A 2 g amount of chitosan flake was added into 100 ml 2%(w/w) acetic acid in a beaker and the contents in the beaker were mixed on a hot plate stirrer at 70 °C and 200 rpm for 6 h. Then, a 2 g amount of cellulose powder was added into the chitosan solution and the mixing was continued for another 6 h at room temperature (22–23 °C) and 200 rpm on the stirrer. The blended solution was then injected in droplets into a 1 M NaOH solution to form hydrogel beads through a vibration nozzle system (Nisco Encapsulation Unit, LIN-0018, with a nozzle size of 300 μm; see Fig. 1). The chitosan–cellulose hydrogel beads were allowed to stay in the NaOH solution with slow stirring for another 12 h for hardening. The hardened beads were finally separated from the NaOH solution and were washed with DI water in a large beaker until the solution pH became the same as that of the fresh DI water. Then, the beads were stored in DI water for further use