Every year, an estimated 1 million children tear the articulate cartilage that lines their knees. Unfortunately, these types of injuries are extremely hard to repair because of the cartilage’s poor healing qualities and unique physiochemical properties.
Now, a new study by Children’s National Health System researchers has found that a three dimensional (3D) printed synthetic implant can be successfully used as a scaffold to encourage the healing and repair of articulate cartilage lesions.
Three bones meet in the knee joint: the femur, the tibia and the patella. The surface of these bones is covered with articulate cartilage, which can be damaged by injury or by normal wear and tear. Because articulate cartilage has poor healing qualities, these injuries will rarely heal or regenerate on their own, especially in younger and more active patients.
“These are active 12 to 19 year olds, so it can really affect relatively normal kids,” says Matthew Oetgen, M.D., M.B.A., Division Chief of Orthopaedic Surgery and Sports Medicine at Children’s National. “While there are many ways to repair these lesions — from implanting autogenous cells to using grafts to fill the defect — none of these options are perfect, and they all have some down sides.”
To facilitate repair of these injuries, a team of researchers led by Dr. Oetgen received a grant from the Pediatric Orthopaedic Society of North America (POSNA) to design a 3D printed implant that promotes bone and cartilage growth.
To make the implant, the team used nanoporous thermoplastic polyurethane (TPU), a biodegradable material that is highly elastic and yet strong, very much like the native cartilage in the osteochondral region. TPU is also porous, which allows blood and nutrient flow through the implant.
“The implant is designed to allow native cells to repair the lesions with normal articular cartilage and not scar tissues like some repairs,” says Dr. Oetgen.
The implant itself has a stratified structure: an upper region that contains micro channels to allow for increased perfusion; a middle zone with a nanoporous structure that mimics porous cartilage and encourages stem cell recruitment, growth and differentiation; and a lower region, or articular surface, that allows for smooth transition from the articulating surface to the implant surface and minimizes adverse interactions between the articulate cartilage and the meniscus.
When tested in vitro, the implant was able to support the growth of stem cells and vascular cells, and structurally mature vascularized bone was formed around the implant after 10 days. In animal models with full thickness osteochondral lesions the implant did just as well: The scaffold was able to promote bone, soft tissue and vascular growth without eliciting an immune response.
“Our preliminary study shows this novel 3D printed material is able to allow ingrowth from the bone, so the body started to grow into the material to help fix it in place,” says Dr. Oetgen. “These are the first step requirements for an implant like this to be acceptable for treating lesions.”
Because of the ease with which 3D printing can be scaled up, Dr. Oetgen is hopeful that the implant will one day become a viable option for repairing articulate cartilage injuries. He plans on trying the implants in a larger animal model and on larger lesions, and is also looking at custom printing for the implants to match natural lesion shapes and sizes.