Supplementary Information for Drastically Lowered Protein Adsorption on Microbicidal Hydrophobic/Hydrophilic Polyelectrolyte Multilayers
Sze Yinn Wonga,b, Lin Hanc, Ksenia Timachovaa,b, Jovana Veselinovica,b, Md Nasim Hydera, Christine Ortizc, Alexander M. Klibanovb,d,e, Paula T. Hammonda,b*
1) Typical approach curves on 9.5bi and 10bi (DMLPEI/PAA)n films with COOH functionalized tips and NH2 functionalized tips
50
-0.6
-0.4
50
C
40
40
30
30
Force (nN)
Force (nN)
A
20 10
-0.2
0.2
0.4
-0.6
-0.4
-0.4
0.4
0.2
0.4
-10
50
D
40
30
30
Force (nN)
40
20 10
-0.2
0.2
Distance (µm)
50
Force (nN) -0.6
10
-0.2
-10
Distance (µm)
B
20
0.2
0.4
-0.6
-0.4
-10
Distance (µm)
20 10
-0.2 -10
Distance (µm)
Supplementary Figure 1 Typical approach curves on 9.5bi and 10bi (DMLPEI/PAA)n films with COOH functionalized tips (A and B) and NH2 functionalized tips (C and D).
2) Mechanical Properties of (DMLPEI/PAA)n films Using the Hertz model, the effective indentation modulus, Eind, of the (PAA/DMLPEI) was estimated based on AFM-based nanonidentatino (Fig. S1a) to be 580 ± 50 kPa for the 9.5 BL film, and 610 ± 30 kPa for the 10 BL film, respectively (Fig. S1b). There was no statistical difference in Eind between 9.5 and 10 BL films, as the molecular composition and structure are similar for these two systems, except for their surface properties. The compression resistance of the film was a combined effect of the ionic crosslinks between PAA and DMLPEI at pH 7.4, osmotic swelling due to the presence of charges within the film and the substrate effect from silicon. Because at the measured physiological-relevant ionic strength (0.15 M for PBS), the characteristic length of electrostatic interactions, Debye length, is ~ 1 nm, there was negligible difference in indentation behavior measured via a positively-charged or a negatively
charge probe tips. For an end-attached polymer layer (end-grafted brush or assembled film), the anti-fouling effect due to the conformation entropy and steric interactions of the polymer molecules was induced by the insertion of the proteins into the polymer film that disrupt these molecules from their equilibrium conformation.1 Here, we estimate the compression of a protein molecule into the (PAA/DMLPEI) film due to the mass and dimension of a protein. Given the typical molecular weight of a protein MW = 67 kDa, its mass m ~ 1.1 × 10-22 kg, and the compression force due to weight is F ~ 1.1 × 10-21 N. Using Hertz model, the indentation depth of a spherical protein (radius R ~ 5 nm) into the film could be estimated via the Hertz model, F=
4 Eind R1 / 2 D 3 / 2 2 3 1 −ν
(
)
where ν is the Poisson’s ratio of the film (~ 0.5), R is effective spherical radius of a protein (~ 5 nm), and D is the indentation depth due to the protein mass. The indentation depth, D, was estimated to be ~ 6 × 10-16 m (
