Stable gelatin hydrogels without photo-crosslinking
Published : 01/12/2021 16:42:10
Gelatin is produced from partial hydrolysis of collagen. The cytocompatibility of gelatin promotes a favorable environment for cell proliferation (Davidenko et al. 2016). On cooling, gelatin partially recovers the collagen helical structure (so-called collagen-fold) when the concentration is sufficiently high (Ward and Courts 1977). Nevertheless, 3D printed gelatin hydrogels can easily collapse under physiological conditions (T = 37oC and pH = 7.4). For applications where photo-crosslinking is not allowed, the use of chemical agents such as genipin is recommended.
Genipin is a molecule extracted from the fruit of the gardenia plant. The reaction mechanism with gelatin is a two-step process. In the first step, the genipin molecule undergoes a nucleophilic attack by the primary amines of gelatin, resulting in the heterocyclic linking of genipin to the gelatin amine. The second reaction occurs when the ester group on genipin undergoes a nucleophilic substitution. The resultant covalent crosslinks between the primary amine residues leave minimal residual toxicity (Solorio et al. 2010).
We evaluated the effect of genipin as a crosslinker for preparing 3D printed gelatin hydrogels. Fig. 1 illustrates the printing behavior of ClaroBGI600 in combination with genipin (dry-basis mass ratio gelatin:genipin, 1:1). Extrudable consistency was achieved up to 2hrs of printing (left nozzle).
Fig. 1: ClaroBGI600 + genipin (1:1) printing the 6th lattice after 2hrs (left nozzle). Regular gelatin + genipin (1:1) in the right nozzle. T=25°C. Nozzle 25G was used.
The enhanced printing shown by ClaroBGI600 enabled not only printing longer but with lower pressure. Fig. 2 shows that the maximum printing pressure while printing ClaroBGI600/genipin formulation was about half of the pressure required to print with regular gelatin. This means that the physical gel formed by ClaroBGI600 required fewer shear-stresses to flow through the nozzle. Although the filament formed could retain its shape after deposition with the ideal recovery time to allow the formation of a 3D construct.
Fig. 2: ClaroBGI600 and regular gelatin + genipin (1:1) maximum printing pressures using an Inkredible+ printer T=25°C. Nozzle 25G was used.
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