The knee joint is the strongest and the largest joint of the human body. It consists of the lower end of the thighbone, upper end of the shin bone, and the knee cap. The three bones are connected to each other with articular and meniscal cartilages that act as shock absorbers and help protect and cushion the joint. Degeneration of the knee joint due to age and overuse can cause unwanted friction and bone spurs. The condition, also known as osteoarthritis, is the most prevalent form of arthritis and is often seen in individuals over 50 years of age.

Osteoarthritis develops slowly and leads to worsening pain and stiffness of the knee joint, grinding or clicking noise during movement, and weakness in the knee. Treatment involves lifestyle changes, physical therapy, and viscosupplementation injections. Patients with severe form of the disease may require a surgical intervention. During the process, the doctor may remove cartilage from another part of the body and place it in the knee or may replace the damaged cartilage with plastic and metal implants.
Researchers across the globe are now looking at three-dimensional (3D) medical printing and bioprinting technologies to create highly compatible, patient-specific knee implants that will increase the success rates of total knee arthroplasty by improving patient outcomes and lowering the risks of a revision surgery. Unlike traditional implants that come in a few specific shapes and sizes, 3D printed cartilages can be customized as per the needs of the patient. Surgeons can use the additive printing technology to print larger cartilages as well.

The Biopen: A Handheld Bioprinter Used During Operations
A team of researchers and surgeons from St. Vincent’s Hospital, Melbourne, developed the Biopen, a type of 3D printer that helps doctors create cartilaginous tissue fragments during the actual surgical intervention. The surgeon can customize the size and the shape of the tissue as per the needs of the patient. Researchers predict that the medical-grade plastic and titanium Biopen will lead to 97 percent survival of the cells and will transform knee surgeries forever.

This technology may, however, have some drawbacks. The human cartilage is made of only one type of cell. Scientists, therefore, tried to grow the tissue by embedding specific cells in a hydrogel but the liquid medium may restrict cell growth and intercellular communication. Consequently, the new implant may not have the desired mechanical integrity. Additionally, the degradation of the hydrogel may lead to the formation of toxins that would inhibit cell growth. Hence, researchers began looking for other materials to create cartilage implants.

A New Bio-ink Holds Promise for Printing Cartilage
Scientists at Penn State, under the supervision of Dr. Ibrahim T. Ozbolat, created tiny tubes from algae extracts, injected cow cartilage cells into them, and allowed the tubes to grow for a week to create tiny cartilage strands. A bio-ink made from these strands was fed into a specially designed nozzle of a 3D printer to develop cartilage tissues of the desired size. Although this 3D printed cow cartilage is weaker than its natural counterpart, it is definitely better than the hydrogel version. Dr. Ozbolat believes that the implants will strengthen once they get exposed to the pressure from the joints. His team also hopes to mimic the entire process using human cartilage cells.

The Center for Disease Control and Prevention (CDC) estimates that one in two Americans will be diagnosed with osteoarthritis by the age of 85. An estimated 249,000 children under the age of 18 also suffer from some form of arthritis. Additive printing technology is offering hope to millions of individuals looking to overcome pain and improve quality of life. While most of these products are still at an inceptive stage, researchers are trying to start clinical trials at the earliest and get the required approvals in the not-so-distant future.

Sources:

https://www.engadget.com/2016/04/04/biopen-lets-doctors-3d-print-cartilage-during-surgery/

https://www.sciencedaily.com/releases/2016/06/160627094828.htm