Mechanical properties of micro- and nanocapsules: Single-capsule measurements

Polyethylenimine Inclusion to Develop Aqueous Alginate-Based Core-Shell Capsules for Biomedical Applications

Aqueous core-shell structures can serve as an efficient approach that allows cells to generate 3D spheroids with in vivo-like cell-to-cell contacts. Here, a novel strategy for fabricating liquid-core-shell capsules is proposed by inverse gelation of alginate (ALG) and layer-by-layer (LbL) coating. We hypothesized that the unique properties of polyethylenimine (PEI) could be utilized to overcome the low structural stability and the limited cell recognition motifs of ALG. In the next step, alginate dialdehyde (ADA) enabled the Schiff-base reaction with free amine groups of PEI to reduce its possible toxic effects. Scanning electron microscopy and light microscopy images proved the formation of spherical hollow capsules with outer diameters of 3.0 ± 0.1 mm for ALG, 3.2 ± 0.1 mm for ALG/PEI, and 4.0 ± 0.2 mm for ALG/PEI/ADA capsules. The effective modulus increased by 3-fold and 5-fold when comparing ALG/PEI/ADA and ALG/PEI to ALG capsules, respectively. Moreover, PEI-coated capsules showed potential antibacterial properties against both Staphylococcus aureus and Escherichia coli, with an apparent inhibition zone. The cell viability results showed that all capsules were cytocompatible (above 75.5%). Cells could proliferate and form spheroids when encapsulated within the ALG/PEI/ADA capsules. Monitoring the spheroid thickness over 5 days of incubation indicated an increasing trend from 39.50 μm after 1 day to 66.86 μm after 5 days. The proposed encapsulation protocol represents a new in vitro platform for developing 3D cell cultivation and can be adapted to fulfill the requirements of various biomedical applications.

Pressure Changes Across a Membrane Formed by Coacervation of Oppositely Charged Polymer-Surfactant Systems

We investigate the mass transfer and membrane growth processes during capsule formation by the interaction of the biopolymer xanthan gum with CnTAB surfactants. When a drop of xanthan gum polymer solution is added to the surfactant solution, a membrane is formed by coacervation. It encapsulates the polymer drop in the surfactant solution. The underlying mechanisms and dynamic processes during capsule formation are not yet understood in detail. Therefore, we characterized the polymer-surfactant complex formation during coacervation by measuring the surface tension and surface elasticity at the solution-air interface for different surfactant chain lengths and concentrations. The adsorption behavior of the mixed polymer-surfactant system at the solution-air interface supports the understanding of observed trends during the capsule formation. We further measured the change in capsule pressure over time and simultaneously imaged the membrane growth via confocal microscopy. The cross-linking and shrinkage during the membrane formation by coacervation leads to an increasing tensile stress in the elastic membrane, resulting in a rapid pressure rise. Afterward, the pressure gradually decreases and the capsule shrinks as water diffuses out. This is not only due to the initial capsule overpressure but also due to osmosis caused by the higher ionic strength of the surfactant solution outside the capsule compared to the polymer solution inside the capsule. The influence of polymer concentration and surfactant type and concentration on the pressure changes and the membrane structure are studied in this work, providing detailed insights into the dynamic membrane formation process by coacervation. This knowledge can be used to produce capsules with tailored membrane properties and to develop a suitable encapsulation protocol in technological applications. The obtained insights into the mass transfer of water across the capsule membrane are important for future usage in separation techniques and the food industry and allow us to better predict the capsule time stability.

Microplastic label in microencapsulation field - Consequence of shell material selection

Plastics make our lives easier in many ways; however, if they are not appropriately disposed of or recycled, they may end up in the environment where they stay for centuries and degrade into smaller and smaller pieces, called microplastics. Each year, approximately 42000 tonnes of microplastics end up in the environment when products containing them are used. According to the European Chemicals Agency (ECHA) one of the significant sources of microplastics are microcapsules formulated in home care and consumer care products. As part of the EU's plastics strategy, ECHA has proposed new regulations to ban intentionally added microplastics starting from 2022. It means that the current cross-linked microcapsules widely applied in consumer goods must be transformed into biodegradable shell capsules. The aim of this review is to provide the readers with a comprehensive and in-depth understanding of recent developments in the art of microencapsulation. Thus, considering the chemical structure of the capsule shell's materials, we discuss whether microcapsules should also be categorized as microplastic and therefore, feared and avoided or whether they should be used despite the persisting concern.

Doxorubicin-loaded Niosomes functionalized with gelatine and alginate as pH-responsive drug delivery system: A 3D printing approach

Despite many efforts, breast cancer remains one of the deadliest cancers and its treatment faces challenges related to cancer drug side effects and metastasis. Combining 3D printing and nanocarriers has created new opportunities in cancer treatment. In this work, 3D-printed gelatin-alginate nanocomposites containing doxorubicin-loaded niosomes (Nio-DOX@GT-AL) were recruited as an advanced potential pH-sensitive drug delivery system. Morphology, degradation, drug release, flow cytometry, cell cytotoxicity, cell migration, caspase activity, and gene expression of nanocomposites and controls (Nio-DOX and Free-DOX) were evaluated. Results show that the obtained niosome has a spherical shape and size of 60-80 nm. Sustained drug release and biodegradability were presented by Nio-DOX@GT-AL and Nio-DOX. Cytotoxicity analysis revealed that the engineered Nio-DOX@GT-AL scaffold had 90 % cytotoxicity against breast cancer cells (MCF-7), whereas exhibited <5 % cytotoxicity against the non-tumor breast cell line (MCF-10A), which was significantly more than the antitumor effect of the control samples. Scratch-assay as an indicator cell migration demonstrated a reduction of almost 60 % of the covered surface. Gene expression could provide an explanation for the antitumor effect of engineered nanocarriers, which significantly reduced metastasis-promoting genes (Bcl2, MMP-2, and MMP-9), and significantly enhanced the expression and activity of genes that promote apoptosis (CASP-3, CASP-8, and CASP-9). Also, considerable inhibition of metastasis-associated genes (Bax and p53) was observed. Moreover, flow-cytometry data demonstrated that Nio-DOX@GT-AL decreased necrosis and enhanced apoptosis drastically. The findings of this research can confirm that employing 3D-printing and niosomal formulation can be an effective strategy in designing novel nanocarriers for efficient drug delivery applications.

Quantitative Elasticity Mapping of Submicron Silica Hollow Particles by PeakForce QNM AFM Mode

Silica hollow spheres with a diameter of 100-300 nm and a shell thickness of 8±2 nm were synthesized using a self-templating amphiphilic polymeric precursor, i.e., poly(ethylene glycol)-substituted hyperbranched polyethoxysiloxane. Their elastic properties were addressed with a high-frequency AFM indentation method based on the PeakForce QNM (quantitative nanomechanical mapping) mode enabling simultaneous visualization of the surface morphology and high-resolution mapping of the mechanical properties. The factors affecting the accuracy of the mechanical measurements such as a local slope of the particle surface, deformation of the silica hollow particles by a solid substrate, shell thickness variation, and applied force range were analysed. The Young's modulus of the shell material was evaluated as E=26±7 GPa independent of the applied force in the elastic regime of deformations. Beyond the elastic regime, the buckling instability was observed revealing a non-linear force-deformation response with a hysteresis between the loading and unloading force-distance curves and irreversible deformation of the shell at high applied forces. Thus, it was demonstrated that PeakForce QNM mode can be used for quantitative measurements of the elastic properties of submicon-sized silica hollow particles with nano-size shell thickness, as well as for estimation of the buckling behaviour beyond the elastic regime of shell deformations.

Nanocapsules of ZnO Nanorods and Geraniol as a Novel Mean for the Effective Control of Botrytis cinerea in Tomato and Cucumber Plants

Inorganic-based nanoparticle formulations of bioactive compounds are a promising nanoscale application that allow agrochemicals to be entrapped and/or encapsulated, enabling gradual and targeted delivery of their active ingredients. In this context, hydrophobic ZnO@OAm nanorods (NRs) were firstly synthesized and characterized via physicochemical techniques and then encapsulated within the biodegradable and biocompatible sodium dodecyl sulfate (SDS), either separately (ZnO NCs) or in combination with geraniol in the effective ratios of 1:1 (ZnOGer1 NCs), 1:2 (ZnOGer2 NCs), and 1:3 (ZnOGer2 NCs), respectively. The mean hydrodynamic size, polydispersity index (PDI), and ζ-potential of the nanocapsules were determined at different pH values. The efficiency of encapsulation (EE, %) and loading capacity (LC, %) of NCs were also determined. Pharmacokinetics of ZnOGer1 NCs and ZnOGer2 NCs showed a sustainable release profile of geraniol over 96 h and a higher stability at 25 ± 0.5 °C rather than at 35 ± 0.5 °C. ZnOGer1 NCs, ZnOGer2 NCs and ZnO NCs were evaluated in vitro against B. cinerea, and EC₅₀ values were calculated at 176 μg/mL, 150 μg/mL, and > 500 μg/mL, respectively. Subsequently, ZnOGer1 NCs and ZnOGer2 NCs were tested by foliar application on B. cinerea-inoculated tomato and cucumber plants, showing a significant reduction of disease severity. The foliar application of both NCs resulted in more effective inhibition of the pathogen in the infected cucumber plants as compared to the treatment with the chemical fungicide Luna Sensation SC. In contrast, tomato plants treated with ZnOGer2 NCs demonstrated a better inhibition of the disease as compared to the treatment with ZnOGer1 NCs and Luna. None of the treatments caused phytotoxic effects. These results support the potential for the use of the specific NCs as plant protection agents against B. cinerea in agriculture as an effective alternative to synthetic fungicides.

Targeted Therapy for Glomerulonephritis Using Arterial Delivery of Encapsulated Etanercept

Complex immunosuppressive therapy is prescribed in medical practice to patients with glomerulonephritis to help them overcome symptoms and prevent chronic renal failure. Such an approach requires long-term systemic administration of strong medications, which causes severe side effects. This work shows the efficiency of polymer capsule accumulation (2.8 ± 0.4 µm) containing labeled etanercept (100 μg per dose) in the kidneys of mice. The comparison of injection into the renal artery and tail vein shows the significant superiority of the intra-arterial administration strategy. The etanercept retention rate of 18% and 8% ID in kidneys was found 1 min and 1 h after injection, respectively. The capsules were predominantly localized in the glomeruli after injection in mice using a model of acute glomerulonephritis. Histological analysis confirmed a significant therapeutic effect only in animals with intra-arterial administration of microcapsules with etanercept. The proposed strategy combines endovascular surgery and the use of polymer microcapsules containing a high molecular weight drug that can be successfully applied to treat a wide range of kidney diseases associated with glomerular pathology.

Pressure-deformation relations of elasto-capillary drops (droploons) on capillaries

An increasing number of multi-phase systems exploit complex interfaces in which capillary stresses are coupled with solid-like elastic stresses. Despite growing efforts, simple and reliable experimental characterisation of these interfaces remains a challenge, especially of their dilational properties. Pendant drop techniques are convenient, but suffer from complex shape changes and associated fitting procedures with multiple parameters. Here we show that simple analytical relationships can be derived to describe reliably the pressure-deformation relations of nearly spherical elasto-capillary droplets ("droploons") attached to a capillary. We consider a model interface in which stresses arising from a constant interfacial tension are superimposed with mechanical extra-stresses arising from the deformation of a solid-like, incompressible interfacial layer of finite thickness described by a neo-Hookean material law. We compare some standard models of liquid-like (Gibbs) and solid-like (Hookean and neo-Hookean elasticity) elastic interfaces which may be used to describe the pressure-deformation relations when the presence of the capillary can be considered negligible. Combining Surface Evolver simulations and direct numerical integration of the drop shape equations, we analyse in depth the influence of the anisotropic deformation imposed by the capillary on the pressure-deformation relation and show that in many experimentally relevant circumstances either the analytical relations of the perfect sphere may be used or a slightly modified relation which takes into account the geometrical change imposed by the capillary. Using the analogy with the stress concentration around a rigid inclusion in an elastic membrane, we provide simple non-dimensional criteria to predict under which conditions the simple analytical expressions can be used to fit pressure-deformation relations to analyse the elastic properties of the interfaces via "Capillary Pressure Elastometry". We show that these criteria depend essentially on the drop geometry and deformation, but not on the interfacial elasticity. Moreover, this benchmark case shows for the first time that Surface Evolver is a reliable tool for predictive simulations of elastocapillary interfaces. This opens doors to the treatment of more complex geometries/conditions, where theory is not available for comparison. Our Surface Evolver code is available for download in the ESI.

Tailoring the mechanoresponsive release from silica nanocapsules

Triggering the release of encapsulated cargos using mechanical stress acting on a nanocarrier is a strategy with potential applications from drug delivery to self-healing coatings. The mechanically triggered release of encapsulated molecules can be controlled by tuning the mechanical properties of the nanocapsules, which are strongly linked to the nanocapsule architecture. Here, silica nanocarriers were designed to tune precisely the release initiated by mechanical stress. We synthesized silica nanocapsules (SiNCs) with a finely tunable diameter and shell thickness and performed AFM nanoindentation experiments to determine the breaking force of single SiNCs. We demonstrated that it is possible to trigger the release of encapsulated payload by the application of an external mechanical force on the SiNCs. Furthermore, we successfully controlled the breaking force and the amount of released payload by tailoring the architecture of the nanocarriers, illustrating how such mechanoresponsive SiNCs could be used as responsive nanocarriers for the delivery of molecular cargos.

Optical coherence microangiography of the mouse kidney for diagnosis of circulatory disorders

Optical coherence tomography (OCT) has become widespread in clinical applications in which precise three-dimensional functional imaging of living organs is required. Nevertheless, the kidney is inaccessible for the high resolution OCT imaging due to a high light attenuation coefficient of skin and soft tissues that significantly limits the penetration depth of the probing laser beam. Here, we introduce a surgical protocol and fixation scheme that enables functional visualization of kidney's peritubular capillaries via OCT microangiography. The model of reversible/irreversible glomerulus embolization using drug microcarriers confirms the ability of OCT to detect circulatory disorders. This approach can be used for choosing optimal carriers, their dosages and diagnosis of other blood flow pathologies.

Nanoencapsulation of Essential Oils as Natural Food Antimicrobial Agents: An Overview

The global demand for safe and healthy food with minimal synthetic preservatives is continuously increasing. Natural food antimicrobials and especially essential oils (EOs) possess strong antimicrobial activities that could play a remarkable role as a novel source of food preservatives. Despite the excellent efficacy of EOs, they have not been widely used in the food industry due to some major intrinsic barriers, such as low water solubility, bioavailability, volatility, and stability in food systems. Recent advances in nanotechnology have the potential to address these existing barriers in order to use EOs as preservatives in food systems at low doses. Thus, in this review, we explored the latest advances of using natural actives as antimicrobial agents and the different strategies for nanoencapsulation used for this purpose. The state of the art concerning the antibacterial properties of EOs will be summarized, and the main latest applications of nanoencapsulated antimicrobial agents in food systems will be presented. This review should help researchers to better choose the most suitable encapsulation techniques and materials.

Stabilization and X-ray Attenuation of PEGylated Cholesterol/Polycaprolactone-Based Perfluorooctyl Bromide Nanocapsules for CT Imaging

Contrast-enhanced X-ray computed tomography plays an important role in cancer imaging and disease progression monitoring. Imaging using radiopaque nanoparticle platforms can provide insights on the likelihood of nanoparticle accumulation and can enable image-guided therapies. Perfluorooctyl bromide (PFOB)-loaded nanocapsules designed for this purpose were stabilized using an in-house synthesized PEGylated polycaprolactone-based copolymer (PEG-b-PCL(Ch)) and compared with commercial polycaprolactone employing a Quality-by-Design approach. PFOB is a dense liquid, weakly polarizable, and immiscible in organic and aqueous solvents; thus, carefully designed formulations for optimal colloidal stabilization to overcome settling-associated instability are required. PFOB-loaded nanocapsules exhibited high PFOB loading due to the intrinsic properties of PEG-b-PCL(Ch). Settling and caking are major sources of instability for PFOB formulations. However, the PEG-b-PCL(Ch) copolymer conferred the nanocapsules enough steric impediment and polymer shell elasticity to settle without significant caking, increasing the overall colloidal stability of the formulation. Furthermore, a clear relationship between nanocapsule physical properties and X-ray attenuation was established. Nanocapsules were able to enhance the X-ray contrast in vitro as a function of PFOB loading. This nanocapsule-based platform is promising for future translational studies and image-guided tumor therapy due to its enhanced contrastability and optimal colloidal stability.

Buckling transitions and soft-phase invasion of two-component icosahedral shells

What is the optimal distribution of two types of crystalline phases on the surface of icosahedral shells, such as of many viral capsids? We here investigate the distribution of a thin layer of soft material on a crystalline convex icosahedral shell. We demonstrate how the shapes of spherical viruses can be understood from the perspective of elasticity theory of thin two-component shells. We develop a theory of shape transformations of an icosahedral shell upon addition of a softer, but still crystalline, material onto its surface. We show how the soft component "invades" the regions with the highest elastic energy and stress imposed by the 12 topological defects on the surface. We explore the phase diagram as a function of the surface fraction of the soft material, the shell size, and the incommensurability of the elastic moduli of the rigid and soft phases. We find that, as expected, progressive filling of the rigid shell by the soft phase starts from the most deformed regions of the icosahedron. With a progressively increasing soft-phase coverage, the spherical segments of domes are filled first (12 vertices of the shell), then the cylindrical segments connecting the domes (30 edges) are invaded, and, ultimately, the 20 flat faces of the icosahedral shell tend to be occupied by the soft material. We present a detailed theoretical investigation of the first two stages of this invasion process and develop a model of morphological changes of the cone structure that permits noncircular cross sections. In conclusion, we discuss the biological relevance of some structures predicted from our calculations, in particular for the shape of viral capsids.

Target delivery of drug carriers in mice kidney glomeruli via renal artery. Balance between efficiency and safety

Targeting drug delivery systems is crucial to reducing the side effects of therapy. However, many of them are lacking effectiveness for kidney targeting, due to systemic dispersion and accumulation in the lungs and liver after intravenous administration. Renal artery administration of carriers provides their effective local accumulation but may cause irreversible vessel blockage. Therefore, the combination of the correct administration procedure, suitable drug delivery system, selection of effective and safe dosage is the key to sparing local therapy. Here, we propose the 3-μm sized fluorescent capsules based on poly-L-arginine and dextran sulfate for targeting the kidney via a mice renal artery. Hemodynamic study of the target kidney in combination with the histological analysis reveals a safe dose of microcapsules (20 × 10⁶), which has not lead to irreversible pathological changes in blood flow and kidney tissue, and provides retention of 20.5 ± 3% of the introduced capsules in the renal cortex glomeruli. Efficacy of fluorescent dye localization in the target kidney after intra-arterial administration is 9 times higher than in the opposite kidney and after intravenous injection. After 24 h microcapsules are not observed in the target kidney when the safe dose of carriers is being used but a high level of fluorescent signal persists for 48 h indicating that fluorescent cargo accumulation in tissues. Injection of non-safe microcapsule dose leads to carriers staying in glomeruli for at least 48 h which has consequences of blood flow not being restored and tissue damage being observed in histology.

Influence of microcapsule parameters and initiator concentration on the self-healing capacity of resin-based dental composites

OBJECTIVE

Fracture is one of the main causes for failure of resin-based composite restorations. To overcome this drawback, self-healing resin-based composites have been designed by incorporation of microcapsules. However, the relationship between their self-healing capacity and microcapsule and resin parameters is still poorly understood. Therefore, the objective of this study was to systematically investigate the effect of initiator concentration (in the resin) and microcapsule size and concentration on the self-healing performance of commercially available flowable resin-based composites.

METHODS

Poly(urea-formaldehyde) (PUF) microcapsules containing acrylic healing liquid were synthesized in small (33±8μm), medium (68±21μm) and large sizes (198±43μm) and characterized. Subsequently, these microcapsules were incorporated into a conventional flowable resin-based composite (Majesty Flow ES2, Kuraray) at different contents (5-15wt%) and benzoyl peroxide (BPO) initiator concentrations (0.5-2.0wt%). Fracture toughness (K_IC) of test specimens was tested using a single edge V-notched beam method. Immediately after complete fracture (K_IC-initial), the two fractured parts were held together for 72h to allow for healing. Subsequently, fracture toughness of the healed resin-based composites (K_IC-healed) was tested as well.

RESULTS

The fracture toughness of healed dental composites significantly increased with increasing microcapsule size and concentration (2wt% BPO, p<0.05). The highest self-healing efficiencies (up to 76%) were obtained with microcapsules sized 198±43 um.

SIGNIFICANCE

commercially available resin-based composites can be rendered self-healing most efficiently by incorporation of large microcapsules (198±43μm). However, long-term tests on fatigue and wear behavior are needed to confirm the clinical efficacy.

Nanoparticles in Polyelectrolyte Multilayer Layer-by-Layer (LbL) Films and Capsules—Key Enabling Components of Hybrid Coatings

Originally regarded as auxiliary additives, nanoparticles have become important constituents of polyelectrolyte multilayers. They represent the key components to enhance mechanical properties, enable activation by laser light or ultrasound, construct anisotropic and multicompartment structures, and facilitate the development of novel sensors and movable particles. Here, we discuss an increasingly important role of inorganic nanoparticles in the layer-by-layer assembly—effectively leading to the construction of the so-called hybrid coatings. The principles of assembly are discussed together with the properties of nanoparticles and layer-by-layer polymeric assembly essential in building hybrid coatings. Applications and emerging trends in development of such novel materials are also identified.

Mechano-activated biomolecule release in regenerating load-bearing tissue microenvironments

Although mechanical loads are integral for musculoskeletal tissue homeostasis, overloading and traumatic events can result in tissue injury. Conventional drug delivery approaches for musculoskeletal tissue repair employ localized drug injections. However, rapid drug clearance and inadequate synchronization of molecule provision with healing progression render these methods ineffective. To overcome this, a programmable mechanoresponsive drug delivery system was developed that utilizes the mechanical environment of the tissue during rehabilitation (for example, during cartilage repair) to trigger biomolecule provision. For this, a suite of mechanically-activated microcapsules (MAMCs) with different rupture profiles was generated in a single fabrication batch via osmotic annealing of double emulsions. MAMC physical dimensions were found to dictate mechano-activation in 2D and 3D environments and their stability in vitro and in vivo, demonstrating the tunability of this system. In models of cartilage regeneration, MAMCs did not interfere with tissue growth and activated depending on the mechanical properties of the regenerating tissue. Finally, biologically active anti-inflammatory agents were encapsulated and released from MAMCs, which counteracted degradative cues and prevented the loss of matrix in living tissue environments. This unique technology has tremendous potential for implementation across a wide array of musculoskeletal conditions for enhanced repair of load-bearing tissues.

In situ nanomechanical properties of natural oil bodies studied using atomic force microscopy

Natural oil bodies (OBs) from plant organs represent an important category of functional ingredients and materials in a variety of industrial sectors. Their applications are closely related to the membrane mechanical properties on a single droplet level, which remain difficult to determine. In this research, the mechanical properties of the membranes of OBs from soybean, sesame, and peanut were investigated in-situ by atomic force microscopy (AFM). Different regions of the force-deformation curves obtained during compression were analyzed to extract the stiffness Kb or Young's modulus of the OB membranes using Hooke's law, Reissner theory, and the elastic membrane theory. At higher strains (ε = 0.15-0.20), the elastic membrane theory breaks down. We propose an extension of the theory that includes a contribution to the force from interfacial tension based on the Gibbs energy, allowing effective determination of Young's modulus and interfacial tension of the OB membranes in the water environment simultaneously. The mechanical properties of the OBs of different sizes and species, as well as a comparison with other phospholipid membrane materials, are discussed and related to their membrane compositions and structures. It was found that the natural OBs are soft droplets but do not rupture and can fully recover following compressive strains as large as 0.3. The OBs with higher protein/oil ratio, have smaller size and stronger mechanical properties, and thus are more stable. The low interfacial tension due to the existence of phospholipid-protein membrane also contributes to the stability of the OBs. This is the first report measuring the mechanical properties of OB membranes in-situ directly.

Deterministic paracrine repair of injured myocardium using microfluidic-based cocooning of heart explant-derived cells

While encapsulation of cells within protective nanoporous gel cocoons increases cell retention and pro-survival integrin signaling, the influence of cocoon size and intra-capsular cell-cell interactions on therapeutic repair are unknown. Here, we employ a microfluidic platform to dissect the impact of cocoon size and intracapsular cell number on the regenerative potential of transplanted heart explant-derived cells. Deterministic increases in cocoon size boosted the proportion of multicellular aggregates within cocoons, reduced vascular clearance of transplanted cells and enhanced stimulation of endogenous repair. The latter being attributable to cell-cell stimulation of cytokine and extracellular vesicle production while also broadening of the miRNA cargo within extracellular vesicles. Thus, by tuning cocoon size and cell occupancy, the paracrine signature and retention of transplanted cells can be enhanced to promote paracrine stimulation of endogenous tissue repair.

Shape Tuning and Size Prediction of Millimeter-Scale Calcium-Alginate Capsules with Aqueous Core

Controllable feature and size, good mechanical stability and intelligent release behavior is the capsule products relentless pursuit of the goal. In addition, to illustrate the quantitative relationship of structure and performance is also important for encapsulation technology development. In this study, the sphericity and size of millimeter-scale calcium sodium alginate capsules (mm-CaSA-Caps) with aqueous core were well tuned by manipulating the viscosity, surface tension, and density of CaCl₂/carboxyl methyl cellulose (CMC) drops and sodium alginate (SA) solution. The well-tuned mm-CaSA-Caps showed significant mechanical and control-releasing property effects. The results showed that the prepared mm-CaSA-Caps were highly monodispersed with average diameter from 3.8 to 4.8 mm. The viscosity of the SA solution and the viscosity and surface tension of the CaCl₂/CMC solution had significant effects on the mm-CaSA-Caps sphericity. Uniform and spherical mm-CaSA-Caps could be formed with high viscosity CaCl₂/CMC solution (between 168.5 and 917.5 mPa·s), low viscosity SA solution (between 16.2 and 72.0 mPa·s) and decreased surface tension SA solution (by adding 0.01 wt.% poloxamer 407). The diameter of the mm-CaSA-Caps could be predicted by a modified Tate’s law, which correlated well with the experimental data. The Caps with sphericity factor (SF) < 0.07 had better mechanical stability, with the crushing force 2.91–15.5 times and the surface Young’s modulus 2.1–3.99 times higher than those of the non-spherical Caps (SF > 0.07). Meanwhile, the spherical Caps had a more even permeation rate, which was helpful in producing uniform and sustained releasing applications in foodstuff, medicine, agriculture and chemical industry.

Effect of Systemic Polyelectrolyte Microcapsule Administration on the Blood Flow Dynamics of Vital Organs

Polyelectrolyte microcapsules and other targeted drug delivery systems could substantially reduce the side effects of drug and overall toxicity. At the same time, the cardiovascular system is a unique transport avenue that can deliver drug carriers to any tissue and organ. However, one of the most important potential problems of drug carrier systemic administration in clinical practice is that the carriers might cause circulatory disorders, the development of pulmonary embolism, ischemia, and tissue necrosis due to the blockage of small capillaries. Thus, the presented work aims to find out the processes occurring in the bloodstream after the systemic injection of polyelectrolyte capsules that are 5 μm in size. It was shown that 1 min after injection, the number of circulating capsules decreases several times, and after 15 min less than 1% of the injected dose is registered in the blood. By this time, most capsules accumulate in the lungs, liver, and kidneys. However, magnetic field action could slightly increase the accumulation of capsules in the region-of-interest. For the first time, we have investigated the real-time blood flow changes in vital organs in vivo after intravenous injection of microcapsules using a laser speckle contrast imaging system. We have demonstrated that the organism can adapt to the emergence of drug carriers in the blood and their accumulation in the vessels of vital organs. Additionally, we have evaluated the safety of the intravenous administration of various doses of microcapsules.

Thickness of Polyelectrolyte Layers of Separately Confined Bacteria Alters Key Physiological Parameters on a Single Cell Level

Confinement of bacterial cells in a matrix or in capsules is an integral part of many biotechnological applications. Here, the well-known layer-by-layer method of deposition of a polyelectrolyte film a few nanometers in thickness to confine separated bacterial cells in permeable and physically durable shells has been examined. Due to the physical properties of such a confinement, we found that this method enables investigation of effects of physical barriers against mass gain and cell division. Using the method of time-lapse confocal microscopy, we observed a prolonged lag phase, dependent on the number of polyelectrolyte layers. In the confinement, both the GFP fluorescent signal from the leaking T7 promoter and the cell size were increased by factors of more than five and two, respectively. This creates a paradigm shift that enables use of mechanical entrapment for control of bacterial cell physiology and opens possibilities of controlling the division rate as well as gene expression. These effects can be attributed to the perturbation of the sensing of the cell size, which results in disproportional synthesis of a cell envelope impinging the intracellular material and compels cells to grow rapidly. In addition, the charged surface of cells enables prolonged intercellular physical interaction and results in spherically shaped microcolonies.

Soft Bacterial Cellulose Microcapsules with Adaptable Shapes

Microcapsules with controlled stability and permeability are in high demand for applications in separation and encapsulation. We have developed a biointerfacial process to fabricate strong, but flexible, porous microcapsules from bacterial cellulose at an oil-water emulsion interface. A broad range of microcapsule sizes has been successfully produced, from 100 μm to 5 cm in diameter. The three-dimensional capsule microstructure was imaged using confocal microscopy, showing a cellulose membrane thickness of around 30 μm that is highly porous, with some pores larger than 0.5 μm that are permeable to most macromolecules by free diffusion but can exclude larger structures like bacteria. The mechanical deformation of cellulose microcapsules reveals their flexibility, enabling them to pass through constrictions with a much smaller diameter than their initial size by bending and folding. Our work provides a new approach for producing soft, permeable, and biocompatible microcapsules for substance encapsulation and protection. The capsules may offer a replacement for suspended polymer beads in commercial applications and could potentially act as a framework for artificial cells.

Chemically modifying the mechanical properties of core-shell liquid metal nanoparticles

Eutectic gallium-indium (EGaIn) is a room temperature liquid metal that can be readily fabricated into nanoparticles which naturally form a thin, passivating gallium oxide shell. These core-shell nanoparticles are of interest for a variety of stimuli-responsive applications, which often utilize physical deformation of the particles to release the molten, conductive payload from within the gallium oxide shell. In the present work, we introduce a variety of chemical strategies to produce EGaIn nanoparticles which exhibit a wide range of gallium oxide shell thicknesses. These chemically modified oxide thicknesses are then correlated to the core-shell liquid nanoparticles' mechanical properties by subjecting the particles to orthogonal characterization techniques; XPS for measurement of the gallium oxide shell thickness and nanoindentation for measurement of particle stiffness and elastic modulus. Additionally, nanoindentation is used to determine the onset of particle rupture and resultant conductivity. Ultimately, quantification of the relationships between chemical treatment and derivative mechanical properties in liquid metal nanoparticles will enable advanced applications of these colloids, such as in tailored self-healing and responsive electronic devices.

Shape Recovery of Spherical Hydrogen-Bonded Multilayer Capsules after Osmotically Induced Deformation

The mechanical properties of microparticles intended for in vivo applications as drug delivery vehicles are among important parameters that influence their circulation in the blood and govern particle biodistribution. We report on the synthesis of soft but mechanically robust spherical capsules via a hydrogen-bonded multilayer assembly of (poly(N-vinylpyrrolidone), M_w = 10 000 g mol^-1) with (poly(methacrylic acid) M_w = 100 000 g mol^-1)) (PVPON/PMAA)_n in methanol using 4 μm nonporous silica microparticles as sacrificial templates, where n = 5 and 10 and represents the bilayer number. The mechanical properties of (PVPON/PMAA)_n spherical capsules were assessed using the osmotic pressure difference method and resulted in an elasticity modulus of 97 ± 8 MPa, which is in the range of Young's modulus for elastomeric networks. We also found that hydrogen-bonded (PVPON/PMAA)₁₀ capsules demonstrated almost complete recovery from a concave buckled inward shape induced by the osmotic pressure difference from the addition of polystyrene sulfonate (PSS) to the capsule solution to their initial spherical shape within 12 h after the PSS solution was rinsed off. The permeability measurements through the capsule shell using fluorescently labeled dextran molecular probes revealed that the average mesh size of the hydrogen-bonded network assembled in methanol is in the range of 3 to 9 nm and is not permeable to FITC-dextran with a molecular weight of >40 000 g mol^-1. Our study shows that physically cross-linked polyelectrolyte multilayer capsules are capable of withstanding large deformations, which is essential to the development of adaptable particles for controlled delivery.

Mechanical Properties of Particle Films on Curved Interfaces Probed through Electric Field-Induced Wrinkling of Particle Shells

Similar to the human skin, a monolayer of packed particles capillary bound to a liquid interface wrinkles when subjected to compressive stress. The induced wrinkles absorb the applied stress and do not disappear unless the stress is removed. Experimental and theoretical investigations of wrinkle formation typically concern flat particle monolayers subjected to uniaxial stress. In this work, we extend the results on wrinkling of particle-covered interfaces to the investigation of mechanical properties of particle films on a curved interface, that is, we study particle shells formed on droplets and subjected to hoop stress. Opposed to flat particle layers where liquid buoyancy alone acts as the effective stiffness, the mechanical properties of particle layers on small droplets are also affected by the surface curvature. We show here that this leads to formation of wrinkles with different characteristic wavelengths compared to those found at flat interfaces. Our experimental results also reveal that the wrinkle wavelength of particle shells is proportional to the square root of particle size and the size of the droplets on which the shells are formed. Wrinkling of particle layers composed of microparticles with diameters ranging from around 1-100 μm was induced using a novel approach combining electrodeformation and electrohydrodynamic flows. We demonstrate that our contactless approach for studying the mechanical properties of particle shells enables estimation of elasticity, particle film thickness, and bending stiffness of particle shells. The proposed approach is insensitive to both particle coverage and electric field strength. In addition, it enables manipulation of particle packing that is intimately linked with formation of wrinkling patterns. With a wide range of applications depending on accurate mechanical properties (e.g., drug-delivery capsules to self-healing materials), this work provides a valuable method to characterize the mechanical properties of shells and tailor their surface properties (i.e., permeability and roughness).

Mechanically-Activated Microcapsules for 'On-Demand' Drug Delivery in Dynamically Loaded Musculoskeletal Tissues

Delivery of biofactors in a precise and controlled fashion remains a clinical challenge. Stimuli-responsive delivery systems can facilitate 'on-demand' release of therapeutics in response to a variety of physiologic triggering mechanisms (e.g. pH, temperature). However, few systems to date have taken advantage of mechanical inputs from the microenvironment to initiate drug release. Here, we developed mechanically-activated microcapsules (MAMCs) that are designed to deliver therapeutics in an on-demand fashion in response to the mechanically loaded environment of regenerating musculoskeletal tissues, with the ultimate goal of furthering tissue repair. To establish a suite of microcapsules with different thresholds for mechano-activation, we first manipulated MAMC physical dimensions and composition, and evaluated their mechano-response under both direct 2D compression and in 3D matrices mimicking the extracellular matrix properties and dynamic loading environment of regenerating tissue. To demonstrate the feasibility of this delivery system, we used an engineered cartilage model to test the efficacy of mechanically-instigated release of TGF-β3 on the chondrogenesis of mesenchymal stem cells. These data establish a novel platform by which to tune the release of therapeutics and/or regenerative factors based on the physiologic dynamic mechanical loading environment, and will find widespread application in the repair and regeneration of numerous musculoskeletal tissues.

Mechano-responsive microcapsules with uniform thin shells

Capsules often prolong the shelf-life of active ingredients, such as many types of drugs, food additives, or cosmetic substances, because they delay oxidation of these substances or prevent their reactions with molecules contained in the surrounding. If capsules are appropriately designed, they can offer an additional benefit: they allow close control over the timing and location of the release of active ingredients. To take advantage of these features, capsules must possess shells whose thickness and composition are well-defined. However, the shell thickness of capsules often varies considerably even within a single capsule, thereby hampering good control over the release kinetics of encapsulants. These variations can be reduced, and hence the degree of control over the release kinetics increased, if shells are made thin. Unfortunately, the controlled fabrication of mechanically stable microcapsules with well-defined sub-μm thick shells is difficult. Here, we introduce a method to fabricate capsules with uniform semi-permeable shells with a thickness as low as 400 nm. This is achieved using water-oil-water double emulsions with 800 nm thick shells as templates to fabricate capsules with uniform 400 nm thin shells. These shells occupy less than 2% of the capsule volume, thereby minimizing their footprint. Despite their thin shells, these capsules are mechanically robust: they withstand pressures up to 1.3 MPa without deformation and remain intact if exposed to pressures up to 2.75 MPa. Moreover, while they are permeable towards water, they retain low molecular weight encapsulants even if dried and re-dispersed. The thin shells of the capsules open up new possibilities of their use to functionalize materials with at least one dimension that is small, such as coatings, where thick shells introduce defects, or as building blocks of new types of functional materials.

Shallow shell theory of the buckling energy barrier: From the Pogorelov state to softening and imperfection sensitivity close to the buckling pressure

We study the axisymmetric response of a complete spherical shell under homogeneous compressive pressure p to an additional point force. For a pressure p below the classical critical buckling pressure p_{c}, indentation by a point force does not lead to spontaneous buckling but an energy barrier has to be overcome. The states at the maximum of the energy barrier represent a subcritical branch of unstable stationary points, which are the transition states to a snap-through buckled state. Starting from nonlinear shallow shell theory, we obtain a closed analytical expression for the energy barrier height, which facilitates its effective numerical evaluation as a function of pressure by continuation techniques. We find a clear crossover between two regimes: For p/p_{c}≪1 the postbuckling barrier state is a mirror-inverted Pogorelov dimple, and for (1-p/p_{c})≪1 the barrier state is a shallow dimple with indentations smaller than shell thickness and exhibits extended oscillations, which are well described by linear response. We find systematic expansions of the nonlinear shallow shell equations about the Pogorelov mirror-inverted dimple for p/p_{c}≪1 and the linear response state for (1-p/p_{c})≪1, which enable us to derive asymptotic analytical results for the energy barrier landscape in both regimes. Upon approaching the buckling bifurcation at p_{c} from below, we find a softening of an ideal spherical shell. The stiffness for the linear response to point forces vanishes ∝(1-p/p_{c})^{1/2}; the buckling energy barrier vanishes ∝(1-p/p_{c})^{3/2}; and the shell indentation in the barrier state vanishes ∝(1-p/p_{c})^{1/2}. This makes shells sensitive to imperfections which can strongly reduce p_{c} in an avoided buckling bifurcation. We find the same softening scaling in the vicinity of the reduced critical buckling pressure also in the presence of imperfections. We can also show that the effect of axisymmetric imperfections on the buckling instability is identical to the effect of a point force that is preindenting the shell. In the Pogorelov limit, the energy barrier maximum diverges ∝(p/p_{c})^{-3} and the corresponding indentation diverges ∝(p/p_{c})^{-2}. Numerical prefactors for proportionalities both in the softening and the Pogorelov regime are calculated analytically. This also enables us to obtain results for the critical unbuckling pressure and the Maxwell pressure.

Triple-Stimuli-Responsive Smart Nanocontainers Enhanced Self-Healing Anticorrosion Coatings for Protection of Aluminum Alloy

Novel acid/alkali/corrosion potential triple-stimuli-responsive smart nanocontainers (TSR-SNs) were successfully assembled to regulate the release of an encapsulated corrosion inhibitor, benzotriazole (BTA), by installing specially structured bistable pseudorotaxanes as supramolecular nanovalves onto orifices of mesoporous silica nanoparticles. In normal conditions, BTA molecules were sealed in the mesopores. Upon any stimulus of acid, alkali, or corrosion potential, BTA molecules were quickly released because of the open states of the supramolecular nanovalves. TSR-SNs as smart nanocontainers were added into the SiO₂-ZrO₂ sol-gel coating to fabricate a stimuli-feedback, corrosion-compensating self-healing anticorrosion coating (SF-SHAC). Compared with the conventional pH-responsive smart nanocontainers synthesized for the SHAC, TSR-SNs not only respond to the pH changes occurring on corrosive microregions but also, and more importantly, feel the corrosion potential of aluminum alloys and give quick feedback. This design avoids wasting smart nanocontainers because of the local-dependent, gradient pH stimulus intensities and obviously enhances the response sensitivity of the SF-SHAC. Electrochemical impedance spectroscopy and salt spray tests prove the excellent physical barrier of the SF-SHAC. Through scanning vibrating electrode technique measurements, the SF-SHAC doped with TSR-SNs demonstrates inhibiting rates for corrosive microcathodic/anodic current densities that are faster than other control SHACs. The new incorporated corrosion potential-responsive function ensures the efficient working efficiency of TSR-SNs and makes full use of the preloaded corrosion inhibitors as repair factors.

Strong Deformation of Ferrofluid-Filled Elastic Alginate Capsules in Inhomogenous Magnetic Fields

We present a new system based on alginate gels for the encapsulation of a ferrofluid drop, which allows us to create millimeter-sized elastic capsules that are highly deformable by inhomogeneous magnetic fields. We use a combination of experimental and theoretical work in order to characterize and quantify the deformation behavior of these ferrofluid-filled capsules. We introduce a novel method for the direct encapsulation of unpolar liquids by sodium alginate. By adding 1-hexanol to the unpolar liquid, we can dissolve sufficient amounts of CaCl₂ in the resulting mixture for ionotropic gelation of sodium alginate. The addition of polar alcohol molecules allows us to encapsulate a ferrofluid as a single phase rather than an emulsion without impairing ferrofluid stability. This encapsulation method increases the amount of encapsulated magnetic nanoparticles resulting in high deformations of approximately 30% (in height-to-width ratio) in inhomogeneous magnetic field with magnetic field variations of 50 mT over the size of the capsule. This offers possible applications of capsules as actuators, switches, or valves in confined spaces like microfluidic devices. We determine both elastic moduli of the capsule shell, Young's modulus and Poisson's ratio, by employing two independent mechanical methods, spinning capsule measurements and capsule compression between parallel plates. We then show that the observed magnetic deformation can be fully understood from magnetic forces exerted by the ferrofluid on the capsule shell if the magnetic field distribution and magnetization properties of the ferrofluid are known. We perform a detailed analysis of the magnetic deformation by employing a theoretical model based on nonlinear elasticity theory. Using an iterative solution scheme that couples a finite element/boundary element method for the magnetic field calculation to the solution of the elastic shape equations, we achieve quantitative agreement between theory and experiment for deformed capsule shapes using the Young modulus from mechanical characterization and the surface Poisson ratio as a fit parameter. This detailed analysis confirms the results from mechanical characterization that the surface Poisson ratio of the alginate shell is close to unity, that is, deformations of the alginate shell are almost area conserving.

Capsule-like Safe Genetic Vectors-Cell-Penetrating Core-Shell Particles Selectively Release Functional Small RNA and Entrap Its Encoding DNA

The breakthrough of genetic therapy is set back by the lack of suitable genetic vector systems. We present the development of permeability-tunable, capsule-like, polymeric, micron-sized, core-shell particles for delivery of recombinant nucleic acids into target cells. These particles were demonstrated to effectively release rod-shaped small hairpin RNA and to selectively retain the RNA-encoding DNA template, which was designed to form a bulky tripartite structure. Thus, they can serve as delivery vectors preloaded with cargo RNA or alternatively as RNA-producing micro-bioreactors. The internalization of particles by human tissue culture cells inversely correlated with particle size and with the cell to particle ratio, although at a higher than stoichiometric excess of particles over cells, cell viability was impaired. Among primary human peripheral blood mononuclear cells, up to 50% of the monocytes displayed positive uptake of particles. Finally, these particles efficiently delivered siRNA into HEK293T cells triggering functional knockdown of the target gene lamin A/C. Particle-mediated knockdown was superior to that observed after conventional siRNA delivery via lipofection. Core-shell particles protect encapsulated nucleic acids from degradation and target cell genomes from direct contact with recombinant DNA, thus representing a promising delivery vector system that can be explored for genetic therapy and vaccination.