Research

Introduction

Among the BEAMS department at ULB, FEMTO-ST laboratory at CNRS and LIMMS laboratory at U Tokyo, I developed expertise in capillary forces and mechanical design from micro to macro scale. My interests included fundamental aspects related to micromechanics and precision mechanics, microfluidics, surface tension effects and mechanical design of miniaturized products.

Among the TIPs department, in close collaboration with the group of Physics of Fluids and thanks to the MicroMilli platform, I now develop the field of soft microrobotics, at the intersection between fluidic microrobotics and flexible microrobotics:

Flexible Microrobotics: mechanisms with variable stiffness for medical devices, force sensors with Nanoscribe printed compliant structure, flexible catheter towards in vivo detection of lung cancer…

Fluidic Microrobotics: thermocapillary micromanipulation, self-alignment with capillary forces, capillary microgripper for SMD components handling, capillary adhesion of insects…

This knowledge is applied to various applications fields at the intersection between mechanical engineering and surface tension effects: surface science, microrobotics, micro-assembly, drug delivery, sensors…

Ongoing and recents projects

FNRS GEQ – Glass-Based Optomicromechatronics (FEMTOprint)

Funding source: FNRS GEQ  32930248 (2019-2020)

Collaboration: Prof. Benoit SCHEID (ULB), Prof. Christophe COLLETTE (ULg), Prof. Christophe CAUCHETEUR (UMons)

Summary:

This proposal combines two key ingredients towards the development of resonators for inertial sensors and sensor arrays with embedded photonics for force/strain and biochemical sensing. The first key is related to the outstanding properties of glass, among which low loss factor (excellent for resonators), low thermal expansion (excellent for precision mechanics), optical quality surface finish, optical properties excellent to measure deformation of flexures by photo-elasticity or Bragg gratings, high elastic limit to Young modulus ratio (very good for large range and high resolution force sensors). However shaping glass at the small scale (<1mm) is very challenging. This will be solved thanks to the second key, which is the FEMTOprint machine. This new equipment allows 3D printed micro-devices out of glass and other transparent materials with sub-micron resolution, enabling the integration of fluidic, optical and mechanical functionalities in single monoliths at nano- and micro-scale. The technique is based on a 2 steps process: direct laser writing, followed by a chemical wet etching. Typical applications include precision mechanics (flexure hinges, microfluidics, micromolding, and micro-optics (microlenses, diffractive optical elements, nanogratings, waveguide and lab-on-fiber, integrated optical monitoring and sensing, the latter one is our target). This equipment would enrich our experimental platform micromilli.ulb.be and complement the Nanoscribe Photonic GT platform avaible for micron scale structuration of polymeric structures.

FNRS PDR – Thermo-Magneto-Capillary Self-Assembly

Funding source: FNRS PDR  31252084 (2018-2022)

Collaboration: Prof. Nicolas VANDEWALLE (ULg)

Summary:

Spontaneous generation of order in systems made of numerous components, called self-assembly, is known to be ubiquitous in biology and chemistry at the molecular level. Self-assembly is also encountered across length scales (from μm to cm), offering opportunities to generate 2D and 3D elaborated structures with low cost and simplified manipulations. This scale is called the mesoscale, in between bottom-up and top-down forms of fabrication. Using capillary driven mesoscale self-assembly to create complex structures is a scientific challenge that we will address in this project, focusing in particular on particles trapped along a liquid-air interface (this reduces the viscous drag when compared with the bulk, and enables interfacial phenomena such as long range capillary interactions). Our groups at ULB and ULg have indeed developed complementary ways to manipulate particles along interfaces: (i) The group at ULB has developed a micromanipulation station to manipulate tiny objects along liquid interfaces thanks to the thermocapillary effect. (ii) The group at ULg générâtes magnetocapillary assemblies made of identical soft ferromagnetic particles that are suspended at water-air interface, and subjected to a uniform magnetic field generated by Helmholtz coils. This project aims to combine these magneto- and thermocapillary effects to create complex active structures floating at the water-air interface. Practically, we will study (1) how the thermocapillary effect can affect the magnetocapillary bond and impact magnetocapillary assemblies; (2) how the magnetic field can be used as a elastic restoring force to measure thermocapillary forces (nN-μN range); (3) how the thermocapillary flow can be used to correct selfassembled patterns by adding/removing particles individually; (4) how thermocapillary barriers can confine magnetocapillary swimmers; (5) how thermocapillary flow can be used to improve the swimming capability of magnetocapillary assemblies.

FNRS PDR – Bioinspired passive liquid dispensing strategy at the micrometer scale

Funding source: FNRS PDR  26037417(2016-2020)

Collaborations: Prof. Tristan GILET (ULg) and Prof. Philippe COMPERE (ULg)

Summary:

In nature, capillary forces shape the microscopic realm. However their use in microengineering and microrobotics is currently limited by the lack of a robust handling strategy of the tiny volumes of liquid involved. Most insects rely on capillary forces for terrestrial locomotion. Some (incl. beetles) have hairy adhesive pads on their legs that provide fast and reversible attachment on almost any substrate. A femtoliter of liquid is passively dispensed to the tip of each hair, where it forms a bridge with the substrate and provides robust capillary adhesion. Liquid footprints are minimized when the pad detaches. This research project aims at understanding and mimicking the liquid management strategy of these hairy pads. Through a biomimetic approach, we will (1) identify a robust fluidic design for passive liquid dispensing at the micrometer scale, and (2) determine the optimal kinematics of pad detachment that minimizes liquid residuals on the substrate.

FRIA GRANT – STIFFNESS – Controllable stiffness mechanisms for endoscopic catheter

Funding source: FNRS FRIA PhD grants, Loïc BLANC (2015-2019)

Collaborations: Prof. Alain DELCHAMBRE (ULB)

Summary:

This research project aims at studying controllable stiffness mechanisms for catheters to be used in endoscopy (diameter lower than 3mm). Some applications indeed require to alternate between a flexible state (e.g. to follow a path) and a rigid one (e.g. force transmission). Such variable stiffness is required for applications in robotics, in active control for mechatronics, in aerospace and in biomedical field. Among these applications, the case study chosen for this PhD project is related to catheters used in case of vascular occlusions, transbronchial biopsy or interventional gastroenterology. These case studies require to go beyond the available state of the art with specifications as miniaturisation (diameter lower than 3mm for insertion in the working channels of endo- and bronchoscopes) or bending curvature compatible with anatomic constraints. In order to obtain controllable stiffness, literature already mentioned different principles (use of polymers, granular or layer jamming systems, etc.) which still need to be quantitatively compared and whose limits must be carefully detailed with respect to the above mentioned requirements. Moreover, the questions to answer are to know stiffness order of magnitude and variation range, control stimuli and design rules. Therefore, the plan of work includes 4 steps: (1) Test bench development, (2) Experimental study of granular jamming mechanisms as it seems promising in terms of performances, applications and fundamental questions open to research (no clear design rules available yet to engineer such mechanisms), (3) Study of layer jamming systems for similar reasons, (4) Prototype of a catheter with controllable stiffness. Funded by the FNRS FRIA PhD grants (candidate: Loïc BLANC).

FNRS GEQ (22687275) – 3D microstructuration and microengineering of surfaces with 2 photon lithography

Funding source: FNRS GEQ (2014-2016)

Collaborations: Prof. Pierre COLINET (ULB), Prof. Benoit SCHEID (ULB), Prof. Tristan GILET (ULg), Prof. Joël DE CONINCK (UMons)

Related: Bio-inspired capillary adhesion (PhD, Sophie Gernay)

Summary

Among the research framework of the Belgian research network on microfluidics and micromanipulation (PAI 7/38 MicroMAST) – whose all French speaking partners (ULB, UMons, ULg) support this current application – we aim at studying two scientific domains. The first one is devoted to the study of capillary adhesion (and release) mechanisms developed by some hexapods (insects), and the second one is the study of the wetting dynamics on structured surfaces. Both domains are complementary and full of promising perspectives (as well applied as fundamental perspectives). Let us mention for instance the  possible application of the capillary adhesion mechanism to the industrial pick and place of electronic  components smaller than 100μm. More fundamentally, an exciting perspective of this project would be to unify the current hydrodynamic and molecular theories describing wetting dynamics, especially on textured surfaces. To study these questions experimentally and pioneer beyond the state of the art, it would be necessary to control manufacturing of microstructures below the micron scale, which indeed drives the wetting and adhesion underlying mechanisms. The equipment targeted in this application is the micro/nanomanufacturing station developed by the Nanoscribe company. This equipment is based on 2 photon photo-polymerisation of proprietary resins (resolution of about 0.3μm). It has been demonstrated to produce various microstructures including periodic pattern, controlled disorder, porous structures as well as large aspect ratio geometries observed in the complex geometries of insect legs extremities.

IAP 7/38 MicroMAST – Microfluidics and Micromanipulation: Multiscale Applications of Surface Tension

Funding source: BELSPO (2012-2017)

Collaborations

Website: www.micromast.be

Podcast: MicroMAST, les liquides sous toutes les coutures

Youtube : our best movies

Related: Bio-inspired capillary adhesion (PhD, Sophie Gernay), Thermocapillary micromanipulation (PhD, Ronald Terrazas), capillary self-alignment (Postdoc, Massimo Mastrangeli)

Summary

The scientific objectives of this network are driven by fundamental questions raised in microfluidics, interfacial science, and micromanipulation. The rational use of surface tension, surface stress and capillary effects in micromanipulation will be applied to a selected number of highly relevant case studies by the network partners, including capillary gripping, capillary filling, capillary alignment, capillary sealing, capillary self-assembly and droplet manipulation.

These fundamental questions can be grouped into three categories:

  1. Fluid statics and dynamics: How much force is applied on solids by menisci and micro-flows in a given geometry? What happens if the solid bends when subject to these forces? Are the interfaces stable and what if not? What is the effect of an electric field? How can the microscopic description of wetting be translated into an adequate boundary condition at the macroscopic level?
  2. Surface engineering: How does a contact line move on a rough surface? Can one pattern the surface microscopically to control this motion? How is the motion affected by evaporation, or by the presence of colloid particles in the liquid or at the interface? Do these particles interact with the micro-patterns on the surface? Can one create highly 3D patterns on the surface by using capillary forces?
  3. Liquid engineering: How to measure the interfacial properties of complex liquids where apart from surface tension a surface viscoelastic response is present? How to infer macroscopic properties from the dynamics at the molecular scale? And how to engineer liquids and tailor them to the requirements arising from applications? Can one make a liquid that is biocompatible, and has a large surface tension and a low viscosity?

The proposed program is highly multidisciplinary, as it combines the forefront research in physics, material science, chemistry and engineering. It will cover topics that range from fundamental theory with atomistic simulations to experiments to investigate the fundamentals and selected more applied case studies. It will address both static and dynamic points of view, and establish the link between the microscopic properties of liquids and surfaces, and the macroscopic performances expected in the case studies. To that aim, this IAP project has gathered a multi-disciplinary research team that covers all the disciplines listed above.

The originality of this network relies in the efforts to enhance the collaboration of both the interfacial science, microfluidics and microengineering communities.

ARC – PREDICTION – PRotein dEtection for in vivo DIagnosis using CaTheterlc Optical fibre bioseNsors

Funding source: ARC (2012-2017)

Collaborations

Highly multidisciplinary, this project involves groups of ULB and UMons : Department of Gastroenterology, Hepato-pancreatology and Digestive Oncology – Jacques Devière (Faculté de Médecine, ULB), Bio-, Electro- and Mechanical Systems Department – Pierre Lambert (BEAMS, Ecole Polytechnique de Bruxelles, ULB), Service d’Electromagnétisme et de Télécommunications (SET, UMons) and Service de Protéomique et Microbiologie (ProtMic, UMons).

Related: Design of smart catheter for cancer cells detection in the lungs (PhD, Jean-Charles Larrieu)

Summary

Optical fiber biosensors can perform sensitive and quantitative measurements of the presence and concentration of biomolecules such as proteins or DNA. They can therefore contribute to major advances in medical diagnosis, food quality control, drug development and environmental monitoring. Additionally they offer the prospect of being used for in vivo detection, which would considerably improve the rapidity and reliability of a diagnosis. The key point of such biosensors is the joint development of the sensing platform, the biochemistry around and the protective packaging. The sensing platform comprises the development of the optical fiber sensors and their interrogation while the biochemistry mainly consists in coating the fiber with bioreceptors that will enable to detect ligands through the antibody/antigen affinity. An innovative protective packaging will be developed for the proposed application.

 

FNRS PDR – Micro-Macro study of the capillarity effects on mechanical behaviour of granular materials

Funding source: FNRS PDR (2014-2018)

Collaborations: Prof. Bertrand François (Promotor), Prof. Pierre Gérard, Prof. T.J. Massart

Summary

When the pore space of granular materials is filled by more than one fluid phase, liquid bridges including capillary meniscus link particles together. In the conventional geomechanical approaches, suction is used as the stress variable that controls the mechanical effects linked to the partial saturation of the voids, not considering explicitely the role of the capillary forces. The objective of this project is to quantify the combined effects of suction and capillary forces on mechanical behaviour of granular materials from joined microscopic (at the scale of the meniscus between two grains) and macroscopic (at the scale of an assembly of hundreds of grains) approaches. At microscale, the capillary forces will be evaluated experimentally and corroborated with numerical models based on the geometry of meniscus and surface tensions of the fluids. At macroscale, experimental tests will be developed to follow the compressibility as well as shear strength of granular materials under partial water saturation. The computational development carried out at the small scale will be extended to a larger scale by taking into account the tri-dimensional grain organisations through a granular microstructure generator tool previously developed by one of the promotors. The water retention curve will be used as the macroscopic properties controlling the mechanical response of the material. A computational homogenisation technique will manage the transition between micro- and macro-scales that will allow to perform numerical prediction of geomechanical structural problem (such as slope stability problem). This project encompasses various expertises in a unified research framework: the physics of capillarity, the experimental geomechanics of unsaturated geomaterial and the computational mechanics of porous media.

RW Beware Academia – MULTISCO

Funding source: Région wallonne, BEWARE Academia (2014-2018)

Collaborations: Prof. Jean-Marie RAQUEZ (Promotor, UMons), Endo tools Therapeutics S.A.

Summary

Les matériaux polymères à mémoire de forme (PMFs) trouvent de nombreuses applications dans le domaine biomédical comme fils de suture « intelligents » et cathéters auto-répondants pour applications cardiovasculaires complexes. La plupart des PMFs sont généralement actionnés via une différence de température, combinant un domaine permanent (structure chimiquement ou physiquement réticulée) et un domaine d’actionnement associée à une température de transition (température de transition vitreuse ou de fusion). Leur efficacité dépend de la structure chimique du polymère, du degré de réticulation et de la fraction massique entre les domaines amorphes et cristallins. L’énergie qui est restaurée lors de l’actionnement (changements de forme) est fonction de celle stockée au cours de la programmation. Malheureusement, par rapport aux autres technologies d’actionneurs, la déformation est généralement associée à une faible reprise de la rigidité des matériaux. L’inclusion de nanoparticules telles que des nanotubes de carbone pour leur conductivité électrique a récemment permis d’améliorer les propriétés mécaniques des matériaux polymères à mémoire de forme. L’objectif de ce programme de recherche sera donc de développer des nanocomposites polymères à mémoire de forme à actionnements multiples en termes de nombre de changements de forme à adopter (induits suite à un stimulus thermique), d’amplitude de la réponse et de rigidité pour des applications endoscopiques. En collaboration avec le BEAMS-ULB et la PME Endotools, de tels dispositifs seront, en effet, évaluées dans l’optique d’interventions endoscopiques en développant des aiguilles endoscopiques, alliant ses différentes fonctionnalités techniques lors de l’opération chirurgicale afin de minimiser le nombre d’actes chirurgicales et donc le traumatisme post-opératoire.