Biorelated Polyelectrolyte Coatings Studied by in Situ Attenuated Total Reflection–Fourier Transform Infrared Spectroscopy: Deposition Concepts, Wet Adhesiveness, and Biomedical Applications

Abstract

In this conceptual contribution, thin functional coatings consisting of either pure polyelectrolytes (PELs) or complexes between oppositely charged PELs at model and applied substrates are outlined. Latter PEL/PEL complexes were deposited by two concepts. In a first well-known concept, PEL multilayers (PEM) were consecutively deposited according to the layer-by-layer (LbL) technique. In a second less known concept, PEL complex (PEC) nanoparticles (NPs) preformed by mixing polycation (PC) and polyanion (PA) solutions were deposited in one step. Both concepts based on binary oppositely charged PELs are compared to one based on a single polycation system. Examples shall be given on adhesiveness, nanostructure, and biomedical applications of PEM and PEC NP coatings. In situ attenuated total reflection (ATR) infrared (IR) spectroscopy, circular dichroism (CD), and scanning force microscopy (SFM) were used for molecular, optical, and microscopic characterization. At first, results on the adsorbed amount and wet adhesiveness of pure (single-component) PEL coatings as a function of charge density are given to motivate coatings of mixed oppositely charged PELs. Second, the wet adhesiveness of PEM and PEC NP coatings of identical PEL compounds in aqueous media varying the molar charge ratio ( n-/ n+) and the deposition step z, respectively, is compared. Upon comparing the three PEL deposition concepts, it is suggested that the lack or absence of excess charge at the PEL/surface interface is one of the main factors for the wet adhesiveness of all pure PEL, PEM, and PEC NP coatings. Finally, the potential of PEM and PEC NP coatings for biomedical applications is outlined. Concerning biopassivation, PEM coatings excessed or terminated by PA repel proteins with low isoelectric points. Concerning bioactivation, PEM coatings loaded with antibiotics as well as PEC NP coatings loaded with therapeutic bisphosphonates showed retarded, optionally temperature responsive drug release for applications in acute surgery and bone healing, and immunoglobulin/PEL complex coatings might open theranostic applications.

The Anomalous Influence of Polyelectrolyte Concentration on the Deposition and Nanostructure of Poly(ethyleneimine)/Poly(acrylic acid) Multilayers

“…This can be related to the fact that, upon shearing adsorption of PEL to the PEM, desorption of loosely bound PEL from the PEM might be enhanced, making the adsorption/desorption competition more pronounced. Figure 10 summarizes the assumed PEM formation process, which is based on the competition of uptake of PEL from the bulk solution (A) at the actual oppositely charged outermost PEL layer and the release of outermost PEL (B) under the formation of a soluble complex with the respective oppositely charged PEL in the bulk solution, as has been suggested [28,29,52]. Presumably, released PELs forming soluble complexes may also stem, besides the outermost layer, from the “diffusive zone” of PEMs defined in [24,25,26,27].…”

“…Simplified scheme of the PEM formation process with PEL ad/desorption competition [52] (reprinted by kind permission of the ACS).…”

Thermoresponsive Catechol Based-Polyelectrolyte Complex Coatings for Controlled Release of Bortezomib

“…Since the scale of requirements towards the applied coatings is very broad and can differ significantly with the respective drug, only highly alterable and adjustable systems qualify. Suitable systems are provided e.g., by polyelectrolyte complex nanoparticles (PEC NPs) [8,11,14,15]. In this approach, polyanions and polycations are complexed to nanoparticles in solution, which are subsequently immobilized to form the intended coatings.…”

Switchable Release of Bone Morphogenetic Protein from Thermoresponsive Poly(NIPAM-co-DMAEMA)/Cellulose Sulfate Particle Coatings

“…In detail the PNIPAM-DMAEMA compound was lost to a minor and the CS compound was lost to a larger extent. As an explanation CS was in a slight excess over the PNIPAM-DMAEMA component and not electrostatically loosely bound parts could be rinsed off easier as we pointed out for another PEC system therein [13]. Furthermore, pH = 7.0 was optimum for wet-adhesiveness, while at pH = 9.0 largest loss of PEC coating was observed.…”