PEG-based hydrogels are used widely in exploratory tissue engineering applications but in general lack chemical and structural diversity. Additive manufacturing offers pathways to otherwise unattainable scaffold morphologies but has been applied sparingly to cross-linked hydrogels. Herein, mono methyl ether poly(ethylene glycol) (PEG) and PEG-diol were used to initiate the ring-opening copolymerization (ROCOP) of maleic anhydride and propylene oxide to yield well defined diblock and triblock copolymers of PEG-poly(propylene maleate) (PPM) and ultimately poly(propylene fumarate) (PPF) with different molecular mass PEG macroinitiators and block length ratios. Using continuous digital light processing (cDLP) hydrogels were photochemically printed from an aqueous solution which resulted in a 10-fold increase in elongation at break compared to traditional diethyl fumarate (DEF) based printing. Furthermore, PPF-PEG-PPF triblock hydrogels were also found to be biocompatible in vitro across a number of engineered MC3T3, NIH3T3, and primary Schwann cells.

Hydrogels are hydrophilic, crosslinked polymer networks that can absorb several times their own mass in water; they are frequently used in biomedical applications as a native tissue mimic. The characterization of hydrogels and other covalently crosslinked networks is often limited by their insolubility and infinite molecular weight conferred by crosslinking. In this study, chemically crosslinked hydrogel materials based on poly(ethylene glycol) (PEG) have been characterized directly, without any sample preparation, by mild thermal degradation using atmospheric solids analysis probe mass spectrometry (ASAP-MS) coupled with ion mobility (IM) separation and tandem mass spectrometry (MS/MS) characterization of the degradants. The structural insight gained from these experiments is illustrated with the analysis of oxime-crosslinked PEG hydrogels formed by the click reaction between 4-arm PEG star polymers with either ketone or aminooxy end group functionalities and PEG dimethacrylate (PEGDMA) copolymeric hydrogel networks formed by photopolymerization of PEGDMA. The ASAP-MS, IM, and MS/MS methods were combined to identify the crosslinking chemistry and obtain precursor chemistry information retained in the end-group substituents of the thermal degradation products.

Hydrogels are deployed widely in all areas of regenerative medicine, including bioprinting. The transport and mechanical properties exhibited by hydrogel assemblies are controlled by their organization and hierarchical assembly. This paper points out the role of nanoscale size and ordering of hydrophobic crosslinked domains on the mechanical and degradation properties of 3D printed amphiphilic hydrogels. A series of six poly(propylene fumarate)-block-poly(ethylene glycol)-block-poly(propylene fumarate) (PPF-b-PEG-b-PPF) ABA triblock copolymers were synthesized by varying both the water-soluble PEG block and the crosslinkable hydrophobic terminal PPF block lengths. Self-assembled hydrogels were formed by dissolving these amphiphilic PPF-b-PEG-b-PPF copolymers in water and covalently crosslinking the PPF units via digital light processing (DLP) additive manufacturing. Differential scanning calorimetry (DSC), in situ diffuse reflectance infrared spectroscopy (DRIFTS-IR) measurements, small-angle neutron scattering (SANS) and compressive measurements highlight how structural properties correlate with mechanical properties within this hydrogel system. Finally, swelling and in vitro degradation tests showed the influence of the nanoscale ordering on the degradation timescale.

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.