Temperature-Switchable Control of Ligand Display on Adlayers of Mixed Poly(lysine)‑g‑(PEO) and Poly(lysine)‑g‑(ligand-modified poly‑N‑isopropylacrylamide)

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Temperature-Switchable Control of Ligand Display on Adlayers of Mixed Poly(lysine)‑g‑(PEO) and Poly(lysine)‑g‑(ligand-modified poly‑N‑isopropylacrylamide), Biomacromolecules2016 May 9;17(5):1727-36

 

Spatiotemporal control of surface properties is highly in demand for a diversity of approaches that aim to endow layers of polymers and surface-attached polymer brushes with controlled association to proteins, biocolloids, cells, and recently via in situ stimuli-responsiveness. For instance, thick swellable polymer patterns have been designed to control surface accessibility. Thinner polymer brushes are used in diverse applications including assemblies of nano- or microparticles, biosensors, control of bacterial adhesion  or cell spreading,  and controlled flow in microfluidic and separative techniques. A common design strategy to prepare responsive polymer layers relies on transitions from poor to good solvent conditions, which is conveniently based on conformational transition at the lower critical solution temperature (LCST) in water. LCST properties have been extensively studied in aqueous solutions and in polymer layers (e.g., with derivatives of poly(N -isopropylacrylamide), PNIPAM). The critical challenge for surface-targeted applications is now to achieve specifi city, that is, to tailor polymer layers undergoing phase transitions in 2D that provide on demand switchable accessibility of a particular ligand of interest. Reaching this goal is demanding to chemists, as it depends on controlling many key parameters on surfaces, including grafting density and length of polymer chains, distribution of comonomers in copolymer and/or growth of chains having diff erent chemical natures. Successful proofs of concept have been established based on highly controlled surface polymer chemistry, or deposition of SAM on gold layers. But the need for specialized chemistry limits the broadening of such approaches and their wide adoption by biologists. In this context, it is important to develop more versatile coating systems aff ording robust control and facile modulation, by nonexperts, of surface layer composition, and adjustable responsiveness to stimuli.

 

 

 

Adsorption of cationic comblike derivatives of poly(lysine) allows facile coating and passivation (e.g., PEGylation) of glass. It was here extended to control the surface deposition and presentation of biotin (used as a model ligand), via a versatile strategy based on (i) reactive parent polymer strands, that are easily modified in bulk with any amine-containing side group prior to be coupled on PLL lysine groups, and (ii) T–responsive PNIPAM macrografts that hide the (biotin) ligand in their collapsed form and display them at low temperature. Robust, mixed adlayers with control composition were obtained from simple minute-long bath application on glass. Control of specific binding of beads, by variation of surface composition and/or temperature, was established. Measurements by AFM of the PLL-g -PNIPAM layers showed that sharp surface transition (variation of thickness, rigidity, and roughness) occurs at 32 °C. PLL derivatives enable straightforward functionalization with adjustable surface density of functional, T -responsive strands by deposition of PLL-g -PNIPAM-co -ligand:PLL-g -PEG mixed solutions. This functional coating is implemented with no need for specialized chemistry skills, and it enables to adjust on demand the accessibility of a ligand of interest. This is an asset for applications aiming to optimize specifi c binding and surface density of bioactive ligands.

 

 

Résumé: 

Biomacromolecules2016 May 9;17(5):1727-36

 

Adlayers of poly(lysine)-g -PEG comblike copolymer are extensively used to prepare cell-repellant and proteinrepellent surfaces by a straightforward coulomb-driven adsorption that is compatible with diverse substrates (glass, Petri dish, etc.). To endow surfaces with functional properties, namely, controlled ligand-protein binding, comblike poly(lysine) derivatives were used to deposit temperature-responsive poly(NIPAM) macrografts mixed with PEG ones on glass surfaces. Simple surface immersion in mixed solutions of biotin-modifi ed poly(lysine)-g -poly(N -isopropylacrylamide) and poly(lysine)-g -poly(ethylene oxide) yielded robust adlayers whose composition refl ected the ratio between the two polymers in solution. We show by fluorescence imaging, and comparison with repellent 100% PEGylated patterns, that specifi c binding of model avidin/particle conjugates (diameters of ca. 10 or 200 nm) was controlled by temperature switch. The biotin ligand was displayed and accessible at low T , or hidden at T  > LCST. Topography and mechanical mapping measurements by AFM confi rmed the swelling/collapse status of PNIPAM macrografts in the adlayer at low/high T , respectively. Temperature-responsive comblike PLL derivative that can spontaneously cover anionic interfaces is a promising platform enabling good control on the deposition and accessibility of biofunctional groups on various solid surfaces

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Références: 

Temperature-Switchable Control of Ligand Display on Adlayers of Mixed Poly(lysine)‑g‑(PEO) and Poly(lysine)‑g‑(ligand-modified poly‑N‑isopropylacrylamide)

 

F. Dalier, F. Eghiaian, S. Scheuring, E. Marie, and C. Tribet

 

Biomacromolecules. 2016 May 9;17(5):1727-36

 

doi: 10.1021/acs.biomac.6b00136