Anhydrous citric acid

The following materials
were used in the study: OLP (Tokyo Chemical Industry, Zwijndrecht,
Belgium); Gantrez S-97 (a copolymer of methyl vinyl ether and maleic
acid), PVP (58 and 360 kDa, sold under the product brand names Plasdone
K-29/32 and K-90), and β-CD, HP-β-CD, γ-CD, and
HP-γ-CD (sold under the product brand names of Cavamax W7, Cavitron
W7, Cavamax W8, and Cavasol W8, respectively, Ashland, Vale Industrial
Estate, Kidderminster, U.K.); sorbitol, poly(ethylene glycol) (PEG,
MW 3400 and 10,000 Da), poly(vinyl alcohol) (PVA, MW 85–124
kDa, 87–89% hydrolyzed), PVA (MW 9–10 kDa, 80% hydrolyzed),
and d-α-tocopherol poly(ethylene glycol) 1000 succinate
(TPGS, Sigma-Aldrich, Steinheim, Germany); crospovidone (CPV, sold
under the product brand name Kollidon CL-SF, O-BASF, Ludwigshafen,
Germany); anhydrous citric acid, anhydrous glucose, and anhydrous
sodium carbonate (Na₂CO₃) (BDH Laboratory Supplies,
Poole, Dorset, England); Parafilm M laboratory film (Bemis Company
Inc., Soignies, Belgium); siliconized release liner (Rexam Release
B.V., Apeldoom, The Netherlands); pluronic F-108 (VWR Chemicals LLC,
Solon, OH); poly(lactic acid) (PLA) (Ultimaker, Geldermalsen, Netherlands);
Kinesiology Sports tape (95% cotton, 5% spandex; 5 × 500 cm;
Proworks Corporation, Corvallis, OR); and microfoam surgical tape
and Tegaderm dressing (3 M, Bracknell, Berkshire, U.K.).

PRA base (PRAB) and salt
(PRAS) were purchased from Cangzhou Enke Pharma-tech Co. Ltd. (China).
Acetonitrile (>99.9%), phosphate-buffered saline (PBS) tablets
(pH
7.4), PVA 9–10 kDa, PVA 31–50 kDa, PEG10,000, sorbitol,
and trifluoracetic acid (TFA) were purchased from Sigma-Aldrich (Dorset,
UK). Gantrez S-97 and PVP (MW 58 kDa), sold under the product brand
name Plasdone K-29/32, were obtained from Ashland (Worcestershire,
UK). Microcrystalline cellulose (MCC) was purchased from DFE Pharma
(Klever Strasse, Germany). Anhydrous citric acid and anhydrous sodium
carbonate (Na₂CO₃) were obtained from BDH Laboratory
Supplies (Dorset, UK). LCMS/MS grade methanol and formic acid were
purchased from Sigma-Aldrich (Gillingham, UK), with ultrapure water
(18.2MΩ-cm) produced in-house using a Millipore water purification
system (Millipore, Cork, Ireland).

Glucose, sucrose, fructose, 3,3′,5,5′-tetramethylbenzidine, Glucose oxidase from Aspergillus niger, glutaraldehyde solution grade II 25% in H₂O, copper (II) chloride dihydrate (CuCl₂·2H₂O), hydrogen peroxidase (30%), and urea were purchased from Sigma-Aldrich (MA, USA). Acetic acid (99.8%) was purchased from Honeywell Fluka (Germany). Citric acid anhydrous was purchased from J. T. Baker (NJ, USA). Chitosan (50,000–150,000 Da) was purchased from Biosynth Carbosynth (UK). Milli-Q water of 18.2 MΩ cm was produced using the Millipore water purification system. All the chemicals used in these assays were of analytical grade.
The UV–visible absorbance and fluorescence spectra were recorded on a Spectra Max® ID3 multimode microplate reader (Molecular Devices, CA, USA). X-ray photoelectron spectroscopy was performed on a Thermo scientific K-Alpha X-ray spectrometer (MA, USA). The high-resolution transmission electron microscopy images were acquired using a JEM-2001F instrument (JOEL, Japan). The Cu-CD/chitosan film morphology was recorded using a field emission scanning electron microscope (FE-SEM, JSM-7500F, JOEL, Japan). The Fourier-Transform Infrared (FT-IR) spectra were recorded on a Spectrum One spectrometer (PerkinElmer, MA, USA).