Biomimetic Mineralized Capsules for Haematococcus pluvialis Clustering and Functional Regulation

Astaxanthin is a high-value ketocarotenoid with potent antioxidant activity and wide applications in nutraceutical, cosmetic, and aquaculture industries. The green microalga Haematococcus pluvialis represents the most promising natural source; however, its efficient production requires precise control of growth and stress conditions, while free cells remain susceptible to environmental and mechanical stress. Hydrogel encapsulation offers a protective microenvironment, yet conventional alginate systems are limited by poor mechanical stability and uncontrolled swelling. Here, we report calcium alginate-based biomimetic mineralized core-shell capsules for the encapsulation, cultivation, and high-light-induced astaxanthin production of H. pluvialis. Capsules were fabricated by ionic crosslinking of alginate containing KH2PO4 with a CMC/CaCl2 precursor solution, enabling in situ calcium phosphate formation within the capsule shell. Comprehensive characterization confirmed successful mineralization, reduced swelling, enhanced inorganic content, and improved mechanical strength. Encapsulated cells exhibited sustained growth and metabolic activity under moderate light without cytotoxic effects. Upon high-light exposure, both free and encapsulated cells showed a characteristic transition from green to red, accompanied by a significant increase in astaxanthin content. Notably, astaxanthin accumulation was comparable to that of controls. This study establishes a scalable encapsulation strategy that enhances structural stability without compromising biological function, offering potential for industrial microalgal cultivation and astaxanthin production.