Fabrication of a model continuously graded co-electrospun mesh for regeneration of the ligament-bone interface

Current scaffolds for the regeneration of anterior cruciate ligament injuries are unable to capture intricate mechanical and chemical gradients present in the natural ligament-bone interface. As a result, stress concentrations can develop at the scaffold-bone interface, leading to poor osseointegration. Hence, scaffolds that possess appropriate mechano-chemical gradients would help establish normal loading properties at the interface, while promoting scaffold integration with bone. With the long-term goal of investigating regeneration of the ligament-bone interface, this feasibility study aimed to fabricate a continuously graded mesh. Specifically, graded meshes were fabricated by co-electrospinning nanohydroxyapatite/polycaprolactone (nHAP-PCL) and poly(ester urethane) urea elastomer solutions from offset spinnerets. Next, mineral crystallites were selectively deposited on the nHAP-PCL fibers by treatment with a 5× simulated body fluid (5× SBF). X-ray diffraction and energy-dispersive spectroscopy indicated calcium-deficient hydroxyapatite-like mineral crystallites with an average Ca/P ratio of 1.48. Tensile testing demonstrated the presence of a mechanical gradient, which became more pronounced upon treatment with 5× SBF. Finally, biocompatibility of the graded meshes was verified using an MC3T3-E1 osteoprogenitor cell line. The study demonstrates that graded meshes, for potential application in interfacial tissue engineering, can be fabricated by co-electrospinning.