Simultaneous characterization of physical, chemical, and thermal properties of polymeric multilayers using infrared spectroscopic ellipsometry

Abstract

In this study, multilayered films of polyethylenimine/poly (sodium-p-styrene sulfonate) (PEI)/(PSS) and type I collagen/heparin sodium (COL)/(HEP) were fabricated using the layer-by-layer technique, and fully characterized using Infrared Variable Angle Spectroscopic Ellipsometry (IRVASE) to simultaneously analyze the chemistry, thickness, and roughness of the multilayers with respect to changes in pH of the washing solution, and changes in temperature. Film topography and Young’s modulus were obtained by atomic force microscopy (AFM) and nanoindentation. Our results show that with IRVASE it is possible to analyze the thickness of the multilayers prepared using a washing solution of pH 5, obtaining values of 71.7 nm and 40.3 nm for three bilayers of PEI/PSS and COL/HEP, respectively. Film roughness varies between multilayer systems, obtaining values of 37.76 nm for three bilayers of PEI/PSS and 33.58 nm for three bilayers of COL/HEP. Increasing the pH of the washing solution for PEI/PSS yielded thinner films that were less susceptible to thermal induced changes in film chemistry in the range of 25 – 150 °C. PEI/PSS films decreased in thickness with increasing temperature up to 75 °C, whereas above 75 °C film thickness increased. Through IRVASE, a transition temperature for the PEI/PSS multilayers was observed at 75 °C. Temperatures above 37 °C drastically alter the chemistry and the thickness of the COL/HEP multilayers indicating a possible degradation of the polymers. We obtained, through nanoindentation, a Young’s modulus of 15000 kPa and 9000 kPa for 12 bilayers of PEI/PSS and COL/HEP, respectively. These results demonstrate that, using IRVASE, we can simultaneously evaluate the physical, chemical, and thermal properties of synthetic and natural multilayered polymeric films.

Heparin/collagen surface coatings modulate the growth, secretome, and morphology of human mesenchymal stromal cell response to interferon‐gamma

“…Measurements performed at 0 and 30 days post‐fabrication are shown in Figure 1d. Distinctive functional groups, such as amide I (1700–1,600 cm −1 ) and amide II (1600–1,500 cm −1 ) were identified on the constructed layers confirming the presence of the structural collagen I triple helix and heparin 30 . Functional peaks, including the CH 2 scissoring near 1400 cm −1 , the CN stretching at 1070 and 1040 cm −1 , and the COS stretching vibrations at approximately 950 cm −1 were identified as described in the literature, 30 thus confirming that HEP/COL layers were successfully deposited and preserved their functional groups.…”

“…Distinctive functional groups, such as amide I (1700–1,600 cm −1 ) and amide II (1600–1,500 cm −1 ) were identified on the constructed layers confirming the presence of the structural collagen I triple helix and heparin 30 . Functional peaks, including the CH 2 scissoring near 1400 cm −1 , the CN stretching at 1070 and 1040 cm −1 , and the COS stretching vibrations at approximately 950 cm −1 were identified as described in the literature, 30 thus confirming that HEP/COL layers were successfully deposited and preserved their functional groups. The thickness of the stacked layers was similar between samples (Figure 1e), with an average thickness of 90 nm, which is in concordance to what was previously reported by Castilla et al 29 for layers examined immediately after fabrication at 25°C.…”

“…SPR analysis on the peak min angle of the gold‐coated sensor during HEP/COL assembling support the formation of the polymeric multilayers. The sensogram (Figure 1c) confirms the formation of eight layers of alternating building blocks of HEP and COL, where it can be observed that the growth kinetics of the HEP/COL multilayers is highly dependent by the deposition of COL. Chemical composition of layers deposited on silicon substrates were characterized using the IR‐VASE® instrument, as previously described 29,30 . Measurements performed at 0 and 30 days post‐fabrication are shown in Figure 1d.…”

“…Lyophilized COL from bovine tendon (provided by Integra Lifesciences Holdings Corporation, Añasco, PR) and HEP sodium (PH3005, Celsus Laboratories, Cincinnati, OH) were used to construct multilayers on flat bottom tissue culture treated 96‐well plates from NEST (701,001, ThermoFisher Scientific, Nashville, TN), following the procedure as described by Castilla et al 30 Briefly, polymers were dissolved at a concentration of 1.0 mg/ml in acetate buffer pH 5 (0.1 M sodium acetate anhydrous and 0.1 M acetic acid glacial dissolved in ultrapure water 18 MΩ‐cm from tap producing RiOs™ and Milli‐Q® water system). LbL technique was employed to construct polymeric multilayers of HEP/COL (ended either in HEP or COL).…”

“…Infrared Variable Angle Spectroscopic Ellipsometry (IR‐VASE®‐Mark II, J.A. Woollam Co., Inc. IR‐VASE, Lincoln, Nebraska) was used to determine the thickness and chemistry of the HEP/COL multilayered substrates at 25°C as described by Castilla et al 30 Characterization was performed at 0 and 30 days postfabrication after storage at room conditions, 22°C and 40% relative humidity. The identification of relevant functional groups for all samples was performed in a wavenumber range from 800–1700 cm −1 and the measurements by a deuterated triglycine sulfate (DTGS) detector with an angle of incidence of 70°, a spectral resolution of 16 cm −1 , 200 scans per cycle, 1 cycle, bandwidth of 0, minimum intensity ratio of 5, sample type as isotropic, zone average polarizer, and rotating compensator ellipsometry (RCE) analyzer on zone average analyzer.…”