Silica Hydrogels as Entrapment Material for Microalgae

Despite being a promising feedstock for food, feed, chemicals, and biofuels, microalgal production processes are still uneconomical due to slow growth rates, costly media, problematic downstreaming processes, and rather low cell densities. Immobilization via entrapment constitutes a promising tool to overcome these drawbacks of microalgal production and enables continuous processes with protection against shear forces and contaminations. In contrast to biopolymer gels, inorganic silica hydrogels are highly transparent and chemically, mechanically, thermally, and biologically stable. Since the first report on entrapment of living cells in silica hydrogels in 1989, efforts were made to increase the biocompatibility by omitting organic solvents during hydrolysis, removing toxic by-products, and replacing detrimental mineral acids or bases for pH adjustment. Furthermore, methods were developed to decrease the stiffness in order to enable proliferation of entrapped cells. This review aims to provide an overview of studied entrapment methods in silica hydrogels, specifically for rather sensitive microalgae.

Automated summary

Despite the potential of microalgae as a feedstock for various industries, their production processes are currently uneconomical due to slow growth rates, expensive media, problematic downstream processes, and low cell densities. Entrapment via immobilization in silica hydrogels offers a promising solution to these challenges, allowing continuous processes with protection against shear forces and contaminations. Efforts have been made to improve biocompatibility and, through various methods, enable the proliferation of entrapped microalgae cells. This review provides an overview of entrapment methods in silica hydrogels, specifically for sensitive microalgae.