Poly(N-isopropylacrylamide-co-N-tert-butylacrylamide)-graph-polydopamine as a Thermoresponsive Surface with Adjustable Transformation Temperature for Efficient Microalgal Cell Adhesion and Detachment

Microalgal biofilm is one of the most promising candidates for renewable feedstock accumulation and carbon neutralization. To synergistically enhance cell adhesion during the microalgal biofilm formation stage and detachment during the harvesting stage, a surface possessing controllable properties is expected. However, the enhancement of the adhesion capacity of a conventional N-isopropylacrylamide (NIPAM) coating to microalgal cells only happens when the temperature reaches its lower critical solution temperature (LCST) of 33 °C, but at the optimum growth temperature of microalgae (25 °C) its adhesion capacity is dramatically weakened. In this study, a nondependent and environment-friendly thermoresponsive coating with a flexible LCST (22.3–25.0 °C) was prepared by cross-linking poly(NIPAM-co-N-tert-butylacrylamide) onto polydopamine to accelerate the adhesion of microalgal cells onto the coating at the optimum growth temperature of microalgae (25 °C). The coatings exhibited outstanding temperature-switchable performance due to competition between hydrophobic groups and hydrophilic groups in polymer molecules. Based on the temperature-switchable characteristic, the adhesion density of Chlorella sorokiniana MB-1 (C. sorokiniana) on the coating was increased by 49.4% compared to the conventional coating at 25 °C. Meanwhile, at 15 °C, the detachment efficiency of these cells on the coating reached 96.5%. The energy barrier between the C. sorokiniana and the coating was reduced by 54.8% compared to that of these cells on conventional coating, resulting in excellent cell adhesion and release. This report not only designs smart polymers for adjusting the adhesion of microalgal cells but also provides a sustainable strategy for microalgal biofilm cultivation.