Silk cryogel and electrospun scaffold characterization for bone-tendon interface applications.

Introduction: Hard-to-soft tissue interfaces, such as bone-tendon or bone-ligament junctions, remain a challenge to treat. Low healing success rates stem from the complexities at the interface, creating an urgent need for better models to elucidate the properties that enable these junctions to withstand complex mechanical loads and to function as hubs for crosstalk among different cell populations. Methods: In this work, silk fibroin (SF) scaffolds fabricated via electrospinning and cryogelation were developed as an in vitro model to investigate and optimize the natural repair processes of the bone-tendon interface. Results: It was observed that electrospinning SF with polyhydroxybutyrate (PHB) as a copolymer produced scaffolds with 1-micron fiber diameters, while SF cryogels exhibited 150-200 μm pores, both of which approached native tissue dimensions. Mechanically, the electrospun scaffolds had an elastic modulus of approximately 50 MPa, compared to 0.3-0.5 MPa for the cryogels. FTIR analysis confirmed the successful combination of PHB and SF in the electrospinning process, as well as characteristic amide peaks suggesting β-sheet formation, and a degradation study provided insight to scaffold stability with time. A live dead assay confirmed cell viability with time. Cells aligned along electrospun fibers and clustered within cryogel pores from day 4 to day 12. When combined, the electrospun scaffolds and cryogels supported tendon and bone cell infiltration at days 4 and 8. Discussion: These results demonstrate that a multi-technology, multi- material tissue engineering strategy enables the creation of tunable, heterogeneous scaffolds for modeling the bone-tendon interface.