Background: Most frequently the functionalization of nanoparticles is hampered by time-consuming, sometimes harsh conjugation and purification procedures causing premature drug release and/or degradation. A strategy to circumvent multi-step protocols is to synthesize building blocks with different functionalities and to use mixtures thereof for nanoparticle preparation in one step. Methods: BrijS20 was converted into an amine derivative via a carbamate linkage. The Brij-amine readily reacts with pre-activated carboxyl-containing ligands such as folic acid. The structures of the building blocks were confirmed by different spectroscopic methods and their utility was assessed by one-step preparation and characterization of nanoparticles applying PLGA as a matrix polymer. Results: Nanoparticles were about 200 nm in diameter independent of the composition. Experiments with human folate expressing single cells and monolayer revealed that the nanoparticle building block Brij mediates a “stealth” effect and the Brij-amine-folate a “targeting” effect. As compared to plain nanoparticles, the stealth effect decreased the cell interaction by 13%, but the targeting effect increased the cell interaction by 45% in the monolayer. Moreover, the targeting ligand density and thus the cell association of the nanoparticles is easily fine-tuned by selection of the initial ratio of the building blocks. Conclusions: This strategy might be a first step towards the one-step preparation of nanoparticles with tailored functionalities. Relying on a non-ionic surfactant is a versatile approach as it might be extended to other hydrophobic matrix polymers and promising targeting ligands from the biotech pipeline.

The administration of exogenous hormones emerged as an essential tool for field studies in endocrinology. However, working with wild animals remains challenging, because under field conditions not every available method meets the necessary requirements. Achieving a sustained elevation in hormone levels, while simulta-neously minimising handling time and invasiveness of the procedure is a difficult task in field endocrinology. Facing this challenge, we have investigated the suitability of biocompatible polymeric microparticles, a novel method for drug-administration, as a tool to manipulate hormones in small songbirds. We chose the insulin-like growth factor-1 (IGF-1) as target hormone, because it receives great interest from the research community due to its important role in shaping life-history traits. Moreover, its short half-life and hydrophilic properties imply a major challenge in finding a suitable method to achieve a sustained, systemic long-term release. To study the release kinetics, we injected either IGF-1 loaded polylactic-co-glycolic acid (PLGA) microparticles or dispersion medium (control group) in the skin pocket of the interscapular region of captive bearded reedlings (Panurus biarmicus). We collected blood samples for 7 consecutive days plus an additional sampling period after two weeks and complemented these with an in vitro experiment. Our results show that in vitro, PLGA microparticles allowed a stable IGF-1 release for more than 15 days, following a burst release at the beginning of the measurement. In vivo, the initial burst was followed by a drop to still elevated levels in circulating IGF-1 until the effect vanished by 16 days post-treatment. This study is the first to describe the use of PLGA-microparticles as a novel tool for exogenous hormone administration in a small passerine. We suggest that this method is highly suitable to achieve the systemic long-term release of hydrophilic hormones with short half-life and reduces overall handling time, as it requires only one subcutaneous injection.

Topical testosterone therapy is widely used for testosterone replacement therapy and gender-affirming hormone therapy, but available hydroalcoholic gels contain high ethanol concentrations that may compromise skin barrier integrity during repeated use. In parallel, testosterone creams are prepared through pharmaceutical compounding. However, they lack data on physicochemical stability, skin penetration potential, and cellular compatibility. This study aimed to develop ethanol-free nanostructured lipid carrier (NLC)-based hydrogels as alternatives for dermal testosterone delivery. Testosterone-loaded NLCs were prepared, characterized for physicochemical stability, and incorporated into hydrogel matrices based on Sepinov™ EMT 10, Sepilife™ G305 and Carbopol® 980. Their performance was compared with Ultrasicc®- and Pentravan®-based testosterone creams and the hydroalcoholic reference Testogel® in terms of physicochemical stability, ex vivo human skin penetration, ex vivo skin hydration, and cellular compatibility. The phospholipid-based Lipoid® S75/polysorbate 80 NLCs showed nanoscale particle sizes, high encapsulation efficiency, and sufficient storage stability over 12 weeks. Among the NLC-based hydrogels, the Carbopol-based formulation provided the most robust pH and rheological stability. Confocal Raman spectroscopy showed that NLC gels achieved testosterone accumulation in the stratum corneum comparable to ethanolic Testogel® and compounded Ultrasicc® cream. NLC gels maintained stratum corneum hydration and preserved keratinocyte viability. Remarkably, NLC gels and Ultrasicc® exhibited around 80% cell viability in contrast to Testogel® (71%) and Pentravan® (61%). In summary, Carbopol-based NLC gel exhibited the highest storage stability at both 8 and 23 °C and delivered testosterone to the human stratum corneum in a finite dose ex vivo setup in a similar manner to a marketed reference product.

Experimental setup, sedimentation and shear stress influence cell interaction exposing the limits of static in vitro assays. The FlowCube emerges as a versatile, accessible platform that enables in vitro evaluation in a dynamic flow setting.

Diffusion studies are crucial for cosmetic and pharmaceutical formulation development to assess skin permeation of small molecules, often accessible via ultraviolet-visible (UV/Vis) absorption. For complex plant extracts, ultra high performance liquid chromatography/mass spectrometry (UHPLC/MS) has emerged as a predominant analytical tool. However, the commonly used phosphate-buffered saline (PBS) as physiological receptor fluid can affect LC-MS analysis by altering chromatographic performance and ionization efficiency. Alternative protocols for testing release and skin permeation of phytochemicals remain to be established. We therefore evaluated different buffer media at pH 7.4 (PBS according to European Pharmacopoeia, ammonium acetate 0.1 M, ammonium formate 0.15 M) for their suitability as acceptor fluids in release and permeation studies with cellulose acetate and porcine membranes. Korean red ginseng (KRG) extract was incorporated as model extract in three different formulation types (nanoemulsion, hydroalcoholic gel, amphiphilic cream). Storage stability was assessed via rheology and pH where required. Representative ginsenoside saponins Rb1 and Rg1 (logP 0.23 and 1.12) were quantified via UHPLC/MS. Interestingly, the results and differences between buffer media differed depending on membrane type. Drug release and permeation through the synthetic membrane varied among buffers for all vehicles (23.2-70.8 µg/cm²), whereas permeation through pig skin was comparable for all tested buffers (0.2-10.4 µg/cm²). Using alternative buffers, a comparison of vehicle types showed hydroalcoholic gels superior to the two multiphase systems regarding drug release and permeation. These results suggest that all tested alternative buffer media are suitable for comparative diffusion studies of plant-based actives studies especially when using biological membranes.