Preparation And Bioproperties Of Poly(γ-benzyl-L-glutamate)Modified Hydroxyapatite/Poly(L-Iactic Acid) Bone Tissue Engineering Scaffold

Bone is one kind of the connective tissues, primarily composed of biologicalapatite and osteocollagenous fibers. Hydroxyapatite (HA), the main inorganiccomponent of hard tissues such as human bone tissue and tooth, has endowed thehard tissues with a fine stiffness. The osteocollagenous fiber as a sort of naturalpolymers has given bone wonderful flexibility and excellent bioactivity. From thepoint of view of the material science, nature skillfully combine the organic andinorganic together closely to form bone, which has its special biological andmechanical properties. Over the years, people have been trying their best topreparation of inorganic nonmetallic materials/organic polymer hybrid materials,and make them into various structure to mimic natural bone.Due to its similar chemical composition and strong compatibility with naturalbone, HA has been one of the most popular materials for clinicians and have beenwidely used in the field of bone repair or bone tissue engineering field.Poly(L-lactic acid)(PLLA) is an important biodegradable polymers and has beenadmitted by FDA to be used in clinic, and it also showed excellent perspective indrug delivery and tissue engineering. PLLA/HA composites can combine theosteoconductivity of HA and the biocompatible of PLLA, and thus have becomean important materials. However, the low dispersion of HA nanoparticles and thepoor phase compatibility decrease the osseointegration capacity post-operation,and thus limit its final application. It is necessary to further research into thepreparation technique of nano-HA/PLLA hybrid material, which is proved bettermechanical properties, biocompatibility and osteogenic properties by sufficientreliable statistical analysis of experimental data.In this study, we designed and prepared surface modified HA/PLLA scaffolds,and investigated their properties both in vitro and in vivo. The main contents areas following: The present investigation was to combine poly(γ-benzyl-L-glutamate) surfacegrafted hydroxyapatite(PBLG-g-HA) with PLLA to synthesize a newnanocomposites material PBLG-g-HA/PLLA. Via surface modification method,surface properties of HA was changed to hydrophic from hydrophilic, whichrealize homogeneous dispersion of HA in chloroform, and thus may en-HAnce thephase compatibility of HA and PLLA matrix. PBLG-g-HA/PLLA porous scaffoldswere prepared by the thermal induced phase separation method. Of these scaffolds,the porosity was more than85%, pore size ranged from30to200μm, and thestructure was multi-level with macro-and micro-pores co-existence. The aim ofour study was to evaluate the osteoblast adhesion, expansion, proliferation andexpression of osteogenic-related genes on the surface of the composites byanalyzing results of BMSCs morphology and proliferation and Realtime-PCR; andto investigate the bone regeneration of the scaffold material on rat femoral defectmodels by their in vivo experiments.The results from the present study showed that osteoblast adhesion,expansion, proliferation and expression of osteogenic-related genes such ascollagen I on PBLG-g-HA/PLLA composites were significantly increased due tothe addition of HA nanoparticles. The in vitro analysis illustrated that compositeswith10wt%PBLG-g-HA had the strongest ability to induce BMSC osteogenicdifferentiation. The in vivo analysis demonstrated that new bone formation wasmuch more prominent in HA/PLLA and PBLG-g-HA/PLLA groups as depicted byμ-CT, H&E staining and immunohistochemistry for collagen I. TRAP staining wasalso utilized to determine the influence of osteoclast cell number and stainingintensity to the various scaffolds. No significant differences in either stainingintensity or osteoclast numbers between all treatment modalities was observed,however blank defects did contain a higher number of osteoclast-like cells.When compared published reference, most works of the reference focused onthe modification of the physical properties of HA, few attention was paid to itsbiological properties. In our work, the most important novelty is that, we pay attention not only to the physical properties but biological properties and thusrealized tunning the surface physical properties and improvements of biologicalproperties at the same time. Additionally, the modification method can be carriedout at room temperature, and can apply to many other amino acid monomers, so itis universal to surface modification of many other materials. Finally, thebiocompatibility, osteogenic activity and bone repair capability of PBLG-g-HA/PLLA nanocomposites were investigated thoroughly, which may provide anexperimental basis for the preparation and clinical application of new materials.The results from the present study also illustrated the potential ofPBLG-g-HA/PLLA scaffolds for bone tissue engineering applications bydemonstrating favorable osteogenic properties.