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Characterization of biodegradable hydrogels and dependence of material’ s property on structure and composition

Novel biodegradable hydrogels are prepared that, potentially, can be used for many kinds of in medicine and in pharmacy, inside and outside the body since these hydrophilic polymer networks are capable of absorbing large amounts of water. These novel copolymers consisting of poly(vinyl alcohol) and [poly(rac-lactide) / poly(rac-lactide-co-glycolide)] (PVA-g-(PL/GA)) [1] present progress within a series biodegradable hydrogels based on polyesters such as polylactide, polyglicolide, poly(ε -caprolactone) and their various combination ; mixtures or copolymers. Their combination with hydrophilic PVA segments enables obtaining of a material of improved properties and gives opportunity for tailoring and controlling of the degradation time and pathway. Materials of different properties were obtained by changing the composition ratio of hydrogels, structure and MWs of segments. Mechanical properties of several measured hydrogels, expressed via Young's modulus with values between 1.95 and 3.70 MPa, are within the range of the modulus of articular cartilage [2]. The degradation behavior of hydrogels over a period of time of eight weeks up to 21 weeks was studied. The swelling and mass loss of the crosslinked hydrogels were investigated. The degradation– induced mass loss displays a noticeable difference depending on the structure and composition of the hydrogels. Thus, networks require between 10 and 110 days for 10% of mass loss. The water uptake continues to increase strongly during the whole time of degradation indicating the loosening of the network structure. Hydrogels with the higher polyester content show lower water uptake and lower rate of water uptake upon degradation relative those with a lower polyester content. The glycolide present in samples leads to a significantly higher water uptake than that of sample with pure lactide grafts after about 35 days of degradation. The status of degraded materials was, also, followed by IR analysis. As the degradation proceeds the characteristic C=O band moves toward lower wave numbers, indicating the decrease of ester bonds in the hydrogel, as it is shown in Figure. Moreover, polymer networks were studied in detail with TGA and DSC techniques. There was no significant change in the appearance of TGA and DTGA curves of networks in the course of degradation, except for the degradation onset. It is a two stages decomposition process with an initial small weight loss caused by water evaporation. DSC measurements of all samples show a single glass transition temperature during hydrolytical degradation where the increase of Tg is small. It amounts between 2 oC for hydrogels with polylactide grafts up to 9 oC in these with poly(lactide-co-glycolide) grafts. [1] Vidović, E., Klee, D., Höcker, H. J. Polym. Sci. Part A: Polym Chem., 2007, 45, 4536 [2] Stammen, J.A., Williams S., Ku D.N., Guldberg R.E. Biomaterials, 2001, 22, 799

biodegradable hydrogels; mechanical properties; degradation

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