Looped structure of flowerlike micelles revealed by 1H NMR relaxometry and light scattering

Thermo-responsive Diels-Alder stabilized hydrogels for ocular drug delivery of a corticosteroid and an anti-VEGF fab fragment

In the present study, a novel in situ forming thermosensitive hydrogel system was investigated as a versatile drug delivery system for ocular therapy. For this purpose, two thermosensitive ABA triblock copolymers bearing either furan or maleimide moieties were synthesized, named respectively poly(NIPAM-co-HEA/Furan)-PEG6K-P(NIPAM-co-HEA/Furan) (PNF) and poly(NIPAM-co-HEA/Maleimide)-PEG6K-P(NIPAM-co-HEA/-Maleimide) (PNM). Hydrogels were obtained upon mixing aqueous PNF and PNM solutions followed by incubation at 37 °C. The hydrogel undergoes an immediate (<1 min) sol-gel transition at 37 °C. In situ hydrogel formation at 37 °C was also observed after intravitreal injection of the formulation into an ex vivo rabbit eye. The hydrogel network formation was due to physical self-assembly of the PNIPAM blocks and a catalyst-free furan-maleimide Diels-Alder (DA) chemical crosslinking in the hydrophobic domains of the polymer network. Rheological studies demonstrated sol-gel transition at 23 °C, and DA crosslinks were formed in time within 60 min by increasing the temperature from 4 to 37 °C. When incubated at 37 °C, these hydrogels were stable for at least one year in phosphate buffer of pH 7.4. However, the gels degraded at basic pH 10 and 11 after 13 and 3 days, respectively, due to hydrolysis of ester bonds in the crosslinks of the hydrogel network. The hydrogel was loaded with an anti-VEGF antibody fragment (FAB; 48.4 kDa) or with corticosteroid dexamethasone (dex) by dissolving (FAB) or dispersing (DEX) in the hydrogel precursor solution. The FAB fragment in unmodified form was quantitatively released over 13 days after an initial burst release of 46, 45 and 28 % of the loading for the 5, 10 and 20 wt% hydrogel, respectively, due to gel dehydration during formation. The low molecular weight drug dexamethasone was almost quantitively released in 35 days. The slower release of dexamethasone compared to the FAB fragment can likely be explained by the solubilization of this hydrophobic drug in the hydrophobic domains of the gel. The thermosensitive gels showed good cytocompatibility when brought in contact with macrophage-like mural cells (RAW 264.7) and human retinal pigment epithelium-derived (ARPE-19) cells. This study demonstrates that PNF-PNM thermogel may be a suitable formulation for sustained release of bioactive agents into the eye for treating posterior segment eye diseases.

Modifying the Properties of Microemulsion Droplets by Addition of Thermoresponsive BAB* Copolymers

Oil-in-water (O/W) microemulsions (ME) typically feature a low viscosity and exhibit ordinary viscosity reduction as a function of temperature. However, for certain applications, avoiding or even reverting the temperature trend might be required. This can be conceived by adding thermoresponsive (TR) block copolymers that induce network formation as the temperature increases. Accordingly, various ME-polymer mixtures were studied for which three different block copolymer architectures of BAB*-, B₂AB*-, and B(AB*)₂-types were employed. Here, "B" represents a permanently hydrophobic, "A" a permanently hydrophilic, and "B*" a TR block. For the TR-block, three different poly(acrylamide)s, namely poly(N-n-propylacrylamide) (pNPAm), poly(N,N-diethylacrylamide) (pDEAm), and poly(N-isopropylacrylamide) (pNiPAm), were used, which all exhibit a lower critical solution temperature. For a well-selected ME concentration, these block copolymers lead to a viscosity enhancement with increasing temperature. At a polymer concentration of about 22 g L^-1, the most pronounced enhancement was observed for the pNPAm-based systems with factors up to 3, 5, and 8 for BAB*, B₂AB*, and B(AB*)₂, respectively. This phenomenon is caused by the formation of a transitory network mediated by TR-blocks, as evidenced by the direct correlation between the attraction strength and the viscosity enhancement. For applications requiring a high hydrophobic payload, which is attained via ME droplets, this kind of tailored temperature-dependent viscosity control of surfactant systems should therefore be advantageous.

Association Behavior of Amphiphilic ABA Triblock Copolymer Composed of Poly(2-methoxyethyl acrylate) (A) and Poly(ethylene oxide) (B) in Aqueous Solution

Poly(2-methoxyethyl acrylate) (PMEA) and poly(ethylene oxide) (PEO) have protein-antifouling properties and blood compatibility. ABA triblock copolymers (PMEAl-PEO11340-PMEAm (MEOMn; n is average value of l and m)) were prepared using single-electron transfer-living radical polymerization (SET-LRP) using a bifunctional PEO macroinitiator. Two types of MEOMn composed of PMEA blocks with degrees of polymerization (DP = n) of 85 and 777 were prepared using the same PEO macroinitiator. MEOMn formed flower micelles with a hydrophobic PMEA (A) core and hydrophilic PEO (B) loop shells in diluted water with a similar appearance to petals. The hydrodynamic radii of MEOM85 and MEOM777 were 151 and 108 nm, respectively. The PMEA block with a large DP formed a tightly packed core. The aggregation number (Nagg) of the PMEA block in a single flower micelle for MEOM85 and MEOM777 was 156 and 164, respectively, which were estimated using a light scattering technique. The critical micelle concentrations (CMCs) for MEOM85 and MEOM777 were 0.01 and 0.002 g/L, respectively, as determined by the light scattering intensity and fluorescence probe techniques. The size, Nagg, and CMC for MEOM85 and MEOM777 were almost the same independent of hydrophobic DP of the PMEA block.

Polymer Architecture Effects on Poly(N,N-Diethyl Acrylamide)-b-Poly(Ethylene Glycol)-b-Poly(N,N-Diethyl Acrylamide) Thermoreversible Gels and Their Evaluation as a Healthcare Material

Thermoreversible gels which transition between liquid-like and solid-like states when warmed have enabled significant novel healthcare technologies. Poly(N,N-diethyl acrylamide) (PDEA) is a thermoresponsive polymer which can be used as a trigger to form thermoreversible gels, however its use in these materials is limited and crucial design principles are unknown. Herein ABA copolymers with the structure PDEA-b-poly(ethylene glycol) (PEG)-b-PDEA are synthesized to give four block copolymers with varied molecular weight of PDEA and PEG blocks. Rheometry on solutions of the block copolymers reveals that high molecular weight PEG blocks are required to form thermoreversible gels with predominantly solid-like behavior. Furthermore, small-angle X-ray scattering elucidates clear differences in the nanostructure of the copolymer library which can be linked to distinct rheological behaviors. A thermoreversible gel formulation based on PDEA (20 kDa)-b-PEG (10 kDa)-b-PDEA (20 kDa) is designed by optimizing the polymer concentration and ionic strength. It is found that the gel is mucoadhesive, stable, and non-toxic, as well as giving controlled release of a hydrophobic drug. Overall, this study provides insight into the effect of polymer architecture on the nanostructure and rheology of PDEA-b-PEG-b-PDEA and presents the development of a highly functional thermoreversible gel with high promise for healthcare applications.

Surface Topography of Polyethylene Glycol Shell Nanoparticles Formed from Bottlebrush Block Copolymers Controls Interactions with Proteins and Cells

Although poly(ethylene glycol) (PEG) is commonly used in nanoparticle design, the impact of surface topography on nanoparticle performance in biomedical applications has received little attention, despite showing significant promise in the study of inorganic nanoparticles. Control of the surface topography of polymeric nanoparticles is a formidable challenge due to the limited conformational control of linear polymers that form the nanoparticle surface. In this work, we establish a straightforward method to precisely tailor the surface topography of PEGylated polymeric nanoparticles based on tuning the architecture of shape-persistent amphiphilic bottlebrush block copolymer (BBCP) building blocks. We demonstrate that nanoparticle formation and surface topography can be controlled by systematically changing the structural parameters of BBCP architecture. Furthermore, we reveal that the surface topography of PEGylated nanoparticles significantly affects their performance. In particular, the adsorption of a model protein and the uptake into HeLa cells were closely correlated to surface roughness and BBCP terminal PEG block brush width. Overall, our work elucidates the importance of surface topography in nanoparticle research as well as provides an approach to improve the performance of PEGylated nanoparticles.

LCST polymers with UCST behavior

In this study, temperature dependent behavior of dense dispersions of core crosslinked flower-like micelles is investigated. Micelles were prepared by mixing aqueous solutions of two ABA block copolymers with PEG B-blocks and thermosensitive A-blocks containing PNIPAM and crosslinkable moieties. At a temperature above the lower critical solution temperature (LCST), self-assembly of the polymers resulted in the formation of flower-like micelles with a hydrophilic PEG shell and a hydrophobic core. The micellar core was stabilized by native chemical ligation (NCL). Above the LCST, micelles displayed a radius of ∼35 nm, while a radius of ∼48 nm was found below the LCST due to hydration of the PNIPAM core. Concentrated dispersions of these micelles (≥7.5 wt%) showed glassy state behavior below a critical temperature (Tc: 28 °C) which is close to the LCST of the polymers. Below this Tc, the increase in the micelle volume resulted in compression of micelles together above a certain concentration and formation of a glass. We quantified and compared micelle packing at different concentrations and temperatures. The storage moduli (G') of the dispersions showed a universal dependence on the effective volume fraction, which increased substantially above a certain effective volume fraction of φ = 1.2. Furthermore, a disordered lattice model describing this behavior fitted the experimental data and revealed a critical volume fraction of φc = 1.31 close to the experimental value of φ = 1.2. The findings reported provide insights for the molecular design of novel thermosensitive PNIPAM nanoparticles with tunable structural and mechanical properties.

Innovative coenzyme Q10-loaded nanoformulation as an adjunct approach for the management of moderate periodontitis: preparation, evaluation, and clinical study

Periodontal diseases are worldwide chronic inflammatory conditions that are associated with heavy production of reactive oxygen species followed by damage of the tooth-supporting tissues. Although the mechanical approach of scaling and root planing (SRP) for removing of plaque is considered as the key element for controlling periodontitis, the anatomical complexity of the teeth hinders accessibility to deeper points. The aim of this study was to design a micellar nanocarrier of coenzyme Q10 (Q₁₀) to support the management of moderate periodontitis. Q₁₀ was formulated in nanomicelles (NM_Q10) and evaluated regarding encapsulation efficiency, loading efficiency, percent yield, hydrodynamic size (D_h), polydispersity index (PDI), and zeta potential (ζ potential). NM_Q10 was incorporated to in situ gelling systems and the in vitro release of Q₁₀ was studied. A clinical study including evaluation of periodontal parameters and biochemical assay of total antioxidant capacity (T-AOC) and lipid peroxide was achieved. Results revealed that Q₁₀ was efficiently entrapped in spherical-shaped stable NM_Q10 with D_h, PDI, and ζ potential of 154.0 nm, 0.108, and - 31.67 mV, respectively. The clinical study revealed that SRP only exhibited improvement of the periodontal parameters. Also, assay of T-AOC and lipid peroxide revealed that their values diminished by 21.5 and 23.8%, respectively. On the other hand, SRP combined with local application of NM_Q10 resulted in a significant management of the periodontal parameters, and likewise, the assayed biomarkers proved enhanced antioxidant activity over SRP alone. In conclusion, NM_Q10 can be suggested as a promising nanosystem as an approach to support the management of chronic periodontitis. Such results could be used to conduct larger clinical studies. Graphical abstrac.

Think Beyond the Core: Impact of the Hydrophilic Corona on Drug Solubilization Using Polymer Micelles

Polymeric micelles are typically characterized as core-shell structures. The hydrophobic core is considered as a depot for hydrophobic molecules, and the corona-forming block acts as a stabilizing and solubilizing interface between the core and aqueous milieu. Tremendous efforts have been made to tune the hydrophobic block to increase the drug loading and stability of micelles, whereas the role of hydrophilic blocks is rarely investigated in this context, with poly(ethylene glycol) (PEG) being the gold standard of hydrophilic polymers. To better understand the role of the hydrophilic corona, a small library of structurally similar A-B-A-type amphiphiles based on poly(2-oxazoline)s and poly(2-oxazine)s is investigated by varying the hydrophilic block A utilizing poly(2-methyl-2-oxazoline) (pMeOx; A) or poly(2-ethyl-2-oxazoline) (pEtOx; A*). In terms of hydrophilicity, both polymers closely resemble PEG. The more hydrophobic block B bears either a poly(2-oxazoline) and poly(2-oxazine) backbone with C3 (propyl) and C4 (butyl) side chains. Surprisingly, major differences in loading capacities from A-B-A > A*-B-A > A*-B-A* is observed for the formulation with two poorly water-soluble compounds, curcumin and paclitaxel, highlighting the importance of the hydrophilic corona of polymer micelles used for drug formulation. The formulations are also characterized by various nuclear magnetic resonance spectroscopy methods, dynamic light scattering, cryogenic transmission electron microscopy, and (micro) differential scanning calorimetry. Our findings suggest that the interaction between the hydrophilic block and the guest molecule should be considered an important, but previously largely ignored, factor for the rational design of polymeric micelles.

Dynamics of Soft and Hairy Polymer Nanoparticles in a Suspension by NMR Relaxation

The design of surface-modified functional nanoparticles (NPs) is used to control the properties of the NPs and the NP/environment interactions. The efficient control of the final behavior of the NPs demands a comprehensive understanding of the resulting system. This is particularly challenging for systems with an architecture of the type polymer core-polymer canopy. In such systems, one of the key parameters influencing the behavior of the NPs is the local dynamics of the polymer canopy. However, because the grafting points of the canopy are experiencing their own local dynamics, predicting the final behavior of such systems is difficult. To get a deeper understanding of NPs made of a soft and swollen polymer core and a swollen polymer canopy, we prepared a library of hairy NPs made of a polystyrene (PS) core and a canopy of grafted poly(methyl acrylate) (PMA) chains. The softness of the PS core and the thickness of the PMA canopy were controlled, and the behavior and dynamics of the soft and hairy PS-PMA NPs in suspension were measured by 1H NMR relaxation and dynamic light scattering. It was observed that the rigid PS core slowed down the subsegmental dynamics of the PMA chains, while thick PMA canopies accelerated the relaxation of the PS core. The dynamics of the NPs in suspension was the result of the interplay between the PS core and the PMA canopy.

Structural and dynamical aspects of PEG/LiClO4 in solvent mixtures via NMR spectroscopy

Motivated by the potential usefulness of polyethylene glycol (PEG)/Li⁺ salt mixtures in several industrial applications, we investigated the structure and dynamics of PEG/LiClO₄ mixtures in D₂ O and its mixtures with CD₃ CN and DMSO-d₆ , in a series of PEG-based polymers with a wide variation in their molecular weights. ¹ H NMR chemical shifts, T₁ /T₂ relaxation rates, pulsed-field gradient NMR diffusion experiments, and 2D HOESY NMR studies have been performed to understand the structural and dynamical aspects of these mixtures. Increasing the temperature of the medium results in a significant perturbation in the H-bonded structure of PEG in its PEG/LiClO₄ /D₂ O mixtures as observed from the increase in chemical shifts. On the other hand, the addition of molecular cosolvents has a negligible effect. The hydrodynamic structure of PEG shows a pronounced variation at low temperature with increasing molecular weight, which, however, disappears at higher temperatures. Increasing the temperature leads to a decrease in the hydrodynamic structure of PEG, which can be explained on the basis of solvation-desolvation phenomena. The 2D HOESY NMR spectra reveal a new finding of Li⁺ -water binding in the PEG/LiClO₄ /D₂ O mixtures with the addition of molecular solvents, suggesting that the Li⁺ cation diffuses freely in the D₂ O mixtures of polymers as compared with the polymer mixtures with DMSO or CD₃ CN.

PEGylated NiPAM microgels: synthesis, characterization and colloidal stability

The objective of this work is to synthesize highly stable thermoresponsive microgels that could be used in diverse applications. To achieve this, N-isopropylacrylamide (NiPAM) based microgels were first synthesized by surfactant-free precipitation polymerization of NiPAM in the presence of poly(ethylene glycol)methacrylate (PEG) as a macro-comonomer and methylenebisacrylamide (MBA) as a chemical crosslinker. By combining a complete set of techniques such as dynamic light scattering (DLS), scanning electron microscopy (SEM), zetametry, 1H NMR and micro-differential scanning calorimetry (μDSC), we clearly demonstrate that (i) the incorporation of the PEG chains controls the size and the polydispersity of the NiPAM-based microgels, whereas the thermal behavior in solution (enthalpy, volume phase transition temperature (VPTT)) remains almost the same as for pure NiPAM microgels; (ii) the PEG chains are mainly located on the microgel periphery; and (iii) the presence of the PEG chains strongly increases the colloidal stability of microgels in electrolyte solutions at high temperatures.

Low length dispersity fiber-like micelles from an A–B–A triblock copolymer with terminal crystallizable poly(ferrocenyldimethylsilane) segments via living crystallization-driven self-assembly

Uniform cylindrical micelles with coronas in a looped configuration have been prepared.

Effect of Formulation and Processing Parameters on the Size of mPEG- b-p(HPMA-Bz) Polymeric Micelles

Micelles composed of block copolymers of poly(ethylene glycol)- b-poly( N-2-benzoyloxypropyl methacrylamide) (mPEG- b-p(HPMA-Bz)) have shown great promise as drug-delivery carriers due to their excellent stability and high loading capacity. In the present study, parameters influencing micelle size were investigated to tailor sizes in the range of 25-100 nm. Micelles were prepared by a nanoprecipitation method, and their size was modulated by the block copolymer properties such as molecular weight, their hydrophilic-to-hydrophobic ratio, homopolymer content, as well as formulation and processing parameters. It was shown that the micelles have a core-shell structure using a combination of dynamic light scattering and transmission electron microscopy analysis. By varying the degree of polymerization of the hydrophobic block ( N_B) between 68 and 10, at a fixed hydrophilic block mPEG_5k ( N_A = 114), it was shown that the hydrophobic core of the micelle was collapsed following the power law of ( N_B × N_agg)^1/3. Further, the calculated brush height was similar for all the micelles examined (10 nm), indicating that crew-cut micelles were made. Both addition of homopolymer and preparation of micelles at lower concentrations or lower rates of addition of the organic solvent to the aqueous phase increased the size of micelles due to partitioning of the hydrophobic homopolymer chains to the core of the micelles and lower nucleation rates, respectively. Furthermore, it was shown that by using different solvents, the size of the micelles substantially changed. The use of acetone, acetonitrile, ethanol, tetrahydrofuran, and dioxane resulted in micelles in the size range of 45-60 nm after removal of the organic solvents. The use of dimethylformamide and dimethylsulfoxide led to markedly larger sizes of 75 and 180 nm, respectively. In conclusion, the results show that by modulating polymer properties and processing conditions, micelles with tailorable sizes can be obtained.

Rapid and Quantitative De-tert-butylation for Poly(acrylic acid) Block Copolymers and Influence on Relaxation of Thermoassociated Transient Networks

The synthesis of charged polymers often requires the polymerization of protected monomers, followed by a polymer-analogous reaction to the polyelectrolyte product. We present a mild, facile method to cleave tert-butyl groups from poly(tert-butyl acrylate) blocks that yields poly(acrylic acid) (pAA) blocks free of traces of the ester. The reaction utilizes a slight excess of HCl in hexafluoroisopropanol (HFIP) at room temperature and runs to completion within 4 h. We compare deprotection in HFIP with the common TFA/DCM method and show that the latter does not yield clean pAA. We show the effect of complete tert-butyl cleavage on a ABA triblock copolymer, where poly(N-isopropylacrylamide) (pNIPAM) is A and pAA is B, by means of viscosimetry, DLS, and SAXS on solutions above overlap. The pNIPAM blocks dehydrate, and their increased self-affinity above the lower critical solution temperature (LCST) results in network formation by the triblocks. This manifests itself as an increase in viscosity and a slowing down of the first-order correlation function in light scattering. However, this stickering effect manifests itself exclusively when the pAA block is tert-butyl-free. Additionally, SAXS shows that the conformational properties of tert-butyl-free pAA copolymers are markedly different from those with residual esters. Thus, we illustrate a surprising effect of hydrophobic impurities that act across blocks and assert the usefulness of HCl/HFIP in pAA synthesis.

Native Chemical Ligation for Cross-Linking of Flower-Like Micelles

In this study, native chemical ligation (NCL) was used as a selective cross-linking method to form core-cross-linked thermosensitive polymeric micelles for drug delivery applications. To this end, two complementary ABA triblock copolymers having polyethylene glycol (PEG) as midblock were synthesized by atom transfer radical polymerization (ATRP). The thermosensitive poly isopropylacrylamide (PNIPAM) outer blocks of the polymers were copolymerized with either N-(2-hydroxypropyl)methacrylamide-cysteine (HPMA-Cys), P(NIPAM- co-HPMA-Cys)-PEG-P(NIPAM- co-HPMA-Cys) (PNC) or N-(2-hydroxypropyl)methacrylamide-ethylthioglycolate succinic acid (HPMA-ETSA), P(NIPAM- co-HPMA-ETSA)-PEG-P(NIPAM- co-HPMA-ETSA) (PNE). Mixing of these polymers in aqueous solution followed by heating to 50 °C resulted in the formation of thermosensitive flower-like micelles. Subsequently, native chemical ligation in the core of micelles resulted in stabilization of the micelles with a Z-average of 65 nm at body temperature. Decreasing the temperature to 10 °C only affected the size of the micelles (increased to 90 nm) but hardly affected the polydispersity index (PDI) and aggregation number ( Nagg) confirming covalent stabilization of the micelles by NCL. CryoTEM images showed micelles with an uniform spherical shape and dark patches close to the corona of micelles were observed in the tomographic view. The dark patches represent more dense areas in the micelles which coincide with the higher content of HPMA-Cys/ETSA close to the PEG chain revealed by the polymerization kinetics study. Notably, this cross-linking method provides the possibility for conjugation of functional molecules either by using the thiol moieties still present after NCL or by simply adjusting the molar ratio between the polymers (resulting in excess cysteine or thioester moieties) during micelle formation. Furthermore, in vitro cell experiments demonstrated that fluorescently labeled micelles were successfully taken up by HeLa cells while cell viability remained high even at high micelle concentrations. These results demonstrate the potential of these micelles for drug delivery applications.

Luminescent Gold Nanocluster-Decorated Polymeric Hybrid Particles with Assembly-Induced Emission

Ultrasmall gold atom clusters (<2 nm in diameter) or gold nanoclusters exhibit emergent photonic properties (near-infrared absorption and emission) compared to larger plasmonic gold particles because of the significant quantization of their conduction band. Although single gold nanocluster properties and applications are being increasingly investigated, little is still known about their behavior and properties when assembled into suprastructures, and even fewer studies are investigating their use for biomedical applications. Here, a simple synthetic pathway combines gold nanoclusters with thermosensitive diblock copolymers of poly(ethylene glycol) (PEG) and poly( N-isopropylacrylamide) (PNIPAm) to form a new class of gold-polymer, micelle-forming, hybrid nanoparticle. The nanohybrids' design is uniquely centered on enabling the temperature-dependent self-assembly of gold nanoclusters into the hydrophobic cores of micelles. This nonbulk assembly not only preserves but also enhances the attractive near-infrared photonics of the gold nanoclusters by significantly increasing their native fluorescent signal. In parallel to the fundamental insights into gold nanocluster ordering and assembly, the gold-polymer nanohybrids also demonstrated great potential as fluorescent live-imaging probes in vitro. This innovative material design based on the temperature-dependent, self-assembly of gold nanoclusters within a polymeric micelle's core shows great promise toward bioassays, nanosensors, and nanomedicine.

Toward Achieving Highly Ordered Fluorinated Surfaces of Spin-Coated Polymer Thin Films by Optimizing the Air/Liquid Interfacial Structure of the Casting Solutions

Thin polymer films with well-assembled fluorinated groups on their surfaces are not easily achieved via spin-coating film-fabrication methods because the solution solidifies very rapidly during spin-coating, which hinders the fluorinated moieties from segregating and organizing on the film surface. In this contribution, we have proposed a comprehensive strategy toward achieving well-ordered fluorinated thin films surfaces by optimizing the molecular organization at air/liquid interface of the film-formation solutions. To validate such a route, poly(methyl methacrylate) (PMMA) end-capped with several 2-perfluorooctylethyl methacrylate (FMA) units was employed as the model polymer for investigations. The air/solution interfacial structures were optimized by systematically changing the polymer chain structures and properties of the casting solvents. It was found that the polymers that form loosely associated aggregates (e.g., FMA₁- ec-PMMA₆₅- ec-FMA₁) and a solvent with better solubility to FMA while having not too low surface tension (i.e., toluene) can combine to produce solutions with well-assembled FMA at the interfaces. By spin-coating the solutions with well-organized interfaces, an ultrathin film with perfluorinated groups that were highly oriented toward the film surface was readily achieved, exhibiting surface energies as low as 7.2 mJ/m², which is among the lowest reported so far for the spin-coated thin films, and a very high F/C ratio (i.e., 0.98).

Insights into maleimide-thiol conjugation chemistry: Conditions for efficient surface functionalization of nanoparticles for receptor targeting

Maleimide-thiol chemistry is widely used for the design and preparation of ligand-decorated drug delivery systems such as poly(lactide-co-glycolide) (PLGA) based nanoparticles (NPs). While many publications on nanocarriers functionalized exploiting this strategy are available in the literature, the conditions at which this reaction takes place vary among publications. This paper presents a comprehensive study on the conjugation of the peptide cRGDfK and the nanobody 11A4 (both containing a free thiol group) to maleimide functionalized PLGA NPs by means of the maleimide-thiol click reaction. The influence of different parameters, such as the nanoparticles preparation method and storage conditions as well as the molar ratio of maleimide to ligand used for conjugation, on the reaction efficiency has been evaluated. The NPs were prepared by a single or double emulsion method using different types and concentrations of surfactants and stored at 4 or 20 °C before reaction with the targeting moieties. Several maleimide to ligand molar ratios and different reaction times were studied and the conjugation efficiency was determined by quantification of the not-bound ligand by liquid chromatography. The kind of emulsion used to prepare the NPs as well as the type and concentration of surfactant used had no effect on the conjugation efficiency. Reaction between the maleimide groups present in the NPs and cRGDfK was optimal at a maleimide to thiol molar ratio of 2:1, reaching a conjugation efficiency of 84 ± 4% after 30 min at room temperature in 10 mM HEPES pH 7.0. For 11A4 nanobody the optimal reaction efficiency, 58 ± 12%, was achieved after 2 h of incubation at room temperature in PBS pH 7.4 using a 5:1 maleimide to protein molar ratio. Storage of the NPs at 4 °C for 7 days prior to their exposure to the ligands resulted in approximately 10% decrease in the reactivity of maleimide in contrast to storage at 20 °C which led to almost 40% of the maleimide being unreactive after the same storage time. Our findings demonstrate that optimization of this reaction, particularly in terms of reactant ratios, can represent a significant increase in the conjugation efficiency and prevent considerable waste of resources.

Novel Brassinosteroid-Modified Polyethylene Glycol Micelles for Controlled Release of Agrochemicals

Two synthetic analogues of brassinosteroids (DI31 and S7) exhibit good plant growth enhancer activity. However, their hydrophobicity and quick metabolism in plants have limited their application and benefits in agriculture. Our objective was to prepare novel brassinosteroid-modified polyethylene glycol (PEG) micelles to achieve controlled release with extended stability while retaining agrochemical activity. Spectroscopic studies confirmed quantitative disubstitution of studied PEGs with the brassinosteroids, while elemental analysis assessed purity of the synthesized conjugates. Conjugates were also characterized by X-ray diffraction and thermal analysis. Dynamic and static light scattering showed stable and homogeneous approximately spherical micelles with average hydrodynamic diameters of 22-120 nm and almost neutral ζ potential. Spherical 30-140 nm micelles were observed by electron microscopy. Sustained in vitro releases at pH 5.5 were extended up to 96 h. Prepared PEG micelles showed good agrochemical activity in the radish seed bioassay and no cytotoxicity to the human microvascular endothelial cell line in the MTS test.

Loop-stabilized BAB triblock copolymer morphologies by PISA in water

Assemblies of BAB triblock copolymers are prepared by PISA via aqueous RAFT dispersion polymerization. The importance of charges in the middle of the hydrophilic stabilizer loops is highlighted.

pH/redox dual stimuli-responsive sheddable nanodaisies for efficient intracellular tumour-triggered drug delivery

A series of dual stimuli-responsive poly(l-histidine)_n-S-S-polyurethane-S-S-poly(l-histidine)_n [p(His)_n-SS-PU-SS-p(His)_n; n = 25, 35, 50, and 75] triblock copolymers that bear two pH-responsive p(His)_n end-blocks and PU middle-blocks tethered by a redox-responsive disulphide linker have been synthesized. The resulting triblock copolymers self-assemble to form micelles, nanodaisies (NDs), of uniform size (∼100 nm) and efficiently encapsulate the anticancer drug doxorubicin (Dox) with a high drug loading content (∼19%). The in vitro release profile shows an enhanced release of Dox in an acidic environment in the presence of 10 mM glutathione. The in vitro cell viability assays performed in various cell lines show that the NDs have no acute or intrinsic toxicity. Confocal microscopy images and flow cytometry results show the pH-responsive cellular uptake of Dox-loaded NDs, accelerated at pH ≤ 5.0. The tumour accumulation and in vivo bio-distribution studies of near-infrared dye (IR-820)-labeled NDs show higher tumour accumulation in CT26 tumour-bearing mice within 72 h. Furthermore, the Dox-loaded NDs effectively inhibit the CT26 tumours, suggesting that they are promising nanocarriers for cancer therapy.

Self-Assembling Peptide Epitopes as Novel Platform for Anticancer Vaccination

The aim of the present study was to improve the immunogenicity of peptide epitope vaccines using novel nanocarriers based on self-assembling materials. Several studies demonstrated that peptide antigens in nanoparticulate form induce stronger immune responses than their soluble forms. However, several issues such as poor loading and risk of inducing T cell anergy due to premature release of antigenic epitopes have challenged the clinical success of such systems. In the present study, we developed two vaccine delivery systems by appending a self-assembling peptide (Ac-AAVVLLLW-COOH) or a thermosensitive polymer poly(N-isopropylacrylamide (pNIPAm) to the N-terminus of different peptide antigens (OVA250-264, HPV-E743-57) to generate self-assembling peptide epitopes (SAPEs). The obtained results showed that the SAPEs were able to form nanostructures with a diameter from 20 to 200 nm. The SAPEs adjuvanted with CpG induced and expanded antigen-specific CD8+ T cells in mice. Furthermore, tumor-bearing mice vaccinated with SAPEs harboring the HPV E743-57 peptide showed a delayed tumor growth and an increased survival compared to sham-treated mice. In conclusion, self-assembling peptide based systems increase the immunogenicity of peptide epitope vaccines and therefore warrants further development toward clinical use.

Patchy Supramolecular Bottle-Brushes Formed by Solution Self-Assembly of Bis(urea)s and Tris(urea)s Decorated by Two Incompatible Polymer Arms

In an attempt to design urea-based Janus nanocylinders through a supramolecular approach, nonsymmetrical bis(urea)s and tris(urea)s decorated by two incompatible polymer arms, namely, poly(styrene) (PS) and poly(isobutylene) (PIB), were synthesized using rather straightforward organic and polymer chemistry techniques. Light scattering experiments revealed that these molecules self-assembled in cyclohexane by cooperative hydrogen bonds. The extent of self-assembly was limited for the bis(urea)s. On the contrary, reasonably anisotropic 1D structures (small nanocylinders) could be obtained with the tris(urea)s (Nagg ∼ 50) which developed six cooperative hydrogen bonds per molecule. (1)H transverse relaxation measurements and NOESY NMR experiments in cyclohexane revealed that perfect Janus nanocylinders with one face consisting of only PS and the other of PIB were not obtained. Nevertheless, phase segregation between the PS and PIB chains occurred to a large extent, resulting in patchy cylinders containing well separated domains of PIB and PS chains. Reasons for this behavior were proposed, paving the way to improve the proposed strategy toward true urea-based supramolecular Janus nanocylinders.

Internal Nanoparticle Structure of Temperature-Responsive Self-Assembled PNIPAM-b-PEG-b-PNIPAM Triblock Copolymers in Aqueous Solutions: NMR, SANS, and Light Scattering Studies

In this study, we report detailed information on the internal structure of PNIPAM-b-PEG-b-PNIPAM nanoparticles formed from self-assembly in aqueous solutions upon increase in temperature. NMR spectroscopy, light scattering, and small-angle neutron scattering (SANS) were used to monitor different stages of nanoparticle formation as a function of temperature, providing insight into the fundamental processes involved. The presence of PEG in a copolymer structure significantly affects the formation of nanoparticles, making their transition to occur over a broader temperature range. The crucial parameter that controls the transition is the ratio of PEG/PNIPAM. For pure PNIPAM, the transition is sharp; the higher the PEG/PNIPAM ratio results in a broader transition. This behavior is explained by different mechanisms of PNIPAM block incorporation during nanoparticle formation at different PEG/PNIPAM ratios. Contrast variation experiments using SANS show that the structure of nanoparticles above cloud point temperatures for PNIPAM-b-PEG-b-PNIPAM copolymers is drastically different from the structure of PNIPAM mesoglobules. In contrast with pure PNIPAM mesoglobules, where solidlike particles and chain network with a mesh size of 1-3 nm are present, nanoparticles formed from PNIPAM-b-PEG-b-PNIPAM copolymers have nonuniform structure with "frozen" areas interconnected by single chains in Gaussian conformation. SANS data with deuterated "invisible" PEG blocks imply that PEG is uniformly distributed inside of a nanoparticle. It is kinetically flexible PEG blocks which affect the nanoparticle formation by prevention of PNIPAM microphase separation.

Nanoparticles Based on Linear and Star-Shaped Poly(Ethylene Glycol)-Poly(ε-Caprolactone) Copolymers for the Delivery of Antitubulin Drug

PURPOSE

Biodegradable polymeric nanoparticles of different architectures based on polyethylene glycol-co-poly(ε-caprolactone) block copolymers have been loaded with noscapine (NOS) to study their effect on its anticancer activity. It was intended to use solubility of NOS in an acidic environment and ability of the nanoparticles to passively target drugs into cancer tissue to modify the NOS pharmacokinetic properties and reduce the requirement for frequent injections.

METHODS

Linear and star-shaped copolymers were synthetized and used to formulate NOS loaded nanoparticles. Cytotoxicity was performed using a sulforhodamine B method on MCF-7 cells, while biocompatibility was determined on rats followed by hematological and histopathological investigations.

RESULTS

Formulae with the smallest particle sizes and adequate entrapment efficiency revealed that NOS loaded nanoparticles showed higher extent of release at pH 4.5. Colloidal stability suggested that nanoparticles would be stable in blood when injected into the systemic circulation. Loaded nanoparticles had IC50 values lower than free drug. Hematological and histopathological studies showed no difference between treated and control groups. Pharmacokinetic analysis revealed that formulation P1 had a prolonged half-life and better bioavailability compared to drug solution.

CONCLUSIONS

Formulation of NOS into biodegradable polymeric nanoparticles has increased its efficacy and residence on cancer cells while passively avoiding normal body tissues. Graphical Abstract ᅟ.

Synthesis of highly porous poly(tert-butyl acrylate)-b-polysulfone-b-poly(tert-butyl acrylate) asymmetric membranes

For the first time, self-assembly and non-solvent induced phase separation was applied to polysulfone-based linear block copolymers, reaching mechanical stability much higher than other block copolymer membranes used in this method, which were mainly based on polystyrene blocks.

One-pot preparation of BAB triblock copolymer nano-objects through bifunctional macromolecular RAFT agent mediated dispersion polymerization

Nano-assemblies of a BAB triblock copolymer containing a solvophilic A block and two solvophobic B blocks were prepared through dispersion RAFT polymerization.