Investigation On Sustained Release Of IGF-1 From An Injectable Composited Alginate Hydrogel For The Treatment Of Myocardial Infarction

Aim:Silk fibroin(SF)microspheres were prepared and used for encapsulation of insulin like growth factor 1(IGF-1).These SF microspheres containing IGF-1 were further embedded in an alginate hydrogel to achieve an injectable composite hydrogel with capability of sustained release IGF-1.The repair effect of this composite hydrogel on myocardial infarction(MI)was investigated.Methods:Alginate hydrogels were prepared by mixing sodium alginate solutions of different concentrations(1.0%-2.5%)with 0.68%calcium gluconate solution.H9C2 cardiomyocyte were cultured on the surface of hydrogels and the adhesion and proliferation of cells were examined by immunofluorescence staining assay.The hydrogel with the best performance was screened for the subsequent experiments.SF microspheres with diameter<10 ?m were prepared by the coaxial needle system.These microspheres were used for encapsulation of IGF-1 via physical adsorption,and then mixed into sodium alginate solution together with calcium gluconate solution to obtain a composite hydrogel(Gel+SF/IGF-1).The size and structure of the microspheres were characterized by scanning electron microscopy(SEM).The amount of released IGF-1 at different time points and the release kinetics were investigated by enzyme-linked immunosorbent assay(ELISA).The ability of IGF-1 released from the composite hydrogel to promote cell proliferation(under nonnal condition)and inhibit cell death(under hypoxic condition)was examined by immunofluorescence staining assay and CCK-8 assay.Finally,the composite hydrogel was injected into the peripheral region of MI in rats,and the extent of heart repair were evaluated by echocardiography,hematoxylin-eosin(HE)staining and Masson trichrome.Results:The results of cell experiments showed that the hydrogel prepared using 1.5%sodium alginate solution was most suitable for cell adhesion and growth.The ELISA results showed that the cumulative release of IGF-1 from Gel+SF/IGF-1 was 20.0±2.2%,27.7 ± 1.9%,34.9±1.8%,37.2 ±1.5%,41.0±2.7%,43,6±3.5%and 46.0 ± 2.5%at 1,3,7,10,14,21 and 28 days,respectively.In contrast,the corresponding cumulative release of IGF-1 from the hydrogel that is prepared by direct encapsulation of IGF-1 without using SF microspheres(Gel/IGF-1)was 25.9±3.6%,38.9±2.2%,46.3±1.8%,49.7±2.4%,50.7±2.2%,51.8±3.2%and 52.6±1.8%,respectively.These results indicated that SF microspheres as the microcarriers could effectively slow down the release of IGF-1,making Gel+SF/IGF-1 hold better sustained release ability.The results of in vitro cell experiments showed that Gel+SF/IGF-1 could promote H9C2 proliferation and protect cells under hypoxic conditions.In the rat model of MI,compared with Control,Gel+SF/IGF-1 was particularly effective in improving cardiac ejection fraction(40.3±13.9%vs 14.9±6.1%)and reducing the infarct area(14.9±0.8%vs 37.0±2.9%)of MI.Conclusion:Gel+SF/IGF-1 was capable of sustained release of IGF-1 and maintained IGF-1 activity within 28 days.This composite hydrogel exhibited good biocompatibility and could promote cell proliferation,protect cells under hypoxic conditions.Moreover,it could reduce infarct size and improve cardiac function after MI in rats.