PVDF membrane biofunctionalization by chemical grafting

Abstract The objective of the work was to develop a suitable method for covalent immobilization of labile active biomolecules on inert hydrophobic polyvinylidene fluoride (PVDF) membrane, preserving both membrane stability and biomolecule activity. PVDF is advantageous over other membrane materials due to its high mechanical strength and excellent chemical resistance. On the other hand, its native structure does not have sites for biomolecules covalent immobilization in mild conditions. The strategy of the present work consisted in grafting reactive groups on the hydrophobic PVDF to which attaching functional groups able to covalently bound biomolecules in mild conditions. Tuning grafting conditions were crucial in order to attack the inert membrane while maintaining suitable membrane chemical and mechanical stability. Therefore, surface modification of native PVDF flat-sheet membranes was performed by wet chemical strategy, under basic conditions, using 1,5-diamino-2-methylpentane (DAMP) as carrier of amino groups. Afterwards, these groups were activated with glutaraldehyde (GA) to which biomolecules were easily attached by covalent bond. Two model proteins having different properties (BSA and Lipase) were selected for immobilization test. DAMP concentration, reaction temperature, and reaction time were studied in order to tune both the degree of modification and the loading capacity of the functionalized membrane taking in account the mechanical stability of the membrane. Modified and native PVDF membranes were characterized by Fourier transform infrared spectroscopy (FT-IR), the ninhydrin test, scanning electron microscopy (SEM) and the mechanical resistance test. Enzymatic activity of immobilized lipase was tested in a biphasic systems using the hydrolysis of triglycerides as model reaction. Modified membranes showed higher binding capacities compared with unmodified PVDF membrane. Optimal conditions for grafting reactive amino groups able to guarantee membrane stability and enzyme loading suitable to achieve good enzyme specific activity were identified.