la3051115_si_001.pdf (2.07 MB)
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
journal contribution
posted on 2013-03-26, 00:00 authored by Casey
D. Donahoe, Thomas L. Cohen, Wenlu Li, Peter K. Nguyen, John D. Fortner, Robi D. Mitra, Donald L. ElbertClickable 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 cross-linking
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.