Fundamental Research For Pearl Application As A Bone Repair Material

In recent years, nacre, which offers excellent biocompatibility and carries bioactivemolecules, has drawn much attention in the field of bone tissue engineering. In order tofabricate an ideal scaffold for bone tissue engineering, features of bone formation ofwater soluble matrix (WSM) from nacre were evaluated. Meanwhile, Poly-L-lactide(PLLA)/aragonite and PLLA/vaterite pearl powder scaffolds were prepared andcharacterized. The excellent capacity of PLLA/aragonite and PLLA/vaterite scaffolds topromote bone regeneration was confirmed by a rabbit radial defect model.WSM was separated into WSM<1kDa and WSM>3.5kDa fractions. The effects ofWSM and the two fractions were tested in vitro on rat MC3T3-E1cells and human bonemesenchymal stem cells (hBMSC). All WSMs showed no ability to increase theproliferation, but stimulated osteogenic differentiation of two kinds of cells, which hadno correlation with the molecular weight of WSM. All WSMs could speed up themineralization of rat MC3T3-E1cells, while WSM and WSM<1kDa were capable toaccelerate the mineralization of hBMSC. ALL results are valid for both aragonite andvaterite pearls.PLLA, PLLA/aragonite pearl powder and PLLA/vaterite pearl powder scaffolds werefabricated by freeze-drying. Composite scaffolds and PLLA scaffold displayed porousstructures. The addition of pearl powder increased the compressive strength and thecompressive modulus of the scaffolds. But the porosity of composite scaffoldsdecreased slightly. The hydrophilicity of composite film increased in the followingorder: PLLA/aragonite> PLLA/nacre> PLLA/vaterite, which was in accord with theresult of protein adsorption. In vitro cell culture showed that PLLA/aragonite andPLLA/nacre stimulated proliferation and osteogenic differentiation of rat bonemesenchymal stem cells (rBMSCs). However, PLLA/vaterite scaffold decreasedrBMSCs proliferation as well as the osteogenic differentiation.The in vitro degradation behavior of PLLA, PLLA/aragonite and PLLA/vaterite pearlpowder scaffolds were investigated. The results showed that both composite scaffoldshad a similar degradation behavior. The alkalinity in PBS decreased the degradation rateof composite scaffolds. Alkalinity products from composite scaffolds provided anenvironment neutralizing acid residues from PLLA, influencing changes of porosity of scaffolds and retarding the drop of molecular weight of PLLA. During the degradation,with the dissolution of pearl powders, the composite scaffolds displayed a gradualdecrease of bulk density and mechanical properties, which were still higher than that ofthe PLLA scaffold.Bone regeneration was evaluated using a rabbit radial defect model. The resultssuggested a significant increase in bone formation in PLLA/aragonite scaffold at8weeks compared with other groups, and the newly formed bone was similar to naturalbone at12weeks. PLLA/vaterite scaffolds enhanced bone formation at12weeks. Allresults revealed that PLLA/aragonite and PLLA/vaterite scaffolds significantlyincreased bone regeneration, which provided theoretical and practical supports for theirclinical applications.