**2. Materials and Methods**

#### *2.1. Materials*

Polyamide 6,6 (PA66, also known as nylon 6,6 or Poly(N,N -hexamethyleneadipinediamide)), 2,2,2-Trifluoroethanol (TFE), formic acid (FA), 1,1,1,3,3,3-Hexafluoro-2-propanol (HFIP), human insulin, human Ig G and bovine serum albumin (BSA) were purchased from Sigma-Aldrich, Dorset, UK, and the protein determination kit was purchased from Cayman Chemical, Ann Arbor, MI, USA. Dulbecco's Modified Eagle Medium (DMEM), Roswell Park Memorial Institute 1640 (RPMI-1640) medium, fetal bovine serum (FBS), trypsin-Ethylenediaminetetraacetic acid (EDTA), phosphate-buffered

saline (PBS, 1×), Penicillin-Streptomycin (Pen-Strep, 100×) and Alamar blue were purchased from Thermo Fisher Scientific, Waltham, MA, USA.
