Attachment and morphology of adipose-derived stromal cells and exposure of cell-binding domains of adsorbed proteins on various self-assembled monolayers

Self-assembled monolayers (SAMs) of alkanethiols, 1-decanethiol (DT10), 11-mercapto-1-undecanol (MUOH), 11-mercapto-undecanoic acid (MUA), and 11-amino-1-undecanethiol (AUT), terminated with methyl (-CH₃), hydroxyl (-OH), carboxyl (-COOH), and amino (-NH₂) groups, were chemically adsorbed on Au and used as substrate surfaces. The features of the SAMs adsorbed on Au were characterized using physicochemical and depth-sensing nano-indentation methods. The ordering of various tail-group terminated SAMs on Au was associated with the rate of harmonic contact stiffness of the SAM molecules along with the measured displacement (MUA/Au < AUT/Au ≈ MUOH/Au < DT10/Au). However, the slight difference in nano-mechanical properties among SAMs/Au does not reach the variation required to induce cellular mechano-sensitive responses. Immunostaining analyses of cytoskeleton indicate that initial adipose-derived stromal cell (ADSCs) attachment and cell morphology on SAMs/Au was regulated by the surface chemistry. The effects of surface chemistry on the exposed cell-binding domains of adsorbed bovine fibronectin (bFN) and bovine vitronectin (bVN) under single-protein or multi-protein conditions were also examined to determine the most potent protein for ADSC attachement. The results reveal that under the single-protein condition, the exposed cell-binding domains of both bFN and bVN on SAMs/Au follow the sequence of tail-groups, -NH₂, -COOH, -OH, and -CH₃. However, SAMs with the tail-group -CH₃ behaved significantly differently. Under the multi-protein condition, bFN domains showed a different sequence of tail-groups, -OH, -NH₂ ≈ -COOH, and -CH₃, whereas bVN domains showed the same sequence as that for the single-protein condition. Results of cell behavior and the exposed cell-binding domains of adhesive proteins suggest that vitronectin might be the fundamental adhesive protein for mediating ADSC attachment and spreading.