Mechanically tunable, human mesenchymal stem cell viable poly(ethylene glycol)–oxime hydrogels with invariant precursor composition, concentration, and stoichiometry

Abstract

Hydrogels are used widely for exploratory tissue engineering studies. However, currently no hydrogel systems have been reported that exhibit a wide range of elastic modulus without changing precursor concentration, identity, or stoichiometry. Herein, ester and amide-based PEGoxime hydrogels with tunable moduli (~5-30 kPa) were synthesized with identical precursor mass fraction, stoichiometry, and concentration by varying the pH and buffer concentration of the gelation solution, exploiting the kinetics of oxime bond formation. The observed modulus range can be attributed to increasing amounts of network defects in slower forming gels, as confirmed by equilibrium swelling and small angle neutron scattering (SANS) experiments. Finally, hMSC viability was confirmed in these materials in a 24 h assay. While only an initial demonstration of the potential utility, the controlled variation in defect density and modulus is an important step forward in isolating system variables for hypothesis-driven biological investigations.

Fabrication of Biomedical Scaffolds Using Biodegradable Polymers

“…Synthetic hydrogels are being extensively developed as an alternative to natural polymers, overcoming some of the shortcomings of the latter, such as batch variability and limited mechanical properties . One of the most frequently used synthetic biodegradable hydrogels is poly­(ethylene glycol) (PEG), also termed as poly­(ethylene oxide) (PEO) at higher molecular masses.…”

Physical and Chemical Factors Influencing the Printability of Hydrogel-based Extrusion Bioinks

“…As another dynamic covalent bond similar to imine bonds, oxime bonds are formed through a “click reaction” between hydroxylamine/alkoxyamine and aldehyde or ketone. ,, Compared to that of imine and hydrazone bonds, the reaction equilibrium greatly favors bound oxime linkages and thus the hydrolytic stability of oxime bonds is known to be much higher . Oxime bonds have also been used for the formation of reversible cross-links to prepare diverse dynamic hydrogels. − Most frequently, studied oxime-based cross-linked hydrogels are based on aldehyde-bearing oxidized HA or alginate, which are cross-linked by bifunctional alkoxyamine compounds.…”

Poly(ethylene glycol) Hydrogel Crosslinking Chemistries Identified via Atmospheric Solids Analysis Probe Mass Spectrometry

“…AO- NH -PEG was prepared as previously described . Briefly, 10 kDa 4-arm PEG (5.02 g, 0.5 mmol, 1 equiv) was functionalized with ( tert -butyloxycarbonyl (Boc)-aminooxy)­acetamide (0.291 g, 2.51 mmol, 5 equiv) via DIC-mediated esterification using DIC (0.316 g, 2.50 mmol, 5 equiv) and DPTS (0.074 g, 0.250 mmol, 0.5 equiv) as catalysts and dichloromethane (75 mL) as the solvent.…”

“…AO-NH-PEG was prepared as previously described. 60 Briefly, 10 kDa 4-arm PEG (5.02 g, 0.5 mmol, 1 equiv) was functionalized with (tertbutyloxycarbonyl (Boc)-aminooxy)acetamide (0.291 g, 2.51 mmol, 5 equiv) via DIC-mediated esterification using DIC (0.316 g, 2.50 mmol, 5 equiv) and DPTS (0.074 g, 0.250 mmol, 0.5 equiv) as catalysts and dichloromethane (75 mL) as the solvent. All reagents except DIC were dissolved in a round-bottom flask under a nitrogen atmosphere, and the reaction mixture was cooled to 0 °C on an ice bath for 15 min before the dropwise addition of DIC.…”

“…On the other hand, homolytic C–C bond cleavage produces two methylene radicals that ultimately yield methyl ether end groups through hydrogen abstraction. , This knowledge is essential for interpreting the spectra acquired in our study to determine the molecular connectivity and confirm the primary structure of two types of hydrogels (Scheme ), viz. (a) oxime-crosslinked PEG hydrogels formed by the click reaction between 4-arm PEG stars with levulinamide (LA- NH ) or levulinic acid (LA- O ) end groups and 4-arm PEG stars with aminoxyacetamide (AO- NH ) or aminooxyacetic acid (AO- O ) end groups (the crosslinking end-group functionalities in these gels were attached to the PEG stars by amide or ester bonding); , and (b) crosslinked PEG dimethacrylate (PEGDMA) copolymer hydrogels formed by radical propagation in the presence of a lithium acylphosphazine (LAP) photoinitiator and UV light . ASAP-MS enabled direct characterization of these two covalently crosslinked PEG hydrogels, unveiling crosslinking chemistry and precursor chemistry information retained in pyrolyzate end groups.…”