Development of a novel sensor for cleaning studies.

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Filament Stretching of Carbon Nanotube Suspensions

International audienceThis paper reports the application of a recently developed filament stretching protocol for the study of the extensional rheology of both treated and untreated carbon nanotubes (CNT) suspended within an epoxy resin. It was experimentally observed that filaments formed by treated and untreated CNT suspensions behaved differently after initial stretching. The filament thinning process of the base epoxy was consistent with a simple Newtonian fluid, whilst the filament of treated CNT suspensions also thinned in a Newtonian way but with an enhanced extensional viscosity. Filaments formed with untreated CNT suspensions behaved in a non-uniform way with local fluctuation in filament diameter, and it was not possible to obtain reliable extensional viscosity data. Irregularity of the untreated CNT filaments was consistent with coupled optical images, where spatial variation in CNT aggregate concentration was observed. In the case of treated CNT suspensions, the enhanced extensional viscosity was modelled in terms of the alignment of CNTs in the stretching direction, and the degree of alignment was subsequently estimated using a simple orientation model

Sonochemical Degradation of Gelatin Methacryloyl to Control Viscoelasticity for Inkjet Bioprinting

Inkjet printing enables the mimicry of the microenvironment of natural complex tissues by patterning cells and hydrogels at a high resolution. However, the polymer content of an inkjet-printable bioink is limited as it leads to strong viscoelasticity in the inkjet nozzle. Here it is demonstrated that sonochemical treatment controls the viscoelasticity of a gelatin methacryloyl (GelMA) based bioink by shortening the length of polymer chains without causing chemical destruction of the methacryloyl groups. The rheological properties of treated GelMA inks are evaluated by a piezo-axial vibrator over a wide range of frequencies between 10 and 10 000 Hz. This approach enables to effectively increase the maximum printable polymer concentration from 3% to 10%. Then it is studied how the sonochemical treatment effectively controls the microstructure and mechanical properties of GelMA hydrogel constructs after crosslinking while maintaining its fluid properties within the printable range. The control of mechanical properties of GelMA hydrogels can lead fibroblasts more spreading on the hydrogels. A 3D cell-laden multilayered hydrogel constructs containing layers with different physical properties is fabrictated by using high-resolution inkjet printing. The sonochemical treatment delivers a new path to inkjet bioprinting to build microarchitectures with various physical properties by expanding the range of applicable bioinks.11Nsciescopu

2D and 3D inkjet printing of biopharmaceuticals – A review of trends and future perspectives in research and manufacturing

There is an ongoing global shift in pharmaceutical business models from small molecule drugs to biologics. This increase in complexity is in response to advancements in our diagnoses and understanding of diseases. With the more targeted approach coupled with its inherently more costly development and manufacturing, 2D and 3D printing are being explored as suitable techniques to deliver more personalised and affordable routes to drug discovery and manufacturing. In this review, we explore first the business context underlying this shift to biopharmaceuticals and provide an update on the latest work exploring discovery and pharmaceutics. We then draw on multiple disciplines to help reveal the shared challenges facing researchers and firms aiming to develop biopharmaceuticals, specifically when using the most commonly explored manufacturing routes of drop-on-demand inkjet printing and pneumatic extrusion. This includes separating out how to consider mechanical and chemical influences during manufacturing, the role of the chosen hardware and the challenges of aqueous formulation based on similar challenges being faced by the printing industry. Together, this provides a review of existing work and guidance for researchers and industry to help with the de-risking and rapid development of future biopharmaceutical products

High-Frequency Rheological and Piezo-Voltage Waveform Characterization of Inkjet-Printed Polymer-Based Dopant-Source Inks

This work focuses on developing an understanding of the rheological properties of polymer-based dopant-source inks at the timescales relevant to inkjet printing and their corresponding roles in determining the production of defect-free droplets. Ink-specific optimization of printing processes for phosphorus and boron dopant-source inks with different compositions is demonstrated. Rheological flow curves measured by a piezo axial vibrator (PAV) were used to study the changes in complex viscosity (η*) and in the elastic (G′) and viscous (G″) components of the shear modulus (G*) with respect to changes in frequency (from fmin = 1 kHz to fmax = 10 kHz) to obtain an insight into the high-frequency behaviour of inks, as well as the effects of temperature (25 °C and 45 °C) and the natural aging time of the inks. Inks demonstrating complex viscosity η*min ≥ 2 mPas to η*max ≤ 20 mPas and an elastic modulus G′ ≤ 20 Pa, produced droplets with negligible defects. Of the three rheological parameters (η*, G′ and G″), the elastic component (G′) of the shear modulus was observed to have the greatest significance in determining the stability and homogeneity of ink droplets, thus dictating the quality of the printed structures. The reliability and stability of droplet formation were further investigated through voltage waveform simulation using an oscilloscope

Inkjet printing of weakly elastic polymer solutions

Fluid assessment methods, requiring small volumes and avoiding the need for jetting, are particularly useful in the design of functional fluids for inkjet printing applications. With the increasing use of complex (rather than Newtonian) fluids for manufacturing, single frequency fluid characterisation cannot reliably predict good jetting behaviour, owing to the range of shearing and extensional flow rates involved. However, the scope of inkjet fluid assessments (beyond achievement of a nominal viscosity within the print head design specification) is usually focused on the final application rather than the jetting processes. The experimental demonstration of the clear insufficiency of such approaches shows that fluid jetting can readily discriminate between fluids assessed as having similar LVE characterisation (within a factor of 2) for typical commercial rheometer measurements at shearing rates reaching 10rads.Jetting behaviour of weakly elastic dilute linear polystyrene solutions, for molecular weights of 110-488. kDa, recorded using high speed video was compared with recent results from numerical modelling and capillary thinning studies of the same solutions.The jetting images show behaviour ranging from near-Newtonian to "beads-on-a-string". The inkjet printing behaviour does not correlate simply with the measured extensional relaxation times or Zimm times, but may be consistent with non-linear extensibility L and the production of fully extended polymer molecules in the thinning jet ligament.Fluid test methods allowing a more complete characterisation of NLVE parameters are needed to assess inkjet printing feasibility prior to directly jetting complex fluids. At the present time, directly jetting such fluids may prove to be the only alternative