Physical and Mechanical Characterization of Fibrin-Based Bioprinted Constructs Containing Drug-Releasing Microspheres for Neural Tissue Engineering Applications

Abstract

Three-dimensional bioprinting can fabricate precisely controlled 3D tissue constructs. This process uses bioinks—specially tailored materials that support the survival of incorporated cells—to produce tissue constructs. The properties of bioinks, such as stiffness and porosity, should mimic those found in desired tissues to support specialized cell types. Previous studies by our group validated soft substrates for neuronal cultures using neural cells derived from human-induced pluripotent stem cells (hiPSCs). It is important to confirm that these bioprinted tissues possess mechanical properties similar to native neural tissues. Here, we assessed the physical and mechanical properties of bioprinted constructs generated from our novel microsphere containing bioink. We measured the elastic moduli of bioprinted constructs with and without microspheres using a modified Hertz model. The storage and loss modulus, viscosity, and shear rates were also measured. Physical properties such as microstructure, porosity, swelling, and biodegradability were also analyzed. Our results showed that the elastic modulus of constructs with microspheres was 1032 ± 59.7 Pascal (Pa), and without microspheres was 728 ± 47.6 Pa. Mechanical strength and printability were significantly enhanced with the addition of microspheres. Thus, incorporating microspheres provides mechanical reinforcement, which indicates their suitability for future applications in neural tissue engineering.

3D Bioprinting Mesenchymal Stem Cell-Derived Neural Tissues Using a Fibrin-Based Bioink

“…The degradation ratio was 27.8 ± 0.6%, which is sufficient for short-term experiments [31]. However, the study also found that incorporating microspheres into the bioink lowered the degradation ratio to 15.9 ± 1.0% [31]. Thus, if longer experiments are performed in the future, it would be ideal to incorporate drug-releasing microspheres.…”

“…The tissues had a porosity of 66.1 ± 3.2%, indicating that there is adequate diffusion of nutrients and gases, and removal of metabolic waste, promoting differentiation and proliferation [31]. The degradation ratio was 27.8 ± 0.6%, which is sufficient for short-term experiments [31]. However, the study also found that incorporating microspheres into the bioink lowered the degradation ratio to 15.9 ± 1.0% [31].…”

“…The results from these experiments confirmed that the bioprinted tissues possessed mechanical properties that were similar to native neural tissue. Furthermore, the elastic modulus was around 1 kPa, which is the optimal stiffness for neuronal differentiation [31]. Physical properties such as porosity, microstructure, swelling, and biodegradability were also analyzed.…”

“…Physical properties such as porosity, microstructure, swelling, and biodegradability were also analyzed. The tissues had a porosity of 66.1 ± 3.2%, indicating that there is adequate diffusion of nutrients and gases, and removal of metabolic waste, promoting differentiation and proliferation [31]. The degradation ratio was 27.8 ± 0.6%, which is sufficient for short-term experiments [31].…”

“…Thus, if longer experiments are performed in the future, it would be ideal to incorporate drug-releasing microspheres. These results are promising since typically, fibrin polymerized by thrombin and CaCl 2 degrades in one to two weeks due to proteases released from the incorporated cells [31]. However, the addition of genipin creates a multi-material scaffold by crosslinking with fibrin and chitosan, which stabilizes the bioprinted tissue.…”