Surface characterisation of bags for total parenteral nutrition by tensiometry and atomic force microscopy

Bags made of poly-ethylene and poly-vinylchloride and of the copolymer ethylene-vinylacetate were used as containers of perfusion solutions for total parenteral nutrition. The bags were characterised by tensiometry (free energy and its polar and dispersed components) and atomic force microscopy (AFM) before and after various periods of storage of solutions for total parenteral nutrition containing L-aminoacids, electrolytes or glucose. In most of the cases, after storage of these solutions, tensiometric characterisation and atomic force microscopy analysis of the internal surface of bags showed deep modifications which highlight the adsorption of the solutes. The changes of surface characteristics were found to depend on the time of contact, the wettability of the polymer and the compounds present into the solutions, while their concentration has a negligible effect. Generally, the aminoacid solutions produced a higher increase in the polar component even after short storage times. Poly-ethylene and the copolymer ethylene-vinylacetate showed a greater inertia if compared with the poly-vinylchloride bags.