<p>A key aspect of color change is altering perceived value or intensity. This dissertation presents a methodology to achieve value change through mechanical means via the deflection of bistable structures. We create the Mechxel, two methods of mechanical pixel-based, reversible color change using 3D printed switchable multistability and bistable switch panels that augment the projected area a viewer perceives which enables the creation of image and character tessellation.</p> <p>Switchable multistability (SMS) arises from the combination of pre-strain and shape memory, allowing us to access multiple elastically programmed shapes at elevated temperatures with fast morphing and low actuation forces, while retaining high stiffness at room temperature. We design and manufacture SMS Mechxels using fused deposition modeling (FDM) 3D printing on the Ultimaker 3D printer in a bilayer layup of polylactic acid (PLA) with a [90/0] print direction while iteratively miniaturizing the physical size to enhance the resolution while also reducing the size of the overall tessellated display. Leveraging SMS properties programmed into each Mechxel, the projected area to a viewer will vary between the unit’s stable states, creating a difference in perceived value of coloration due to changes in area. To ease the tessellation process, we also introduce a tessellation user interface that maps images to their tessellated equivalent to reduce tessellation trial and error. This interface also calculates the number of Mechxels required in their respective states and the final physical size of the display. We then carry out image processing to justify this change in value between stable states and run preliminary optical character recognition.</p> <p>Inspired by mechanical bistable mechanisms, the bistable switch Mechxels utilize changes in a surface’s projected area to a viewer via changes in the angle of a bistable tile using a 5-by-5 grid for character replication and display. Comprising of three main components – two bistable switches, a colored tile and a base, design considerations were made to create an easy to assemble and replaceable 3D printed grid system that could be interacted with by audiences or easily electromechanically actuated. Using pixel-by-pixel comparisons and Sorensen-Dice coefficient, characters using the typeface Silkscreen were documented on these tiled grids yielding high similarity and low error when compared to their digital reference images in various positions and orientations. We also experiment with transitional waves as a promising means of actuation to change the Mechxel between their stable states.</p> <p>The Mechxels considered in this research introduce a new means of purely mechanical color change, character, and image display either leveraging the elastic properties of shape memory polymers (SMPs) or bistable mechanisms. With potential applications in passive morphing architecture, adaptive camouflage, and interactive aesthetic, Mechxels opens the door to limitless design possibilities through a new perspective into color change.</p>

No description available.

No description available.

No description available.

No description available.

4D printing is a rapidly emerging field in which 3D printed stimuli-responsive materials produce morphing and multifunctional structures, with time being the fourth dimension. This approach enables the 3D printing of pre-programmed responsive sheets, which transition into complex curved shapes upon exposure to external stimuli, resulting in a substantial reduction in material consumption and printing time (70 - 90 %). Commonly used materials for 4D printing are polymer composites, such as hydrogels, polydimethylsiloxane (PDMS), liquid crystal elastomers (LCEs), and shape memory polymers (SMPs). However, the low elastic modulus (E) that these materials exhibit during shape change (E range of 10-4 – 10 MPa) limits their scalability, actuation stress, and load bearing. Moreover, these materials exhibit low ultimate stresses, leading to correspondingly low toughness (K) values in the range of 0.08 to 5 MJ m-3. Consequently, this results in structures with low damage tolerance. Therefore, an existing challenge for the field of 4D printing is to develop materials that can maintain their large and predictable morphing mechanism for complex shape transformation, while improving the E and K for high performance applications. Furthermore, many existing approaches rely on passive structures that necessitate the control of global conditions of the surrounding environment (e.g., hot plates, ovens, external magnets, water baths) to provide the stimulus for actuation. In this work, we tackle these challenges by introducing novel materials, ink formulations, and innovative printing techniques for multi-material Direct Ink Writing (DIW). We aim to create electrically controllable 4D printed structures that exhibit exceptional stiffness and toughness, all while preserving a large and predictable morphing mechanism for intricate shape transformations. First, we introduce multiscale heterogeneous polymer composites as a novel category of stiff, electrically controllable thermally responsive 4D printed materials. These composites consist of an epoxy matrix with an adjustable cross-link density and a plurality of isotropic and anisotropic nanoscale and microscale fillers. Leveraging this platform, we generate a set of 37 inks covering a broad range of negative and positive linear coefficients of thermal expansion. This set of inks exhibits an elastic modulus range that is four orders of magnitude greater than that of existing 4D printed materials and offers tunable electrical conductivities for simultaneous Joule heating actuation and self-sensing capabilities. Utilizing electrically controllable bilayers as building blocks, we design and print a flat geometry that changes shape into a 3D self-standing lifting robot, displaying record actuation stress and specific force when compared to other 3D printed actuators. We integrate this lifting robot with a closed-loop control system, achieving autoregulated actuation exhibiting a 4.8 % overshoot and 0.8 % undershoot, while effectively rejecting disturbances of up to 170 times the robot's weight. Furthermore, we employ our ink palette to create and 3D print planar lattice structures that transform into various self-supporting complex 3D surfaces. Ultimately, we achieve a 4D printed electrically controlled crawling robotic lattice structure, highlighting its capacity to transport loads up to 144 times its own weight. Finally, we introduced a printable PDMS adhesive that serves as synthetic fascia to hold our epoxy-based synthetic muscle together, enhancing the K of our 4D printed structures, all while maintaining high stiffness, large, predictable, and addressable actuation mechanism. Through the integration of these soft adhesive materials with high-stiffness thermally responsive epoxies via DIW, we achieved an improvement of about two orders of magnitude in the K of the resulting synthetic muscle composite, all while maintaining high stiffness and morphing mechanism. Utilizing this fabrication method, we printed an electrically controllable bilayer exhibiting damage detection and tolerance, enduring up to 7 fractures while continuing to function effectively. Furthermore, we integrated the synthetic muscle composite into our lifting robot design, setting yet again new records in specific force and actuation stress when compared to other 3D printed actuators. Notably, even after failure, the actuator maintained its operational integrity and high performance. Ultimately, we present a 4D printed lattice structure featuring the incorporation the synthetic muscle composite, showcasing a sensitive electrically responsive surface with fracture detection capabilities. To emphasize this, we subjected one of these 4D printed lattices to extreme conditions, driving a car over it. Notably, the lattice structure detected fractures and exhibited high resilience, enduring external compressive damage equivalent to 331,060 times its own weight. / 2026-05-23T00:00:00Z

Inventée en 1983, comme procédé de prototypage rapide, la fabrication additive (FA) est aujourd’hui considérée comme un procédé de fabrication quasiment au même titre que les procédés conventionnels. On trouve par exemple des pièces obtenues par FA dans des structures d’aéronef. Cette évolution de la FA est due principalement à la liberté de forme permise par le procédé. Le développement de diverses techniques sur le principe de fabrication couche par couche et l’amélioration en quantité et en qualité de la palette de matériaux pouvant ainsi être mis en forme, ont été les moteurs de cette évolution. De nombreuses autres techniques et matériaux de FA continuent de voir le jour. Dans le sillage de la FA (communément appelée impression 3D) a émergé un autre mode de fabrication : l’impression 4D (I4D). L’I4D consiste à explorer l’interaction matériaux intelligents (MIs) – FA. Les MIs sont des matériaux dont l’état change en fonction d’un stimulus ; c’est le cas par exemple des matériaux thermochromiques dont la couleur change en réponse à la chaleur ou des hydrogels qui peuvent se contracter en fonction du pH d’un milieu aqueux ou de la lumière. Les objets ainsi obtenus ont – en plus d’une forme initiale (3D) – la capacité de changer d’état (en fonction des stimuli auxquels sont sensibles les MIs dont ils sont faits) d’où la 4e dimension (temps). L’I4D fait – à juste titre – l’objet d’intenses recherches concernant l’aspect fabrication (exploration de nouveaux procédés et matériaux, caractérisation, etc.). Cependant très peu de travaux sont entrepris pour accompagner les concepteurs (qui, a priori, ne sont ni experts FA ni des experts de MIs) à l’utiliser dans leurs concepts. Cette nouvelle interaction procédé-matériau requiert en effet des modèles, des méthodologies et outils de conception adaptés. Cette thèse sur la conception pour l’impression 4D a pour but de combler ce vide méthodologique. Une méthodologie de conception pour la FA a été proposée. Cette méthodologie intègre les libertés (forme, matériaux, etc.) et les contraintes (support, résolution, etc.) spécifiques à la FA et permet aussi bien la conception de pièces que celle d’assemblages. En particulier, la liberté de forme a été prise en compte en permettant la génération d’une géométrie minimaliste basée sur les flux fonctionnels (matière, énergie, signal) de la pièce. Par ailleurs, les contributions de cette thèse ont porté sur la conception avec les matériaux intelligents. Parce que les MIs jouent plus un rôle fonctionnel que structurel, les préoccupations portant sur ces matériaux doivent être menées en amont du processus de conception. En outre, contrairement aux matériaux conventionnels (pour lesquels quelques valeurs de paramètres peuvent suffire comme information au concepteur), les MIs requièrent d’être décrits plus en détails (stimulus, réponse, fonctions, etc.). Pour ces raisons un système d’informations orientées conception sur les MIs a été mis au point. Ce système permet, entre autre, d’informer les concepteurs sur les capacités des MIs et aussi de déterminer des MIs candidats pour un concept. Le système a été matérialisé par une application web. Enfin un cadre de modélisation permettant de modéliser et de simuler rapidement un objet fait de MIs a été proposé. Ce cadre est basé sur la modélisation par voxel (pixel volumique). En plus de la simulation des MIs, le cadre théorique proposé permet également le calcul d’une distribution fonctionnelle de MIs et matériau conventionnel ; distribution qui, compte tenu d’un stimulus, permet de déformer une forme initiale vers une forme finale désirée. Un outil – basé sur Grasshopper, un plug-in du logiciel de CAO Rhinoceros® – matérialisant ce cadre méthodologique a également été développé. / Invented in 1983, as a rapid prototyping process, additive manufacturing (AM) is nowadays considered as a manufacturing process almost in the same way as conventional processes. For example, parts obtained by AM are found in aircraft structures. This AM evolution is mainly due to the shape complexity allowed by the process. The driving forces behind this evolution include: the development of various techniques on the layer-wise manufacturing principle and the improvement both in quantity and quality of the range of materials that can be processed. Many other AM techniques and materials continue to emerge. In the wake of the AM (usually referred to as 3D printing) another mode of manufacturing did emerge: 4D printing (4DP). 4DP consists of exploring the smart materials (SM) – AM interaction. SMs are materials whose state changes according to a stimulus; this is the case, for example, with thermochromic materials whose color changes in response to heat or hydrogels which can shrink as a function of an aqueous medium’s pH or of light. The objects thus obtained have – in addition to an initial form (3D) – the capacity to shift state (according to the stimuli to which the SMs of which they are made are sensitive) hence the 4th dimension (time). 4DP is – rightly – the subject of intense research concerning the manufacturing aspect (exploration of new processes and materials, characterization, etc.). However, very little work is done to support the designers (who, in principle, are neither AM experts nor experts of SMs) to use it in their concepts. This new process-material interaction requires adapted models, methodologies and design tools. This PhD on design for 4D printing aims at filling this methodological gap. A design methodology for AM (DFAM) has been proposed. This methodology integrates the freedoms (shape, materials, etc.) and the constraints (support, resolution, etc.) peculiar to the AM and allows both the design of parts and assemblies. Particularly, freedom of form has been taken into account by allowing the generation of a minimalist geometry based on the functional flows (material, energy, and signal) of the part. In addition, the contributions of this PhD focused on designing with smart materials (DwSM). Because SMs play a functional rather than a structural role, concerns about these materials need to be addressed in advance of the design process (typically in conceptual design phase). In addition, unlike conventional materials (for which a few parameter values may suffice as information to the designer), SMs need to be described in more detail (stimulus, response, functions, etc.). For these reasons a design-oriented information system on SMs has been developed. This system makes it possible, among other things, to inform designers about the capabilities of SMs and also to determine SMs candidates for a concept. The system has been materialized by a web application. Finally, a modeling framework allowing quickly modeling and simulating an object made of SMs has been proposed. This framework is based on voxel modeling (volumetric pixel). In addition to the simulation of SMs behaviors, the proposed theoretical framework also allows the computation of a functional distribution of SMs and conventional material; distribution which, given a stimulus, makes it possible to deform an initial form towards a desired final form. A tool – based on Grasshopper, a plug-in of the CAD software Rhinoceros® – materializing this methodological framework has also been developed.

No description available.

The field of biomedical sciences has been expanded through the introduction of a novel cohort of soft and intelligent microrobots that can be remotely operated and controlled through the use of external stimuli, such as ultrasound, magnetic fields, or electric fields, or internal stimuli, such as chemotaxis. The distinguishing factor of these microrobots lies in their propulsion system, which may encompass chemical, physical, or biohybrid mechanisms. Particularly, microrobots propelled by motile cells or microorganisms have found extensive usage because they combine the control/steerability and image-enhancement capabilities of the synthetic microstructures with the taxis and cell-interaction capabilities of the biological components. Spermatozoa (sperms), among other types of motile microorganisms and cells, are promising biological materials for building biohybrid microrobots because they are inherently designed to swim through complex fluids and organs, like those in the reproductive system, without triggering negative immune responses. Sperms are suitable for a variety of gynecological healthcare applications due to their drug encapsulating capability and high drug-carrying stability, in addition to their natural role of fertilization. One objective of this project is to help sperms reach the site of fertilization in vivo where the sperm count is low (20 million sperm per mL), a condition known as oligospermia. In order to reach this goal, we are developing alternative strategies for transporting a significant number of sperms, as well as improving the functionality of sperm-hybrid microcarriers. Here, we use a thermoresponsive hydrogel made of poly(N-isopropylacrylamide) (PNIPAM) and a non-stimuli-responsive polymer (IPS photoresist) to create four dimensional (4D)-printed sperm-hybrid microcarriers via two-photon polymerization (TPP). We present a multifunctional microcarrier that can: i) transport and deliver multiple motile sperms to increase the likelihood of fertilization, ii) capacitate/hyperactivate the sperms in situ through the local release of heparin, and iii) assist the degradation of the hyaluronic acid (HA), present in extracellular matrix (ECM) of oocyte-cumulus surrounded the Egg. HA degradation occurs through the local action of hyaluronidase-loaded polymersomes (HYAL-Psomes) that have been immobilized on the microcarrier's surface. Dual ultrasonic (US)/photoacoustic (PA) imaging technology can also be used to visualize a swarm of microcarriers, making them ideal candidates for upcoming in vivo applications. In addition, as a second objective, we demonstrate that similar sperm-hybrid microcarriers can be utilized to deliver targeted enzymes and medication for the treatment of gynecological cancer. As proof of concept, we show that combined therapy using enzymes and anti-cancer drugs is an appealing strategy for disrupting the tumor tissue microenvironment and inducing cell apoptosis, thereby offering a more effective cancer therapy. To achieve this, we functionalize the microcarriers with polymersomes loaded with enzymes (such as hyaluronidase and collagenase) and anti-cancer drugs (such as curcumin), respectively, and demonstrate their cargo-release capability, enzyme function, and therapeutic effect for targeting cervical cancer cells in vitro.:Abstract iv 1 Introduction 1 1.1 Motivation 1 1.2 Objectives 3 1.3 Structure of this dissertation 4 2 Background 5 2.1 Introduction on additive manufacturing technology 5 2.2 Direct laser writing (DLW) based on two-photon polymerization 6 2.2.1 Writing principles of two-photon lithography 8 2.2.2 Available materials for two-photon lithography 9 2.2.3 Engineering (Preprogrammed designs) 12 2.3 4D Lithography 13 2.3.1 Biodegradable microrobot 13 2.3.2 Stimuli-responsive micromotors 15 2.3.3 Other 4D-printing approaches 17 2.4 Motion at the microscale (Micromotility) 21 2.4.1 Physical propelled micromotors 23 2.4.2 Chemical propelled micromotors 32 2.4.3 Biohybrid micromotors 34 2.5 Other two-photon polymerized microrobots and their biomedical applications 35 2.5.1 Functionalized carriers 36 2.5.2 Multiple-cell carrying scaffolds 38 2.5.3 Single particle and cell transporters 39 2.6 Comparison of 3D and 4D-lithography with other fabrication methods 42 3 Materials and methods 44 3.1 Synthesis and fabrication 44 3.1.1 Synthesis of PNIPAM 44 3.1.2 Fabrication of microcarrier 44 3.1.3 Preparation of sperm medium and sperm solution 45 3.1.4 Preparation and composition of different body fluids 45 3.1.5 Fluidics channels 46 3.1.6 In situ preparation of microcarriers and sperms 46 3.1.7 Loading of microcarriers with heparin 46 3.1.8 Synthesis of block copolymers (BCPs) 47 3.1.9 Fabrication of Empty-Psomes A and D 48 3.1.10 Preparation of Curcumin complex CU(βCD)2 and calibration curve 49 3.1.11 Fabrication of cargo-loaded Psomes with enzymes and antitumoral drug 50 3.2 Characterization 51 3.2.1 MTS-Assay 51 3.2.2 Toluidine blue assay 52 3.2.3 Characterization of Empty-Psomes A and D: pH cycles and pH titration by dynamic light scattering (DLS) 53 3.2.4 Characterization of cargo-loaded Psomes with enzymes and antitumoral drug 54 3.2.5 Loading efficiency of HYAL-Psomes 55 3.2.6 Loading efficiency of MMPsomes 56 3.2.7 Loading efficiency, stability and release study of CU(βCD)2-Psomes 57 3.2.8 Size and polydispersity analysis of cargo-loaded Psomes in different simulated body fluids by DLS 58 3.2.9 Conformation and stability study of cargo-loaded Psomes in different simulated body fluids by asymmetric flow field flow fractionation (AF4) 59 3.2.10 Immobilization of the cargo-loaded Psomes on the surfaces 61 3.2.11 Enzymatic assay of HYAL for enzyme activity measurement 62 3.2.12 Enzymes assay in different simulated body fluids 64 3.2.13 Stability study of RhB-HYAL-Psomes in different pH 65 3.2.14 Calculation of the magnetic field flux of an external hand-held magnet 66 3.3 Temperature actuation and imaging 67 3.3.1 Temperature actuation test of PNIPAM and video recording 67 3.3.2 Hybrid ultrasound (US) and photoacoustic (PA) Imaging 67 3.4 Other useful information 68 3.4.1 pH and temperature through the female reproductive tract 68 3.4.2 Calculation of the light-to-heat conversion during imaging process 69 4 Multifunctional 4D-printed sperm-hybrid microcarriers for assisted reproduction 72 4.1 Background 72 4.2 Concept and fabrication of the 4D-printed microcarriers 74 4.3 Sperm coupling and geometrical optimization of microcarrier 77 4.4 Characterization of the 4D-printed streamlined microcarriers 78 4.5 Microcarrier loaded with heparin for in situ sperm capacitation 82 4.6 Microcarriers decorated with HYAL-Psomes for in situ degradation of the HA-cumulus complex 86 4.6.1 Immobilization of HYAL-Psomes on the microcarrier’s surface 89 4.6.2 Qualitative study of cumulus cell removal 90 4.7 Sperm-microcarrier motion performance in oviduct-mimicking fluids 91 4.7.1 Capture, transport, and release of sperms 92 4.7.2 Sperm-microcarrier motion performance on ex vivo oviduct tissue 93 4.8 Tracking of a swarm of microcarriers with a dual ultrasound (US) and photoacoustic (PA) imaging system 95 4.9 Summary 96 5 Polymersomes-decorated micromotors with multiple cargos for gynecological cancer therapy 98 5.1 Background 98 5.2 Characterization and size quantification of Psomes before and after loading of cargoes by DLS, and Cryo-TEM 103 5.3 Characterization and size quantification of cargo-loaded Psomes by DLS, and Cryo-TEM in different simulated bodily fluids 104 5.4 Immobilization and characterization of cargo-loaded Psomes on the microcarrier’s surface 106 5.5 Immobilization and characterization of dual cargo-loaded Psomes on the microcarrier’s surface 108 5.6 Investigation of ECM degradation and antitumoral effect of cargo-loaded Psomes 110 5.7 Magnetic and bio-hybrid guidance of microcarriers toward targeted cargo delivery 115 5.8 Summary 117 6 Conclusion and Outlook 119 6.1 Achievements 119 6.2 Outlook 121 Bibliography I List of Figures and Tables XXI Acknowledgements and funding XXIV Scientific publications and contributions XXVI Curriculum Vitae XXVII