Differences in time-dependent mechanical properties between extruded and molded hydrogels.

Area of Science:

• Biomaterials Science
• Tissue Engineering
• Additive Manufacturing

Background:

• Mechanical properties of hydrogels are crucial for biomaterial and tissue engineering applications.
• Extrusion-based 3D bioprinting is a growing biofabrication technique, but its impact on hydrogel mechanics is understudied.

Purpose of the Study:

• To compare the mechanical and swelling properties of gelatin-based hydrogels fabricated by conventional molding versus 3D bioprinting.
• To investigate the influence of bioprinting parameters on construct properties.

Main Methods:

• Crosslinked gelatin-based hydrogels were prepared using conventional molding and 3D bioprinting (BioBots Beta pneumatic extruder).
• Mechanical properties (Young's modulus, creep) and swelling properties were measured.
• Bioprinting parameters (polymer content, pressure, speed, nozzle gauge) were characterized.
• Fibroblast viability was assessed to confirm cytocompatibility.

Main Results:

• Young's modulus and optimal extruding pressure increased with polymer content; printing resolution improved with speed and nozzle gauge.
• No significant difference in Young's modulus between extruded and molded hydrogels.
• Extruded hydrogels exhibited increased rate and extent of time-dependent creep behavior.
• Extruded hydrogels showed greater swelling over time compared to molded hydrogels, despite similar polymer densities.

Conclusions:

• The extrusion process in 3D bioprinting alters the microstructure and fluid flow of gelatin hydrogels, affecting their time-dependent mechanical behavior and swelling.
• These differences are critical for cell and tissue behavior, necessitating careful consideration of extrusion effects in biofabrication.
• The bioprinting process demonstrated high cytocompatibility for encapsulated fibroblasts (>95% viability).