Chitosan and polycaprolactone blended PDMS coatings improve biocompatibility of magnetic elastomers

PDMS/NdFeB composites are promising materials for soft magnetic actuators, but NdFeB particles corrode in body fluids and release toxic metal ions, limiting their biomedical use. We developed ~ 100 µm spin-coated PDMS-chitosan (PDMS-CHIT) and PDMS-polycaprolactone (PDMS-PCL) coatings that solve this problem. Over 24 weeks of immersion, these coatings reduced neodymium and iron release by more than 95%, keeping ion concentrations well below cytotoxicity thresholds. Importantly, the PDMS-PCL coating fully preserved magnetorheological actuation (ΔG' ≈ 61 kPa under 0.5 T, comparable to uncoated composite), while PDMS-CHIT provided superior ion barrier at the cost of reduced actuation force. Biological validation confirmed cytocompatibility with fibroblasts, hemocompatibility with erythrocytes, and strong suppression of bacterial biofilm formation. These results establish a validated materials platform for biocompatible soft magnetic actuators.