Browsing by Author "Yu, Juan"

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High Axial Ratio Nanochitins for Ultrastrong and Shape-Recoverable Hydrogels and Cryogels via Ice Templating
(2019-03-26) Liu, Liang; Bai, Long; Tripathi, Anurodh; Yu, Juan; Wang, Zhiguo; Borghei, Maryam; Fan, Yimin; Rojas, Orlando J.
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
High yield (>85%) and low-energy deconstruction of never-dried residual marine biomass is proposed following partial deacetylation and microfluidization. This process results in chitin nanofibrils (nanochitin, NCh) of ultrahigh axial size (aspect ratios of up to 500), one of the largest for bioderived nanomaterials. The nanochitins are colloidally stable in water (ζ-potential = +95 mV) and produce highly entangled networks upon pH shift. Viscoelastic and strong hydrogels are formed by ice templating upon freezing and thawing with simultaneous cross-linking. Slow supercooling and ice nucleation at -20 °C make ice crystals grow slowly and exclude nanochitin and cross-linkers, becoming spatially confined at the interface. At a nanochitin concentration as low as 0.4 wt %, highly viscoelastic hydrogels are formed, with a storage modulus of ∼16 kPa, at least an order of magnitude larger compared to those measured for the strongest chitin-derived hydrogels reported so far. Moreover, the water absorption capacity of the hydrogels reaches a value of 466 g g -1 . Lyophilization is effective in producing cryogels with a density that can be tailored in a wide range of values, from 0.89 to 10.83 mg·cm -3 , and corresponding porosity, between 99.24 and 99.94%. Nitrogen adsorption results indicate reversible adsorption and desorption cycles of macroporous structures. A fast shape recovery is registered from compressive stress-strain hysteresis loops. After 80% compressive strain, the cryogels recovered fast and completely upon load release. The extreme values in these and other physical properties have not been achieved before for neither chitin nor nanocellulosic cryogels. They are explained to be the result of (a) the ultrahigh axial ratio of the fibrils and strong covalent interactions; (b) the avoidance of drying before and during processing, a subtle but critical aspect in nanomanufacturing with biobased materials; and (c) ice templating, which makes the hydrogels and cryogels suitable for advanced biobased materials.
Simple synthesis of self-assembled nacre-like materials with 3D periodic layers from nanochitin via hydrogelation and mineralization
(2022-02-07) Xu, Junhua; Liu, Liang; Yu, Juan; Zou, Yujun; Pei, Wenhui; Zhang, Lili; Ye, Wenbo; Bai, Long; Wang, Zhiguo; Fan, Yimin; Yong, Qiang; Rojas, Orlando J.
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
The superb mechanical properties of some natural materials usually result from highly ordered, multiscale and hierarchical architectures such as bone, nacre, exoskeleton, etc. Nonetheless, the involved gene regulated process cannot be realized artificially. Here we report bioinspired 3D structures with similar performance following a rapid, green, one-pot synthesis route based on the concept of "brick-and-mortar" biomineralization by introducing Ca2+ and PO43- into a nanochitin dispersion followed by ammonia vapor diffusion. The process leads to self-stratified, periodic assemblies formed under ion diffusion gradients and hydrogelation of nanochitin with simultaneous mineral coprecipitation. Specifically, an organic hydrogel network is formed from partially deacetylated chitin nanofibers together with hydroxyapatite. The components are structured in periodic bands by alternating (organic/inorganic) precipitation as layer-by-layer stacks. The layer space is adjustable by changing the ion concentration and temperature of regulators. Endowed with directional diffusion, customizable 3D forms are self-assembled and demonstrated to function as optical waveguides with selective light transmission. Upon hot pressing, the synthesized material shows structural similarity to natural nacre and displays exceptional strength. This artificial method can reduce the synthesis time from years in nature to a few days in a lab, with no need for complex treatments or facilities; moreover, the designable structure can be customized for uses ranging from structural support in biomedical implants to optical waveguides.