On the non-uniqueness and inconsistency of properties measured in a hydrolytic degrading hydrogel

OTTONE, MARIEL LORENA; DEIBER, JULIO ALCIDES

Los Cocos

Simposio; XII Simposio Argentino de Polímeros - SAP 2017; 2017

Typical experimental procedures used to characterize hydrogel network degradation and controlled drug release in vitro consist in preparing a vial containing the hydrogel sample in a formulated solution, where at different times a very little volume of liquid is taken to perform appropriate measurements, including equivalent fresh solution repositions (see for instance [1]). Here this procedure is designated one system method (OSM). The OSM is simple when the study of the hydrogel performance is limited to the analysis of species released in the immersion solution at each time only. To get experimental data of average species concentrations and other physicochemical properties from both immersion solution and hydrogel, in this work a modified experimental procedure different from the OSM is proposed. It is designated multiple systems method (MSM)where the number of initial equivalent systems used is equal to the number of time measurements required to get the hydrogel degradation kinetics and drug release rates among the other properties [2]. Under these experimental conditions one is able to measure the perfect cup mixing values of species concentration in the immersion solution at each time and calculates those pertaining to the hydrogel. Further additional hydrogel physicochemical properties can be reported as functions of time, like wet and dry hydrogel masses, crystal concentration and number of crosslinks. Here the OSM and MSM are compared through the case-study involving the hydrolytic degradation of a gelatin hydrogel crosslinked with poly(vinyl alcohol) to illustrate situations of non-uniqueness and inconsistency of experimental measurements associated with a rather complex hydrogel. It is shown that the OSM gives concentration profiles that are dependent on the time interval of solution repositions. The OMS and MSM provide the same asymptotic species concentrations at very long times only because both systems are reaching the equilibrium as expected.