Magnesium chloride hexahydrate

Hydroxypropylmethylcellulose (HPMC; Methocel K100 Premium LV) was a gift from Colorcon Limited (Dartford, UK), and magnesium aluminium silicate (MAS) was a gift from R.T. Vanderbilt Company Inc. (Norwalk, CT, USA). Sodium hydroxide, potassium dihydrogen phosphate, and gelatine were purchased from Fluka Analytical (Buchs, Switzerland). Nicotine (liquid form), sodium alginate (SA; molecular weight 120,000–190,000 g/mol, mannuronate/guluronate ratio 1.56), submaxillary mucin from porcine stomach, PBS tablets (pH 7.4), 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), Krebs–Ringer bicarbonate buffer, and dimethyl sulfoxide (DMSO) were all obtained from Sigma Aldrich (Dorset, UK). Sodium acetate, trimethylamine, and glycerol (GLY) were purchased from Fisher Scientific (Loughborough, UK). Commercially available NIC-loaded strips (NiQuitin^®) was purchased from a local pharmacy (Gillingham, Kent). Calcium chloride dehydrate, sodium chloride, sodium phosphate dibasic, magnesium chloride hexahydrate, potassium carbonate hemihydrate, sodium phosphate monobasic monohydrate, Sodium acetate, and trimethylamine were all purchased from Fisher Scientific (Loughborough, UK). The EpiOral^TM buccal tissue kit (ORL-200) was purchased from MatTek Corporation (Ashland, MA, USA).

Iron(II) chloride tetrahydrate, Iron(III) chloride hexahydrate, sodium borohydride, sodium hydroxide, 30% ammonium hydroxide, Tris buffer (2 M), magnesium chloride hexahydrate, calcium chloride hexahydrate and dextran-low fraction for biochemistry (M_w ~ 90 kDa) were obtained from Fisher Scientific (Fair Lawn, NJ) and used as received. Pentaerythritol glycidyl ether was obtained from Frontier Scientific, Inc. (Logan, UT) and used as received. Water was double-deionized using a Millipore Milli-Q system to produce 18 MΩ deionized water. Sealable 5 mL microwave vials (CG-4920- 01) were obtained from Chemglass, Inc. (Vineland, NJ) and used as received. Stock electrolyte solutions were prepared by dissolving the appropriate amount of electrolyte into DI H₂O followed by filtration through a 0.2 μm nylon filter to remove any impurities or dust particles. Tangential flow filtration was performed using a KrosFlo Research IIi TFF system from Spectrum Labs, Inc. (Rancho Dominguez, CA).

First, 4-tert-butylcalix[4]arene-tetraacetic acid tetraethyl ester (sodium ionophore X), bis(2-ethylhexyl) sebacate (DOS), poly(vinyl chloride) (PVC), tetrahydrofuran (THF), hydrochloric acid (HCl), silver nitrate (AgNO₃), and polyvinyl butyral (PVB) were purchased from Sigma Aldrich. Sodium tetrakis-[3,5-bis(trifluoromethyl)phenyl] borate (NaTFPB) was purchased from Alfa Aesar. Sodium chloride (NaCl), potassium chloride (KCl), calcium chloride dihydrate (CaCl₂·2H₂O), and magnesium chloride hexahydrate (MgCl₂·6H₂O) were purchased from Fisher Chemical. Carbon black (Vulcan XC 72R) was obtained from FuelCellStore. Silicone elastomers, including Ecoflex 00-30 and polydimethylsiloxane (PDMS, Sylgard 184), were obtained from Smooth-On and Dow Corning, respectively. Fast-drying silver paint was purchased from Ted Pella. 1X Phosphate-buffered saline (PBS; pH = 7.4) was obtained from Gibco by Life Technologies (Carlsbad, CA, USA).