Anionic block copolymer vesicles act as Trojan horses to enable efficient occlusion of guest species into host calcite crystals

Dual Nanofillers Reinforced Polymer-Inorganic Nanocomposite Film with Enhanced Mechanical Properties

Simultaneously improving the strength and toughness of polymer-inorganic nanocomposites is highly desirable but remains technically challenging. Herein, a simple yet effective pathway to prepare polymer-inorganic nanocomposite films that exhibit excellent mechanical properties due to their unique composition and structure is demonstrated. Specifically, a series of poly(methacrylic acid)x-block-poly(benzyl methacrylate)y diblock copolymer nano-objects with differing dimensions and morphologies is prepared by polymerization-induced self-assembly (PISA) mediated by reversible addition-fragmentation chain transfer polymerization (RAFT). Such copolymer nano-objects and ultrasmall calcium phosphate oligomers (CPOs) are used as dual fillers for the preparation of polymer-inorganic composite films using sodium carboxymethyl cellulose (CMC) as a matrix. Impressively, the strength and toughness of such composite films are substantially reinforced as high as up to 202.5 ± 14.8 MPa and 62.3 ± 7.9 MJ m-3, respectively. Owing to the intimate interaction between the polymer-inorganic interphases at multiple scales, their mechanical performances are superior to most conventional polymer films and other nanocomposite films. This study demonstrates the combination of polymeric fillers and inorganic fillers to reinforce the mechanical properties of the resultant composite films, providing new insights into the design rules for the construction of novel hybrid films with excellent mechanical performances.

Implications of intracrystalline OC17 on the protection of lattice incorporated proteins

Biogenic CaCO3 formation is regulated by crystallization proteins during crystal growth. Interactions of proteins with nascent mineral surfaces trigger proteins to be incorporated into the crystal lattice. As a result of incorporation, these intracrystalline proteins are protected in the lattice, an example of which is ancient eggshell proteins that have persisted in CaCO3 for thousands of years even under harsh environmental conditions. OC17 is an eggshell protein known to interact with CaCO3 during eggshell formation during which OC17 becomes incorporated into the lattice. Understanding protein incorporation into CaCO3 could offer insights into protein stability inside crystals. Here, we study the protection of OC17 in the CaCO3 lattice. Using thermogravimetric analysis we show that the effect of temperature on intracrystalline proteins of eggshells is negligible below 250 °C. Next, we show that lattice incorporation protects the OC17 structure despite a heat-treatment step that is shown to denature the protein. Because incorporated proteins need to be released from crystals, we verify metal chelation as a safe crystal dissolution method to avoid protein denaturation during reconstitution. Finally, we optimize the recombinant expression of OC17 which could allow engineering OC17 for engineered intracrystalline entrapment studies.

Controlling Adsorption of Diblock Copolymer Nanoparticles onto an Aldehyde-Functionalized Hydrophilic Polymer Brush via pH Modulation

Sterically stabilized diblock copolymer nanoparticles with a well-defined spherical morphology and tunable diameter were prepared by RAFT aqueous emulsion polymerization of benzyl methacrylate at 70 °C. The steric stabilizer precursor used for these syntheses contained pendent cis-diol groups, which means that such nanoparticles can react with a suitable aldehyde-functional surface via acetal bond formation. This principle is examined herein by growing an aldehyde-functionalized polymer brush from a planar silicon wafer and studying the extent of nanoparticle adsorption onto this model substrate from aqueous solution at 25 °C using a quartz crystal microbalance (QCM). The adsorbed amount, Γ, depends on both the nanoparticle diameter and the solution pH, with minimal adsorption observed at pH 7 or 10 and substantial adsorption achieved at pH 4. Variable-temperature QCM studies provide strong evidence for chemical adsorption, while scanning electron microscopy images recorded for the nanoparticle-coated brush surface after drying indicate mean surface coverages of up to 62%. This fundamental study extends our understanding of the chemical adsorption of nanoparticles on soft substrates.

Trojan-horse mineralization of trigger factor to impregnate non-woven alginate fabrics for enhanced hemostatic efficacy

Uncontrolled hemorrhage remains a leading cause of mortality after trauma. This work describes a facile mineralization strategy for enhancing hemostatic efficacy of alginate non-woven fabrics, involving the precipitation of amorphous CaCO3 induced by alginate fibers, along with Trojan-horse-like tissue factor (TF) encapsulation. The amorphous CaCO3 served as a transient carrier, capable of releasing Ca2+ and TF upon contact with blood. Coagulation test and rat tail cut and hemorrhaging liver models all revealed superior hemostatic capability of mineralized TF-in-alginate fabrics compared to bare fabrics, solely mineralized form, or commercial zeolite-modified gauze, benefiting from the combined hemostatic properties of alginate matrix and released Ca2+ and TF. Meanwhile, comprehensive biocompatibility and mechanical stability evaluations demonstrate the ternary composite's good biosafety. These results along with the extension study with chitosan- and cellulose-based dressings underline the great potential and versatility of polysaccharide-hemostat-mediated CaCO3 mineralization with TF integration for achieving rapid hemorrhage control.

Interfacial Supra-Assembly of Copolymer Nanoparticles Enables the Formation of Nanocomposite Crystals with a Tunable Internal Structure

It is highly desirable but technically challenging to precisely control the spatial composition and internal structure of crystalline nanocomposite materials, especially in a one-pot synthetic route. Herein, we demonstrate a versatile pathway to tune the spatial distribution of guest species within a host inorganic crystal via an incorporation strategy. Specifically, well-defined block copolymer nanoparticles, poly(methacrylic acid)x-block-poly(styrene-alt-N-phenylmaleimide)y [PMAAx-P(St-alt-NMI)y], are synthesized by polymerization-induced self-assembly. Such anionic nanoparticles can supra-assemble onto the surface of larger cationic nanoparticles via an electrostatic interaction, forming colloidal nanocomposite particles (CNPs). Remarkably, such CNPs can be incorporated into calcite single crystals in a spatially controlled manner: the depth of CNPs incorporation into calcite is tunable. Systematic investigation indicates that this interesting phenomenon is governed by the colloidal stability of CNPs, which in turn is dictated by the PMAAx-P(St-alt-NMI)y adsorption density and calcium ion concentration. This study opens up a general and efficient route for the preparation of a wide range of crystalline nanocomposite materials with a controlled internal composition and structure.

Preparation of Polymer-Based Nano-Assembled Particles with Fe3O4 in the Core

Organic-inorganic nanocomposite particles, possessing defined morphologies, represent the next frontier in advanced materials due to their superior collective performance. In this pursuit of efficient preparation of composite nanoparticles, a series of diblock polymers polystyrene-block-poly(tert-butyl acrylate) (PS-b-PtBA) were initially synthesized using the Living Anionic Polymerization-Induced Self-Assembly (LAP PISA) technique. Subsequently, the tert-butyl group on the tert-butyl acrylate (tBA) monomer unit in the diblock copolymer, yielded from the LAP PISA process, was subjected to hydrolysis using trifluoroacetic acid (CF₃COOH), transforming it into carboxyl groups. This resulted in the formation of polystyrene-block-poly(acrylic acid) (PS-b-PAA) nano-self-assembled particles of various morphologies. The pre-hydrolysis diblock copolymer PS-b-PtBA produced nano-self-assembled particles of irregular shapes, whereas post-hydrolysis regular spherical and worm-like nano-self-assembled particles were generated. Utilizing PS-b-PAA nano-self-assembled particles that containing carboxyl groups as polymer templates, Fe₃O₄ was integrated into the core region of the nano-self-assembled particles. This was achieved based on the complexation between the carboxyl groups on the PAA segments and the metal precursors, facilitating the successful synthesis of organic-inorganic composite nanoparticles with Fe₃O₄ as the core and PS as the shell. These magnetic nanoparticles hold potential applications as functional fillers in the plastic and rubber sectors.

Synergistic Effect of Hydroxyl and Carboxyl Groups on Promoting Nanoparticle Occlusion within Calcite

Direct occlusion of guest nanoparticles into host crystals enables the straightforward preparation for various of nanocomposite materials with emerging properties. Therefore, it is highly desirable to elucidate the 'design rules' that govern efficient nanoparticle occlusion. Herein, a series of sterically-stabilized nanoparticles are rationally prepared, where the surface stabilizer chains of such nanoparticles are composed of either poly(methacrylic acid), or poly(glycerol monomethacrylate), or poly((2-hydroxy-3-(methacryloyloxy)propyl)serine). Systematic investigation reveals that hydroxyl groups and carboxyl groups play a synergistic role in driving nanoparticle incorporation into calcite crystals, where the hydroxyl groups enhance colloidal stability of the nanoparticles and the carboxyl groups provide binding sites for efficient occlusion. The generality of these findings is further validated by extending it to polymer-stabilized gold nanoparticles. This study demonstrates that precision synthesis of polymer stabilizers comprising of synergistic functional groups can significantly promote nanoparticle occlusion, thus enabling the efficient construction of organic-inorganic hybrid materials via nanoparticle occlusion strategy.

Metal-Organic Frameworks@Calcite Composite Crystals

The direct incorporation of guest crystals into another type of host crystals during the formation of the latter is technically challenging due to the large difference in surface energy for different crystalline components. Nevertheless, we herein demonstrate that metal-organic frameworks (MOFs, UiO-66-NH₂ as a model guest crystal) after postsynthetic modification with poly(methacrylic acid) can be efficiently incorporated into calcite single crystals, forming a unique composite structure where the MOF crystals are uniformly distributed throughout the whole calcite host crystals. Remarkably, such MOF@calcite composite crystals exhibit superior performance in fluoride removal compared with the MOF or calcite alone. Moreover, this incorporation strategy is general as it can be extended to other guest particles. In principle, this study opens up a versatile avenue for the rational design and preparation of a wide range of hybrid functional materials with controllable compositions and enhanced physicochemical properties.

Positively Charged Additives Facilitate Incorporation in Inorganic Single Crystals

Incorporation of guest additives within inorganic single crystals offers a unique strategy for creating nanocomposites with tailored properties. While anionic additives have been widely used to control the properties of crystals, their effective incorporation remains a key challenge. Here, we show that cationic additives are an excellent alternative for the synthesis of nanocomposites, where they are shown to deliver exceptional levels of incorporation of up to 70 wt % of positively charged amino acids, polymer particles, gold nanoparticles, and silver nanoclusters within inorganic single crystals. This high additive loading endows the nanocomposites with new functional properties, including plasmon coupling, bright fluorescence, and surface-enhanced Raman scattering (SERS). Cationic additives are also shown to outperform their acidic counterparts, where they are highly active in a wider range of crystal systems, owing to their outstanding colloidal stability in the crystallization media and strong affinity for the crystal surfaces. This work demonstrates that although often overlooked, cationic additives can make valuable crystallization additives to create composite materials with tailored composition-structure-property relationships. This versatile and straightforward approach advances the field of single-crystal composites and provides exciting prospects for the design and fabrication of new hybrid materials with tunable functional properties.

RAFT-mediated polymerization-induced self-assembly (RAFT-PISA): current status and future directions

Polymerization-induced self-assembly (PISA) combines polymerization and self-assembly in a single step with distinct efficiency that has set it apart from the conventional solution self-assembly processes. PISA holds great promise for large-scale production, not only because of its efficient process for producing nano/micro-particles with high solid content, but also thanks to the facile control over the particle size and morphology. Since its invention, many research groups around the world have developed new and creative approaches to broaden the scope of PISA initiations, morphologies and applications, etc. The growing interest in PISA is certainly reflected in the increasing number of publications over the past few years, and in this review, we aim to summarize these recent advances in the emerging aspects of RAFT-mediated PISA. These include (1) non-thermal initiation processes, such as photo-, enzyme-, redox- and ultrasound-initiation; the achievements of (2) high-order structures, (3) hybrid materials and (4) stimuli-responsive nano-objects by design and adopting new monomers and new processes; (5) the efforts in the realization of upscale production by utilization of high throughput technologies, and finally the (6) applications of current PISA nano-objects in different fields and (7) its future directions.

Polymer-Inorganic Crystalline Nanocomposite Materials via Nanoparticle Occlusion

Efficient occlusion of guest nanoparticles into host single crystals opens up a straightforward and versatile way to construct functional crystalline nanocomposites. This new technique has attracted increasing research interest because it enables the composition, structure and property of the resulting nanocomposites to be well-controlled. In this review article, we aim to provide a comprehensive summary of nanoparticle occlusion within inorganic crystals. First, we summarize recently-developed strategies for the occlusion of various colloidal particles (e.g., diblock copolymer nanoparticles, polymer-modified inorganic nanoparticles, oil droplets, etc.) within host crystals (e.g., CaCO₃ , ZnO or ZIF-8). Second, new results pertaining to spatially-controlled occlusion and the physical mechanism of nanoparticle occlusion are briefly discussed. Finally, we highlight the physicochemical properties and potential applications of various functional nanocomposite crystals constructed via nanoparticle occlusion and we also offer our perspective on the likely future for this research topic. This article is protected by copyright. All rights reserved.

Incorporation of nanogels within calcite single crystals for the storage, protection and controlled release of active compounds

Nanocarriers have tremendous potential for the encapsulation, storage and delivery of active compounds. However, current formulations often employ open structures that achieve efficient loading of active agents, but that suffer undesired leakage and instability of the payloads over time. Here, a straightforward strategy that overcomes these issues is presented, in which protein nanogels are encapsulated within single crystals of calcite (CaCO3). Demonstrating our approach with bovine serum albumin (BSA) nanogels loaded with (bio)active compounds, including doxorubicin (a chemotherapeutic drug) and lysozyme (an antibacterial enzyme), we show that these nanogels can be occluded within calcite host crystals at levels of up to 45 vol%. Encapsulated within the dense mineral, the active compounds are stable against harsh conditions such as high temperature and pH, and controlled release can be triggered by a simple reduction of the pH. Comparisons with analogous systems - amorphous calcium carbonate, mesoporous vaterite (CaCO3) polycrystals, and calcite crystals containing polymer vesicles - demonstrate the superior encapsulation performance of the nanogel/calcite system. This opens the door to encapsulating a broad range of existing nanocarrier systems within single crystal hosts for the efficient storage, transport and controlled release of various active guest species.

Particle-attachment crystallization facilitates the occlusion of micrometer-sized Escherichia coli in calcium carbonate crystals with stable fluorescence

Inspired from the occlusion of macromolecules in mineral crystals during the biomineralization process, the occlusion mechanism of functional guest species into a host matrix is gradually revealed in artificial systems. However, the guest species within calcite crystals are limited to the nanometer scale. Herein, using amorphous calcium carbonate (ACC) as a precursor and taking advantage of the crystallization of vaterite by the attachment of ACC nanoparticles, micrometer-sized modified Escherichia coli (E. coli) was incorporated into vaterite crystals. The occlusion content of bacteria within the vaterite crystal could reach up to 16 wt%. On the contrary, the occlusion of E. coli into calcite crystals, which proceeded via ion-by-ion addition growth, was only confined to the surface layer. Through modifying the surface structure or chemical composition of bacteria, the strong interaction between the surface of the bacteria and calcium carbonate has proved to be the key factor for successful occlusion. Interestingly, the genetically modified green fluorescent protein (GFP)-E. coli/vaterite composites exhibited stable fluorescence for more than six months with little attenuation and the lifetime could be more than 1.2 μs. It was demonstrated that a combination of the amorphous precursor crystallization pathway and a suitable surface structure of the foreign species can significantly enhance the occlusion efficiency of micrometer-sized species in crystals.

Exerting Spatial Control During Nanoparticle Occlusion within Calcite Crystals

In principle, nanoparticle occlusion within crystals provides a straightforward and efficient route to make new nanocomposite materials. However, developing a deeper understanding of the design rules underpinning this strategy is highly desirable. In particular, controlling the spatial distribution of the guest nanoparticles within the host crystalline matrix remains a formidable challenge. Herein, we show that the surface chemistry of the guest nanoparticles and the [Ca²⁺ ] concentration play critical roles in determining the precise spatial location of the nanoparticles within calcite crystals. Moreover, in situ studies provide important mechanistic insights regarding surface-confined nanoparticle occlusion. Overall, this study not only provides useful guidelines for efficient nanoparticle occlusion, but also enables the rational design of patterned calcite crystals using model anionic block copolymer vesicles.

Efficient Occlusion of Nanoparticles within Inorganic Single Crystals

In principle, the incorporation of guest nanoparticles within host crystals should provide a straightforward and versatile route to a wide range of nanocomposite materials. However, crystallization normally involves expelling impurities, so nanoparticle occlusion is both counter-intuitive and technically challenging. Clearly, the nanoparticles should have a strong interaction with the growing crystalline lattice, but quantifying such an affinity has been challenging; the basic principles that govern efficient nanoparticle occlusion within inorganic single crystals are rather poorly understood. In the past few years, we have focused on the elucidation of robust design rules for such systems; our progress is summarized in this article.Polymerization-induced self-assembly (PISA) is widely recognized as a powerful platform technology for the preparation of a broad range of model organic nanoparticles. Herein, PISA was exploited to prepare sterically stabilized diblock copolymer nano-objects (e.g., spheres, worms, or vesicles) of varying size using steric stabilizers of well-defined chain length, variable anionic charge density, tunable surface density, and adjustable chemical functionality (e.g., carboxylic acid, phosphate, sulfate or sulfonate groups). Thus, we were able to systematically investigate how such structural parameters influence nanoparticle occlusion. Given its commercial importance for many industrial sectors, calcium carbonate was selected as the model host crystal for nanoparticle occlusion studies. Perhaps surprisingly, the extent of nanoparticle occlusion is not particularly sensitive to nanoparticle size or morphology. However, the steric stabilizer chain length can play a key role: relatively short chains lead to surface-confined occlusion, while sufficiently long chains enable uniform nanoparticle occlusion to be achieved throughout the crystal lattice (albeit sometimes inducing a significant change in crystal morphology). Optimizing the anionic charge density and surface density of the stabilizer chains is required to maximize the extent of nanoparticle occlusion, while steric stabilizer chains comprising anionic carboxylate groups led to greater occlusion compared to those composed of phosphate, sulfate, or sulfonate groups when examining a model vesicle system.Subsequently, our occlusion studies were extended to include functional hybrid nanocomposite crystals. For example, the spatially controlled occlusion of poly(glycerol monomethacrylate)-stabilized gold nanoparticles was achieved within semiconductive ZnO crystals by either controlling the nanoparticle concentration or by delaying their addition to the reaction mixture. Moreover, oil droplets of up to 500 nm have been incorporated into calcite crystals at up to 11% by mass, despite the large mismatch in surface energy between the hydrophobic oil droplets and the ionic crystal lattice. We have also explored a "Trojan horse" strategy, whereby cargos comprising nanoparticles or soluble dye molecules are first encapsulated within anionic block copolymer vesicles prior to their incorporation within calcite crystals. This approach offers a generic and efficient strategy for the occlusion of many types of guest species into single crystals. In summary, we have established important guidelines for efficient nanoparticle occlusion within crystals, which opens up new avenues for the synthesis of next-generation hybrid materials.

Ptychographic X-ray tomography reveals additive zoning in nanocomposite single crystals

Single crystals containing nanoparticles represent a unique class of nanocomposites whose properties are defined by both their compositions and the structural organization of the dispersed phase in the crystalline host. Yet, there is still a poor understanding of the relationship between the synthesis conditions and the structures of these materials. Here ptychographic X-ray computed tomography is used to visualize the three-dimensional structures of two nanocomposite crystals - single crystals of calcite occluding diblock copolymer worms and vesicles. This provides unique information about the distribution of the copolymer nano-objects within entire, micron-sized crystals with nanometer spatial resolution and reveals how occlusion is governed by factors including the supersaturation and calcium concentration. Both nanocomposite crystals are seen to exhibit zoning effects that are governed by the solution composition and interactions of the additives with specific steps on the crystal surface. Additionally, the size and shape of the occluded vesicles varies according to their location within the crystal, and therefore the solution composition at the time of occlusion. This work contributes to our understanding of the factors that govern nanoparticle occlusion within crystalline materials, where this will ultimately inform the design of next generation nanocomposite materials with specific structure/property relationships.

Efficient occlusion of oil droplets within calcite crystals

It is well known that oil and water do not mix. Similarly, the incorporation of oil droplets within inorganic crystals is highly counter-intuitive because there is a large difference in surface energy for these two components. Nevertheless, herein we demonstrate the efficient occlusion of ∼250-500 nm oil droplets within 20-40 μm calcite crystals. These droplets are stabilized using various amphiphilic poly(methacrylic acid)-poly(n-alkyl methacrylate) diblock copolymer emulsifiers. Both copolymer concentration and diblock compositions affect the extent of occlusion, with optimized conditions producing calcite crystals containing up to 11% oil by mass. Moreover, compressive forces exerted by the growing crystals cause significant deformation of the oil droplets during occlusion. In principle, this protocol enables the incorporation of water-insoluble dyes or hydrophobic nanoparticles within calcite, which is a cheap, naturally-occurring and environmentally-benign mineral. The single crystal nature of this host lattice ensures efficient retention of such guests, while lowering the solution pH leads to triggered release via acid dissolution.

Light-Triggered Reversible Slimming of Azobenzene-Containing Wormlike Nanoparticles Synthesized by Polymerization-Induced Self-Assembly for Nanofiltration Switches

Photoresponsive wormlike block copolymer nanoparticles (NPs) have potential applications in versatile fields, but their preparation suffers from narrow worm phase region and tedious approaches. In this work, azobenzene-containing wormlike NPs based on poly(methylacrylic acid)-b-poly(4-((4-butylphenyl)diazenyl)phenyl methacrylate) are prepared via polymerization-induced self-assembly at high solids concentration in ethanol. The pure wormlike NPs occupy a remarkably broad region in the morphological phase diagram because of the rigid nature of the core-forming block. These wormlike NPs expand resulting from trans-cis transformation upon UV irradiation, and slim near to the original state via visible light irradiation. The diameter and its variation amplitude of worms increase with the chain length of core-forming block. Moreover, a nanofiltration switch for rhodamine B is assembled to illustrate one of its potential applications by remote trigger using light.

Spatially Controlled Occlusion of Polymer-Stabilized Gold Nanoparticles within ZnO

In principle, incorporating nanoparticles into growing crystals offers an attractive and highly convenient route for the production of a wide range of novel nanocomposites. Herein we describe an efficient aqueous route that enables the spatially controlled occlusion of gold nanoparticles (AuNPs) within ZnO crystals at up to 20 % by mass. Depending on the precise synthesis protocol, these AuNPs can be (i) solely located within a central region, (ii) uniformly distributed throughout the ZnO host crystal or (iii) confined to a surface layer. Remarkably, such efficient occlusion is mediated by a non-ionic water-soluble polymer, poly(glycerol monomethacrylate)₇₀ (G₇₀ ), which is chemically grafted to the AuNPs; pendent cis-diol side groups on this steric stabilizer bind Zn²⁺ cations, which promotes nanoparticle interaction with the growing ZnO crystals. Finally, uniform occlusion of G₇₀ -AuNPs within this inorganic host leads to faster UV-induced photodegradation of a model dye.