No abstract

A diffusion chamber technique based on time-lag analysis for the estimation of effective diffusion coefficients of radiolabelled macromolecules of varying molecular weights through native mucus gel is reported. For all solutes studied, a reduction in effective diffusion coefficients was observed with a retardation of solute flux in both aqueous and mucus layers. Over the molecular weight range of solutes investigated (126-186,000 Daltons), a consistent effect of molecular weight was evident with regard to the retarding effect of mucus. No apparent or absolute molecular weight cut-off for macromolecular transfer was exhibited. However, at high molecular weights (greater than 30,000 Daltons) the retardation was greatly enhanced. The results confirm that mucus can be regarded as a gel with finite pores, but that it does not constitute an absolute barrier to even high molecular weight solutes.

Sensors are a sample contacting technology, and when exposed to biological matrices tend to suffer from the problem of poor biocompatibility and surface fouling. The effects are evidenced by time dependant signal drift (particularly for those devices which are implanted intravascularly). Practical methods to reduce such effects require an understanding of the interface between the electrode and its environment prior to assessment of the potential areas for improvement. Current procedures employed to overcome the observed losses in electrode sensitivity (following exposure to whole blood) include surface modification of the outer diffusion limiting membrane (via variation in film porosity) or even biomimicry of the fluid cell membrane. At amperometric electrodes incorporation of additional inner perm‐selective membranes has achieved a reduction in electrode passivation from undesirable surface active compounds as has the use of low polarisation potentials. Other studies have attempted to induce an aqueous barrier between the matrix and the electrode tip which physically prevents passage of cellular components from the sensor surface.Careful choice of the system and materials will ultimately lead to biocompatible non‐fouling devices capable of functioning in an array of bio‐environments suitable for clinical monitoring of the critically ill patient.