Characterization of direct ink write pure silk fibroin based on alcohol post-treatments

Silk fibroin (SF) has been successfully used for medical devices due to its biodegradability with non-toxic end products, high tensile strength and mechanical robustness, but also because of its high flexibility potential. Although natural silk fibers have excellent strength and flexibility, regenerated silk materials generally become brittle in the dry state. For this reason, researchers have studied the effects that manufacturing and post-treatment parameters have on their mechanical properties, but they have also studied the impact on other factors such as biodegradability on the environment. This work presents an optimized process for direct ink write a regenerated SF bioink and its possible post-treatments. A simple method to concentrate the aqueous SF has been reported. The technique was then employed to 3D print test specimens for multiple mechanical analysis to characterize the resulting parameters of the processed silk. The effect of post-treating the material with different processes (no-treatment, immersion in ethanol for 24 h, and subsequently immersion in methanol for 30, 60 or 120 min) was explored. The different post-treatments resulted in distinct effects on the silk properties, suggesting that SF molecular structure could be controlled by the post-treatment process. The results showed a transition to phosphate-buffered saline (PBS)-insoluble silk when the silk was treated with alcohols. This resulted in a more brittle material than the untreated group, with a lower strain at break. Nevertheless, the post-treatments enhanced the stability of silk in water, as they reported greater insolubility in PBS than the untreated group. This study characterizes and discusses the mechanical properties of SF processed with a novel additive manufacturing method intended for customization of medical devices.