Steven R. Carter

Highly branched poly-(N-isopropylacrylamide)s with arginine–glycine–aspartic acid (RGD)- or COOH-chain ends that form sub-micron stimulus-responsive particles above the critical solution temperature

Highly branched poly(-isopropyl acrylamide)s with peptide-end groups form colloidally stable dispersions of sub-micron particles above the lower critical solution temperature.

Sub-micron poly(N-isopropylacrylamide) particles as temperature responsive vehicles for the detachment and delivery of human cells

We describe the first example of particulate materials that can detach cultured cells and then release them intact in a temperature controlled manner. Topologically open microgels composed of water swollen highly branched polymers prepared from poly(N-isopropylacrylamide) (PNIPAM) were modified with a cell-adhesive peptide (GRGDS) to produce particles for gently detaching and then transferring cultured cells to new substrates. The particles bind to cell surface integrins on both dermal fibroblasts and endothelial cells and at temperatures above the lower critical solution temperature (34 °C) remove cells from their normal culture substrates. Brief (45 min) cooling of the resultant particle–cell dispersion to beneath 34 °C releases the cells to grow on new substrates. This avoids the need for trypsinisation to detach cells or centrifugation to collect cells post-detachment and offers a flexible approach to cell detachment and transport which is compatible with normal cell culture methodologies.

Temperature-dependent phagocytosis of highly branched poly(N-isopropyl acrylamide-co-1,2 propandiol-3-methacrylate)s prepared by RAFT polymerization

Highly branched poly(N-isopropyl acrylamide-co-1,2 propandiol-3-methacrylate)s with imidazole end groups and containing anthramethyl methacrylate (AMMA) were prepared. The branch points were produced by incorporating a styryl dithioate ester (a RAFT monomer). The inclusion of AMMA ensures that the polymers fluoresce in the blue region so that they can be visualized in cells in culture. The feed composition was designed to provide lower critical solution temperatures (LCST) between 30 and 37 °C, and therefore the polymers are above the LCST at the usual temperature for culture of human cells. Inclusion of 1,2 propandiol-3-methacrylate (GMA) results in the formation of stable aggregates above the LCST rather than flocculated masses of polymer, and these colloidally stable sub-micron particles can undergo phagocytosis into human dermal fibroblasts. The phagocytosis is temperature dependant and does not occur below the LCST (at 30 °C) when the polymers are in the open-chain fully solvated and non-aggregated state.