Polar-Group Activated Isospecific Coordination Polymerization of ortho-Methoxystyrene: Effects of Central Metals and Ligands.

Stereoselective polymerization of polar vinyl monomers has been a long-standing challenge because the employed transition-metal catalysts are easily poisoned by polar groups of monomers. In this contribution, a series of ß-diketiminato rare-earth metal complexes 1-5 (L1-5 Ln(CH2 SiMe3 )2 (THF)n , Ln=Gd-Lu, Y, and Sc) were successfully synthesized. In combination with AliBu3 and [Ph3 C][B(C6 F5 )4 ], complexes 1 c(Tb)-1 g(Tm) exhibited high activities and excellent isoselectivities for the polymerization of ortho-methoxystyrene (oMOS), in which, the polar methoxy group of oMOS did not poison but activated the polymerization through σ-π chelation to the active species together with the vinyl group. Moreover, the large Gd-attached precursor 1 b showed a higher activity, albeit with a slightly decreased isoselectivity. The small Sc-attached precursor 1 i was completely inert. Meanwhile, the spatial steric arrangement and the coordination mode of the ß-diketiminato ligand could clearly affect and even block oMOS polymerization. This work sheds new light on the coordination polymerization of polar monomers.

Flexible Graphene Electrodes for Prolonged Dynamic ECG Monitoring.

This paper describes the development of a graphene-based dry flexible electrocardiography (ECG) electrode and a portable wireless ECG measurement system. First, graphene films on polyethylene terephthalate (PET) substrates and graphene paper were used to construct the ECG electrode. Then, a graphene textile was synthesized for the fabrication of a wearable ECG monitoring system. The structure and the electrical properties of the graphene electrodes were evaluated using Raman spectroscopy, scanning electron microscopy (SEM), and alternating current impedance spectroscopy. ECG signals were then collected from healthy subjects using the developed graphene electrode and portable measurement system. The results show that the graphene electrode was able to acquire the typical characteristics and features of human ECG signals with a high signal-to-noise (SNR) ratio in different states of motion. A week-long continuous wearability test showed no degradation in the ECG signal quality over time. The graphene-based flexible electrode demonstrates comfortability, good biocompatibility, and high electrophysiological detection sensitivity. The graphene electrode also combines the potential for use in long-term wearable dynamic cardiac activity monitoring systems with convenience and comfort for use in home health care of elderly and high-risk adults.

Quaternary ammonium grafted chitosan hydrogel with enhanced antibacterial performance as tannin acid and deferoxamine carrier to promote diabetic wound healing.

The delay of diabetic wound healing puts a huge burden on the society. The key factors hindering wound healing include bacterial infection, unresolved inflammation and poorly generated blood vessels. In this paper, glycidyl trimethyl ammonium chloride (GTA) was grafted to chitosan (CS) to obtain quaternary ammonium grafted chitosan (QCS) with enhanced antibacterial performance, and then cross-linked by dialdehyde terminated poly(ethylene oxide) (PEO DA) to construct QCS/PEO DA hydrogel with tissue adhesion, biodegradation and self-healing properties. The QCS/PEO DA hydrogel is loaded with tannin acid (TA) and deferoxamine (DFO) to enhance antioxidant property and angiogenesis. At the same time, the TA and DFO loaded TA@DFO/hydrogel preserved the biocompatibility and biodegradability of chitosan. Moreover, the multifunctional hydrogel behaved excellent hemostatic properties in mice model and significantly promoted the healing efficacy of diabetic wounds. Overall, the TA@DFO/hydrogel is promising anti-infection dressing material for diabetic wound healing.

Self-healing hydrogel from poly(aspartic acid) and dextran with antibacterial property for burn wound healing.

Designing hydrogel dressing with intrinsic antibacterial property to promote skin injury recovery remains a significant challenge. In this research, poly(aspartic hydrazide) with grafted betaine (PAHB) was designed and reacted with oxidized dextran (OD) to fabricate biodegradable PAHB/OD hydrogel and its application as wound dressing was systematically investigated. The PAHB/OD hydrogels exhibited fast gelation, strong tissue adhesion, preferable mechanical properties and biocompatibility. The grafted betaine endowed the hydrogel with antibacterial property and antibacterial rate enhanced through photothermal performance of composited CuS nanoparticles under near infrared (NIR) radiation. The CuS composited PAHB/OD hydrogel (CuS/hydrogel) with microporous morphology was used as burn wound dressing with loaded anti-inflammatory drug diclofenac sodium (DS) in mouse model. The results showed the DS loaded CuS/hydrogel (CuS@DS/hydrogel) promoted the tissue regeneration and suppressed the inflammatory response. The histological analysis and immunohistochemical expression confirmed the CuS@DS/hydrogel promote angiogenesis of the burn wound by regulating the expression of inflammatory cytokines (IL-6 and CD68) and vascular endothelial growth factor (VEGF). Overall, the CuS@DS/hydrogel hydrogel is a promising candidate as wound dressing due to its tissue adhesive, antioxidant, antibacterial and anti-inflammatory activities.

Preparation of antibacterial hydrogel from poly(aspartic hydrazide) and quaternized N-[3-(dimethylamino) propyl] methylacrylamide copolymer with antioxidant and hemostatic effects for wound repairing.

Hydrogels as wound dressing have attracted extensive attention in past decade because they can provide moist microenvironment to promote wound healing. Herein, this research designed a multifunctional hydrogel with antibacterial property and antioxidant activity fabricated from quaternary ammonium bearing light emitting quaternized TPE-P(DAA-co-DMAPMA) (QTPDD) and poly(aspartic hydrazide) (PAH). The protocatechuic aldehyde (PCA) grafted to the hydrogel through dynamic bond endowed the hydrogel with antioxidant activity and the tranexamic acid (TXA) was loaded to enhance the hemostatic performance. The hydrogel possesses preferable gelation time for injectable application, good antioxidant property and tissue adhesion, improved hemostatic performance fit for wound repairing. Furthermore, the hydrogel has excellent antimicrobial property to both E. coli and S. aureus based on quaternary ammonium structure. The hydrogel also showed good biocompatibility and the in vivo experiments proved this hydrogel can promote the wound repairing rate. This study suggests that TXA/hydrogel with quaternary ammonium structure and dynamic grafted PCA have great potential in wound healing applications.

Liquid crystalline phase behavior and sol-gel transition in aqueous halloysite nanotube dispersions.

The liquid crystalline phase behavior and sol-gel transition in halloysite nanotubes (HNTs) aqueous dispersions have been investigated by applying polarized optical microscopy (POM), macroscopic observation, rheometer, small-angle X-ray scattering, scanning electron microscopy, and transmission electron microscopy. The liquid crystalline phase starts to form at the HNT concentration of 1 wt %, and a full liquid crystalline phase forms at the HNT concentration of 25 wt % as observed by POM and macroscopic observation. Rheological measurements indicate a typical shear flow behavior for the HNT aqueous dispersions with concentrations above 20 wt % and further confirm that the sol-gel transition occurs at the HNT concentration of 37 wt %. Furthermore, the HNT aqueous dispersions exhibit pH-induced gelation with more intense birefringence when hydrochloric acid (HCl) is added. The above findings shed light on the phase behaviors of diversely topological HNTs and lay the foundation for fabrication of the long-range ordered nano-objects.

A Graphene-Based Flexible Pressure Sensor with Applications to Plantar Pressure Measurement and Gait Analysis.

In the present study, we propose and develop a flexible pressure sensor based on the piezoresistive effect of multilayer graphene films on polyester textile. The pressure response results from the deformation of graphene conductive network structure and the changes in resistance. Here, we show that the graphene pressure sensor can achieve a sensitivity value of 0.012 kPa - 1 , the measurement range can be as high as 800 kPa, and the response time can reach to 50 ms. Subsequently, a stable in-shoe wireless plantar pressure measurement system is developed and dynamic pressure distribution is acquired in real-time. Overall, the graphene textile pressure sensor has the advantage of wide dynamic range, flexibility and comfort, which provides the high possibility for footwear evaluation, clinical gait analysis and pathological foot diagnosis.