Fabrication of 3D soft polymeric constructs at high structural integrity through bioprinting optimization of suspended hydrogels

In vitro models of soft tissues, such as neural, vitreous, or hematopoietic human tissues, require three-dimensional (3D), soft, and functionalized constructs that mimic the complex extracellular microenvironment and support tissue growth and differentiation. While bioprinting has gained significant interest in bioengineering, there is limited research on process control for the biomanufacturing of soft tissues, which is still in its early stages. Material extrusion of suspended hydrogels has shown promise in processing low-viscosity inks, but challenges in developing bioinks that maintain good shape fidelity, repeatability, and long-term stability in culture media have slowly progressed. In this study, we optimize the bioprinting process for the suspended extrusion of low-viscosity autoclaved bioinks (η = 121 ± 4 mPa s from 50 to 100 s−1) into 3D soft polymeric constructs. The stability of the process is evaluated using a full factorial design approach. Bone marrow-derived stromal cells are bioprinted at a low concentration (5 × 105 cells/mL), showing excellent metabolic activity up to day 7 compared to 2D cell culture controls. The final soft constructs exhibit a compression Young's Modulus of 7.8 ± 0.9 kPa, a water uptake of 60 %, and minimal gel degradation over 21 days. This work offers new insights into optimizing this advanced bioprinting process towards the development and study of 3D in vitro soft tissue models.