pH-Responsive PEG/PAA Multilayer Assemblies for Reversible Adhesion of Micro-Objects

Abstract

Manipulating micro-objects plays a crucial role in a wide range of fundamental and applied research works. Here, we propose an original strategy based on the chemical modification of a substrate by hydrogen-bonded films elaborated by layer-by-layer (LbL) assemblies of poly­(ethylene glycol) (PEG) and poly­(acrylic acid) (PAA). First, the influence of the polymer molecular weight on the growth of the PEG/PAA multilayer was evaluated. Optical reflectometry analysis used to follow in situ the film buildup revealed a strong dependence of the deposited amount of polymer on the ratio of monomer units of each polymer (n PAA/n PEG). Then, colloidal probe atomic force microscopy (AFM) microscopy was carried out in an aqueous medium to monitor the adhesion forces of multilayer surfaces composed of N polymer layers. Pull-off forces were converted using the Johnson–Kendall–Roberts (JKR) model to access the thermodynamic work of adhesion. Results indicated that PEG/PAA multilayer films exhibit weak adhesion forces that are sensitive to the number of deposited polymer layers at pH 2. In addition, a progressive increase of the solution pH reduced the adhesion due to the destruction of the hydrogen-bonded multilayer film. To simulate the capture and the release of a micro-object, borosilicate particles acting as spherical micro-objects were adsorbed onto a PEG/PAA film. Once again, an increase of the solution pH led to desorption of particles, as shown by optical microscopy. Finally, an AFM tip functionalized by a PEG/PAA multilayer was used to achieve successful micromanipulation operations (capture and release) of a 10 μm diameter borosilicate sphere in an aqueous solution.

The Effects of Temperature on the Assembly of Gold Nanoparticle by Interpolymer Complexation

“…Whereas the assemblies of PEG5k-AuNPs induced at neutral pH have a variation in lattice constant by temperature control, the assemblies induced at lower pH continue to be close-packed with the consecutive thermal treatments. This result, we suggest, reflects that PAA acts as a hook between PEG-AuNPs through hydrogen bonding with PEG (IPC formation), 39 making robust nanoparticle assemblies with high thermal stability (as depicted in Figure 2). Figure 3b shows crystal quality cq = Q 1 /fwhm (fwhm is the full width at half-maximum of the primary peak), the cube of which (cq 3 ) roughly represents the average number of unit cells in a crystalline assembly.…”

Tunable Adhesion and Interfacial Structure of Layer‐by‐Layer Assembled Block co‐polymer Micelle and Polyelectrolyte Coatings

“…Similar behavior has been demonstrated for linear polyelectrolytes, whereby soft uneven LbL structures improve both pull off force and adhesion distance, however even at high layer numbers (>10) linear polyelectrolytes do not achieve the pull off forces measured for BCP assemblies. [26,[30][31][32] Both CAT-and ANI-BCP micelle multilayers show excellent wet adhesion, with values comparable to or better than well-known strong, biological wet adhesives such as mussel adhesive protein [28,33,34] and collagen [17] or bioinspired wet adhesives. [35][36][37] Specifically, CAT-and ANI-BCP micelles exhibited a maximum pull off force of 134 ± 18 and 81 ± 14 mN m −1 , respectively, compared to 136 mN m −1 for mussel protein fibers measured using CP-AFM.…”

“…Similar behavior has been demonstrated for linear polyelectrolytes, whereby soft uneven LbL structures improve both pull off force and adhesion distance, however even at high layer numbers (>10) linear polyelectrolytes do not achieve the pull off forces measured for BCP assemblies. [ 26,30–32 ]…”

Switchable Adhesion: On‐Demand Bonding and Debonding

“…Weak alkaline groups, which can be protonated or deprotonated, are usually utilized for preparing pH‐responsive materials. [ 46 , 122 , 123 , 124 ] Driven by the Schiff base chemistry and catechol groups, Jin et al. developed a pH‐controlled adhesive.…”

“…Weak alkaline groups, which can be protonated or deprotonated, are usually utilized for preparing pH-responsive materials. [46,[122][123][124] Driven by the Schiff base chemistry and catechol groups, Jin et al developed a pH-controlled adhesive. [125] As shown in Figure 12A, the dynamic network is composed of amino-decorated boron nitride nanosheets and aldehyde groupterminated PEG side chains.…”