Dityrosine-inspired photocrosslinking technique for 3D printing of silk fibroin-based composite hydrogel scaffolds.

Photoinduced self-crosslinking technology is a great facilitator of 3D bioprinting of silk fibroin (SF) by allowing rapid solidification of a deliberately formulated SF-based photocrosslinkable bioink. An SF-based, photocrosslinked hydrogel was fabricated with tyramine-modified sodium carboxymethyl cellulose (CMC-Na) as a co-crosslinkable constituent and Ru(bpy)3Cl2 (Ru(II)) and potassium persulfate (KPS) as blue light photoinitiators. Photorheological studies demonstrated that the photocrosslinking and viscoelasticity of the composite could be tuned by varying the relative content of the two constituents. Xanthan gum (XG) was employed in formulating the SF-based photocrosslinkable bioink, and the improved rheological properties and printability were evidenced by the resulting tunable shear-thinning behavior and shear thixotropy. 3D SF-based hydrogel scaffolds with uniform pores with a size of approximately 550 µm × 1000 µm were constructed via extrusion-based printing and a simple 30 s post-photocrosslinking combined process. Furthermore, the CMC-Na incorporated 3D hydrogel scaffolds exhibited sufficient structural strength, adequate filament fineness, and tunable transparency, which shows a promising prospect in the application of tissue engineering and regenerative medicine.

Blue Light Induced Photopolymerization and Cross-Linking Kinetics of Poly(acrylamide) Hydrogels.

Blue light induced photopolymerization and photo-cross-linking kinetics of acrylamide (AM), with camphorquinone/diphenyl iodonium hexafluorophosphate (CQ/DPI) as photoinitiators, were investigated. The effects of a number of parameters, including mass fraction of CQ, DPI, and AM (wCQ, wDPI, and wAM) and light intensity (I), on photopolymerization efficiency and photogelation process were systematically studied by photo-differential scanning calorimetry (DSC) and photo-rheometry. Photo-DSC indicated that the maximum photopolymerization rate (Rp, max) was proportional to wCQ0.5, wDPI0.5, I0.5, and wAM, while Photo-Rheometry showed linear relationships between gel time tgel and wCQ and I, respectively, and power law relationships between tgel and wDPI and wAM, respectively. In addition, both peak cross-linking rate Rc,max, and delay time td, which were both linearly proportional to wCQ0.5, wDPI0.5, and I0.5, showed power law relationships with wAM. Furthermore, exponential patterns were observed between all these factors, wCQ, wDPI, wAM, and I and plateau modulus G'∞. Combining such correlations obtained from experimental data, an empirical model was established describing the projected mechanical properties of poly(acrylamide) hydrogels from blue light initiated photopolymerization and photo-cross-linking.

Patterned SiO2/Polyurethane Acrylate Inverse Opal Photonic Crystals with High Color Saturation and Tough Mechanical Strength.

Patterned structural color photonic crystals (PCs) based on periodic photonic nanostructures have attracted great interest in developing high-performance sensors and other smart optical materials as well as tunable structurally colored fashion textiles. However, previously reported patterned PCs with both high color saturation and tough mechanical strength were difficult to achieve, which restricts their practical applications. Herein, arbitrarily patterned silica/polyurethane acrylate (SiO2/PUA) inverse opal photonic crystals (IOPCs) with high color saturation and tough mechanical strength were innovatively designed and fabricated by writing with photopolymerizable PUA "ink" on a self-assembled hollow SiO2 PC template. The high color saturation of the prepared SiO2/PUA IOPCs originated from the high refractive index contrast between the encapsulated air-filled core and the SiO2/PUA composite skeleton. The cross-linked flexible PUA matrix tightly warped the self-assembled hollow SiO2 nanospheres together, endowing the obtained SiO2/PUA IOPCs a structural color pattern with tough mechanical strength. The structural colors of SiO2/PUA IOPCs could be finely tuned by regulating their basic parameters, and a redshift in the resultant structural color was observed due to an increase in the lattice constant when increasing the core size and/or shell thickness of the hollow SiO2 nanospheres.

Development of Highly Flexible Piezoelectric PVDF-TRFE/Reduced Graphene Oxide Doped Electrospun Nano-Fibers for Self-Powered Pressure Sensor.

The demand for self-powered, flexible, and wearable electronic devices has been increasing in recent years for physiological and biomedical applications in real-time detection due to their higher flexibility and stretchability. This work fabricated a highly sensitive, self-powered wearable microdevice with Poly-Vinylidene Fluoride-Tetra Fluoroethylene (PVDF-TrFE) nano-fibers using an electrospinning technique. The dielectric response of the polymer was improved by incorporating the reduced-graphene-oxide (rGO) multi-walled carbon nano-tubes (MWCNTs) through doping. The dielectric behavior and piezoelectric effect were improved through the stretching and orientation of polymeric chains. The outermost layer was attained by chemical vapor deposition (CVD) of conductive polymer poly (3,4-ethylenedioxythiophene) to enhance the electrical conductivity and sensitivity. The hetero-structured nano-composite comprises PVDF-TrFE doped with rGO-MWCNTs over poly (3,4-ethylenedioxythiophene) (PEDOT), forming continuous self-assembly. The piezoelectric pressure sensor is capable of detecting human physiological vital signs. The pressure sensor exhibits a high-pressure sensitivity of 19.09 kPa-1, over a sensing range of 1.0 Pa to 25 kPa, and excellent cycling stability of 10,000 cycles. The study reveals that the piezoelectric pressure sensor has superior sensing performance and is capable of monitoring human vital signs, including heartbeat and wrist pulse, masticatory movement, voice recognition, and eye blinking signals. The research work demonstrates that the device could potentially eliminate metallic sensors and be used for early disease diagnosis in biomedical and personal healthcare applications.

High Structural Stability of Photonic Crystals on Textile Substrates, Prepared via a Surface-Supported Curing Strategy.

Over the past years, photonic crystals (PCs) with a periodically ordered nanostructure have attracted great attention due to their potential as advanced optical materials for structural coloration of textiles. However, the weak structural stability of PCs on flexible textile substrates makes them vulnerable to strong external forces, hampering their large-scale application. In this work, a waterborne polyurethane (wPU) is chosen for enhancing the structural stability of PCs. The composite PCs (PCs/wPU) show both brilliant structural colors and significantly improved structural stability. The structural color produced by the encapsulated PCs is found to depend on the properties of encapsulating agents. The wPU with high surface tension solidifies mainly on the PC surface in the form of a transparent film, protecting the overall structure of PCs. Meanwhile, a small amount of wPU, infiltrating into the interior of PCs, provides strong adhesion and ensures stability among nanospheres. In turn, polydimethylsiloxane (PDMS) with low surface tension is easy to infiltrate into the interior of PCs, forming fully encapsulated PCs. This reduces the brightness of structural color produced by the final PCs/PDMS composite over the original PCs, due to the replacement of air by PDMS, and thus the decrease in the refractive index contrast of PCs. The supported curing strategy using the encapsulating agent with high surface tension is shown to not only improve the structural stability of PCs but also exert almost no influence on the optical properties of PCs, facilitating the practice application of structural coloration in the textile industry.

Facile Fabrication of Amorphous Photonic Structures with Non-Iridescent and Highly-Stable Structural Color on Textile Substrates.

Amorphous photonic structures with non-iridescent and highly-stable structural color were fabricated via a simple one-step spray-coating technique. With this strategy, the obtained films on textile substrates presented short-ordered and amorphous photonic structures (APSs) similar to the amorphous nanostructures of avian feathers. The structural color presented the same hue when viewed at different angles and could be well controlled by varying the diameters of the SiO2 nanospheres. The prepared fabrics with structural color exhibited high color stability due to stability in both the assembled physical structure and the refractive index. The high stability of the assembled physical structure was attributed to the cementing effect of Poly(methylmethacrylate-butylacrylate) P(MMA-BA) existing between textile substrate and SiO2 nanospheres and among SiO2 nanospheres, while the high stability in the refractive index was contributed by the liquid-resistance achieved by both the surface roughness and the low-surface-energy of the as-sprayed APSs. With the resistances to external forces and liquid invasion, the non-iridescent brilliant structural color of the as-prepared fabrics could be kept steady. In this study, an approach of fabricating APSs with non-iridescent and stable structural color was established to enhance its potential application in structural coloration of textiles, and other color-related smart textiles. .

Conductive Textiles via Vapor-Phase Polymerization of 3,4-Ethylenedioxythiophene.

We fabricated electrically conductive textiles via vapor-phase polymerization of poly(3,4-ethylenedioxythiophene) (PEDOT) layers on cotton, cotton/poly(ethylene terephthalate) (PET), cotton/Lycra, and PET fabrics. We then measured the electrical resistivity values of such PEDOT-coated textiles and analyzed the effect of water treatment on the electrical resistivity. Additionally, we tested the change in the electrical resistance of the conductive textiles under cyclic stretching and relaxation. Last, we characterized the uniformity and morphology of the conductive layer formed on the fabrics using scanning electron microscopy and electron-dispersive X-ray spectroscopy.

Reduction of colorants in nylon flock dyeing effluent.

The batch dyeing of fiber materials such as staple fibers and flock is usually carried out by exhaustion methods. However, the dyeing of flock fibers, either nylon, PET or acetate, with acid or disperse dyes is not 100% efficient in terms of dye utilization. Therefore, the remaining dyes in the spent dye bath are generally not reused, and are usually discharged with minimum treatment, together with the dyeing chemicals into the sewage wastewater system causing environmental pollution. We found that the colorants and chemical auxiliaries in the fiber dyeing effluents can be reduced by: (1) optimizing the acid dyeing conditions such as salt addition and pH control; (2) reuse of the spent dye bath that remain after the original dyeing process. In the lab scale trials, we have successfully raised the acid dye exhaustion to over 90% by optimizing the dyeing conditions. The reuse of the spent acid dye bath also showed promising results with dye exhaustion ranging from 91 to 93% after four times of reuse.