Poly (vinyl alcohol) hydrogels: Influence of processing variables on general behavior and drug release device performance

Abstract

Poly (vinyl alcohol) (PVA) hydrogels have a number of interesting properties whose make it an excellent candidate for several applications. One of the well known uses of these materials is like drug delivery device for their high hydrophilicity and water uptake capability. Hydrogels of PVA were obtained by two different routes: chemical method (by using a crosslinking agent, such as glutaraldehyde (GA)) and by physical method (carried out by freezing/thawing (F/T), resulting in cryogels). The main advantages of F/T are its easiness that does require neither high temperatures nor toxic agents as waste that can be harmful to the human body. It is possible, for biomedical applications, that un-reacted residue from the crosslinking agent may eluted slowly over time resulting in the release of toxic agents; being this toxicity undesirable for pharmaceutical applications because the activity of the drug or agent being released could be destroyed. The properties of PVA hydrogels depend mainly on their density or degree of crosslinking and crystallinity. Nevertheless, it is still unclear what role of processing variables play on the significant properties of the material. These properties can be driven by the numbers of F/T cycles, the cycle extent, the freezing temperature, the rate of thawing, the polymer concentration and its molecular weight (Mw). The aim of this chapter was to analyze the effect of some processing variables on the characteristic and properties of PVA hydrogels and to look at the delivery system behavior in aspirin and ibuprofen drugs. For this purpose, cryogels with different: numbers of F/T cycles (1 to 4), cycles extent (1, 12 and 24 h), Mw (18000; 40500, 93500 and 155000 g/mol) and polymer concentration (5 to 15 wt.%) were synthesized and 266 Jimena Soledad Gonzalez and Vera Alejandra Alvarez analyzed by means of thermogravimetric analysis (TGA), differential scanning calorimetric (DSC), swelling studies, X-ray diffraction (XRD), rheological tests and mechanical properties. In addition, cryogels were compared with chemically based hydrogels by means of selected characterization techniques. The results obtained in the present study suggest that it is possible to obtain cryogels with controlled properties and to be optimist about the future use of these kinds of hydrogels, avoiding the use of toxic crosslinking agent, for applications such as drug delivery.