Connecting two dissimilar biological materials together is a big challenge because large, localized stresses develop at the interface between the materials. However, nature has a way of overcoming this problem by producing a material whose mechanical structure and stiffness varies across its interface. One example of such a material is between healthy tendon (a soft tissue) and bone (a hard tissue).

Unfortunately, the situation is very different in injured tissue – the mechanical stiffness gradient is not recreated at the interface between the biomaterials produced during tendon-to-bone healing. As a result, surgery to reattach tendon and bone together often fails.

Stavros Thomopoulos and Younan Xia's team has now developed a new technique to make nanofibre-based scaffolds in which the mechanical stiffness gradient is present. Their method consists of depositing the mineral calcium phosphate in differing amounts over the surface of a mat of electrospun nanofibres. The technique produces a continuously graded, bone-like mineral coating on the nanofibre mat.

Repairing tendon-to-bone sites
"Thanks to the change in mineral gradient, the scaffold exhibits a continuous variation in mechanical stiffness across the surface," Xia told "This property is a prerequisite for attaching two dissimilar biomaterials together."

According to the researchers, the scaffold could be used to repair tendon-to-bone sites and possibly to regenerate many other connective tissues.

The team is now preparing in vivo animal trials and has identified a rat model for the study. "We are seeking to combine our engineered scaffolds with mesenchymal cells to enhance tendon-to-bone healing in rats with rotator cuff injuries," said Xia.

The work was reported in Nano Letters.