High-Performance Strain Sensors Based on Organohydrogel Microsphere Film for Wearable Human-Computer Interfacing.

Stretchable hydrogel-based strain sensors suffer from limited sensitivity, which urgently requires further breakthroughs for precise and stable human-computer interaction. Here, an efficient microstructural engineering strategy is proposed to significantly enhance the sensitivity of hydrogel-based strain sensors by sandwiching an emulsion-polymerized polyacrylamide organohydrogel microsphere membrane between two Ecoflex films, which are accompanied by crack generation and propagation effects upon stretching. Consequently, the as-developed strain sensor exhibits ultrahigh sensitivity (gauge factor (GF) of 1275), wide detection range (100% strain), low hysteresis, ultralow detection limit (0.05% strain), good fatigue resistance, and low fabrication cost. In addition, the sensor features good water, dehydration, and frost resistance, enabling real-time strain monitoring in various complex conditions due to the encapsulation of Ecoflex film and the addition of glycerol and KCl. Through further structural manipulation, the device achieves superior response to tiny strains, with a GF value of 98.3 in the strain range of less than 1.5%. Owing to the high strain sensing performance, the sensor is able to detect various human activities from swallowing to finger bending even under water. On this basis, a wireless sensing system with apnea warning and single-channel gesture recognition capabilities is successfully demonstrated, demonstrating its great promise as wearable electronics.

Starch-based nanospheres modified filter paper for o/w emulsions separation and contaminants removal.

There is a pressing need around the world to develop novel functional biodegradable materials to separate oil/water mixtures and emulsions completely. Recently, superhydrophilicity and underwater superoleophobicity materials have been attracted attention due to their high efficiency in oil/water separation. However, it is still a challenge to prepare materials that combine oil/water separation and water purification in an environment-friendly way. In this work, biodegradable starch-based nanospheres (SNPs) coated filter paper was prepared in a low-cost, simple, and environmentally friendly manner. The SNPs coating could not only help to change the wettability of the substrate material but also build the hierarchical micro and nano structures which are conducive to separation and purification process. After modification by coating SNPs, the filter paper exhibited excellent performance in a wide range of oil/water mixtures or emulsions separation and the wettability of the filter paper could be regulated by adjusting the pH value. The modified filter paper presented good recyclability after several separation process. Furthermore, the as-prepared filter paper could also remove water-soluble contaminants during the oil/water separation process, thus realizing to combine separation and purification process in one single step. This biodegradable starch-based separating material with good separation performance, stability and recyclability has significant application potential in practical separation and purification process.

Thermoresponsive starch-based particle-stabilized Pickering high internal phase emulsions as nutraceutical containers for controlled release.

Pickering high internal phase emulsions (HIPEs) stabilized solely by bioderived starch-based particles hold potential for application in the food and pharmaceutical fields. This paper reports the use of a thermoresponsive 2-hydroxy-3-butoxypropyl starch (HBPS) particle as a representative natural biocompatible material for use as an effective stabilizer for HIPE formation. HBPS is synthesized by using butyl glycidyl ether as a hydrophobic reagent to change the hydrophobic-hydrophilic balance of starch, and then starch-based particles are fabricated by a simple nanoprecipitation procedure. The size of particles increased with an increase in temperature, and the particles are essentially monodisperse with a PDI of about 0.1 when the temperature was above 15 °C. These HBPS particles were subsequently used as an effective stabilizer to fabricate stable oil-in-water (o/w) Pickering HIPEs with an internal phase volume of 80% at different stabilizer concentrations. The results demonstrated that increasing the particle concentration is conducive to the formation of stable Pickering HIPEs with greater stiffnesses. In addition, the nutraceutical material (ß-carotene) was encapsulated into HIPEs and in vitro release experiments revealed that the release in this system can be controlled by adjusting the temperature.

A facile method to synthesize strong salt-enhanced hydrogels based on reversible physical interaction.

To overcome the adverse effects of salt on the mechanical properties of hydrogels, a facile double cross-linking method has been proposed to synthesize salt-enhanced tough hydrogels. Herein, a poly(hexafluorobutyl methacrylate-acrylamide) hydrogel [P(AAm-co-HFBMA) hydrogel] is prepared by the copolymerization of acrylamide (AAm) and hexafluorobutyl methacrylate (HFBMA) with N,N'-methylene bisacrylamide (NMBA) as a cross-linking agent in a dimethylformamide (DMF)/aqueous solution; DMF is then replaced by water. The results indicate that the tensile fracture stress of the P(AAm-co-HFBMA) hydrogel (20 mol% HFBMA) is as high as 0.43 MPa, which is far better than that of the PAAm hydrogel (ca. 30 kPa). Additionally, with a further increase in the hydrophobic structural units (25 mol% HFBMA), the tensile fracture stress of the P(AAm-co-HFBMA) hydrogel can be increased up to 2.34 MPa. The mechanical strength of the P(AAm-co-HFBMA) hydrogel is significantly enhanced to 3.50 MPa (2 M) from 2.34 MPa (0 M) after it is soaked in aqueous NaCl solutions with various salt concentrations. The mechanical properties and the results of the DSC analysis indicate that the main reason for its mechanical strength to exhibit a unique salt-enhancement trend can be explained as follows. After the P(AAm-co-HFBMA) hydrogel is soaked in the salt solution, the network gradually collapses with the penetration of the small molecules of salt. Thus, the hydrophobic C-F units easily form dynamic cross-linking junctions due to the switchable hydrophobic interaction between C-F groups, which can endow the P(AAm-co-HFBMA) hydrogel with a more effective dynamic energy dissipation mechanism in salt solution.

Polymer Brush Graft-Modified Starch-Based Nanoparticles as Pickering Emulsifiers.

We study biosourced core-shell particles with a starch-based core and thermo-responsive polymer brush shell using surface-initiated single-electron transfer living radical polymerization (SI-SET-LRP) as a Pickering stabilizer. The shell endows the Pickering stabilizer with reversible emulsification/demulsification of oil and water properties. The initiator attached to the starch-based nanosphere (Br-SNP) core particle was first fabricated using the precipitation method. Subsequently, dense poly( N-isopropylacrylamide) (PNIPAM) brush graft-modified starch-based nanoparticles (SNP- g-PNIPAM) were obtained via the SI-SET-LRP process. Interfacial properties of the resultant particles were analyzed by interfacial tensiometer measurements, as were the effects of the grafted polymer chain length and temperature on the interfacial activity. Pickering emulsion was obtained using SNP- g-PNIPAM particles as the stabilizer. The effect of the concentration of the Pickering stabilizer on the size of emulsion droplets was analyzed. The emulsification/demulsification process of the Pickering emulsion can be reversed and easily repeated by changing the temperature.

Water-in-oil Pickering emulsion polymerization of N-isopropyl acrylamide using starch-based nanoparticles as emulsifier.

Inverse Pickering emulsions stabilized by naturally derived particles are of interesting during the past decade. In this study, starch-based nanoparticles were used as a particulate emulsifier to stabilize a w/o Pickering emulsion. The effects of particle concentration and oil volume fraction on the emulsion type and stability were investigated in detail. Catastrophic phase inversion from o/w to w/o emulsions occurred at a volume fraction of oil of 0.3-0.4, without altering the particle wettability. Further, a linear relation existed between the average droplet diameter and total amounts of starch-based nanoparticles. The obtained starch-based nanoparticles also served as a Pickering stabilizer to conduct a w/o Pickering polymerization. Raspberry-like thermoresponsive starch-poly(N-isopropyl acrylamide) nanocomposites with a well-defined structure were synthesized.

Fabrication of shape-tunable macroparticles by seeded polymerization of styrene using non-cross-linked starch-based seed.

Nonspherical colloidal particles with various geometries and different compositions have attracted tremendous attention and been widely researched. The preparation of polymer colloidal particles with controlled shapes by seeded polymerization is recognized as the most promising technique owing to the precise control of various morphologies and using non-cross-linked seed particles are of particular interest. Seeds particles derived from natural biopolymers are seldom applied. Hence, non-cross-linked starch-based seed could be used to fabricate the anisotropic particles by soap-free seed polymerization. Non-cross-linked starch-based seed particles were prepared by a nanoprecipitation method. Starch/polystyrene composite colloidal particles with shape-tunable were fabricated by soap-free seeded polymerization using starch-based seed. The effect of the polymerization time, monomer feed ratio and seed type were investigated. The seed particles with a single- or multi-hole structure were obtained after swelling with styrene. The resulting particles including golf-like, raspberry-like, octahedron-like and snowman-like structures, was fabricated on the polymerization process. This study firstly reports that the morphology of composite particles from golf-like to snowman-like at high monomer feed ratio using starch-based seed. At low monomer feed ratio, raspberry-like particles were obtained by surface nucleation increasing process. In addition, seed type also effect the morphology of composite particles.

Tough, rapid-recovery composite hydrogels fabricated via synergistic core-shell microgel covalent bonding and Fe3+ coordination cross-linking.

We developed tough, rapid-recovery composite hydrogels that are fabricated via core-shell microgel covalent bonding and Fe3+ dynamic metal coordination cross-linking. First, core-shell microgels are used as cross-linking agents and initiators to prepare homogeneous hydrogel networks with rapid recovery in the absence of an organic cross-linking agent. The toughness and recoverability of the composite hydrogels can be improved by adding the dynamic reversibility of ionic cross-linking. Owing to the synergistic effect of microgel covalent bonding, Fe3+ coordination cross-linking, and H-bond cross-linking, the multi-cross-linked composite hydrogels exhibit excellent toughness and a fast recovery rate. These characteristics demonstrate that the dynamic reversibility of the ionic cross-linking can significantly improve the toughness and recoverability of the hydrogels. In addition, the core-shell microgels play a key role in toughening the hydrogels and accelerating their recovery by transferring stress to grafted polymer chains and homogenizing the hydrogel network.

Interfacial Activity of Starch-Based Nanoparticles at the Oil-Water Interface.

Understanding the interfacial activity of polysaccharide nanoparticles adsorbed at oil-water interfaces is essential and important for the application of these nanoparticles as Pickering stabilizers. The interfacial properties of starch-based nanospheres (SNPs) at the interface of an n-hexane-water system were investigated by monitoring the interfacial tension at different bulk concentrations. The three-phase contact angle (θ) and the adsorption energy (ΔE) increased with increasing size and degree of substitution with octenyl succinic groups (OSA) in the particles. Compared with the OSA-modified starch (OSA-S) macromolecule, the SNPs effectively reduced the interfacial tension of the n-hexane-water system at a relatively higher concentration. These results and the method reported herein are useful for selecting and preparing polysaccharide nanoparticles as Pickering stabilizers for oil-water emulsions.