Bones are a unique artifact of nature as they possess an inbuilt mechanism for regeneration and repair during skeletal development and remodeling, as well as in case of any injury. The regeneration process, which is quite complex in itself, constitutes of well-organized series of biological events in an effort to achieve skeletal repair and restore its function. Different cell types, molecular signaling pathways, as well as different growth factors play an important role in natural healing of bones (Dimitriou, et al., 2011). However, under certain conditions, this natural process is impaired as in the case when the fractured ends are no longer in contact with blood vessels which provide nutrition for the healing process resulting in delayed unison or non-unison where the broken bone fails to heal. This condition is most common in the tibia, humerus, talus, and fifth metatarsal bone (Cleveland Clinic). Apart from this, normal regeneration process is also hampered where bone is damaged beyond the point to which it self-heal, such as skeletal reconstruction required for large bone defects created by trauma, infection, tumour resection and skeletal abnormalities, or in situations where regenerative process is compromised such as during avascular necrosis and osteoporosis (Dimitriou, et al., 2011).
However, clinically multiple treatment strategies are available to supplement bone regeneration. One of them is tissue engineering and bone grafting.
The process of tissue engineering involves a combination of cells and growth factors combined with a porous biodegradable scaffold to repair and regenerate tissues (Chan, et al., 2009). Growth factors must be frequently administered to enhance the growth and differentiation of the cells. The scaffold provides mechanical support along with controlling the release of growth factors (Sensenig, et al., 2012).
How is it done?
Two different approaches can be used in tissue engineering of bones; osteoconductive and osteoinductive. Osteoconductive approach involves placement of a scaffold to stimulate bone cells to grow on its surface. The 3D scaffold acts as a base of seeded cells to which cells attach and grow. Osteoinductive approach involves stimulation of mesenchymal stem cells to differentiate into preosteoblasts to begin the bone-forming process. The cells are induced according to predefined organization that will help in formation of new bone by ingrowth of cells from the surrounding tissues (Polo-Corrales, et al., 2014; Sensenig, et al., 2012).
Chan, WD., Perinpanayagam, H., Goldberg, HA., Hunter, GK., Dixon, SJ., Santos GC. Jr. & Rizkalla, AS. (2009). Tissue Engineering Scaffolds for the Regeneration of Craniofacial Bone. JCDA; 75(5).
Cleveland Clinic. Foot & Ankle Fractures Nonunion. Retrieved from https://my.clevelandclinic.org/services/orthopaedics-rheumatology/diseases-conditions/foot-ankle-fractures-nonunion.
Dimitriou, R., Jones, E., McGonagle, D. & Giannoudis, PV. (2011). Bone regeneration: current concepts and future directions. BMC Medicine; 9:66.