Synthesis and characterization of well-defined ligand-terminated block copolymer brushes for multifunctional biointerfaces

- Polymer brushes of acrylamide afford long term (> 4 weeks) passivation in cell culture.
- Fibroblasts adhesion confirmed on RGD modified block copolymer brushes.
- Well-defined block copolymer brushes synthesized by SI-ATRP were fully characterized.

Polymer brush-functionalized surfaces promise to provide access to absolute control over the biointerface functionality. To enable in this context systematic studies of cell attachment and proliferation, we investigated the synthesis of well-defined block copolymer brushes of poly(acrylamide) (PAAm), poly(oligo(ethylene glycol)methylether methacrylate) (POEGMA) and poly(acrylic acid) (PAA) by surface-initiated atom transfer radical polymerization (SI-ATRP) and subsequently the introduction of exposed ligands for cell adhesion. Detailed X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy, time of flight secondary ion mass spectrometry (ToF-SIMS) and ellipsometry measurements unraveled the progress and the livingness of the homo- and copolymerization of the three monomers. In particular, the correlation of the temporal evolution of the ellipsometric thickness with the decrease in bromine content pointed to a progressive loss of active chain ends, which limits the attainable maximum brush thickness. Non-fouling brushes of POEGMA and PAAm exhibited long term stability and full functionality in cell medium for more than 1 month. Block copolymer brushes with defined thickness comprising a non-fouling POEGMA or PAAm block and a short terminal PAA block were functionalized with a peptide containing the arginine-glycine-aspartic acid (RGD) sequence. Cell attachment assays with fibroblasts revealed facilitated cell adhesion on RGD modified block copolymer brushes. The specific signaling was further confirmed with inhibited cell adhesion on arginine-alanine-aspartic acid (RAD) functionalized brushes (negative control). Hence on the basis of the unraveled synthesis behavior of block copolymer brushes and side chain modification a versatile strategy to fabricate biologically inert surfaces that facilitate integrin-specific cell adhesion has been developed.

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