Multifunctional Material Building Blocks from Plant Pollen.

With its multifaceted nature, plant pollen serves not only as a key element in the reproductive cycle of seed plants but also as an influential contributor to environmental, human health, safety, and climate-related concerns. Pollen functions as a carrier of nutrients and organisms and holds a pivotal role in sustaining pollinator populations. Moreover, it is vital in ensuring the safety and quality of our food supply while presenting potential therapeutic applications. Pollen, often referred to as the diamond of the organic world due to its distinctive physical structures and properties, has been underappreciated from a material science and engineering standpoint. We propose adopting a more interdisciplinary and comprehensive approach to its study. Recent groundbreaking research has focused on the development of pollen-based building blocks that transform practically indestructible plant pollen into microgel, paper, and sponge, thereby unveiling numerous potential applications. In this review, we highlight the transformative potential of plant pollen as it is converted into a variety of building blocks, thereby unlocking myriad prospective applications through eco-friendly processing.

A sodium alginate/carboxymethyl chitosan dual-crosslinked injectable hydrogel scaffold with tunable softness/hardness for bone regeneration.

Recently, injectable dual-crosslinked (DC) hydrogel scaffolds have attracted many attentions as a class of excellent bone regeneration biomaterials with in-situ tunable functions. However, the design of injectable DC hydrogels with cell behavior-compatible network structure and mechanical property remains a bottleneck. Herein, based on the in-situ gelling method, we constructed an injectable CMCS/PEG+SA/CaCl2 (CPSC) chemical/physical DC hydrogel scaffold with tunable softness/hardness mechanical properties and good biocompatibility. The formation mechanism and properties of the CPSC hydrogel scaffold were investigated by FTIR, XRD, rheometry, and mechanical testing. It is found that proper softness/hardness mechanical properties can be obtained by adjusting the secondary network structure of the hydrogel. The CPSC hydrogel scaffold prepared under optimal conditions can effectively promote cell infiltration, nutrient transport, and the osteogenic differentiation of rat bone mesenchymal stem cells (rBMSCs). The in vivo experiments show that the rBMSCs-loaded injectable CPSC hydrogels with appropriate mechanical properties can effectively promote bone reconstruction. This study has provided important guidance for the construction of injectable DC hydrogels with adjustable softness/hardness to promote osteogenesis for bone defect repair.

A natural polymer-based hydrogel with shape controllability and high toughness and its application to efficient osteochondral regeneration.

Hydrogels prepared from sustainable natural polymers have broad prospects in the biological field. However, their poor mechanical properties and challenges in achieving shape control have limited their application. Herein, a novel preforming dual-effect post-enhancing method is proposed to address these issues. The method utilizes the hydrogen bonding of agar to obtain a shape-controllable preformed hydrogel at low polymer concentrations using casting, injection, or 3D printing techniques. Subsequently, the preformed hydrogel was subjected to a permeation process to form a post-enhanced multi-network (PEMN) hydrogel with hierarchical chain entanglements to ensure its high toughness, which exhibits tensile and compressive strengths of up to 0.51 MPa and 1.26 MPa with solely physically crosslinking networks. The excellent biocompatibility of the PEMN hydrogel prepared without the need for additional initiator agents under mild conditions was confirmed by both in vitro and in vivo experiments. Furthermore, the adaptability for irregular defects, suitable toughness, adhesive properties, and degradability of PEMN hydrogels are beneficial to provide mechanical support, induce endogenous cell mineralization, and accelerate the regeneration of cartilage and subchondral bone with more than 40% bone regeneration in 12 weeks. Our work has provided a novel solution to simultaneously achieve shape controllability and high toughness based on natural polymers among the already well-explored strategies for osteochondral regeneration.

Electroactive injectable hydrogel based on oxidized sodium alginate and carboxymethyl chitosan for wound healing.

Electroactive hydrogel is of great significance in restoring wound currents, promoting cell proliferation, and accelerating the wound healing process. However, the poor dispersity and underlying toxicity of electronic conductive fillers and high concentration of ionic conductors in traditional electroactive hydrogel limited its application in medical care. Herein, an electroactive oxidized sodium alginate/carboxymethyl chitosan/silver nanoparticles (OSA/CMCS/AgNPs) hydrogel was constructed with no additional conductive fillers or synthesized conductive polymers being added, in which the dynamic imine bonds were rapidly formed between aldehyde groups in OSA and amino groups in CMCS, and AgNPs were further in situ formed by UV irradiation. The electroactive hydrogel exhibited the injectable property, strong self-healing ability, excellent biocompatibility, and high antibacterial activities. Moreover, the electroactive hydrogel can significantly promote the proliferation of L929 cells under electrical stimulation. Furthermore, the electroactive hydrogel was proved to significantly accelerate the wound healing process in the full-thickness skin defect model, exhibiting anti-inflammation, promoting the fibroblasts proliferation, angiogenesis, and collagen deposition under electrical stimulation. In summary, the current work explored a novel strategy to construct the polysaccharides-based electroactive hydrogel with good biocompatibility and multi-functions, which is promising to be used in deep wound treatment.

Green Conductive Hydrogel Electrolyte with Self-Healing Ability and Temperature Adaptability for Flexible Supercapacitors.

Conductive hydrogels (CHs) are ideal electrolyte materials for the preparation of flexible supercapacitors (FSCs) due to their excellent electrochemical properties, mechanical properties, and deformation restorability. However, most of the reported CHs are prepared by the chemical crosslinking of synthetic polymers and thus usually display the disadvantages of poor self-healing abilities and nonadaptability at environmental temperatures, which greatly limits their application. To overcome these problems, in the present work, we constructed a sodium alginate-borax/gelatin double-network conductive hydrogel (CH) by a dynamic crosslinking between sodium alginate (SA) and borax via borate bonds and hydrogen bonding between amino acids in gelatin and SA chains. The CH displays an excellent elongation of 305.7% and fast self-healing behavior in 60 s. Furthermore, a phase-change material (PCM), Na2SO4·10H2O, was introduced into the CH, which, combined with the nucleation effect of borax, improved the ionic conductivity and temperature adaptability of the CH. The flexible supercapacitor (FSC) assembled with the obtained CH as the electrolyte exhibits a high specific capacitance of 185.3 F·g-1 at a current density of 0.25 A·g-1 and good stability with 84% capacitance retention after 10 000 cycles and excellent temperature tolerance with a resistance variation of 2.11 Ω in the temperature range of -20-60 °C. This green CH shows great application potential as an electrolyte for FSCs, and the preparation method can be potentially expanded to the fabrication of self-repairing FSCs with good temperature adaptabilities.

High-Sensitivity and Environmentally Friendly Humidity Sensors Deposited with Recyclable Green Microspheres for Wireless Monitoring.

The reliable, high-sensitive, wireless, and affordable requirements for humidity sensors are needed in high-precision measurement fields. Quartz crystal microbalance (QCM) based on the piezoelectric effect can accurately detect the mass changes at the nanogram level. However, water-capture materials deposited on the surface of QCM generally show disadvantages in either cost, sensitivity, or recyclability. Herein, novel QCM-based humidity sensors (NQHSs) are developed by uniformly depositing green microspheres (GMs) of natural polymers prepared by the chemical synthesis of the emulsification/inner gel method on QCM as humidity-sensitive materials. The NQHSs demonstrate high accuracy and sensitivity (27.1 Hz/% RH) owing to the various hydrophilic groups and porous nano-3D deposition structure. Compared with the devices deposited with a smooth film, the frequency of the NQHSs shows almost no changes during the cyclic test and exhibits long-term stability. The NQHSs have been successfully applied to non-contact sensing human activities and remote real-time humidity monitoring via Bluetooth transmission. In addition, the deposited humidity-sensitive GMs and QCM substrate are fully recycled and reused (72% of the original value). This work has provided an innovative idea to construct environmental-friendly, high-sensitivity, and wireless humidity sensors.

Construction of a physically cross-linked carrageenan/chitosan/calcium ion double-network hydrogel for 3-Nitro-1, 2, 4-triazole-5-one removal.

3-Nitro-1, 2, 4-triazole-5-one (NTO) is an important insensitive explosive. The discharge of NTO wastewater not only pollutes the environment but also causes the economic loss of the valuable explosive. Currently, the NTO wastewater in industrial production is often treated with activated carbon adsorbents. There are no green, efficient and specific adsorption materials for the NTO treatment yet. In the present work, polymer materials suitable for NTO adsorption were screened by molecular dynamics simulation. With the optimized materials, a carrageenan/chitosan/calcium ion physically cross-linked double network hydrogel (KC/CTS/Ca2+ PCDNH) was successfully prepared by the semi-soluble-acidified sol-gel conversion method. The structure and NTO adsorption performance of the hydrogel were investigated by scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The NTO adsorption kinetics, isotherm, and thermodynamics were further studied to understand the adsorption behavior and mechanism. In addition, the adsorbed NTO was successfully released and recovered by soaking the hydrogel in NaOH solution. Our work has provided an environmentally friendly and targeted preparation method of NTO adsorbent materials for NTO wastewater treatment.

Construction of chitosan/polyacrylate/graphene oxide composite physical hydrogel by semi-dissolution/acidification/sol-gel transition method and its simultaneous cationic and anionic dye adsorption properties.

In the current study, a novel CTS/PAA/GO composite polyampholyte physical hydrogel was prepared by the SD-A-SGT method to achieve desired adsorption properties for printing and dyeing wastewater treatment. The hydrogels exhibited controllable and stable structure. The linear PAA significantly improved the swelling and adsorption properties of the hydrogel, and the composition of GO enhanced its mechanical and adsorption properties. The batch adsorption experiments revealed the ability to simultaneously absorb the cationic model dye, MB, and anionic model dye, FY3, with the similar equilibrium adsorption capacities of 296.5±31.7 mg·g-1 and 280.3±23.9 mg·g-1, respectively. The factors affecting the dye adsorption performance, including the hydrogel composition, initial dye concentration and dye solution pH, were investigated. The dye adsorption kinetics was studied and the adsorption mechanisms were proposed. The unique structure and properties of the hydrogel make it a great candidate adsorbent for wastewater treatments.

Synthesis and application of a series of amphipathic chitosan derivatives and the corresponding magnetic nanoparticle-embedded polymeric micelles.

Magnetic nanoparticle-embedded polymeric micelles (MNP-PMs) prepared with amphipathic polymers are an important sustained-release carrier for hydrophobic drugs. The amphipathic chitosan derivatives (ACDs) based stimuli-responsive slow-release carriers have attracted considerable attentions because of the bioactivities and modifiability of chitosan. In the current study, a series of ACDs including alkylated N-(2-hydroxy) propyl-3-trimethyl ammonium chitosan chloride (alkyl-HTCC) and alkylated polyethylene glycol N-(2-hydroxy) propyl-3-trimethyl ammonium chitosan chloride (alkyl-PEG-HTCC) were prepared by the reductive amination of HTCC and PEG-HTCC, and their structures and properties were characterized. Octyl-HTCC/O-Fe3O4 and octyl-PEG-HTCC/O-Fe3O4 MNP-PMs were prepared by the hydrophobic interactions between the corresponding ACDs and oil soluble Fe3O4 magnetic nanoparticles (O-Fe3O4 MNPs), and characterized for the structure, magnetic performance and surface charge state. Their potential application as a drug delivery carrier was investigated upon the embedding efficiency and pH dependent sustained-release performance using the hydrophobic drug, paclitaxel (PTX), as a model drug. Our work has provided a new application strategy of ACDs in the multi-functional drug delivery carrier.

In situ synthesis of poly (γ- glutamic acid)/alginate/AgNP composite microspheres with antibacterial and hemostatic properties.

In the present work, a poly(γ-glutamic acid)/alginate/silver nanoparticle (PGA/Alg/AgNP) composite microsphere with excellent antibacterial and hemostatic properties was prepared by the in situ UV reduction and emulsion internal gelation method, and its potential application for antibacterial hemostatic dressing was explored. Well dispersed AgNPs were in situ synthesized by a UV reduction method with alginate as stabilizer and reductant. The AgNPs showed excellent antibacterial activities against both gram-negative and gram-positive bacteria. Additionally, the AgNPs prepared by the in-situ UV reduction exhibited better biocompatibility and antibacterial effects than those prepared by the conventional chemical reduction method. PGA/Alg/AgNP composite microspheres were then prepared with the AgNPs by an emulsion internal gelation method. Such microspheres were found to be a porous and hollow network with pH-sensitive swelling properties and excellent hemostatic performance, indicating its application potentials as an advanced antibacterial hemostatic material.

Preparation of the chitosan/poly(glutamic acid)/alginate polyelectrolyte complexing hydrogel and study on its drug releasing property.

In the current study, a novel semi-dissolution/acidification/sol-gel transition (SD-A-SGT) method was explored for the preparation of polyelectrolyte complexing (PEC) composite hydrogels with natural polymers only. A chitosan (CS) powder was uniformly dispersed in a solution of poly(glutamic acid) (PGA) and alginate (SA) to form a semi-dissolved slurry mixture that was then exposed to an gaseous acidic atmosphere. CS was gradually dissolved and interacted with PGA and SA to form a CS/PGA/SA PEC composite hydrogel with a homogeneous structure. The SD-A-SGT procedure was able to overcome the shortcomings of direct mixing method via the PEC interaction. The effects of the hydrogel composition on its structure and properties were investigated by FTIR, XRD, rheology study, XPS, SEM, and swelling kinetics. The drug delivery performance of the CS/PGA/SA hydrogel was explored using piroxicam (PXC) as a model drug. PXC was in situ embedded in the hydrogel by the SD-A-SGT method. The hydrogel exhibited pH responsive drug release behaviors that were affected by the hydrogel composition. In all, the SD-A-SGT method for preparing PEC composite hydrogels has a great application potential in constructing the CS based hydrogels as medical materials.