In the clinic, lack of bone regeneration may result in a poor prognosis, even in common bone fractures. It has been reported that approximately 2% to 10% of bone fractures may develop non-union due to insufficient bone growth, and patients suffer from disabilities and may even have a shorter life expectancy as a result. The surgical removal of carcinomas is another major cause of insufficient bone regeneration, especially in patients with cancer-related bone metastasis . Additionally, a higher incidence of obesity results in more pronounced musculoskeletal illnesses and decreased bone regeneration . The ageing of the population exacerbates this situation. Aging not only results in a higher bone fracture risk due to loss of bone density but also diminishes the capability of bone regeneration. Therefore, how to promote bone regeneration, especially in patients with large bone defects, remains a major challenge for the clinicians.
The current “gold standard” treatment in the clinical settings promotes bone regeneration through the use of autologous and allogeneic bone grafting. However, approximately 20%–30% of patients who undergo autologous bone grafts suffer from morbidity at the graft-harvesting site. Moreover, autologous bone grafts cannot provide patients with large defects with sufficient bones. After an allogeneic bone grafts, over 30% of patients suffer from complications, including fracture, non-union, and infection. Allogeneic bone grafts may also result in graft-versus-host disease (GVHD). In addition, in cases in which patients received successful bone grafts, the recovery is time-consuming, up to one and half years, Therefore, neither of these two options is the optimal, because they are expensive, uncomfortable for the patients, and have high risks of complication.
Biomaterials and the cell-based therapies are two major research fields in bone regeneration. However, there are some drawbacks to both treatments. The toxicity and immunogenicity of biomaterials may culminate in severe complications. Cell-based therapy is closely related to tumor and emboli formation . Today, exosomes, ranging in size from 50–120 nm , with fewer safety considerations and powerful pro-osteogenesis abilities, provide researchers with a novel way to stimulate bone regeneration. This type of vesicles is endocytic origin and released by various cells and organs. Exosomes deliver various content, including DNAs, RNAs and proteins and are widely distributed, and are especially enriched in breast milk, semen, saliva, urine and sputum. Exosomes can effectively stimulate regeneration in tissues and organs, including the heart, lung, liver and kidney. Small vesicles can also stimulate bone regeneration in vitro and in vivo. The good bone specificity and powerful bone regenerative properties make exosomes a potential treatment to enhance bone growth and to treat clinical bone diseases. (read more...)