Hollow Polycaprolactone Microspheres with/without a Single Surface Hole by Co-Electrospraying

Chitin nanocrystals-stabilized emulsion as template for fabricating injectable suspension containing polylactide hollow microspheres

One of the promising applications of rod-like chitin nanocrystals (ChNCs) is the use as particle emulsifier to develop Pickering emulsions. We reported a ChNC-stabilized oil-in-water emulsion system, and developed a Pickering emulsion-templated method to prepare polylactide (PLA) hollow microspheres here. The results showed that both non-modified ChNCs and acetylated ChNCs could well emulsify the dichloromethane (DCM) solution of PLA-in-aqueous mannitol solution systems, forming very stable emulsions. At the same oil-to-water ratios and ChNC loadings, the emulsion stability was improved with increasing acetylation levels of ChNCs, accompanied by reduced size of droplets. Through the solvent evaporation, the PLA hollow microspheres were templated successfully, and the surface structure was also strongly dependent on the acetylation level of ChNCs. At a low level of acetylation, the single-hole or multi-hole surface structure formed, which was attributed to the out-diffusion of DCM caused by the solvent extraction and evaporation. These surface defects decreased with increased acetylation levels of ChNCs. Moreover, the aqueous suspension with as-obtained PLA microspheres revealed shear-thinning property and good biocompatibility, thereby had promising application as injectable fillers. This work can provide useful information around tuning surface structures of the Pickering emulsion-templated polymer hollow microspheres by regulating acetylation level of ChNCs.

Coaxial electrospray of uniform polylactide core-shell microparticles for long-acting contraceptive

Despite its high efficacy and good patient compliance, the only long-acting injectable (LAI) contraceptive currently available in the US, depot medroxyprogesterone acetate (DMPA), is limited by significant side effects and a delayed return to fertility for up to 10 months after its intended duration of action. To overcome these limitations, we sought to develop an injectable poly(D,l-lactide) (PLA) microparticle for sustained release of contraceptive hormone, etonogestrel (ENG). A one-step technique, coaxial electrospray method was applied to prepare uniform ENG loaded core-shell structured and slow-degrading PLA microparticles (ENG-cs-MPs) to provide release control while minimizing polymer content. By adjusting voltage, polymer concentration and flow rate of the coaxial jetting solution, the prepared ENG-cs-MPs exhibited uniformly small particle size with volume mean diameter of 14.7 ± 0.5 μm and a shell thickness of 2.5 ± 0.1 μm, high drug loading of ~54%, high encapsulation efficiency of ~99%, and initial 1-day burst release of just ~10%. Long-term in vitro release of ENG was continuous for more than 3 months without change of the shell structure in 6 months. In PK studies, ENG-cs-MPs achieved a steady and continuous drug release for approximately 3 months and then quickly tapered off within 3 weeks. Hence, ENG-cs-MPs prepared by the coaxial electrospray method may be useful as a LAI contraceptive with an improved PK profile relative to DMPA.

Polydopamine Nanobottles with Photothermal Capability for Controlled Release and Related Applications

Nanobottles refer to colloidal particles featuring a hollow body connected to a single opening on the surface. This unique feature makes them ideal carriers for the encapsulation and controlled release of various types of cargos. Here a facile route to the fabrication of uniform nanobottles made of polydopamine by leveraging swelling-induced pressure is reported. When polystyrene spheres are coated with polydopamine and then incubated with a toluene/water emulsion, the polystyrene will be swollen to automatically poke a single hole in the shell because of the pressure inside the shell. After quenching the swelling with ethanol and then removing all the polystyrene with tetrahydrofuran, polydopamine nanobottles are obtained. The dimensions of the hollow body are determined by the polystyrene template, while the size of the opening can be tuned by varying the shell thickness. Through the opening, different types of cargos, including small molecules and biomacromolecules, can be easily loaded with a thermoresponsive material into the cavity. The cargos can be released in a controllable manner through direct heating or polydopamine-enabled photothermal heating. In a proof-of-concept experiment, the polydopamine nanobottles are used for temperature-controlled release of thrombin to trigger the formation of fibrin gels in situ.

PEOT/PBT Polymeric Pastes to Fabricate Additive Manufactured Scaffolds for Tissue Engineering

The advantages of additive manufactured scaffolds, as custom-shaped structures with a completely interconnected and accessible pore network from the micro- to the macroscale, are nowadays well established in tissue engineering. Pore volume and architecture can be designed in a controlled fashion, resulting in a modulation of scaffold’s mechanical properties and in an optimal nutrient perfusion determinant for cell survival. However, the success of an engineered tissue architecture is often linked to its surface properties as well. The aim of this study was to create a family of polymeric pastes comprised of poly(ethylene oxide therephthalate)/poly(butylene terephthalate) (PEOT/PBT) microspheres and of a second biocompatible polymeric phase acting as a binder. By combining microspheres with additive manufacturing technologies, we produced 3D scaffolds possessing a tailorable surface roughness, which resulted in improved cell adhesion and increased metabolic activity. Furthermore, these scaffolds may offer the potential to act as drug delivery systems to steer tissue regeneration.

Electrohydrodynamic atomisation driven design and engineering of opportunistic particulate systems for applications in drug delivery, therapeutics and pharmaceutics

Electrohydrodynamic atomisation (EHDA) technologies have evolved significantly over the past decade; branching into several established and emerging healthcare remits through timely advances in the engineering sciences and tailored conceptual process designs. More specifically for pharmaceutical and drug delivery spheres, electrospraying (ES) has presented itself as a high value technique enabling a plethora of different particulate structures. However, when coupled with novel formulations (e.g. co-flows) and innovative device aspects (e.g., materials and dimensions), core characteristics of particulates are manipulated and engineered specifically to deliver an application driven need, which is currently lacking, ranging from imaging and targeted delivery to controlled release and sensing. This demonstrates the holistic nature of these emerging technologies; which is often overlooked. Parametric driven control during particle engineering via the ES method yields opportunistic properties when compared to conventional methods, albeit at ambient conditions (e.g., temperature and pressure), making this extremely valuable for sensitive biologics and molecules of interest. Furthermore, several processing (e.g., flow rate, applied voltage and working distance) and solution (e.g., polymer concentration, electrical conductivity and surface tension) parameters impact ES modes and greatly influence the production of resulting particles. The formation of a steady cone-jet and subsequent atomisation during ES fabricates particles demonstrating monodispersity (or near monodispersed), narrow particle size distributions and smooth or textured morphologies; all of which are successfully incorporated in a one-step process. By following a controlled ES regime, tailored particles with various intricate structures (hollow microspheres, nanocups, Janus and cell-mimicking nanoparticles) can also be engineered through process head modifications central to the ES technique (single-needle spraying, coaxial, multi-needle and needleless approaches). Thus, intricate formulation design, set-up and combinatorial engineering of the EHDA process delivers particulate structures with a multitude of applications in tissue engineering, theranostics, bioresponsive systems as well as drug dosage forms for specific delivery to diseased or target tissues. This advanced technology has great potential to be implemented commercially, particularly on the industrial scale for several unmet pharmaceutical and medical challenges and needs. This review focuses on key seminal developments, ending with future perspectives addressing obstacles that need to be addressed for future advancement.

Electrospraying as a novel process for the synthesis of particles/nanoparticles loaded with poorly water-soluble bioactive molecules

Hydrophobicity and low aqueous-solubility of different drugs/nutraceuticals remain a persistent challenge for their development and clinical/food applications. A range of nanotechnology strategies have been implemented to address this issue, and amongst which a particular emphasis has been made on those that afford an improved biological performance and tunable release kinetic of bioactives through a one-step process. More recently, the technique of electrospraying (or electrohydrodynamic atomization) has attained notable impulse in virtue of its potential to tune attributes of nano/micro-structured particles (e.g., porosity, particle size, etc.), rendering a near zero-order release kinetics, diminished burst release manner, as well as its simplicity, reproducibility, and applicability to a broad spectrum of hydrophobic and poorly water-soluble bioactives. Controlled morphology or monodispersity of designed particles could be properly obtained via electrospraying, with a high encapsulation efficiency and without unfavorable denaturation of thermosensitive bioactives upon encapsulation. This paper overviews the recent technological advances in electrospraying for the encapsulation of low queues-soluble bioactive agents. State-of-the-art, advantages, applications, and challenges for its implementation in pharmaceutical/food researches are also discussed.

Drug-zein@lipid hybrid nanoparticles: Electrospraying preparation and drug extended release application

The reasonable selection and elaborate conversion of raw materials into desired functional products represent a main topic in modern material engineering. In this study, zein (a plant protein) and lipids (extracted from egg yolk) are converted into a new type of drug-polymer@lipid hybrid nanoparticles (HNPs) via modified coaxial electrospraying. Tamoxifen citrate (TC) is used as a model anticancer drug to prepare TC-zein monolithic nanocomposites (MNCs) via traditional blended electrospraying; these MNCs are then used for comparison. Modified coaxial electrospraying is a continuous and robust process for the preparation of solid particles because of the action of unsolidifiable shell lipid solutions. HNPs have a round morphology with clear core-shell nanostructures, whereas MNCs have an indented flat morphology. Although both hold the drug in an amorphous state because of the fine compatibility of TC and zein, HNPs demonstrate a better sustained release of TC compared with MNCs in terms of retarding initial burst release (6.7 %±2.9 % vs. 37.2 %±4.3 %) and prolonged linear release period (20.47 h vs. 4.97 h for releasing 90 % of the loaded drug). Mechanisms by which the shell's lipid layer adjusts the release behavior of TC molecules are proposed. The present protocol based on coaxial electrospraying shows a new strategy of combining edible protein and lipids to fabricate advanced functional nanomaterials.

Nanobottles for Controlled Release and Drug Delivery

Nanobottles refer to colloidal particles with a hollow interior and a single opening in the wall. These unique features make them ideal carriers for the loading, encapsulation, release, and delivery of various types of theranostic agents in an array of biomedical applications. The hollow interior gives them a high loading capacity while the opening enables quick loading and controlled release of the payload(s). More significantly, on-demand release can be readily achieved by adding a stimuli-responsive material as the inner matrix or cork stopper. This progress report begins with an introduction to the general structures and properties of nanobottles, followed by a brief discussion on the methods developed for their fabrication. The use of nanobottles for loading different types of payloads is then showcased, including small-molecule drugs, biomacromolecules, imaging contrast agents, and functional nanoparticles. The strategies explored for controlling the release by varying the size of the opening and/or integrating with a stimuli-responsive material are also highlighted. This paper concludes with some perspectives on future directions for this class of nanomaterials in terms of fabrication, functionalization, and application.

Structured micro/nano materials synthesized via electrospray: a review

The development of synthetic methods for micro/nano materials with precisely controlled structures, morphologies, and local compositions is of great importance for the advancement of modern nanotechnology. The electrospray method is a "platform" approach for the preparation of a broad range of micro-/nanostructures; electrospray is simple and scalable. This review summarizes recent research on the micro-/nanostructures prepared via the electrospray route. These include spherical structures (e.g. simple, porous, Janus, and core-shell particles), non-spherical structures (e.g. red blood cell-like and spindle-like particles, multi-compartment microrods, 2D holey nanosheets, and nanopyramids), and assembled structures. The experimental details, underlying physical/chemical principles, and key benefits of these structures are comprehensively discussed. The effects and importance of nozzle design, properties of feeding solutions (e.g. concentration of solute, polymer additives, solvent/nonsolvent combinations), working environment (e.g. temperature and humidity), and types of collection media are highlighted.

Core–shell particles for drug-delivery, bioimaging, sensing, and tissue engineering

Core–shell particles offer significant advantages in their use for bioimaging and biosensors.

Room-Temperature Synthesis of Hollow Polymer Microparticles with an Open Hole on the Surface and Their Application

Compared with hollow microparticles with a completely closed shell structure, hollow polymer microparticles with an open hole on their surface have attracted considerable attention because of the obvious importance of the open hole on their surface; however, the development of a facile method to synthesize such unique open-ended hollow particles has remained a great challenge. In this study, an easy-to-use method was developed to rapidly produce monodispersed hollow and pored microparticles in high reaction yield at room temperature. The key to achieving the unusually shaped polystyrene (PS) microparticles was the use of anisotropic PS seeds. When hollow and dimpled PS seeds prepared using a modified dispersion polymerization method were dispersed in a water-toluene mixture followed by solvent evaporation under ambient conditions, they transformed into hollow PS microparticles with an open hole on their surface. A plausible mechanism for the transformation of the PS microparticles during the swelling and drying processes was proposed on the basis of our results and observations. The structural features of the hollow and pored PS microparticles motivated us to use the particles as a catalyst support. By using modified heterophase polymer dispersion processing involving the addition of a Ag precursor, hollow and pored PS microparticles covered with Ag nanocrystals were obtained on the basis of the in situ reduction of metal precursor on the surface of polymer particles. The resulting Ag nanocrystals/PS hybrid microparticles exhibited enhanced catalytic activity at low concentrations of nanocrystals and could be reused several times without loss of activity when used as catalysts for the reduction of 4-nitrophenol to 4-aminophenol with sodium borohydride.

Co-electrospraying of tumour cell mimicking hollow polymeric microspheres for diffusion magnetic resonance imaging

Diffusion magnetic resonance imaging (dMRI) is considered as a useful tool to study solid tumours. However, the interpretation of dMRI signal and validation of quantitative measurements of is challenging. One way to address these challenges is by using a standard reference material that can mimic tumour cell microstructure. There is a growing interest in using hollow polymeric microspheres, mainly prepared by multiple steps, as mimics of cells in healthy and diseased tissue. The present work reports on tumour cell-mimicking materials composed of hollow microspheres for application as a standard material in dMRI. These microspheres were prepared via one-step co-electrospraying process. The shell material was poly(d,l-lactic-co-glycolic acid) (PLGA) polymers with different molecule weights and/or ratios of glycolic acid-to-lactic, while the core was polyethylene glycol (PEG) or ethylene glycol. The resultant co-electrosprayed products were characterised by optical microscopy, scanning electron microscopy (SEM) and synchrotron X-ray micro-CT. These products were found to have variable structures and morphologies, e.g. from spherical particles with/without surface hole, through beaded fibres to smooth fibres, which mainly depend on PLGA composition and core materials. Only the shell material of PLGA polymer with ester terminated, Mw 50,000-75,000 g mol-1, and lactide:glycolide 85:15 formed hollow microspheres via the co-electrospraying process using the core material of 8 wt% PEG/chloroform as the core. A water-filled test object (or phantom) was designed and constructed from samples of the material generated from co-electrosprayed PLGA microspheres and tested on a 7 T MRI scanner. The preliminary MRI results provide evidence that hollow PLGA microspheres can restrict/hinder water diffusion as cells do in tumour tissue, implying that the phantom may be suitable for use as a quantitative validation and calibration tool for dMRI.

Electrospraying: Possibilities and Challenges of Engineering Carriers for Biomedical Applications-A Mini Review

Electrospraying, a liquid atomization-based technique, has been used to produce and formulate micro/nanoparticular cargo carriers for various biomedical applications, including drug delivery, biomedical imaging, implant coatings, and tissue engineering. In this mini review, we begin with the main features of electrospraying methods to engineer carriers with various bioactive cargos, including genes, growth factors, and enzymes. In particular, this review focuses on the improvement of traditional electrospraying technology for the fabrication of carriers for living cells and providing a suitable condition for gene transformation. Subsequently, the major applications of the electrosprayed carriers in the biomedical field are highlighted. Finally, we finish with conclusions and future perspectives of electrospraying for high efficiency and safe production.

A biomimetic tumor tissue phantom for validating diffusion-weighted MRI measurements

PURPOSE

To develop a biomimetic tumor tissue phantom which more closely reflects water diffusion in biological tissue than previously used phantoms, and to evaluate the stability of the phantom and its potential as a tool for validating diffusion-weighted (DW) MRI measurements.

METHODS

Coaxial-electrospraying was used to generate micron-sized hollow polymer spheres, which mimic cells. The bulk structure was immersed in water, providing a DW-MRI phantom whose apparent diffusion coefficient (ADC) and microstructural properties were evaluated over a period of 10 months. Independent characterization of the phantom's microstructure was performed using scanning electron microscopy (SEM). The repeatability of the construction process was investigated by generating a second phantom, which underwent high resolution synchrotron-CT as well as SEM and MR scans.

RESULTS

ADC values were stable (coefficients of variation (CoVs) < 5%), and varied with diffusion time, with average values of 1.44 ± 0.03 µm2 /ms (Δ = 12 ms) and 1.20 ± 0.05 µm2 /ms (Δ = 45 ms). Microstructural parameters showed greater variability (CoVs up to 13%), with evidence of bias in sphere size estimates. Similar trends were observed in the second phantom.

CONCLUSION

A novel biomimetic phantom has been developed and shown to be stable over 10 months. It is envisaged that such phantoms will be used for further investigation of microstructural models relevant to characterizing tumor tissue, and may also find application in evaluating acquisition protocols and comparing DW-MRI-derived biomarkers obtained from different scanners at different sites. Magn Reson Med 80:147-158, 2018. © 2017 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.