Mechanism Of Mechanical Properties Improvement And Bioactivity Enhancement Of Polyester Bone Scaffolds

Polyester is a potential bone repair material due to its good biodegradability,biocompatibility and processability.However,polyester bone scaffolds have insufficient mechanical properties and lack of biological activity,which restricts their further application in the field of bone tissue engineering.In this paper,polyester bone scaffolds were prepared by selective laser sintering（SLS）technology to achieve personalized customization of the structure.Montmorillonite（MMT）-carbon nanotubes（CNT）nanocomposites were prepared by self-assembly process and introduced into polyester to enhance the mechanical properties of bone scaffolds.Rod-shaped nano-hydroxyapatite particles（n HAP）were prepared by hydrothermal method and introduced into polyester to impart bioactivity to bone scaffolds.n HAP was generated on the surface of graphene oxide（GO）by in situ growth process to improve the dispersity of n HAP and give full play to its enhancing effect on the bioactivity of polyester bone scaffolds.The main work and innovations of the paper are as follows:（1）The excellent mechanical properties of MMT-CNT nanocomposite were proposed to improve the mechanical properties of l-polylactic acid（PLLA）bone scaffold.The modified CNT was inserted into the MMT layer through sodium ion exchange with MMT by the cation exchange property of MMT.The MMT-CNT self-assembled structure combines the excellent mechanical properties of the two,while suppressing the stacking of MMT and the curling of CNTs,thereby improving the mechanical properties of the PLLA bone scaffold.Among them,the compressive strength is increased by 63.27%,and the tensile strength is increased by 111.46%.It was found that the mechanism of mechanical properties improvement was as follows:the good dispersion of MMT-CNT in PLLA was beneficial to the transfer of stress inside the bone scaffold,and the stress concentration caused by agglomeration could avoid the weakening of mechanical properties.Meanwhile,MMT-CNT with high strength and modulus can withstand the stress from PLLA and dissipate the energy of bone scaffold destruction.（2）It was proposed that the bioactivity of polycaprolactone（PCL）bone scaffolds was endowed by the mineralization properties of n HAP.The rod-shaped n HAP with high crystallinity was prepared by hydrothermal method,and the composition and morphology of n HAP were regulated by adjusting the hydrothermal temperature to control the crystal growth along the c-axis.The simulated body fluid（SBF）immersion experiment found that a bone-like apatite layer was formed on the surface of the composite bone scaffold after 28 days.The specific mechanism of the formation of the bone-like apatite layer was identified as follows:as the composite bone scaffold degrades in body fluids,n HAP is gradually exposed and dissolved to release Ca²⁺,PO₄^3-and HPO₄^2-,which promotes the increase of local ion concentration on the surface of the composite bone scaffold.When the concentration threshold was reached,Ca²⁺,PO₄^3-and HPO₄^2-formed apatite crystal nuclei on the surface of the composite bone scaffold,and continued to adsorb mineralization-related ions through electrostatic action to form a bone-like apatite layer.（3）The chelating properties of GO oxygen-containing functional groups were used to regulate the growth of n HAP and improve the dispersibility of n HAP to improve its enhanced effect on the bioactivity of polyester bone scaffolds.In a hydrothermal environment,the oxygen atoms in the carboxyl and epoxy functional groups on GO utilize the chelating properties to form coordination bonds with Ca²⁺to fix it on the surface of GO,and the deposited Ca²⁺adsorbs HPO₄^2-in solution through electrostatic interaction to form HAP crystals Through the further adsorption of mineralization-related ions,the HAP nuclei gradually grow and crystallize,and finally form a stable rod-shaped n HAP.It is found that GO-n HAP has good dispersibility in the polyester matrix,and the mechanism is identified as follows:on the one hand,GO promotes the uniform growth of n HAP through the precise control of growth sites in the in-situ growth process.Oxygen-containing functional groups make good interfacial compatibility between GO-n HAP and polyester matrix.Simulated body fluid immersion experiments found that GO-n HAP could act as a nucleation site to attract the deposition of mineralization-related ions,thereby inducing the formation of a bone-like apatite layer and endowing the composite bone scaffold with good biological activity.Figures:36,Tables:1,References:133...