Preparation Of Cennunos Nanofibrins And Their Appnication In Tissue Engineering Scaffonds

Cellulose is accumulated as the most abundant renewable biopolymer present primarilyin wood biomass. Cellulose nanofibrils （CNFs） are biocompatible ultrafine nanomaterials thathave high aspect ratios, outstanding mechanical properties, low thermal expansion and lowdensity. Additionally, C6-carboxyl cellulose can be absorbed in vivo and has been used inmedical areas. Thus preparation of C6-carboxyl CNFs not only promotes advances innamomaterial science but also opens new field for the application of CNFs.2,2,6,6-tetramethylpiperidinyl-1-oxyl （TEMPO）/NaClO/NaClO₂system was applied toonce-dried eucalyptus pulp and dissolving pulp and the oxidation laws were studied.Combined with high pressure homogenization, highly crystalline individual CNFs wereprepared continuously in high cellulosic consistency and in quantity, crystallinity degree andmorphology of CNFs were characterized. Besides, three dimensional porous tissueengineering scaffolds were fabricated by freeze drying CNFs/poly（vinyl alcohol）（PVA）suspension. Influences of the consistency of CNFs suspension, mass ratios between CNFs andPVA, the types of PVA and frozen temperature on the morphology and architecture of thescaffolds were determined, and mechanical properties of the scaffolds were also probed.Furthermore, NIH3T3cells were cultured on the scaffolds, cell viability was determined byConfocal Laser Scanning Microscopy （CLSM） and cell morphology was characterized byScanning Electronic Microscopy （SEM）. The results are showed as follows.Oxidized cellulose with carboxylate content of0.8mmol/g was obtained by catalyticoxidizing cellulose at pH6.8and60℃for16h, which was38h faster than previous methodin references, when the adding order of reagent was changed from TEMPO, NaClO₂andNaClO to TEMPO, NaClO and NaClO₂. Ultimate degree of polymerization （DP） has directrelationship with the original DP of raw materials.Transmittance Electronic Microscopy （TEM） images showed that individual NCFs withcrystallinity degree of68.4%were of3-5nm in width and several hundred nanometers inlength, the aspect ratio was more than100. Atomic Force Microscopy （AFM） picturesrevealed that CNFs easily aggregated into bundles in width of20-30nm, and these bundlesrandomly overlapped each other to form web-like structure. CNFs films were of33-35μm inthickness with densities of1.48-1.57g/cm3, transmittance of the films was more than90%and elastic modulus of the films were6.2±1.6GPa.The obtained scaffolds formed into hgdrogel after absorbing water, and had excellentwater absorption and water retention properties. CNFs/high molecular weight PVA scaffolds displayed an irregular open pore geometry and an interconnected pore morphology, PVAformed the wall of the big pores and CNFs bundles in width of100-200nm bridged eachother to form web-like structure, which was similar to collagen skeleton in extra cellularmatrix （ECM）, on the surface of the PVAwall throughout the scaffold. The optimal proportionbetween cellulose and PVA was1:2and the optimal freezing temperature was-80℃for thefabrication of scaffolds, at which point the scaffolds had abundant microfilaments withoutstanding web structure. PVA played key role in providing the mechanical strength of thescaffolds, and the compressive modulus of the scaffold were equivalent to that of cartilagetissue, which was on the kilopascal magnitude.CLSM images indicated that the NIH3T3cells kept viable and the scaffolds weresuitable for cell attachment and proliferation while SEM photos showed that the cellsaggregated into clusters and formed typical spherical cell colonies which mainly distributedon the microfilament web inside the big pores, CNFs bundles were the anchor points of cells.