The development of materials for 3D printing adapted for tissue engineering represents one of the main concerns nowadays. Our aim was to obtain suitable 3D-printed scaffolds based on methacrylated gelatin (GelMA). In this respect, three degrees of GelMA methacrylation, three different concentrations of GelMA (10%, 20%, and 30%), and also two concentrations of photoinitiator (I-2959) (0.5% and 1%) were explored to develop proper GelMA hydrogel ink formulations to be used in the 3D printing process. Afterward, all these GelMA hydrogel-based inks/3D-printed scaffolds were characterized structurally, mechanically, and morphologically. The presence of methacryloyl groups bounded to the surface of GelMA was confirmed by FTIR and ¹H-NMR analyses. The methacrylation degree influenced the value of the isoelectric point that decreased with the GelMA methacrylation degree. A greater concentration of photoinitiator influenced the hydrophilicity of the polymer as proved using contact angle and swelling studies because of the new bonds resulting after the photocrosslinking stage. According to the mechanical tests, better mechanical properties were obtained in the presence of the 1% initiator. Circular dichroism analyses demonstrated that the secondary structure of gelatin remained unaffected during the methacrylation process, thus being suitable for biological applications.

Biocompatible methacrylamide-modified gelatin (GELMA) hydrogels with tuned characteristics, obtained through network-forming photopolymerization, have recently attracted increasing attention due to their wide range of possible applications such as drug release, tissue regeneration and generation of bioartificial implants. Due to the controlled number of CC bonds, GELMA may simultaneously act as macromonomer and crosslinker leading through polymerization to hydrogels with rationally designed performances. This study provides effortless one-pot synthesis of hybrid hydrogels based on covalently linked GELMA and polyacrylamide (PAA), using photo-induced network-forming polymerization. Conventional synthesis of similar hydrogels leads to interpenetrating gelatin and PAA networks, usually involving multistep crosslinking of the components and the use of toxic crosslinkers. Through the described one-pot chemistry, the synthetic water superabsorbent PAA with its well-recognized advantages can rationally benefit from the high biocompatibility and cell-adherence of GELMA in a simple covalent way. This work provides a correlation between the composition and the corresponding hydrogel properties (including swelling, pH influence, mechanical behaviour, ability to generate porous scaffolds, enzymatic degradation). The addition of PAA modulated the network density and the water affinity allowing the control of elasticity and degradability. Supplementary crosslinking of the synthetic component provided additional control over hydrophilicity. The capacity of such hydrogels to generate porous scaffolds was proved; interesting morphologies were developed only by varying the composition. In vitro cellular studies indicated that the presence of GELMA conferred controlled cell-affinity properties to the bicomponent hydrogels. Nevertheless, the drug release potential of such hydrogels was preliminarily investigated using sodium nafcillin. GELMA–PAA hydrogels may be useful for tissue regeneration due to effortless synthesis, compositional flexibility and variable properties.

The present study investigated the possibility of obtaining 3D printed composite constructs using biomaterial-based nanocomposite inks. The biopolymeric matrix consisted of methacrylated gelatin (GelMA). Several types of nanoclay were added as the inorganic component. Our aim was to investigate the influence of clay type on the rheological behavior of ink formulations and to determine the morphological and structural properties of the resulting crosslinked hydrogel-based nanomaterials. Moreover, through the inclusion of nanoclays, our goal was to improve the printability and shape fidelity of nanocomposite scaffolds. The viscosity of all ink formulations was greater in the presence of inorganic nanoparticles as shear thinning occurred with increased shear rate. Hydrogel nanocomposites presented predominantly elastic rather than viscous behavior as the materials were crosslinked which led to improved mechanical properties. The inclusion of nanoclays in the biopolymeric matrix limited hydrogel swelling due the physical barrier effect but also because of the supplementary crosslinks induced by the clay layers. The distribution of inorganic filler within the GelMA-based hydrogels led to higher porosities as a consequence of their interaction with the biopolymeric ink. The present study could be useful for the development of soft nanomaterials foreseen for the additive manufacturing of customized implants for tissue engineering.