Parametric Study of Jet/Droplet Formation Process during LIFT Printing of Living Cell-Laden Bioink

Bioprinting offers great potential for the fabrication of three-dimensional living tissues by the precise layer-by-layer printing of biological materials, including living cells and cell-laden hydrogels. The laser-induced forward transfer (LIFT) of cell-laden bioinks is one of the most promising laser-printing technologies enabling biofabrication. However, for it to be a viable bioprinting technology, bioink printability must be carefully examined. In this study, we used a time-resolved imaging system to study the cell-laden bioink droplet formation process in terms of the droplet size, velocity, and traveling distance. For this purpose, the bioinks were prepared using breast cancer cells with different cell concentrations to evaluate the effect of the cell concentration on the droplet formation process and the survival of the cells after printing. These bioinks were compared with cell-free bioinks under the same printing conditions to understand the effect of the particle physical properties on the droplet formation procedure. The morphology of the printed droplets indicated that it is possible to print uniform droplets for a wide range of cell concentrations. Overall, it is concluded that the laser fluence and the distance of the donor–receiver substrates play an important role in the printing impingement type; consequently, a careful adjustment of these parameters can lead to high-quality printing.

Accurate high-throughput screening based on digital protein synthesis in a massively parallel femtoliter droplet array

We report a general strategy based on digital counting principle that enables an efficient acquisition of enzyme mutants with desired activities from just a few clones within a day. We prepared a high-density femtoliter droplet array, consisting of 1 million uniform droplets per 1 cm2 to carry out high-throughput protein synthesis and screening. Single DNA molecules were randomly distributed into each droplet following a Poisson process to initiate the protein synthesis with coupled cell-free transcription and translation reactions and then recovered by a microcapillary. The protein yield in each droplet was proportional to the number of DNA molecules, meaning that droplets with apparent intensities higher than the Poisson distribution–predicted maximum can be readily identified as the exact hits exhibiting the desired increased activity. We improved the activity of an alkaline phosphatase up to near 20-fold by using less than 10 nl of reagents.

Spray Conditioning for the Preparation of Spray Dried Submicron Particles

Particle size reduction down to the submicron range (0.1-1 µm) is an effective option to increase the bioavailabilityof low water soluble active pharmaceutical ingredients. According to the Nernst-Brunner equation, the preparation of submicron sized particles increases the specific surface area, thus increases the dissolution rate. Conventional spray drying devices for submicron particles show certain limitations. The main challenge is the preparation of small and uniform droplets during the atomisation step. In this work, fine droplets were generated combining a nozzle with a droplet separator. Therefore, the aerosol is generated with a pneumatic nozzle and is sprayed into a cyclone droplet separator. Depending on the characteristics of the cyclone, droplets larger than the cut-off-size were separated and returned into the liquid feed. The conditioned aerosol at the top of the cyclone separator can then be introduced into the drying chamber. With this concept the usable part is separated, thus no classification process after drying is necessary. The investigations show that the dependencies during atomisation of the droplets size on the liquid-to-gas mass flow ratio µm and the liquid properties (e.g. viscosity) do not apply to the separation step. The conditioned aerosol only depends on the separation characteristics of the cyclone droplet separator. However, the amount of droplets separated is determined by the atomisation step. Hence, the amount of droplets smaller than the cut-off-size can be increased by decreasing the droplet size of the primary aerosol. This is realised by secondary droplet fragmentation. An impact surface causes breakup of the droplets of theprimary aerosol before separation. The investigations show an increased amount of droplets <2µm.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4701

Energy Aspects in Spray Formation by Homogenous Flash Boiling Process

When a pressurized bubbly mixture is driven out through an orifice, the mixture pressure abruptly drops and thebubbles undergo a rapid expansion process, which under some circumstances results in a rapid disintegration of the liquid bulk into small droplets (atomization). Depending on the initial conditions, heterogeneous or homogeneous nucleation of vapor bubbles may occur. For homogeneous nucleation, the vapor bubbles grow rapidly one towards the other, and when they touch each other the bubbles “explode”. In this stage, the liquid around the bubbles is teared, and a spray with small and uniform droplets is formed. In the literature, it seems that the efficiency of the homogenous flash boiling process is very low. In this work, we analyse this process andanalyse it for possible energy losses.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4773

Recent Developments in Micro/Nanochannel Emulsification for Controlled Production of Monodisperse Emulsions

Microfluidic techniques for producing emulsions have been proposed over the last decade. Major advantages of microfluidic techniques include the production of monodisperse emulsions with a coefficient of variation (CV) of typically <5%, superior controllability of droplet size and monodispersity, and in situ microscopic monitoring. Microchannel (MC) emulsification, proposed by our research group, is a unique and robust technique to produce monodisperse emulsions with controlled droplet sizes of >1 μm. In MC emulsification, droplet generation via MC arrays does not require any external shear/elongational stress; i.e., the dispersed phase that passed through MCs is transformed spontaneously into uniform droplets due to hydrodynamic instability of the oil-water interface. Here we present some of the recent findings obtained from MC emulsification studies and the controlled production of monodisperse submicron emulsions by novel nanochannel (NC) emulsification. The first topic on MC emulsification is the influence of operating temperature (10 to 70 °C) on production of oil-in-water (O/W) emulsions using a surface-oxidized silicon MC array plate with an MC depth of 8 μm. The droplet generation results were correlated well with the contact angle of the dispersed phase to the MC walls that was measured using a novel method using parallel long MCs. Another topic on MC emulsification is the development of stainless-steel MC emulsification devices. Stainless-steel MC array plates with an MC depth of 100 or 150 μm were mechanically fabricated using an end mill. The use of the stainless-steel MC array plates enabled stably producing monodisperse O/W emulsions with an average droplet diameter of up to 550 μm. We also recently developed silicon NC array plates with the smallest NC depth of 50 nm. NC emulsification experiments demonstrated successful production of monodisperse submicron O/W emulsions with the smallest average droplet diameter of 480 nm. The diameter of the droplets generated by NC emulsification was measured by a novel technique that exploits nanospace.

Effect of Field Strength on Polymer Aggregation in Electrohydrodynamic Spraying of Thermoplastic Polyurethane

Polymer solution interacts with the electric field in an electrohydrodynamic (EHD) spraying process. Charged polymeric solution forces polymer liquids to move, break into spray of fine droplets. EHD spraying has the ability to generate very small & uniform droplets of polymeric solution. It is envisaged that EHD Spraying is a promising technology to coat a polymer on substrate at submicron range. The polymer aggregation is important while coating. The process parameters including applied voltage, nozzle-collector distance, solution flow rate, and solution concentration plays an important role in polymer droplets aggregation on surface. Field strength is also plays important role while EHD spraying. Field strength is the rate of change of potential with respect to distance. This research paper investigates the effect of field strength on aggregation of polymer droplets.

Preparation of ZrO2 Micro Beads by Sol-Gel Method

ZrO2 micro beads are widely used as abrasive media in many areas. This paper introduces a sol-gel process for preparation of ZrO2 micro beads. First, zirconium nitrate solution and urea were mixed to prepare the sol, then the sol was converted to uniform droplets by vibrating dispersion method. The droplets were emitted from the nozzles into an ammonia solution. Along the way from the nozzle to ammonia solution, the liquid droplets first form spherical shape by their surface tension in air, and were then surface-hardened through ammonia gas. The microspheres complete gelation in the ammonia solution. The gel spheres were treated successively by aging, washing, drying, calcination and sintering to yield ZrO2 ceramic micro beads. The crystal structure of micro beads was examined by X-ray diffraction (XRD). The microstructure of the micro beads was observed by scanning electron microscopy (SEM). The results indicate that the sol-gel process can be used to prepare ZrO2 ceramic micro beads with good sphericity and uniform distribution of diameter.

Effect of Applied Voltage on Polymer Aggregation in Electrospraying of Thermoplastic Polymer

In an electrospraying process, the polymer solution interacts with the electric field. Charged polymeric solutions causing polymer liquids to move, break into drops or spray into fine droplets. Electrospraying has the ability to generate very small & uniform droplets of polymeric solution. It is envisaged that electrospraying is a promising technology to coat a polymer on surface at submicron range. The polymer aggregation is important while coating. The process parameters including applied voltage, nozzle-collector distance, solution flow rate, and solution concentration play an important role in polymer droplets aggregation on surface. This research paper investigates the effect of applied voltage on aggregation of polymer droplets.