Ultralow Protein Adsorbing Coatings from Clickable PEG Nanogel Solutions: Benefits of Attachment under Salt-Induced Phase Separation Conditions and Comparison with PEG/Albumin Nanogel Coatings

Abstract

Clickable nanogel solutions were synthesized by using the copper catalyzed azide/alkyne cycloaddition (CuAAC) to partially polymerize solutions of azide and alkyne functionalized poly(ethylene glycol) (PEG) monomers. Coatings were fabricated using a second click reaction: a UV thiol-yne attachment of the nanogel solutions to mercaptosilanated glass. Because the CuAAC reaction was effectively halted by the addition of a copper-chelator, we were able to prevent bulk gelation and limit the coating thickness to a single monolayer of nanogels in the absence of the solution reaction. This enabled the inclusion of kosmotropic salts, which caused the PEG to phase-separate and nearly double the nanogel packing density, as confirmed by Quartz Crystal Microbalance with Dissipation (QCM-D). Protein adsorption was analyzed by single molecule counting with total internal reflection fluorescence (TIRF) microscopy and cell adhesion assays. Coatings formed from the phase-separated clickable nanogel solutions attached with salt adsorbed significantly less fibrinogen than other 100% PEG coatings tested, as well as poly-L-lysine-g-PEG (PLL-g-PEG) coatings. However, PEG/albumin nanogel coatings still outperformed the best 100% PEG clickable nanogel coatings. Additional surface crosslinking of the clickable nanogel coating in the presence of copper further reduced levels of fibrinogen adsorption closer to those of PEG/albumin nanogel coatings. However, this step negatively impacted long-term resistance to cell adhesion and dramatically altered the morphology of the coating by atomic force microscopy (AFM). The main benefit of the click strategy is that the partially polymerized solutions are stable almost indefinitely, allowing attachment in the phase-separated state without danger of bulk gelation, and thus, producing the best performing 100% PEG coating that we have studied to date.

Reactive Precursor Particles as Synthetic Platform for the Generation of Functional Nanoparticles, Nanogels, and Microgels

“…Elbert and co‐workers exploited the concept of separate, sequential “click” reactions for the preparation and attachment of PEG nanogels to glass surfaces in order to prepare protein resistant coatings . The PEG nanogels were prepared via CuAAC of multiarmed PEG‐azide and PEG‐alkyne monomers.…”

“…Then, radical thiol–yne reaction was used to attach the nanogels to mercaptosilanated glass. Additional surface crosslinking of the nanogel coating was performed via CuAAC of residual end groups after attachment to the glass substrate …”

Gradient polymer networks formed by photopolymerization with self‐floating polysiloxane‐containing nanogel

“…Nanogels, formed by physically or chemically cross‐linked polymer networks with nanoscale size, have been widely researched in the fields of tissue engineering, photonic materials, drug delivery, dental materials, modifiers for coatings and polymer composites, because of their versatile structures, large number of chain ends and the ability to incorporate stimuli‐responsive functionalities …”

Tuning the surface microstructure and gradient properties of polymers with photopolymerizable polysiloxane-modified nanogels

“…Nanogels, which are internally crosslinked and cyclized single or multi-chain polymeric particles with three-dimensional polymer networks 13 , have great potential for use in drug delivery 14 , dental materials 15 , tissue engineering 16 , photonic materials 17 , modifiers for coatings and polymer composites 18 because of their tunable chemical composition and three-dimensional physical structures, large number of chain ends, good mechanical properties, and biocompatibility. It has been demonstrated that high molecular weight, reactive nanogels of approximately 10 nm in dimension when dispersed in and swollen by matrix monomer can be used to reduce polymerization shrinkage and stress without compromise to other critical polymer properties 19 and help reinforce the mechanical properties of the final polymer network by physical entanglement and potential covalent crosslinking between nanogel and the resin matrix.…”