The Application Of Osteoinductive Small Molecules In Bone Tissue Engineering

Background:Although the growth factor is one important element in BTE,and even have approved by FDA,such as BMP2 and BMP7,some problems have been found in clinical practice.Apart form the high cost and unstability,they may cause abnormal bone metabolism and immune response.The osteoinductive small molecules are promising to be used as the alternative for growth factors in BTE.The osteoinductive small molecules can be divided into two categories,namely the natural small molecules,including decaenoic acid,flavonoids,and quinones,and the synthtic small molecule,including GSK-3β inhibitor,Necro X-7,and SVAK-12.More and more osteoinductive small molecules have been discovered and designed,and the osteogenic mechanism becomes clearer and osteogenesis effect become stronger.Although the osteoinductive small molecules are safe,stable,and low cost compared to growth factors,the long-term system administration for patients can also cause the disorder of bone metabolism and toxicity for liver and kidney.Therfore,a safe and effective drug delivery system is needed in BTE for sustained release to promote bone regeneration and reduce the toxic effect.Objectives:In this study,two composite scaffold have been designed and loaded with different osteoinductive small molecules to repair bone defect.In these two drug-loaded systems,it is demonstrated that the local sustained release and combination of osteoinductive small molecule drugs can effectively promote bone regeneration via different animal models.Methods:In the first experimental system,r GO-HA was added to the temperature-sensitive hydrogel PLGA-PEG-PLGA to improve the local sustained release,and the small molecule alendronate(ALD)was loaded to repair the mouse critical skull defect.In the second experimental system,the small molecule drug alendronate(ALD)andnaringin(NG)were loaded on the gelatin coating of PLGA scaffold for a combination.We used bone morphology parameters from micro-CT,H&E staining and special staining to evaluate the effect of bone repair,and the expression of osteogenic genes was further determined by PCR and western bolt experiments.Results:In the first system,y adding a small amount of r GO-HA,the strength of Gel/r GO-HA composite hydrogel was found to increase 1.5 times,and releasing perivod of ALD release pervoid could be prolonged to 14 days from 7 days.By the analysis of micro-CT 3D reconstruction and bone morphological parameter,it was found that Gel/r GO-HA/ALD has the best bone repair effect.Furthermore,it can promote the proliferation and differentiation of osteoblasts and inhibit the activity of osteoclasts through BMP2 and RANKL signaling pathways via molecular studies.In the second experimental system,due to a large amount of RGD sequences,it can effectively promote cell adhesion and proliferation,and improve the properties of PLGA scaffold.At the meantime,the mechanical properties and degradability were also significantly improved.From results of micro-CT,H&E staining,PCR and western blot,we found that the co-loaded drug scaffold(PLGA+Gelatin/ALD/NG)has a better osteoginc property than PLGA+ Gelatin/ALD and PLGA+Gelatin/NG.Conclusion:In this study,we designed two different osteoinductive drug-loading systems and carried different drug molecules to demostrate the osteoginc effect by different animal model.It was found that osteoinductive small molecules had great prospects in bone tissue engineering,and could effectively promote bone regeneration through local sustained release and combination therapy,and was hoped to transform into clinical applications.