Bioinspired Functional Gradients For Toughness Augmentation In Synthetic Polymer Systems

In nature, load-bearing polymeric materials that do not present significant trade-off between elongation and elastic modulus are often found, but are rare in synthetic systems. One mechanism for emulating these natural systems is with functionally graded materials (FGMs). The development of synthetic FGM systems with varying moduli gradient using tuned poly(meth)acrylate multilayers is shown. Such localized tuning of crosslink density is shown as a mechanism to increase rigidity without significant compromise to maximum strain. The toughest FGM shows 43% higher tensile strength and 9% higher stiffness than copolymer elastomers with similar maximum strain (εmax ≈ 110%), increasing toughness by 25%. These improved tensile mechanical properties can be due to beneficial interlayer crack deflection and delamination. This gradient approach provides potential to improve toughness of various load-bearing polymeric materials

Bioinspired Catecholic Primers for Rigid and Ductile Dental Resin Composites

In the construction of dental restorative polymer composite materials, surface priming on mineral fillers is essential to improve the mechanical performance of the composites. Here we present bioinspired catechol-functionalized primers for a tougher dental resin composite containing glass fillers. The catecholic primers with different polymerizable end groups were designed and then coated on glass surfaces using a simple drop-casting or dip-coating process. The surface binding ability and possible cross-linking (coupling or chemical bridging between the glass substrate and the dental resin) of the catecholic bifunctional primers were evaluated using atomic force microscopy, contact angle measurements, and the knife shear bonding test and compared to a state-of-the-art silane-based coupling agent. Various mechanical tests including shrinkage and compression tests of the dental resin composites were also conducted. Compression tests of the composites containing the catecholic primed fillers exhibited enhanced mechanical properties, owing to the bidentate hydrogen bonding of catechol moieties to the oxide mineral surface. Furthermore, the superior biocompatibility of the primed surface was confirmed via cell attachment assay, thus providing applicability of catecholic primers for practical dental and biomedical applications

Surface-initiated self-healing of polymers in aqueous media.

Polymeric materials that intrinsically heal at damage sites under wet or moist conditions are urgently needed for biomedical and environmental applications. Although hydrogels with self-mending properties have been engineered by means of mussel-inspired metal-chelating catechol-functionalized polymer networks, biological self-healing in wet conditions, as occurs in self-assembled holdfast proteins in mussels and other marine organisms, is generally thought to involve more than reversible metal chelates. Here we demonstrate self-mending in metal-free water of synthetic polyacrylate and polymethacrylate materials that are surface-functionalized with mussel-inspired catechols. Wet self-mending of scission in these polymers is initiated and accelerated by hydrogen bonding between interfacial catechol moieties, and consolidated by the recruitment of other non-covalent interactions contributed by subsurface moieties. The repaired and pristine samples show similar mechanical properties, suggesting that the triggering of complete self-healing is enabled underwater by the formation of extensive catechol-mediated interfacial hydrogen bonds

Surface-initiated self-healing of polymers in aqueous media.

Polymeric materials that intrinsically heal at damage sites under wet or moist conditions are urgently needed for biomedical and environmental applications. Although hydrogels with self-mending properties have been engineered by means of mussel-inspired metal-chelating catechol-functionalized polymer networks, biological self-healing in wet conditions, as occurs in self-assembled holdfast proteins in mussels and other marine organisms, is generally thought to involve more than reversible metal chelates. Here we demonstrate self-mending in metal-free water of synthetic polyacrylate and polymethacrylate materials that are surface-functionalized with mussel-inspired catechols. Wet self-mending of scission in these polymers is initiated and accelerated by hydrogen bonding between interfacial catechol moieties, and consolidated by the recruitment of other non-covalent interactions contributed by subsurface moieties. The repaired and pristine samples show similar mechanical properties, suggesting that the triggering of complete self-healing is enabled underwater by the formation of extensive catechol-mediated interfacial hydrogen bonds

MUSSEL-INSPIRED CATECHOLIC PRIMERS FOR RIGID AND DUCTILE DENTAL RESIN COMPOSITES

In the construction of dental restorative material, surface priming is essential for improving mechanical performance for practical applications. We present catechol functionalized primers for resin composite inspired by interfacial mussel foot proteins. The catecholic primers with different chain end group were designed and coated on the surface using simple process. The surface binding ability and possible crosslinking of the bifunctional primer were evaluated by the knife shear test. Compression tests of dental resin composite using primed glass filler demonstrated the enhanced mechanical properties such as toughness and elastic modulus owing to the bidentate hydrogen bonding of catechol moieties. Furthermore, the superior biocompatibility of the priming surface was confirmed via cell attachment test, thus providing applicability of catecholic primers as dental materials

1D and 2D NMR of nanocellulose in aqueous colloidal suspensions.

This is the first report on surface structural elucidation of individual nanocellulose as colloidal suspensions by 1D 1H, 2D heteronuclear single quantum coherence (HSQC) as well as 13C nuclear magnetic resonance (NMR). 1H NMR of rice straw CNCs (4.7 nm thick, 143 nm long, 0.04 sulfate per AG or 19.0% surface hydroxyl to sulfate conversion) resembled that of homogeneous cellulose solution. Conventional 2D HSQC NMR of CNC, CNF 1.5 (2-14 nm thick, several micrometers long, 0.10 COOH per AG) and CNF10 (2.0 nm thick, up to 1 μm long, 0.28 COOH per AG) gave H1:H2 ratios of 1.08:1, 0.97:1 and 0.94:1, respectively, all close to the theoretical 1:1 value for cellulose. The H1:H6 ratios determined from 2D HSQC NMR for CNCs, CNF1.5 and CNF10 were 1:1.47, 1:0.88 and 1:0.14, respectively, and corresponded to 26%, 56% and 93% C6 primary hydroxyl conversion to sulfate and carboxyl groups, consistent with, but more sensitive than those by conductometric titration and X-ray diffraction. Both 1H and 2D HSQC NMR data confirm that solution-state NMR detects nanocellulose surface carbons and protons primarily, validating this technique for direct surface characterization of nanocellulose in aqueous colloidal suspensions, presenting a sensitive and meaningful NMR tool for direct characterizing individual nanocellulose surfaces in never-dried state