Moreover, area and shape of cells on plasma-treated surfaces were significantly different from that of the control i.e corresponding mean cell area was 509 �� 108 ��m2 and 684 �� 130 ��m2 respectively. Additionally, the shape factor, which is related to the cell roundness, was Enzalutamide 1.15 �� 0.01 for untreated PVA (almost discoid cells) and 1.43 �� 0.28 for plasma-treated PVA substrates. Cell culture results also evidenced that a homogenous monolayer of endothelial cells could be formed onto the surface of plasma-treated substrates (Fig. 5D). Thus based on prior works from our laboratories, amine-grafted PVA hydrogels appear as promising scaffolds for vascular biomaterials.9 Future studies will investigate hemocompatibility of this material. Figure 5.
(A) Endothelial cells were stained with Phalloidin/DAPI and observed on (left) untreated PVA and (right) plasma-treated PVA substrates with fluorescence microscopy at day 3. Scale bar: 50 ��m. Cell area (B) and shape factor ( … Surface characterization and cytocompatibility results demonstrated that cell-contacting properties of PVA substrates significantly improve due to the presence of surface amine groups. Recent works on various synthetic substrates also demonstrated that nitrogen-containing groups, especially amine and amide functionalities, were optimal for adhesion proteins adsorption and cell adhesion.33,34 Most authors ascribe the observed enhancements to a combination of increased hydrophilicity and surface charge.
Cell-substrate adhesion is a process that involves several steps, including adsorption of extracellular matrix (ECM) proteins on the surface, recognition of ECM components by cells through integrins, cytoskeletal reorganization and overall cell spreading. A large portion of cells, serum and ECM proteins (fibronectin, vitronectin and collagen) are recognized as being negatively charged, so they tend to be more adsorbed through electrostatic interactions on positively charged surfaces.35 Amine groups are protonated at a physiological pH (pKa~10) and can interact with negatively charged proteins and/or with proteoglycans of the cellular membrane. Therefore in the early stage of cellular attachment, amines are likely to enhance proteins adsorption from the culture medium and subsequent cellular interactions of adherent cells with the adsorbed protein layer.
A drawback generally observed with plasma techniques is the limited stability of the treated surfaces toward aging and washing.36 This is particularly important when designing a biomaterial that will eventually have to be stored, sterilized and implanted. The aging behavior of amine-grafted surfaces prepared by plasma has been GSK-3 extensively described, and is usually due to post-plasma oxidation and surface rearrangements.27,37 Latkany et al. also noticed that nitrogen species grafting on PVA substrates by ammonia plasma treatment, was not effective on enhancing cell adhesion.