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Wenger Raphaël

Wenger Raphaël

Adjoint scientifique HES

Main skills

Bioprinting

Impression 3D

Inkjet

Management de projet

Dropwatching

Traitement d'images

Python

  • Contact

  • Publications

  • Conferences

Main contract

Adjoint scientifique HES

Desktop: MIC_10_160

Haute école d'ingénierie et d'architecture de Fribourg
Boulevard de Pérolles 80, 1700 Fribourg, CH
HEIA-FR
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2024

Multimaterial inkjet printing of mechanochromic materials
Scientific paper ArODES

Muriel Mauron, Lucie Castens Vitanov, César Michaud, Raphaël Wenger, Nicolas Muller, Roseline Nussbaumer, Céline Calvino, Christoph Weder, Stephen Schrettl, Gilbert Gugler, Derek John Kiebala

The European Physical Journal Special Topics,  2024

Link to the publication

Summary:

Inkjet printing technology achieves the precise deposition of liquid-phase materials via the digitally controlled formation of picoliter-sized droplets. Beyond graphical printing, inkjet printing has been employed for the deposition of separated drops on surfaces or the formation of continuous layers, which allows to construct materials gradients or periodic features that provide enhanced functionalities. Here, we explore the use of multinozzle, drop-on-demand piezoelectric inkjet technology for the manufacturing of mechanochromic materials, i.e., materials that change their color or fluorescence in response to mechanical deformation. To accomplish this, suitable polyurethane polymers of differing hardness grades were tested with a range of organic solvents to formulate low-viscosity, inkjet-printable solutions. Following their rheological characterization, two solutions comprising “soft” and “hard” polyurethanes were selected for in-depth study. The solutions were imbibed with a mechanochromic additive to yield fluorescent inks, which were either dropcast onto polymeric substrates or printed to form checkerboard patterns of alternating hardness using a laboratory-built, multimaterial inkjet platform. Fluorescence imaging and spectroscopy were used to identify different hardness grades in the dropcast and printed materials, as well as to monitor the responses of these gradient materials to mechanical deformation. The insights gained in this study are expected to facilitate the development of inkjet-printable, mechanochromic polymer materials for a wide range of applications.

2023

Predicting inkjet jetting behavior for viscoelastic inks using machine learning
Scientific paper ArODES

Seongju Kim, Raphaël Wenger, Olivier Bürgy, Gioele Balestra, Unyong Jeong, Sungjune Jung

Flexible and Printed Electronics,  2023, no. 8, article no. 035007

Link to the publication

Summary:

Inkjet printing offers significant potential for additive manufacturing technology. However, predicting jetting behavior is challenging because the rheological properties of functional inks commonly used in the industry are overlooked in printability maps that rely on the Ohnesorge and Weber numbers. We present a machine learning-based predictive model for jetting behavior that incorporates the Deborah number, the Ohnesorge number, and the waveform parameters. Ten viscoelastic inks have been prepared and their storage modulus and loss modulus measured, showing good agreement with those obtained by the theoretical Maxwell model. With the relaxation time of the viscoelastic ink obtained by analyzing the Maxwell model equations, the Deborah number could be calculated. We collected a large data set of jetting behaviors of each ink with various waveforms using drop watching system. Three distinct machine learning models were employed to build predictive models. After comparing the prediction accuracy of the machine learning models, we found that multilayer perceptron showed outstanding prediction accuracy. The final predictive model exhibited remarkable accuracy for an unknown ink based on waveform parameters, and the correlation between jetting behavior and ink properties was reasonable. Finally, we developed a printability map characterized by the Ohnesorge and Deborah numbers through the proposed predictive model for viscoelastic fluids and the chosen industrial printhead.

2018

3D Printing Applied to Tissue Engineered Vascular Grafts
Scientific paper

Wenger Raphaël

MDPI applied sciences, 2018 , vol.  8(12)

Link to the publication

Summary:

The broad clinical use of synthetic vascular grafts for vascular diseases is limited by their thrombogenicity and low patency rate, especially for vessels with a diameter inferior to 6 mm. Alternatives such as tissue-engineered vascular grafts (TEVGs), have gained increasing interest. Among the different manufacturing approaches, 3D bioprinting presents numerous advantages and enables the fabrication of multi-scale, multi-material, and multicellular tissues with heterogeneous and functional intrinsic structures. Extrusion-, inkjet- and light-based 3D printing techniques have been used for the fabrication of TEVG out of hydrogels, cells, and/or solid polymers. This review discusses the state-of-the-art research on the use of 3D printing for TEVG with a focus on the biomaterials and deposition methods.

2024

Smart materials by Inkjet
Conference ArODES

Muriel Mauron, Lucie Castens Vitanov, César Michaud, Raphaël Wenger, Derek Kiebala, Roseline Nussbaumer, Gilbert Gugler, Stephen Schrett

Proceedings of the Advanced Inkjet Technology Conference, 29-31 January 2024, Fribourg, Switzerland

Link to the conference

Summary:

There is growing interest in voxelated matter as it allows to build up tailored made surface functionalization and innovative new gradient materials. Inkjet-based printing is the only method that can create voxelated materials with high precision, digital and extremely versatile through high controlled formation of small pico-liter droplets [1, 2]. In this case the droplet will be the smallest material unit called voxel. The spatially controlled deposition allows to functionalize surfaces, build materials gradients, and combine different materials to generate printed surfaces with new features. In this way, the preparation of surfaces and coatings with a tailored functionalization and performance on demand becomes possible. Through the vehicle of inks with different softness grades which are doped with mechanochromic additive, we have developed a multi-material inkjet platform, which allows to create gradient materials with new performance. The additive has helped to characterize this new kind of materials on one hand and on the other hand it will be the start of creating new smart materials with gradient properties by inkjet. The first drop casting tests of these two inks has proven the mechanochromism by the measurement of the ratio between the intensity of the monomer and the excimer under UV light. The intensity in the mixing zone was measured at different strain. Finally, it was proven that the hardness in the mixing zone could be defined.

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