Stable and permeable polyion complex vesicles designed as enzymatic nanoreactors

Polymeric vesicles are perspective vehicles for fabricating enzymatic nanoreactors towards diverse biomedical and catalytic applications, yet the design of stable and permeable vesicles remains challenging. Herein, we developed polyion complex (PIC) vesicles featuring high stability and a permeable membrane for adequate enzyme loading and activation. Our design relies on co-assembly of an anionic diblock copolymer (PSS96-b-PEO113) with cationic branched poly(ethylenimine) (PEI). The polymer combination endows strong electrostatic interaction between the PSS and PEI building blocks, so their assembly can be implemented at a high salt concentration (500 mM NaCl), under which the charge interaction of the enzyme-polymer is inhibited. This control realizes the successful and safe loading of enzymes associated with the formation of stable PIC vesicles with an intrinsic permeable membrane that is favourable for enhancing enzymatic activity. The control factors for vesicle formation and enzyme loading were investigated, and the general application of loading different enzymes for cascade reaction was validated as well. Our study reveals that proper design and combination of polyelectrolytes is a facile strategy for fabricating stable and permeable polymeric PIC vesicles, which exhibit clear advantages for loading and activating enzymes, consequently boosting their diverse applications as enzymatic nanoreactors.

Effects of catechol grafting on chitosan-based coacervation and adhesion

In this study, we investigated detailedly the contribution of catechol in tuning the formation and adhesive properties of coacervates. We have constructed a series of catechol-grafted Chitosan (Chitosan-C), and investigated their coacervation with gum arabic (GA) and the corresponding adhesion. We demonstrate that, increasing catechol grafting ratio from 0 %-44 % impacted the coacervation moderately, while enhanced the adhesion of the coacervate up to 438 % when the catechol faction was 37 %. Further increasing the grafting ratio to 55 % led to precipitated coacervates associated with a declined adhesion. Our findings identify the optimal grafting threshold for coacervation and adhesion, providing insights into the underlying mechanism of coacervate binding. Moreover, the catechol enhancement on adhesion of coacervates tolerates different substrates and diverse polyelectrolyte pairs. The revealed principles shall be helpful for designing adhesive coacervates and boosting their applications in various industrial and biomedical areas.

Effects of Control Factors on Protein-Polyelectrolyte Complex Coacervation

Protein-polyelectrolyte complex coacervation is of particular interest for mimicking intracellular phase separation and organization. Yet, the challenge arises from regulating the coacervation due to the globular structure and anisotropic distributed charges of protein. Herein, we fully investigate the different control factors and reveal their effects on protein-polyelectrolyte coacervation. We prepared mixtures of BSA (bovine serum albumin) with different cationic polymers, which include linear and branched polyelectrolytes covering different spacer and charge groups, chain lengths, and polymer structures. With BSA-PDMAEMA [poly(N,N-dimethylaminomethyl methacrylate)] as the main investigated pair, we find that the moderate pH and ionic strength are essential for the adequate electrostatic interaction and formation of coacervate droplets. For most BSA-polymer mixtures, excess polyelectrolytes are required to achieve the full complexation, as evidenced by the deviated optimal charge mixing ratios from the charge stoichiometry. Polymers with longer chains or primary amine groups and a branched structure endow a strong electrostatic interaction with BSA and cause a bigger charge ratio deviation associated with the formation of solid-like coacervate complexes. Nevertheless, both the liquid- and solid-like coacervates hardly interrupt the BSA structure and activity, indicating the safe encapsulation of proteins by the coacervation with polyelectrolytes. Our study validates the crucial control of the diverse factors in regulating protein-polyelectrolyte coacervation, and the revealed principles shall be instructive for establishing other protein-based coacervations and boosting their potential applications.

Protein separation by sequential selective complex coacervation

In food manufacturing and particular biomedical products selected proteins are often required. Obtaining the desired proteins in a pure form from natural resources is therefore important, but often very challenging. Herein, we design a sequential coacervation process that allows to efficiently isolate and purify proteins with different isoelectric points (pIs) from a mixed solution, namely Bovine Serum Albumin (BSA, pI = 4.9) and Peroxidase from Horseradish (HRP, pI = 7.2). The key to separation is introducing a suitable polyelectrolyte that causes selective complex coacervation at appropriate pH and ionic strength. Specifically, polyethyleneimine (PEI), when added into the mixture at pH 6.0, produces a coacervation which exclusively contains BSA, leading to a supernatant solution containing 100 % HRP with a purity of 91 %. After separating the dilute and dense phases, BSA is recovered by adding poly(acrylic acid) (PAA) to the concentrated phase, which displaces BSA from the complex because it interacts more strongly with PEI. The supernatant phase after this step contains approximately 75 % of the initial amount of BSA with a purity of 99 %. Our results confirm that coacervation under well-defined conditions can be selective, enabling separation of proteins with adequate purity. Therefore, the established approach demonstrates a facile and sustainable strategy with potential for protein separation at industrial scale.

Ion-Induced Reassembly between Protein Nanotubes and Nanospheres

Proteins used as building blocks to template nanostructures with manifold morphologies have been widely reported. Understanding their self-assembly and reassembly mechanism is important for designing functional biomaterials. Herein, we show that enzyme-hydrolyzed α-lactalbumin (α-lac) can self-assemble into either nanotubes in the presence of Ca2+ ions or nanospheres in the absence of Ca2+ in solution. Remarkably, such assembled α-lac nanotubes can be elongated by adding preassembled α-lac nanospheres and Ca2+ solution, which suggests that the self-assembled α-lac nanospheres undergo disassembly and reassembly processes into existing nanotube nuclei. By performing atomic force microscopy (AFM), transmission electron microscopy (TEM), and confocal laser scanning microscopy (CLSM), it indicates that there is an equilibrium among nanotubes, nanospheres, hydrolyzed α-lac, and Ca2+ in solution. The structural transition between nanotubes and nanospheres is driven from a less stable structure into a more stable structure determined by the conditions. During the transition from nanospheres into nanotubes, the hydrolyzed α-lac in nanospheres transfers into helical ribbon form at both nanotube extremities. Then helical ribbons close into mature nanotubes, extending the length of the initial nuclei. Besides, by dilution or adding ethylene glycol bis(2-aminoethyl ether) tetraacetic acid (EGTA), the decreased Ca2+ concentration in solution drives the Ca2+ dissociating from nanotubes into solution, leading to the transitions from nanotubes into nanospheres. The reversible transformation between nanotubes and nanospheres is achieved by adjusting the pH value from 7.5 to 5.0 and back to 7.5. This is because the stability of nanotubes decreases from pH 7.5 to 5 but increases from 5 to 7.5. Significantly, this approach can be used for the fabrication of various responsive nanomaterials from the same starting material.

Rational design of polymeric nanozymes with robust catalytic performance via copper-ligand coordination

Incorporating copper (Cu) ions into polymeric particles can be a straightforward strategy for mimicking copper enzymes, but it is challenging to simultaneously control the structure of the nanozyme and of the active sites. In this report, we present a novel bis-ligand (L₂) containing bipyridine groups connected by a tetra-ethylene oxide (4EO) spacer. In phosphate buffer the Cu-L₂ mixture forms coordination complexes that (at proper composition) can bind polyacrylic acid (PAA) to produce catalytically active polymeric nanoparticles with well-defined structure and size, which we refer to as 'nanozymes'. Manipulating the L₂/Cu mixing ratio and using phosphate as a co-binding motif, cooperative copper centres are realized that exhibit promoted oxidation activity. The structure and activity of the so-designed nanozymes remain stable upon increasing temperature and over multiple cycles of application. Increasing ionic strength causes enhanced activity, a response also seen for natural tyrosinase. By means of our rational design we obtain nanozymes with optimized structure and active sites that in several respects outperform natural enzymes. This approach therefore demonstrates a novel strategy for developing functional nanozymes, which may well stimulate the application of this class of catalysts.

Cationic Nanogels Enable Gold Nanoparticle Immobilization and Regulated Catalytic Activity

Polyelectrolyte nanogel consisting of charged network is a prospective platform for developing nanoreactor due to their integrated features of both polyelectrolyte and hydrogel. In this work, cationic poly (methacrylatoethyl trimethyl ammonium chloride) (PMETAC) nanogels with regulated size (30-82 nm) and crosslinking degree (10-50%), has been synthesized by Electrostatic Assembly Directed Polymerization (EADP) method and applied to load gold nanoparticles (AuNPs). Based on the typical reduction reaction of 4-nitrophenol (4-NP), the catalytic performance of the constructed nanoreactor was examined by studying their kinetic process, where the loaded AuNPs exhibited dependent activity on crosslinking degree of nanogels, while independent catalytic activity on nanogel size. Our results validate that, polyelectrolyte nanogels are capable of loading metal NPs and regulating their catalytic performance, therefore demonstrates potential for developing functional nanoreactors.

Hierarchical self-assembly of metal-organic supramolecular fibers with lanthanide-derived functionalities

Achieving organized assembly structures with high complexity and adjustable functionalities is a central quest in supramolecular chemistry. In this report, we study what happens when a discotic benzene-1,3,5-tricarboxamide (BTA) ligand containing three dipicolinic acid (DPA) groups is allowed to coordinate with lanthanide (Ln) ions. A multi-BTA coordination cluster forms, which behaves as a type of "supramolecular monomer", stacking into fibers via hydrogen bonds enabled by multiple BTA cores. The fibrous morphology and size, as well as the packing unit and the process by which it grows, were investigated by light scattering measurements, luminescence spectra, TEM images and molecular simulation data. More notably, by selecting the kind of lanthanide or mixture of lanthanides that is incorporated, tunable luminescence and magnetic relaxation properties without compromising the fibrous structure can be realized. This case of hierarchical self-assembly is made possible by the special structure of our BTA-like building block, which makes non-covalent bond types that are different along the radial (coordination bonds) and axial (H-bonds) directions, respectively, each with just the right strength. Moreover, the use of lanthanide coordination leads to materials with metal-derived optical and magnetic properties. Therefore, the established approach demonstrates a novel strategy for designing and fabrication of multi-functional supramolecular materials.

Synthesis of zwitterionic polyelectrolyte nanogels via electrostatic-templated polymerization

Zwitterionic polyelectrolyte nanogels are prospective nanocarriers due to their soft loading pocket and regulated charges. We here report a facile strategy, namely, electrostatic-templated polymerization (ETP) for synthesizing zwitterionic nanogels with controlled size and properties. Specifically, with anionic-neutral diblock polymers as the template, zwitterionic monomers such as carboxybetaine methacrylate (CBMA) or carboxybetaine acrylamide (CBAA) are polymerized together with a cross-linker at pH 2 where the monomers exhibit only positive charge due to the protonation of the carboxyl group. The obtained polyelectrolyte complex micelles dissociate upon introducing a concentrated salt. The subsequent separation yields the released template and zwitterionic nanogels with regulated size and swelling ability, achieved by tuning the salt concentration and cross-linker fraction during polymerization. The obtained PCBMA nanogels exhibit charges depending on the pH, which enables not only the selective loading of different dye molecules, but also encapsulation and intracellular delivery of cytochrome c protein. Our study develops a facile and robust way for fabricating zwitterionic nanogels and validates their potential applications as promising nanocarriers for load and delivery of functional charged cargos.

Fluorescent Probes Based on AIEgen-Mediated Polyelectrolyte Assemblies for Manipulating Intramolecular Motion and Magnetic Relaxivity

Uniting photothermal therapy (PTT) with magnetic resonance imaging (MRI) holds great potential in nanotheranostics. However, the extensively utilized hydrophobicity-driven assembling strategy not only restricts the intramolecular motion-induced PTT, but also blocks the interactions between MR agents and water. Herein, we report an aggregation-induced emission luminogen (AIEgen)-mediated polyelectrolyte nanoassemblies (APN) strategy, which bestows a unique "soft" inner microenvironment with good water permeability. Femtosecond transient spectra verify that APN well activates intramolecular motion from the twisted intramolecular charge transfer process. This de novo APN strategy uniting synergistically three factors (rotational motion, local motion, and hydration number) brings out high MR relaxivity. For the first time, APN strategy has successfully modulated both intramolecular motion and magnetic relaxivity, achieving fluorescence lifetime imaging of tumor spheroids and spatio-temporal MRI-guided high-efficient PTT.

Chemical signal regulated injectable coacervate hydrogels

In the quest for stimuli-responsive materials with specific, controllable functions, coacervate hydrogels have become a promising candidate, featuring sensitive responsiveness to environmental signals enabling control over sol-gel transitions. However, conventional coacervation-based materials are regulated by relatively non-specific signals, such as temperature, pH or salt concentration, which limits their possible applications. In this work, we constructed a coacervate hydrogel with a Michael addition-based chemical reaction network (CRN) as a platform, where the state of coacervate materials can be easily tuned by specific chemical signals. We designed a pyridine-based ABA triblock copolymer, whose quaternization can be regulated by an allyl acetate electrophile and an amine nucleophile, leading to gel construction and collapse in the presence of polyanions. Our coacervate gels showed not only highly tunable stiffness and gelation times, but excellent self-healing ability and injectability with different sized needles, and accelerated degradation resulting from chemical signal-induced coacervation disruption. This work is expected to be a first step in the realization of a new class of signal-responsive injectable materials.

Switchable Electrostatically Templated Polymerization

We report a switchable, templated polymerization system where the strength of the templating effect can be modulated by solution pH and/or ionic strength. The responsiveness to these cues is incorporated through a dendritic polyamidoamine-based template of which the charge density depends on pH. The dendrimers act as a template for the polymerization of an oppositely charged monomer, namely sodium styrene sulfonate. We show that the rate of polymerization and maximum achievable monomer conversion are directly related to the charge density of the template, and hence the environmental pH. The polymerization could effectively be switched "ON" and "OFF" on demand, by cycling between acidic and alkaline reaction environments. These findings break ground for a novel concept, namely harnessing co-assembly of a template and growing polymer chains with tunable association strength to create and control coupled polymerization and self-assembly pathways of (charged) macromolecular building blocks.

Synthesis of Anionic Nanogels for Selective and Efficient Enzyme Encapsulation

Polyelectrolyte nanogels containing cross-linked ionic polymer networks feature both soft environment and intrinsic charges which are of great potential for enzyme encapsulation. In this work, well-defined poly(acrylic acid) (PAA) nanogels have been synthesized based on a facile strategy, namely, electrostatic assembly directed polymerization (EADP). Specifically, AA monomers are polymerized together with a cross-linker in the presence of a cationic-neutral diblock copolymer as the template. Effects of control factors including pH, salt concentration, and cross-linking degree have been investigated systematically, based on which the optimal preparation of PAA nanogels has been established. The obtained nanogel features not only compatible pocket for safely loading enzymes without disturbing their structures, but also abundant negative charges which enable selective and efficient encapsulation of cationic enzymes. The loading capacities of PAA nanogels for cytochrome (cyt c) and lysozyme are 100 and 125 μg/mg (enzyme/nanogel), respectively. More notably, the PAA network seems to modulate a favorable microenvironment for cyt c and induces 2-fold enhanced activity for the encapsulated enzymes, as indicated by the steady-state kinetic assay. Our study reveals the control factors of EADP for optimal synthesis of anionic nanogels and validates their distinctive advances with respect to efficient loading and activation of cationic enzymes.

Rational Polyelectrolyte Design Enables Multifunctional Polyion Complex Vesicles

Polyion complex (PIC) vesicles prepared by polyelectrolyte assembly have attracted extensive attention as distinctive carriers and nanoreactors, particularly for biological cargoes. However, the constrained regulation of their structure and functionality at this stage hinder the application of PIC vesicles. Herein, we design a new asymmetric assembly system, namely cationic-neutral-cationic triblock copolymer co-assembly with a supramolecular ionic coordination polymer. The former creates poly(ethylene oxide) (PEO) loops upon complexation, which are favorable for vesicle fabrication, while the coordination polyelectrolyte composed of metal ions and a dipicolinic acid (DPA)-based bis-ligand features well-defined functionalities depending on the incorporated metal ions. Thus, the rational combination allows controlled fabrication of PIC vesicles with a modulated structure and functionalities. Moreover, the encapsulation and release of hydrophilic dextran based on different PIC vesicles has been realized. Our design integrates the advantages of both triblock and coordination polymers, and therefore demonstrates a novel strategy for harmonious regulation of the structure and functionality of PIC vesicles. The revealed findings and achieved properties shall be inspirational for developing functional PIC vesicles and boosting their applications towards demand encapsulation and delivery.

Regulated Polyelectrolyte Nanogels for Enzyme Encapsulation and Activation

Polyelectrolyte (PE) nanogels consisting of cross-linked PE networks integrate the advanced features of both nanogels and PEs. The soft environment and abundant intrinsic charges are of special interest for enzyme immobilization. However, the crucial factors that regulate enzyme encapsulation and activation remain obscure to date. Herein, we synthesized cationic poly (dimethyl aminoethyl methacrylate), PDMAEMA, nanogels with well-defined size and cross-link degrees and fully investigated the effects of different control factors on lipase immobilization. We demonstrate that the cationic PDMAEMA nanogels indeed enable efficient and safe loading of anionic lipase without disturbing their structures. Strong charge interaction achieved by tuning pH and larger particle size are favorable for lipase loading, while the enhanced enzymatic activity demands nanogels with smaller size and a moderate cross-link degree. As such, PDMAEMA nanogels with a hydrodynamic radius of 35 nm and 30% cross-linker fraction display the optimal catalytic efficiency, which is fourfold of that of free lipase. Moreover, the immobilization endows enhanced enzymatic activity in a broad scope of pH, ionic strength, and temperature, demonstrating effective protection and activation of lipase by the designed nanogels. Our study validates the crucial controls of the size and structure of PE nanogels on enzyme encapsulation and activation, and the revealed findings shall be helpful for designing functional PE nanogels and boosting their applications for enzyme immobilization.

Complex supramolecular fiber formed by coordination-induced self-assembly of benzene-1,3,5-tricarboxamide (BTA)

HYPOTHESIS

In the quest for large but well-controlled supramolecular structures, the discotic benzene-1,3,5-tricarboxamide (BTA) has received quite some attention, because it can form hydrogen-bonded stacks that can be regarded as supramolecular polymers of which the single BTA molecule is the monomer. In this report, we consider a more complex BTA-based supramolecular polymer, namely one that is built up from supramolecular 'monomers'.

EXPERIMENTS

We design a tris-ligand L₃ consisting of a BTA core carrying three dipicolinic acid (DPA) groups. L₃ itself is too small to form polymers, but in the presence of appropriate metal ions, each L₃ can form three coordination bonds and so form (L₃)_n clusters that are large enough to stack successfully: at an appropriate metal dose, long and stable filaments with a cross-sectional diameter of 12 nm appear. We monitor the growth process by UV-vis spectroscopy and light scattering, and use small angle X-ray scattering (SAXS), TEM as well as molecular simulation to confirm the filamentous structure of the fibers and determine their dimensions.

FINDINGS

The formation and structure of the fiber are very similar for various transition metal ions, which enables introducing different functionalities, e.g., magnetic relaxivity, by proper choice of the metal ions. Hence, we obtain a doubly supramolecular polymer, connected axially by hydrogen bonds, and radially by coordination bonds. Not only does this realize a higher level of complexity, but it also allows to easily introduce and vary metal-derived functionalities.

Dendrimer-Based Polyion Complex Vesicles: Loops Make Loose

Associations of amphiphiles assume their various morphologies according to the so-called packing parameter under thermodynamic control. However, one may raise the question of whether polymers can always relax fast enough to obey thermodynamic control, and how this may be checked. Here, a case of polyion complex (PIC) assemblies where the morphology appears to be subject to kinetic control is discussed. Poly (ethylene oxide)-b-(styrene sulfonate) block copolymers are combined with cationic PAMAM dendrimers of various generations (2-7). The PEO-PSS diblocks, and the corresponding PSS-PEO-PSS triblocks should have nearly identical packing parameters, but surprisingly creat different assemblies, namely core-shell micelles and vesicles, respectively. Moreover, the micelles are very stable against added salt, whereas the vesicles are not only much more sensitive to added salt, but also appear to exchange matter on relevant time scales. The small and largely quenched early-stage precursor complexes are responsible for the morphological and dynamic differences, implying that kinetic control may also be a way to obtain particles with well-defined and useful properties. The exciting new finding that triblocks produce more "active" vesicles will hopefully trigger the exploration of more pathways, and so learn how to tune PICsomes toward specific applications.

Supramolecular virus-like particles by co-assembly of triblock polypolypeptide and PAMAM dendrimers

Virus-like particles are of special interest as functional delivery vehicles in a variety of fields ranging from nanomedicine to materials science. Controlled formation of virus-like particles relies on manipulating the assembly of the viral coat proteins. Herein, we report a new assembly system based on a triblock polypolypeptide C4-S10-BK12 and -COONa terminated PAMAM dendrimers. The polypolypeptide has a cationic BK12 block with 12 lysines; its binding with anionic PAMAM triggers the folding of the peptide's middle silk-like block and leads to formation of virus-like nanorods, stabilized against aggregation by the long hydrophilic "C" block of the polypeptide. Varying the dendrimer/polypeptide mixing ratio hardly influences the structure and size of the nanorod. However, increasing the dendrimer generation, that is, increasing the dendrimer size results in increased particle length and height, without affecting the width of the nanorod. The branched structure and well-defined size of the dendrimers allows delicate control of the particle size; it is impossible to achieve similar control over assembly of the polypeptide with linear polyelectrolyte as template. In conclusion, we report a novel protein assembling system with properties resembling a viral coat; the findings may therefore be helpful for designing functional virus-like particles like vaccines.

Optimal synthesis of polyelectrolyte nanogels by electrostatic assembly directed polymerization for dye loading and release

Polyelectrolyte (PE) nanogels which combine features of nanogels and polyelectrolytes have attracted significant attention as outstanding nano-carriers. However, and crucially, any large-scale application of PE nanogels can only materialize when an efficient production method is available. We recently developed such a robust approach, namely Electrostatic Assembly Directed Polymerization (EADP), in which ionic monomers are polymerized together with cross-linker in the presence of a polyion-neutral diblock copolymer as template. Although EADP achieves efficient and scalable preparation of diverse PE nanogels, the essential factors for the optimal and controlled synthesis of nanogels have remained elusive. In this article, we investigate systematically the effects of pH, salt concentration, and cross-linker fractions on the formation and properties of a PDMAEMA nanogel prepared with PAA-b-PEO as the template. We find that the electrostatic interaction between the building blocks is crucial to obtain assembly-controlled polymerization, and we establish preferred pH, salt concentration and cross-linker fractions. The obtained PDMAEMA nanogel exhibits dual-responses to pH and salt, which allow manipulation of the positive charges of the nanogels for selective loading and controlled release of anionic substances; we demonstrate this with an anionic dye. The study presented here fully addresses the process parameters of EADP regarding optimal and controlled preparation of PE nanogels, which should allow exploration of their potential vis-a-vis a variety of applications.

Efficient Synthesis of Stable Polyelectrolyte Complex Nanoparticles by Electrostatic Assembly Directed Polymerization

Polyelectrolyte complex nanoparticles with integrated advances of coacervate complexes and nanomaterials have attracted considerable attention as soft templates and functional nano-carriers. Herein, a facile and robust strategy, namely electrostatic assembly directed polymerization (EADP), for efficient and scalable preparation of stable coacervate nanoparticles is presented. With homo-polyelectrolyte PAA (polyacrylic acid) as template and out of charge stoichiometry, the cationic monomers are polymerized together with cross-linkers, which creates coacervate nanoparticles featuring high stability against salt through one-pot synthesis. The particle size can be tuned by varying the cross-linker amount and salt concentrations during the polymerization and the composition of nanoparticles, as well as the corresponding properties can be regulated by combining different charged blocks from both strong and weak ionic monomers. The strategy can tolerate both high monomer concentrations and increased volume of up to l L, which is favorable for scaled-up preparations. Moreover, the coacervate nanoparticles can be freeze-dried to produce a product in powder form, which can be redispersed without any effect on the particle size and size distribution. Finally, the obtained nanoparticles loaded with enzyme and Au nanoparticles exhibit enhanced catalytic performance, demonstrating a great potential for exploring various applications of coacervate particles as soft and functional nano-carriers.

Facile Preparation of Tilmicosin-Loaded Polymeric Nanoparticle with Controlled Properties and Functions

As one of the effective broad-spectrum antimicrobial and anti-inflammatory drugs, tilmicosin (TIM) is applied extensively in a wide range of veterinary treatments. However, the low bioavailability typically leads to overuse of TIM in practical applications, which can cause residual accumulation in the environment and contamination of foodstuffs. Here, we report a precipitation method that allows us to prepare TIM-loaded poly(methyl methacrylate-co-methacrylic acid) (P(MMA-co-MAA)) nanoparticles. Specifically, TIM and biocompatible P(MMA-co-MAA) are dissolved in methanol and then water is introduced as an antisolvent, which triggers the co-precipitation and leads to well-controlled nanoparticles. Depending on the drug/polymer mass ratio and the total concentration of drug and polymer, the formed nanoparticles display a tunable radius from 27 to 80 nm with a narrow size distribution, a high drug loading content, and a controlled release of TIM. The encapsulation does not interrupt the antibacterial function of TIM while reducing its cytotoxicity enormously. Moreover, the formed nanoparticles could be dried to powder through freeze-drying, and the redispersion of the particles hardly disturbs the particle size, size distribution, and drug loading content. Our study developed a facile and robust precipitation method for the controlled construction of TIM-loaded polymeric nanoparticles with tunable properties and functions, as well as improved biocompatibility, which shall improve the bioavailability of TIM and enhance the practical applications.

Dendrimicelles with pH-controlled aggregation number of core-dendrimers and stability

We present a simple way to build up well-controlled coacervate-core dendrimicelles by assembly of anionic PAMAM dendrimers with a cationic-neutral diblock copolymer. Upon increasing pH, the formation of micellar structures shows constant size but the number of dendrimer molecules incorporated in one micelle decreases, following the charge stoichiometry formation rules; concomitantly, the salt stability increases. This study shows the straightforward tuning of macromolecular core-units and related micelle properties.

Effects of pH on the Formation of PIC Micelles from PAMAM Dendrimers

Dendrimer-based PIC micelles are novel nanostructures from the assembly of dendrimers with polyion-neutral diblock copolymers. Because of the branched and three-dimensional structure of dendrimers, understanding the electrostatic assembly is challenging yet essential for manipulating the formation and property of the PIC micelles. Herein, we present the pH effects on the assembly of amine-terminated PAMAM dendrimers with PSS₉₂-b-PEO₁₁₃ diblock copolymers. The step-wise protonation of primary and tertiary amine groups of PAMAM allows us to manipulate the number of the positive charges by tuning pH. We find that the assembly based on the surface charges of PAMAM from G2 to G7 at pH 7 leads to well-defined micelles with high stability against salt. At pH 3, both the interior and surface charges contribute to the assembly, and the formed micelles are sensitive to ionic strength, namely, increasing salt concentration results in the formation of elongated (G2-G5) or bigger (G7) aggregates. Our study reveals the pH manipulation on the assembly of PAMAM dendrimers with linear polyelectrolytes and displays new findings that shall be helpful for understanding the assembly of asymmetric polyelectrolytes, as well as for designing new PIC micelles and functional soft nanocarriers.

Europium based coordination polyelectrolytes enable core-shell-corona micelles as luminescent probes

Core-shell-corona (CSC) micelles have multiple layers, which can serve as separate compartments. This property allows them to combine multiple functionalities in a single nanoparticle, with obvious application potential. Here, we propose a new type of CSC micelles with an apolar core and a polyelectrolyte complex shell incorporating coordination polymers. We obtain these particles by using a poly(styrene)-b-poly(vinyl pyridine)-b-poly(ethylene oxide) (PS-b-PVP-b-PEO) triblock copolymer with quaternized PVP blocks. This polymer leads to well-defined CSC micelles with a cationic shell, which allows us to entrap anionic coordination polymers without disturbing the micellar structure. Useful properties can be imported in this way, e.g., europium (Eu)-based coordination polymers endow the CSC micelles with strong luminescence. Moreover, copper ions (Cu2+) can quench the luminescence because they disturb the Eu-ligand coordination. Upon adding sulfide ions (S2-), copper ions precipitate as CuS and the Eu-ligand bond as well as the corresponding luminescence are restored. This effect is highly specific for Cu2+ and S2-: other cations or anions hardly interfere with this "on-off-on" luminescence response towards Cu2+ and S2-, demonstrating the selectivity of these CSC micelles as detectors of copper and sulfide ions.

Controlled Synthesis of Manganese Oxide Nanoparticles Encaged in Hollow Mesoporous Silica Nanoreactors and Their Enhanced Dye Degradation Activity

In this study, controlled synthesis of hollow mesoporous silica nanoreactors with small manganese oxide nanoparticles in their cavities (Mn _x O _y @HMSNs) is reported, and the dye degradation performance in the presence of hydrogen peroxide over Mn _x O _y @HMSNs is investigated. Specifically, triple ligands (a compound with three dipicolinic acid groups) were used to coordinate manganese ions to form negatively charged coordination complex networks, which further combine with positively charged copolymers to obtain metal ion-containing polymer micelles. Following silica deposition onto micellar coronas and calcinations simultaneously result in hollow mesoporous silica nanoreactors and manganese oxide nanoparticles in their cavities. In this work, the influences of synthetic parameters on the structures are studied in detail. The obtained Mn _x O _y @HMSNs show greatly enhanced activity and stability for a series of dye degradations. The performance enhancement is ascribed to their unique nanostructures, where mesoporous silica walls provide protection to the inner Mn _x O _y nanoparticles and the small size of the manganese oxide nanoparticles greatly enhances the dye degradation activity.

Response of metal-coordination-based polyelectrolyte complex micelles to added ligands and metals

Polyelectrolyte complex based micelles have attracted significant attention due to their potential regarding bio-applications. Although the morphology and functions have been studied extensively, dynamic properties, particularly component exchange with other surrounding molecules, have remained elusive to date. Here, we show how micelles based on metal-ligand coordination complex coacervate-core micelles (M-C3Ms) respond to addition of extra ligand and metal ions. The micelles are prepared from a polycationic-neutral diblock copolymer and an anionic coordination polyelectrolyte, which is obtained by coordination between metal ions (lanthanides Ln³⁺ and Zn²⁺) and a bis-ligand (LEO) containing two dipicolinic acid (DPA) groups connected by a tetra-ethylene oxide spacer (4EO). Our findings show that the bis-ligand LEO is essential for the growth of coordination polymers and consequently the formation of micelles, leading to equilibrium structures with the same micellar composition and structure independent of the order of mixing. In other words, adding single DPA has no effect on the formed M-C3Ms. As for metal exchange, we find that added Zn²⁺ can replace some of the Ln³⁺ from Ln-C3Ms, leading to a hybrid coordination structure with both Ln³⁺ and Zn²⁺. We find that component exchange occurs in these coordination polyelectrolyte micelles, but it is more favorable in the direction of replacing the weak binding components with strong ones. Hence, the designed M-C3Ms based on the strong binding components, such as Ln-C3Ms, shall be relatively stable in biological surroundings, paving the way for the application of such particles as bio-imaging probes.

Supramolecular crosslinks enable PIC micelles with tuneable salt stability and diverse properties

The stability of polyion complex (PIC) nanoparticles, like PIC micelles or PICsomes, in water is typically affected by added salt because salt screens the electrostatic driving force. This lack of salt stability seriously hampers numerous potential applications and a remedy is needed. Extending an earlier idea, we develop here a general strategy for preparing PIC micelles, with not only tuneable salt stability but also built-in functions. Using two different dipicolinic (DPA)-based ligands (a linear bis-ligand and a branched tris-ligand), as well as various metal ions we obtain anionic coordination polymers that subsequently co-assemble with a polycationic-neutral diblock copolymer to form PIC micelles. By a judicious choice of the metal ions and/or an appropriate mixture of the ligands we can create micellar cores with two types of reversible cross-links. In this way, we construct PIC micelles with not only tuneable and enhanced salt stability, but also tuned metal-derived properties, such as luminescence or magnetic relaxation. This non-covalent cross-link strategy, exclusively based on building block composition, is generally applicable with different metal ions and ligand combinations, and is therefore a robust approach for preparing stable and functional PIC micelles. Extension to other types of assemblies such as 'PICsomes' is possible, and therefore a range of applications becomes feasible.

Production of protein-based polymers in Pichia pastoris

Materials science and genetic engineering have joined forces over the last three decades in the development of so-called protein-based polymers. These are proteins, typically with repetitive amino acid sequences, that have such physical properties that they can be used as functional materials. Well-known natural examples are collagen, silk, and elastin, but also artificial sequences have been devised. These proteins can be produced in a suitable host via recombinant DNA technology, and it is this inherent control over monomer sequence and molecular size that renders this class of polymers of particular interest to the fields of nanomaterials and biomedical research. Traditionally, Escherichia coli has been the main workhorse for the production of these polymers, but the methylotrophic yeast Pichia pastoris is finding increased use in view of the often high yields and potential bioprocessing benefits. We here provide an overview of protein-based polymers produced in P. pastoris. We summarize their physicochemical properties, briefly note possible applications, and detail their biosynthesis. Some challenges that may be faced when using P. pastoris for polymer production are identified: (i) low yields and poor process control in shake flask cultures; i.e., the need for bioreactors, (ii) proteolytic degradation, and (iii) self-assembly in vivo. Strategies to overcome these challenges are discussed, which we anticipate will be of interest also to readers involved in protein expression in P. pastoris in general.

A Generic Method for Preparing Hollow Mesoporous Silica Catalytic Nanoreactors with Metal Oxide Nanoparticles inside Their Cavities

We report a facile and generic method for the synthesis of hollow mesoporous silica nanoreactors (HMSNs) with small-sized metal oxide nanoparticles (NPs) inside their cavities. They were made by deposition of silica onto metal-containing charge-driven polymer micelles and subsequent calcination. The micelles consist of 1) negatively charged supramolecular polyelectrolyte chains of bis-ligand-bound metal ions, and 2) water-soluble, neutral/positive diblock copolymers. Owing to the facile coordination between transition-metal ion and the employed bidentate ligand, a series of HMSNs with <2 nm M_x O_y NPs inside cavities (M=Mn, Co, Ni, Cu, or Zn) were obtained by simply varying the metal ions inside the micelles. The developed method circumvents the pre- and post-synthesis of metal oxide NPs; after calcination, hollow mesoporous nanostructures containing small-sized metal oxide NPs inside their cavities are directly obtained. The Co_x O_y -functionalized HMSNs catalyze the degradation of various dyes with H₂ O₂ .

Morphology Tuning of Aggregation-Induced Emission Probes by Flash Nanoprecipitation: Shape and Size Effects on in Vivo Imaging

Aggregation-induced emission (AIE) imaging probes have recently received considerable attention because of their unique property of high performance in the aggregated state and their imaging capability. However, the tendency of AIE molecules to aggregate into micron long irregular shapes, which significantly limits their application in vivo, is becoming a serious issue that needs to be addressed. Here, we introduce a novel engineering strategy to tune the morphology and size of AIE nanoaggregates, based on flash nanoprecipitation (FNP). Quinolinemalononitrile (ED) is encapsulated inside properly selected amphiphilic block copolymers of varying concentration. This leads to a variety of ED particle morphologies with different sizes. The shape and size are found to have strong influences on tumor targeting both in vitro and in vivo. The current results therefore indicate that the FNP method together with optimal choice of an amphiphilic copolymer is a universal method to systematically control the aggregation state of AIE materials and hence tune the morphology and size of AIE nanoaggregates, which is potentially useful for precise imaging at specific tumor sites.

Electrostatic stiffening and induced persistence length for coassembled molecular bottlebrushes

A self-consistent field analysis for tunable contributions to the persistence length of isolated semiflexible polymer chains including electrostatically driven coassembled deoxyribonucleic acid (DNA) bottlebrushes is presented. When a chain is charged, i.e., for polyelectrolytes, there is, in addition to an intrinsic rigidity, an electrostatic stiffening effect, because the electric double layer resists bending. For molecular bottlebrushes, there is an induced contribution due to the grafts. We explore cases beyond the classical phantom main-chain approximation and elaborate molecularly more realistic models where the backbone has a finite volume, which is necessary for treating coassembled bottlebrushes. We find that the way in which the linear charge density or the grafting density is regulated is important. Typically, the stiffening effect is reduced when there is freedom for these quantities to adapt to the curvature stresses. Electrostatically driven coassembled bottlebrushes, however, are relatively stiff because the chains have a low tendency to escape from the compressed regions and the electrostatic binding force is largest in the convex part. For coassembled bottlebrushes, the induced persistence length is a nonmonotonic function of the polymer concentration: For low polymer concentrations, the stiffening grows quadratically with coverage; for semidilute polymer concentrations, the brush chains retract and regain their Gaussian size. When doing so, they lose their induced persistence length contribution. Our results correlate well with observed physical characteristics of electrostatically driven coassembled DNA-bioengineered protein-polymer bottlebrushes.