Biomineralization Of Modified Carbon Nanotubes And Preparation The Nanofibrous Composite Scaffold

In bone tissue engineering, an ideal scaffold should mimic theadvantageous features of the natural extracellular matrix (ECM) in order tosupport cell attachment and guide three dimensional (3D) tissue formation.Moreover, the scaffold should have suitable mechanical properties to matchthe requirement of bone tissue. To emulate certain advantageous features ofthe natural ECM, the3D nanofibrous scaffold was fabricated via phaseseparation. Carbon nanotubes (CNTs), with their nanometer scale size, highlength/radius ratio, extraordinary mechanical strength, and excellentelectromagnetical and thermal conductivity, are ideal candidates as reinforcingfillers in the bone repair. In this thesis, the modified CNTs with dispersibilityand surfactivity were gained by chemical oxidation and biomineralizaiton.Then, to improve the mechanical properties and biological performance ofscaffold, the modified CNTs were introduced to the macroporous andnanofibrous scaffold fabricated via phase separation combined withparticle leaching. First, in order to introduce the groups of COOH and OH, themulti walled carbon nanotubes(MWNTs) was modified via acid treatment bysolution of H₂SO₄/HNO₃. Phosphatic MWNTs (p MWNTs) were obtained bysimple chemical reactions. The improved5times simulated body fluid(i5SBF) was balanced with CO₂bubbling all the time to stabilize pH value ofi5SBF at6.4±0.02in order to mimic the procedure of biomineralization. Then,the modified MWNTs with different group were incubated in i5SBF toinvestigate the effect of the group on the process of biomineralization. Variouskinds of MWNT apatite, with different chemical compositions and shapes,were obtained at different incubation time. The products werecharacterizations of SEM, TEM, EDX, XRD, FT IR and TGA etc. The resultsrevealed that the nucleation and growth of HA crystals depended remarkablyon the surface functional groups of MWNTs and the mineralization time. Heattreatment could improve the crystallization degree of HA. And theMWNT amorphous apatite composite, with core shell structure, favourablemorphology and dispersibility, were selected to enhance the the macroporousand nanofibrous scaffold.Then, the nanofibrous aliphatic polyester, include PLLA, PDLGA7525and PLGA5050, matrix was fabricated by phase separation. PLGA5050,which is an utterly amorphous polymer, was first reported to be made intonanofibrous networks (fiber diameter around500nm) using phase separationfrom PLGA5050/THF solutions in this study. The effect of THF/H₂O solution on formation of fibrous amorphous PLGA was investigated, and the cause ofdifferent structures was speculated. The results revealed that the nanofibrousPDLGA matrix could be found at the locations of bottom of sample.Nonsolvent (e.g. H₂O) was unnecessary to form the PLGA5050gel, whichwas critical to nanofibrosis, as if the environmental temperature for gelationoccurrence was low enough (70T). Associating with the phase separationmethod, particle leaching technique was applied to fabricatethree dimensional scaffolds with macroporous and nanofbrous structures. Toensure the occurrence of nanofibrosis on macropore walls, the temperature ofsalt particles should be best lowed to70T beforehand. Accordingly,scaffolds prepared under varied parameters exhibited different nanofiber andpore morphologies, which affected the pore size, porosity, specific surfacearea, water contact angle and protein adsorption ability etc. The preliminarycell (MC3T3E1) culture confirmed the cell ingrowth into the macroporousand nanofibrous PLGA5050scaffolds in comparison with the solelynanofibrous matrixes.Finally, nanofibrous PLLA/a MWNTsI MWNT ACPI composite wasgained by using phase separation. From the results of SEM and water contactangle, it was found that with the addition of a MWNTs, there was nosignificant difference could be detected. However, the contact angle exhibiteda decreasing trend with additive amount of a MWNTs increasing.Macroporous and nanofibrous PLLA/a MWNTs3D scaffold was fabricated via phase separation combined with particle leaching. The addition ofa MWNTs showed notable impact on the mechanical properties of thePLLA/a MWNTs3D scaffold. When the content of a MWNTs reached to5wt%, the modulus of compressibility of the scaffold increased more thantriple than without a WMNTs sample. With the same addition, the strengthenhancing efficiency of a MWNTs was higher than MWNT ACP.Macroporous and nanofibrous of PLLA/MWNT ACP3D scaffold, effectiveintegrated the advantages of nanofibrous PLLA3D scaffold, MWNTs andapatite, can be superior candidate scaffolds for bone tissue engineeringapplications.