Surgical intervention and grafting are sometimes necessary to restore mechanical function and reconstruct the morphology of bone and cartilage, resulting from trauma, tumors, or abnormal bone developments.
Synthetic materials such as metals and bone cements have also been used for restoring and reconstructing bone for many years, but often result in stress-shielding to the surrounding bone and fatigue failure of the implant. Another possibility is autologous bone grafting, although the supply of autologous bone tissue is limited and its collection is painful, with the risk of infection, hemorrhage, cosmetic disability, nerve damage, and loss of bone function. In addition, significant morbidity is associated with autograft harvest sites. These problems may be overcome by engineering tissue using scaffolds made of synthetic or natural biomaterials that promote the adhesion, migration, proliferation, and differentiation of bone marrow stem cells, also known as mesenchymal stem cells (MSCs). An association between biocomponents and biologic regenerative and repair responses can be promoted by providing a scaffold containing spaces morphologically compatible with osteons and their vascular interconnections.
The immediate microenvironment and the three-dimensional (3D) organization are important factors in differentiation in general and particularly in chondrogenic and osteogenic differentiation.
Some bone tissue engineering scaffolds consists of natural polymers, such as collagen, alginate, hyaluronic acid, and chitosan. Natural materials offer the advantages of specific cell interaction, easy seeding of cells because of their hydrophilic interactions, low toxicity and low chronic inflammatory response. However, these scaffolds often are mechanically unstable and do not readily contribute to the creation of tissue structures with a specific predefined shape for transplantation. To obtain mechanical strength, chemical modification is required, which may lead to toxicity.
Defects and degeneration of the articular cartilage surfaces of joints causes pain and stiffness. Damage to cartilage which protects joints can result from either physical injury as a result of trauma, sports or repetitive stresses (e.g., osteochondral fracture, secondary damage due to cruciate ligament injury) or from disease (e.g. osteoarthritis, rheumatoid arthritis, aseptic necrosis, osteochondritis dissecans).
Osteoarthritis (OA) results from general wear and tear of joints, most notably hip and knee joints. Osteoarthritis is common in the elderly but, in fact, by age 40 most individuals have some osteoarthitic changes in their weight bearing joints. Another emerging trend increasing the prevalence of osteoarthritis is the rise in obesity. The CDC estimates that 30% of American adults (or 60 million people) are obese. Obese adults are 4 times more likely to develop knee OA than normal weight adults Rheumatoid arthritis is an inflammatory condition which results in the destruction of cartilage. It is thought to be, at least in part, an autoimmune disease with sufferers having a genetic predisposition to the disease.
Orthopedic prevention and repair of damaged joints is a significant burden on the medical profession both in terms of expense and time spent treating patients. In part, this is because cartilage does not posses the capacity for self-repair. Attempts to re-grow hyaline cartilage for repair of cartilage defects remain unsuccessful. Orthopedic surgery is available in order to repair defects and prevent articular damage in an effort to forestall serious degenerative changes in a joint. The use of surgical techniques often requires the removal and donation of healthy tissue to replace the damaged or diseased tissue. Techniques utilizing donated tissue from autografts, allografts, or xenografts are wholly unsatisfactory as autografts add additional trauma to a subject and allografts and xenografts are limited by immunological reactivity to the host subject and possible transfer of infective agents. Surgical attempts to utilize materials other than human or animal tissue for cartilage regeneration have been unsuccessful.
An ideal material which restores mechanical function and reconstructs the morphology of bone and cartilage is as yet, lacking.