Fig. 5. Utilizing the elastic property of sponges for recyclability and enhancing rate of reaction: (a and b) optical images showing compression and decompression (C–D) of (1 cm × 1 cm) the Si-PEI NPs sponge immobilized with either nALP or ALP-PS with the help of a mechanical stage. The sponge regains its original size and shape from to 40% of its initial height after removal of compressive stress (decompression). (c) Multiple reaction cycles were performed on a single sponge (containing 0.2 mg ALP-PS) using 2 mM pNPP at room temperature. Reusability cycles using nALP (green, open circles) and ALP-PS sponges (black, open circles). A typical reusability cycle consists of addition of substrate to the sponge, performing 1 C–D cycle per min for 10 minutes, extruding the product, washing the sponge first with 50 mM NaCl then with MilliQ water and reusing the sponge for next cycle (inset in panel (c)). (d) Graph depicting dependence of compression and decompression rate on the formation of pNP. Three different sets of C–D frequencies viz. 1, 2, 4 min⁻¹ were applied and [pNP] was measured by absorption spectroscopy at 410 nm at different time intervals of 5, 10, 15, 20 and 25 minutes. Inset in (d) clearly demonstrates that [pNP] is approximately 3 higher within the first 5 minutes when 4 C–D cycles per min are employed.