Optimisation of grafting of low fouling polymers from three-dimensional scaffolds via surface-initiated Cu(0) mediated polymerisation

Abstract

Electrospun fibres represent a realistic implantable scaffold containing most of the structural three-dimensional (3D) characteristics of the extracellular matrix. However, as a result of their often synthetic nature, surface energy and chemistry, these scaffolds may adsorb a layer of non-specific proteins which can evoke a foreign body response. The precise surface modification of the scaffolds is challenging due to the complex geometrical and structural organization of the fibre meshes, that may limit the efficacy and completeness of approaches used. One flexible strategy that has gained attention is the use of reversible deactivation radical polymerisation (RDRP) techniques, which allow the creation of polymer brushes with controlled molecular weight, whilst retaining fibre morphology. In this study, protein adsorption was reduced with grafting of poly(N,N-dimethylacrylamide) (PDMA), poly(N-(2-hydroxypropyl)acrylamide) (PHPA) and poly(N-acryloylmorpholine) (PNAM) via surface-initiated (SI)-Cu(0) mediated radical polymerisation, from the surface of electrospun fibres prepared using a blend of bromine terminated poly(L-lactide) (PLA-Br) and poly(D,L-lactide-co-glycolide) (PLGA). Optimisation of the levels of Cu(I)Br, Me₆TREN and the presence and concentration of a sacrificial initiator facilitated the grafting of well-controlled polymers brushes in less than one hour. Surface characterisation of the grafted scaffolds using X-ray photoelectron spectroscopy (XPS) and time of flight secondary ion mass spectroscopy (ToF-SIMS), and direct analysis of the molecular weight and polydispersity of polymer formed in solution during the reaction as well as the grafted polymer layer confirmed successful, controlled modification. Finally, protein adsorption experiments demonstrated the low adsorption properties of all polymer coatings with PDMA showing superior performance.