The Fabrication And Bioactivity Evaluation Of Biodegradable Scaffolds By Cryogenic 3D Printing

Traumatic injuries,tumor resections,and orthopedic operations often cause severe bone defects.As autografts and allografts have respective limitations in donor source and customized bone repair with a critical size,developing new biomaterials with excellent osteogenic potent to achieve personalised bone regeneration with a critical size is of great importance.The 3D printing technology has the characteristics of precise regulation and rapid prototyping,showing advantage in the preparation of customized bone tissue engineering scaffold materials.Conventional 3D printing often needs the assistance of heat,laser or electricity which is unable to in situ loaded the bioactive reagents.Therefore,how to fabricate a scaffold with mechanical properties and degradation rate that matching the regeneration process of native bone as well as osteoinductivity is the main problem to solve in this study.In this dissertation,three kinds of scaffolds aiming at bone tissue regeneration were fabricated via cryogenic 3D printing.The osteogenic ability and antibacterial ability were evaluated in vitro and in vivo.The main contents are as follows:(1)The graphene oxide(GO)was in situ loaded into poly(lactic-co-glycolic acid)/?-tricalcium phosphate(PLGA/?-TCP)bone tissue engineering scaffolds through cryogenic 3D printing(PTG).The chemical and physical properties,as well as the biocompatibility of the resulting scaffolds,were evaluated in vitro and in vivo.Our results suggest that the novel cryogenic 3D printed scaffold owns excellent mechanical properties and the unique macro/micro/nano morphology which is favorable for bone regeneration.The scaffolds generate no obvious cytotoxicity and genotoxicity.The low level of GO could promote the proliferation rate of r MSC.However,the high GO concentration could inhibit the proliferation of r MSCs.We found that,the reactive oxygen species(ROS)production associate the exposure time and GO concentration.Also,the protein expression level of TNF-? was up-regulated with the increase of GOcontent in the scaffolds.Altogether these studies suggest that 0.1 wt% GO in the scaffolds appeared to be favorable for biomedical applications and can be a potential candidate as bone substitute.(2)In order to further promote the osteogenic ability of the scaffolds and combing with the advantage of cryogenic 3D printing,we fabricated a novel bioactive poly(lactic-co-glycolic acid)(PLGA)/?-tricalcium phosphate(?-TCP)composite scaffold,in which graphene oxide(GO)and BMP-2-like peptide were in situ incorporated(PTG/P).The scaffolds were mechanically comparable to human cancellous bone and hierarchically porous,and the scaffold wettability and mechanical strength were further improved with the incorporation of GO.The in situ loaded peptides retained a high level of biological activity for extended time,and the loading of GO in scaffold matrix further tuned the peptide release into a more sustained way.In addition,our in vitro study showed that the scaffolds loaded with peptide and GO promoted r MSCs in growth into the scaffolds and enhanced the osteogenic differentiation.Moreover the in vivo study indicated the PTG/P scaffold could significantly enhance new bone formation.Thus,the novel PTG/P scaffold with bioactive substance provides direction for fabricating biomaterials for bone repair?(3)Considering that many bone defects are caused by infection,it is important to prepare materials with dual effects of antibacterial and osteogenesis.Based on the PTG/P scaffold,chlorhexidine(CHX)were incorporated in to the scaffolds to fabricate a bifunctional poly(lactic-co-glycolic acid)(PLGA)/?-tricalcium phosphate(?-TCP)/GO@peptide@CHX composite scaffold.The prepared PTG/P-CHX scaffolds owns a desirable micro-nano morphology for cell growth and porous structure for bone in growth.The release of CHX and osteogenic peptide in the PTG/P-CHX scaffold showed excellent antibacterial effect to S.aureus.without inhibiting the growth of r MSCs.While the PTG-CHX scaffolds showed compromise results of cyto-compatibility.Meanwhile,the in vivo experiments showed the PTG/P-CHX scaffold could effectively repair the critical-sized bone defect.These results successfully demonstrated that the prepared PTG/P-CHX scaffolds have the potential value in the application of bone regenerationand antibacterial therapy.