are better suited for drug delivery and biomedical applications by reducing the possible cytotoxicity.

Cell Isolation and Recovery Using Hollow Glass Microspheres Coated with Nanolayered Films for Applications in Resource-Limited Settings

Established cell isolation and purification techniques such as fluorescence-activated cell sorting (FACS), isolation through magnetic micro/nanoparticles, and recovery via microfluidic devices have limited application as disposable technologies appropriate for point-of-care use in remote areas where lab equipment as well as electrical, magnetic, and optical sources are restricted. We report a simple yet effective method for cell isolation and recovery that requires neither specialized lab equipment nor any form of power source. Specifically, self-floating hollow glass microspheres were coated with an enzymatically degradable nanolayered film and conjugated with antibodies to allow both fast capture and release of subpopulations of cells from a cell mixture. Targeted cells were captured by the microspheres and allowed to float to the top of the hosting liquid, thereby isolating targeted cells. To minimize nonspecific adhesion of untargeted cells and to enhance the purity of the isolated cell population, an antifouling polymer brush layer was grafted onto the nanolayered film. Using the EpCAM-expressing cancer cell line PC-3 in blood as a model system, we have demonstrated the isolation and recovery of cancer cells without compromising cell viability or proliferative potential. The whole process takes less than 1 h. To support the rational extension of this platform technology, we introduce extensive characterization of the critical design parameters: film formation and degradation, grafting with a poly(ethylene glycol) (PEG) sheath, and introducing functional antibodies. Our approach is expected to overcome practical hurdles and provide viable targeted cells for downstream analyses in resource-limited settings.