Green Extraction of Chitosan from <i>Pinctada Maxima</i> Shells: Comprehensive Physicochemical Properties and Antibacterial Performance For Biomedical Applications

The growing demand for eco-friendly biomaterials with sustained bacterial activity highlights chitosan as a promising medical material, yet conventional extraction often yields inconsistent quality. This research established a sustainable extraction route by varying isolation sequence, NaOH concentration (40–60%), and microwave-assisted deacetylation time (0–20 min). Chitosan was characterized by FTIR, 1H NMR, XRD, viscometry, EDX, and FESEM, and antibacterial activity against Staphylococcus aureus and Escherichia coli was evaluated by broth microdilution and plate-count assays. The optimal process demineralization followed by deacetylation with 60% NaOH for 15 minutes under microwave irradiation (Ch-MW60-15) produced a high degree of deacetylation (95.37%), reduced molecular weight (206–148 kDa), lower viscosity (3.17–2.45 cP L/g), and higher crystallinity (60.89%). XRD and EDX indicated residual CaCO3, so the product is best described as a high-DD chitosan-CaCO3 composite. 1H NMR showed characteristic chitosan resonances without a prominent acetyl-methyl signal (∼2 ppm), confirming a high-DD backbone. FESEM revealed an interconnected porous-layered morphology with uniform particles (273.98 ± 10.49 nm), supporting improved antibacterial performance. Ch-MW60-15 reduced Escherichia coli (3.12 to ∼2.0 log CFU/mL) and Staphylococcus aureus (3.0 to ∼1.92 log CFU/mL) at 20 ppm, with complete inhibition at 80 ppm, indicating suitability for biomedical applications.