Carbodiimide-mediated immobilization of acidic biomolecules on reversed-charge zwitterionic sensor chip surfaces

Three-Dimensional Polyglycerol-PEG-Based Hydrogels as a Universal High-Sensitivity Platform for SPR Analysis

We developed a three-dimensional (3D) polyglycerol-poly(ethylene glycol)-based hydrogel as a new biosensing matrix for affinity analysis by surface plasmon resonance to enable a high loading of ligands for small molecule analysis while lacking a carbohydrate structure to reduce nonspecific binding. The hydrogel was synthesized by cross-linking a polyglycerol functionalized with carboxylate and maleimide groups with a dithiolated poly(ethylene glycol) by thiol-click chemistry. We demonstrated that the hydrogel coating enabled a high immobilization capacity of biomolecules and led to less nonspecific binding. Here, the degree of loading with carbonic anhydrase II and the resulting binding signal of acetazolamide were increased by a factor of 5 compared to standard CMD sensors (CM5), and the loading was comparable to CMD sensors specialized for maximum loading (CM7). This high loading capacity, combined with the reduced nonspecific binding due to the missing carbohydrate structure, presents an innovative matrix for a broad application range of surface plasmon resonance (SPR) experiments since no current commercial SPR biosensor combines these two key features.

A Facile Strategy for Preparing Flexible and Porous Hydrogel-Based Scaffolds from Silk Sericin/Wool Keratin by In Situ Bubble-Forming for Muscle Tissue Engineering Applications

In the present study, it is aimed to fabricate a novel silk sericin (SS)/wool keratin (WK) hydrogel-based scaffolds using an in situ bubble-forming strategy containing an N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) coupling reaction. During the rapid gelation process, CO2 bubbles are released by activating the carboxyl groups in sericin with EDC and NHS, entrapped within the gel, creating a porous cross-linked structure. With this approach, five different hydrogels (S2K1, S4K2, S2K4, S6K3, and S3K6) are constructed to investigate the impact of varying sericin and keratin ratios. Analyses reveal that more sericin in the proteinaceous mixture reinforced the hydrogel network. Additionally, the hydrogels' pore size distribution, swelling ratio, wettability, and in vitro biodegradation rate, which are crucial for the applications of biomaterials, are evaluated. Moreover, biocompatibility and proangiogenic properties are analyzed using an in-ovo chorioallantoic membrane assay. The findings suggest that the S4K2 hydrogel exhibited the most promising characteristics, featuring an adequately flexible and highly porous structure. The results obtained by in vitro assessments demonstrate the potential of S4K2 hydrogel in muscle tissue engineering. However, further work is necessary to improve hydrogels with an aligned structure to meet the features that can fully replace muscle tissue for volumetric muscle loss regeneration.

Hyaluronic acid-based hydrogels with tunable mechanics improved structural and contractile properties of cells

Extracellular matrix (ECM) regulates cellular responses through mechanotransduction. The standard approach of in vitro culturing on plastic surfaces overlooks this phenomenon, so there is a need for biocompatible materials that exhibit adjustable mechanical and structural properties, promote cell adhesion and proliferation at low cost and for use in 2D or 3D cell cultures. This study presents a new tunable hydrogel system prepared from high-molecular hyaluronic acid (HA), Bovine serum albumin (BSA), and gelatin cross-linked using EDC/NHS. Hydrogels with Young's moduli (E) ranging from subunit to units of kilopascals were prepared by gradually increasing HA and BSA concentrations. Concentrated high-molecular HA network led to stiffer hydrogel with lower cluster size and swelling capacity. Medium and oxygen diffusion capability of all hydrogels showed they are suitable for 3D cell cultures. Mechanical and structural changes of mouse embryonic fibroblasts (MEFs) on hydrogels were compared with cells on standard cultivation surfaces. Experiments showed that hydrogels have suitable mechanical and cell adhesion capabilities, resulting in structural changes of actin filaments. Lastly, applying hydrogel for a more complex HL-1 cell line revealed improved mechanical and electrophysiological contractile properties.

Layer-by-Layer Surface Modification of Alendronate-Loaded Polyester Microparticles-Enabling Protein Immobilization

The highly inert surface of polyester micro- and nano- drug carriers is a challenging substrate for further modification. The presence of surface moieties suitable for macromolecule coupling is crucial in the development of targeted drug delivery systems. Among available methods of surface activation, those based on adsorption of charged macromolecules may be carried out in mild conditions. In this work, alendronate-loaded microcores of three polyesters: poly-ε-caprolactone (PCL), poly(l-lactide-co-ε-caprolactone) (PLA-co-PCL) and poly(lactic-co-glycolic acid) (PLGA) were coated with three polyelectrolyte shells composed of chitosan/heparin (CHIT/HEP), polyallylamine/heparin (PAH/HEP), and polyethyleneimine/heparin (PEI/HEP) via the layer-by-layer method. Subsequently, the feasibility of model protein immobilization on obtained shells was assessed. Electrokinetic potential measurements confirmed the possibility of deposition of all investigated coating variants, and a positive correlation between initial core ζ potential and intensity of charge alterations after deposition of subsequent layers was identified. PEI/HEP assembly was stable in physiological-like conditions, while PAH/HEP multilayers disassembled in presence of phosphate ions, and CHIT/HEP shell showed limited stability in pH 7.4. Fluorescence assays of fluorescein tagged lysozyme surface coupled via ethylcarbodiimide hydrochloride/N-Hydroxysuccinimide (EDC/NHS) click reaction with all shell variants indicated satisfying reaction efficiency. Poly-ε-caprolactone cores coated with CHIT/HEP tetralayer were selected as suitable for model IgG surface immobilization. Antibodies immobilized on the shell surface exhibited a moderate degree of affinity to fluorescent IgG binding protein.

Conjugation of Native-Like HIV-1 Envelope Trimers onto Liposomes Using EDC/Sulfo-NHS Chemistry: Requirements and Limitations

The display of native-like human immunodeficiency virus type 1 envelope (HIV-1 Env) trimers on liposomes has gained wide attention over the last few years. Currently, available methods have enabled the preparation of Env-liposome conjugates of unprecedented quality. However, these protocols require the Env trimer to be tagged and/or to carry a specific functional group. For this reason, we have investigated N-(3-Dimethylaminopropyl)-N'-ethylcarbodiimide/N-Hydroxysulfosuccinimide (EDC/Sulfo-NHS) chemistry for its potential to covalently conjugate tag-free, non-functionalized native-like Env trimers onto the surface of carboxyl-functionalized liposomes. The preservation of the liposome's physical integrity and the immunogen's conformation required a fine-tuned two-step approach based on the controlled use of β-mercaptoethanol. The display of Env trimers was strictly limited to activated liposomes of positive charge, i.e., liposomes with a positive zeta potential that carry amine-reactive Sulfo-NHS esters on their surface. In agreement with that, conjugation was found to be highly ionic strength- and pH-dependent. Overall, we have identified electrostatic pre-concentration (i.e., close proximity between negatively charged Env trimers and positively charged liposomes established through electrostatic attraction) to be crucial for conjugation reactions to proceed. The present study highlights the requirements and limitations of potentially scalable EDC/Sulfo-NHS-based approaches and represents a solid basis for further research into the controlled conjugation of tag-free, non-functionalized native-like Env trimers on the surface of liposomes, and other nanoparticles.