The Basic Investigation Of Mesoporous Bioactive Glass Applications For Scaffold Of Bone Tissue Engineering

Objectives:Highly ordered mesoporous bioactive glasses 80S(Mesoporous Bioactive Glasses MBG80S)is designed and prepared by Yanxiaoxia et al from Fudan University,using non-ionic block copolymers as structure-directing agents through an evaporation-induced self-assembly(EISA) process.Recently,the research show the superior bioactivity and satisfactory biocompatibility of MBG80S.The aim of our study is to investigate the mechanical properties,the adsorption and releasing properties of the MBG80S,and the effect to the proliferation, differentiation,mineralization and adhesion of osteoblast is also be detected.Methods:In the first part of the experiment,compared with BG80S discus,the MBG80s discus were soaked in the Stimulated Body Fluid(SBF),the change of appearance in the surface and interior was evaluated by scanning electron microscope(SEM),the Young's modulus and compressive strength of the disc were measured,meanwhile the concentration of the ion in solution was investigated by ICP.In the second part,a-chymotrypsin(a-Chy),a protein with similar dimer structure, molecular weight and isoelectric point to rhBMP-2,was used as the simulation of rhBMP-2 and marked with I¹²⁵.The adsorption and releasing curves of MBG80S powder and discus were drawn and analyzed.Finally,the rhBMP-2 was marked with I¹²⁵ and the releasing curve of MBG80S discus -rhBMP-2 was analyzed.In the third part,firstly,the osteoblastic cells were harvested by sequential enzyme digestion from calvaria of Sprague Dawley rat sand then cultured.They were treated with leaching liquor of MBG80S,then the proliferation was analyzed by MTT methods;PNPP method was used to assay the ALP activity of osteoblastic cell;to analyze the mineralization ability of osteoblastic cells,the number and area of mineralization nodes were observed.Secondly,rhBMP-2 was diluted by 0.0625% leaching liquor of MBG80S into different concentration from 3.125ng/ml to 50ng/ ml,the osteoblastic cells were treated with these rhBMP-2-MBG80S culture medium, then the proliferation was analyzed by MTT methods;PNPP method was used to assay the ALP activity of osteoblastic cell,the rhBMP-2 culture medium in the same concentrations were the comparison.In the last,the osteoblastic cells were harvested by sequential enzyme digestion from calvaria of Sprague Dawley rat sand then cultured on the MBG discus,evaluated cellular morphology and adhesion by SEM.Resault:1.The SEM showed that there were a mass of hydroxyapatite ceramic(HAC) crystal appeared in the surface and interior of the MBG80S discus.The quantity and size of the crevice between particles were reduced,the particles were fusing together. Conversely,there was no change in the BG80S.The same circumstance were occered in the mechanical properties.Before soaked in the SBF MBG80S and BG80S discus had same Young's modulus and compressive strength.After 4 hours,MBG80S discus went up to100—150MPa(Young's modulus) and 20—30MPa(compressive strength),after 48 hours sustained in 200-250MPa and 30-40MPa.The BG80S dropped rapidly,sustained in 20MPa and 10MPa.The major cause of these changes was the rapid growth of HAC crystal,it also changed the material crossover exterior and interior the discus.2.The a-Chy adsorption of MBG80S and BG80S powder were fast,at 4 hours, the maximum amount was 47.080ug/mg and 19.912ug/mg(protein/ materials),after then With the growth of HAC crystal,the a-Chy adsorption of MBG80S still increased tardily.In the discus,the maximum amount and shape of curves changed compared with powder,both MBG80S and BG80S;but the greater change appeared in the MBG80S.Both MBG80S and BG80S had property of a-Chy releasing,but the curve of MBG80S was more smooth.The release profile of rhBMP-2 from MBG80S discus was scaled and its kinetics was assayed.Results showed that rhBMP-2 had been released rapidly in the first 2 days,slowly and lastingly during the 3rd to 94th day.The release of rhBMP-2 from MBG80S/rhBMP-2 compound during the 3rd to 94th days followed the Higuchi model equation,and the 50%releasing time is 248.38days.It can be concluded that MBG80S showed it's characteristics as a sustained delivery system for rhBMP-2 and may be used as a novel carrier for rhBMP-2 in clinic.3.MBG didn't' interrupt the proliferation of osteoblastic cells but at the concentration of 1%(P＜0.01);The ALP activity were higher in all concentration compared to control,particularly at 0.0625,0.125,0.25%(P＜0.01);MBG significantly enhanced osteoblast mineralization at the concentration of 0.0625%.The rhBMP-2-MBG80S culture medium didn't' interrupt the proliferation and differentiation of osteoblastic cells compared with the blank culture medium.But compared with the rhBMP-2 culture medium in the same concentration,the difference is apparent.It suggested that the ionic products from the dissolution of MBG had interaction to rhBMP-2 on the molecular level.4.The SEM showed that viable osteoblasts could be seen on the MBG80S discus and presented perfect adhesion.It suggested that the MBG80S has satisfactory biocompatibility and adhesion to osteoblast.Conclusion:In vitro,the MBG80S present fine mechanical properties,excellent adsorption and releasing properties to the protein like rhBMP-2 and satisfactory biocompatibility and adhesion to osteoblast.As a new family of biomaterial,MBG80S may be used as important bone-repairing and bone tissue engineering scaffold materials in the future.