Nanocellulose properties and applications in colloids and interfaces

In this review we introduce recent advances in the development of cellulose nanomaterials and the construction of high order structures by applying some principles of colloid and interface science. These efforts take advantage of natural assemblies in the form of fibers that nature constructs by a biogenetic bottom-up process that results in hierarchical systems encompassing a wide range of characteristic sizes. Following the reverse process, a top-down deconstruction, cellulose materials can be cleaved from fiber cell walls. The resulting nanocelluloses, mainly cellulose nanofibrils (CNF) and cellulose nanocrystals (CNC, i.e., defect-free, rod-like crystalline residues after acid hydrolysis of fibers), have been the subject of recent interest. This originates from the appealing intrinsic properties of nanocelluloses: nanoscale dimensions, high surface area, morphology, low density, chirality and thermo-mechanical performance. Directing their assembly into multiphase structures is a quest that can yield useful outcomes in many revolutionary applications. As such, we discuss the use of non-specific forces to create thin films of nanocellulose at the air–solid interface for applications in nano-coatings, sensors, etc. Assemblies at the liquid–liquid and air–liquid interfaces will be highlighted as means to produce Pickering emulsions, foams and aerogels. Finally, the prospects of a wide range of hybrid materials and other systems that can be manufactured via self and directed assembly will be introduced in light of the unique properties of nanocelluloses.     

High‐Internal‐Phase Pickering Emulsions Stabilized Solely by Peanut‐Protein‐Isolate Microgel Particles with Multiple Potential Applications

High‐internal‐phase Pickering emulsions have various applications in materials science. However, the biocompatibility and biodegradability of inorganic or synthetic stabilizers limit their applications. Herein, we describe high‐internal‐phase Pickering emulsions with 87 % edible oil or 88 % n‐hexane in water stabilized by peanut‐protein‐isolate microgel particles. These dispersed phase fractions are the highest in all known food‐grade Pickering emulsions. The protein‐based microgel particles are in different aggregate states depending on the pH value. The emulsions can be utilized for multiple potential applications simply by changing the internal‐phase composition. A substitute for partially hydrogenated vegetable oils is obtained when the internal phase is an edible oil. If the internal phase is n‐hexane, the emulsion can be used as a template to produce porous materials, which are advantageous for tissue engineering.     

Recent developments in Pickering emulsions for biomedical applications

Pickering emulsions, stabilised by organic or inorganic particles, offer long-term dispersibility of liquid droplets and resistance to coalescence. The versatility of stabilising particles and their ability to encapsulate and release cargo with high internal payload capacity makes them attractive in a wide variety of applications, ranging from catalysis to the cosmetic and food industry. While these properties make them an equally promising material platform for pharmaceutical and clinical applications, the development of Pickering emulsions for healthcare is still in its infancy. Herein, we summarise and discuss recent progress in the development of Pickering emulsions for biomedical applications, probing their design for passive diffusion-based release as well as stimuli-responsive destabilisation. We further comment on challenges and future directions of this exciting and rapidly expanding area of research.     

Pickering emulsions: Versatility of colloidal particles and recent applications

The versatility of colloidal particles endows the particle stabilized or Pickering emulsions with unique features and can potentially enable the fabrication of a wide variety of derived materials. We review the evolution and breakthroughs in the research on the use of colloidal particles for the stabilization of Pickering emulsions in recent years for the particle categories of inorganic particles, polymer-based particles, and food-grade particles. Moreover, based on the latest works, several emulsions stabilized by the featured particles and their derived functional materials, including enzyme immobilized emulsifiers for interfacial catalysis, 2D colloidal materials stabilized emulsions as templates for porous materials, and Pickering emulsions as adjuvant formulations, are also summarized. Finally, we point out the gaps in the current research on the applications of Pickering emulsions and suggest future directions for the design of particulate stabilizers and preparation methods for Pickering emulsions and their derived materials.     

Behavior of nanocelluloses at interfaces

Despite being non-surface active, nanocelluloses position efficiently at interfaces, already at very low concentration. This behavior has lately triggered a strong interest in the cellulose and colloids communities. This review reports the recent developments on the use of nanocelluloses at interfaces and highlights the fundamental principles governing the high efficiency observed in reinforcing the boundary between two phases. The use of nanocelluloses as emulsifier and emulsion stabilizer is first discussed, and the structural properties of nanocelluloses such as aspect ratio and surface properties are correlated with the high efficiency in forming colloidally-stable multiphase systems. Then, the behavior at the air/water interface is presented and the most recent advances are reviewed with focus on the surface free energy of nanocelluloses and their role in the interfacial self-assembly process.     

Sustainable food-grade Pickering emulsions stabilized by plant-based particles

This review summarizes the major advances that have occurred over the last 5 years in the use of plant-based colloidal particles for the stabilization of oil-in-water and water-in-oil emulsions. We consider the characteristics of polysaccharide-based particles, protein-based particles and organic crystals (flavonoids) with respect to their particle size, degree of aggregation, anisotropy, hydrophobicity and electrical charge. Specific effects of processing on particle functionality are identified. Special emphasis is directed towards the issue of correctly defining the stabilization mechanism to distinguish those cases where the particles are acting as genuine Pickering stabilizers, through direct monolayer adsorption at the liquid–liquid interface, from those cases where the particles are predominantly behaving as ‘structuring agents’ between droplets without necessarily adsorbing at the interface, for example, in many so-called high internal phase Pickering emulsions. Finally, we consider the outlook for future research activity in the field of Pickering emulsions for food applications.     

Pickering乳状液的研究进展

随着纳米技术的发展以及Pickering乳液在食品、化妆品、医药等领域的潜在应用前景,人们对Pickering乳液给予了关注。本文全面总结了近些年来Pickering乳液的研究进展,对本课题组在Pickering乳液研究领域所取得的成果进行了介绍。本文主要分为4个部分:第一部分概述了Pickering乳液的研究现状;第二部分全面考察了Pickering乳液的各种影响因素;第三部分介绍了Pickering乳液的转相特性;最后综述了颗粒和表面活性物质协同稳定乳液的研究进展。这些研究成果促进了乳液基础理论的发展,并且拓展了乳液的应用范围。     

Nanocellulose–surfactant interactions

Biomass-derived nanomaterials, such as cellulose nanocrystals and nanofibrils, are attractive building blocks for the formulation of foams, emulsions, suspensions and multiphase systems. Depending on their surface chemistry, aspect ratio and crystallinity, nanocelluloses can control the rheology and stability of dispersions; they can also confer robust mechanical properties to composites. Synthetic modification of fibrillar cellulose is an option to achieve chemical compatibility in related systems, in the formation of composites, etc. However, this can also limit the environmental benefits gained from the use of the cellulosic component. Thus, an attractive mean to compatibilize and to further expand the applications of nanocelluloses is through the use of surfactants. The chemical toolbox of surfactants developed over the last 60 years allows for a large versatility while their environmental impact can also be minimized. Furthermore, relatively small amounts of surfactants are sufficient to significantly impact the interfacial forces, which has implications in material development, from the colloidal scale to the macro-scale. In this review we attempt to cover the literature pertaining to the combined uses of surfactants and nanocelluloses. We summarize reports on the incorporation with nanocellulose of nonionic, anionic, amphoteric and cationic surfactants. With the ever-expanding interest in the use of renewable materials in a vast range of applications, we hope to provide insights into the application of surfactants as a tool to tailor the compatibility and the surface chemistry of nanocelluloses.     

两亲性Janus粒子的合成及其在Pickering乳液中的应用

Janus粒子由于在光、电、力、磁及表面亲/疏水性等方面表现出各向异性,因此在稳定乳液、生物医药及功能涂层等方面展现出广阔的应用价值。两亲性Janus粒子是指一侧具有亲水性、另一侧具有疏水性的不对称材料,由于同时具有表面活性剂的性质和固体颗粒的效应,在稳定Pickering乳液方面极具优势。基于此,本文对两亲性Janus粒子的制备方法进行了综述,并对比分析了其优缺点,同时总结了两亲性Janus粒子对Pickering乳液稳定性的影响,最后对其今后的发展进行了展望。     

Recent Advances and Applications of Plant-Based Bioactive Saponins in Colloidal Multiphase Food Systems

The naturally occurring saponins exhibit remarkable interfacial activity and also possess many biological activities linking to human health benefits, which make them particularly attractive as bifunctional building blocks for formulation of colloidal multiphase food systems. This review focuses on two commonly used food-grade saponins, Quillaja saponins (QS) and glycyrrhizic acid (GA), with the aim of clarifying the relationship between the structural features of saponin molecules and their subsequent self-assembly and interfacial properties. The recent applications of these two saponins in various colloidal multiphase systems, including liquid emulsions, gel emulsions, aqueous foams and complex emulsion foams, are then discussed. A particular emphasis is on the unique use of GA and GA nanofibrils as sole stabilizers for fabricating various multiphase food systems with many advanced qualities including simplicity, ultrastability, stimulability, structural viscoelasticity and processability. These natural saponin and saponin-based colloids are expected to be used as sustainable, plant-based ingredients for designing future foods, cosmetics and pharmaceuticals.     

纳米纤维素研究及应用进展Ⅱ

纳米纤维素是一种新型的高分子功能材料,具有独特的结构和优良的性能,特别是细菌纤维素,其三维纳米网状结构,生物适应性,良好的机械稳定性,抗菌性等优良性能使它越来越收到重视。本文是"纳米纤维素研究及应用进展Ⅰ"的下篇,本文中介绍了近年来对于纳米纤维素应用和研究的进展。文中主要内容有纳米纤维素在生物、医学、增强剂、造纸工业、净化、传导、与无机物复合、食品工业、磁性复合物等方面的应用。     

颗粒乳化剂的研究及应用

近年来,颗粒乳化剂因其在食品、采油、化妆品、医药、催化以及功能纳米材料制备等领域具有潜在应用前景而备受关注。本文综述了近来颗粒乳化剂的研究进展,归纳了颗粒乳化剂的种类,包括:无机纳米粒子、表面改性或杂化的无机粒子、有机纳米粒子以及特殊的颗粒乳化剂Janus粒子;并对颗粒乳化剂能够在油水界面稳定吸附的热力学机理和动力学行为进行了阐述,颗粒乳化剂在油水界面接触角以及粒径大小是其在界面稳定吸附的关键参数,而颗粒在油水界面的排布方式则主要受粒子之间相互作用的影响。重点介绍了颗粒乳化剂的热点应用,包括:(1)利用颗粒乳化剂制备Pickering乳液,以及通过对颗粒乳化剂的功能化,使得Pickering乳液具备环境响应性(即pH、盐浓度、温度、紫外光、磁场敏感响应性);(2)以颗粒乳化剂为构筑基元、以Pickering乳液为模板制备Janus颗粒、Colloidosome、具有多级结构的粒子或膜,以及多孔结构材料;(3) Janus粒子在催化领域的应用。     

Nanocellulose Materials – Different Cellulose,Different Functionality

Summary: Nanocelluloses combine in a very exciting manner important properties of cellulose with amazing features of nano-scale materials. With a view to the increasing discussion on the potential risks of nanoparticles and nanotechnology to human health and the environment, it is important to point out that the nanocellulose fibers are irreversibly networked in the supramolecular cellulose structure. This contribution assembles the current knowledge in research, development, and application in the field of nanocelluloses through examples. The topics combine selected results on nanocelluloses from bacteria and wood as well as the formation and in situ shaping of cellulose bodies, the coating of materials with nanosized cellulose networks/supports, and the preparation of nanocellulose composites as well as the use of bacterial cellulose as novel type of medical implants.     

纳米纤维素研究及应用进展Ⅰ

纳米纤维素是一种新型的高分子功能材料,具有独特的结构和优良的性能。特别是细菌纤维素,其三维纳米网状结构,生物适应性,良好的机械稳定性,抗菌性等优良性能使它越来越收到重视。本文介绍了近年来对于纳米纤维素制备和应用的研究进展,主要涉及细菌纤维素,植物纤维素和纤维素纳米复合物的制备。本文的下篇《纳米纤维素研究及应用进展Ⅱ》将继续介绍纳米纤维素在生物,医学,增强剂,造纸工业,净化,传导,与无机物复合,食品工业,磁性复合物等方面的应用。     

Influence of microgel architecture and oil polarity on stabilization of emulsions by stimuli-sensitive core-shell poly(N-isopropylacrylamide-co-methacrylic acid) microgels: Mickering versus Pickering behavior?

Charged poly(N-isopropylacrylamide-co-methacrylic acid) [P(NiPAM-co-MAA)] microgels can stabilize thermo- and pH-sensitive emulsions. By placing charged units at different locations in the microgels and comparing the emulsion properties, we demonstrate that their behaviors as emulsion stabilizers are very different from molecular surfactants and rigid Pickering stabilizers. The results show that the stabilization of the emulsions is independent of electrostatic repulsion although the presence and location of charges are relevant. Apparently, the charges facilitate emulsion stabilization via the extent of swelling and deformability of the microgels. The stabilization of these emulsions is linked to the swelling and structure of the microgels at the oil-water interface, which depends not only on the presence of charged moieties and on solvent polarity but also on the microgel (core-shell) morphology. Therefore, the internal soft and porous structure of microgels is important, and these features make microgel-stabilized emulsions characteristically different from classical, rigid-particle-stabilized Pickering emulsions, the stability of which depends on the surface properties of the particles.     

Trends in structuring edible emulsions with Pickering fat crystals

The pace of development of edible Pickering emulsions has recently soared, as interest in their potential for texture modification, calorie reduction and bioactive compound encapsulation and delivery has risen. In the broadest sense, Pickering emulsions are defined as those stabilized by interfacially-adsorbed solid particles that retard and ideally prevent emulsion coalescence and phase separation. Numerous fat-based species have been explored for their propensity to stabilize edible emulsions, including triglyceride and surfactant-based crystals and solid lipid nanoparticles. This review explores three classes of fat-based Pickering stabilizers, and proposes a microstructure-based nomenclature to delineate them: Type I (surfactant-mediated interfacial crystallization), Type II (interfacially-adsorbed nano- or microparticles) and Type III (shear-crystallized droplet encapsulation matrices). Far from simply reporting the latest findings on these modes of stabilization, challenges associated with these are also highlighted. Finally, though emphasis is placed on food emulsions, the fundamental precepts herein described are equally applicable to non-food multicomponent emulsion systems.     

Amphiphilic micro- and nanogels: Combining properties from internal hydrogel networks,solid particles,and micellar aggregates

Polymeric micro- and nanogels are defined by their water-swollen hydrophilic networks that can often impart outstanding biocompatibility and high-colloidal stability. Unfortunately, this highly hydrophilic nature limits their potential in areas where hydrophobic or amphiphilic interactions are required, for example, the delivery of hydrophobic cargoes or tailored interactions with amphipathic (bio-)surfaces. To overcome this limitation, amphiphilic micro−/nanogels are emerging as new colloidal materials that combine properties from hydrogel networks with hydrophobic segments, known from solid hydrophobic polymer particles or micellar cores. The ability to accurately adjust the balance of hydrophobic and hydrophilic components in such amphiphilic colloidal systems enables new tailored properties. This opens up new applications ranging from the controlled and sustained delivery of hydrophobic drugs, over carriers for catalytic moieties, to their assembly at hydrophilic/hydrophobic interfaces, for example, as advanced stabilizers in Pickering emulsions. While promising, the synthetic realization of such amphiphilic materials remains challenging since hydrophobic and hydrophilic moieties need to be combined in a single colloidal system. As a result, adjusting the micro−/nanogel amphiphilicity often changes the colloidal features too. To overcome these limitations, various strategies have been reported. The aim of this review is to give a brief overview of important synthetic tools, considering both advantages and disadvantages, thus critically evaluating their potential in different research fields.     

Cellulose esters in drug delivery

Cellulose esters have played a vital role in the development of modern drug delivery technology. They possess properties that are not only well-suited to the needs of pharmaceutical applications, but that enable construction of drug delivery systems that address critical patient needs. These properties include very low toxicity, endogenous and/or dietary decomposition products, stability, high water permeability, high T _g, film strength, compatibility with a wide range of actives, and ability to form micro- and nanoparticles. This suite of properties has enabled the creation of a wide range of drug delivery systems employing cellulose esters as key ingredients. The following is a review of the most important types of these systems, and of the critical roles played by cellulose esters in making them work, focusing on more recent developments.     

Cellulose gel dispersions: fascinating green particles for the stabilization of oil/water Pickering emulsion

A facile approach for the preparation of cellulose gel dispersions with particle size less than 5 μm has been developed. The particles were obtained by dissolving cellulose in NaOH/urea solvent, followed by regeneration in ethanol/H₂O mixed solution with homogenizer shearing. The characteristics of the cellulose gel dispersions were evaluated in terms of particle dimensions and crystalline structure, size distribution and rheology behavior. The cellulose gel dispersions had low crystallinity, and the concentration of the cellulose solution had little influence on the particle size of the gel dispersions. Furthermore, the cellulose gel dispersions could be well dispersed in deionized water, and they could be used to stabilize oil/water emulsion without addition of any surfactant. The formed Pickering emulsion had typical shear-thinning behavior and higher storage modulus. The concentration of cellulose gel dispersions had a significant influence on the emulsion stability. The Pickering emulsion stabilized by the cellulose gel dispersions would open opportunities for the development of food emulsion systems or environmentally friendly functional materials.     

基于纤维素的先进功能材料（专题报道）

 收集整理了近几年间发表在国内外重要期刊上的约360篇文献,以纤维素功能材料的制备方法为线索,简要综述了该领域的最新进展,对纤维素基纤维材料、膜材料、光电材料、杂化材料、智能材料、生物医用材料等功能材料的制备过程、功能和应用前景做了概括性描述.