Sprouting angiogenesis under a chemical gradient regulated by interactions with an endothelial monolayer in a microfluidic platform.

Microfluidic cell culture assays are versatile tools for studying cell migration, particularly angiogenesis. Such assays can deliver precisely controlled linear gradients of chemical stimuli to cultured cells in a microfluidic channel, offering excellent optical resolution and in situ monitoring of cellular morphogenesis in response to a gradient. Microfluidic cell culture assays provide a chemical gradient subject to molecular diffusion, although cellular metabolism can perturb it. The actual gradient perturbed by cells has not been precisely described in the context of regulated cellular morphogenesis. We modeled the chemical gradient in a microfluidic channel by simulating the analyte(VEGF) distribution during cellular interactions. The results were experimentally verified by monitoring sprouting angiogenic response from a monolayer of human umbilical vein endothelial cells (hUVECs) into a type 1 collagen scaffold. The simulation provided a basis for understanding a real distribution of the analyte interrupted by cells in microfluidic device. The new protocol enables one to quantify the morphogenesis of hUVECs under a flat, less-steep, or steep gradient.

A low-energy-consumption electroactive valveless hydrogel micropump for long-term biomedical applications.

Stimuli-responsive hydrogels have attracted considerable interest in the field of microfluidics due to their ability to transform electrical energy directly into mechanical work through swelling, bending, and other deformations. In particular, electroactive hydrogels hold great promise for biomedical micropumping applications such as implantable drug delivery systems. In such applications, energy consumption rate and durability are key properties. Here, we developed a valveless micropump system that utilizes a hydrogel as the main actuator, and tested its performance over 6 months of continuous operation. The proposed micropump system, powered by a single 1.5 V commercial battery, expended very little energy (less than 750 µWs per stroke) while pumping 0.9 wt% saline solution under a low voltage (less than 1 V), and remained fully functional after 6 months. CFD simulations were conducted to improve the microchannel geometry so as to minimize the backflow caused by the valveless mechanism of the system. Based on the simulation results, an asymmetric geometry and a stop post were introduced to enhance the pumping performance. To demonstrate the feasibility of the proposed system as a drug delivery pump, an anti-cancer drug (adriamycin) was perfused to human breast cancer cells (MCF-7) using the pump. The present study showed that the proposed system can operate continuously for long periods with low energy consumption, powered by a single 1.5 V battery, making it a promising candidate for an implantable drug delivery system.

Microfluidic assay of endothelial cell migration in 3D interpenetrating polymer semi-network HA-Collagen hydrogel.

Cell migration through the extracellular matrix (ECM) is one of the key features for physiological and pathological processes such as angiogenesis, cancer metastasis, and wound healing. In particular, the quantitative assay of endothelial cell migration under the well-defined three dimensional (3D) microenvironment is important to analyze the angiogenesis mechanism. In this study, we report a microfluidic assay of endothelial cell sprouting and migration into an interpenetrating polymer semi-network HA-Collagen (SIPNs CH) hydrogel as ECM providing an enhanced in vivo mimicking 3D microenvironment to cells. The microfluidic chip could provide a well-controlled gradient of growth factor to cells, whereas the hydrogel could mimic a well-defined 3D microenvironment in vivo. (In addition/Furthermore, the microfluidic chip gives a well-controlled gradient of growth factor to cells) For this reason, three types of hydrogel, composed of semi-interpenetrating networks of collagen and hyaluronic acid were prepared, and firstly we proved the role of the hydrogel in endothelial cell migration. The diffusion property and swelling ratio of the hydrogel were characterized. It modulated the migration of endothelial cells in quantified manner, also being influenced by additional synthesis of Matrix metalloproteinase(MMP)-sensitive remodeling peptides and Arginine-glycine-lycinee (RGD) cell adhesion peptides. We successfully established a novel cell migration platform by changing major determinants such as ECM material under biochemical synthesis and under growth factor gradients in a microfluidic manner.

Electrically-driven hydrogel actuators in microfluidic channels: fabrication, characterization, and biological application.

The utility of electro-responsive smart materials has been limited by bubble generation (hydrolysis) during application of electrical fields and by biocompatibility issues. Here we describe the design of a device that overcomes these limitations by combining material properties, new design concepts, and microtechnology. 4-hydroxybutyl acrylate (4-HBA) was used as a backbone hydrogel material, and its actuating behavior, bending force, and elasticity were extensively characterized as a function of size and acrylic acid concentration. To prevent bubble generation, the system was designed such that the hydrogel actuator could be operated at low driving voltages (<1.2 V). A microfluidic channel with an integrated electroactive hydrogel actuator was developed for sorting particles. This device could be operated in cell culture media, and the sorting capabilities were initially assessed by sorting droplets in an oil droplet emulsion. Biocompatibility was subsequently tested by sorting mouse embryoid bodies (mEBs) according to size. The sorted and collected mEBs maintained pluripotency, and selected mEBs successfully differentiated into three germ layers: endoderm, mesoderm, and ectoderm. The electroactive hydrogel device, integrated into a microfluidic system, successfully demonstrated the practical application of smart materials for use in cell biology.

Fabrication of three-dimensional microarray structures by controlling the thickness and elasticity of poly(dimethylsiloxane) membrane.

In this paper, we propose a method to construct three-dimensional curved microstructures with easy control of the size, position and shape, by exploiting the elasticity of poly(dimethylsiloxane) (PDMS) membranes and basic physics. For this end, we developed the method to handle thin PDMS membrane safely, and to replicate PDMS microstructure from the PDMS mold. Using this method, we demonstrated two potential applications: (1) the use of concave well for the formation of embryoid body (EB) to differentiate into neuronal cells, and (2) the fabrication of SU-8 and hydrogel microparticles having diverse curved shapes. The curved structures were successfully fabricated with simple process, and EBs were formed in the concave well and differentiated into the neuronal cells. Microparticles with diverse shapes were fabricated from a range of materials for potential use as drug carrier and pH responsive micro-actuator elements.

Hydrophilic electrospun polyurethane nanofiber matrices for hMSC culture in a microfluidic cell chip.

Mimicking cellular microenvironments by MEMS technology is one of the emerging research areas. Integrated biomimetic systems with nanofiber polymer networks and microfluidic chips were fabricated and cellular behaviors were observed by changing surface characteristics of nanofibers and flow rates of microchannels. Modification of polyurethane nanofiber surfaces were achieved by grafting acrylic acid with plasma treatment and these nanofiber matrices were employed in a poly(dimethylsiloxane) based microfluidic chip. The surface characteristics of both electrospun nanofiber matrices was evaluated by measuring contact angle, porosity, and chemical structure using attenuated total reflection-Fourier transform infrared spectrometry. After modification, a terminal carboxyl group formed on the nanofiber surface and the wettability increased significantly. Human MSCs were seeded on the nanofiber matrices and a morphological investigation with actin filament staining and scanning electron microscopy was performed. A proliferation test by WST-1 and Live/Dead assay were performed to investigate the cell culture environment. It was observed that the cells on the AA-grafted nanofibers spread and proliferate compared to untreated nanofibers. It has also shown that flow rates in the microchannels played an important role for cell proliferation (Sim et al., Lab Chip 2007;7:1775-1782). Integration of nanofiber matrices into the microchannels provides the useful tools for mimicking cellular microenvironments and elucidating basic questions of cell and ECM assembly and interactions.