Bioresponses Of Stem Cell And Protein To Surface Chemistry Designed By Self-assembled Monolayers

Bioresponses of biomaterials are largely dependent on surface properties, which are extremely important in designing biomaterials. However, because of differences in composition and structure of various materials, we can not effectively get conclusions of the cellular biology of mono surface property. The aim of this project is to build model surfaces using self-assembled monolayers(SAMs), then further to study the influence of charge and wettability on stem cell response and protein adsorption. This study will provide a useful guidance on the design of biomaterial surfaces for bone regeneration.(1) Construction and bioresponsive properties of surfaces with various functional groupsSAMs possessing varying functional groups(-OEG,-CH3,-PO3H2,-OH,-NH2 and-COOH) have been designed to investigate effects of surface chemical functional groups on mouse mesenchymal stem cells(m MSCs) fate and protein adsorption. Much more bovine serum albumin(BSA) and osteopontin(OPN) adsorbed on-CH3 terminated SAMs than on-OH group, mainly due to the hydrophobic interaction. However, there was a strong preference for cell adhesion and proliferation on-OH surfaces. Compared to the surfaces of strongly negative charge(-PO3H2 and-COOH),-NH2 functionalized surface showed a significantly larger amount of BSA and OPN adsorption. However, cells can also be adhered well on-PO3H2 and-COOH modified surfaces. The-OEG terminated SAMs adsorbed BSA and OPN least due to its non-fouling character, where cells can not adhere and spread. Overall,-PO3H2,-OH,-NH2 and-COOH terminated SAMs promoted mMSCs adhesion, proliferation and osteogenic differentiation compared with-OEG and-CH3 functionalities in the presence of biological stimuli.(2) Construction and bioresponsive properties of surfaces with different chargesMixed-OEG/-NH2 and-NH2/-COOH functional groups using SAMs, respectively, were prepared to build surfaces with varying proportions of-NH2 groups. It was investigated that effects of surface charge on MSCs adhesion, proliferation and osteogenic differentiation from human and mouse origins, as well as adsorption of BSA and OPN. The results showed that with the increase of-NH2 on-OEG/-NH2 mixed SAMs, the amount of protein adsorption can stay constant, which will provide a cue for the design variable parenteral products. The-OEG/-NH2 mixed SAMs with low density of-OEG remain anti-adhesion of protein, while requiring higher density for cells, which demonstrated the anti-adhesive difference between proteins and cells for the density of-OEG. The adsorption amount of OPN decreased monotonically with increasing of-NH2 groups on-NH2/-COOH mixed SAMs. However, no significant differences in MSCs adhesion on-NH2/-COOH mixed SAMs can be observed, which may be related with cations in solution. In the presence of biological stimuli, surfaces with high ratio of-NH2 groups on-OEG/-NH2 and-NH2/-COOH mixed SAMs benefited best osteogenic differentiation of hMSCs, while moderate ratio of-NH2 on mixed SAMs for mMSCs. The effects of surface charge on osteogenic gene expression in our studies were clearly differed between human and mouse cells.(3) Construction and bioresponsive properties of surfaces with different wettabilityThe-OH/-CH3 mixed SAMs were prepared to form substrates with varying wettability. It was investigated effects of wettability on MSCs fate from human and mouse origins and protein adsorption. And the underlying molecular mechanism was further studied. Hydrophilic mixed SAMs with a moderate wettability tended to promote adhesion, spreading, proliferation and osteogenic differentiation of MSCs. The numbers of adhered hMSCs and mMSCs were maximized on-OH/-CH3 mixed SAMs with water contact angles of 40-70° and 70-90°, respectively. Proliferation of both hMSCs and mMSCs was most favored on hydrophilic SAMs with a water contact angle around 70°. In addition, a moderate hydrophilic surface(with a contact angle of 40-90° for hMSCs and 70° for mMSCs) promoted osteogenic differentiation in the presence of biological stimuli. The maximal amount of adsorbed BSA was observed on-CH3 terminated SAMs. But there was not a linear increase of the amount of protein adsorption with the increase of surface hydrophobicity. The largest amount of OPN seemed to be absorbed on moderate hydrophilic surface(-OH/-CH3(7/3, v/v) mixed SAMs), possibly related with changes of orientation and conformation of protein.Finally, we investigated the molecular mechanism of wettability to affect mMSCs adhesion. The results showed that moderate wettability could up-regulated αv and β1 integrins, promoted FAK expression and phosphorylation, then further activated MAPK signaling pathway. Combining the analysis of differentially expressed genes by gene chip technology, it was suggested that moderate wettability may activate p38 MAPK signaling pathways to affect the mMSCs adhesion then osteogenetic differentiation.In summary, surface chemistry designed on SAMs model can regulate MSCs adhesion, proliferation and osteogenesis, as well as protein adsorption. Our work provides cues for the design of biomaterials with controllable and functional surface chemistry for bone regeneration.