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.

Influence of processing conditions in the manufacture of O/W creams: I. Effect on dispersion grade and rheological characteristics.

Two series of O/W creams having the same general formulation were prepared in three different mechanical conditions (F with an hand blender; S with a turbomixer; T with a vacuum turbo emulsor) using two types of surfactants, polyoxyethylene-cetostearyl alcohols and polyglyceryl-3-methylglucose-distearate. By means of microscopic image analysis it was possible to point out the dispersion grade of the oil internal phase increasing with the energy applied under the conditions of manufacture (F < S < T). The level of dispersion influenced significantly on the rheological characteristics of the creams. With polyoxyethylene-cetostearyl alcohols, the viscosity of creams increased as the energy applied in manufacturing increased, with polyglyceryl-3-methylglucose-distearate on the contrary decreased. Moreover, indifferently to the manufacturing conditions, even in the same concentration of surfactant, the creams obtained with the last produced a much greater viscosity. At a parity of manufacturing conditions the differences between the batches of productions were not significant.

Influence of processing conditions in the manufacture of O/W creams: II. Effect on drug availability.

O/W creams prepared in three mechanical conditions (F with a hand blender; S turbomixer; T vacuum turbo-emulsor) produced different dispersion grades of the internal phase and different rheological characteristics by using surfactants of different chemical nature (polyoxyethylene-cetostearyl alcohols and polyglyceryl-3-methylglucose distearate). Three tests were used (an in vitro release test across a porous membrane; an in vitro simulated absorption test across a porous membrane impregnated with isopropyl myristate; an in vivo absorption test based on the intensity and duration of the erythema produced by methyl nicotinate after application of the cream on the skin) to assess whether the different physical characteristics influence drug availability from the creams. The different physical characteristics due to the mechanical conditions of emulsifying and gelification appeared not to influence drug release and in vivo absorption.