Alexander Sommereyns

Nutraceuticals provide health benefits and particularly profit from a sensitive, high-purity production process. Microparticle laser fragmentation in liquids is an emerging technique for the contamination-free comminution of organic drugs and nutraceuticals aiming at solubility enhancements. However, current discontinuously operated fragmentation setups suffer from chemical degradation by multipulse laser excitation at high fluence and do not allow for systematic studies of the fragmentation mechanisms. In this work, continuous-flow microparticle laser fragmentation in liquids with ultrashort-pulsed lasers was studied in a circular jet reactor using curcumin and cannabidiol as model substances and single-pulse-per-volume element conditions to compare the fragmentation efficiency for these two nutraceuticals. Fragmentation efficiency based on the yield of submicrometer particles and nanoparticles was quantified using UV–vis extinction spectroscopy, scanning electron microscopy, and analytical centrifugation, while high-performance liquid chromatography determined degradation. We found improved fragmentation efficiency at lower mass concentrations. In all experiments, chemical degradation was minimal (<2%), and increased mass concentration of curcumin enabled ultralow by-product formation of 0.01%. The process selectivity against degradation was defined by the application-relevant descriptor of mole degradation per produced submicrometer particle surface and quantified regarding feedstock mass concentration and nutraceutical type. Cytotoxicity in HepG2 cancer cells was significantly reduced in cells treated with laser-processed curcumin in comparison to unirradiated curcumin controls, and antioxidant effects were proven, ensuring high viability even at high curcumin concentrations.

It is well known that scan strategies have an essential role in powder bed fusion (PBF). For the comparison of different scan strategies, however, it is usually necessary to evaluate manufactured samples or run simulations. Given the typically lengthy nature of these processes, this study focuses on finding a rapid preprocess evaluation method for scan strategies using geometrical approaches: line buffer‐based calculations and a point density field. Both approaches only depend on the geometry of the scan strategy. While these calculations should apply to most PBF processes, this study uses the evaluation methods to predict the differences that four unique scanning strategies have in PBF of polymers using an near‐infrared laser source. Polyamid 12 powder with Lanthanum hexaboride nanoparticles and a commercial black‐dyed Polyamid 12 powder are used for processing. The calculation of the line buffer‐based surface energies of these scanning strategies correctly predicted the sequence in which the scanning curve appeared to have received the laser energy. Moreover, the defects observed in the manufactured samples appear to be related to the variation in point density of the scanning strategies. These promising results are the first step towards new preprocess evaluation methods, leading to improved predictability of different scan strategies.

Near‐infrared laser sources have the potential to change the process dynamics in laser powder bed fusion of polymers. To take full advantage of the shorter processing laser wavelength, the addition of absorbing additives, such as carbon black nanoparticles, becomes inevitable. Many nanoparticle characteristics can influence the laser‐material interaction, such as quantity, dispersion, and position relative to the polymer matrix, but have not been investigated under processing conditions. Therefore, this study improves the understanding of the optical material properties present in laser powder bed fusion by quantifying the thermo‐optical properties of PA11 powder, melt and solid, additivated with minute amounts of carbon black nanoparticles on the surface and throughout the volume of the particles. Surface‐additivation results in the highest increase in laser attenuation overall and creates a segregated network that acts as a barrier to laser penetration in the molten and solid state. By contrast, the random distribution of agglomerated nanoparticles throughout the particle volume allows most of the laser radiation to pass through. Other nanoparticle effects, such as thermal stabilization and crystal formation, affect the volume‐additivated particles the most. The thermo‐optical results are complemented by analysis of process‐relevant powder, thermal, structural, and compositional material properties.

The development of new feedstock materials is a central prerequisite for advances in Additive Manufacturing (AM). To increase the breadth of potential applications for 3D and 4D printing of polymers, micro- and nano-additives incorporated into the feedstock material play an important role. In this context, magnetic materials are of great interest. Our study describes a way to fabricate polymer powders for laser powder bed fusion (PBF-LB) with a homogeneous, well-dispersed coating of iron oxide nanoparticles. Without the addition of chemical precursors, spherical superparamagnetic FeO_x nanoparticles with monomodal size distribution below 10 nm are generated from FeO_x micropowder by laser fragmentation in liquid. The adsorption of the nanoparticles on polyamide (PA12) powder is conducted directly in an aqueous dispersion after laser fragmentation, followed by drying, powder analysis and PBF-LB processing. Via Mössbauer spectroscopy and magnetometry, we determined that the saturation magnetization and structure of the iron oxide nanoparticles were not influenced by PBF-LB processing, and the magnetic properties were successfully transferred to the final 3D-printed magnetic part.

Driven by the rapid development of additive manufacturing technologies and the trend towards mass customization, the development of new feedstock materials has become a key aspect. Additivation of the feedstock with nanoparticles is a possible route for tailoring the feedstock material to the printing process and to modify the properties of the printed parts. This study demonstrates the colloidal additivation of PA12 powder with laser-synthesized carbon nanoparticles at >95% yield, focusing on the dispersion of the nanoparticles on the polymer microparticle surface at nanoparticle loadings below 0.05 vol%. In addition to the descriptors “wt%” and “vol%”, the descriptor “surf%” is discussed for characterizing the quantity and quality of nanoparticle loading based on scanning electron microscopy. The functionalized powders are further characterized by confocal dark field scattering, differential scanning calorimetry, powder rheology measurements (avalanche angle and Hausner ratio), and regarding their processability in laser powder bed fusion (PBF-LB). We find that heterogeneous nucleation is induced even at a nanoparticle loading of just 0.005 vol%. Finally, analysis of the effect of low nanoparticle loadings on the final parts’ microstructure by polarization microscopy shows a nanoparticle loading-dependent change of the dimensions of the lamellar microstructures within the printed part.