Novel in Situ Forming, Degradable Dextran Hydrogels by Michael Addition Chemistry:  Synthesis, Rheology, and Degradation

Abstract

Various vinyl sulfone functionalized dextrans (dex-VS) (M n,dextran ) 14K or 31K) with degrees of substitution (DS) ranging from 2 to 22 were conveniently prepared by a one-pot synthesis procedure at room temperature. This procedure involved reaction of a mercaptoalkanoic acid with an excess amount of divinyl sulfone yielding vinyl sulfone alkanoic acid, followed by conjugation to dextran using N,N′-dicyclohexylcarbodiimide (DCC)/4-(dimethylamino)pyridinium 4-toluenesulfonate (DPTS) as a catalyst system. By using two different mercaptoalkanoic acids, 3-mercaptopropionic acid (1a) and 4-mercaptobutyric acid (1b), dex-VS conjugates with either an ethyl spacer (denoted as dex-Et-VS) or a propyl spacer (denoted as dex-Pr-VS) between the thioether and ester groups were obtained. Linear and four-arm mercaptopoly(ethylene glycol) (M n ) 2.1K) with two or four thiol groups (denoted as PEG-2-SH and PEG-4-SH, respectively) were also prepared. Hydrogels were rapidly formed in situ under physiological conditions by Michael type addition upon mixing aqueous solutions of dex-VS and multifunctional PEG-SH at a concentration of 10-20% w/v. The gelation time ranged from 0.5 to 7.5 min, depending on the DS, concentration, dextran molecular weight, and PEG-SH functionality. Rheological studies showed that these dextran hydrogels are highly elastic. The storage modulus increased with increasing DS, concentration, and dextran molecular weight, and hydrogels with a broad range of storage moduli from 3 to 46 kPa were obtained. Swelling/degradation studies revealed that these dextran hydrogels have a low initial swelling and are degradable under physiological conditions. The degradation time varied from 3 to 21 days depending on the DS, concentration, dextran molecular weight, and PEG-SH functionality. Interestingly, dex-Pr-VS hydrogels showed prolonged degradation times, but otherwise similar properties compared to dex-Et-VS hydrogels. The hydrolysis of the linker ester bonds of the dex-VS conjugates under physiological conditions was confirmed by 1 H NMR. The results showed that the hydrolysis kinetics were independent of the DS and the dextran molecular weight. Therefore, the degradation rate of these hydrogels can be precisely controlled.

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.…”

In-Situ Forming Biomimetic Hydrogels for Tissue Regeneration

“…By this approach, in-situ forming hydrogels can be obtained by mixing aqueous solutions of polymers bearing nucleophilic (amine or thiol) and electrophilic groups (vinyl, acrylate or maleimide) (Mather et al, 2006). For example, Feijen et al prepared in-situ forming hydrogels based on vinyl sulfoneconjugated dextran and poly(ethylene glycol) (PEG) thiols through Michael-type addition (Hiemstra et al, 2007a). The gelation times can be tailored from 7 to 0.5 min when the drgree of vinyl sulfone subsititution increased from 4 to 13.…”

Skeletal tissue engineering using embryonic stem cells

“…We investigated chondrogenic differentiation of ESCs in hydrogels that have been studied in cartilage research, such as agarose and alginate, and commercially available hydrogels such as Matrigel and Puramatrix. The project "An artificial extra cellular matrix for the regeneration of cartilage", which was the basis for the research described in this thesis, resulted in a newly developed dextran-based hydrogel [170,171]. We analyzed its potential for cartilage tissue engineering using both bovine chondrocytes and mouse ESCs (Chapter 3).…”

“…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].…”

“…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]. Hydrogels of Dex-VS crosslinked with PEG-4-SH have been investigated for controlled release of proteins [175].…”