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Lookup NU author(s): Glenn Hurst,
Dr Katarina Novakovic
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Smart polymer gels can exhibit significant and reversible conformational rearrangements upon variation in an applied stimulus such a pH or temperature. These networks are ideally suited for biomedical use as drug delivery systems or scaffolds for tissue engineering. Effective distribution of imbibed constituents requires a controlled and sustained therapeutic release regime. This can be realised by coupling responsive hydrogels to oscillatory reactions producing oscillations in the appropriate stimuli to induce a simultaneous volume change within a smart polymer gel.1 One such reaction is the palladium catalysed phenylacetylene oxidative carbonylation (PCPOC) reaction which generates pronounced oscillations in heat output (e.g. 0.6 kJ/oscillation at 40 °C) and pH (1-6) over a wide temperature range (10-40 °C).2, 3 The present work focuses on determining and optimising the suitability of pH-sensitive genipin-crosslinked chitosan-poly(vinyl pyrrolidone) hydrogels for coupling to chemical oscillators. This semi-interpenetrating polymer network combines properties such as biocompatibility, low toxicity, biodegradability and haemocompatibility using genipin, a natural crosslinking agent with low cytotoxicity that fluoresces upon crosslink formation. The effects of polymerisation time, temperature and composition on the structure and swelling behaviour of these cationic hydrogels are investigated. Fluorescence intensity is found to increase with extent of crosslinking in all cases. This is corroborated qualitatively using scanning electron microscopy (SEM) where two different drying techniques are employed and quantitatively following porosity analysis. Equilibrium swelling behaviour is determined using a range of buffers (pH 2, 4, 7 and 10) both gravimetrically and via fluorescence visualisation. The accuracy of these techniques is compared. Variation in the porous microstructure of the gel during swelling is also studied for the first time via confocal microscopy where three-dimensional images of the network morphology and changes in surface topography are examined (Figure 1). Compared to SEM, this is a non-destructive technique for analysing gel microstructure. Information acquired from these studies is used to determine the optimum formulation for prospective combination with the oscillatory PCPOC reaction. Subsequently, to assess hydrogel response dynamics, oscillatory behaviour has been simulated by immersing the hydrogel in pH 2 and pH 4 buffers in an alternate fashion to coincide with the time period of the oscillatory reaction and the swelling behaviour is determined. The ease at which these networks can be prepared coupled to their autofluorescent nature aids development towards a prospective application in controlled; pulsatile and sustained release, distinguishing this system from current delivery modes. a b c Figure 1 Variation in porous architecture of smart hydrogel (a) during swelling via three-dimensional structure (b) and topographical (c) evaluation. 1. Yoshida, R. Advanced Materials 2010, 22, 3463. 2. Novakovic, K.; Grosjean, C.; Scott, S. K.; Whiting, A.; Willis, M. J.; Wright, A. R. Chemical Physics Letters 2007, 435, 142. 3. Novakovic, K.; Mukherjee, A.; Willis, M.; Wright, A.; Scott, S. Physical Chemistry Chemical Physics 2009, 11, 9044.
Author(s): Hurst G, Novakovic K
Publication type: Conference Proceedings (inc. Abstract)
Publication status: Unpublished
Conference Name: RSC Biomaterials Chemistry Group - 7th Annual Meeting
Year of Conference: 2013