Fabrication And Cytocompatibility Evaluation Of Surface Functionalization For PLA Film

One of the central contents of tissue engineering is to fabricate a composite containing cell and scaffold.The adhesion,proliferation and differentiation functions of cells depend mainly on the physical and chemical characters of materials surface,hence the preparation of different characters surface and the interaction between surfaces and cells become the research hotspot at present.Due to the restriction of preparation method and surface modification technique,most researches of the effect of surfaces characters on cells behavior use the easily functionlized materials which aren't applied widely in tissue engineering as substrate such as polystyrene(PS) and quartz,and few report utilizes frequently-used biomaterials like polylactide acid(PLA) as substrate,however the latter has more actual significant to the investigation and exploiture of tissue engineering.In order to discuss the interaction between the surface of popular scaffolds and cells,the PLA film is used as substrate to review the effects of different surfaces on the capability of cell in this study to offer some academic basics and actual skills in tissue engineering.In order to study the interactions between surface and cells systemically,the PLA films with different morphology and chemical compositive functionlized surfaces were prepared in this study.Firstly,the PLA with molecular weight of 4.86×10~4 and 10.47×10~4 were synthesized by microwave irradiation at natural pressure with nitrogen protection,which differed from traditional thermal polymerization.Afterwards the SNS(Solvent-Non-Solvent) technique was used to fabricate micro-pits surfaces of PLA film and PS film with different diameters between 1μm and 20μm,which could be controlled by changing the solution concentration,non-solvent, temperature and volatilization speed of solvent.The micro-pits PS film was used as template ulteriorly to fabricate micro-islands patterned PLA film.Finally the hydrophilic monomers like acrylic(AA),acrylamide(AAm) and hydroxyethyl acrylate(HEA) were grafted onto PLA surface to introduce carboxyl,amide and hydroxyl group respectively.The contact angel measurements appeared that the introduction of polar groups improved its hydrophilicity and increased its surface energy.As the bone tissue engineering scaffold,it is important to understand not only the interaction between materials and osteocyte but also the effect of surface characters on the biomineralization and collagen adsorption abilities.The results of induced mineralization showed that pure PLA film made against mineral formed on its surface because it lacked nuclear site,correspondingly the lower molecular weight PLA appeared better mineralization ability than higher molecular weight due to its higher carboxyl density.For the different patterned surfaces,a great number of crystallization mineral was aggraded on PLA film with 1μm micro-islands,proved that this structure would stimulate mineralization,however the other three kinds of patterned surfaces had no obvious crystallization mineral formed and the least mineral was aggraded on the patterned surface with 20μm micro-pits.Compared the group functionlized surfaces,plentiful of crystallization mineral,which was proved to be hydroxyapatite(HA) by X-ray diffraction(XRD), was formed on all of the surfaces because of their negative charges.Collagen adsorption on the surfaces of different molecular weight and group functionlized PLA films was measured by quartz crystal microbalance(QCM).The results showed that the collagen adsorption on these surfaces accorded with Langmuir isothermal adsorption equation.Collagen could achieve adsorption balance faster and the adsorption force was stronger on group functionlized PLA film than pure PLA film.Furthermore the most quality of collagen was adsorbed on the carboxyl surface among three kinds of group functionlized films.The images of atomic force microscope (AFM) appeared that the quantity of adsorbed collagen was less and the conformation was curly on lower molecular weight PLA surface,however,the adsorption quantity on higher molecular weight PLA surface was more and some of them were straight.The collagen adsorbed on the carboxyl functionlized surface appeared a compact dicyto-structure,which meant that carboxyl functionlized surface benefited collagen adsorption.The cytocompatibility of different PLA film was evaluated by osteoblast incubation in vitro. Although lower molecular weight PLA showed better adhesion for osteobalst than higher molecular weight,it restrained osteoblast extended growth because of its faster degradation.The PLA film with micro-patterned surface offered a better substrate for cells adhesion and spread, however,it contributed less for cells proliferation.In spite of having "adherence" ability,the pseudopodium of cells only spread on the top surface of PLA film and couldn't grow along the curvature walls of pits and islands.Both cells adhesion and proliferation abilities were improved on the group functionlized surfaces,and the best cytocompatibility surface was the amide functionlized film.Lastly,the effect of surface characters on the differentiation of bone mesenchymal stem cells (BMSCs) was investigated innovatively in this study.BMSCs could differentiate normally towards osteoblast direction on pure PLA film in existence of revulsant.The PLA film with 1μm micro-islands showed a same trend with pure PLA film to affect BMSCs differentiation,whereas the other morphologies restrained its differentiation;The introduction of amide could accelerate BMSCs differentiating to wards osteoblast on PLA film,it also had a weak ability to induce BMSCs differentiation in a certain extend without revulsant.