DN Gels Research Articles

Antifouling properties of tough gels against barnacles in a long-term marine environment experiment

In the marine environment, the antifouling (AF) properties of various kinds of hydrogels against sessile marine organisms (algae, sea squirts, barnacles) were tested in a long-term experiment. The results demonstrate that most hydrogels can endure at least 2 months in the marine environment. In particular, mechanically tough PAMPS/PAAm DN and PVA gels exhibited AF activity against marine sessile organisms, especially barnacles, for as long as 330 days. The AF ability of hydrogels toward barnacles is explained in terms of an ‘easy-release’ mechanism in which the high water content and the elastic modulus of the gel are two important parameters.

True Chemical Structure of Double Network Hydrogels

We elucidate why the anomalous high strength of double network gels is obtained when the second network is polymerized without any cross-linkers. We have synthesized truly independent-DN gels (named “t-DN” gels), which do not have any covalent bonds between the first and the second networks, and showed that the t-DN gels cannot be toughened by the un-cross-linked second network. It means that the high strength of usual DN gels without the cross-linker of the second network is actually achieved by the interconnection between the two networks through covalent bonds (so usual DN gels were named “c-DN” gels). Further, we found that the t-DN gels become stronger than the c-DN gels when the second network is loosely cross-linked. As the t-DN gels have a more simple structure than the c-DN gels, we expect that the toughening mechanism of DN gels will be clarified by studying the t-DN gels in the future.

Localized Yielding Around Crack Tips of Double‐Network Gels

AbstractDouble‐network (DN) gels, a type of interpenetrating polymer network (IPN) consisting of rigid and flexible polymer components, exhibit two outstanding mechanical behaviors: yielding deformation of the entire specimen in tensile tests and quite high fracture energy in tearing tests. In this study, atomic force microscope (AFM) measurements were conducted on DN gels to determine the local Young's moduli immediately below the fracture surfaces Ef and below the usual molded surfaces Em, and compare the local modulus with bulk Young's moduli measured before and after the yielding deformation, denoted as Eh and Es, respectively. Em and Eh are around 0.1 MPa; Ef and Es, around 0.01 MPa, one order lower than the former two moduli. The order relation indicates that yielding deformation occurred locally around the crack tip of the DN gel during fracture. This supports the basic assumption of phenomenological models recently proposed to explain high fracture energy of DN gels. (H. R. Brown, Macromolecules 2007, 40, 3815–3818; Y. Tanaka, Europhys. Lett. 2007, 78, 56005).magnified image

Biological responses of novel high-toughness double network hydrogels in muscle and the subcutaneous tissues

The study evaluated biological reaction of four types of novel double network gels in muscle and subcutaneous tissues, using implantation tests according to the international guideline. The implantation tests demonstrated that, although poly (2-acrylamide-2-metyl-propane sulfonic acid)/poly (N,N'-dimetyl acrylamide) (PAMPS/PDMAAm) gel induced a mild inflammation at 1 week, the degree of the inflammation significantly decreased into the same degree as that of the negative control at 4 and 6 weeks. This gel has a potential to be applied as artificial cartilage. In addition, Cellulose/Gelatin gel showed the same degree of inflammation as that of the negative control at 1 week, and then, showed a gradually absorbable property at 4 and 6 weeks. This gel has a potential to be applied as an absorbable implant. The PAMPS/polyacrylamide and Cellulose/PDMAAm gels induced a significant inflammation at each week. These DN gels are difficult to be applied as clinical implants in the current situation.