Methocel k 100 m

Triethoxysilane (TREOS, 99%), isopropanol (iPrOH, 99%), HCl (35%), and NH₄OH (28%) were acquired from Merck (Darmstadt, Germany). Hydroxyl terminated polydimethyl siloxane (PDMS, M = 1700 g·mol⁻¹) and γ-aminopropyl trimethoxy silane (APS, 98%) were supplied by ABCR (Karlsruhe, Germany) and Gelest (Morrisville, PA, USA), respectively.
Chitosan (MW = 10⁵ g/mol, deacetylation degree = 97% and viscosity = 92 mPa·s [21 (link)]) was supplied by Nessler (Madrid, Spain) and hydroxypropyl methylcellulose Methocel^® K 100 M (HPMC, MW = 72 × 10⁴ g/mol) was a kind gift from Colorcon Ltd. (Kent, UK). Kollidon^® 30 (polyvinyl pyrrolidone K30, PVP) and magnesium stearate PRS-CODEX (MgSt) were supplied by BASF (Ludwingshafen, Germany) and Panreac (Barcelona, Spain), respectively. Tenofovir (TFV) was acquired from Carbosynth Limited (Compton, UK). Eudragit^® RS (ERS, MW = 407.932 g/mol) was kindly supplied by Evonik (Essen, Germany). Triethyl citrate (TEC) and acetone were acquired from Sigma-Aldrich^® (St. Louis, MO, USA) and Panreac (Barcelona, Spain), respectively.
All other reagents in this study were of analytical grade and used without further purification. Demineralized water was used in all cases.

Hydroxypropyl cellulose (HPC), average molecular weight 850,000, viscosity of 2% aqueous solution 4–6.5 mPa (Klucel™ MF, Ashland, Inc., Covington, KY, USA), and hypromellose 2208 (hydroxypropyl methylcellulose, HPMC), average molecular weight 1,000,000, viscosity of 2% aqueous solution 100 Pa.s (Methocel™ K100M, Colorcon, Orpington, UK), were acquired from Dow, UK. Ethanol (reagent grade) was purchased from Fisher Chemical, UK and ultra-purified water (18.2 MΩ·cm) was produced using a Triple Red Laboratory Technology filtering system (Avidity Science, Aylesbury, UK).