On the Non-Uniqueness and Inconsistency of Properties Measured in a Hydrolytic Degrading Hydrogel

OTTONE MARIEL L.; DEIBER JULIO A.

Los Cocos

Simposio; XII Simposio Argentino de Polímeros SAP 2017; 2017

Typicalexperimental procedures used to characterize hydrogel network degradation and controlleddrug release in vitro consist in preparing a vial containing the hydrogelsample in a formulated solution, where at different times a very little volumeof liquid is taken to perform appropriate measurements, including equivalent freshsolution repositions (see for instance [1]). Here this procedure is designated?one system method? (OSM). The OSM is simple when the study of the hydrogelperformance is limited to the analysis of species released in the immersionsolution at each time only. To get experimental data of average speciesconcentrations and other physicochemical properties from both immersionsolution and hydrogel, in this work a modified experimental procedure differentfrom the OSM is proposed. It is designated ?multiple systems method? (MSM)where the number of initial equivalent systems used is equal to the number oftime measurements required to get the hydrogel degradation kinetics and drugrelease rates among the other properties [2]. Under these experimentalconditions one is able to measure the perfect ?cup mixing? values of speciesconcentration in the immersion solution at each time and calculates thosepertaining to the hydrogel. Further additional hydrogel physicochemicalproperties can be reported as functions of time, like wet and dry hydrogel masses,crystal concentration and number of crosslinks. Here theOSM and MSM are compared through the case-study involving the hydrolyticdegradation of a gelatin hydrogel crosslinked with poly(vinyl alcohol) toillustrate situations of non-uniqueness and inconsistency of experimentalmeasurements associated with a rather complex hydrogel. It is shown that theOSM gives concentration profiles that are dependent on the time interval ofsolution repositions. The OMS and MSM provide the same asymptotic species concentrationsat very long times only because both systems are reaching the equilibrium asexpected.