Silk and Ceramics Offer Hope for Long-term Repair of Joint Injuries

Bioengineered scaffold combines two materials to retain flexibility, resilience, in cell culture

Complete joint replacement, while highly successful, is major surgery with rigorous and often painful therapy regimens and lengthy recovery time. Driven by the need to develop more effective therapies requiring less recovery time for common joint conditions such as osteoarthritis, an international team including NIBIB-funded researchers has developed an integrated two-part scaffold for implantation into damaged joints — with cartilage scaffold made from silk, and bone scaffold made from ceramics. This combination of materials mimics the cartilage and bone of natural joints in both mechanical strength and pore structure. It also allows stem cells to successfully populate the graft and differentiate into cartilage and bone cells. The cells fill the damaged areas to reconstitute the original structure of the joint, after which the scaffold biodegrades, leaving the smooth surface required for a pain-free, functioning interface. The scaffold is a significant step towards improved and lasting treatment of common and often debilitating joint injuries.

“It’s a challenging problem to tackle,” says Rosemarie Hunziker, Ph.D., NIBIB Director for the Program for Tissue Engineering. “One of the big problems in cartilage tissue engineering is that the cartilage does not integrate well with host tissue after implantation, so the graft doesn’t ‘take.’ In this new approach there is a greater chance of success because the materials have architectures and physical properties that more closely resemble the native tissue.”

The natural structure at the joint where two bones meet is a two-part material composed of cartilage and bone, called osteochondral tissue: osteo meaning bone and chondral meaning cartilage. This “biphasic” material combines flexible cartilage and more rigid bone, which enables joints to flex and function properly, while maintaining weight-bearing strength.

Existing clinical treatments generally fall into two categories. Non-surgical treatment involves immobilization and restricted weight-bearing, with gradual progression of weight-bearing and physical therapy. Current surgical treatments include debriding (removing injured cartilage and bone), or grafting of new bone and cartilage. Both surgical techniques are aimed at restoring the natural shape and gliding surface of the cartilage. The existing approaches are typically successful at alleviating pain and restoring some function in the short-term, but rarely achieve full restoration of functional osteochondral tissue in the long-term. In particular, poor healing of bones that were cut in surgery is a common problem.

NIBIB-funded researchers at Tufts University in Medford, Massachusetts and researchers at the Biomaterials and Tissue Engineering Research Unit, University of Sydney, Australia, teamed-up to develop materials that mimic the unique and complex nature of osteochondral tissue. The goal was to develop an artificial scaffold with mechanical and bioactive properties that successfully promotes healing of damaged tissue to restore a fully functional joint. Bioactive properties include having a scaffold with the correct pore sizes that allow cells to enter and populate the scaffold after implantation, and being fully degradable over time to remove barriers to tissue regeneration.