The primary objective of this research is to develop an efficient protocol which can be used to 3D print multi-material microfluidic devices with a high resolution. During this research, the fabrication of multi-material microfluidic valves is discussed as a showcase to verify the multi-material protocol, using a single affordable printer and multiple resin vats. In contrast to single material microfluidic fabrication methods, complex geometries can be created by the use of combinations of stiff and flexible materials in a single 3D print. This protocol aims to streamline the fabrication process while ensuring precise feature reproduction and robust mechanical properties in multi-material 3D printed microfluidic parts.

In this study, the effects of UV light exposure on feature accuracy and mechanical performance is systematically investigated. It is observed that for the rigid material, Anycubic High Clear, sample sizes increase and void features shrink when the exposure to UV light increases. For the soft material, Liqcreate Elastomer-X, shrinkage rates after swelling due to IPA absorption are compared under different conditions, revealing that shrinkage occurs more rapidly with a heat source than at ambient temperature.

Mechanical properties are further evaluated through tensile testing of four sets of printed dogbones, showing that extended UV exposure enhances mechanical properties such as the Young's modulus, ultimate tensile strength and strength at break. Elastomeric materials assessed in this study demonstrate an optimal measurement accuracy within a strain range of 10% to 50%. The influence of print orientation is assessed for the hard material. This experiment is executed for layer thicknesses from 10 µm to 200 µm across horizontal, vertical, and diagonal orientations, with vertically printed samples being closest to the intended dimensions.

A comprehensive multi-material 3D printing protocol based on the existing "print-pause-print" technique and utilizing the software UVTools is presented. Finally, a microfluidic Quake valve is designed and optimized for 3D printing, its performance is analyzed through finite element (FEM) simulation and analytical calculations.

The results of this study offer valuable insights into the optimization of multi-material 3D printing for microfluidic applications, highlighting several critical parameters that affect feature resolution and mechanical performance. The proposed protocol and findings serve as a foundation for future advancements in the fabrication of complex microfluidic devices.

Atrial fibrillation is a cardiac arrhythmia resulting from abnormal electrical conduction and impulse formation within the atria. To address this condition, a minimally invasive procedure called cardiac ablation is performed. Real-time visual feedback during this procedure plays a critical role in determining its success.

Photoacoustic imaging is a technique capable of providing real-time visual feedback. Integrating photoacoustic capabilities into existing Radiofrequency ablation catheters poses a significant challenge, which this thesis addresses. The proposed integrated solution employs optical fibers for light delivery and an ultrasound transducer for signal reception.

This work investigates the design of two light delivery systems for integrated photoacoustic-guided surgery. Monte Carlo simulations are employed to study three-dimensional light propagation in tissue, informing the catheter design specifications. Optimal fiber distances and orientations within the catheter are determined based on normalized fluence values and illumination spot size—critical parameters for assessing the amount of delivered light, its area of coverage, and depth of penetration. The methodology presented applies to various photoacoustic applications.

The simulation study was able to successfully inform design specifications and it was able to establish a relation between design variables and the evaluation criteria such that it can be referred to for future designs. The comparative study yielded a better-performing design configuration and its optimal specifications were found out. This proves the use of a simulation-based evaluation to design a photoacoustic intracardiac catheter. In the final phase of this research, an experiment is set up to validate the light delivery of the design, which provides a clear outlook for the future of these designs into fabricated products.

In conventional aircrafts, lift control is achieved by using flap systems. It would be beneficial if flap systems could be replaced by a variable-camber morphing wing. It has been shown that variable-camber morphing wings can significantly improve the aerodynamic performance of the aircraft due to the smoothness of the surface, making it possible to fly more efficiently, reduce fuel consumption and reduce the impact on the environment. However, the design of such a variable-camber morphing wing is challenging due to the conflicting requirements of the structure. The wing should be flexible so it can morph, stiff so it can withstand aerodynamic pressures and light weight to reduce fuel consumption. The aim of this work is to provide a method for the density-based topology optimization of compliant morphing structures. The method includes a novel formulation for the objective function which compares the deformed shape of the structure with a desired deformed shape by using a dot product. This method is applied to obtain an optimized design of a compliant variable-camber morphing wing. The obtained design was converted to a prototype by 3D printing and an experiment was performed to assess if the deformed shapes of the prototype were similar to the ones predicted by the analysis in the topology optimization. The experiment showed that for small deformations the output shape matched the predicted output shape. For larger deflections, there was a slight difference. However, the obtained shapes were still quadratic-like and so it is expected that for larger deformations the designed trailing edge will still have superior aerodynamic performance than conventional flap systems.

Applications for thermoelastic metamaterials, in which extremely positive, zero or negative thermal expansion is desired, are plentiful. Nevertheless they are rarely applied, due to their poor manufacturability. To enhance their applicability, a topology optimization framework is proposed and verified, able to generate finite thermoelastic metamaterials with tailored unidirectional thermal expansion, manufacturable through automated multi-material additive manufacturing methods. The superelement method is utilized to optimize for finite thermoelastic unit cell arrays connected to solid strips allowing for easy mounting, instead of non-realizable infinite arrays which are optimized in existing frameworks that use the homogenization method. The robust formulation is combined with a filter domain extension approach, to obtain manufacturing tolerant, black and white solutions and minimum length scale control. Uniform material layers are enforced, to obtain layered designs manufacturable with multi-material additive manufacturing methods. Using the proposed framework, a finite thermoelastic unit cell array is optimized for near zero thermal expansion. It is validated that the superelement method is more suitable for the computation of the thermoelastic response of small unit cell arrays, compared to the commonly used homogenization method. A physical sample is manufactured and experimentally validated. Experimental validation confirms numerical predictions and shows that the proposed design approach is able to generate performant and realizable thermoelastic metamaterials.

The work presented in this report is an attempt to allow density-based topology optimization algorithms to take into account machining costs when optimizing. To this end, and estimation model for the cost of 2.5-axis CNC milling was developed based on the principles of Design for Manufacturing.
This estimation model was implemented in a generic topology optimization algorithm in five steps of complexity. The behaviour of the model was evaluated at each step by means of a set of experiments, showing how the addition of the cost estimation influences the optimization results.
The most promising results from the experiments are validated with Autodesk Fusion 360, with which the designs were programmed to be machined on a CNC mill. The machining times from this software were used to calculate the actual machining costs and these were compared to the machining costs estimated by the optimizer.
Two formulations of the method were found to be useful for estimating the machining cost of designs. A simple formulation that uses the shape factor and the differentiation between internal and external pockets to estimate the cost resulted in a cost saving of 13% at the expensive of a compliance increase of 9%. The more complex formulation uses multiple pocket domains to evaluate pocket-specific properties. This allowed a more accurate estimation of the costs, but did not result in a better performing optimization. The cost saving was comparable at 12%, but the compliance increased by 16%.
It was concluded that there is a use for both methods. The simple formulation allows to find cheaper designs, but does not allow much control in the cost estimation. The complex formulation however can be used to fine-tune the method for a specific situation, which could enable it to perform better that the simple formulation.

The concept of metamaterials has been extended from electromagnetics and acoustics to the field of mechanics. Metamaterials do not derive their properties from those of the composite, but from the artificial meso-scale geometry as well as from the unit cell structure. Mechanical metamaterials are constrained in that the mechanical properties are precisely defined and fixed; alteration between these properties simply is not feasible. However, if activated, metamaterials can be controlled and mechanical properties can be influenced. In this research project, a novel active metamaterial unit cell design for controlled damping has been introduced. Centimeter-scale electromagnetic actuators are integrated as activators in an elastic mechanical metamaterial structure. The design effectively exploits the way in which the reluctance actuator functions, and tuning of the integrated electromagnet allows for ranging Coulomb damping. A proof-of-principle unit cell demonstrator of 90mm and one of 45mm, in length have been made. The electrically controlled damping behaviour of the active unit cells has been validated for cyclic loading deformations and the force-displacement curve has resulted in a damped over stored energy range from 3% and 20% up to 34% and 132% respectively.

Production and manipulation of microdroplets is an active are of research. The demand for finding new ways to produce microdroplets has resulted in a challenge to characterize these droplets. The problem becomes especially difficult for microdroplets which are placed on a transparent hydrophilic substrate. Ink-jet printing, Digital microfluidics, DNA synthesis are some of the applications which need topography measurements of low contact angle microdroplets. One application which is of interest is the sample preparation for Cryo Electron Microscopy (cryo-EM). A recent development in the search for efficient sample preparation for cryo-EM is to use hollow microcantilevers (HMC). HMCs can isolate even a single sub-cellular component and help prepare samples confined in a femtoliter droplet. These droplets are dispensed on a hydrophilic Electron Microscopy grid (EM-grid). By controlling the thickness of the water layer on the EM-grid through evaporation, it is possible to make the HMC technology more reliable by reducing sample wastage. However, such a control loop is absent. A real-time topography measurement of such droplets can serve as a control signal which can be used as feedback for a control loop. The objective of this project is to investigate the feasibility of optical methods to measure the topography information of a low contact angle microdroplet. The scope of this project is limited to develop a tool for a droplet which is supported by a glass slide (droplet-on-glass). In a subsequent study, the tool will be tested for droplets supported on grid (droplet-on-grid). An optical interferometry setup is proposed as a solution. A Mach-Zehnder interferometer is built to obtain the experimental fringes. A Single Frame Fourier Transform technique was used to analyze the data and obtain the results. Droplets of glycerol were dispensed on a glow discharged glass slide. Topography of the droplet was obtained until complete evaporation and a detection limit of 165nm was achieved. The accuracy of the method was found by comparing the results obtained with a Bruker White Light Interferometer (Bruker-WLI) in Phase Shifting Interferometry mode. An accuracy of 23\% was observed. The proposed setup had a repeatability of 14.7nm. To measure the reproducibility of the setup, a 3d printed structure which had the same size and shape as that of a droplet was used. The reproducibility of the setup was found to be 19.8nm over three days. Simulations were performed to analyze the effect of filter shape, filter width and the carrier frequency. Based on these findings, steps to measure a droplet-on-grid system with the proposed setup is explained. Further, to test the capabilities of the instrument the evaporation of a large water droplet on a EM-grid was observed using the proposed setup. It was found that the motion of fringe pattern as the droplet evaporates could give a good indication to control the evaporation time of even conventional machines, which do not employ hollow microcantilevers to dispense small droplets. However, final validation of the proposed setup with the cryo-EM is yet to be performed due to time constraints. As a recommendation for future work, new ways of dispensing samples on the EM-grid are explored. The necessary steps required to validate the setup with a cryo-EM are explained. Further, some ways in which the analysis time could be reduced are explored. This will be helpful in developing a software necessary to implement a real-time solution.

Microvalves are important flow-control devices in many standalone and integrated microfluidic applications. PDMS-based (Polydimethylsiloxane) pneumatic microvalves are the most commonly used type for research purposes, but they require large peripheral connections and cannot be used for controlling gases due to the high gas permeability of PDMS. There are many alternatives found in the literature that use Si-based microvalves, but variants that can throttle even moderate pressures (1 bar) tend to be bulky (cm-range), have a complex fabrication process, or consume high power. This thesis details the development of a low-power, normally-open piezoelectric microvalve to control flows with a maximum driving pressure of 1 bar, but also retain a small effective form-factor of 5mm x 5mm x 1.8mm. A novel combination of rapid-prototyping methods like stereolithography and laser-cutting was used to realize this device. The maximum displacement of the fabricated microactuator was measured to be 8.5 μm at 150V. The fabricated microvalve has a flow-range of 0 - 90 μL/min - water at 1 bar inlet pressure. When fully closed, a leakage of 0.8% open-flow was observed with a power-consumption of 37.5 μW. A flow resolution of 0.2 μL/min was measured at 0.5 bar pressure.

In the industry motion systems with electric motors are used for transporting and positioning thin flexible substrates at high throughput rates. A possible alternative actuation solution could be to apply contactless air film actuators which make use of air bearing principles. The air film actuators use a thin film of air to levitate and propel a substrate. The main advantage of such a technique is that it actuates directly on the substrate and therefore eliminates the moving mass of a carrier. This drastically reduces the actuation force required to accelerate the substrate, which reduces unwanted deformations and excitations of the machine frame. Because the substrate is not in direct contact with the bearing surface, the substrate does not experience any wear, stiction or backlash effects. In this project a demonstrator with opposed air film actuators is designed and manufactured to actuate a flexible substrate in one degree of freedom. To predict the performance of the motion system, the air film actuators are modelled with the use of the Reynolds equation for compressible air, determined both analytically and numerically. The demonstrator consists of two manifolds with their bearing surfaces facing each other and where a substrate is placed between the two bearing surfaces. By using pressurized air, the substrate can be levitated between the two bearing surfaces. By controlling proportional valves, the substrate can be moved in negative or positive x-direction. The theoretical models show good resemblance with the measurement results. However, the substrate vibrated and did not float fully contactless between the two bearing surfaces. Based on these results, improvements can be made on the bearing function of the system, but the demonstrator shows promising results for actuating substrates with large accelerations and fast responses.

In this thesis, a methodology is developed that allows for both reliable and computational efficient robustness analysis of aircraft component distortion. This research applies to dis- tortion caused by reductive manufacturing processes that are used to obtain monolithic components from pre-stressed stock material. With the developed methodology, orienta- tions of any component within rolled plate stock material can be found where distortion is most robust. Part distortion is defined as a deviation in shape of an aircraft component from original intent as a result of the component’s reductive manufacturing process. As extreme precision is required in aircraft component assembly, the distortion phenomenon is highly undesired. The developed methodology in this thesis contributes to AIRBUS’ objectives to minimize part distortion related issues. In this thesis, the fundamentals of part distortion are studied. It is found that aircraft com- ponents distort as a result of residual stresses that are present in stock material from which the components are manufactured. As residual stress in rolled plate is subjected to substan- tial variation, part distortion is stochastic in nature. Positions of the components in rolled plate are searched for where distortion is most robust. The robustness of distortion refers to the insensitivity of distortion to uncertainty in residual stress. A mathematical stochastic representation of residual stress in rolled plate is developed showing high coherence with experimental measurement data provided by AIRBUS. For elementary geometries, the rela- tionship between distortion robustness and residual stress is derived analytically. The developed method for predicting distortion robustness is more than one hundred times more efficient in terms of computation cost compared to state-of-the-art methods and al- lows for reliable robustness predictions. In the developed method, three-dimensional po- sitioning of a component in rolled plate can be simulated where state-of-the-art distortion modeling tools usually stick to one dimension. The developed methodology is put to the test in a case study concerning an aircraft stiffener component. The case study emphasizes the significance of robustness predictions; distor- tion dispersion is found to be relatively large compared to the distortion magnitude and significant correlation is found between the component’s orientation in rolled plate and the level of robustness. Positions of components in rolled plate can be found where distortion is extremely robust. Moreover, a relationship is found between the component’s degree of symmetry and the level of robustness.

Suspended hollow micro-cantilevers have been employed for zeptogram (10^-21 g) mass measurements, pipetting of femtoliter
(10^-15 L) volumes, and studies on mechanical interaction with single cells. The main fabrication method of these devices is by standard clean room micro/nano fabrication techniques, however, they are inherently planar, thus limiting three dimensional design, and the required masks make prototyping time-consuming and expensive. In this work maskless 3D-printing by two-photon polymerization (2PP) was used to fabricate hollow microfluidic cantilevers. A novel fluidic interfacing approach was developed by directly 2PP-printing the cantilever on a stereolithographic microfluidic device for handling and connecting to the external world. Several 350 µm long cantilevers with an aperture of 25 µm were mechanically characterised by laser Doppler vibrometry and the fundamental frequency was measured at 99,6 kHz, with a quality factor of approximately 174 in air. A hydraulic model was constructed and fluidic functionality was demonstrated. The non-optimised printing time of the full device was approximately 2.5 hours, performed by only two automated maskless fabrication steps. This printing method enables rapid prototyping of ready-to-use suspended microfluidic devices.

Organ on a Chip (OoC) systems are of high interest through its use for medicine testing in a small time scale without the need for animal testing. Membranes used in OoCs form a base to grow cells on and need to be suitable for cell-attachment and porous. Fouling is the 'Achilles heel' in membrane performance. Research shows that as a result of fouling the viability of the skin cells grown in the chip decreased to zero after 3 weeks. If research on organs is to extend and research on cell- or tissue growth will include longer time spans, the influence of membrane fouling with conditions similar to the OoC is an important factor to understand.
In this research a microfluidic flow cell is produced and used to explore fouling within the OoC. Static and dynamic fouling experiments are executed on membranes having pore sizes ranging from 0.4 to 5 μm.
Scanning electron microscope (SEM) images indicate that standard blocking and cake layer formation are dominating fouling mechanisms.
Membranes with 1 μm pore size are the most susceptible to standard blocking. Further a decrease in pore area of 0%, 11% and 20% and a decrease in uncovered amount of pores of 27%, 34% and 80% for Glycine, BSA and λ-DNA respectively are measured after one week of fouling.
Cake layer formation is seen after fouling for a shorter duration for BSA (one day) than for Glycine (one hour) and a higher concentration of BSA particles is permitted through all tested membranes than Glycine, therefore the conclusion is drawn that BSA causes less fouling than Glycine.

A manufacturing technology is proposed to manufacture polymeric membrane scaffolds for culturing of cells, tissues, and organoids with integrated sensor capabilities and fluidic functionalities. A multilayer substrate is imprinted with a soft mold to manufacture polymeric membrane scaffolds for culturing of cells, tissues, and organoids with integrated sensor capabilities and fluidic functionalities. Aside from exploiting the well characterized, simple and low cost techniques that can be employed in polymer manufacturing, the use of solely polymeric materials increases the opportunities for functional integration, while at the same time allowing for the translation of complex cleanroom fabrication processes into mold-based replication techniques. With this developed manufacturing technology, it is demonstrated that it is possible to manufacture membrane scaffolds with integrated porous electrode up to 1mm by 1mm in effective surface area, with a thickness of 10 µm, with control over the pore diameter (as small as 400 nm), the porosity, and the location of the pores. The morphological characterization is done by scanning electron microscopy. The integrated porous electrode’ performance is characterized electrically by a 4-point probe and electrochemically by cyclic voltammetry and electrochemical impedance spectroscopy. Showing the possibility to use the conductive layer to give cells electrical stimuli and for the use as a biosensor.

Transmission electron microscopy is a powerful and commonly used tool to study nanoparticles, nanowires and 2D materials. It provides static information from the sample with atomic resolution, in high vacuum and at ambient temperature. However, in real processes, the environment is often different and dynamic.

MEMS-based sample carriers became a breakthrough for in-situ TEM where they function as a micro-sized laboratory and enable dynamic studies. The Nanoreactor allows for manipulation of samples by simultaneously applying heat and gas stimuli, through which real-time studies of solid-gas interactions are enabled inside the TEM. Many challenges are still to be faced in further optimization of Nanoreactors. Especially because the tiny scale and the extreme conditions at which these devices must operate, limit the number of suitable tools to characterize and help understand their behavior.

In this project, the electro-thermo-mechanical behavior of the Nanoreactor is characterized using various microscale analytical techniques. The obtained results are used to model the Nanoreactor with finite element analysis, including electric current, mechanical stability, heat transfer, gas flow, and their interdependence. Using the acquired knowledge and the model, an optimized Nanoreactor design is proposed that improves membrane deflection, spatial sample drift, temperature homogeneity, temperature stability, gas flow speed and gas switching time.

Microfluidics has changed the way we think about laboratory experimental design. With the use of lab-on-chip devices, we are capable of carrying out experiments that include several functions on a single chip. Despite a lot of progress in the miniaturization of these devices, the peripheral systems which control the microfluidic functionalities like valves and pumps, remain bulky, making the microfluidic devices less portable. Conducting polymers are potential candidates that show promise to solve this issue and make the microfluidic devices portable. They are a class of polymer materials with intrinsic conductive properties and the ability to be formed and deformed at a low applied electric potential.
This thesis presents the different aspects of the conceptualisation and creation of the actuator for an all polymer conducting polymer microfluidic valve. The proposed system uses the widely studied multi-layer bending beam actuator, commonly used as an artificial muscle or soft actuator. The actuation of the all polymer system is the result of the different expansion rates during an electrochemical reaction.
The system consist of three polymer layers. The first layer is the flexible base layer that also functions as a fluid barrier in the microfluidic system. The second layer is the electrode material that is used as an electrode in both the fabrication and actuation of the expanding layer. The final layer is the electrochemically polymerized layer of expanding conducting polymer.
The all polymer actuator can eventually form the basis for new opportunities regarding the miniaturisation and commercialisation of Lab on Chip devices

The structuring of polymers on the micro and nanoscale is performed largely by lithographic techniques, which require complex steps and suffer from geometrical and scaling limits. Techniques such as Nanoimprint Lithography and Hot Embossing are attractive alternatives as they can produce high quality nanoscale structures with a high throughput. Colloidal building blocks offer a way to self-assemble the masters required for these replication steps. However, the difficulty with self-assembly lies in the creation of stable structures with little defect that are well controlled. This work sets out to provide a
comprehensive overview of the aspects of the fabrication of colloidal crystals, the most influential parameters and how they can be qualified. Offering a basis for future research on microscale replication by colloidal crystals and resulting in development of a method for the fabrication of colloidal crystal, which can be used as a master to replicate microscale patterns through Hot Embossing.