Heparin-Mimicking Sulfonated Polymer Nanoparticles via RAFT Polymerization-Induced Self-Assembly

Synthesis, Biological Evaluation and Reversal of Sulfonated Di- and Triblock Copolymers as Novel Parenteral Anticoagulants

Despite targeting different coagulation cascade sites, all Food and Drug Administration-approved anticoagulants present an elevated risk of bleeding, including potentially life-threatening intracranial hemorrhage. Existing studies have not thoroughly investigated the efficacy and safety of sulfonate polymers in animal models and fully elucidate the precise mechanisms by which these polymers act. The activity and safety of sulfonated di- and triblock copolymers containing poly(sodium styrenesulfonate) (PSSS), poly(sodium 2-acrylamido-2-methylpropanesulfonate) (PAMPS), poly(ethylene glycol) (PEG), poly(sodium methacrylate) (PMAAS), poly(acrylic acid) (PAA), and poly(sodium 11-acrylamidoundecanoate) (PAaU) blocks are synthesized and assessed. PSSS-based copolymers exhibit greater anticoagulant activity than PAMPS-based ones. Their activity is mainly affected by the total concentration of sulfonate groups and molecular weight. PEG-containing copolymers demonstrate a better safety profile than PAA-containing ones. The selected copolymer PEG47-PSSS32 exhibits potent anticoagulant activity in rodents after subcutaneous and intravenous administration. Heparin Binding Copolymer (HBC) completely reverses the anticoagulant activity of polymer in rat and human plasma. No interaction with platelets is observed. Selected copolymer targets mainly factor XII and fibrinogen, and to a lesser extent factors X, IX, VIII, and II, suggesting potential application in blood-contacting biomaterials for anticoagulation purposes. Further studies are needed to explore its therapeutic applications fully.

Glycopolymer-grafted nanoparticles as glycosaminoglycan mimics with cell proliferation and anti-tumor metastasis activities

Glycosaminoglycans (GAGs) are naturally existing extracellular components with a variety important biological functions. However, their heterogeneous chemical compositions and the challenges in purification have become the main disadvantages for clinical applications. Thus, various synthetic glycopolymers have been designed to mimic the structures and functions of natural GAGs. In the current study, glycopolymers from structurally simple glucose or N-acetylglucosamine monomers were synthesized, which were further subjected to sulfation of different degrees and grafting onto silica nanoparticles, leading to spherical-shaped nano-structures of uniform diameters. With the successively strengthened multivalent effect, the obtained glycopolymer nanoparticles not only showed excellent effects on promotion of cell proliferation by stabilizing growth factors, but also significantly inhibited tumor metastasis by weakening the adhesion between tumor cells and activated platelets. Among the prepared nanoparticles, S3-PGNAc@Si with N-acetylglucosamine segment and the highest sulfation degree exhibited the strongest bioactivities, which were even close to those of heparin. This work presents a novel approach for structural and functional mimicking of natural GAGs from simple and low-cost monosaccharides, holding great potential for a range of biomedical applications.

Polymerization-Induced Self-Assembly for Efficient Fabrication of Biomedical Nanoplatforms

Amphiphilic copolymers can self-assemble into nano-objects in aqueous solution. However, the self-assembly process is usually performed in a diluted solution (<1 wt%), which greatly limits scale-up production and further biomedical applications. With recent development of controlled polymerization techniques, polymerization-induced self-assembly (PISA) has emerged as an efficient approach for facile fabrication of nano-sized structures with a high concentration as high as 50 wt%. In this review, after the introduction, various polymerization method-mediated PISAs that include nitroxide-mediated polymerization-mediated PISA (NMP-PISA), reversible addition-fragmentation chain transfer polymerization-mediated PISA (RAFT-PISA), atom transfer radical polymerization-mediated PISA (ATRP-PISA), and ring-opening polymerization-mediated PISA (ROP-PISA) are discussed carefully. Afterward, recent biomedical applications of PISA are illustrated from the following aspects, i.e., bioimaging, disease treatment, biocatalysis, and antimicrobial. In the end, current achievements and future perspectives of PISA are given. It is envisioned that PISA strategy can bring great chance for future design and construction of functional nano-vehicles.

Supramolecular self-assembly of glycosaminoglycan mimetic nanostructures for cell proliferation and 3D cell culture application

Glycosaminoglycans (GAGs), such as heparin, heparan sulfate and chondroitin sulfate, are playing important roles in various biological processes. Due to the laborious work of organic or enzymatic total synthesis of GAGs, different approaches, including glycopolymers, dendrimers, etc., have been developed to mimic the structures and bioactivities of GAGs, but the syntheses can still be difficult. In the current study, a new format of GAG mimetic structure, supramolecularly assembled polymers, have been easily prepared by mixing fluorenylmethoxycarbonyl-diphenylalanine (Fmoc-FF) and sulfated glyco-modified fluorenylmethoxy derivatives (FGS and FG3S). The self-assembly behavior of these polymers into different structural formats of nanoparticles, nanofibers and macroscopic hydrogels upon adjusted concentrations and composite ratios have been detailed studied. The nanofibers modified with highly sulfated glycol groups (FG3S/Fmoc-FF) showed strong promotion effect for cell proliferation, which efficiency was even similar to that of natural heparin, higher than nanoparticles or non-/low-sulfated glyco-modified nanofibers. Moreover, the supramolecular polymers were further made into hydrogels that capable of 3D cell culture. This study provided a novel and efficient approach for GAG mimicking, showing great potential for tissue engineering related applications.

Probing the Effect of Rigidity on the Cellular Uptake of Core-Shell Nanoparticles: Stiffness Effects are Size Dependent

Nanoparticles are well established vectors for the delivery of a wide range of biomedically relevant cargoes. Numerous studies have investigated the impact of size, shape, charge, and surface functionality of nanoparticles on mammalian cellular uptake. Rigidity has been studied to a far lesser extent, and its effects are still unclear. Here, the importance of this property, and its interplay with particle size, is systematically explored using a library of core-shell spherical PEGylated nanoparticles synthesized by RAFT emulsion polymerization. Rigidity of these particles is controlled by altering the intrinsic glass transition temperature of their constituting polymers. Three polymeric core rigidities are tested: hard, medium, and soft using two particle sizes, 50 and 100 nm diameters. Cellular uptake studies indicate that softer particles are taken up faster and threefold more than harder nanoparticles with the larger 100 nm particles. In addition, the study indicates major differences in the cellular uptake pathway, with harder particles being internalized through clathrin- and caveolae-mediated endocytosis as well as macropinocytosis, while softer particles are taken up bycaveolae- and non-receptormediated endocytosis. However, 50 nm derivatives do not show any appreciable differences in uptake efficiency, suggesting that rigidity as a parameter in the biological regime may be size dependent.

Strategically designed SPEEK nanofibrous scaffold with tailored delivery ofresveratrolfor skin wound regeneration

Electro-spinnable polymeric materials can easily form two-dimensional (2D) nanofibrous scaffolds improving biochemical functionalities specially in the area of skin wound healing and nanomedicine, but it has been hard to achieve this on a highly mechanically stable biopolymer, Poly ether ether ketone (PEEK), due to its intrinsic hydrophobicity and chemical inertness. Herein, we demonstrated a novel nanomedicine healing system consisting of sulphonated poly ether ether ketone combined withresveratrol(SPEEK+RSV), which could act as an effective 2D nano bio-materialin vitroandin vivo, without observable cytotoxicity. The fabricated nanocomposites exhibited enriched skin cell proliferation and adhesion as confirmed from the results of MTT, cell adhesion and live-dead assay. Results of SEM analysis showed a uniform nano-sized distribution with adequate pore size and porosity % facilitating a desired breathable environment at the wound site. The results of FT-IR, tensile studies and TGA analyses confirmed the presence of appropriate bonds and improved mechanical stability of theRSVincorporated nanofibrous scaffold. Results of anti-microbial analysis portrayed good potentiality of the fabricated nanofibers in treating wounds colonized with bacterial infections. Controlled drug release of resveratrol established the bio-compatibility of the nanofibers in skin wound regeneration.In vivoanalysis assessed in female Wistar rats enabled complete wound closure with 100 % wound contraction within 16 days. Results of histopathology analysis through H-E and MT staining presented the re-surfing of the wound environment with regeneration of epithelium, granulation tissue and collagen. Thus, the fabricated 2D nanofibrous scaffold incorporated with pharmaceutical RSV bio-medicine perceptively mimicked skin ECM convincingly aiding the progression of skin wound regeneration mechanism.

(Bio)degradable and Biocompatible Nano-Objects from Polymerization-Induced and Crystallization-Driven Self-Assembly

Polymerization-induced self-assembly (PISA) and crystallization-driven self-assembly (CDSA) techniques have emerged as powerful approaches to produce a broad range of advanced synthetic nano-objects with high potential in biomedical applications. PISA produces nano-objects of different morphologies (e.g., spheres, vesicles and worms), with high solids content (∼10-50 wt %) and without additional surfactant. CDSA can finely control the self-assembly of block copolymers and readily forms nonspherical crystalline nano-objects and more complex, hierarchical assemblies, with spatial and dimensional control over particle length or surface area, which is typically difficult to achieve by PISA. Considering the importance of these two assembly techniques in the current scientific landscape of block copolymer self-assembly and the craze for their use in the biomedical field, this review will focus on the advances in PISA and CDSA to produce nano-objects suitable for biomedical applications in terms of (bio)degradability and biocompatibility. This review will therefore discuss these two aspects in order to guide the future design of block copolymer nanoparticles for future translation toward clinical applications.

Protected Poly(3-sulfopropyl methacrylate) Copolymers: Synthesis, Stability, and Orthogonal Deprotection

Because of their permanent charge, strong polyelectrolytes remain challenging to characterize, in particular, when they are combined with hydrophobic features. For this reason, they are typically prepared through a postmodification of a fully hydrophobic precursor. Unfortunately, these routes often result in an incomplete functionalization or otherwise require harsh reaction conditions, thus limiting their applicability. To overcome these problems, in this work a strategy is presented that facilitates the preparation of well-defined strong polyanions by starting from protected 3-sulfopropyl methacrylate monomers. Depending on the chemistry of the protecting group, the hydrophobic precursor could be quantitatively converted into a strong polyanion under nucleophilic, acidic, or basic conditions. As a proof of concept, orthogonally protected diblock copolymers were synthesized, selectively deprotected, and allowed to self-assemble in aqueous solution. Further conversion into a fully water-soluble polyanion was achieved by deprotecting the second block as well.

Influence of Solvent on RAFT-mediated Polymerization of Benzyl Methacrylate (BzMA) and How to Overcome the Thermodynamic/Kinetic Limitation of Morphology Evolution during Polymerization-Induced Self-Assembly

Polymerization-induced self-assembly (PISA) has been demonstrated to be a powerful strategy to produce polymeric nano-objects of various morphologies. Dependent on the solubility of monomers, PISA is usually classified into two...

Silica nanoparticle-loaded thermoresponsive block copolymer vesicles: a new post-polymerization encapsulation strategy and thermally triggered release

A thermoresponsive amphiphilic diblock copolymer that can form spheres, worms or vesicles in aqueous media at neutral pH by simply raising the dispersion temperature from 1 °C (spheres) to 25 °C (worms) to 50 °C (vesicles) is prepared via polymerization-induced self-assembly (PISA). Heating such an aqueous copolymer dispersion from 1 °C up to 50 °C in the presence of 19 nm glycerol-functionalized silica nanoparticles enables this remarkable ‘shape-shifting’ behavior to be exploited as a new post-polymerization encapsulation strategy. The silica-loaded vesicles formed at 50 °C are then crosslinked using a disulfide-based dihydrazide reagent. Such covalent stabilization enables the dispersion to be cooled to room temperature without loss of the vesicle morphology, thus aiding characterization and enabling the loading efficiency to be determined as a function of both copolymer and silica concentration. Small-angle X-ray scattering (SAXS) analysis indicated a mean vesicle membrane thickness of approximately 20 ± 2 nm for the linear vesicles and TEM studies confirmed encapsulation of the silica nanoparticles within these nano-objects. After removal of the non-encapsulated silica nanoparticles via multiple centrifugation–redispersion cycles, thermogravimetric analysis indicated that vesicle loading efficiencies of up to 86% can be achieved under optimized conditions. Thermally-triggered release of the silica nanoparticles is achieved by cleaving the disulfide bonds at 50 °C using tris(2-carboxyethyl)phosphine (TCEP), followed by cooling to 20 °C to induce vesicle dissociation. SAXS is also used to confirm the release of silica nanoparticles by monitoring the disappearance of the structure factor peak arising from silica–silica interactions.

A loading efficiency of up to 86% is achieved for silica nanoparticles encapsulated within crosslinkable redox-sensitive thermoresponsive diblock copolymer vesicles in water at 50 °C; triggered release is also demonstrated for this system.

In situ monitoring of PISA morphologies

Fluorescent spectroscopy is a convenient method for monitoring the progression of polymerization-induced self-assembly (PISA).

Towards nanoparticles with site-specific degradability by ring-opening copolymerization induced self-assembly in organic medium

Radical ring-opening copolymerization-induced self-assembly (rROPISA) was successfully applied to the synthesis of core-, surface- or surface plus core-degradable nanoparticles in heptane, leading to site-specific degradability by rROPISA.

Enthalpic incompatibility between two steric stabilizer blocks provides control over the vesicle size distribution during polymerization-induced self-assembly in aqueous media

Over the past two decades, block copolymer vesicles have been widely used by many research groups to encapsulate small molecule drugs, genetic material, nanoparticles or enzymes. They have also been used to design examples of autonomous self-propelled nanoparticles. Traditionally, such vesicles are prepared via post-polymerization processing using a water-miscible co-solvent such as DMF or THF. However, such protocols are invariably conducted in dilute solution, which is a significant disadvantage. In addition, the vesicle size distribution is often quite broad, whereas aqueous dispersions of relatively small vesicles with narrow size distributions are highly desirable for potential biomedical applications. Alternatively, concentrated dispersions of block copolymer vesicles can be directly prepared via polymerization-induced self-assembly (PISA). Moreover, using a binary mixture of a relatively long and a relatively short steric stabilizer block enables the convenient PISA synthesis of relatively small vesicles with reasonably narrow size distributions in alcoholic media (C. Gonzato et al., JACS, 2014, 136, 11100-11106). Unfortunately, this approach has not yet been demonstrated for aqueous media, which would be much more attractive for commercial applications. Herein we show that this important technical objective can be achieved by judicious use of two chemically distinct, enthalpically incompatible steric stabilizer blocks, which ensures the desired microphase separation across the vesicle membrane. This leads to the formation of well-defined vesicles of around 200 nm diameter (size polydispersity = 13-16%) in aqueous media at 10% w/w solids as judged by transmission electron microscopy, dynamic light scattering and small-angle X-ray scattering.

Sulfonated RAFT Copolymers as Heparin Mimetics: Synthesis, Reactivity Ratios, and Anticoagulant Activity

The glycosaminoglycan heparin is a clinically important anticoagulant drug, primarily used to reduce the risk of blood clots (thrombosis) during surgery. Despite its importance in medicine and its continuous use over many decades, heparin suffers from several limitations associated with its heterogeneity and its extraction from animal tissues. In order to address these limitations, reversible addition-fragmentation chain transfer polymerization is utilized to prepare a library of heparin mimetic copolymers from the sulfonated monomers sodium 4-styrene sulfonate, potassium-3-sulfopropyl acrylate, potassium-3-sulfopropyl methacrylate, and sodium-2-acrylamido-2-methyl-1-propane sulfonate. Copolymers are prepared using combinations of two different monomers in various ratios. Monomer reactivity ratios are also determined for some representative monomer combinations, and all polymers are characterized by ¹ H NMR spectroscopy and gel permeation chromatography. The anticoagulant activities of the copolymers are determined by activated partial thromboplastin time and thrombin clotting time assays and structure-activity relationships are explored.

Exploring precision polymers to fine-tune magnetic resonance imaging properties of iron oxide nanoparticles

The use of bio-polymers as stabilising agents for iron oxide-based negative magnetic resonance imaging (MRI) contrast agents has become popular in recent years, however the wide polydispersity of biologically-derived and commercially available polymers limits the ability to produce truly tuneable and reproducible behaviour, a major challenge in this area. In this work, stable colloids of iron oxide nanoparticles were prepared utilising precision-engineered bio-polymer mimics, poly(2-acrylamido-2-methylpropane sodium sulfonate) (P(AMPS)) polymers, with controlled narrow polydispersity molecular weights, as templating stabilisers. In addition to producing magnetic colloids with excellent MRI contrast capabilities (r₂ values reaching 434.2 mM^-1 s^-1 at 25 °C and 23 MHz, several times higher than similar commercial analogues), variable field relaxometry provided unexpected important insights into the dynamic environment of the hydrated materials, and hence their exceptional MRI behaviour. Thanks to the polymer's templating backbone and flexible conformation in aqueous suspension, nanocomposites appear to behave as "multi-core" clustered species, enhancing interparticle interactions whilst retaining water diffusion, boosting relaxation properties at low frequency. This clustering behaviour, evidenced by small-angle X-ray scattering, and strong relaxometric response, was fine-tuned using the well-defined molecular weight polymer species with precise iron to polymer ratios. By also showing negligible haemolytic activity, these nanocomposites exhibit considerable potential for MRI diagnostics.

Polymerization-induced self-assembly for the fabrication of polymeric nano-objects with enhanced structural stability by cross-linking

This review discusses the strategies of core-cross-linking in most of the PISA literatures (including post-polymerization cross-linking, photo-cross-linking and in situ cross-linking) and the applications of the cross-linked nano-objects.

Self-assembly of amphiphilic copolymers containing polysaccharide: PISA versus nanoprecipitation, and the temperature effect

The self-assembly methods and the temperature have a considerable impact on the morphology of the resulting nanoobjects in the case of amphiphilic glycopolymers.

A study on the preparation of alkyne functional nanoparticlesviaRAFT emulsion polymerisation

We evaluate the parameters surrounding the preparation of colloidally stable alkyne functional latex nanoparticlesviaRAFT emulsion polymerisation.

A mild and quantitative route towards well-defined strong anionic/hydrophobic diblock copolymers: synthesis and aqueous self-assembly

Well-defined hydrophobic/strong anionic diblock copolymers were synthesized through a protected hydrophobic intermediate. Their self-assembly in aqueous solution was subsequently studied.

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

We report a versatile 'Trojan Horse' strategy using highly anionic poly(methacrylic acid)-poly(benzyl methacrylate) vesicles to incorporate two types of model payloads, i.e. either silica nanoparticles or an organic dye (fluorescein), within CaCO3 (calcite). Uniform occlusion of silica-loaded vesicles was confirmed by scanning electron microscopy, while thermogravimetry studies indicated extents of vesicle occlusion of up to 9.4% by mass (∼33% by volume). Efficient dye-loaded vesicle occlusion produces highly fluorescent calcite crystals as judged by fluorescence microscopy. In control experiments, silica nanoparticles alone are barely occluded, while only very weakly fluorescent calcite crystals are obtained when using just the fluorescein dye. This new 'Trojan Horse' strategy opens up a generic route for the efficient occlusion of various nanoparticles and organic molecules within inorganic host crystals.

Reverse-phase high performance liquid chromatography (RP-HPLC) as a powerful tool to characterise complex water-soluble copolymer architectures

A novel analytical method, based on RP-HPLC, for the characterisation of monomer distribution in charged water-soluble copolymers.