Mechanical Strengthening And Functional Design Of Poly (L-Lactic Acid) Bone Scaffolds

With the improvement of living standards and the development of medical technology,people hope urgently to achieve the repair of damaged bone tissues.However,most of the current artificial bone implants usually can only serve as a temporary functional replacement rather than achieve repairing the function of damaged bone tissues.Poly-L-lactide(PLLA)is widely used as artificial bone scaffold material because of its good biocompatibility and good processability.Nevertheless,the insufficient mechanical properties,lack of antibacterial ability and biological activity limit its further application.Therefore,this thesis proposes to prepare porous PLLA bone scaffolds by selective laser sintering(SLS),and improve the crystallinity and crystallization rate of PLLA scaffolds through the heterogeneous nucleation effect of cellulose nanocrystals(CNC),so as to strengthen the mechanical properties of the scaffolds;Ag nanoparticles with spectral antibacterial properties were in situ grown on CNC to endow the scaffold strong antibacterial ability;Finally,nitrogen doped carbon/zinc oxide(NC-Zn O)heterojunction was constructed to achieve synchronous photodynamic antibacterial and bioactivity enhancement of the scaffold.The main research contents of this thesis are listed as follows:1.Aiming at the problem of the poor mechanical properties of PLLA bone scaffolds,it was proposed to use the heterogeneous nucleation effect of CNC to change the crystallization mode of PLLA from homogeneous nucleation to heterogeneous nucleation.In the melting and crystallization stage of PLLA,CNC could promote the growth and orderly arrangement of PLLA molecular chains with CNC as nucleation sites,so as to improve the crystallinity and strengthen the mechanical strength of the scaffolds.It was found that when the amount of CNC was 3 wt.%,the crystallinity of the scaffold was significantly improved,and the compressive strength,compressive modulus,tensile strength,tensile modulus and hardness of the scaffold were respectively increased by191%,351%,34%,83.5%and 56%.2.Aiming at the problem of the bacterial infection encountered after the implantation of the PLLA bone scaffold,Ag nanoparticles with broad-spectrum bactericidal properties were in-situ reduced on CNC to construct mice-like CNC@Ag nanosystem.The in-situ growth mechanism of Ag nanoparticles was revealed:CNC with numerous negatively charged sulfate groups and abundant hydroxyl groups could anchor Ag~+through electrostatic adsorption and ion-dipole interaction,thus promoting the uniformly in-situ growth and distribution of Ag on CNC under the assistance of reducing agents.After the nanosystem was introduced into PLLA scaffolds,it was found that the scaffolds had good antibacterial activity,and the inhibition rate of E.coli reached 95%.The Ag~+release behavior of bone scaffolds was studied.It was found that the scaffolds had the ability of slow and controlled release of Ag~+and achieved long-term antibacterial effect.3.In order to avoid bacterial infection caused by bone scaffold implantation in vivo and the need for bioactivity to promote bone repair,NC-Zn O heterojunction was proposed to be constructed and further compounded with polymer to prepare a new scaffold.The effects of NC Zn O heterojunction on the antibacterial properties and bioactivity of scaffolds were studied.It was found that the scaffold could kill bacteria by releasing ROS under light,and the bacteriostatic rate of E.coli exceeded 99%;It was found that the scaffold had strong ability to adsorb nutrients,significantly promoted cell adhesion and proliferation,and the cells had strong ability of cytoplasmic matrix mineralization on the scaffold.