PLL–Poly(HPMA) Bottlebrush-Based Antifouling Coatings: Three Grafting Routes

In this work, we compare three routes to prepare antifouling coatings that consist of poly­(l-lysine)–poly­(N-(2-hydroxypropyl)­methacrylamide) bottlebrushes. The poly­(l-lysine) (PLL) backbone is self-assembled onto the surface by charged-based interactions between the lysine groups and the negatively charged silicon oxide surface, whereas the poly­(N-(2-hydroxypropyl)­methacrylamide) [poly­(HPMA)] side chains, grown by reversible addition–fragmentation chain-transfer (RAFT) polymerization, provide antifouling properties to the surface. First, the PLL–poly­(HPMA) coatings are synthesized in a bottom-up fashion through a grafting-from approach. In this route, the PLL is self-assembled onto a surface, after which a polymerization agent is immobilized, and finally HPMA is polymerized from the surface. In the second explored route, the PLL is modified in solution by a RAFT agent to create a macroinitiator. After self-assembly of this macroinitiator onto the surface, poly­(HPMA) is polymerized from the surface by RAFT. In the third and last route, the whole PLL–poly­(HPMA) bottlebrush is initially synthesized in solution. To this end, HPMA is polymerized from the macroinitiator in solution and the PLL–poly­(HPMA) bottlebrush is then self-assembled onto the surface in just one step (grafting-to approach). Additionally, in this third route, we also design and synthesize a bottlebrush polymer with a PLL backbone and poly­(HPMA) side chains, with the latter containing 5% carboxybetaine (CB) monomers that eventually allow for additional (bio)­functionalization in solution or after surface immobilization. These three routes are evaluated in terms of ease of synthesis, scalability, ease of characterization, and a preliminary investigation of their antifouling performance. All three coating procedures result in coatings that show antifouling properties in single-protein antifouling tests. This method thus presents a new, simple, versatile, and highly scalable approach for the manufacturing of PLL-based bottlebrush coatings that can be synthesized partly or completely on the surface or in solution, depending on the desired production process and/or application.