Rigidity of Two-Component Hydrogels Prepared from Alginate and Poly(ethylene glycol)−Diamines

Abstract

Alginate hydrogels have been attractive for a variety of biomedical applications, but they possess limited mechanical properties when ionically cross-linked with divalent cations. Therefore, covalent cross-linking of alginate with poly(ethylene glycol)−diamines of various molecular weights was investigated as a means to generate hydrogels with a range of mechanical properties. Hydrogels with a range of elastic moduli could be generated by controlling either the chain length of the cross-linking molecule or the cross-linking density. The elastic modulus increased gradually with an increase in cross-linking density or weight fraction of PEG in the hydrogel up to ∼27% (w/w) of PEG. The change of mechanical properties was interpreted in terms of molecular weight between cross-links (M c) according to the rubber-elasticity model, and the results of this analysis were generally consistent with the measured PEG−diamine incorporation efficiencies in this range. However, as the weight fraction of PEG in the hydrogels increased above 27%, regardless of the molecular weight of PEG, the elastic moduli decreased. This is not consistent with prediction based on the rubber-elasticity theory, and this is likely due to the fact that this model does not consider cross-linking with a second macromolecule. Importantly, the results of this study suggest that the mechanical properties of hydrogels will be strongly affected by the properties of the cross-linking molecule as the M c of hydrogels falls below the molecular weight of the cross-linking molecule.

Versatile click alginate hydrogels crosslinked via tetrazine–norbornene chemistry

“…While recent work has used similar click chemistry for localized drug delivery, this work presents the first use of the tetrazine-norbornene click reaction to covalently crosslink polysaccharides into hydrogels [29,38]. Crosslinking of alginate by different methods has been extensively explored to make covalently crosslinked hydrogels that are mechanically robust, but these chemistries lack the cytocompatibility inherent in the bioorthogonal click reaction reported here [19,21,39]. The simplicity of this crosslinking modality provides the opportunity to control the mechanical properties of the click alginate hydrogel by adjusting the ratio of the polymers, rather than changing the total concentration of polymers in the system.…”

“…To overcome many of the challenges associated with ionic crosslinking, alternative covalent crosslinking strategies have been developed, though none are completely biologically inert [18][19][20][21]. Many of these covalent crosslinking strategies produce stable and uniform gels with mechanical properties that are controllable over a wider range compared to ionically crosslinked gels, but they may not be optimal for protein or cell encapsulation due to the cross-reactivity of the crosslinking chemistry with cells and proteins.…”

Self‐Assembly of Rod–Coil Polyethylenimine–Poly(ethylene glycol)–α‐Cyclodextrin Inclusion Complexes into Hollow Spheres and Rod‐Like Particles

“…[ 12 ] More insights into the structures of spherical and rodlike aggregates are obtained by fi lling the cavity of aggregates with a series of model molecules. Except Vitamin B 6 and Vitamin B 12 , other model molecules are proteins or enzyme that have a globular shape and possess isoelectric point between 7.8 and 9.6 (the characteristic of model molecules are listed in Supporting Information Table S1). At the experimental pH (pH 4.0), the proteins are in a cationic form, which should minimize ionic adsorption to the positive charged PEI.…”

“…[ 6 ] PEI (0.1 mmol) was dissolved in a 10 mL buffer solution of MES (0.1 M ) and NaCl (0.5 M ). Then, 0.05 mmol NHS and 0.1 mmol EDC (molar ration of EDC-NHS-COO − = 1:0.5:1) were added to mPEG-COOH (0.1 mmol) solution (20 mL) to activate the carboxylic acid groups and the pH was adjusted to 6.0.…”

Preparation and characterization of a poly(ethylene glycol) grafted carboxymethyl konjac glucomannan copolymer

“…mPEG-OCOCH 2 NH-Boc was synthesized according to the method of Eiselt, Lee, and Mooney (1999). Briefly, mPEG was dried under high vacuum at 50°C for 24 h before use.…”