Porous polymeric microparticles foamed with supercritical CO2as scattering white pigments

Nowadays, titanium dioxide (TiO₂) is the most commercially relevant white pigment. Nonetheless, it is widely criticized due to its energy-intensive extraction and costly disposal of harmful by-products. Furthermore, recent studies discuss its potential harm for the environment and the human health. Environment-friendly strategies for the replacement of TiO₂as a white pigment can be inspired from nature. Here whiteness often originates from broadband light scattering air cavities embedded in materials with refractive indices much lower than that of TiO₂. Such natural prototypes can be mimicked by introducing air-filled nano-scale cavities into commonly used polymers. Here, we demonstrate the foaming of initially transparent poly(methyl methacrylate) (PMMA) microspheres with non-toxic, inert, supercritical CO₂. The properties of the foamed, white polymeric pigments with light scattering nano-pores are evaluated as possible replacement for TiO₂pigments. For that, the inner foam structure of the particles was imaged by phase-contrast x-ray nano-computed tomography (nano-CT), the optical properties were evaluated via spectroscopic measurements, and the mechanical stability was examined by micro compression experiments. Adding a diffusion barrier surrounding the PMMA particles during foaming allows to extend the foaming process towards smaller particles. Finally, we present a basic white paint prototype as exemplary application.

Investigation of the spermathecal morphology, reproductive strategy and fate of stored spermatozoa in three important thysanopteran species

In insects, females can keep sperm capable of fertilisation over a long period with the help of the spermatheca. The effectiveness of storing fertile sperm is expected to reflect in the reproductive strategy and, thus, the morphology of the involved organs. In this work, we focused on the relationship between reproduction and morphology in the haplodiploid Thysanoptera, especially if a loss of these traits occurs under thelytoky. The spermathecal morphology and the fate of stored spermatozoa were studied by microscopic techniques (high-resolution x-ray computed tomography and transmission electron microscopy) in three species with different reproductive modes and lifestyles (Suocerathrips linguis, Echinothrips americanus, Hercinothrips femoralis). Mating experiments were conducted to analyse the use of the transferred sperm in the thelytokous H. femoralis. Results show that the spermathecae are relatively simple, which can be explained by the availability of sperm and the short lifespan of the females. However, the spermatheca in H. femoralis seems to be vestigial compared to the arrhenotokous species and females do not use sperm for fertilisation. No substantial change was observed in the structure of spermatozoa, despite an enlargement of the sperm organelles being measured during storage in all three species. The results of this work demonstrate differences in the morphology of the spermatheca, especially concerning the reproduction mode, promoting the understanding of the complex interaction between morphology and behaviour.

Direct three-dimensional imaging for morphological analysis of electrospun fibers with laboratory-based Zernike X-ray phase-contrast computed tomography

Electrospinning is a well-established and widely used method for the production of protein-based fibrous biomaterials. The visualization of the morphology and the characterization of sample features related to the three-dimensional (3D) structure, like the porosity and fibers thickness, is crucial for the design and fabrication of tailor-made and application-optimized materials. Here, we evaluated the benefits of using 3D X-ray imaging in a laboratory setup with a resolution in the sub-micrometer range for the characterization of electrospun gelatin fibrous mats. We used phase-contrast X-ray computed tomography at the nanoscale (nano-CT) for the evaluation of the time-course morphological changes of the mats induced by chemical cross-linking of the gelatin fibers. We present an image processing protocol that enables the segmentation of the fibers and quantification of the mats porosity, the analysis of the shape and size of the pores, and of the fibers thickness and orientation. We compared the results obtained from the processed nano-CT data with those obtained with the conventional methods used for the characterization of electrospun fibrous materials, and we discuss the advantages and limitations of each method when applied to gelatin electrospun samples. Our results reveal that the use of phase-contrast nano-CT provides quick additional and relevant information for the characterization of fibrous mats and, thus, provides beneficial insights for the design and fabrication of novel fibrous materials.

Plate-nanolattices at the theoretical limit of stiffness and strength

Though beam-based lattices have dominated mechanical metamaterials for the past two decades, low structural efficiency limits their performance to fractions of the Hashin-Shtrikman and Suquet upper bounds, i.e. the theoretical stiffness and strength limits of any isotropic cellular topology, respectively. While plate-based designs are predicted to reach the upper bounds, experimental verification has remained elusive due to significant manufacturing challenges. Here, we present a new class of nanolattices, constructed from closed-cell plate-architectures. Carbon plate-nanolattices are fabricated via two-photon lithography and pyrolysis and shown to reach the Hashin-Shtrikman and Suquet upper bounds, via in situ mechanical compression, nano-computed tomography and micro-Raman spectroscopy. Demonstrating specific strengths surpassing those of bulk diamond and average performance improvements up to 639% over the best beam-nanolattices, this study provides detailed experimental evidence of plate architectures as a superior mechanical metamaterial topology.

Plate-lattices are predicted to reach the upper bounds of strength and stiffness compared to traditional beam-lattices, but they are difficult to manufacture. Here, the authors use two-photon polymerization 3D-printing and pyrolysis to make carbon plate-nanolattices which reach those theoretical bounds, making them up to 639% stronger than beam-nanolattices.

Risperidone-Loaded PLGA-Lipid Particles with Improved Release Kinetics: Manufacturing and Detailed Characterization by Electron Microscopy and Nano-CT

For parenteral controlled drug release, the desired zero order release profile with no lag time is often difficult to achieve. To overcome the undesired lag time of the current commercial risperidone controlled release formulation, we developed PLGA-lipid microcapsules (MCs) and PLGA-lipid microgels (MGs). The lipid phase was composed of middle chain triglycerides (MCT) or isopropylmyristate (IPM). Hydroxystearic acid was used as an oleogelator. The three-dimensional inner structure of Risperidone-loaded MCs and MGs was assessed by using the invasive method of electron microscopy with focused ion beam cutting (FIB-SEM) and the noninvasive method of high-resolution nanoscale X-ray computed tomography (nano-CT). FIB-SEM and nano-CT measurements revealed the presence of highly dispersed spherical structures around two micrometres in size. Drug release kinetics did strongly depend on the used lipid phase and the presence or absence of hydroxystearic acid. We achieved a nearly zero order release without a lag time over 60 days with the MC-MCT formulation. In conclusion, the developed lipid-PLGA microparticles are attractive alternatives to pure PLGA-based particles. The advantages include improved release profiles, which can be easily tuned by the lipid composition.

Electrospun nanofibers - A promising solid in-situ gelling alternative for ocular drug delivery

A serious problem of the treatment of eye diseases is the very short residence time of the drug. The majority of the drug is cleared within few seconds due to the poor capability of the eye to accommodate additional liquids. We developed a new ocular drug delivery system, which is applied in dry form and forms immediately a gel after administration. The system is based on gellan gum/pullulan electrospun nanofibers. The rheological behavior of the spinning solution was investigated followed by further characterization of the in situ formed gel. Three-dimensional X-ray imaging with nanometric resolution (nano-CT) and electron scanning microscopy were used for a detailed characterization of the diameter and alignment of the fibers. A high porosity (87.5 ± 0.5%) and pore interconnectivity (99%) was found. To ensure a good fit to the eye anatomy, the prepared fibers were shaped into curved geometries. Additionally, a new innovative moistening chamber for the in vitro determination of the ocular residence time in porcine eyes was developed which mimics the tear turnover. A clear prolongation of the fluorescein residence time compared to conventional eye drops was achieved with the application of the curved nanofiber in situ gelling mat. In summary, the developed in situ gelling system with adapted geometry is a promising alternative system for ocular drug delivery.