Fig. 4. (a) Optical image of the lysozyme-loaded BSA nanogel/calcite system and SEM micrographs of a fractured composite crystal showing the uniform occlusion of the loaded nanogels in calcite. (b) Cumulative release of lysozyme from the composite crystals over time (citrate buffer, pH = 3.5). Inset shows the increased absorbance of the characteristic peak of lysozyme (λ = 280 nm) corresponding to the released enzyme over time. (c) Native (red) and encapsulated (purple) lysozyme activity stored at room temperature for 2 months and subjected to heat treatment at 100 °C for 2 h or NaOH solution (2.5 M, pH 14). Encapsulation of lysozyme within the BSA/calcite system enables preservation of enzymatic activity compared to the free enzyme in solution. (d) CD spectra of the native and encapsulated lysozyme when stored at room temperature for 2 months and heated at 100 °C for 2 h or subjected to high basic solution (2.5 M NaOH, pH 14) for 2 h. Compared to the free native enzyme, the encapsulated lysozyme retains its secondary structure and therefore stability when exposed to extreme conditions.