*2.4. Protein Diffusion Assay*

PA66 capsules (1 cm width × 2 cm length × 1 mm thickness) made from 7.5% (*w*/*v*) polymer solution with 15 kV voltage, 15 cm distance and 0.5 mL/min flow rate, were sterilized by autoclaving and saturated with 1× PBS for 3 h in an incubator (5% CO2, 37 ◦C). Capsules were placed in a 6-well plate and simultaneously loaded with insulin, Ig G or BSA solution (1 mg/mL). The capsule loading port was tied tightly with a sterile nylon thread and kept in a CO2 incubator overnight. The contents were manually mixed at regular intervals. The spent protein solution released from the capsule was collected and assayed by the Bradford method following the kit instructions (Cayman Chemical, Ann Arbor, MI, USA). Briefly, 100 μL of diluted protein solution was mixed with equal amounts of assay reagent. The contents were incubated at room temperature for 5 min and the absorbance was read at 595 nm in a multi-well plate reader (Spectra Max i3x, Molecular Devices, San Jose, CA, USA). Results were compared with a standard curve made using known concentrations of insulin, Ig G and BSA.
