Anisotropic silk fibroin/ionic-doped tricalcium phosphate composite structure for osteochondral regeneration

3D structures made of doped Silk Fibroin have been proposed for the regeneration of the osteochondral tissue^1,2. In order to mimic this interfaced tissue, a calcium phosphate gradient is required. However, the current techniques mainly apply multilayered-scaffolds with abrupt interfaces. Moreover, there is still a need of a single step fabrication method to create a highly calcified transitional tidemark-like zone similar to the native osteochondral one with a polymeric organization mimicking the anisotropic-to-radial distribution of collagen fibrils in the osteochondral interface. In the present study, we aimed to create gradient structures in TCP content with controlled over such gradient and polymeric/porous architecture. Herein, by controlling the sedimentation of the TCP powder during the crosslinking process, it was possible to obtain a continuous gradient from the cartilage- to the subchondral bone-like layer of the structure. By means of tuning the crosslinking time and the production steps sequence, a peak in the transitional tidemark-like zone was obtained in which the TCP is concentrated. Furthermore, the typical orientation of the native osteochondral collagen fibrils was recapitulated by using a top-down programmed ice-templating imprinting system. To allow the proper formation of the pores, a two-section mold was designed. Overall, a simple fabrication technique was developed to produce acellular implants for osteochondral regeneration, which resemble its native mineral composition with control over the pores anisotropic and radial orientation. Ultimately, the proposed scaffolds may have a broader application to other musculoskeletal interfaces, such as bone-ligament and bone-tendon, for clinical and tissue modeling applications.

Keywords: Osteochondral; Interfaced tissue; Anisotropic structures; Ice-templating.

Acknowledgments: This work has been funded under the FCT project “HierarchiTech”, Hierarchical Ionic-doped Nanocomposite Scaffolds for Osteochondral Tissue Engineering. Nicolas Cristini thanks the support from Erasmus+ program.

References:

1. Yan, L.-P. et al. Macro/microporous silk fibroin scaffolds with potential for articular cartilage and meniscus tissue engineering applications. Acta Biomater. 8, 289-301 (2012).
2. Viviana P.R. et al. Combinatory approach for developing silk fibroin scaffolds for cartilage regeneration. Acta Biomater. 72, 167-181 (2018).