OSTEOCHONDRAL DEFECTS
Osteochondral defects (OCDs) – localized joint damage extending from cartilage into subchondral bone – are characterized by progressive deterioration resulting in joint pain, loss of function and osteoarthritis. Clinically, OCDs of the knee, as well as other joints, are often treated with autograft-based surgeries (e.g. autologous transfer system or “OATS” and mosaicplasties) in which cylindrical autologous grafts are transferred from a non-load bearing region into pre-drilled holes in the defect area. However, these methods are limited by donor site morbidity, patient age (~ 50 years) and defect size (~ 1-4 cm2). Thus, joint replacement is required at significant numbers and costs (e.g. total knee replacements: ~500k persons and ~$11b annually in US). Tissue engineering represents a promising alternative to heal OCDs of the knee and other joints. Conventionally, the regeneration of the osteochondral interface has been attempted by connecting two pre-formed, compositionally homogenous scaffolds capable of individually promoting either bone- or cartilage-tissue growth.

However, the lack of a bone-to-cartilage transition zone necessary for appropriate load transfer and failure to integrate into surrounding tissue limits their success. In addition, the surgical implementation of the scaffold and corresponding cell-loaded construct is often not carefully considered, making clinical translation challenging. Thus, an approach that may overcome these challenges would be a significant advancement to improving the clinical treatment of OCDs.

 

MAXIOFACIAL DEFECTS
Cranio-maxillofacial (CMF) bones defects are caused by trauma, infection, tumor removal or congenital deformities. While autologous grafts are the most common treatment, they are associated with lengthy harvesting procedures, potential donor site morbidity and high failure rates. Tissue engineering as emerged as a promising alternative to heal CMF bone defects. However, its success is limited by the lack of an appropriate scaffold (“filler”). Bone healing requires a scaffold which is both osteoconductive (i.e. permitting bone conformal growth onto a porous surface) as well as bioactive (i.e. promoting integration/bonding with surrounding bone tissue and the attachment and differentiation of osteogenic cells). Also, it is highly desirable for the scaffold to be implanted with a minimally invasive technique to reduce patient discomfort, infection and scarring. Thus, an osteoconductive-bioactive scaffold inserted via a minimally invasive technique would advance the treatment of CMF bone defects as well as potentially other bone defects.