Hydrogels are three-dimensional polymeric network with the capability to absorb a large amount of water or biological fluids. Usually, these materials are made of hydrophilic crosslinked polymer chains able to swell in water and present a soft rubbery consistency similar to living tissues. For this reason, hydrogels are used for biomedical, biotechnology and pharmaceutical applications [1,2]. The crosslinker nature separates hydrogels in two large families namely chemical or physical crosslinked. In the former, crosslinking is obtained by covalent bonding the chains either during the polymerization or in a post polymerization process [3]. In the latter, hydrogels are obtained using physical interaction such as hydrophobic association, ionic bond or hydrogen bond. In this work we prepared physically crosslinked hydrogels by radical micellar polymerization. This type of polymerization involves a hydrophilic monomer (acrylamide), a hydrophobic monomer (octadecylacrylate, C18A), a surfactant (sodium dodecyl sulfate), and a salt (sodium chloride). The polymerization was initiated using a redox initiator consisting of ammonium persulfate and sodium metabisulfite. In addition, a multifunctional monomer, divinylbenzene (DVB), was used with the aim of creating branched chains and evaluating their effect on the material characteristics. Three series of samples were prepared by varying the amount of octadecylacrylate and divinylbenzene. The samples were characterized with thermal (DSC) and rheological analysis, both before and after each purification steps. As the concentration of C18A increases, the amount of water within the hydrogels decreases. In addition, the melting and crystallization enthalpies of the hydrophobic domains increase, and in a parallel fashion an increase in mechanical modulus G' takes place. Furthermore, as the DVB concentration increases, the water content decreases, and the mechanical modulus G’ increases. This effect is probably due to the formation of additional chemical crosslinkings within the polymer network. The self-healing behavior of these materials was also demonstrated by several rheology measurements and other specific experiment. As the DVB concentration increases, the self-healing efficiency decrease and so does the shape-memory behavior. Heating the materials above Tm, hydrogels could be deformed into different shapes that can be fixed on cooling. Then, heating again above Tm, the original shape is recovered. This effect can be observed only for samples containing more than 20% of hydrophobic monomer.
SELF-HEALING AND SHAPE-MEMORY HYDROGELS BY MICELLAR POLYMERIZATION
Podda E.;Antonioli D.;Croce G.;Sparnacci K.;Gianotti V.;Laus M.
2022-01-01
Abstract
Hydrogels are three-dimensional polymeric network with the capability to absorb a large amount of water or biological fluids. Usually, these materials are made of hydrophilic crosslinked polymer chains able to swell in water and present a soft rubbery consistency similar to living tissues. For this reason, hydrogels are used for biomedical, biotechnology and pharmaceutical applications [1,2]. The crosslinker nature separates hydrogels in two large families namely chemical or physical crosslinked. In the former, crosslinking is obtained by covalent bonding the chains either during the polymerization or in a post polymerization process [3]. In the latter, hydrogels are obtained using physical interaction such as hydrophobic association, ionic bond or hydrogen bond. In this work we prepared physically crosslinked hydrogels by radical micellar polymerization. This type of polymerization involves a hydrophilic monomer (acrylamide), a hydrophobic monomer (octadecylacrylate, C18A), a surfactant (sodium dodecyl sulfate), and a salt (sodium chloride). The polymerization was initiated using a redox initiator consisting of ammonium persulfate and sodium metabisulfite. In addition, a multifunctional monomer, divinylbenzene (DVB), was used with the aim of creating branched chains and evaluating their effect on the material characteristics. Three series of samples were prepared by varying the amount of octadecylacrylate and divinylbenzene. The samples were characterized with thermal (DSC) and rheological analysis, both before and after each purification steps. As the concentration of C18A increases, the amount of water within the hydrogels decreases. In addition, the melting and crystallization enthalpies of the hydrophobic domains increase, and in a parallel fashion an increase in mechanical modulus G' takes place. Furthermore, as the DVB concentration increases, the water content decreases, and the mechanical modulus G’ increases. This effect is probably due to the formation of additional chemical crosslinkings within the polymer network. The self-healing behavior of these materials was also demonstrated by several rheology measurements and other specific experiment. As the DVB concentration increases, the self-healing efficiency decrease and so does the shape-memory behavior. Heating the materials above Tm, hydrogels could be deformed into different shapes that can be fixed on cooling. Then, heating again above Tm, the original shape is recovered. This effect can be observed only for samples containing more than 20% of hydrophobic monomer.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
