Facile preparation of hydrogel glue with high strength and antibacterial activity from physically linked network.

Constructing plant-based hydrogel glues with outstanding adhesiveness, antibacterial activity and suitable mechanical properties has great practical importance in multiple areas. However, preparation of traditional antibacterial adhesive hydrogels usually requires of complex chemical reactions as well as expensive and toxic ingredients. Here, we develop a type of physically crosslinked hydrogel glues, which contains polyvinyl alcohol (PVA) for generating mechanical property, ß-cyclodextrin (ß-CD) for creating adhesion strength and acting as the drug carrier for curcumin (CUR), and silica nanoparticles for resolving the conflict between strength and adhesion within the gel matrix. The physically linked composite showed tunable mechanical strengths ranged from 150 kPa to 560 kPa, as well as high maximum strains up to 380%. Moreover, the composite gel exhibited high swelling ratio and significant antibacterial property. This study demonstrates that the pure physical strategy can be well used to prepare antibacterial hydrogel glues with high performance. The combining of the facile method with conventional and biocompatible materials provides a viable way for fabricating antibacterial hydrogel glues for practical applications.

Double-network hydrogels with superior self-healing properties using starch reinforcing strategy.

Constructing hybrid double network (DN) hydrogels has become an important strategy to prepare strong and tough hydrogels with good self-healing properties for durable usage. However, the recoverable and self-healing efficiencies of DN hydrogels are usually low. We develop a type of hybrid DN hydrogel, which contain the starch network for generating strong dynamic interactions within the gel matrix. The composite gels show tensile strength over 200 kPa with the elastic modulus of ∼29.7 kPa. Gelatinization of cassava starch is a key procedure that can significantly raise mechanical strengths. The healing efficiency of the composite gel gradually increased to as high as 99 % after 24 h at room temperature. This work shows that dynamic physical bonding in hydrogels can be greatly enhanced by a simple starch reinforcing tactic. The combination of naturally abundant starch with hydrophilic polymers provides a general approach to design functional soft materials for applications in various fields.

Cellulose-starch Hybrid Films Plasticized by Aqueous ZnCl2 Solution.

Starch and cellulose are two typical natural polymers from plants that have similar chemical structures. The blending of these two biopolymers for materials development is an interesting topic, although how their molecular interactions could influence the conformation and properties of the resultant materials has not been studied extensively. Herein, the rheological properties of cellulose/starch/ZnCl2 solutions were studied, and the structures and properties of cellulose-starch hybrid films were characterized. The rheological study shows that compared with starch (containing mostly amylose), cellulose contributed more to the solution's viscosity and has a stronger shear-thinning behavior. A comparison between the experimental and calculated zero-shear-rate viscosities indicates that compact complexes (interfacial interactions) formed between cellulose and starch with ≤50 wt % cellulose content, whereas a loose structure (phase separation) existed with ≥70 wt % cellulose content. For starch-rich hybrid films prepared by compression molding, less than 7 wt % of cellulose was found to improve the mechanical properties despite the reduced crystallinity of the starch; for cellulose-rich hybrid films, a higher content of starch reduced the material properties, although the chemical interactions were not apparently influenced. It is concluded that the mechanical properties of biopolymer films were mainly affected by the structural conformation, as indicated by the rheological results.

Starch-zinc complex and its reinforcement effect on starch-based materials.

In this work, we found that ZnCl2 solution can not only be used as a plasticizer for starch but also provide a mechanical reinforcement effect to the resultant starch-based materials. By a one-step compression molding process, well-plasticized starch-based films could be obtained at 120 °C with a 15 wt.% ZnCl2 solution. Both the tensile strength and elongation at break of the films increased with a rise in ZnCl2 concentration, which demonstrates a mechanical reinforcement. This reinforcement could be mainly ascribed to the in-situ formed starch-zinc complexes and the enhanced starch molecular interactions. Moreover, if the processing method was changed into firstly mixing followed by compression molding, the tensile strength increased by more than three folds at no cost of the elongation at break. Regarding this, we propose that shear could further enhance the molecular interactions within the material. However, if the ZnCl2 concentration was too high, the mechanical properties were then reduced irrespective of the processing protocol, which could be due to the weakened molecular interactions by ZnCl2. Thus, we have demonstrated a new, simple method for preparing starch-based composite materials with enhanced mechanical properties, which could be potentially applied to many fields such as packaging, coating and biomedical materials.

Zinc chloride aqueous solution as a solvent for starch.

It is important to obtain starch-based homogeneous systems for starch modification. Regarding this, an important key point is to find cheap, low-cost and low-toxicity solvents to allow complete dissolution of starch and its easy regeneration. This study reveals that a ZnCl2 aqueous solution is a good non-derivatizing solvent for starch at 50 °C, and can completely dissolve starch granules. The possible formation of a "zinc-starch complex" might account for the dissolution; and the degradation of starch, which was caused by the H(+) inZnCl2 aqueous solution, could not contribute to full dissolution. From polarized light microscopic observation combined with the solution turbidity results, it was found that the lowest ZnCl2 concentration for full dissolution was 29.6 wt.% at 50 °C, with the dissolving time being 4h. Using Fourier-transform infrared (FTIR), solid state (13)C nuclear magnetic resonance (NMR), and X-ray diffraction (XRD), it was revealed that ZnCl2 solution had no chemical reaction with starch glucosides, but only weakened starch hydrogen bonding and converted the crystalline regions to amorphous regions. In addition, as shown by intrinsic viscosity and thermogravimetric analysis (TGA), ZnCl2 solution caused degradation of starch macromolecules, which was more serious with a higher concentration of ZnCl2 solution.

Understanding the structural features of high-amylose maize starch through hydrothermal treatment.

In this study, high-amylose starches were hydrothermally-treated and the structural changes were monitored with time (up to 12h) using scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM), small-angle X-ray scattering (SAXS), X-ray diffraction (XRD), and differential scanning calorimetry (DSC). When high-amylose starches were treated in boiling water, half-shell-like granules were observed by SEM, which could be due to the first hydrolysis of the granule inner region (CLSM). This initial hydrolysis could also immediately (0.5h) disrupt the semi-crystalline lamellar regularity (SAXS) and dramatically reduce the crystallinity (XRD); but with prolonged time of hydrothermal treatment (≥2 h), might allow the perfection or formation of amylose single helices, resulting in slightly increased crystallinity (XRD and DSC). These results show that the inner region of granules is composed of mainly loosely-packed amylopectin growth rings with semi-crystalline lamellae, which are vulnerable under gelatinization or hydrolysis. In contrast, the periphery is demonstrated to be more compact, possibly composed of amylose and amylopectin helices intertwined with amylose molecules, which require greater energy input (higher temperature) for disintegration.