WEB Tailored mechanical properties of alginate-based hydrogels and the impact on NIH/3T3 cell morphology
Mechanical properties, particularly stiffness and stress-relaxation time, were shown to have a severe impact on cell behavior. Not only cell viability, but also cell differentiation, proliferation and migration are affected. Alginate is a common material in tissue engineering applications and can be modified in many ways. In our study, bioinks of alginate, oxidized alginate and gelatin were used for bioprinting. Their mechanical properties were tailored and correlated to the morphology of NIH/3T3 cells.
A droplet printing approach was chosen in order to prepare samples based on three different bioinks for cell viability and morphology assays imaged in 2D and 3D, respectively. Apart from this, the Young’s moduli of these bioinks were investigated with compression tests over a period of 28 days. Additionally to the Young’s modulus, also the swelling behavior and water content of non-printed hydrogels were measured and put in relation to varying crosslinking conditions.
The three tested bioinks revealed Young’s moduli between below 1 kPa, up to around 10 kPa. Moreover, due to their different compositions, cell adhesive binding sites were only present in two of these bioinks. Thus, it was possible to create two “low-stiffness” hydrogels, with and without binding sites and, in comparison to that, one “high-stiffness” hydrogel with binding sites. Our results show that NIH/3T3 cells did not express a significant change in morphology over a time-period of 28 days, when embedded in “high-stiffness” hydrogels, even though binding sites were available. In contrast to this, cells were infiltrating the “low-stiffness” sample with binding sites already after 3-7 days. Additionally, the influence on stiffness of various parameters, such as crosslinking-time, -concentration and -ion, were investigated and can help to tailor the mechanical properties accordingly.
It was shown that the mechanical properties of bioinks have a significant impact on cell morphology in 3D cell culture. Moreover, a variety of methods to tailor these properties in alginate-based bioinks is presented, highlighting the ones with the greatest impact.