Gelatin acrylamide with improved UV crosslinking and mechanical properties for 3D biofabrication.

Photocrosslinkable gelatin has attracted increasing interest in the field of biofabrication, with the most studied and widely used photocrosslinkable gelatin being gelatin methacrylate (GelMa). However, the 3D fabrication of GelMa has presented several limitations and challenges, primarily due to its slow crosslinking speed. It is generally known that acryl-based functional groups have faster reaction kinetics than methacryl-base groups. However, gelatin acrylamide (GelAc) has not been widely investigated, largely due to its increased complexity of synthesis relative to GelMA. In this study, we developed a novel synthesis method for GelAc. By varying the reaction ratio of reagents, GelAc with a degree of substitution from 20% to 95% was produced. The UV crosslinking properties of GelAc was studied, demonstrating significantly faster crosslinking kinetics than GelMa, especially at lower concentrations and low photoinitiator concentrations. The swelling ratio and mechanical properties of the crosslinked GelAc hydrogel were also characterized, and biocompatibility experiments conducted via both surface seeding and hydrogel encapsulation of cells, with good cell viability observed. The application of GelAc for 3D biofabrication was demonstrated by 3D printing. GelAc can be a useful material for the fabrication of 3D conduits for tissue engineering applications.

Synthesis and 3D Printing of Conducting Alginate-Polypyrrole Ionomers.

Hydrogels composed of calcium cross-linked alginate are under investigation as bioinks for tissue engineering scaffolds due to their variable viscoelasticity, biocompatibility, and erodibility. Here, pyrrole was oxidatively polymerized in the presence of sodium alginate solutions to form ionomeric composites of various compositions. The IR spectroscopy shows that mild base is required to prevent the oxidant from attacking the alginate during the polymerization reaction. The resulting composites were isolated as dried thin films or cross-linked hydrogels and aerogels. The products were characterized by elemental analysis to determine polypyrrole incorporation, electrical conductivity measurements, and by SEM to determine changes in morphology or large-scale phase separation. Polypyrrole incorporation of up to twice the alginate (monomer versus monomer) provided materials amenable to 3D extrusion printing. The PC12 neuronal cells adhered and proliferated on the composites, demonstrating their biocompatibility and potential for tissue engineering applications.

On Low-Concentration Inks Formulated by Nanocellulose Assisted with Gelatin Methacrylate (GelMA) for 3D Printing toward Wound Healing Application.

Cellulose nanofibrils (CNFs) in the form of hydrogels stand out as a platform biomaterial in bioink formulation for 3D printing because of their low cytotoxicity and structural similarity to extracellular matrices. In the present study, 3D scaffolds were successfully printed with low-concentration inks formulated by 1 w/v % 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-oxidized CNF with less than 1 w/v % gelatin methacrylate (GelMA). Quartz crystal microbalance with dissipation monitoring (QCM-D) measurements showed strong interaction between the two biopolymers. The UV cross-linking ability of GelMA (≤1 w/v %) was enhanced in the presence of TEMPO-oxidized CNFs. Multiple factors including strong physical interaction between CNF and GelMA, in situ cross-linking of CNF by Ca2+, and UV cross-linking of GelMA enabled successful 3D printing of low-concentration inks of CNF/GelMA into scaffolds possessing good structural stability. The mechanical strength of the scaffolds was tuned in the range of 2.5 to 5 kPa. The cell culture with 3T3 fibroblasts revealed noncytotoxic and biocompatible features for the formulated inks and printed scaffolds. More importantly, the incorporated GelMA in the CNF hydrogel promoted the proliferation of fibroblasts. The developed low-concentration CNF/GelMA formulations with a facile yet effective approach to fabricate scaffolds showed great potential in 3D printing for wound healing application.

3D Scaffolds of Polycaprolactone/Copper-Doped Bioactive Glass: Architecture Engineering with Additive Manufacturing and Cellular Assessments in a Coculture of Bone Marrow Stem Cells and Endothelial Cells.

The local delivery of Cu2+ from copper-doped bioactive glass (Cu-BaG) was combined with 3D printing of polycaprolactone (PCL) scaffolds for its potent angiogenic effect in bone tissue engineering. PCL and Cu-BaG were, respectively, dissolved and dispersed in acetone to formulate a moderately homogeneous ink. The PCL/Cu-BaG scaffolds were fabricated via direct ink writing into a cold ethanol bath. The architecture of the printed scaffolds, including strut diameter, strut spacing, and porosity, were investigated and characterized. The PCL/Cu-BaG scaffolds showed a Cu-BaG content-dependent mechanical property, as the compressive Young's modulus ranged from 7 to 13 MPa at an apparent porosity of 60%. The ion dissolution behavior in simulated body fluid was evaluated, and the hydroxyapatite-like precipitation on the strut surface was confirmed. Furthermore, the cytocompatibility of the PCL/Cu-BaG scaffolds was assessed in human bone marrow stem cell (hBMSC) culture, and a dose-dependent cytotoxicity of Cu2+ was observed. Here, the PCL/BaG scaffold induced the higher expression of late osteogenic genes OSTEOCALCIN and DLX5 in comparison to the PCL scaffold. The doping of Cu2+ in BaG elicited higher expression of the early osteogenic marker gene RUNX2a but decreased the expression of late osteogenic marker genes OSTEOCALCIN and DLX5 in comparison to the PCL/BaG scaffold, demonstrating the suppressing effect of Cu2+ on osteogenic differentiation of hBMSCs. In a coculture of hBMSCs and human umbilical vein endothelial cells, both the PCL/BaG and PCL/Cu-BaG scaffolds stimulated the formation of a denser tubule network, compared to the PCL scaffold. Meanwhile, only slightly higher gene expression of vWF was observed with the PCL/Cu-BaG scaffold than with the PCL/BaG scaffold, indicating the potent angiogenic effect of the released Cu2+.