Emerging methods for the fabrication of polymer capsules

Bioinspired polymer vesicles and membranes for biological and medical applications

Biological membranes play an essential role in living organisms by providing stable and functional compartments, supporting signalling and selective transport. Combining synthetic polymer membranes with biological molecules promises to be an effective strategy to mimic the functions of cell membranes and apply them in artificial systems.

Synthesis of amphiphilic block-type macromolecular brushes with cleavable pendant chains and fabrication of micelle-templated polymer nanocapsules

Macromolecular brushes with cleavable pendant chains were synthesized by controlled free radical polymerizations and functional nanocapsules were fabricated on the basis of the brush polymers.

Polymer-based vehicles for therapeutic peptide delivery

During the last decades increasing attention has been paid to peptides as potential therapeutics. However, clinical applications of peptide drugs suffer from susceptibility to degradation, rather short circulation half-life, limited ability to cross physiological barriers and potential immunogenicity. These challenges can be addressed by using polymeric materials as peptide delivery systems, owing to their versatile structures and properties. A number of polymer-based vehicles have been developed to stabilize the peptides and to control their release rates. Unfortunately, no single polymer or formulation strategy has been considered ideal for all types of peptide drugs. In this review, currently used and potential polymer-based systems for the peptide delivery will be discussed.

Multifunctional Thrombin-Activatable Polymer Capsules for Specific Targeting to Activated Platelets

Smart poly(2-oxazoline) (POx)-based multifunctional polymer capsules that specifically target glycoprotein (GP) IIb/IIIa on the surface of activated platelets are degraded by the serine protease thrombin and release the urokinase plasminogen activator loaded into the polymer capsules, only in the area of acute thrombosis.

Thermal Transitions in Polyelectrolyte Assemblies Occur via a Dehydration Mechanism

Hydrated polyelectrolyte (PE) complexes and multilayers undergo a well-defined thermal transition that bears resemblance to a glass transition. By combining molecular simulations and differential scanning calorimetry (DSC) of poly(diallyldimethylammonium) (PDAC) and poly(styrenesulfonate) (PSS) multilayers, we establish for the first time that dehydration drives the thermally induced change in plasticization of the complex and in the diffusion behavior of its components. DSC experiments show that the thermal transition appears when the assemblies are hydrated in water but not in the presence of alcohols, which supports that water is required for this transition. These findings connect PE complexes more generally to thermoresponsive polymers and liquid crystal phases, which bear phase transitions driven by the (de)hydration of functional groups, thus forming a fundamental link toward an integrated understanding of the thermal response of molecular materials in aqueous environments.

Small Wonders-The Use of Nanoparticles for Delivering Antigen

Despite the discovery of many potential antigens for subunit vaccines, universal protection is often lacking due to the limitations of conventional delivery methods. Subunit vaccines primarily induce antibody-mediated humoral responses, whereas potent antigen-specific cellular responses are required for prevention against some pathogenic infections. Nanoparticles have been utilised in nanomedicine and are promising candidates for vaccine or drug delivery. Nanoparticle vehicles have been demonstrated to be efficiently taken up by dendritic cells and induce humoral and cellular responses. This review provides an overview of nanoparticle vaccine development; in particular, the preparation of nanoparticles using a templating technique is highlighted, which would alleviate some of the disadvantages of existing nanoparticles. We will also explore the cellular fate of nanoparticle vaccines. Nanoparticle-based antigen delivery systems have the potential to develop new generation vaccines against currently unpreventable infectious diseases.

Biocompatible long-sustained release oil-core polyelectrolyte nanocarriers: From controlling physical state and stability to biological impact

It has been generally expected that the most applicable drug delivery system (DDS) should be biodegradable, biocompatible and with incidental adverse effects. Among many micellar aggregates and their mediated polymeric systems, polyelectrolyte oil-core nanocarriers have been found to successfully encapsulate hydrophobic drugs in order to target cells and avoid drug degradation and toxicity as well as to improve drug efficacy, its stability, and better intracellular penetration. This paper reviews recent developments in the formation of polyelectrolyte oil-core nanocarriers by subsequent multilayer adsorption at micellar structures, their imaging, physical state and stability, drug encapsulation and applications, in vitro release profiles and in vitro biological evaluation (cellular uptake and internalization, biocompatibility). We summarize the recent results concerning polyelectrolyte/surfactant interactions at interfaces, fundamental to understand the mechanisms of formation of stable polyelectrolyte layered structures on liquid cores. The fabrication of emulsion droplets stabilized by synergetic surfactant/polyelectrolyte complexes, properties, and potential applications of each type of polyelectrolyte oil-core nanocarriers, including stealth nanocapsules with pegylated shell, are discussed and evaluated.

Synthesis of multi-functional nanocapsules via interfacial AGET ATRP in miniemulsion for tumor micro-environment responsive drug delivery

Novel multi-functional polymeric hollow nanocapsules (PHN) based on the crosslinked poly(tert-butyl acrylate) (PtBA) shells were synthesized in a miniemulsion interfacial polymerization via activator generated electron transfer atom transfer radical polymerization (AGET ATRP) technique with N,N'-bis(acryloyl) cystamine (BACy) as cross-linking agent, CuBr₂ as catalyst, ascorbic acid (VC) as reducing agent and hexadecane as inert solvent. In the AGET ATRP, a folate-conjugated block copolymer, folate-poly(ethylene glycol)-b-poly(tert-butyl acrylate) (FA-PEG-tBA-Br), was used as macroinitiator/stabilizer, and the specific amphiphilic nature of the copolymer led the extending inward of polymer chains. The DLS analysis directly showed the PHN with an average diameter of 150 nm was obtained. After the PtBA shells were transformed into poly(acrylic acid) (PAA) by hydrolysis, doxorubicin (DOX), as a model drug, was loaded efficiently into the hydrolyzed polymeric hollow nanocapsules (HPHN), then the in vitro release of drug was carried out in phosphate buffer solution (PBS, pH 7.4 or 5.0, with or without DTT or GSH of different concentrations). It showed that the existence of folate group significantly improved pH stimuli-responsive and DOX-loading capacity of the polymeric nanocapsules. An acidic pH (5.0) and presence of GSH would accelerate the DOX release behavior. Thus, these multi-functional polymeric nanocapsules have excellent available properties in the field of targeted and controlled drug delivery for cancer therapy.

Electrostatically Directed Self-Assembly of Ultrathin Supramolecular Polymer Microcapsules

Supramolecular self-assembly offers routes to challenging architectures on the molecular and macroscopic scale. Coupled with microfluidics it has been used to make microcapsules-where a 2D sheet is shaped in 3D, encapsulating the volume within. In this paper, a versatile methodology to direct the accumulation of capsule-forming components to the droplet interface using electrostatic interactions is described. In this approach, charged copolymers are selectively partitioned to the microdroplet interface by a complementary charged surfactant for subsequent supramolecular cross-linking via cucurbit[8]uril. This dynamic assembly process is employed to selectively form both hollow, ultrathin microcapsules and solid microparticles from a single solution. The ability to dictate the distribution of a mixture of charged copolymers within the microdroplet, as demonstrated by the single-step fabrication of distinct core-shell microcapsules, gives access to a new generation of innovative self-assembled constructs.

Hierarchically functionalized magnetic core/multishell particles and their postsynthetic conversion to polymer capsules

The controlled synthesis of hierarchically functionalized core/multishell particles is highly desirable for applications in medicine, catalysis, and separation. Here, we describe the synthesis of hierarchically structured metal-organic framework multishells around magnetic core particles (magMOFs) via layer-by-layer (LbL) synthesis. The LbL deposition enables the design of multishell systems, where each MOF shell can be modified to install different functions. Here, we used this approach to create controlled release capsules, in which the inner shell serves as a reservoir and the outer shell serves as a membrane after postsynthetic conversion of the MOF structure to a polymer network. These capsules enable the controlled release of loaded dye molecules, depending on the surrounding media.

Physicochemical and immunological assessment of engineered pure protein particles with different redox states

The development of subunit antigen delivery formulations has become an important research endeavor, especially in cases where a whole cell vaccine approach has significant biosafety issues. Particle-based systems have shown particular efficacy due to their inherent immunogenicity. In some cases, fabrication techniques can lead to changes in the redox states of encapsulated protein antigens. By employing a uniform, well-characterized, single-protein system, it is possible to elucidate how the molecular details of particle-based protein antigens affect their induced immune responses. Using mesoporous silica-templated, amide bond-stabilized ovalbumin particles, three types of particles were fabricated from native, reduced, and oxidized ovalbumin, resulting in particles with different physicochemical properties and immunogenicity. Phagocytosis, transcription factor activation, and cytokine secretion by a mouse macrophage cell line did not reveal significant differences between the three types of particles. Oxidation of the ovalbumin, however, was shown to inhibit the intracellular degradation of the particles compared with native and reduced ovalbumin particles. Slow intracellular degradation of the oxidized particles was correlated with inefficient antigen presentation and insignificant levels of T cell priming and antibody production in vivo. In contrast, particles fabricated from native and reduced ovalbumin were rapidly degraded after internalization by macrophages in vitro and resulted in significant T cell and B cell immune responses in vivo. Taken together, the current study demonstrates how the redox state of a protein antigen significantly impacts the immunogenicity of the particulate vaccine formulations.

Engineering poly(ethylene glycol) particles for improved biodistribution

We report the engineering of poly(ethylene glycol) (PEG) hydrogel particles using a mesoporous silica (MS) templating method via tuning the PEG molecular weight, particle size, and the presence or absence of the template and investigate the cell association and biodistribution of these particles. An ex vivo assay based on human whole blood that is more sensitive and relevant than traditional cell-line based assays for predicting in vivo circulation behavior is introduced. The association of MS@PEG particles (template present) with granulocytes and monocytes is higher compared with PEG particles (template absent). Increasing the PEG molecular weight (from 10 to 40 kDa) or decreasing the PEG particle size (from 1400 to 150 nm) reduces phagocytic blood cell association of the PEG particles. Mice biodistribution studies show that the PEG particles exhibit extended circulation times (>12 h) compared with the MS@PEG particles and that the retention of smaller PEG particles (150 nm) in blood, when compared with larger PEG particles (>400 nm), is increased at least 4-fold at 12 h after injection. Our findings highlight the influence of unique aspects of polymer hydrogel particles on biological interactions. The reported PEG hydrogel particles represent a new class of polymer carriers with potential biomedical applications.

Preparation of polydopamine nanocapsules in a miscible tetrahydrofuran–buffer mixture

A non-emulsion soft template method based on a miscible tetrahydrofuran–tris buffer mixture has been used to fabricate polydopamine nanocapsules.

Encapsulated enzymes with integrated fluorescence-control of enzymatic activity

Capsules filled with enzymes and fluorescence probes allow in situ enzymatic activity as well as kinetics on a single particle level to be monitored.

An overview of nanotoxicity and nanomedicine research: principles, progress and implications for cancer therapy

The studies of nanomaterial-based drug delivery and nanotoxicity are closely interconnected.

Enhanced water retention and proton conductivity of proton exchange membranes by incorporating hollow polymer microspheres grafted with sulfonated polystyrene brushes

The paper describes the synthesis of hollow polymer microspheres with sulfonated polystyrene brushes and investigation of the enhanced water retention and proton conductivity of proton exchange membranes.

Preparation of elastic polyurethane microcapsules using CaCO3 microparticles as templates for hydrophobic substances loading

Elastic polyurethane (PU) microcapsules were fabricated via a simple and well controllable adsorption and crosslinking method on porous CaCO₃ templates in organic solvent.

Covalently cross-linked poly(2-oxazoline) materials for biomedical applications – from hydrogels to self-assembled and templated structures

We discuss covalently cross-linked poly(2-oxazoline)s including gels, nanogels and capsules on the basis of their synthetic origin in a biomedical context.

Hollow polyphosphazene microspheres with cross-linked chemical structure: synthesis, formation mechanism and applications

Hollow polyphosphazene microspheres with highly cross-linked chemical structures were prepared by a template-induced assembly mechanism. The hollow microspheres display good stability towards Au nanoparticles.

Controllable microfluidic fabrication of Janus and microcapsule particles for drug delivery applications

Janus and microcapsule particles are very attractive for drug delivery applications due to their capability of targeted and/or programmed drug release.

Encapsulation of anticancer drug by hydrogen-bonded multilayers of tannic acid

Tannic acid (TA)-based multilayer assemblies have attracted increasing interest for biomedical applications. Here we explore properties of TA-poly(N-vinylpyrrolidone) (TA-PVPON) hydrogen-bonded multilayers for drug encapsulation and long-term storage. We demonstrate that the small molecular weight anticancer drug, doxorubicin (DOX), can be successfully loaded into (TA-PVPON) capsules with high encapsulation efficiency. We have also found that the encapsulated DOX can be efficiently stored inside the capsules for the pH range from pH = 7.4 to pH = 5. We show that the chemical and functional stability of TA at neutral and basic pH values is achieved through complexation with PVPON. The UV-vis spectrophotometry and in situ ellipsometry analyses of the hydrogen bonding interactions between TA and PVPON at different pH values reveal pH-dependent behavior of TA-PVPON capsules for the pH range from pH = 7.4 to pH = 5. Increasing deposition pH value from pH = 5 to pH = 7.4 leads to a 2-fold decrease in capsule thickness. However, this trend is reversed when salt concentration of the deposition solutions is increased from 0.01 M to 0.1 M NaCl. We have also demonstrated that the permeability of (TA-PVPON) capsules prepared using low salt deposition conditions and pH = 7.4 can be increased 2-fold by exposure of the capsules to 0.1 M NaCl salt solutions at the same pH. Our work opens new perspectives for design of novel polymer carriers for controlled drug delivery in cancer therapy.

Fabrication of nanocapsule carriers from multilayer-coated vaterite calcium carbonate nanoparticles

Nanosized luminescent sensors were prepared as reagents for optical sensing and imaging of oxygen using ratiometric emission properties of a two-dye system. Polymeric capsules were fabricated utilizing poly(vinylsulfonic acid) (PVSA)-stabilized vaterite CaCO3 nanoparticles (CCNPs) as sacrificial templates. The buffer and polymeric surfactant requirements of the layer-by-layer (LbL) process were evaluated toward deposition of multilayer coatings and, ultimately, formation of hollow capsules using these interesting materials. CCNPs were found to be more stable in alkaline NaHCO3 buffer after repeated cycles of washing under sonication and resuspension. An intermediate PVSA concentration was required to maximize the loading of oxygen-sensitive porphyrin and oxygen-insensitive fluorescent nanoparticles in the CCNPs while maintaining minimal nanoparticle size. The CCNPs were then coated with polyelectrolyte multilayers and subsequent removal of the CaCO3 core yielded nanocapsules containing dye and fluorescent nanoparticles. The resulting nanocapsules with encapsulated luminophores functioned effectively as oxygen sensors with a quenching response of 89.28 ± 2.59%, and O2 (S = 1/2) = 20.91 μM of dissolved oxygen.

Templated assembly of albumin-based nanoparticles for simultaneous gene silencing and magnetic resonance imaging

In this article, we address the design of innovative human serum albumin (HSA)-based nanoparticles loaded with silencing RNA and grafted with gadolinium complexes having average sizes ranging from ca. 50 to 150 nm according to the siRNA/HSA composition. The non-covalent siRNA/HSA assembly is formed on isobutyramide-modified mesoporous silica and the self-supported HSA-based nanoparticles are obtained following the silica template dissolution. These original protein particles provide simultaneous magnetic resonance imaging contrast enhancement and cellular in vitro gene silencing.