Synthesis of nanostructured protein-mineral-microcapsules by sonication

We propose a simple and eco-friendly method for the formation of composite protein-mineral-microcapsules induced by ultrasound treatment. Protein- and nanoparticle-stabilized oil-in-water (O/W) emulsions loaded with different oils are prepared using high-intensity ultrasound. The formation of thin composite mineral proteinaceous shells is realized with various types of nanoparticles, which are pre-modified with Bovine Serum Albumin (BSA) and subsequently characterized by EDX, TGA, zeta potential measurements and Raman spectroscopy. Cryo-SEM and EDX mapping visualizations show the homogeneous distribution of the densely packed nanoparticles in the capsule shell. In contrast to the results reported in our previous paper,¹ the shell of those nanostructured composite microcapsules is not cross-linked by the intermolecular disulfide bonds between BSA molecules. Instead, a Pickering-Emulsion formation takes place because of the amphiphilicity-driven spontaneous attachment of the BSA-modified nanoparticles at the oil/water interface. Using colloidal particles for the formation of the shell of the microcapsules, in our case silica, hydroxyapatite and calcium carbonate nanoparticles, is promising for the creation of new functional materials. The nanoparticulate building blocks of the composite shell with different chemical, physical or morphological properties can contribute to additional, sometimes even multiple, features of the resulting capsules. Microcapsules with shells of densely packed nanoparticles could find interesting applications in pharmaceutical science, cosmetics or in food technology.

Nanodeformations of microcapsules: comparing the effects of cross-linking and nanoparticles

The mechanical properties of proteinaceous and composite microcapsules loaded with oil were measured by SFM and evaluated using the Reissner model. Comparison of the obtained results reveals significantly higher Young’s moduli of protein capsules due to intermolecular crosslinking. In contrast, conformational restrictions in composite microcapsules inhibit protein crosslinking leading to the reduction of their elasticity.

SFM results for protein and composite microcapsules are evaluated by the Reissner model. Protein capsules show higher Young’s moduli due to crosslinking, which is absent in composite capsules because of restrictions in the protein conformations.

Deposition of non-porous calcium phosphate shells onto liquid filled microcapsules

The efficient encapsulation of small molecule active ingredients has been a challenge for many decades across many commercial applications. Recently, successful attempts to address this issue have included deposition of thin metal shells onto liquid filled polymer microcapsules or emulsion droplets to provide an impermeable barrier to diffusion. In this work we have developed a novel method to protect small molecule active ingredients by deposition of thin mineral shells. Platinum nanoparticles are used to catalyse and direct growth of a calcium phosphate shell onto liquid filled polymer microcapsules under various reaction conditions. Findings indicate that a non-porous protective shell is formed on the majority of the microcapsule population, with small concentrations of the core material being released only from those microcapsules with defects, over a 7 days period, when conducting forced release studies into a solvent for the core oil. The resulting microcapsules show no significant cell toxicity when exposed to HEK 293 cells for 72 h.

Surface pressure of liquid interfaces laden with micron-sized particles

We consider the surface pressure of a colloid-laden liquid interface. As micron-sized particles of suitable wettability can be irreversibly bound to the liquid interface on experimental timescales, we use the canonical ensemble to derive an expression for the surface pressure of a colloid-laden interface. We use this expression to show that adsorption of particles with only hard-core interactions has a negligible effect on surface pressures from typical Langmuir-trough measurements. Moreover, we show that Langmuir-trough measurements cannot be used to extract typical interparticle potentials. Finally, in the case of relatively weakly interacting sterically stabilized particles at a liquid interface, we argue that the dependence of measured surface pressure on surface fraction can be explained by particle coordination number at low to intermediate particle surface fractions. At high surface fractions, where the particles are jammed and cannot easily rearrange, we argue that contact-line sliding and/or deformations of the liquid interface at the length scale of the particles might play a pivotal role.

Toward the Formulation of Stable Micro and Nano Double Emulsions through a Silica Coating on Internal Water Droplets

Delivery systems able to coencapsulate both hydrophilic and hydrophobic species are of great interest in both fundamental research and industrial applications. Water-in-oil-in-water (w₁/O/W₂) emulsions are interesting systems for this purpose, but they suffer from limited stability. In this study, we propose an innovative approach to stabilize double emulsions by the synthesis of a silica membrane at the water/oil interface of the primary emulsion (i.e., inner w₁/O emulsion). This approach allows the formulation of stable double emulsions through a two-step process, enabling high encapsulation efficiencies of model hydrophilic dyes encapsulated in the internal droplets. This approach also decreases the scale of the double droplets up to the nanoscale, which is not possible without silica stabilization. Different formulation and processing parameters were explored in order to optimize the methodology. Physicochemical characterization was performed by dynamic light scattering, encapsulation efficiency measurements, release profiles, and optical and transmission electron microscopies.

Curcumin nanocapsules stabilized by bovine serum albumin-capped gold nanoclusters (BSA-AuNCs) for drug delivery and theranosis

Nanotechnology plays an important role in the development of drug delivery, imaging, and diagnosis. In this study, nanocapsules containing protein-functionalized gold nanoclusters (AuNCs) as the shell and hydrophobic drug curcumin as the core were prepared as a tumor cell theranostic agent. After the nanocapsules were added into tumor cell media, they entered the cells with high efficiency and exhibited strong fluorescence within the cells. The results indicated that the nanocapsules were broken up in the cells and curcumin was released. Simultaneously, the nanocapsules exhibited significant inhibition effect against tumor cell proliferation in a concentration- and time-dependent manner, and the images of atomic force microscopy (AFM) showed that the cell morphology underwent obvious changes after the capsule treatment. Additionally, cell membrane appeared wrinkles after the cells treated with the nanocapsules, resulting in a rough cell surface, implying that the cytoskeleton would involve in the cell uptake of nanocapsules. Moreover, the AuNCs and curcumin in the system could exert synergistic effect on the inhibition of tumor cell growth and induction of cell apoptosis. The study highlights the potential of the system as a promising agent for drug delivery and tumor cell theranosis.

Flat Drops, Elastic Sheets, and Microcapsules by Interfacial Assembly of a Bacterial Biofilm Protein, BslA

Protein adsorption and assembly at interfaces provide a potentially versatile route to create useful constructs for fluid compartmentalization. In this context, we consider the interfacial assembly of a bacterial biofilm protein, BslA, at air-water and oil-water interfaces. Densely packed, high modulus monolayers form at air-water interfaces, leading to the formation of flattened sessile water drops. BslA forms elastic sheets at oil-water interfaces, leading to the production of stable monodisperse oil-in-water microcapsules. By contrast, water-in-oil microcapsules are unstable but display arrested rather than full coalescence on contact. The disparity in stability likely originates from a low areal density of BslA hydrophobic caps on the exterior surface of water-in-oil microcapsules, relative to the inverse case. In direct analogy with small molecule surfactants, the lack of stability of individual water-in-oil microcapsules is consistent with the large value of the hydrophilic-lipophilic balance (HLB number) calculated based on the BslA crystal structure. The occurrence of arrested coalescence indicates that the surface activity of BslA is similar to that of colloidal particles that produce Pickering emulsions, with the stability of partially coalesced structures ensured by interfacial jamming. Micropipette aspiration and flow in tapered capillaries experiments reveal intriguing reversible and nonreversible modes of mechanical deformation, respectively. The mechanical robustness of the microcapsules and the ability to engineer their shape and to design highly specific binding responses through protein engineering suggest that these microcapsules may be useful for biomedical applications.

Silk sericin microcapsules with hydroxyapatite shells: protection and modification of organic microcapsules by biomimetic mineralization

Silk protein sericin based organic–inorganic hybrid microcapsules are fabricated by incubating sericin microcapsules with a supersaturated calcium phosphate solution containing citric acid.

Bio-templated bioactive glass particles with hierarchical macro-nano porous structure and drug delivery capability

Hierarchically porous bioactive glass particles (BGPs) were synthesized by a facile sol-gel process using pollen grains as the templates. The synthesized pollen-templated bioactive glass particles (PBGPs) exhibited dual macro-nano porous structure. The macro pores (∼ 1 μm) were inherited from the template of pollen grains while the nano pores (∼ 9.5 nm) were induced by the intrinsic mechanism of the sol-gel process. PBGPs possessed a high specific surface area (111.4m(2)/g) and pore volume (0.35 cm(3)/g). Hydroxyapatite (HA) formation on PBGPs was detected within 3 days after immersion in simulated body fluid (SBF). Due to their larger specific surface area and pore volume, PBGPs could be loaded with more tetracycline hydrochloride (TCH) than non-templated BGPs and conventional melt-derived 45S5 BGPs. In addition, PBGPs exhibited a low initial burst release (within 10% of the loaded amount) within 18 h and a sustained release with a two-stage release pattern for up to 6 days in phosphate buffered saline (PBS). The antibacterial assay confirmed that the TCH-loaded PBGPs could release TCH within 5 days, and the released TCH could reach the minimum inhibitory concentration (MIC) against Escherichia coli. MTT assay indicated that PBGPs showed non-cytotoxic effects toward human hepatocellular carcinoma (Hep G2) cells after co-culture for up to 72 h in vitro. These results showed that the biocompatible hierarchically macro-nano porous PBGPs are potential for bone regeneration and local drug delivery applications.

Biomimetic synthesis of novel calcium carbonate heterogeneous dendrites

Three-dimensional dendrites of calcium carbonate were successfully synthesized via a nonclassical crystallization pathway by combining two different functional additives. They showed fascinating heterogeneous superstructures made up of calcite scaffolding, aragonite shells, and an external amorphous coating.

Fabrication of calcium phosphate microcapsules using emulsion droplets stabilized with branched copolymers as templates

An efficient emulsion templating route using branched copolymers as droplet stabilizers for the synthesis of fluorescently labelled calcium phosphate capsules.

Self-assembled micelles based on branched poly(styrene-alt-maleic anhydride) as particulate emulsifiers

The self-assembled micelles of branched poly(styrene-alt-maleic anhydride) (BPSMA) are prepared and exhibit much superior emulsifying performance over the corresponding linear copolymer micelles as particulate emulsifiers.

Ultrathin hybrid films of polyoxohydroxy clusters and proteins: layer-by-layer assembly and their optical and mechanical properties

The hierarchical assembly of inorganic and organic building blocks is an efficient strategy to produce high-performance materials which has been demonstrated in various biomaterials. Here, we report a layer-by-layer (LBL) assembly method to fabricate ultrathin hybrid films from nanometer-scale ionic clusters and proteins. Two types of cationic clusters (hydrolyzed aluminum clusters and zirconium-glycine clusters) were assembled with negatively charged bovine serum albumin (BSA) protein to form high-quality hybrid films, due to their strong electrostatic interactions and hydrogen bonding. The obtained hybrid films were characterized by scanning electron microscope (SEM), UV-vis, Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), X-ray fluorescence (XRF), and X-ray diffraction (XRD). The results demonstrated that the cluster-protein hybrid films exhibited structural homogeneity, relative transparency, and bright blue fluorescence. More importantly, these hybrid films displayed up to a 70% increase in hardness and up to a 100% increase in reduced Young's modulus compared to the pure BSA film. These hybrid cluster-protein films could be potentially used as biomedical coatings in the future because of their good transparency and excellent mechanical properties.

Morphology control and surface functionalization of protein-SiO2 hybrid capsules

In this contribution, we describe ways to introduce additional complexity and functionality to protein mediated capsule formation based on biomineralization in Pickering templated systems in order to enable possible post-mineralization modifications. Here the shell morphology is influenced by addition of ionic additives to the reaction system which significantly alters the surface structure. By changing the oil-phase (tetraethyl orthosilicate), even more complexity is introduced as well as reactive groups by adding (3-aminopropyl)trimethoxysilane to the oil phase. The incorporated amino-functionality is easily addressed via mild peptide coupling reaction.

MOF-polymer composite microcapsules derived from Pickering emulsions

Hollow composite microcapsules are prepared by the assembly of pre-formed nanocrystals of metal-organic frameworks (MOFs) around emulsion droplets, followed by interfacial polymerisation of the interior. The micropores of the MOF crystals embedded within a semipermeable hierarchically structured polymeric membrane are an effective combination for the retention of encapsulated dye molecules. Release can be triggered however by acid dissolution of the MOF component.

New developments in polymer-controlled, bioinspired calcium phosphate mineralization from aqueous solution

The polymer-controlled and bioinspired precipitation of inorganic minerals from aqueous solution at near-ambient or physiological conditions avoiding high temperatures or organic solvents is a key research area in materials science. Polymer-controlled mineralization has been studied as a model for biomineralization and for the synthesis of (bioinspired and biocompatible) hybrid materials for a virtually unlimited number of applications. Calcium phosphate mineralization is of particular interest for bone and dental repair. Numerous studies have therefore addressed the mineralization of calcium phosphate using a wide variety of low- and high-molecular-weight additives. In spite of the growing interest and increasing number of experimental and theoretical data, the mechanisms of polymer-controlled calcium phosphate mineralization are not entirely clear to date, although the field has made significant progress in the last years. A set of elegant experiments and calculations has shed light on some details of mineral formation, but it is currently not possible to preprogram a mineralization reaction to yield a desired product for a specific application. The current article therefore summarizes and discusses the influence of (macro)molecular entities such as polymers, peptides, proteins and gels on biomimetic calcium phosphate mineralization from aqueous solution. It focuses on strategies to tune the kinetics, morphologies, final dimensions and crystal phases of calcium phosphate, as well as on mechanistic considerations.

Self-assembly process of soft ferritin-PNIPAAm conjugate bionanoparticles at polar-apolar interfaces

We describe an in-depth investigation on the dynamics and assembly behavior at polar-apolar interfaces of ferritin-PNIPAAm conjugates (poly-N-isopropylacrylamide). The stabilization of oil-water interfaces by the modified ferritin was investigated by dynamic surface tension measurements and compared to the individual components of the bionanoparticle conjugate, namely, unmodified ferritin and pure PNIMAAm of similar molecular weight. It was found that the modified ferritin, even at a low particle concentration, rapidly reduces the interfacial tension. The difference in interfacial stabilization was also shown by cryo-scanning electron microscopy and scanning force microscopy, which displayed very different morphologies at the polar-apolar interface for the unmodified ferritin, pure PNIPAAm, and the ferritin-PNIPAAm conjugate, respectively. The self-assembly of the ferritin-PNIPAAm was further analyzed by cryo-transmission electron microscopy and fluorescence microscopy, for which a fluorescently labeled polymer was used. Both techniques revealed details on the assembly of the protein-polymer conjugate at the oil-water interface.