Novel photocurable hydrogels obtained by thiol-methacrylate Michael addition reaction

S. V. ASMUSSEN; M. L. GOMEZ; C. I. VALLO

Mar del Plata, Buenos Aires

Simposio; SLAP 2018 ? XVI Simposio latinoamericano de Polímeros ? XIV Congreso Iberoamericano de Polímeros; 2018

INTEMA

INTRODUCTIONHydrogels and their response to external environments have attracted much academic and industrial interest because of the potential for many applications including tissue engineering, drug delivery, soft contact lenses and wound dressings1. This work describes the preparation and swelling behaviour of novel hydrogels based on a water soluble dimethacrylate monomer (EBisEMA). This monomer is characterized by a relatively high molar mass (Mn ~1700 g/ mol) and contains a high proportion of aliphatic ether bonds in its structure which results in moderately crosslinked and flexible polymer networks. EXPERIMENTAL METHODSHydrogels derived from EBisEMA were prepared at room temperature by both bulk photopolymerization and aqueous solution photopolymerization using either UV or visible radiation. In addition, EBisEMA was copolymerized with a tetrafunctional thiol through free-radicals and amine catalysed Michael addition reaction. EBisEMA was also copolymerized with different proportions of dimethylaminoethyl-methacrylate (DMAEMA) and the sensitivity of EBisEMA-DMAEMA networks to changes in pH was examined. Measurement of water uptake in hydrogels were carried out using a classic gravimetric sorption technique. The conversions of methacrylate and thiol groups were monitored by Raman and NIR spectroscopies. RESULTS AND DISCUSSIONEBisEMA photopolymerized in bulk absorbs 68 wt. % water after 24 h immersion while the water uptake of EBisEMA photopolymerized in aqueous solution (0.5 g EBisEMA/ml) is 104 wt. % after 48 h immersion. Thiol-methacrylate hydrogels were prepared by visible light photopolymerization of EBisEMA with a tetrafunctional thiol (PETMP) at different EBisEMA: PETMP molar ratios. These hydrogels contained unreacted thiol groups because of a faster homopolymerization reaction of EBisEMA. Hydrogels were also prepared in bulk by propylamine catalysed Michael addition reaction. No significant differences in swelling were observed between specimens prepared from pure EBisEMA and photocured EBisEMA/PETMP specimens. Conversely, a marked increase in water uptake (110 wt. %) was seen in the EBisEMA-PETMP hydrogels prepared by the Michael addition reaction catalysed by propylamine. These trends are explained in terms of a balance between the mass fraction of hydrophilic groups and the crosslinking density of the network. EBisEMA/PETMP hydrogels formulated with thiol in excess showed a marked tendency to adhere to a variety of substrates, including metals, glass, paper and skin. This feature makes them especially attractive in applications for which adhesion is particularly critical. pH sensitive hydrogels were prepared by copolymerization of EBisEMA with dimethylaminoethylmethacrylate (DMAEMA). Swelling studies showed that, as a result of the high molar mass of EBisEMA, the pH sensitivity was evident at EBisEMA:DMAEMA molar ratios lower than 0.2:0.8. CONCLUSIONThe work carried out demonstrates the versatility of EBisEMA for obtaining hydrogels using various synthesis pathways. The properties of the materials vary significantly depending on the materials and routes of synthesis employed, which makes them versatile in the manufacture of hydrogels for various applications (contact surfaces, tissue engineering, encapsulation/drug release, etc.).