Agarose Hydrogel Research Articles

Transient transition from Stable to Dissipative Assemblies in Response to the Spatiotemporal Availability of a Chemical Fuel

AbstractThe transition from inactive to active matter implies a transition from thermodynamically stable to energy‐dissipating structures. Here, we show how the spatiotemporal availability of a chemical fuel causes a thermodynamically stable self‐assembled structure to transiently pass to an energy‐dissipating state. The system relies on the local injection of a weak affinity phosphodiester substrate into an agarose hydrogel containing surfactant‐based structures templated by ATP. Injection of substrate leads to the inclusion of additional surfactant molecules in the assemblies leading to the formation of catalytic hotspots for substrate conversion. After the local disappearance of the substrate as a result of chemical conversion and diffusion the assemblies spontaneously return to the stable state, which can be reactivated upon the injection of a new batch of fuel. The study illustrates how a dissipating self‐assembled system can cope with the intermittent availability of chemical energy without compromising long‐term structural stability.

A Novel Nano-Hydroxyapatite Agarose-Based Hydrogel for Biomimetic Remineralization of Demineralized Human Enamel: An in-vitro Study.

This study aims to investigate the biomimetic effect of agarose hydrogel loaded with enamel matrix derivative (EMD-agarose) alone or in combination with nano-hydroxyapatite (n-HA-EMD-agarose) on the remineralization of human demineralized enamel. Extracted human mandibular third molars were sectioned into 54 buccal and lingual halves. Acid-resistant nail varnish was applied to each half, except for two enamel windows. Enamel surface microhardness, energy-dispersive X-ray spectroscopy (EDX), and scanning electron microscopy (SEM) analyses were conducted to evaluate enamel surfaces at baseline, following demineralization with 37% phosphoric acid, and after each hydrogel application and remineralization for two, four, and six days. Remineralization was performed using a phosphate solution at 37°C. At day 6 following remineralization, a statistically significant higher mean microhardness was recorded in n-HA-EMD-agarose hydrogel (260.87 ± 3.52) as compared to EMD-agarose hydrogel (244.63 ± 2.76) (p = 0.027). Similarly, n-HA-EMD-agarose hydrogel showed a higher mean calcium (46.31 ± 2.78), phosphorous (24.92 ± 0.826), and fluoride (0.909 ± 0.053) weight percentage compared to EMD-agarose hydrogel calcium (19.64 ± 1.092), phosphorous (19.64 ± 1.092), and fluoride (0.7033 ± 0.0624) weight percentage (p < 0.05). Further, SEM analysis revealed a substantial deposition of n-HA following the application of the n-HA-EMD-agarose hydrogel, whereas the EMD-agarose exhibited a relatively smooth enamel surface with less visible enamel rods due to mineral deposition. The combined n-HA-EMD-agarose hydrogel demonstrated improved surface microhardness of the remineralized enamel and enhanced mineral content deposition, indicating its potential as a biomimetic approach for dental enamel repair.

Coencapsulating TMB Probes and Bimetallic MOF Nanozymes in a Hydrogel Patch for Fabricating Reusable Visual VC Sensors.

As a typical chromogenic probe, 3,3',5,5'-tetramethylbenzidine (TMB) has been widely applied in the field of visual detection due to its low toxicity and highly sensitive response. Due to the hydrophobic nature of TMB, encapsulating it into a hydrogel, which serves as an ideal matrix for wearable sensors, presents significant challenges that complicate the fabrication of visual wearable devices. Herein, the TMB probe and bimetallic MOF nanozymes are coencapsulated in a hydrogel patch for the fabrication of reusable visual sensors. Hydrophobic TMB is oxidized to hydrophilic ox-TMB by a bimetallic MOF (CuFe-MOF), allowing its diffusion into a hydrophilic agarose hydrogel patch, where it is reduced back to TMB. This process allows the coimmobilization and coencapsulation of CuFe-MOF and TMB within the hydrogel patch. Leveraging the color change between TMB and ox-TMB, as a proof-of-concept application, a reusable visual "On-Off-On" sensor is simply constructed and successfully applied to detect vitamin C in human sweat. Color changes can be quickly read by the naked eye or by smart devices without the need for external equipment. Meanwhile, based on the reversible conversion relationship between TMB and ox-TMB, a reusable sensor construction strategy is proposed. This approach not only facilitates the use of a TMB probe in hydrogel applications but also offers inspiration for the development of point-of-care testing equipment, demonstrating significant application potential.

Transient transition from stable to dissipative assemblies in response to the spatiotemporal availability of a chemical fuel.

The transition from inactive to active matter implies a transition from thermodynamically stable to energy-dissipating structures. Here, we show how the spatiotemporal availability of a chemical fuel causes a thermodynamically stable self-assembled structure to transiently pass to an energy-dissipating state. The system relies on the local injection of a weak affinity phosphodiester substrate into an agarose hydrogel containing surfactant-based structures templated by ATP. Injection of substrate leads to the inclusion of additional surfactant molecules in the assemblies leading to the formation of catalytic hotspots for substrate conversion. After the local disappearance of the substrate as a result of chemical conversion and diffusion the assemblies spontaneously return to the stable state, which can be reactivated upon the injection of a new batch of fuel. The study illustrates how a dissipating self-assembled system can cope with the intermittent availability of chemical energy without compromising long-term structural stability.

Nanozyme-mediated ratiometric fluorescence hydrogel for on-site detection of sulfite in food

In this work, a ratiometric fluorescence hydrogel nanosensor was developed by integrating a composite consisting of o-phenylenediamine (OPD), manganese dioxide nanoflakes (MnO2 NFs), and N-doped carbon dots (N-CDs) into an agarose hydrogel for sulfite detection. MnO2 NFs demonstrated intense oxidase-like activity, facilitating the conversion of non-fluorescent OPD into yellow-emissive 2,3-diaminophenazine (DAP). As a result, a significant emission peak belongs to DAP, alongside the fluorescence quenching of N-CDs through FRET. Upon interaction with sulfite, MnO2 NFs lost their oxidase-like function. This process decreased the fluorescence of DAP and restored the blue fluorescence of N-CDs, producing a typical ratiometric response, ranging from 3 nM ∼ 400 μM, with a detection limit (LOD) of 3.79 nM. Employing a smartphone, the fluorescence color change demonstrated by the hydrogel sensor was translated into quantitative data (LOD: 8.44 nM). This hydrogel sensor offers an affordable, portable, and user-friendly solution for sulfite detection and food safety monitoring.

From Bioink to Tissue: Exploring Chitosan-Agarose Composite in the Context of Printability and Cellular Behaviour

This study presents an innovative method for producing thermosensitive bioink from chitosan hydrogels saturated with carbon dioxide and agarose. It focuses on a detailed characterisation of their physicochemical properties and potential applications in biomedicine and tissue engineering. The ORO test approved the rapid regeneration of the three-dimensional structure of chitosan–agarose composites in a unidirectional bench press simulation test. The diffusion of dyes through the chitosan–agarose hydrogel membranes strongly depended on the share of both polymers in the composite and the molecular weight of the dyes. Glucose, as a nutrient marker, also diffused through all membranes regardless of composition. Biocompatibility assessment using MTT tests on 46BR.1N fibroblasts and HaCaT keratinocytes confirmed the safety of the bioink. The regenerative potential of the bioink was confirmed by efficient cell migration, especially HaCaT. Long-term viability studies showed that chitosan–agarose scaffolds, unlike the agarose ones, support cell proliferation and survival, especially 14 days after bioink extrusion. Experiments in a skin wound model in mice confirmed the biocompatibility of the tested dressing and the beneficial action of chitosan on healing. Studies on vessel formation in chicken embryos highlight the potential of the chitosan–agarose composition to enhance proangiogenic effects. This composition meets all entry criteria and possesses excellent biological properties.

Comprehensive characterization of natural polysaccharide-based hydrogels with gradient structure in concentration and stiffness

Gradient hydrogels are functionally graded biomaterials that over the last decades have garnered significant attention as valuable materials for tissue repair and regeneration. This study elucidates key factors crucially determining the character or pattern of a buoyancy-driven gradient in agarose hydrogels and also provides fundamental information regarding the complex interpretation of the formed gradient hydrogels obtained by the different characterization techniques, including rheology, UV-Vis spectroscopy, FCS, AFM, SEM. The employed techniques were successfully optimized to enhance the understanding of the gradient properties of these hydrogels. Demonstrated results showed that the agarose concentration gradient could be successfully controlled and tailored, which offers a valuable contribution to the design of gradient hydrogel. Moreover, a novel method for determining the average agarose concentration along the gradient axis is presented, improving the precision of gradient characterization. The integration of these approaches significantly enhances the comprehension of the internal structure and properties of gradient materials, contributing to advancements in their understanding and application.

Effect of Silk Fibroin on the Mechanical and Transport Properties of Agarose Hydrogels.

In this work, the effect of incorporating silk fibroin, a fibrous biocompatible protein, into physically cross-linked agarose hydrogels was investigated as a simple model study to examine how supramolecular fibrous structures influence the properties of the hydrogels. The rheological and transport properties were studied. Fibroin did not change the general viscoelastic properties of the investigated hydrogels but changed the viscoelastic moduli values and also the mesh size, as calculated from rheometry data. Fibroin influenced the mechanical properties depending on its concentration: at lower concentrations, it increased the mesh size, while at higher concentrations, it acted as a filler, decreasing the mesh size. Similarly, the storage and loss moduli were affected, either increasing or decreasing based on the fibroin concentration. The fibroin effect on the diffusion of two dyes differing in their charge was the result of a combination of structural effects, responsible also for changes in the rheological properties, and a result of electrostatic interactions between the charged groups. For positively charged methylene blue, low fibroin concentrations accelerated diffusion, while higher concentrations slowed it by filling network vacancies. In contrast, for negatively charged eosin-B, fibroin strongly impeded diffusion at all concentrations due to electrostatic repulsion, leading to its accumulation at the hydrogel interface. The findings of this work may contribute to an understanding of the behavior of the extracellular matrix or soft tissues as well as to the development of the tailored design of hydrogel materials.

Characterization of Composite Agarose-Collagen Hydrogels for Chondrocyte Culture.

To elucidate the mechanisms of cellular mechanotransduction, it is necessary to employ biomaterials that effectively merge biofunctionality with appropriate mechanical characteristics. Agarose and collagen separately are common biopolymers used in cartilage mechanobiology and mechanotransduction studies but lack features that make them ideal for functional engineered cartilage. In this study, agarose is blended with collagen type I to create hydrogels with final concentrations of 4% w/v or 2% w/v agarose with 2 mg/mL collagen. We hypothesized that the addition of collagen into a high-concentration agarose hydrogel does not diminish mechanical properties. Acellular and cell-laden studies were completed to assess rheologic and compressive properties, contraction, and structural homogeneity in addition to cell proliferation and sulfated glycosaminoglycan production. Over 21days in culture, cellular 4% agarose-2mg/mL collagen I hydrogels seeded with primary murine chondrocytes displayed structural and bulk mechanical behaviors that did not significantly alter from 4% agarose-only hydrogels, cell proliferation, and continual glycosaminoglycan production, indicating promise toward the development of an effective hydrogel for chondrocyte mechanotransduction and mechanobiology studies.

Development of a 3D Hydrogel SERS Chip for Noninvasive, Real-Time pH and Glucose Monitoring in Sweat.

Traditional diagnostic methods, such as blood tests, are invasive and time-consuming, while sweat biomarkers offer a rapid physiological assessment. Surface-enhanced Raman spectroscopy (SERS) has garnered significant attention in sweat analysis because of its high sensitivity, label-free nature, and nondestructive properties. However, challenges related to substrate reproducibility and interference from the biological matrix persist with SERS. This study developed a novel ratio-based 3D hydrogel SERS chip, providing a noninvasive solution for real-time monitoring of pH and glucose levels in sweat. Encapsulating the probe molecule (4-MBN) in nanoscale gaps to form gold nanoflower-like nanotags with internal standards and integrating them into an agarose hydrogel to create a 3D flexible SERS substrate significantly enhances the reproducibility and stability of sweat analysis. Gap-Au nanopetals modified with probe molecules are uniformly dispersed throughout the porous hydrogel structure, facilitating the effective detection of the pH and glucose in sweat. The 3D hydrogel SERS chip demonstrates a strong linear relationship in pH and glucose detection, with a pH response range of 5.5-8.0 and a glucose detection range of 0.01-5 mM, with R2 values of 0.9973 and 0.9923, respectively. In actual sweat samples, the maximum error in pH detection accuracy is only 1.13%, with a lower glucose detection limit of 0.25 mM. This study suggests that the ratio-based 3D hydrogel SERS chip provides convenient, reliable, and rapid detection capabilities with substantial application potential for analyzing body fluid pH and glucose.

Heat conduction simulation of chondrocyte-embedded agarose gels suggests negligible impact of viscoelastic dissipation on temperature change

Agarose is commonly used for 3D cell culture and to mimic the stiffness of the pericellular matrix of articular chondrocytes. Although it is known that both temperature and mechanical stimulation affect the metabolism of chondrocytes, little is known about the thermal properties of agarose hydrogels. Thermal properties of agarose are needed to analyze potential heat production by chondrocytes induced by various experimental stimuli (carbon source, cyclical compression, etc). Utilizing ASTM C177, a custom-built thermal conductivity measuring device was constructed and used to calculate the thermal conductivity of 4.5 % low gelling temperature agarose hydrogels. Additionally, Differential Scanning Calorimetry was used to calculate the specific heat capacity of the agarose hydrogels. Testing of chondrocyte-embedded agarose hydrogels commonly occurs in Phosphate-Buffered Saline (PBS), and thermal analysis requires the free convection coefficient of PBS. This was calculated using a 2D heat conduction simulation within MATLAB in tandem with experimental data collected for known boundary and initial conditions. The specific heat capacity and thermal conductivity of 4.5 % agarose hydrogels was calculated to be 2.85 J/g°C and 0.121 W/mK, respectively. The free convection coefficient of PBS was calculated to be 1000.1 W/m2K. The values of specific heat capacity and thermal conductivity for agarose are similar to the reported values for articular cartilage, which are 3.20 J/g°C and 0.21 W/mK (Moghadam, et al. 2014). These data show that cyclical loading of hydrogel samples with these thermal properties will result in negligible temperature increases. This suggests that in addition to 4.5 % agarose hydrogels mimicking the physiological stiffness of the cartilage PCM, they can also mimic the thermal properties of articular cartilage for in vitro studies.

Elucidating the unexpected cell adhesive properties of agarose substrates. The effect of mechanics, fetal bovine serum and specific peptide sequences

2D agarose substrates have recently been surprisingly shown to be permissive for cell adhesion, depending on their mechanics and the use of the adhesive proteins of fetal bovine serum (FBS) in the cell culture medium. Here, we elucidate how the cells exhibit two anchoring mechanisms depending on the amount of FBS. Under low FBS conditions, the cells recognize the surface-coupled adhesive sequences of fibronectin via the binding of the heterodimer α5β1 integrin. Functionality of the actomyosin axis and mechanoactivation of focal adhesion kinase (FAK) are essential for the stretching of the protein, thereby accessing the “synergy” PPSRN site and enhancing cell adhesion in combination with the downstream RGD motif. Under high FBS conditions, the specific peptide sequences are much less relevant as the adsorbed serum proteins conceal the coupled fibronectin and the cells recognize the adhesive protein vitronectin, which is constitutively present in FBS, via the binding of the heterodimer αvβ3 integrin. Similarly, the intracellular tension and FAK activity are decisive, which collectively indicate that the cells stretch the partially cryptic RGD site of vitronectin and thus make it more accessible for integrin binding. Both anchoring mechanisms only work properly if the agarose substrate is mechanically compliant in terms of linear stress-strain response, unraveling a critical balance between the mechanics of the agarose substrate and the presentation of the adhesive peptides. Statement of significanceIn the context of biomaterial design, agarose hydrogels are known to lack intrinsic cell-adhesive peptide motifs and are therefore commonly used for the development of non-permissive 2D substrates. However, we unexpectedly found that agarose hydrogels can become permissive substrates for cell adhesion, depending on a compliant mechanical response of the substrate and the use of fetal bovine serum (FBS) as protein reservoir in the cell culture medium. We describe here two anchoring mechanisms that cells harness to adhere to agarose substrates, depending on the amount of FBS. Our results will have a major impact on the field of mechanobiology and shed light on the central role of FBS as a natural source of adhesive proteins that could promote cell anchoring.

Thermoresponsive and Substrate Self-Cycling Nanoenzyme System for Efficient Tumor Therapy.

Cerium oxide (CeO2-x) performs well in photothermal and catalytic properties due to its abundance of oxygen vacancies. Based on this, we designed a thermosensitive therapeutic nanoplatform to achieve continuous circular drug release in tumor. It can solve the limitation caused by insufficient substrate in the process of tumor treatment. Briefly, CeO2-x and camptothecin (CPT) were wrapped in an agarose hydrogel, which could be melted by the photothermal effect of CeO2-x. At the same time, the local temperature increase provided photothermal treatment, which could induce the apoptosis of tumor cell. After that, CPT was released to damage the DNA in tumor cells to realize chemical treatment. In addition, CPT could active nicotinamide adenine dinucleotide oxidase to react with O2 to increase the intracellular H2O2. After that, the exposed CeO2-x could catalyze H2O2 to generate cytotoxic reactive oxygen species for chemodynamic therapy. More importantly, CeO2-x could catalyze H2O2 to produce O2, which could combine with the catalytic action of CPT to construct a substrate self-cycling nanoenzyme system. Overall, this self-cycling nanoplatform released hypoxia in the tumor microenvironment and built a multimode tumor treatment, which achieved an ideal antitumor affect.

Generation of mouse testicular organoids with highly compartmentalized tubular lumen structure and their cryopreservation

Testicular organoids have great potential for maintaining male fertility and even restoring male infertility. However, existing studies on generating organoids with testis-specific structure and function are scarce and come with many limitations. Research on cryopreservation of testicular organoids is even more limited, and inappropriate cryopreservation methods may result in the loss of properties in resuscitated or regenerated organoids, rendering them unsuitable for clinical or research needs. In this paper, we investigated the effects of mouse age and cell number on the self-aggregation of testicular cells into spheres in low-adsorption plates. Various media compositions, culture systems, and cell numbers were used to culture cell spheres for 14 days to form testicular organoids, and the self-organization of the organoids was assessed by histological and immunofluorescence staining. We determined the appropriate cryopreservation conditions for testicular cells, cell spheres, and tissues. Subsequently, organoids derived from cryopreserved testicular tissues, testicular cells, and testicular cell spheres were compared and evaluated by histological and immunofluorescence staining. The results indicate that testicular cell spheres consisting of 30 × 104 testicular cells from 2-week-old mice were able to form organoids highly similar to the luminal structure and cell distribution of natural mouse testicular tissues. This transformation occurred over 14 days of incubation in α-MEM medium containing 10 % knockout serum replacer (KSR) using an agarose hydrogel culture system. Additionally, the Sertoli cells were tightly connected to form a blood-testis barrier. The relative rates of tubular area, germ cells, Sertoli cells, and peritubular myoid cells were 36.985 % ± 0.695, 13.347 % ± 3.102, 47.570 % ± 0.379, and 27.406 % ± 1.832, respectively. The optimal cryopreservation protocol for primary testicular cells involved slow freezing with a cryoprotectant consisting of α-MEM with 10 % dimethyl sulfoxide (DMSO). Slow freezing with cryoprotectants containing 5 % DMSO and 5 % ethylene glycol (EG) was optimal for all different volumes of testicular cell spheres. Compared to testicular organoids generated from frozen testicular tissue and cell spheres, freezing testicular cells proved most effective in maintaining organoid differentiation characteristics and cell-cell interactions. The findings of this study contribute to a “universal” testicular organoid in vitro culture protocol with promising applications for fertility preservation and restoration in prepubertal cancer patients and adult infertile patients.

Patterned PVA Hydrogels with 3D Petri Dish® Micro-Molds of Varying Topography for Spheroid Formation of HeLa Cancer Cells: In Vitro Assessment.

Cell spheroids are an important three-dimensional (3D) model for in vitro testing and are gaining interest for their use in clinical applications. More natural 3D cell culture environments that support cell-cell interactions have been created for cancer drug discovery and therapy applications, such as the scaffold-free 3D Petri Dish® technology. This technology uses reusable and autoclavable silicone micro-molds with different topographies, and it conventionally uses gelled agarose for hydrogel formation to preserve the topography of the selected micro-mold. The present study investigated the feasibility of using a patterned Poly(vinyl alcohol) hydrogel using the circular topography 12-81 (9 × 9 wells) micro-mold to form HeLa cancer cell spheroids and compare them with the formed spheroids using agarose hydrogels. PVA hydrogels showed a slightly softer, springier, and stickier texture than agarose hydrogels. After preparation, Fourier transform infrared (FTIR) spectra showed chemical interactions through hydrogen bonding in the PVA and agarose hydrogels. Both types of hydrogels favor the formation of large HeLa spheroids with an average diameter of around 700-800 µm after 72 h. However, the PVA spheroids are more compact than those from agarose, suggesting a potential influence of micro-mold surface chemistry on cell behavior and spheroid formation. This was additionally confirmed by evaluating the spheroid size, morphology, integrity, as well as E-cadherin and Ki67 expression. The results suggest that PVA promotes stronger cell-to-cell interactions in the spheroids. Even the integrity of PVA spheroids was maintained after exposure to the drug cisplatin. In conclusion, the patterned PVA hydrogels were successfully prepared using the 3D Petri Dish® micro-molds, and they could be used as suitable platforms for studying cell-cell interactions in cancer drug therapy.

Indirect Voltammetry Detection of Non-Electroactive Neurotransmitters Using Glassy Carbon Microelectrodes: The Case of Glutamate

Glassy carbon (GC) microelectrodes have been successfully used for the detection of electroactive neurotransmitters such as dopamine and serotonin through voltammetry. However, non-electroactive neurotransmitters such as glutamate, lactate, and gamma-aminobutyric acid (GABA) are inherently unsuitable for detection through voltammetry techniques without functionalizing the surface of the microelectrodes. To this end, we present here the immobilization of the L-glutamate oxidase (GluOx) enzyme on the surface of GC microelectrodes to enable the catalysis of a chemical reaction between L-glutamate, oxygen, and water to produce H2O2, an electroactive byproduct that is readily detectable through voltammetry. This immobilization of GluOx on the surface of bare GC microelectrodes and the subsequent catalytic reduction in H2O2 through fast-scan cyclic voltammetry (FSCV) helped demonstrate the indirect in vitro detection of glutamate, a non-electroactive molecule, at concentrations as low as 10 nM. The functionalized microelectrodes formed part of a four-channel array of microelectrodes (30 μm × 60 μm) on a 1.6 cm long neural probe that was supported on a flexible polymer, with potential for in vivo applications. The types and strengths of the bond between the GC microelectrode surface and its functional groups, on one hand, and glutamate and the immobilized functionalization matrix, on the other hand, were investigated through molecular dynamic (MD) modeling and Fourier transform infrared spectroscopy (FTIR). Both MD modeling and FTIR demonstrated the presence of several covalent bonds in the form of C-O (carbon–oxygen polar covalent bond), C=O (carbonyl), C-H (alkenyl), N-H (hydrogen bond), C-N (carbon–nitrogen single bond), and C≡N (triple carbon–nitrogen bond). Further, penetration tests on an agarose hydrogel model confirmed that the probes are mechanically robust, with their penetrating forces being much lower than the fracture force of the probe material.

A Cautionary Perspective on Hydrogel-Induced Concentration Gradient Generation for Studying Chemotaxis.

The achievement of consistent and static chemical gradients is critically important in the study of diffusion and chemotaxis at the micro- and nanoscales. In this context, a number of groups have reported on hydrogel-based systems for generating concentration gradients. Here, we analyze the behavior of agarose and gelatin-based hydrogels in hybridization chambers of different heights. Our focus is on the issues that are caused by the presence of robust bulk fluid flows in such systems due to the solutes present in the hydrogel and/or the surrounding fluid. We describe the key insights derived from these experiments, offering practical guidelines for establishing gradients using hydrogel-based systems and make the community aware of different variables that can make the experiments nonreproducible and prone to misinterpretations.

Mechanical properties of agarose hydrogels tuned by amphiphilic structures

Agarose is a biocompatible polysaccharide that is capable to form physically cross-linked hydrogels in aqueous dispersion. These materials offer a wide range of applications and are commonly used in the food industry or electrophoresis. Moreover, due to their favourable characteristics (biocompatibility, high water absorption, porosity), agarose hydrogels have recently also found applications also in drug delivery systems, wound dressing, and extracellular matrix (ECM) modelling. This paper presents a comprehensive rheological characterization of agarose hydrogels with various self-assembled amphiphilic structures (CTAB, TTAB, SDS, Tween 20) acting as simple membrane structure models. These findings demostrated that the presence of surfactants of diverse charge above their critical micellar concentration (CMC) can enhance hydrogel mechanical properties. Moreover, pronounced enhancement was observed for cationic surfactant, and even concentrations below CMC resulted in a higher stiffness of the hydrogel. Therefore, both the electrostatic effect and the amphiphilic structure effect can have a significant impact on the rheological properties on agarose hydrogels. These findings are of a significant interest in the field of polymer and surfactants interactions, since agarose is widely considered essentially uncharged. However, it is assumed, that traces of negatively charged groups on the agarose backbone can have a significant impact when interacting with oppositely charged surfactants. Moreover, these findings could be beneficial for better understanding of interaction of polysaccharides (e.g. agarose) and self-assembled amphiphilic structures and can also be considered as a crude model of ECM in which membrane structures are embedded.

Nanoarchitectonics of Fe single-atom catalyst modified with flexible wearable patch for sweat biomarker analysis

In personalized medical diagnostics and health monitoring, the analysis of biomarkers in sweat, such as uric acid (UA) and dopamine (DA), offers valuable insights into metabolic states. This study introduces a flexible wearable patch based on Fe single-atom catalysts (FeSAs) to simultaneously detect UA and DA in sweat for comprehensive health assessment. Our wearable patch demonstrated linear response ranges of 1–800 μM for UA and 1–500 μM for DA, with detection limits of 2.68 μM and 3.76 μM, and sensitivities of 0.015 μA μM−1 cm−2 and 0.0176 μA μM−1 cm−2, respectively. Additionally, we integrated agarose hydrogel into the wearable patches, optimizing sweat collection efficiency at agarose concentrations ranging from 2 % to 3.8 %. This innovation enables effective biomarker enrichment directly from the skin surface. In conclusion, our study presents an innovative FeSAs-based electrocatalyst capable of simultaneous detection of low-concentration UA and DA biomarkers.

Characterization of 3D oxygen concentrations in microfluidic systems combining astigmatic particle tracking with phosphorescence decay measurements

In this work, we combine astigmatic particle tracking with phosphorescence decay measurements to determine 3D-resolved oxygen concentration in microfluidic systems. In our experiments we achieve uncertainties in the out-of-plane position of less than 1 µm and uncertainties in oxygen concentration of less than 2 ppm. The calibrated measurement range covers oxygen concentrations of 0.6 ppm to 27.6 ppm. A method is presented to correct for measurement errors caused by photobleaching. For this, the excitation energy, the cumulative exposure time and the spatially varying intensity profile of the laser are taken into account in the correction. With this method, low measurement errors of less than 2ppm at ambient oxygen levels can be achieved even after thousands of excitation cycles. Hence, 3D oxygen concentrations are measured in an agarose hydrogel filled microfluidic chamber across which different pressure and oxygen gradients can be set independently. The results show that oxygen diffusion is superposed by an interstitial flow, which significantly alters the resulting oxygen concentration.