Spatial Separation of Microbeads into Detection Levels by a Bioorthogonal Porous Hydrogel for Size-Selective Analysis and Increased Multiplexity

Multifaceted Hydrogel Scaffolds: Bridging the Gap between Biomedical Needs and Environmental Sustainability

Hydrogels are dynamically evolving 3D networks composed of hydrophilic polymer scaffolds with significant applications in the healthcare and environmental sectors. Notably, protein-based hydrogels mimic the extracellular matrix, promoting cell adhesion. Further enhancing cell proliferation within these scaffolds are matrix-metalloproteinase-triggered amino acid motifs. Integration of cell-friendly modules like peptides and proteins expands hydrogel functionality. These exceptional properties position hydrogels for diverse applications, including biomedicine, biosensors, environmental remediation, and the food industry. Despite significant progress, there is ongoing research to optimize hydrogels for biomedical and environmental applications further. Engineering novel hydrogels with favorable characteristics is crucial for regulating tissue architecture and facilitating ecological remediation. This review explores the synthesis, physicochemical properties, and biological implications of various hydrogel types and their extensive applications in biomedicine and environmental sectors. It elaborates on their potential applications, bridging the gap between advancements in the healthcare sector and solutions for environmental issues.

Sieving and Clogging in PEG-PEGDA Hydrogel Membranes

Hydrogels are promising systems for separation applications due to their structural characteristics (i.e., hydrophilicity and porosity). In our study, we investigate the permeation of suspensions of rigid latex particles of different sizes through free-standing hydrogel membranes prepared by photopolymerization of a mixture of poly(ethylene glycol) diacrylate (PEGDA) and large poly(ethylene glycol) (PEG) chains of 300,000 g·mol-1 in the presence of a photoinitiator. Atomic force microscopy and cryoscanning electron microscopy (cryoSEM) were employed to characterize the structures of the hydrogel membranes. We find that the 20 nm particle permeation depends on both the PEGDA/PEG composition and the pressure applied during filtration. In contrast, we do not measure a significant permeation of the 100 nm and 1 μm particles, despite the presence of large cavities of 1 μm evidenced by the cryoSEM images. We suggest that the PEG chains induce local nanoscale defects in the cross-linking of PEGDA-rich walls separating the micrometer-sized cavities, which control the permeation of particles and water. Moreover, we discuss the decline of the permeation flux observed in the presence of latex particles compared to that of pure water. We suggest that a thin layer of particles forms on the surface of the hydrogels.

A multiparametric fluorescence assay for screening aptamer-protein interactions based on microbeads

For improving aptamer-ligand binding we have developed a screening system that defines optimal binding buffer composition. Using multiplex assays, one buffer system is needed which guarantees the specific binding of all aptamers. We investigated nine peer-reviewed DNA aptamers. Non-specific binding of aptamers is an obstacle. To address this, we investigated 16 proteins as specificity controls bound covalently to encoded microbeads in a multiplex assay. Increasing the NaCl concentration decreased the binding for all aptamers. Changing pH values by one unit higher or lower did not influence the aptamer binding significantly. However, pH < 5 led to non-specific binding for all aptamers. The PfLDH-aptamer selected in the absence of divalent cations exhibited doubling of its binding signal by the addition of Ca²⁺ and Mg²⁺. We confirmed Ca²⁺ and Mg²⁺ dependency of the aptamers for streptavidin and thrombin by observing a 90% and 50% binding decrease, respectively. We also achieved a doubling of binding for the streptavidin aptamer when replacing Ca²⁺ and Mg²⁺ by Mn²⁺. A buffer suitable for all aptamers can have considerable variations in pH or ionic strength, but divalent cations (Ca²⁺, Mg²⁺, Mn²⁺) are essential.

Hydrogel-Assisted 3D Volumetric Hotspot for Sensitive Detection by Surface-Enhanced Raman Spectroscopy

Effective hotspot engineering with facile and cost-effective fabrication procedures is critical for the practical application of surface-enhanced Raman spectroscopy (SERS). We propose a SERS substrate composed of a metal film over polyimide nanopillars (MFPNs) with three-dimensional (3D) volumetric hotspots for this purpose. The 3D MFPNs were fabricated through a two-step process of maskless plasma etching and hydrogel encapsulation. The probe molecules dispersed in solution were highly concentrated in the 3D hydrogel networks, which provided a further enhancement of the SERS signals. SERS performance parameters such as the SERS enhancement factor, limit-of-detection, and signal reproducibility were investigated with Cyanine5 (Cy5) acid Raman dye solutions and were compared with those of hydrogel-free MFPNs with two-dimensional hotspots. The hydrogel-coated MFPNs enabled the reliable detection of Cy5 acid, even when the Cy5 concentration was as low as 100 pM. We believe that the 3D volumetric hotspots created by introducing a hydrogel layer onto plasmonic nanostructures demonstrate excellent potential for the sensitive and reproducible detection of toxic and hazardous molecules.

Hydrogels and Their Role in Biosensing Applications

Hydrogels play an important role in the field of biomedical research and diagnostic medicine. They are emerging as a powerful tool in the context of bioanalytical assays and biosensing. In this context, this review gives an overview of different hydrogels and the role they adopt in a range of applications. Not only are hydrogels beneficial for the immobilization and embedding of biomolecules, but they are also used as responsive material, as wearable devices, or as functional material. In particular, the scientific and technical progress during the last decade is discussed. The newest hydrogel types, their synthesis, and many applications are presented. Advantages and performance improvements are described, along with their limitations.

Particle Diffusivity and Free-Energy Profiles in Hydrogels from Time-Resolved Penetration Data

A combined experimental and theoretical method to simultaneously determine diffusivity and free-energy profiles of particles that penetrate into inhomogeneous hydrogel systems is presented. As the only input, arbitrarily normalized concentration profiles from fluorescence intensity data of labeled tracer particles for different penetration times are needed. The method is applied to dextran molecules of varying size that penetrate into hydrogels of polyethylene-glycol chains with different lengths that are covalently cross-linked by hyperbranched polyglycerol hubs. Extracted dextran bulk diffusivities agree well with fluorescence correlation spectroscopy data obtained separately. Empirical scaling laws for dextran diffusivities and free energies inside the hydrogel are identified as a function of the dextran mass. An elastic free-volume model that includes dextran as well as polyethylene-glycol linker flexibility quantitively describes the repulsive dextran-hydrogel interaction free energy, which is of steric origin, and furthermore suggests that the hydrogel mesh-size distribution is rather broad and particle penetration is dominated by large hydrogel pores. Particle penetration into hydrogels for steric particle-hydrogel interactions is thus suggested to be governed by an elastic size-filtering mechanism that involves the tail of the hydrogel pore-size distribution.

Polyglycerol-based hydrogels and nanogels: from synthesis to applications

Hydrogels and nanogels have emerged as promising materials for biomedical applications owing to their large surface area and tunable mechanical and chemical properties. Their large surface area is well suited for bioconjugation, whilst the interior porous network can be utilized for the transport of valuable biomolecules. The use of biocompatible hydrophilic building blocks/linkers for the preparation of hydrogels and nanogels not only avoids undesired side effects within the biological system, but also retains high water content, thereby creating an environment which is very similar to extracellular matrix. Their tunable multivalency and hydrophilicity and excellent biocompatibility, together with ease of functionalization, makes polyglycerol macromonomers well suited for synthesizing cross-linked networks that can be used as extracellular matrix mimics. Here we provide an overview of the synthesis of polyglycerol-based hydrogels and nanogels for various biomedical applications.

Enhancing hydrogel-based long-lasting chemiluminescence by a platinum-metal organic framework and its application in array detection of pesticides and d-amino acids

Organophosphorus pesticides (OPs) are harmful to people's health and d-amino acids (d-AAs) in the human body are closely related to various diseases. So, detection of OPs in foods and d-AAs in serum is important for food safety and clinical diagnosis. Herein, a long-lasting chemiluminescence (CL) imaging sensor was constructed for the detection of OPs and d-AAs. The method was based on N-(4-aminobutyl)-N-ethylisoluminol/Co2+/chitosan (ABEI/Co2+/CS) hydrogels, where metal organic framework materials (MOF-Pt) were selected as catalysts to improve the sensitivity greatly. Under the catalysis of acetylcholinesterase (AChE) and choline oxidase (CHO), H2O2 was produced by using acetylcholine chloride (ACh) as a substrate, which was sensitive to the proposed CL system. OPs inhibited the activity of AChE and decreased the production of H2O2, reducing CL intensity. The linear range of the method for chlorpyrifos was 0.5 ng mL-1-1.0 μg mL-1, with a limit of detection (LOD) of 0.21 ng mL-1. Seventeen kinds of OPs can be visually and simultaneously discerned by the CL imager. On the other hand, d-AAs were catalyzed and oxidized by d-α-amino oxidase (DAAO) to produce H2O2. Thus, d-Ala in serum was used as a model to be detected by the proposed method. The linear range for d-Ala was 1.0 μM-10 mM, with an LOD of 0.12 μM.

In Situ Measurement of Thermodynamic Partitioning in Open Hydrogels

Thermodynamic partitioning dictates solute loading and release from a hydrogel. Design of drug delivery vehicles, cell and tissue matrices, and immunoassay scaffolds that utilize hydrogel materials is informed by an understanding of the thermodynamic partitioning properties of those hydrogels. We develop aberration-compensated laser scanning confocal microscopy (AC-LSCM), a technique that can be applied to all fluorescence microscopy-based equilibrium partition coefficient measurements where the fluorescence is uniformly distributed in the reference material (e.g., many solutes in thermodynamic equilibrium). In this paper, we use AC-LSCM to measure spatially resolved in situ equilibrium partition coefficients of various fluorescently labeled solutes in single-layer and multilayer open hydrogels. In considering a dynamic material, we scrutinize solute interactions with a UV photoactive polyacrylamide gel that incorporates a benzophenone methacrylamide backbone. We observed strong agreement with an adjusted version of Ogston's ideal size-exclusion model for spatially resolved in situ equilibrium partition coefficients across a wide range of polyacrylamide hydrogel densities (R2 = 0.98). Partition coefficients of solutes differing in hydrodynamic radius were consistent with size-based theory in the photoactive hydrogels, but exceed those in unmodified polyacrylamide gels. This observation suggests a deviation from the size-exclusion model and a shift in the thermodynamic equilibrium state of the solutes toward the gel phase. AC-LSCM also resolves differential partitioning behavior of the model solute in two-layer gels, providing insight into the transport phenomena governing the partitioning in multilaminate gel structures. Furthermore, AC-LSCM identifies and quantifies depth-dependent axial aberrations that could confound quantitation, highlighting the need for the "aberration compensated" aspect of AC-LSCM.