AAOS Now

Published 10/1/2012
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Mark Crawford

Fighting Osteoarthritis with Tissue Engineering

OREF grant recipient hopes to find the winning combination

Nicole Belkin knows cartilage.
While playing rugby at the University of Florida she sustained a traumatic rupture of her anterior cruciate ligament (ACL). Although her ACL was reconstructed, she still has symptomatic cartilage lesions, which can interfere with normal movement and create discomfort.

Now, as a resident physician at the University of Pennsylvania’s (UPenn) department of orthopaedic surgery in Philadelphia, Nicole S. Belkin, MD, is using an Orthopaedic Research and Education Foundation (OREF) Resident Clinician Scientist Training Grant to explore ways to repair damaged cartilage and reverse the effects of osteoarthritis.

“Cartilage damage afflicts more than 21 million patients per year in the United States,” said Dr. Belkin. “It typically results from normal wear and aging, disease, or traumatic injuries. The natural healing response of cartilage to injury is unsatisfactory, largely due to its avascular nature and demanding physical environment. As a result, 9 percent of Americans age 30 and older have osteoarthritis of the hip or knee, and treating those conditions costs about $28 billion annually. More than 500,000 knee replacements are performed every year in the United States alone.”

Focal traumatic defects in the articular surface heal with fibrous tissue that is mechanically inferior to cartilage. Various reconstructive procedures have been developed to treat focal defects, including débridement, microfracture, osteochondral allografts, and autologous chondrocyte implantation (ACI). However, none of these is completely successful in restoring the complex mechanical properties of articular cartilage and normal joint function.

Cartilage tissue engineering
Dr. Belkin’s research project, “In Vivo Full-thickness Cartilage Defect Repair with Stem-cell-laden Hyaluronic Acid Hydrogels,” is being performed at the McKay Orthopaedic Research Laboratory at UPenn and the Philadelphia Veterans Administration (VA) Medical Center.

“My OREF project focuses on cartilage tissue engineering,” said Dr. Belkin. “We are testing a novel hydrogel that is composed of hya-luronic acid, a natural component of articular cartilage.”

Hydrogels are attractive biomaterials for cartilage regeneration because they can fill in complex chondral defects, adhere to and integrate with surrounding tissues and encapsulate cells, and capture formed matrix. They also stimulate the differentiation of adult stem cells toward a cartilage-like phenotype.

“We are optimizing seeding with bone marrow-derived cells and growth factors to replicate natural cartilage,” continued Dr. Belkin. “So essentially, within a Petri dish, we can mix these ingredients in specific concentrations and grow what looks like, feels like, and has the same composition as cartilage.”

When the hydrogel is combined with adult mesenchymal stem cells and cultured in the presence of pro-chondrogenic factors, it achieves material properties of greater than 50 percent of normal bovine articular cartilage in vitro. Now, with OREF funding, Dr. Belkin will further test these promising indications by implanting this technology into seven adult Yucatan minipigs. This species was chosen for cartilage thickness and surgical access, consistency with human anatomy and loading patterns, and the extensive body of literature on studies using this model of comparable cartilage repair. Dr. Belkin’s team may also use tissue-engineered constructs to create substrates for implanting the hydrogel into the pigs’ stifle joints.

The results of this research will deepen the understanding of how growth factors stimulate chondrogenic differentiation in stem cells and how this material can be translated for in vivo development of cartilage-like tissue. How these novel hydrogels behave in native articular cartilage in vivo, under load-bearing conditions and immersed in the synovial milieu, will also be evaluated.

“We expect that improved construct maturation will occur in near-normal tissue biochemical and histologic profiles, hydrogel-cartilage integration in vitro will improve, and the unique in vivo biologic environment will stimulate chondrogenesis and integration strength,” said Dr. Belkin.

Looking to the future
Dr. Belkin is grateful for the OREF grant, which is allowing her to carry out the in vivo phase of her research. “It would have been difficult to attract bigger sources of funding without it,” she said. “Because of our successful preliminary data we have received a large VA merit grant to continue refining our work. For us in particular, OREF really facilitated our first translational model, which led to this next opportunity.”

Dr. Belkin often thinks of patients who have undergone reconstructive procedures like microfracture or ACI only to be highly disappointed with the results. “This patient population really motivates my work,” she said. “It’s also the young, healthy people who just want to be back to normal. At the moment all we’re able to do is counsel them to try to slow down, so that the rate at which osteoarthritis develops also slows. Hopefully our work will change that.”

If all goes as expected, Dr. Belkin’s research will confirm that hyaluronic-acid–based hydrogels are highly effective in promoting chondrogenesis and resultant integration strength within cartilage defects—possibly even in replacing entire diseased articular surfaces.

“Ultimately our goal is the development of clinical implants that will be used to treat cartilage pathology,” said Dr. Belkin. “This will be especially relevant for sports medicine and total joint arthroplasty specialties.”

Mark Crawford is a contributing writer for OREF. He can be reached at communications@oref.org