3D printing of gelatin/chitosan biodegradable hybrid hydrogel: Critical issues due to the crosslinking reaction, degradation phenomena and process parameters

Hydrogel materials are being investigated for application as scaffolds in tissue engineering owing to their many advantages, such as high water content, softness and flexibility similar to many soft tissues, tuneable physical, chemical, and biological properties, excellent biocompatibility and biodegradability, and extensive framework for cell proliferation and survival. During the past decade, because of the great versatility offered in terms of processing approach, material selection, and customization, 3D printing has become a leading technology used to fabricate hydrogel scaffolds. Furthermore, high reproducibility and unparalleled control over structural and compositional characteristics make additive manufacturing the preferred technology for the fabrication of biodegradable hydrogel scaffolds. However, the production time could become critical in relation to any crosslinking reactions and degradation that may occur in the hydrogel and make the printing process unstable. In this study an analysis of the critical issues due to the crosslinking reaction and degradation phenomena have been executed following a statistical approach. In particular, three different experimental campaign demonstrate how the printing process became instable due to the mentioned phenomena. Finally, a procedure was developed to print gelatine-based biocompatible hydrogels with chitosan and functionalized polyethylene glycol as a cross linker (G-PEG-CH). In order to reach the printing temperature, the hydrogel mixture was initially stored in the refrigerator at 4°C for 12 h, followed by a 10 min incubation in warm water at 40°C. Based on this procedure, a filament strand of 950 μm with a standard deviation in the range of 20% was obtained by imposing a printing pressure of 1 bar and a printing speed of 100 mm/s at a temperature of 28 °C.