Rapidly in Situ-Forming Degradable Hydrogels from Dextran Thiols through Michael Addition

Abstract

Thiol-functionalized dextrans (dex-SH) (M(n,dextran) = 14K or 31K) with degrees of substitution (DS) ranging from 12 to 25 were synthesized and investigated for in situ hydrogel formation via Michael type addition using poly(ethylene glycol) tetra-acrylate (PEG-4-Acr) or a dextran vinyl sulfone conjugate with DS 10 (dex-VS DS 10). Dex-SH was prepared by activation of the hydroxyl groups of dextran with 4-nitrophenyl chloroformate and subsequent reaction with cysteamine. Hydrogels were rapidly formed in situ under physiological conditions upon mixing aqueous solutions of dex-SH and either PEG-4-Acr or dex-VS DS 10 at polymer concentrations of 10 to 20 w/v%. Rheological studies showed that these hydrogels are highly elastic. By varying the DS, concentration, dextran molecular weight, and type of cross-linker, hydrogels with a broad range of storage moduli of 9 to 100 kPa could be obtained. Varying the ratio of thiol to vinyl sulfone groups from 0.9 to 1.1 did not alter the storage modulus of the hydrogels, whereas larger deviations from equimolarity (thiol to vinyl sulfone ratios of 0.75 and 1.5) considerably decreased the storage modulus. The plateau value of hydrogel storage modulus was reached much faster at pH 7.4 compared to pH 7, due to a higher concentration of the thiolate anion at higher pH. These hydrogels were degradable under physiological conditions. Degradation times were 3 to 7 weeks for dex-SH/dex-VS DS 10 hydrogels and 7 to over 21 weeks for dex-SH/PEG-4-Acr hydrogels, depending on the DS, concentration, and dextran molecular weight.

Diels−Alder Click Cross-Linked Hyaluronic Acid Hydrogels for Tissue Engineering

“…By altering the pH of the cross-linking reaction, or the VS:Cys ratio, they were able to tune both the degradation and mechanical properties of the gel. Hydrogels that were cross-linked with an equimolar ratio of VS:Cys maintained their mechanical stability for longer than 21 days in vitro, similar to dextran hydrogels cross-linked by Michael addition 45 . Their hydrogels also exhibited a rapid gelation time, suggesting utility for in situ surgical procedures, and displayed a microporous network when visualized under environmental scanning electron microscopy.…”

Controlled Synthesis of Cell-Laden Microgels by Radical-Free Gelation in Droplet Microfluidics

“…In YPD (pH 6.5), we do not observe any degradation of the microgels over time, whereas, for microgels dispersed in water, degradation through hydrolysis of the ester bond close to the thioether bond is observed over a time of several weeks. 48,49 To investigate the viability of the encapsulated cells 90 min after their encapsulation, we perform a live−dead assay by adding two fluorescent dyes: Syto 9 is a green fluorescent dye that stains both living and dead cells, whereas propidium iodide is a red fluorescent dye that stains dead cells only. As a result, dead cells appear red or orange, whereas living cells appear green when observed with a fluorescence microscope.…”

Skeletal tissue engineering using embryonic stem cells

“…The swelling profile of the Dex-PEG hydrogel was influenced by the DS of dextran. Further fine-tuning of the mechanical and degradation properties can be achieved by varying the molecular weight of the polymer, the concentration of polymer, or choosing another crosslinker [170,171]. As such, the hydrogel can be designed for the desired application, for example articular chondrocyte injection.…”

“…Chemically crosslinked hydrogels that can be formed under mild conditions meet our requirements. Recently, we developed dextran hydrogels prepared by Michael type addition [170,171].…”

“…Dextran was functionalized with either thiol (SH) or vinyl sulfone (VS) groups. Thiol-functionalized dextran (Dex-SH) could form a hydrogel with tetra-acrylated star PEG (PEG-4-Acr) or vinyl sulfone-functionalized dextran (Dex-VS) [170]. Dex-VS reacted with multifunctional mercapto PEG (PEG-2-SH or PEG-4-SH) or dithioerythritol (DTE) [171].…”