Reinforcement of injectable hydrogels through melt electro-written structures: Influence of shape and pore size on the injection force

Hydrogels are commonly used for tissue engineering applications due to their high water content, biocompatibility, injectability, and ability to mimic the extracellular matrix of native tissues. However, their weak mechanical properties limit their use, especially in load-bearing applications. In this study, we developed fibrous architectures with a pre-defined shape using melt electro-writing (MEW) to strengthen injectable hydrogels. We assessed the injection forces required to successfully extrude the hydrogel reinforced with MEW-printed structures, varying their geometry (square/hexagonal pores) and pore sizes (0.6, 0.8, 1.0 mm) through needles having a size compatible with clinical applications. Our findings indicate that MEW structures with hexagonal pores exhibit a higher tensile modulus than those with square pores. Additionally, the injection forces required to extrude hydrogels embedding MEW structures through needles were greater for hexagonal pores. Thinner pores and smaller needle diameters resulted in higher injection forces; a few conditions among the ones tested were compatible with the limits defined by the EU ISO 7886–1:2018 standard. After injection and crosslinking, hydrogels reinforced with MEW structures showed improved mechanical properties (up to 6.34-fold), particularly when structures with hexagonal pores were used.