A continuous tubular crystallizer system with an inner diameter of 2.0 mm and an overall length of 27 m was used to generate acetylsalicylic acid seeds in situ from ethanolic solution via cooling and ultrasound irradiation and to grow the crystals in the tubing with a controlled temperature trajectory. In order to minimize the residence time distribution, air bubbles were introduced into the system to generate a segmented gas-slurry flow. The narrow residence time distribution and the tight temperature control in the small tubing due to the large surface to volume ratio resulted in relatively narrow crystal size distributions of the product. Generally, all experiments clearly demonstrated significant crystal growth for the product crystals in comparison to the seeds and yielded product masses on the g/min scale. Furthermore, it was demonstrated that the size of the product can be easily controlled via fines removal by dissolution due to rapid heating and varying the mass of seeds per mL of solution.

The formation mechanism of iron oxide nanoparticles reveals an initial segregation into ferrihydrite seeds and a Fe2+ rich growth reservoir.

Co-precipitation is by far the most common synthesis for magnetic iron oxide nanoparticles (IONPs), as cheap and environmentally friendly precursors and simple experimental procedures facilitate IONP production in many labs. Optimising co-precipitation syntheses remains challenging however, as particle formation mechanisms are not well understood. This is partly due to the rapid particle formation (within seconds) providing insufficient time to characterise initial precipitates. To overcome this limitation, a flow chemistry approach has been developed using steady-state operation to "freeze" transient reaction states locally. This allowed for the first time a comprehensive analysis of the early stages of co-precipitation syntheses via in-situ Small Angle X-ray Scattering and in-situ synchrotron X-Ray Diffraction. These studies revealed that after mixing the ferrous/ferric chloride precursor with the NaOH base solution, the most magnetic iron oxide phase forms within 5 s, the particle size changes only marginally afterwards, and co-precipitation and agglomeration occur simultaneously. As these agglomerates were too large to achieve colloidal stability via subsequent stabiliser addition, co-precipitated IONPs had to be de-agglomerated. This was achieved by adding the appropriate quantity of a citric acid solution which yielded within minutes colloidally stable IONP solutions around a neutral pH value. The new insights into the particle formation and the novel stabilisation procedure (not requiring any ultra-sonication or washing step) allowed to design a multistage flow reactor to synthesise and stabilise IONPs continuously with a residence time of less than 5 min. This reactor was robust against fouling and produced stable IONP solutions (of ~ 1.5 mg particles per ml) reproducibly via fast mixing (< 50 ms) and accurate temperature control at large scale (> 500 ml/h) for low materials cost.

This paper describes a simple model-free (i.e., empirical) control strategy for crystal size tuning in a continuously operated tubular crystallizer. The crystallizer is designed for a seeded cooling crystallization process and acetylsalicylic acid crystallization from an ethanol solution was used as model system. Using a crystal size distribution (CSD) analyzer and minor initial studies, we developed a feedback controller that accurately tuned the mean crystal size within the range of 90–140 μm. In addition, we created a cleaning concept for long-term runs based on a consistency study, which demonstrated that the CSD of the products remained robust when process settings were kept constant. Sufficiently small and uniform seed crystals were generated via ultrasound irradiation.

Size, shape, and polymorphic form are the critical attributes of crystalline particles and represent the major focus of today’s crystallization process design. This work demonstrates how crystal properties can be tuned efficiently in solution via a tubular crystallizer that facilitates rapid temperature cycling. Controlled crystal growth, dissolution, and secondary nucleation allow a precise control of the crystal size and shape distribution, as well as polymorphic composition. Tubular crystallizers utilizing segmented flow such as the one presented in our work can provide plug flow characteristics, fast heating and cooling, allowing for rapid changes of the supersaturation. This makes them superior for crystal engineering over common crystallizers. Characterization of particle transport, however, revealed that careful selection of process parameters, such as tubing diameter, flow rates, solvents, etc., is crucial to achieve the full benefits of such reactors.

The scientific community has made great efforts in advancing magnetic hyperthermia for the last two decades after going through a sizeable research lapse from its establishment. All the progress made in various topics ranging from nanoparticle synthesis to biocompatibilization and in vivo testing have been seeking to push the forefront towards some new clinical trials. As many, they did not go at the expected pace. Today, fruitful international cooperation and the wisdom gain after a careful analysis of the lessons learned from seminal clinical trials allow us to have a future with better guarantees for a more definitive takeoff of this genuine nanotherapy against cancer. Deliberately giving prominence to a number of critical aspects, this opinion review offers a blend of state-of-the-art hints and glimpses into the future of the therapy, considering the expected evolution of science and technology behind magnetic hyperthermia.

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The approximation of a well mixed reactor is prevalent when it comes to the modeling of a crystallization process. Since temperature, concentration, and mass content vary due to inhomogeneous mixing, this approximation is a very loose one. The continuously operated seeded tubular crystallizer system developed in our group overcomes obstacles like a slow response to changes in the outer parameters and inhomogeneous mixing. Therefore the applicable well mixed assumption facilitates detailed modeling of the crystallization process by means of population balance equations (PBE) coupled with mass and energy balances. Modeled results were validated by means of experiments. The amount of aggregation events during the crystallization could be quantified and it was proven that the growth of seeded crystals is almost exclusively responsible for solid mass uptake if the reactor is operated appropriately. The performed sensitivity analysis exposed which process settings should be maintained most accurately to avoid fluctuations in the product crystals' quality attributes and to limit undesired nucleation events.