Optimization Design And Osteogenic Activity Of Chitin Whiskers/Polylactic Acid Composite Material

Polylactic acid has been widely studied and applied as a bone tissue repair material due to its good biocompatibility,biodegradability and processibility,but there are still some deficiencies such as insufficient mechanical strength,poor hydrophilicity and lack of osteoinductive activity.Chitin whiskers(CHWs),with a certain aspect ratio and nano size,not only have the excellent biocompatibility,osteogenic activity,anti-inflammatory and antibacterial properties,but also have extremely excellent mechanical property,and their longitudinal modulus can be as high as 150 GPa.Therefore,the CHWs have been widely used as reinforcing and toughening fillers for polymer matrix in recent years.It is particularly worth mentioning that the CHWs aqueous suspension has liquid crystal properties under certain conditions,and the liquid crystal and liquid crystal elastomer materials have unique advantages in guiding cell behavior and tissue repair,and have attracted many scientists` research interest in recent years.As we all know,3D printing technology is the first choice for the preparation of scaffold materials due to its advantages such as fast,efficient and personalized design.Among them,the emerging solvent 3D printing technology is highly concerned due to its simple printing equipment,strong operability and support for the introduction of bioactive substances or fillers into the matrix materials.Based on the above analysis,this paper aims to make full use of the excellent properties of CHWs to prepare CHWs/polylactic acid new bone tissue repair composite material with excellent comprehensive performance,from which the shortcomings of single polylactic acid bone tissue repair material can be made up.Focusing on this research purpose,this paper mainly carried out the following work:1.In view of the bottleneck problems of 3D printing poly(L-lactic acid)(PLLA)porous scaffolds,such as poor mechanical strength,weak osteogenic activity,and particularly insufficient toughness,this study designed to introduce CHWs into the PLLA matrix.Taking into account that natural polysaccharides are not resistant to high temperature,the solvent 3D printing technology was chosen in this study.Moreover,in order to improve the printability of composite ink and the interfacial adhesion between fibers,a trisolvent system,including dichloromethane(DCM),2-butoxyethanlol(2-Bu)and dibutyl phthalate(DBP),was chosen to prepare the CHWs/PLLA composite inks.With these composite inks,the CHWs/PLLA composite porous scaffolds with different whisker mass ratios were further fabricated through 3D printing technology.The effects of the contents of the CHWs on the physicochemical properties cell affinity,osteogenic activity and anti-inflammatory properties of the composite scaffold were studied.The results showed that the prepared CHWs/PLLA composite scaffolds have good 3D porous structures with the pore size of 400±14 ?m and porosity of 80±5%.Compared with pure PLLA scaffold,the CHWs/PLLA composite scaffolds showed significantly superior hydrophilicity and compression performance,and also were more conducive to cells adhesion,proliferation,and up-regulating alkaline phosphate(ALP)activity and calcium deposition due to the presence of CHWs.Moreover,compared with other composite scaffolds containing lower mass content of CHWs,only the CHWs/PLLA composite scaffolds with 40 wt% of CHWs have obvious anti-inflammatory effects.2.In view of the fact that CHWs can exhibit specific liquid crystal properties under certain conditions,this chapter first prepares CHWs by acid hydrolysis,and then obtains three groups of samples of 0CHWs,0.5CHWs and 2CHWs by deacetylation treatment of 0,0.5 and 2 h via alkaline hydrolysis,and the CHWs liquid crystals with different degrees of deacetylation were obtained by ultrasounic dispersion.The effects of different deacetylation times on the zeta potential,morphology,crystallization properties,liquid crystal and rheological properties of the whiskers were studied.The results showed that the CHWs with different degrees of deacetylation all exhibited chiral nematic liquid crystal properties,and the viscosity,G' and G'' values all increased with the increase of the degree of deacetylation in 0CHWs,0.5CHWs and 2CHWs.Based on this,genipin was further used to cross-link the 0CHWs,0.5CHWs and 2CHWs liquid crystals.Thus,the liquid crystal elastomers of the 0CHWG,0.5CHWG and 2CHWG with different degrees of crosslinking were prepared.And the liquid crystal and rheological properties,as well as compression properties of the as-prepared liquid crystal elastomers were studied.The results showed that the liquid crystal texture of each group of the liquid crystal elastomers after genipin crosslinking changed from chiral nematic liquid crystals to nematic liquid crystals,and the viscosity,G' and G'' of the crosslinked 0CHWG,0.5CHWG and 2CHWG are significantly improved,moreover,the G' is always greater than G''.In particular,the G' and G''of the 2CHWG group were the highest,and G' is much larger than G'',showing the elastic gel state liquid crystals.In addition,compared with the solution state or soft gel state exhibited by the 0CHWG and 0.5CHWG liquid crystal elastomers respectively,the 2CHWG showed better elasticity,and the elasticity remained well after multiple manual cycles of compression.3.In view of the unique liquid crystal properties,good elasticity and biological properties of liquid crystal elastomers,and on the basis of the research in the previous chapter,the CHWs,0CHWG and 2CHWG were further modified onto PDLLA film to prepare PDLLA/PDA-CHWs,PDLLA/PDA-0CHWG and PDLLA/PDA-2CHWG composite films with the help of polydopamine(PDA)as a secondary reaction platform.The liquid crystal properties,stability,tensile properties,hydrophilicity,cytocompatibility and osteogenic activity of these series of composite films were studied.The results showed that only the surfaces of the PDLLA/PDA-0CHWG and PDLLA/PDA-2CHWG composite films can always exhibit typical nematic liquid crystal characteristics.Moreover,the 0CHWG and 2CHWG liquid crystal elastomer layers are stable grounded on the PDLLA film under the strong adhesion of PDA.In addition,the introduction of PDA and CHWs layers can significantly improve the tensile strength and modulus of PDLLA film,and effectively promoted the proliferation and adhesion of MC3T3-E1 cells.Although the tensile properties of PDLLA film modified with 0CHWG and 2CHWG liquid crystal elastomer layers have not been significantly improved,their hydrophilicity,cell affinity and osteogenic activity have significantly increased.Furthermore,compared to the PDLLA/PDA-0CHWG with a low modulus liquid crystal elastomer layer,the 2CHWG liquid crystal elastomer layer with a relative high modulus on the surface of the PDLLA/PDA-2CHWG composite membrane can better withstand the traction force formed during the process of cell adhesion,thus it can significantly improve the expression of ALP and calcium deposition of cells.