The fluid handling capacity of hydrocolloid dressings depends on many factors such as the physico-chemical properties of the hydrocolloid formulation, and the design of the dressing, i.e., the layer construction. Among these parameters, the initial thickness of the hydrocolloid layer plays an important role that needs to be investigated. This analysis may help the manufacturer to produce dressings with different designs, and thus eventual different performance characteristics. It may also help the clinician to select a specific dressing.
The moisture uptake is measured by placing a dressing sample in contact with water and monitoring the time evolution of its thickness at small regular time intervals by means of a video camera linked to a computer. This experiment yields the total height of swelling hf‑ho, (where hf and ho are respectively the final and initial thickness) which is proportional to the absorbed volume of solvent. A characteristic swelling time t, is also determined, such that after an exposure time of 2t, the dressing has reached 90% of its total possible moisture uptake.
A mathematical model then relates hf‑ho and t to the physico-chemical composition of the dressing, and to ho. The experimental results obtained with the same hydrocolloid formulation but different initial thickness (from 0.5 to 3mm), could indeed be predicted by the model within 20%. This shows that a moisture uptake measurement for one hydrocolloid thickness allows to predict the total absorption capacity hf‑ho and the characteristic time t for any thickness. It is found that the characteristic time and total uptake capacity increase with thickness.
(a) gel, (b) concentration layer, (c): saline solution.(Lanel et al. Biorheology 1997)