Surface Biochemical and Physical-Chemical Properties of Artificial Membranes Functionalized With Lipase

Lipase is an enzyme with a hydrophilic main body and a lipophilic cover lid that protects the active site. This structure gives the macromolecule amphiphilic properties and is responsible of the interfacial activation. Besides the well known biocatalytic properties of lipase immobilized on membrane, the possibility to modify and tune surface physical-chemical properties has been investigated.

Lipase is both adsorbed and cross-linked to inorganic and polymeric hydrophilic membranes. The effect of the use of substrate or inhibitors during immobilization methods is explored. The idea was to change the membrane surface wettability, by loading the lipase in such a way that the lipophilic cover lid is exposed towards the bulk, while maintaining the thickness wettability unchanged. This leads to membranes with asymmetric wettability, which are of great importance in processes such as membrane emulsification. For example, having hydrophilic thickness and hydrophobic membrane surface permits to improve the productivity of water-in-oil emulsion preparation at lower energy consumption (since water wets the membranes) while achieving narrow droplets size distribution (thanks to the high interfacial tension assured by the hydrophobic surface). The same will be obtained for o/w emulsion with membranes having thickness hydrophobic and surface hydrophilic.

In this work we focus on the use of modified membranes for w/o emulsion preparation where water is used as dispersed phase pressed through the membrane pores and oil is used as continuous phase circulated along the lumen of tubular membrane. When on the surface of the membrane is present the lipase and water is put in contact the surface will be hydrophilic while if organic phase is put in contact a hydrophobic character is exhibited. This is obtained thanks to the behaviour of the cover lid present as closed or open depending on the polarity of the contacting phase.

Results on the emulsion properties obtained with such functionalized membranes as well as on membrane characterization in terms of surface roughness and contact angle will be discussed.