The present invention relates to polymer microgel beads having a polymeric matrix with nanomagnetic particles dispersed substantially uniformly therethrough, wherein a steric stabiliser is associated with the particles, the steric stabiliser being a polymeric material that (i) does not form part of the polymeric matrix of the beads, and (ii) comprises a steric stabilising polymeric segment and an anchoring polymeric segment, wherein the steric stabilising polymeric segment is different from the anchoring polymeric segment, and wherein the anchoring polymeric segment has an affinity toward the surface of the nanomagnetic particles and secures the stabiliser to the particles.
