Synthesis of biocompatible superparamagnetic iron oxide nanoparticles (SPION) under different microfluidic regimes. - In: ACS applied materials & interfaces, ISSN 1944-8252, Bd. 14 (2022), 42, S. 48011-48028
Superparamagnetic iron oxide nanoparticles (SPION) have a great potential in both diagnostic and therapeutic applications as they provide contrast in magnetic resonance imaging techniques and allow magnetic hyperthermia and drug delivery. Though various types of SPION are commercially available, efforts to improve the quality of SPION are highly in demand. Here, we describe a strategy for optimization of SPION synthesis under microfluidics using the coprecipitation approach. Synthesis parameters such as temperature, pH, iron salt concentration, and coating materials were investigated in continuous and segmented flows. Continuous flow allowed synthesizing particles of a smaller size and higher stability than segmented flow, while both conditions improved the quality of particles compared to batch synthesis. The most stable particles were obtained at a synthesis condition of 6.5 M NH4OH base, iron salt (Fe2+/Fe3+) concentration ratio of 4.3/8.6, carboxymethyl dextran coating of 20 mg/mL, and temperature of 70 ˚C. The synthesized SPION exhibited a good efficiency in labeling of human platelets and did not impair cells. Our study under flow conditions provides an optimal protocol for the synthesis of better and biocompatible SPION that contributes to the development of nanoparticles for medical applications.
https://doi.org/10.1021/acsami.2c13156
Integration of biofunctional molecules into 3D-printed polymeric micro-/nanostructures. - In: Polymers, ISSN 2073-4360, Bd. 14 (2022), 7, 1327, S. 1-12
Three-dimensional printing at the micro-/nanoscale represents a new challenge in research and development to achieve direct printing down to nanometre-sized objects. Here, FluidFM, a combination of microfluidics with atomic force microscopy, offers attractive options to fabricate hierarchical polymer structures at different scales. However, little is known about the effect of the substrate on the printed structures and the integration of (bio)functional groups into the polymer inks. In this study, we printed micro-/nanostructures on surfaces with different wetting properties, and integrated molecules with different functional groups (rhodamine as a fluorescent label and biotin as a binding tag for proteins) into the base polymer ink. The substrate wetting properties strongly affected the printing results, in that the lateral feature sizes increased with increasing substrate hydrophilicity. Overall, ink modification only caused minor changes in the stiffness of the printed structures. This shows the generality of the approach, as significant changes in the mechanical properties on chemical functionalization could be confounders in bioapplications. The retained functionality of the obtained structures after UV curing was demonstrated by selective binding of streptavidin to the printed structures. The ability to incorporate binding tags to achieve specific interactions between relevant proteins and the fabricated micro-/nanostructures, without compromising the mechanical properties, paves a way for numerous bio and sensing applications. Additional flexibility is obtained by tuning the substrate properties for feature size control, and the option to obtain functionalized printed structures without post-processing procedures will contribute to the development of 3D printing for biological applications, using FluidFM and similar dispensing techniques.
https://doi.org/10.3390/polym14071327
Towards Funnel MPC for nonlinear systems with relative degree two. - In: Extended abstracts presented at the 25th International Symposium on Mathematical Theory of Networks and Systems MTNS 2022, (2022), S. 656-659
Funnel MPC, a novel Model Predictive Control (MPC) scheme, allows guaranteed output tracking of smooth reference signals with prescribed error bounds for nonlinear multi-input multi-output systems. To this end, the stage cost resembles the high-gain idea of funnel control. Without imposing additional output constraints or terminal conditions, the Funnel MPC scheme is initially and recursively feasible for systems with relative degree one and stable internal dynamics. Using an additional funnel for the derivative as a penalty term in the stage cost, these results can be also extended to single-input single-output systems with relative degree two.
https://doi.org/10.15495/EPub_UBT_00006809
A note on efficient and reliable prediction-based control in the Koopman framework. - In: Extended abstracts presented at the 25th International Symposium on Mathematical Theory of Networks and Systems MTNS 2022, (2022), S. 584-587
Extended Dynamic Mode Decomposition, embedded in the Koopman framework, is a widely-applied technique to predict the evolution of an observable along the flow of a dynamical (control) system. However, despite its popularity, the error analysis for control systems is still fragmentary. Here, we provide a complete and rigorous analysis of the approximation error for control systems. To this end, the approximation error is split up according to its two sources of error: the finite dictionary size (projection) and the finite amount of i.i.d. data used to generate the surrogate model (estimation). Then, invoking - among others - finite-elements techniques and the Chebyshev inequality, probabilistic error bounds are derived. Finally, we demonstrate the applicability of the novel error bounds in optimal control with state and control constraints.
https://doi.org/10.15495/EPub_UBT_00006809
Port-Hamiltonian system nodes. - In: Extended abstracts presented at the 25th International Symposium on Mathematical Theory of Networks and Systems MTNS 2022, (2022), S. 441-444
We present a framework to formulate infinite dimensional port-Hamiltonian systems by means of system nodes, which provide a very general and powerful setting for unbounded input and output operators that appear, e.g., in the context of boundary control or observation. One novelty of our approach is that we allow for unbounded and not necessarily coercive Hamiltonian energies. To this end, we construct finite energy spaces to define the port-Hamiltonian dynamics and give an application in case of multiplication operator Hamiltonians where the Hamiltonian density does not need to be positive or bounded. In order to model systems involving differential operators on these finite energy spaces, we show that if the total mass w.r.t. the Hamiltonian density (and its inverse) is finite, one can define a unique weak derivative.
https://doi.org/10.15495/EPub_UBT_00006809
Systems theoretic properties of linear RLC circuits. - In: Extended abstracts presented at the 25th International Symposium on Mathematical Theory of Networks and Systems MTNS 2022, (2022), S. 108-111
We consider the differential-algebraic systems obtained by modified nodal analysis of linear RLC circuits from a systems theoretic viewpoint. We derive expressions for the set of consistent initial values and show that the properties of controllability at infinity and impulse controllability do not depend on parameter values but rather on the interconnection structure of the circuit. We further present circuit topological criteria for behavioral stabilizability. This extended abstract is a shortened version of the full paper Glazov and Reis (2020) which has been accepted for the cancelled MTNS 2020 in Cambridge.
https://doi.org/10.15495/EPub_UBT_00006809
New results in multiobjective model predictive control. - In: Extended abstracts presented at the 25th International Symposium on Mathematical Theory of Networks and Systems MTNS 2022, (2022), S. 105-107
In model predictive control, it is a natural idea that not only one but multiple objectives have to be optimized. This leads to the formulation of a multiobjective optimal control problem (MO OCP). In this talk we introduce a multiobjective MPC algorithm, which yields on the one hand performance estimates for all considered objective functions and on the other hand stability results of the closed-loop solution. To this end, we build on the results in Zavala and Flores-Tlacuahuac (2012); Grüne and Stieler (2019) and introduce a simplified version of the algorithm presented in Grüne and Stieler (2019). Compared to Grüne and Stieler (2019), we allow for more general MO OCPs than in Grüne and Stieler (2019) and get rid of restrictive assumption on the existence of stabilizing stage and terminal costs in all cost components. Compared to Zavala and Flores-Tlacuahuac (2012), we obtain rigorous performance estimate for the MPC closed loop.
https://doi.org/10.15495/EPub_UBT_00006809
Flat outputs for funnel control of non-minimum-phase systems. - In: Extended abstracts presented at the 25th International Symposium on Mathematical Theory of Networks and Systems MTNS 2022, (2022), S. 85-86
We consider adaptive ouput feedback tracking control of linear time-invariant systems which are not necessarily minimum phase. The zero dynamics is split into a stable and an unstable part, we show that a flat output of the unstable part can contribute to the design of a funnel controller of the system. More precisely, we consider an auxiliary output based of the ”true output” of the system and the flat output of the unstable part of the zero dynamics. The funnel controller is designed for this auxiliary output, and the consequences for the true output are discussed.
https://doi.org/10.15495/EPub_UBT_00006809
Approaches for the RCWA-based non-destructive characterization of subwavelength-structured gratings. - In: EOS Annual Meeting (EOSAM 2022), (2022), 05012, S. 1-2
Nano-structuring enables us to add additional degrees of freedom to the design of optical elements. Especially the possibility of controlling the polarization is of great interest in the field of nano-structured optics. For being able to exploit the whole range of form-birefringent phase shifts, the aspect ratios of the resulting element are typically much higher than the aspect ratios of conventional diffractive optical elements (DOEs), which does not only pose a challenge on fabrication but also on characterization. We evaluate several well-established approaches for the nondestructive characterization, including Müller-Matrix-Ellipsometry, measurement of the diffraction efficiencies, scattering measurements and calibration with rigorous coupled-wave modelling. The goal is to understand the challenges with all these techniques and combine them to a reliable method for structural reconnaisance of high aspect ratio nanostructures.
https://doi.org/10.1051/epjconf/202226605012
Verbund: 05M2018 - KONSENS : Schlussbericht : Förderzeitraum: 01.01.2018-30.06.2021. - Ilmenau : Technische Universität Ilmenau. - 1 Online-Ressource (16 Seiten, 450,82 KB)Förderkennzeichen BMBF 05M18SIA
https://edocs.tib.eu/files/e01fb23/1870887948.pdf