Micro-physiological in vitro models providing in vivo like environment has abundant prospects in the field of drug discovery and monitoring the physiological events. These models are currently achieved in setups like dual compartment cell culture Transwell system in which cells are grown in an insert with a porous membrane. Such in vitro tools are static in nature and therefore cannot simulate fully the in vivo conditions inside body [1]. Using these techniques needs a large amount of cells, reagents and culture media, which makes this a rather expensive approach. These models are also limited with number of simulated parameters, and are dedicated to a particular application [2-3]. In our previous work [4], we have tested an intestinal model using porous silicon membrane with pores of well controlled dimensions.

In this study, we are developing a microfluidic-based lab-on-chip platform for studying the interaction of various types of cells by co-culturing them and to use this platform for in vitro modeling of human organs. Here, the processes used in typical cell culture experiments are incorporated in an independent microfluidic platform. We report the characterization and optimization of device designs accomplished by means of in-depth FEA simulations (Fig. 1). The chip is made from silicon substrate, which allows us to create features with well controlled dimensions and the critical structures are realized by Deep reactive-ion etching (DRIE) process. The silicon chip itself is 15 mm wide and 40 mm long, capped with glass by means of anodic bonding which provides a leak proof fluidic system and the fluidic channels are accessed through a polymethyl methacrylate (PMMA) jig (Fig. 3). We have developed different chip designs suitable for diverse applications. The major component of the microfluidic device is a perfusion-based microflouidic structure (Fig. 2) which allows the communication between different cell types as well as facilitates the fluid flow. The cell co-culture (Fig. 4b) is achieved by growing them in discrete chambers separated by porous barriers which forms the perfusion structure. The perfusion channels provide opening ranging from 4 to 30 µm² optimized based on the function of each chamber.

This platform provides dynamic environment by precisely controlling the flow rate, spatiotemporal gradients, mechanical stress by fluid flow etc. which enable us to mimic the tissue structure and functions with better physiological relevance. This Organ-on-a-chip design can offer several cell culture chambers with either identical or different cellular structures to study the role of each cell type as well as to compare the cell response to various chemical exposures in parallel experiments.

Rapid, sensitive and selective detection of bioparticles is of prime importance in point of care diagnostic devices and various micro- and nano-systems [1] relying on microfluidics are being developed. This paper reports a design of a new optoacoustic microfluidic device which can quantitatively detect the concentration of micron sized bioparticles in a solution. In our previous work [2], we have introduced a new sensing scheme utilizing surface acoustic wave (SAW) detection of the photoacoustic (PA) signal generated from optical absorption of bioanalytes present in the microfluidic channel. In the current work, we combine a SAW based particle concentration on a microfluidic reservoir with the SAW-PA sensor to enable rapid, quantitative and sensitive microparticle detection (polystyrene) on a single piezoelectric substrate. The detection of analytes from the bulk of the solution, along with the mechanical scanning, particle concentration and continuous fluid flow, highlights the device capability to handle clinically relevant sample volume (millilitres) in comparison to the low throughput (microlitre sample) of the existing devices.

A schematic view of the device is illustrated in Fig. 1. Orthogonal interdigital transducers (IDT) on the 128⁰ YX lithium niobate (LiNbO3) piezoelectric substrate is used for actuating and sensing. An IDT excited at 15.8 MHz (labelled ‘A’) oriented in the Y direction is used for particle concentration inside the microfluidic reservoir. The IDT at centre frequency of 10 MHz oriented in the X direction is used for sensing. The numerical simulation results confirms that the SAW-PA frequency for a 10 μm (diameter) polystyrene particle is sensitive for frequencies less than 50 MHz. Table I shows the SAW device specifications. A pulsed laser at repetition rate of 10 Hz at a wavelength of 532 nm is used, with an optical spot size of 200 μm. A mechanical scanner focusses the laser spot across the particles located inside the microfluidic reservoir. Fig. 2 shows the schematic of the experimental setup used for sensing. Black polystyrene microparticles with an optical absorbance of ~ 0.7 at 532 nm is used as the sensing sample for the experiment.

Fig. 3 shows 10 μm particles aggregating after SAW exposure for 40-50 sec. The particles are concentrated at a vertical height close to the liquid-air free surface. The preconcentration before detection bounds the mechanical scanning to only half of the cavity, thereby reducing the detection time. Fig. 4 shows the experimental results for the detection of the 10 μm particles for a concentration varying from ~10-200 particles per 10 μL. The power spectral density of the SAW-PA signals for varying particle concentration demonstrates a quadratic response, with a detection of 7 particles in 10 μL of solution. The sensitivity can be improved further to a single particle by optimizing the SAW design to match the acoustic frequency generated due to microfluidic channel resonance. Furthermore, utilizing dual SAW IDTs aggregates the particles at a preferred location, thereby eliminating the mechanical scanner. Thus, a rapid (few sec) and sensitive (single) particle detection device could be envisaged, comparable to the 3D droplet detection device[3].

This paper reports a drug-loaded three-phase microbubble fabrication method using a simple three-dimensional microfluidic chip. The three-dimensional microfluidic chip has a simple design of the nozzle using multilayer exposure technique, so that it has much lower manufacture cost, and it can still generate microbubbles with a small size. Microbubbles made by this chip have uniform size and low diameter, which could be controlled under 5 μm. We not only reduced microbubble’s size greatly, but also got stabilized a higher yield of microbubbles with a high yield. We generated stabilized doxorubicin-loaded microbubbles with a phospholipid shell by adjusting oil phase formula. The microbubbles could stay more than half a month. The effects on doxorubicin payload, encapsulation efficiency and in vitro enhancement were explored as well.

The design, formulation and manufacturing of engineered composites containing solid active pharmaceutical ingredient (API) and polymeric excipient(s), with precisely tailored composition and structure, have been of tremendous academic and industrial interest in recent years for two primary reasons. Firstly, from the perspective of pharmaceutical materials science and product design, engineered solid composites allow new and exciting possibilities in the creation of drug products with tailored dosage and release profiles. [1] Secondly, and equally importantly, such granular materials can have enhanced processability in terms of flow properties, and enable paradigm-shifting intensification (and simplification) of the traditional pharmaceutical manufacturing workflow, while also facilitating agile and decentralized supply chain models that can rapidly respond to evolving market forces. In particular, the latter is made possible by the use of engineered composites as intermediate drug products, which can be converted to the final dose form on-demand with minimal further processing, in customized and decentralized fashion.

This paper focuses on a recently developed technique, which combines microfluidic generation of droplets carrying dissolved API (with or without dissolved excipient material), and evaporative crystallization/solidification in thin films, to produce monodisperse spherical microparticles of crystalline API co-formulated with solid excipient in ‘bottom up’ fashion.[2-4] The formulation of both hydrophilic and hydrophobic drug molecules has been demonstrated using this technique. Interestingly, it has also been shown that the simultaneous solidification of hydrophobic drugs, such as 5-methyl-2-[(2-nitrophenyl)amino]-3-thiophenecarbonitrile (ROY) or carbamazepine (CBZ), with a polymeric excipient, such as ethyl cellulose (EC), not only enables shorter crystallisation times, but also allows a remarkable degree of process-based selectivity over the polymorphic form of the crystalline drug. This method has the potential to be widely adopted as a simple method for single-step crystallisation and direct compaction of drugs and excipients, which circumvents several energy intensive downstream steps in the pharmaceutical manufacturing workflow, while also allowing the creation of ‘designer’ drug products with a hitherto unprecedented level of control over solid particle attributes. In this paper, we focus on a phenomenological study of the dynamics of simultaneous API/excipient solidification and structure formation within evaporating microfluidic emulsion droplets, in an attempt to delineate the basic and general elements of these processes [5]. In a model system comprising 5-Methyl-2-[(2-nitrophenyl)amino]-3-thiophenecarbonitrile (‘ROY’) as the drug and ethyl cellulose (‘EC’) as the excipient, we are able to demonstrate a diversity of particle structures, with exquisite control over the structural outcome at the single-particle level. Specifically, we demonstrate a coarse ‘macro’ particle structure and a finer ‘micro’ structure with our chosen model system. Further, we elucidate the key mechanistic elements responsible for the observed structural diversity using a combination of systematic experiments, thermodynamic arguments, and dissipative particle dynamics (DPD) simulations. We validate our method by applying it to fabricate microparticles containing ROY and a different matrix material, poly(lactic-co-glycolic acid) (‘PLGA’), and those comprising EC and a different drug, carbamazepine (‘CBZ’). Finally, we present preliminary investigations of in vitro drug release from two different types of CBZ-EC particles, highlighting how structural control allows the design of drug release profiles. 

Sepsis is a fatal infectious disease claiming thousands of lives every year. Antimicrobial susceptibility testing (AST) plays a pivotal role in the success of treatments. However, the turnaround time for the outcome of conventional AST usually requires over 24 hours, resulting in high patient mortality¹. Moreover, antibiotics abuse can also incubate the booming of superbugs. A reliable and efficient drug screen becomes increasingly important to date to save lives in a timely fashion. To this end, a technique combining optical diffusometry and bead-based immunoassays is developed herein to achieve a rapid quantification of target microorganisms. 

For rapid ASTs, a variety of techniques, such as image analysis², dielectrophoretic force³, and Raman-enhancing spectrum⁴, have been developed in the recent years. Nevertheless, complicated procedures and equipments impede their prevalence in clinics. Lately, bead-based immunoassays are emerging because of high flexibility. Taking advantaging of the concept, Kinnunen et al.⁵ used magnetic bead rotation integrating immunoassays to monitor growth of bacteria. However, a sophisticated driving magnetic source was required. Unlike the abovementioned techniques, Brownian motion is a self-driven phenomenon. According to the Stokes-Einstein relation, particle diffusivity is a function of particle size⁶. When the particle size is increased from conjugated target analytes, the particle diffusivity will decrease. A proof of concept was firstly carried out in a pilot study conducted by Gorti et al.⁶ in detecting the M13 virus. In this work, they explored the detection of virus by measuring the change of particle diffusivity. The successful attempt then enabled the potential to quantify low-abundance microorganisms in the same manner. 

In this study, an optical diffusometric platform was used to monitor two microorganisms, P. aeruginosa and S. aureus. The platform was composed of an inverted epifluorescent microscope (IX71), a digital camera (Flea^®3, Point Grey), a microchip and a computer. Bead-based immunoassays were used to detect desired bacteria suspended in physiological fluids (Fig. 1). Quantitative analysis of Brownian motion was realized by the spatially cross-correlation algorithm. Two amine-modified color particles (2-μm, Sigma) were respectively conjugated with anti-P. aeruginosa IgG and anti-S. aureus IgG and then incubated with P. aeruginosa and S. aureus bacteria for an hour. The bacteria were firmly attached to the functionalized particles. The limit of detection could achieve 100 CFU/mL. Two bacteria were also measured at different concentrations in a mixed sample by using triple color particles composed of equal amounts of anti-P. aeruginosa Ab- (orange), anti-S. aureus Ab- (red), and anti-TNF-α (green) Ab-functionalized particles (Fig. 2). The experimental result agrees with the theoretical prediction (Fig. 3). When the bacterium-conjugated particles were further mixed with gentamicin in the TSB solution at 37 °C for 2 h, particle images were recorded every 20 min with a 10× objective to monitor the bacterial activity. Results indicated that effective concentrations of the antibiotic, gentamicin, on the co-cultured bacteria could be explicitly distinguished from their temporal diffusivity changes (Fig. 4). This study provides valuable information to timely treatments against polymicrobial diseases in the near future.

Microfluidics is vital for cell analysis because it is the only technology capable of simulating the physiological environment of cells and cell assemblies to investigate cellular transport mechanisms and cell proliferation events in the presence of test reagents, temperature or shear force gradients. In light of the benefits of microfluidics, my research group at TUW is developing lab-on-a-chip systems containing integrated fluid handling, degassing and biosensing systems to non-invasively monitor dynamic cell population responses. In course of the presentation various components including microvalves, micropumps, degassers and sensing systems for lab-on-a-chip will be presented as well as the application of three selected organ-on-a-chip technologies in placenta research, rheumatic arthritis and osteoarthritis studies as well as Parkinson’s diseases progression.

The hollow microspheres are attractive components of artificial scaffold as extracellular matrix for cell proliferation.The main advantages include efficient fabrication, flexible self-assemble and more interface for cell attachment and more interspace for cell location provided by the hollow structure.^[1]  However, the available fabrication technique has limitations due to the complex chemical process and few material choices.^[2] In this study, we have developed a microfluidic process to fabricate hollow nanofibrous microspheres using bacterial cellulose (BC), which is a promising biocompatible material with ultra-high purity and excellent mechanic strength.

Since BC fibers is not soluble in water and most organic solvents , it is difficult to manipulate directly in microfluidic system.Here, we encapsulated the cellulose producing bacteria strain Gluconacetobacter xylinus inside a double-layer template microparticle with alginate core and agarose shell generated by microfluidic control as shown in Fig. 1(a). The G. xylinus was encapsulated and confined in the agarose area during the long-time static culture due to the density differences between the agarose and alginate. The cellulose produced by G. Xylinus were then entangled to form the desired hollow structure. The agarose and alginate could be removed using high temperature and chemical process after the hollow BC microsphere formation as shown in Fig. 1(b).

Figure 2 shows the quantification of cellulose production process with different number of G. xylinus encapsulated inside the agarose template microparticles. Fluorescent brightener 28 was used to stain the cellulose fiber and the productivity was indicated by the fluorescent area ratio. The result shows that for a constant number of G. xylinus inside a single agarose microparticle, the cellulose production increased over time. After 12 days culture, compact cellulose microsphere could be collected. On the other hand, the amount and rate of cellulose production was depending on the initial number of G. xylinus encapsulated in a single agarose microparticle.

The hollow BC microspheres produced in the same batch were highly monodispersed with the same diameter and hollow structure as shown in Fig. 3(a-b). Fig. 5 (c) shows the SEM graphs of the cellulose fiber produced by G. xylinus cultured in agarose. Comparing with the bulk produced cellulose, the fiber generated was thinner and with the morphology of novel uniform. The hollow structure of the microsphere could also be controlled by encapsulating alginate particles with different sizes. Fig. 5(d-f) shows the hollow microspheres fabricated with the alginate cores of the diameter of 20 μm, 40 μm, 50 μm, respectively.

To examine the potential of application of the hollow BC microspheres for cell culture scaffold, the growth of PC-9 cell on three different types of artificial scaffold (BC membrane, packed BC microspheres and packed hollow BC microspheres) was carried out. We used confocal microscope to observe the growth of the cells in z direction. For the BC membrane, the cells are observed only attached to the surface of the scaffold. Meanwhile, cells are observed with a penetration depth of 65µm for the BC microsphere scaffold and deeper penetration depth of 95µm for hollow BC microspheres scaffold. The advantages on cell penetration depth of hollow BC micrspheres may induced by the larger gaps and flexibility of the scaffolds.

The rheology studies of complex fluid with deformable particles such as red blood cells (RBCs) are highly interested for a broad range of research works in biological systems, the cosmetic industries, mining and petroleum industries and home products. However, predicting the rheological behavior of soft particles in matrix is one of the most challenging and complicated problems in material and fluid sciences. The complication is arisen by the particles collision and interactions with the surrounding fluid. A full description of the rheology of soft particles requires a complete understanding of the deformation of particles itself [1], interactions among particles, interaction between the particles and the surrounding fluid [2], and interactions between channel and particles. Thus consideration of above factors can lead to a better understanding of the rheological behavior of suspensions with soft particles.

A suspension system of soft particles which is composed of a fluid-filled interior covered by an elastic membrane is simulated to study its rheological characteristics under various condition as shown in Fig. 1. In this study, the rheological behaviors of the soft particle suspension are observed with respect to several variations, for instance, shear rate, volume fraction, deformability of the particles, and various channel. A combination model of the three dimensional lattice Boltzmann method (LBM) and the immersed boundary method (IBM) are used to simulate these suspension systems.

With the aid of a numerical simulation, which can help in visualizing the particle behavior, and correlate it to rheological behavior of each particles, the physics behind the relative viscosity change was analyzed. To validate the soft particle model, the ratio of length to width for the stretching of soft particle was measured. For the single particle deformation in the flow, the boundary thickness was analyzed, which was related to the repulsive force critical for the interaction between the particle and wall, the effect of stiffness of RBCs on transit time in a microchannel was analyzed, which was proven to not be crucial for modeling of the soft particle. To see the interaction between wall property and suspension flow, soft particles in hydrophobic and hydrophilic surface microfluidic channels was simulated. To see the interaction among cells, red blood cells in shear flow with various aggregation condition was simulated

The time for cells to pass through the channel is measured at different values of shear modulus, along with analysis of the degree of deformation and transit time in Fig.2. Moreover, the velocity and deformation of cells as a function of boundary thickness and the effect of volume conservation stiffness were studied in Fig.3. The surface properties of the channel are changed using the tangential momentum accommodation coefficient on the channel boundary to set the hydrophobic surface in the simulation. The relative apparent viscosity is used to calculate systematic flow resistance in Fig.4. The results indicate that the flow rate and flow profile varied with respect to the surface property under a constant pressure gradient in Fig.5.

Rotational diffusion processes are correlated with nanoparticle visualization and manipulation techniques, widely used in nanocomposites, nanofluids, bioscience and so on. In the current work, three molecular dynamics (MD) schemes, including two equilibrium (based on MSD relation and autocorrelation function of the angular velocity) and one nonequilibrium methods, are developed to calculate the rotational diffusion coefficient, taking a single rigid carbon nanotube in fluid argon as a case. The three methods produce the same results on the basis of plenty of data with variation of the calculation parameters (tube length, diameter, fluid temperature, density and viscosity), indicative of the validity and accuracy of the MD simulations. However, these results have a non-negligible deviation from the classical literature theory, which is in the framework of continuum-based fluid mechanics and predicts the rotational diffusion coefficient of rodshaped particles. The above deviation may come from some unrevealed factors of the theory at the molecular level, and the adequecy of the theory when applied to pratical situations should be further checked.

When a linear shear flow is imposed to the above system, the single carbon nanotube reveals three forms of anomalous orientation behavior in MD simulations: (i) “Aligned orientation” when the nanotube oscillates around a particular direction which is close to the flow direction at a small angle of about 10º in the velocity-gradient plane; (ii) “Interrupted orientation” when the oscillation is interrupted by a 180º rotation now and then; (iii) “Random orientation” when 180º rotations dominate with the rotational direction coinciding with the local fluid flow direction. The Peclet number serves as an important scaling parameter for processing the results. The orientation order has a positive correlation with the Peclet number, and in turn a negative correlation with the rotational diffusion coefficient, when the diameter of the tube is kept fixed.

Polarizable graphene oxide (GO) particles are prepared by a modified Hummers method, and then they are dispersed in silicone oil to test its electro-responsive thermal properties under imposed DC electric fields. Experiments show a fibrillar structure along the DC electric direction is formed and the structure becomes more ordered with the increase of the electric strength. We further observe that along the oriented direction the thermal conductivity can be enhanced compared to the equilibrium state and the situation can be reversed when the electric fields are removed. At the experimental temperature of 25°C and 50°C, the dispersion with a GO mass fraction of about 1% shows a tunable thermal conductivity in the range of 100%~130% below the electric strength of 300 V/mm. In this way, the method of tuning thermal conductivities based on the orientation control of low-dimensional particles is proposed to meet the situation in which a real-time regulation of the thermal properties is required.

This paper presents a novel method for directly imaging and counting bacteria at single cell level under low optical resolution condition by inducing nanoprobes aggregation on the cell surface and forming cell-core shell particles. Two kinds of gold nanoprobes with polyethyleneimine (PEI-AuNPs) and citrate (SC-AuNPs) modified respectively have been fabricated and could form quick multi-layer adsorption on the bacteria cells. The adsorption leads to a visible precipitate particle which could be automatically imaged and counted in the microdroplet. To validate the method, E.coli samples has been quantified in less than 0.5 hour. Compared with traditional plate-spread counting and PCR, no time-consuming procedures of culture and high cost biochemical reagent needed in the developed method.