Search Results (80)

Background: Micro-reservoirs in implant surfaces represent a promising drug carrier concept for drug delivery systems. For drug loading, inkjet printing enables highly precise droplet positioning. However, droplet drying influences drug crystallization from printed drug solution. This study investigates how evaporation-driven phenomena affect the precision and homogeneity of inkjet-based deposition of a crystallizing drug into exemplary micro-reservoirs. The aim is to guide the selection of suitable solvents and inkjet process parameters. Methods: Laser-drilled micro-reservoirs were fabricated as blind holes with entrance diameters of 100 µm and 400 µm in the surface of specimens of EN 1.4404 (equivalent to AISI 316L) stainless steel, a commonly used biomaterial. The reservoirs were loaded with two different drug solutions using piezoelectric drop-on-demand inkjet printing. Acetylsalicylic acid (ASA) was applied as a model drug representing crystallizing small-molecule drugs. Solvents with markedly different evaporation rates, ethanol (EtOH) as a representative high-volatility solvent and dimethyl sulfoxide (DMSO) as a representative low-volatility solvent, were selected. The number of jetted droplets per dispensing step was varied. Precision and homogeneity of the drug deposition were investigated using light and laser scanning microscopy. Results: Over the course of droplet drying, two phenomena, the coffee-ring effect and creeping, can impair drug deposition quality. The coffee-ring effect leads to inhomogeneous, ring-shaped drug deposits. Creeping is the evaporation-driven spreading of crystalline structures and reduces the precision of drug deposition. The EtOH-based ASA solution (c = 10 g/L) was intensely affected by both phenomena. Inhomogeneities could be partially compensated via tailoring the droplet count per dispensing step. The DMSO-based solution (c = 100 g/L) exhibited a more compact crystallization of ASA (requiring ~20% less volume in an exemplary experiment), no coffee-ring effect, and only minor creeping. Conclusions: The DMSO-based ASA solution enabled a more precise and homogeneous drug deposition than the EtOH-based solution under the investigated printing and crystallization conditions. EtOH-related limitations could be counteracted by controlling the number of jetted droplets per dispensing step. Full article

Functional coatings based on natural bioactive compounds have attracted increasing interest in topical and biomedical applications. In this study, textile substrates were coated with formulations containing propolis and selected biopolymers to create biocompatible surfaces with enhanced physicochemical and biological properties. The coating preparation process was optimized to achieve uniform deposition and stable incorporation of bioactive constituents. The chemical composition and interactions between propolis, biopolymers, and textile fibers were investigated using Fourier-transform infrared spectroscopy (FTIR), while surface morphology and coating distribution were characterized by scanning electron microscopy (SEM). The presence and stability of key phenolic compounds in propolis were analyzed by high-performance liquid chromatography (HPLC). Optical properties and UV-shielding performance of the coated textiles were evaluated using UV–Vis spectroscopy. The coffee-ring effect was investigated during coating formulation, as this phenomenon significantly reveals coating homogeneity, surface microstructure, and the spatial distribution of active compounds. The influence of formulation parameters on deposit morphology and coating quality was systematically assessed. The biocompatibility of the developed coatings was evaluated through in vitro cytotoxicity testing, demonstrating their suitability for direct skin contact. The combined analytical results confirmed successful incorporation of propolis into the biopolymer matrix, indicating that propolis–biopolymer coatings represent a promising approach for the fabrication of functional textiles intended for topical applications, including wound care, skin protection, and antimicrobial textile products. Full article

Raman spectroscopy is a commonly used label-free technique for the chemical analysis of microplastics (MPs), which are defined as plastic particles larger than 1 μm but smaller than 5 mm size; given its small signal strength and diffraction-limited spatial resolution, Raman spectroscopy has limited applicability in the study of nanoplastics (NPs), which are defined as particles smaller than 1 μm. Tip-enhanced Raman scattering (TERS) is a promising technique that can overcome these limitations by using a single plasmonic tip of an atomic force microscope (AFM) to enhance the Raman signal from a small sample volume. Here we used TERS for the analysis of NPs in human bronchoalveolar lavage (BAL) fluid. We developed a sub-sampling procedure for nanoscale TERS imaging on an SiO₂/Si substrate and performed control experiments. We investigated the experimental coffee-ring effect on the spatial distribution of NPs on the substrate. We compared the results of TERS imaging with the conventional confocal Raman microscopy and observed the presence of similar types of plastic, pigments, and mineral particles, revealing the origin of NPs from the corresponding MPs. The total nanoparticle density observed in BAL using TERS was ~50 billion particles per liter, most of which were NPs. Our TERS approach may be extended to other types of human fluids and tissue samples to provide insights into the health effects of NPs. Full article

Precise quantitative monitoring of 17β-estradiol (E2) is important for reproductive management in precision livestock farming. However, E2 determination in complex biological matrices remains challenging because of matrix-derived background and signal variability. Here, we developed a nanoconfinement-assisted solid-state ratiometric fluorescent aptasensor integrating target-induced strand displacement (TISD), magnetic separation, and anodic aluminum oxide (AAO) nanochannel confinement. The sensing probe consisted of streptavidin-coated magnetic nanoparticles (MNPs) carrying a FAM-labeled cDNA internal reference and a Texas Red-labeled E2 aptamer reporter. E2 binding promoted dissociation of the Texas Red-labeled aptamer from the magnetic probe. Magnetic separation and washing reduced soluble matrix-derived interference, while subsequent deposition of the sensing complexes onto an AAO membrane mitigated coffee-ring-associated nonuniformity and produced a more spatially uniform dual-color fluorescence distribution for ratiometric analysis. Under matrix-matched calibration conditions, linear ranges of 5.0–50.0 pM were obtained in tap water and sow saliva, 5.0–40.0 pM in whole milk, and 5.0–15.0 pM in post-estrus sow urine. The LOD determined in tap water was 3.62 pM. The different calibration slopes obtained among the four matrices indicated that residual matrix-dependent effects remained and that matrix-specific calibration was required for quantitative analysis. Matrix-matched spike recoveries ranged from 86.92% to 119.54% across the investigated matrices. The aptasensor exhibited the strongest response toward 17β-E2 among the tested compounds; however, cross-reactivities of 77.3% for E3 and 47.3% for 17α-E2 indicated preferential rather than exclusive recognition. Molecular docking suggested a putative binding pose but did not experimentally establish the molecular recognition mechanism. Overall, the platform demonstrated laboratory-scale analytical feasibility in pretreated tap water, sow saliva, whole milk, and post-estrus sow urine. Further development of sample preparation, magnetic handling, membrane loading, probe selectivity, and portable fluorescence readout will be required before in situ or on-site application. Full article

Geisha coffee (Coffea arabica L. cv. Geisha) is internationally recognized for its exceptional sensory quality; however, its functional properties and bioactive composition remain insufficiently explored. This study evaluated the phytochemical profile, antioxidant capacity, vascular bioactivity, and toxicological safety of an aqueous extract of roasted Geisha coffee (AErGC) from the Chiriquí highlands, Panama. The chemical composition was determined using HPLC-PDA. Antioxidant activity was assessed using DPPH, ABTS, and lipid peroxidation assays. Vascular effects were studied in rat aortic rings, and safety was evaluated through Artemia salina and a single-dose acute oral toxicity model in rats (OECD 423). Chemical characterization was performed by HPLC-PDA, revealing notably elevated levels of caffeine (69.5 ± 6.4 mg/g) and 5-O-caffeoylquinic acid (74.5 ± 6.9 mg/g). The extract exhibited strong free radical scavenging capacity, with an IC₅₀ value of 14.7 ± 4.9 µg/mL in the DPPH assay, and inhibited lipid peroxidation by 72.71 ± 1.63% at 15.6 µg/mL. In endothelium-intact rings, AErGC induced a concentration-dependent vasorelaxant effect, reaching a maximum relaxation of 70.84 ± 2.9%. Toxicological results showed an LC₅₀ > 1000 µg/mL in A. salina and an oral LD₅₀ > 2000 mg/kg, classifying the extract as Category 5 (low toxicity). These findings highlight Panamanian Geisha coffee as a promising functional beverage with antioxidant and vascular protective properties, supporting its potential as a nutraceutical. Full article

Propolis is a complex mixture of natural compounds, including resinous terpenoids, flavonoids, aromatic acids, and essential oils, and has strong antimicrobial, antifungal, and antioxidant properties. The chemical composition of propolis determines its properties and strongly depends on a wide variety of different plant sources, as well as other climate and environmental parameters. In order to determine the main compounds, in this study, we applied an integrated analysis of propolis by thin-layer chromatography (TLC) to characterize and compare the phytochemical profiles of selected bioactive materials in raw propolis. TLC served as a rapid, cost-effective, and highly visual technique to separate and identify key constituents, including terpenoids, flavonoids, and phenolic compounds in propolis, without a need for further precleaning steps after performing ultrasonic extraction. Complementary methods, such as FTIR spectroscopy, were employed to validate and quantify the active components detected through TLC screening. In addition, the UV-VIS method revealed the solubility of raw propolis in different solvents, after testing for coffee ring effects. The results confirmed that the complex structure of the raw sample can be more thoroughly revealed by two-dimensional TLC, which enables not only rapid and verifiable qualitative results but also detection of overlapping spots. Moreover, by comparing the results with data from the literature, not only can particular chemical compounds be efficiently determined by TLC but also the regional origin of samples. Full article

The reproducibility of oxygen reduction reaction (ORR) activity assessment for platinum-based electrocatalysts using the rotating disk electrode (RDE) method is critically dependent on the quality of the fabricated catalytic layer. This work presents a comprehensive study on optimizing catalytic ink formulation—specifically the water-to-isopropanol (H₂O:IPA) solvent ratio and the ionomer-to-carbon (I/C) ratio—to achieve a homogeneous catalytic layer and ensure high data reproducibility for monometallic Pt/C and bimetallic PtCu/C catalysts. A key aspect of this research is the implementation of a simple and effective visual inspection method using a benchtop digital microscope to rapidly assess catalytic layer quality, which was shown to correlate directly with electrochemical performance. The optimal ink composition was found to be catalyst-specific. For Pt/C, the highest mass activity of 353 A/g~Pt~ was achieved with a solvent ratio of 1:3 (H₂O:IPA) and an I/C ratio of 0.3. For PtCu/C, the best performance was obtained with the same solvent ratio (1:3) but a higher I/C ratio of 0.4, yielding a mass activity of 491 A/g~Pt~. It was demonstrated that ink compositions leading to layer inhomogeneities, such as aggregates and “coffee-ring” effects, significantly impair mass transport and lead to underestimated ORR activity. The study underscores the absence of a universal ink recipe and establishes that the optimization of ink parameters for each specific catalyst is essential for obtaining reliable and reproducible electrochemical data. Full article

Graphene is considered one of the most promising flexible transparent electrode materials as it has high charge carrier mobility, high electrical conductivity, low optical absorption, excellent mechanical strength, and good bendability. However, graphene-based flexible transparent electrodes face a critical challenge in balancing electrical conductivity and optical transmittance. Here, we present a green and scalable direct ink writing (DIW) strategy to fabricate graphene grid patterns by optimizing ink formulation with sodium dodecyl sulfate (SDS) and ethanol. SDS eliminates the coffee ring effect via Marangoni flow, while ethanol enhances graphene flake alignment during hot-pressing, achieving a high conductivity of 5.22 × 10⁵ S m⁻¹. The grid-patterned graphene-based flexible transparent electrodes exhibit a low sheet resistance of 21.3 Ω/sq with 68.5% transmittance as well as a high stability in high-temperature and corrosive environments, surpassing most metal/graphene composites. This method avoids toxic solvents and high-temperature treatments, demonstrating excellent stability in harsh environments. Full article

The coffee-ring effect, while harnessed in diverse fields such as biosensing and printing, poses challenges for achieving uniform particle deposition. Controlling this phenomenon is thus essential for precision patterning. This study proposes a novel method to regulate coffee-ring formation by tuning surface wettability via integrated nanoporous and hexagonal microstructures. Four distinct surface types were fabricated using UV nanoimprint lithography: planar, porous planar, hexagonal wall, and porous hexagonal wall. The evaporation behavior of colloidal droplets and subsequent particle aggregation were analyzed through contact angle measurements and confocal microscopy. Results demonstrated that nanoscale porosity significantly increased surface wettability and accelerated evaporation, while the hexagonal pattern enhanced droplet stability and suppressed contact line movement. The porous hexagonal surface, in particular, enabled the formation of connected dual-ring patterns with higher particle accumulation near the contact edge. This synergistic design facilitated both stable evaporation and improved localization of particles. The findings provide a quantitative basis for applying patterned porous surfaces in evaporation-driven platforms, with implications for enhanced sensitivity and reproducibility in surface-enhanced Raman scattering (SERS) and other biosensing applications. Full article

The present study concerns the utilization of spent coffee grounds (SCGs) as an alternative bio-based modifier for a petroleum-based penetration grade 70/100 bitumen at 5%, 10% and 15% by weight of bitumen. The conventional properties of the binders were examined with a series of penetration, ring and ball, elastic recovery, dynamic viscosity and storage stability tests. Their rheological properties were assessed with a Dynamic Shear Rheometer. The aforementioned tests were conducted before and after applying a short-term ageing protocol to quantify the ageing susceptibility of the binders using different rheological ageing metrics. Furthermore, a statistical analysis was conducted to discover whether any correlations exist between the conventional and rheological properties of the binders. It was observed that spent coffee grounds can be incorporated into bitumen at an optimal content of up to 5% without downgrading the binder’s rheological properties or its structural integrity. Additionally, the bio-modifier slightly improved the ageing resistance of bitumen. Finally, the ring and ball test’s results had the strongest correlation with the DSR findings. Full article

The drying structures of droplets of colloidal aqueous dispersions exhibit a wide variety of patterns depending on experimental conditions. It has been established by previous researchers that capillary flows and Marangoni convection significantly influence the macroscopic pattern formation. To the best of our knowledge, this study is the first to focus on sessile droplets of aqueous dispersions containing hollow particles. These hollow particles have a lower density than water and thus float in the medium. The drying pattern of these droplets was markedly different from the well-known ring pattern. Instead, a bump-shaped structure—often referred to as a “coffee-eye”—was formed due to the accumulation of particles at the center of the dried film. While a ring pattern was still present, it was extremely narrow and barely noticeable. This behavior is attributed to the dominance of the buoyant motion of the hollow particles, which prevented their transport by capillary flow. The findings of this study provide fundamental and important insights into the drying structures of various types of colloidal droplets. Full article

Graphene oxide (GO) films have attracted significant attention due to their potential in separation and filtration applications. Based on their unique lamellar structure and ultrathin nature, GO films are difficult to maintain in a free-standing form and typically require substrate support. Consequently, understanding their film formation behavior and mechanisms on substrates is of paramount importance. This work employs commonly used nonwoven fibrous membranes as substrates and guided by the coffee-ring theory, systematically investigates the film formation behaviors, film morphology, and underlying mechanisms of GO films on fibrous membranes with varying wettability. Fibrous membranes with different wetting properties—hydrophilic, hydrophobic, and superhydrophobic—were prepared via electrospinning and initiated chemical vapor deposition (iCVD) surface modification techniques. The spreading behaviors, deposition dynamics, capillary effects, and evaporation-induced film formation mechanisms of GO suspensions on these substrates were thoroughly examined. The results showed that GO formed belt-like, ring-like, and circular patterns on the three fibrous membranes, respectively. GO films encapsulated more than the upper half, approximately the upper half, and the top portion of fibers, respectively. Pronounced wrinkling of GO films was observed except for those on the hydrophilic fibrous membrane. This work demonstrates that tuning the wettability of fibrous substrates enables precise control over GO film morphology, including fiber encapsulation, wrinkling, and coverage area. Furthermore, it deepens the understanding of the interactions between 1D nanofibers and 2D GO sheets at low-dimensional scales, laying a foundational basis for the optimized design of membrane engineering. Full article

This study focuses on the extraction, characterization, and biological evaluation of diterpenes from green coffee beans, specifically, cafestol and kahweol. These compounds, known for their potential health benefits, were isolated via optimized extraction and saponification processes. Separation was achieved using silver nitrate-impregnated silica gel, and structural elucidation was performed through advanced 1D and 2D NMR techniques, including HSQC, HMBC, and (IN)ADEQUATE. Due to kahweol’s instability, the research prioritized cafestol for the synthesis of rhodamine B conjugates. Initial ester-linked conjugates proved unstable, prompting the development of more robust derivatives through amide linkage strategies and further functionalization via acetylation and oxidation reactions. Some oxidation methods led to furan ring cleavage, impacting structural integrity. Selected compounds were tested for cytotoxicity using SRB assays on human tumor cell lines (MCF7, A2780) and non-malignant fibroblasts (NIH 3T3). While the parent diterpenes and many derivatives showed minimal activity, several cafestol–rhodamine B conjugates demonstrated notable cytotoxic effects. Compound 6, in particular, exhibited selective activity against cancer cells with reduced toxicity toward non-malignant cells. Full article

The increasing accumulation of polymer waste presents a significant environmental challenge and a critical opportunity for the development of circular and sustainable membranes. The answer to this complex topic requires an integral approach covering different aspects of the problem. This paper, therefore, explores innovative approaches for the chemical recycling of polymer waste into value-added products, with a specific emphasis on the production of advanced biopolymer membranes. By converting discarded materials into functional polymers through depolymerization and chemical modification processes, new pathways are emerging for the fabrication of high-performance membranes used in filtration, biomedical applications, and energy systems. Among these, electrospinning has gained prominence as a versatile and scalable technique for producing nanostructured membranes with tailored properties. As a key case study presented, the focus was on the optimization of electrospinning parameters, including solvents, polymer concentration, voltage, and flow rate, for the investigation of membranes derived from recycled materials to achieve net-zero technology. Moreover, the environmental benefits of this approach are discussed within a zero-waste and net-zero carbon framework, emphasizing the integration of life cycle assessment to evaluate sustainability metrics. This paper underscores the potential of polymer waste as a feedstock for circular membrane technologies and provides a roadmap for future innovations in waste-to-resource strategies. The results of the demonstrated case example clearly demonstrate how the effects of processing conditions on the production of fine-tuned biodegradable membranes with controlled porosity influenced membrane properties, including mechanical strength and surface functionality, for the desired suppression of the coffee-ring effect. Full article

Magnetoelectric composites enable strain-mediated coupling between magnetic and electric fields, supporting applications in sensors, actuators, and tunable devices. This study presents a finite element modeling framework for simulating the direct magnetoelectric effect in core–shell and layered nanocomposites fabricated by material jetting (inkjet printing). The model incorporates nonlinear magnetostrictive behavior of cobalt ferrite nanoparticles and size-dependent piezoelectric properties of barium titanate, allowing efficient simulation of complex interfacial strain transfer. Results show a strong dependence of coupling on field orientation, particle arrangement, and interfacial geometry. Simulations of printed droplet geometries, including coffee ring droplet morphologies, reveal enhanced performance through increased surface area and directional alignment. These findings highlight the potential of material jetting for customizable, high-performance magnetoelectric devices and provide a foundation for simulation-guided design. Full article