Disclosed are polymer microgel beads (a) having a polymeric matrix that can absorb and be swollen by an aqueous liquid, and (b) incorporating nanomagnetic particles, wherein a steric stabiliser is associated with the particles which are distributed substantially uniformly throughout the polymeric matrix, the steric stabiliser being a polymeric material that (i) forms at least 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. Also disclosed is a method for the preparation of the polymer microgel beads comprising providing a dispersion comprising (i) providing a dispersion comprising a continuous organic phase and a dispersed aqueous phase, the dispersed aqueous phase comprising hydrophilic liquid and nanomagnetic particles dispersed throughout the aqueous phase, the nanomagnetic particles being maintained in their dispersed state by a steric stabiliser, wherein the steric stabiliser is a polymeric material comprising: a) 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 nanomagnetic particles and binds the steric stabiliser to the particles and b) one or more reactive functional group (ii) removing hydrophilic liquid from the aqueous phase and (iii) promoting a reaction between the reactive functional groups of the steric stabilisers to thereby form the polymer microgel beads incorporating the nanomagnetic particles. The microgel beads are useful in hyperthermia treatments of tissue such as cancerous tissue. The beads are administered to a subject and exposed to a magnetic field, causing the beads to radiate heat at a target site.
