Figure 1. Descriptive images of the MDP.

(a) 3D schematic of the MDP (Solidworks, Dassault Systemes, USA). The MDP is composed of two distinct units: a drug reservoir and an actuator. The actuator is composed of a plunger and barrel. The drug reservoir is filled with insulin solution (109 U ml⁻¹) after assembly. To prepare the insulin solution, insulin in powder form (short acting; Sigma-Aldrich, MO, USA) was dissolved in sterile PBS at pH 7.4. (b) Optical image of the MDP and pen-type external device. Scale bar, 1 cm. (c) The actuation principle of the MDP (Solidworks, Dassault Systemes, USA) is as follows: the external magnet is applied; the plunger moves upward; the drug solution in the reservoir is aspirated into the barrel; the external magnet is removed; the plunger moves downward; and the insulin is released through the one-way check valve.