Micro, Volume 6, Issue 2 (June 2026) – 13 articles

Freeform optics belong to the increasingly important elements in optical research and industry, which pose several challenges regarding design and highly precise manufacturing. First being used in cameras and for focusing, nowadays freeform optics are used in a broad range of applications, from lighting to LiDAR, from endoscopy to photovoltaics, and from astronomical instruments to quantum cryptography. Designing freeform optics can be based on different theories and methods. Fabrication is possible by mechanical methods, such as diamond turning or high-precision milling, often followed by different polishing techniques, as well as laser-based techniques, mainly applying different lithographic techniques. Here, we give an overview of recent design and optimization methods, production methods used during the last years, and applications of freeform optics, including the possibility to combine freeform optics with tunability for different applications. We describe the opportunities of new applications as well as common problems and give an outlook towards future directions of research and development. Full article

The present work investigates the composition-dependent thermoresistive behavior of polylactic acid/polycaprolactone (PLA/PCL) composites reinforced with 4 wt.% graphene nanoplatelets (GNP), prepared by twin-screw extrusion at PLA/PCL ratios of 95/5, 70/30, 60/40, and 30/70 wt.%/wt.%. Their morphology, thermal properties, and structure were characterized by scanning electron microscopy, differential scanning calorimetry, thermogravimetric analysis, and wide-angle X-ray diffraction. Thermoresistive measurements over four cycles (30–130 °C) revealed two distinct regimes: PLA-rich compositions exhibited a stable, monotonic positive temperature coefficient (PTC) response after the first conditioning cycle, with TCR values up to 0.38% °C⁻¹, whereas compositions with 40–70 wt.% PCL displayed a non-monotonic PTC-to-NTC transition linked to PCL melting and subsequent conductive network rearrangement. The magnitude of both PTC and NTC responses increased systematically with PCL content. These results demonstrate that the thermoresistive characteristics of biodegradable PLA/PCL/GNP composites, including the sign, magnitude, and switching temperature of the TCR, can be effectively tuned through blend composition, offering a practical route for designing thermally responsive sensing materials. Full article

The increasing incidence of foodborne diseases and the limitations of conventional preservation methods have driven the search for safer, more effective, and sustainable antimicrobial strategies. In this context, essential oil nanoemulsions have emerged as promising alternatives to synthetic preservatives due to their broad-spectrum antimicrobial activity, natural origin, and potential applicability across diverse food matrices. This study critically examines the mechanisms of action of essential oils against pathogenic and spoilage microorganisms and discusses how their incorporation into nanoemulsions can overcome limitations such as low volatility, poor solubility, and chemical instability. The physicochemical principles governing the formation and stability of these nanoemulsions are addressed, alongside the influence of food matrix components (proteins, lipids, polysaccharides, pH, and ionic strength) on antimicrobial efficacy. Evidence from real food systems indicates that nanoemulsions often outperform free essential oils, although the magnitude of the effect strongly depends on matrix complexity and processing or storage conditions. The review further discusses critical aspects related to toxicity, safety, bioaccessibility, sensory acceptance, and regulatory considerations, as well as emerging evidence on adaptive responses and antimicrobial resistance risks associated with sublethal exposure to essential oil nanoemulsions. It is concluded that, despite their considerable technological potential, the industrial application of essential oil nanoemulsions requires further systematic studies in real foods, standardized protocols, and integrated risk assessments to ensure efficacy and safety under practical conditions. Full article

The effects of different surface pretreatments on the microtensile bond strength (µTBS) between a bulk-fill resin-based composite cavity base material (Bulk Base HARD II) and 4-META/MMA-TBB resin (Super-Bond EX), which is often used as a luting agent for indirect dental restorations, were investigated. Six experimental treatments were established: 10% citric acid/3% ferric chloride conditioner (10-3), self-etching primer (Teeth Primer; TP), silane coupling agent (M&C Primer; MC), 10-3+MC, TP+MC, and a control group with no treatment. The µTBS was measured after 1 week (immediate group) and 6 months (aged group) of water storage. There were no significant differences in µTBS among the immediate subgroups. However, the aged 10-3+MC group exhibited the highest bond strength, significantly outperforming the control group. On the other hand, the µTBS of the aged TP group was significantly lower than those of both aged 10-3 and 10-3+MC. MC alone did not enhance bond strength, and its application after TP led to a nonuniform surface morphology, raising concerns about adhesive stability. Failure mode analysis indicated that cohesive failure within the luting cement was predominant, with mixed failures being more frequent in the aged TP group. Overall, MC may not be necessary, and 10-3 conditioning does not adversely affect bond strength. Based on the results of this in vitro study, the most effective clinical practice entails pretreatment of the prepared cavity employing a citric acid/ferric chloride conditioner. Full article

Bias temperature instability (BTI) degradation is commonly described using empirical power-law kinetics; however, extraction of the time exponent and projection of lifetime remain highly sensitive to baseline definition and data representation. In conventional approaches, the threshold voltage shift is referenced to an initial value that cannot be measured simultaneously with stress, introducing uncertainty that can produce apparent curvature and variability in the extracted exponent. In this work, a baseline-independent linearization method is applied to representative published datasets spanning advanced silicon, SiC MOSFETs, and GaN power devices. By analyzing the measured degradation trajectories directly in a transformed time coordinate, the method removes curvature associated with baseline ambiguity and enables consistent extraction of the effective power-law exponent. Across all material systems examined, the extracted exponent exhibits systematic dependence on applied stress once baseline effects are reduced. This behavior challenges the commonly assumed constant-exponent formulation used in conventional lifetime projections and shows that even modest variations in the exponent can produce large differences in projected time-to-failure. A transformed lifetime representation based on is introduced, in which the influence of exponent variation is separated from the intrinsic voltage and temperature acceleration of the degradation rate. In this representation, the extracted acceleration parameters become more stable and physically interpretable. This formulation is consistent with standard reliability frameworks, including JEDEC JEP122G, in which the time exponent enters directly into the lifetime expression. These results demonstrate that baseline-independent analysis provides a unified framework for interpreting BTI degradation across disparate semiconductor technologies and suggest that explicit treatment of stress-dependent exponents is required for physically consistent lifetime modeling. Full article

The hydrogen evolution reaction (HER) plays a central role in electrochemical hydrogen production and requires catalysts that combine high activity with reduced noble metal usage. In this work, palladium nanoparticles (PdNPs) were deposited onto silver nanowire-modified graphite electrodes (Pd/AgNW/C) to investigate the influence of Pd loading on HER kinetics and catalytic efficiency. The electrodes were prepared by constant-current electrodeposition and characterized using polarization measurements and electrochemical impedance spectroscopy (EIS). The direct current (DC) results showed a pronounced enhancement of HER activity in the presence of Pd, while the highest mass-specific activity was observed at low Pd loadings. Increasing the Pd content further increased the overall current but reduced the catalytic efficiency when normalized to the Pd mass. EIS measurements revealed two contributions to the impedance response associated with processes occurring on different timescales. With increasing cathodic overpotential, both the charge transfer resistance and the low-frequency resistance decreased markedly, indicating accelerated reaction kinetics. The combined DC and alternating current (AC) analyses suggest that the silver nanowire network facilitates efficient electron transport and promotes a favorable dispersion of Pd nanoparticles at low loadings, enabling efficient HER catalysis with reduced noble metal usage. Full article

Resin 3D-printed molds are being increasingly favored for PDMS microfluidics across many disciplines. However, resin diversity, as well as secret manufacturer formulations, leads to a lack of standardization when using 3D printing for microscale applications. The impact of physical resin properties, both in its monomeric concoction and polymerized lattices at 100 µm or lower scales, needs quantification. We tested the performance of locally available resin formulations, isolating the impact of resin pigments and how it impacted the resin’s properties and performance. Lower resin viscosity improved feature fidelity (edge filleting < 25 µm) and improved resolution limit for recessed features, while cured polymer mechanical strength impacted the limit for positive mold features. We combined our findings to fabricate quality negative and positive mold structures in the mold and determined the best protocols associated with limitations during the fabrication of such structures. The methodologies in this study are expected to be widely applicable across various resin types and simplify the adoption of 3D printing protocols for specific feature fabrication in microscale molds for PDMS devices. Full article

Vascularization remains a central challenge in thick tissue engineering. Building on our prior demonstration that carbonate buffer concentration governs multi-channel collagen gel (MCCG) architecture and perfusion culture performance, this study aimed to establish non-contact, orthogonal control of pore size and density in riboflavin-sensitized Type I collagen hydrogels via UV irradiation intensity and preparation temperature. UV intensity was modulated by varying the source-to-sample distance (25–52 mm); preparation temperature was set at 5, 25, or 40 °C; gelation kinetics were quantified using a vial-tilt assay. Pore area fraction ranged from 0.9% to 8.6% and Young’s modulus from 16 to 49 kPa depending on UV dose. Higher preparation temperatures accelerated gelation and produced smaller, more densely distributed pores, consistent with kinetically arrested phase separation. NIH/3T3 fibroblasts cultured on intermediate- and low-intensity UV scaffolds achieved >80% confluency by Day 7, with three-dimensional tissue-like organization and directionally aligned cellular bundles within large pores; cell metabolic activity, assessed by CCK-8 assay, remained consistently high throughout the culture period. These results demonstrate that UV irradiation intensity and preparation temperature are independently tunable, non-contact parameters for reproducible fabrication of collagen scaffolds with tunable vascular-like pore networks, complementing and extending the chemical (buffer concentration) design space of MCCG-based perfusion culture systems. Full article

The widespread use of herbicides such as paraquat and glyphosate is a serious environmental and health concern due to their persistence, mobility, and toxicity in aquatic ecosystems. Composites of alginic acid (Alg) are prepared with carbonaceous materials such as graphene oxide (GO), carbon particles (CPs), porous carbon particles (PCPs), carbon black (CB), and carbon nanotubes (CNTs) were synthesized and evaluated as sorbents for the removal of cationic herbicide paraquat and the anionic herbicide glyphosate. The resulting Alg-based beads are environmentally safe because of the materials used during their preparation, such as a biopolymer, Alg, carbonaceous substances (GO, CPs, PCPs, and CB) as composite moieties, and Ca(II) ions as cross-linkers. The Alg–bead composite possessed strong swelling ability ranging from 1700% to 2500%, which led to swollen beads of spherical shape and an average diameter of 3 mm, each containing 20% of carbonaceous materials. Amongst all Alg-based beads prepared for paraquat and glyphosate removal from the aquatic environment, the highest adsorption capacity was attained for Alg–porous carbon particle (Alg-PCP) composites. The Alg-PCP beads were capable of adsorbing 85.7 ± 2.9 mg/g and 31.6 ± 2.2 mg/g from 50 mL of 250 ppm solutions of paraquat and glyphosate, respectively. In contrast, bare Alg beads adsorbed only 39.7 ± 1.8 mg/g and 12.9 ± 1.7 mg/g, respectively. A 250 mg Alg-PCP bead composite achieved a 91% removal of paraquat from a 50 mL solution containing 250 ppm of paraquat. These results show that Alg–PCP can be used to mitigate herbicide contamination in water, protecting aquatic ecosystems and addressing associated environmental and health risks. Full article

Mechanical confinement plays an important role in regulating tumor growth and invasion; however, the quantitative, time-resolved, three-dimensional evaluation of confined tumor spheroids remains technically challenging. In this study, we developed a custom-built selective plane illumination microscopy (SPIM)-based monitoring platform for long-term volumetric imaging of tumor spheroids under mechanically confined conditions. This system integrates a culture housing unit and a transparent cuvette-based spheroid culture method optimized for SPIM observation. Colorectal adenocarcinoma-derived cell spheroids were embedded in agarose gels with defined concentrations to modulate the stiffness of the surrounding matrix. Bright-field imaging and viability analyses confirmed sustained spheroid growth without necrotic core formation over a 4-day culture period, demonstrating that the SPIM-based system maintained the physiological culture conditions. Three-dimensional imaging using SPIM enabled a quantitative evaluation of spheroid growth and anisotropic invasion. Volumetric expansion was observed under all confinement conditions. Notably, increasing the matrix stiffness enhanced both the volumetric growth rate and anisotropic invasion, indicating stiffness-dependent directional growth under mechanical confinement. The developed SPIM-based platform has the potential to serve as a practical tool for the time-resolved three-dimensional analysis of tumor spheroid growth and may provide a useful approach for investigating the mechanobiological regulation of tumor progression in confined microenvironments. Full article

The environmental persistence of β-lactam antibiotics represents a growing ecological concern, requiring materials capable of combined adsorption and catalytic degradation. Herein, pure ZnS and 1% Fe-doped ZnS nanoparticles were synthesized via microwave-assisted treatment and evaluated for the removal of ceftaroline fosamil from aqueous media. Transmission electron microscopy revealed quasi-spherical nanoparticles below 10 nm, while selected area electron diffraction confirmed a face-centered cubic structure retained after Fe incorporation. UV-Vis spectroscopy showed similar absorption edges (~316 nm), indicating negligible band-gap variation, whereas photoluminescence analysis demonstrated strong emission quenching in Fe-ZnS, indicating suppressed electron–hole recombination. Point-of-zero charge measurements (pH_PZC ≈ 4.6 for ZnS; 4.5 for Fe-ZnS) indicated negatively charged surfaces under circumneutral conditions, influencing interfacial interactions with the antibiotic. Adsorption experiments followed the Langmuir isotherm model, with Fe-ZnS exhibiting a higher maximum adsorption capacity (156 mg g⁻¹) compared to ZnS (115 mg g⁻¹). Under UV irradiation (302 nm), Fe-ZnS achieved near-complete degradation at a catalyst loading of 500 ppm. Liquid chromatography–mass spectrometry analysis revealed the transformation of ceftaroline fosamil (m/z 685.01) into ceftaroline (m/z 605.05) via phosphate group loss, followed by the formation of intermediate fragments at m/z 492.08 and 308.03, associated with cleavage of the thiadiazol-amine moiety and subsequent opening of the cephalosporin ring. After extended irradiation, these intermediates diminished, and a fragment at m/z 356.01 was detected, suggesting further breakdown through thioether bond cleavage. These results support a degradation pathway involving sequential dephosphorylation and fragmentation of the cephalosporin core. Overall, the enhanced performance of Fe-ZnS arises from the synergistic interplay between surface charge characteristics and dopant-modulated charge carrier dynamics, highlighting its potential for antibiotic remediation in aquatic environments. Full article

Nitridation of different materials using ion implantation is of considerable interest for many applications. As electronic components, oxynitride (SiO_xN_y) layers exhibit beneficial properties such as precise compositional variability, refractive index tunability, oxidation resistance, and low mechanical stress. In the present study we investigate nanoscale SiO_xN_y synthesized using ion implantation methods. To introduce N⁺ ions into a shallow Si subsurface region, both conventional ion beam implantation and plasma immersion ion implantation with subsequent high-temperature treatment in dry O₂ are used. The optical and morphological properties and chemical bonding of formed SiO_xN_y layers were studied by applying spectroscopic ellipsometry in the range of VIS-Near IR (SE) and IR (IR-SE), Raman spectroscopy and Atomic Force Microscopy (AFM). Monte Carlo modeling of implant profiles contributed to understanding physical and chemical processes and predicted different influences of the incorporated N⁺ ions on the oxidation mechanism, confirmed by the thickness dependence of SiO_xN_y/Si layers obtained from the SE data analysis. IR-SE spectral analysis established the formation of Si-O, Si-N, Si-N-O and Si-Si chemical bonds in the grown layers. The occurrence of amorphization of the Si crystal lattice due to incorporation of high-energy N⁺ ions into the Si lattice is confirmed by the Raman and ellipsometry results. The free Si atoms can congregate, forming nanocrystalline clusters. AFM imaging revealed that both implantation methods left the surface of the resulting SiO_xN_y layers considerably smooth with similar roughness parameter values. The results of the studies imply that the technological approaches used allow the production of high-quality nanoscale silicon oxynitride films with appropriate tunable composition and properties for possible application in advanced electronic devices for nanoelectronics, optoelectronics and sensor applications. Full article

This study investigates the properties of ZnO nanorod-based sensors and ZnO nanorods modified with tin dioxide (ZnO/SnO₂) and gold (ZnO/Au) nanoclusters and their response to low concentrations of carbon monoxide (CO). It was demonstrated that the ZnO/SnO₂(3) nanorod-based sensor exhibited the highest sensitivity (S = 1.64) to 10 ppm CO, while the ZnO/Au(3) sensor displayed the shortest response (69–207 s) and recovery (203–233 s) times. This behavior can be explained by ZnO/Au and ZnO/SnO₂ nanostructures having low activation energies (0.23–0.25 eV) and high potential barrier values (0.37–0.43 eV). Sensors based on ZnO/Au and ZnO/SnO₂ nanorods demonstrate sensitivity to 10 ppm CO at 250 °C and at 200 °C. In contrast, ZnO nanorod-based sensors are sensitive to 2 ppm CO at 250 °C. Full article