Chitosan Gels and Cryogels Cross-Linked with Diglycidyl Ethers of Ethylene Glycol and Polyethylene Glycol in Acidic Media

Abstract

Here we show that the efficacy of the chitosan interaction with diglycidyl ethers of glycols significantly depends on pH and the nature of acid used to dissolve chitosan. In solutions of hydrochloric acid, cross-linking with diglycidyl ethers of ethylene glycol (EGDGE) and polyethylene glycol (PEGDGE) at room and subzero temperatures yields mechanically stable chitosan gels and cryogels, while in acetic acid solutions only weak chitosan gels can be formed under the same conditions. A combination of elemental analysis, FT-IR spectroscopy, and solid state 13 C and 15 N NMR spectroscopy was used to elucidate possible differences in the mechanism of chitosan cross-linking in alkaline and acidic media at room and subzero temperatures. We have proved that in acidic media diglycidyl ethers of glycols interacted with chitosan mainly via hydroxyl groups at the C6 position of the glucosamine unit. Besides, not only cross-linkages but also grafts were formed at room temperature. The cryo-concentration effect facilitates cross-linkages formation at −10 °C and, despite lower modification degrees compared to those of gels obtained at room temperature, supermacroporous chitosan cryogels with Young's moduli up to 90 kPa can be fabricated in one step. Investigations of chitosan cryogels biocompatibility in a mouse model have shown that a moderate inflammatory reaction around the implants is accompanied by formation of a normal granulation tissue. No toxic, immunosuppressive, and sensitizing effects on the recipient's tissues have been observed.

In Vitro Synthesis of Branchless Linear (1 → 6)-α-d-Glucan by Glucosyltransferase K: Mechanical and Swelling Properties of Its Hydrogels Crosslinked with Diglycidyl Ethers

“…Peaks corresponding to the oxirane ring carbons at around 52 and 45 ppm were not detected. 21 , 28 This means that the epoxy ring-opening reaction went to completion, regardless of the amount of the crosslinker added. When the crosslinker dosage was large, a multi-step epoxy ring-opening reaction occurred, and the ring-opening reaction proceeded further from the hydroxy group that had been generated by the ring-opening reaction.…”

“…This is probably due to relatively high concentrations of NaOH solution (2%, w/v) used for the crosslinking reaction. 21 , 28 …”

“…(b) Compression and restoration of the G-EGDE-2 hydrogel until the maximum strain at 60% and its stress–strain curves after five repeated compression tests. (c) Elastic moduli of polysaccharide-based hydrogels plotted against the solid content of the hydrogels: (i) aminated (1 → 3)-α- d -glucan crosslinked with EGDE; 28 (ii) azide (1 → 3)-α- d -glucan crosslinked with 1,8-nonadiyne and reduced by NaBH 4 ; 29 (iii,iv) chitosan crosslinked with EGDE and poly(ethylene glycol) diglycidyl ether 500; 21 (v) cellulose–chitosan regenerated from LiOH/urea aqueous solution; 30 (vi) cellulose–chitosan crosslinked with dialdehyde cellulose; 31 (vii) cellulose regenerated from LiBr aqueous solution; 32 (viii) agarose; 33 and (ix) N -acetylated chitosan. 34 …”

Effect of Crosslinking Type on the Physical-Chemical Properties and Biocompatibility of Chitosan-Based Electrospun Membranes

“…However, such temporary crosslinking points require a much shorter time to be formed with respect to the covalent bonds, as they are rapidly created when chitosan comes into contact with the phosphate ions. In contrast, the chemical reaction occurring between chitosan amino groups and EGDE epoxy groups necessitates a certain time to happen, during which the nanofibers tend to swell, thereby increasing their size and partially collapsing and/or coalescing with each other [40]. In any case, despite of the described differences, both the proposed mats showed a suitable structure to foster cell viability owing to their great resemblance with the extra-cellular matrix [41,42].…”

Palladium Supported on Porous Chitosan–Graphene Oxide Aerogels as Highly Efficient Catalysts for Hydrogen Generation from Formate

“…There have been several ways to increase the mechanical stability of these porous chitosan microspheres by crosslinking with glutaraldehyde, glyoxal, and other dialdehydes [20,21]. Another alternative that we used in the present study, was to use highly reactive graphene oxide (GO) sheets to crosslink chitosan fibrils [22].…”