Gelatin methacryloyl (GelMA) hydrogel scaffolds and GelMA-based bioinks are widely used in tissue engineering and bioprinting due to their ability to support cellular functions and new tissue development. Unfortunately, while terminal sterilization of the GelMA is a critical step for translational tissue engineering applications, it can potentially cause thermal or chemical modifications of GelMA. Thus, understanding the effect of terminal sterilization on GelMA properties is an important, though often overlooked, aspect of material design for translational tissue engineering applications. To this end, we characterized the effects of FDA-approved terminal sterilization methods (autoclaving, ethylene oxide treatment, and gamma (γ)-irradiation) on GelMA prepolymer (bioink) and GelMA hydrogels in terms of the relevant properties for biomedical applications, including mechanical strength, biodegradation rate, cell culture in 2D and 3D, and printability. Autoclaving and ethylene oxide treatment of the GelMA decreased the stiffness of the hydrogel, but the treatments did not modify the biodegradation rate of the hydrogel; meanwhile, γ-irradiation increased the stiffness, reduced the pore size and significantly slowed the biodegradation rate. None of the terminal sterilization methods changed the 2D fibroblast or endothelial cell adhesion and spreading. However, ethylene oxide treatment significantly lowered the fibroblast viability in 3D cell culture. Strikingly, γ-irradiation led to significantly reduced ability of the GelMA prepolymer to undergo sol-gel transition. Furthermore, printability studies showed that the bioinks prepared from γ-irradiated GelMA had significantly reduced printability as compared to the GelMA bioinks prepared from autoclaved or ethylene oxide treated GelMA. These results reveal that the choice of the terminal sterilization method can strongly influence important properties of GelMA bioink and hydrogel. Overall, this study provides further insight into GelMA-based material design with consideration of the effect of terminal sterilization.

Silver nanoparticles (AgNPs) have gained much attention in biomedical research because of their antibacterial properties. However, they have also exhibited cytotoxicity toward certain mammalian cells. In order to improve therapeutic efficacy, the incorporation of gold (Au) and Ag into bimetallic Ag–Au NPs is a promising strategy, as it has the potential to increase biocompatibility and maintain antibacterial activity. Toward this end, we prepared a series of bimetallic Ag–Au NPs and studied them with X-ray absorption spectroscopy (XAS) in order to elucidate the correlation of atomic structure to their bioactivities. The addition of Au was found to drastically change the atomic structure of the Ag NPs; namely, the Ag core of the NPs was gradually replaced with Au, while Ag was found mostly on the surface. Next, NP antibacterial activity toward S. aureus and cytotoxicity toward NIH-3T3 fibroblast cells were assessed. It was found that the antibacterial activity of the bimetallic NPs was lower than pure Ag NPs and dependent on the Ag location within the NPs. On the other hand, the cytotoxicity of bimetallic NPs was much lower than the pure Ag NPs and dependent on the overall Au concentration. Using the structural information garnered from XAS, we were able to rationalize the bioactivity results of the NPs based on their atomic structure and provide guiding principles to design Au–Ag NPs with balanced antibacterial and cytotoxic activities. This work represents an important step toward engineering the atomic structure of bimetallic Au–Ag NPs for biomedical applications.

In this study the affinity of three amino acids for the surface of non-stoichiometric hydroxyapatite nanoparticles (ns-nHA) was investigated under different reaction conditions. The amino acids investigated were chosen based on their differences in side chain polarity and potential impact on this surface affinity. While calcium pre-saturation of the calcium-deficient ns-nHA was not found to improve attachment of any of the amino acids studied, the polarity and fraction of ionized functional side groups was found to have a significant impact on this attachment. Overall, amino acid attachment to ns-nHA was not solely reliant on carboxyl groups. In fact, it seems that amine groups also notably interacted with the negative ns-nHA surface and increased the degree of surface binding achieved. As a result, glycine and lysine had greater attachment to ns-nHA than aspartic acid under the reaction conditions studied. Lastly, our results suggest that a layer of each amino acid forms at the surface of ns-nHA, with aspartic acid attachment the most stable and its surface coverage the least of the three amino acids studied.

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3D biomaterial printing requires an ink to have suitable printability characteristics, as well as creating a final construct of controllable swelling and stiffness. To tune such properties, the impact of adding different levels of chloride salts (NaCl and CaCl2) and hydroxyapatite nano‐particles (nHA) to a highly concentrated and photo‐crosslinkable methacrylated gelatin (GelMA) is investigated. By adding up to 100 mm CaCl2 or 1.11 m NaCl, the GelMA viscosity decreases from that of control GelMA (no salt). Interestingly, a 25G needle and strong photo‐polymerization kinetics are able to overcome the low viscosity of the 50CaG ink during printing. Adding further CaCl2 increases GelMA viscosity, while decreasing both the swelling and dynamic modulus of the UV‐cured construct observed in water. As all UV‐cured constructs have a dynamic modulus greater than 1 MPa, this novel system is able to match the dynamic modulus of articular cartilage—a feat not previously reported for a GelMA‐based system. Lastly, nHA inclusion improves ink printability, as well as decreases swelling and increases dynamic modulus of the final construct. Overall, this study leads to the successful development of a new advanced functional ink which will be beneficial in the 3D printing of biomaterials toward tissue engineering applications.

Perfluorodecalin (PFD) is a chemically and biologically inert biomaterial and, as many perfluorocarbons, is also hydrophobic, radiopaque and has a high solute capacity for gases such as oxygen. In this article we have demonstrated, both in vitro and in vivo, that PFD may significantly enhance bone regeneration. Firstly, the potential benefit of PFD was demonstrated by prolonging the survival of bone marrow cells cultured in anaerobic conditions. These findings translated in vivo, where PFD incorporated into bone-marrow-loaded 3D-printed scaffolds substantially improved their capacity to regenerate bone. Secondly, in addition to biological applications, we have also shown that PFD improves the radiopacity of bone regeneration biomaterials, a key feature required for the visualisation of biomaterials during and after surgical implantation. Finally, we have shown how the extreme hydrophobicity of PFD enables the fabrication of highly cohesive self-setting injectable biomaterials for bone regeneration. In conclusion, perfluorocarbons would appear to be highly beneficial additives to a number of regenerative biomaterials, especially those for bone regeneration.

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