Glutaraldehyde

Alginic acid sodium salt from brown algae with medium viscosity (guluronic acid/mannuronic acid ratio: 70/30, Mw 403 kDa, 3170 cps) and calcium chloride (CaCl₂; Mw 110.98 g/mol, 99.99% purity) were provided by Sigma Aldrich (Madrid, Spain). Hydroxyapatite (HA; Mw 502.31 g/mol, reagent grade purity, micropowder) was provided by Fluidinova (Moreira da Maia, Portugal), glutaraldehyde (GA; 50% aqueous solution) by Scharlau (Barcelona, Spain) and hydrogen peroxide (H₂O₂; 30% aqueous solution) by Honeywell Fluka (Madrid, Spain). CO₂ (purity > 99.9%) was supplied by Nippon Gases (Madrid, Spain) and absolute ethanol (EtOH) by VWR (Radnor, PA, USA). Water was purified using reverse osmosis (resistivity > 18 MΩ·cm; Milli-Q, Millipore^®, Madrid, Spain).

Polymer used was polyvinyl alcohol (Mol.wt. 72000; degree of hydrolysis ≥98 %; Merck, Germany). The monomer used was acrylic acid (Sigma-Aldrich, Netherland). Crosslinkers used were ethylene glycol dimethacrylate (Sigma-Aldrich, Germany) and glutaraldehyde (Scharlau, Spain). Benzoyl peroxide (Fisher Scientific, UK) was used as an initiator and HCl (Fluka, Switzerland) was used as a catalyst. Distilled water was used as a solvent. Potassium dihydrogen phosphate was purchased from Merck, Germany. Metformin hydrochloride was gifted by Popular International (PVT) LTD., Karachi, Pakistan.

Poly (3-hydroxybutirate-co-3-hydroxyvalerate), PHBV, with 2% wt of 3-hydroxyvalerate (Mw 410,000 g/mol) was supplied by Goodfellow (Huntingdon, UK), product code BV336010. Poly (vinyl alcohol), PVA, (Mw 13,000–23,000, 87–89% hydrolyzed, product code 363170), polypyrrole nanoparticles (PPy) doped with an organic sulfonic acid as dopant (conductivity 10–50 S/cm and stable up to 290 °C, product code 577030) and 1-metil-2-pyrrolidone (NMP) were purchased from Sigma Aldrich-Merck (St. Louis, MO, USA). PVA with a low molecular weight was selected because it biodegrades faster [49 (link)]. However, PVA with lower molecular weight exhibits lower mechanical performance [50 (link)]. Thus, since the mechanical properties and thermal stability of PHBV increases rapidly with molecular weight [51 (link)] we selected a PHBV with a high molecular weight to enhance the physical properties of PVA. Chloroform (99–99.6% pure), glutaraldehyde (GA) solution 25 wt.% in H₂O, methanol and sulfuric acid (95–98% extra pure) and acetic acid glacial (99% extra pure) were supplied by Scharlab (Barcelona, Spain). All reagents were used as received.