RESUMO
Spinal cord injury (SCI) is a serious condition with limited treatment options. Neural progenitor cell (NPC) transplantation is a promising treatment option, and the identification of novel biomaterial scaffolds that support NPC engraftment and therapeutic activity is a top research priority. The objective of this study is to evaluate in situ assembled poly (ethylene glycol) (PEG)-based granular hydrogels for NPC delivery in a murine model of SCI. Microgel precursors are synthesized by using thiol-norbornene click chemistry to react four-armed PEG-amide-norbornene with enzymatically degradable and cell adhesive peptides. Unreacted norbornene groups are utilized for in situ assembly into scaffolds using a PEG-di-tetrazine linker. The granular hydrogel scaffolds exhibit good biocompatibility and do not adversely affect the inflammatory response after SCI. Moreover, when used to deliver NPCs, the granular hydrogel scaffolds supported NPC engraftment, do not adversely affect the immune response to the NPC grafts, and successfully support graft differentiation toward neuronal or astrocytic lineages as well as axonal extension into the host tissue. Collectively, these data establish PEG-based granular hydrogel scaffolds as a suitable biomaterial platform for NPC delivery and justify further testing, particularly in the context of more severe SCI.
RESUMO
Polymer-polymer aqueous two-phase systems (ATPSs) are attractive for microgel synthesis, but given the complexity of phase separation, predicting microgel material properties from ATPS formulations is not trivial. The objective of this study was to determine how the phase diagram of a poly(ethylene glycol) (PEG) and dextran ATPS is related to the material properties of PEG microgel products. PEG-dextran ATPSs were prepared from four-arm 20 kDa PEG-norbornene and 40 kDa dextran in phosphate buffered saline (PBS), and the phase diagram was constructed. PEG microgels were synthesized from five ATPS formulations using an oligopeptide cross-linker and thiol-norbornene photochemistry. Thermogravimetric analysis (TGA) revealed that the polymer concentration of microgel pellets linearly correlates with the average concentration of PEG in the ATPS rather than the separated phase compositions, as determined from the phase diagram. Atomic force microscopy (AFM) and bulk rheology studies demonstrated that the mechanical properties of microgels rely on both the average concentration of PEG in the ATPS and the ATPS volume ratio as determined from the phase diagram. These findings suggest that PEG-dextran ATPSs undergo homogenization upon mixing, which principally determines the material properties of the microgels upon gelation.
RESUMO
The objective of this study was to evaluate the utility of gelatin-norbornene (GelNB), which is cross-linkable via thiol-ene click chemistry, and the photoinitiator lithium phenyl-2,4,6 trimethylbenzoylphosphinate (LAP) for 3D bioprinting. These materials were compared to two widely used materials, gelatin-methacryloyl (GelMA) and 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone (I2959). Characterization of photocuring kinetics revealed that LAP markedly improved the kinetics compared to I2959, which improved stability and print fidelity. Additionally, GelNB exhibited improved photocuring kinetics, improved stability, and decreased filament spreading compared to GelMA. However, inks containing GelMA yielded at lower stress, were more easily extruded, and produced smoother filaments. NIH 3T3 fibroblasts exhibited high viability in printed constructs, regardless of the gelatin derivative or photoinitiator used. Overall, these results support the selection of LAP over I2959 and suggest that GelNB could be a useful alternative to GelMA, although further work is needed to optimize GelNB extrusion.