Fabrication Of Microspheres Research Articles

Droplet Microfluidics-Based Fabrication of Monodisperse Poly(ethylene glycol)-Fibrinogen Breast Cancer Microspheres for Automated Drug Screening Applications.

Spheroidal cancer microtissues are highly advantageous for a wide range of biomedical applications, including high-throughput drug screening, multiplexed target validation, mechanistic investigation of tumor-extracellular matrix (ECM) interactions, among others. Current techniques for spheroidal tissue formation rely heavily on self-aggregation of single cancer cells and have substantial limitations in terms of cell-type-specific heterogeneities, uniformity, ease of production and handling, and most importantly, mimicking the complex native tumor microenvironmental conditions in simplistic models. These constraints can be overcome by using engineered tunable hydrogels that closely mimic the tumor ECM and elucidate pathologically relevant cell behavior, coupled with microfluidics-based high-throughput fabrication technologies to encapsulate cells and create cancer microtissues. In this study, we employ biosynthetic hybrid hydrogels composed of poly(ethylene glycol diacrylate) (PEGDA) covalently conjugated to natural protein (fibrinogen) (PEG-fibrinogen, PF) to create monodisperse microspheres encapsulating breast cancer cells for 3D culture and tumorigenic characterization. A previously developed droplet-based microfluidic system is used for rapid, facile, and reproducible fabrication of uniform cancer microspheres with either MCF7 or MDA-MB-231 (metastatic) breast cancer cells. Cancer cell-type-dependent variations in cell viability, metabolic activity, and 3D morphology, as well as microsphere stiffness, are quantified over time. Particularly, MCF7 cells grew as tight cellular clusters in the PF microspheres, characteristic of their epithelial morphology, while MDA-MB-231 cells displayed elongated and invasive morphology, characteristic of their mesenchymal and metastatic nature. Finally, the translational potential of the cancer microsphere platform toward high-throughput drug screening is also demonstrated. With high uniformity, scalability, and control over engineered microenvironments, the established cancer microsphere model can be potentially used for mechanistic studies, fabrication of modular cancer microtissues, and future drug-testing applications.

Facile electrodeposition fabrication of raspberry-like gold microspheres decorated polydiphenylamine nanohybrid coated electrode for efficient direct methanol fuel cell application

In this work, a simple two-step electrodeposition strategy has been successfully developed to fabricate morphology-controlled gold microspheres (AuMS) decorated polydiphenylamine (PDPA) nanohybrid modified FTO electrode. The physicochemical characterization of PDPA/AuMS modified electrode has been explored using XRD and SEM/EDX mapping techniques. Results showed the controlled synthesis of uniform-sized raspberry-like AuMS were decorated in the PDPA matrix to form the electrocatalytically active PDPA/AuMS nanohybrid material on the FTO electrode. As-fabricated PDPA/AuMS modified FTO electrode was used as an efficient electrocatalyst for methanol oxidation reaction under an alkaline environment for fuel cell applications. Cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy techniques were employed to investigate the as-prepared electrode's electrochemical responses and methanol oxidation reaction (MOR). PDPA/AuMS hybrid electrode showed 1.04 mA/cm2 as the current density at a lower scan rate (50 mV/sec) with a lower potential value of 0.43 V, which indicates the excellent electrocatalytic activity of the fabricated electrode. Moreover, the as-prepared electrode showed more extended stability and durability (60 min) towards MOR due to the combined existence of AuMS and PDPA matrix, which enhances the catalytic property. Based on the above results, an as-prepared PDPA/AuMS nanohybrid composite can be applied as a potential electrocatalyst/alternative electrode for direct methanol fuel cell (DMFC) applications.

Fabrication of multifunctional alginate microspheres containing hydroxyapatite powder for simultaneous cell and drug delivery.

Novel alginate-hydroxyapatite hybrid microspheres were developed for simultaneous delivery of drugs and cells as a multifunctional bone substitute for osteoporotic bone tissue regeneration. The microspheres were used to enhance osteogenesis and to carry and deliver quercetin, a representative phytoestrogen that controls bone tissue regeneration metabolism in osteoporosis patients, through sustained release over a long period. To overcome quercetin’s hydrophobicity and low solubility in aqueous environments, we added it to the surface of hydroxyapatite (HAp) nanoparticles before mixing them with an alginate solution. The homogeneous distribution of the HAp nanoparticles in the alginate solution was essential for preventing nozzle clogging and achieving successfully fabricated hybrid microspheres. To this end, a 3D ultrasonic treatment was applied. Electrostatic microencapsulation was then used to fabricate hybrid alginate-HAp microspheres containing quercetin and cells. The microspheres were approximately 290.7 ± 42.5 μm (aspect ratio of 1). The sustained release of quercetin was confirmed during a test period of 20 weeks. The cells in the hybrid microspheres maintained good cell viability during the entire testing period, and their osteogenic differentiation behavior was boosted by the presence of HAp. Thus, osteogenic differentiation could be greatly improved by adding quercetin. These novel multi-biofunctional hybrid microspheres have great potential for the regeneration of osteoporotic bone tissue at indeterminate defect sites.

Fabrication of microspheres containing coagulation factors by reverse microemulsion method for rapid hemostasis and wound healing

Traditional dressings, such as bandages, gauze, and cotton pads stick to new granulation tissue, thereby aggravating wound injury or causing secondary injury during replacement. Microspheres that are biodegradable and adaptable to various wound shapes are a good alternative to traditional dressings. In this work, a novel microsphere was prepared by reverse microemulsion method using sodium alginate and silk peptide (SP) as the aqueous phase. After cross-linking by Ca2+, calcium alginate (CA) and SP composite microspheres called CA/SP were prepared. By adjusting the SP content, the swelling rate of microspheres reached 1050 % and the pore diameter reached 19.59 nm. In addition, the introducing SP provided a stable loading site for thrombin (Th). This platform (called CA/SP@Th)—integrating rapid blood enrichment, calcium release, and Th catalysis—can ensure rapid hemostasis in a variety of bleeding models. Additionally, the SP present in this modality also promoted fibroblast proliferation, this increased the wound closure rate in a total cortex injury mouse model (more than 97 % within 15 days). Therefore, CA/SP@Th can be used as a multifunctional dressing for rapid hemostasis and wound healing.

Porous carbon microspheres with controlled porosity and graphitization degree for high-performance supercapacitor

• Porous carbon microspheres are synthesized via a simple template-free method. • Porous structure and graphitization degree are controlled. • Ni-based salts and ethanolamine affect porous structure and graphitization degree. • Porous carbon microspheres exhibited excellent supercapacitor performance. The fabrication of porous carbons plays an important role in improving electrochemical performance for supercapacitors. The fabrication of carbon microspheres with controlled porous structure and graphitization degree is still a challenge in synthetic methodology, since it is difficult to achieve both goals at the same time. Porous carbon microspheres with controlled porous structure and graphitization degree are realized here via a simple template-free method, using Ni-based salts and resorcinol-formaldehyde resin microspheres as raw materials. The amount and types of Ni-based salts as well as ethanolamine significantly affect the porous structure and graphitization degree for the carbon microspheres. The porous carbon microspheres prepared with 4.0 g of Ni(CH 3 COO) 2 ·4H 2 O and 0.25 mL of ethanolamine possess the surface area of 392.1 m 2 g −1 , the pore volume of 0.395 cm 3 g −1 and the I G /I D ratio of 1.18. The as-synthesized porous carbon microspheres can serve as excellent candidates for electrode materials in supercapacitors to achieve excellent electrochemical behaviors. The as-prepared porous carbon microspheres exhibit a specific capacitance of 193.8F g −1 at 1 A g −1 , good rate capability and long cycle life in a two-electrode system. The superior electrochemical performance can be attributed to both the unique hierarchical porous structure and high graphitization degree. The hierarchical porous structure can provide fine transportation pathways and a large number of adsorption sites for electrolyte ions, and high graphitization degree can ensure rapid electron transport.

Localized Controlled Release of Kynurenic Acid Encapsulated in Synthetic Polymer Reduces Implant-Induced Dermal Fibrosis.

Excessive fibrosis following surgical procedures is a challenging condition with serious consequences and no effective preventive or therapeutic option. Our group has previously shown the anti-fibrotic effect of kynurenic acid (KynA) in vitro and as topical cream formulations or nanofiber dressings in open wounds. Here, we hypothesized that the implantation of a controlled release drug delivery system loaded with KynA in a wound bed can prevent fibrosis in a closed wound. Poly (lactic-co-glycolic acid) (PLGA), and a diblock copolymer, methoxy polyethylene glycol-block-poly (D, L-lactide) (MePEG-b-PDLLA), were used for the fabrication of microspheres which were evaluated for their characteristics, encapsulation efficiency, in vitro release profile, and in vivo efficacy for reduction of fibrosis. The optimized formulation exhibited high encapsulation efficiency (>80%), low initial burst release (~10%), and a delayed, gradual release of KynA. In vivo evaluation of the fabricated microspheres in the PVA model of wound healing revealed that KynA microspheres effectively reduced collagen deposition inside and around PVA sponges and α-smooth muscle actin expression after 66 days. Our results showed that KynA can be efficiently encapsulated in PLGA microspheres and its controlled release in vivo reduces fibrotic tissue formation, suggesting a novel therapeutic option for the prevention or treatment of post-surgical fibrosis.

Fabrication of highly conductive natural rubber-based composite films via Pickering emulsion interfacial assembly

The development of conductive rubber-based composites with low percolation thresholds and excellent mechanical properties has attracted great attention. Herein, we propose a simple and effective interfacial assembly strategy to prepare natural rubber (NR)-based composite films with three-dimensional carbon nanotube (CNT) conductive networks by using Pickering emulsion as designer platform. The synergistic assembly of CNT/regenerated cellulose (RC) and the oppositely charged surfactants at the oil-water interface resulted in the formation of stable Pickering emulsions that served as templates for the fabrication of CNT-wrapped conductive microspheres. After hot-compressing, the obtained NR-based composite film features a high electrical conductivity of 11.5 S/m, a low percolation threshold of 0.27 vol% at 4.59 vol% CNT loading. Therefore, the Pickering emulsion interfacial assembly strategy provides a new way for the fabrication of functional conductive rubber-based composites from mesoscale (e.g., structured emulsions) to macroscale (e.g., film).

Precise Fabrication of Porous Microspheres by Iso-Density Emulsion Combined with Microfluidics

Polymer porous microspheres with large specific surface areas and good fluidity have promising important applications in the biomedical field. However, controllable fabrication of porous microspheres with precise size, morphology, and pore structure is still a challenge, and phase separation caused by the instability of the emulsion is the main factor affecting the precise preparation of porous microspheres. Herein, a method combining the iso-density emulsion (IDE) template and microfluidics was proposed to realize the controllable preparation of polymer porous microspheres. The IDE exhibited excellent stability with minimal phase separation within 4 h, thus showing potential advantages in the large-scale preparation of porous microspheres. With the IDE template combined microfluidics technique and the use of a customized amphoteric copolymer, PEG-b-polycaprolactone, polycaprolactone (PCL) porous microspheres with porosity higher than 90% were successfully prepared. Afterwards, the main factors, including polymer concentration, water–oil ratio and homogenization time were investigated to regulate the pore structure of microspheres, and microspheres with different pore sizes (1–30 μm) were obtained. PCL porous microspheres exhibited comparable cell viability relative to the control group and good potential as cell microcarriers after surface modification with polydopamine. The modified PCL porous microspheres implanted subcutaneously in rats underwent rapid in vivo degradation and tissue ingrowth. Overall, this study demonstrated an efficient strategy for the precise preparation of porous microspheres and investigated the potential of the as-prepared PCL porous microspheres as cell microcarriers and micro-scaffolds.

Effect of the modification of spray drying parameters on the fabrication of bovine-derived hydroxyapatite microspheres for biomedical applications

In this work, the effect of the spray dryer parameters on bovine-derived hydroxyapatite (BHAp) was studied to fabricate microspheres with controlled particle size distribution and morphology. A factorial design was implemented to establish the impact of spray drying process parameters on the final BHAp powder properties. The critical process factors were solid content in the slurry, atomization pressure, and hot air flow rate, whereas the studied experimental outputs were particle size distribution and morphology, characterized by laser diffraction and scanning electron microscopy, respectively. Additionally, the Ca/P molar ratio was evaluated from X-ray diffraction data. The obtained results showed a strong influence of the atomization pressure and the solid slurry content on the particle size distribution (increasing from 2.56 ± 0.02 µm to 32.46 ± 0.78 µm) and particle morphology (with an increased circularity from 0.3502 ± 0.0172 to 0.8688 ± 0.0039), being both properties suitable for thermal spray (TS) applications. Moreover, the BHAp crystalline structure and Ca/P molar ratio did not present any changes with the spray drying process parameters employed. Finally, it was found that magnesium was preserved in the spray dried particles, the former being also present in the starting powder feedstock.

One-step fabrication of porous carbon microspheres with in situ self-doped N, P, and O for the removal of anionic and cationic dyes

Porous carbon microspheres (NPO-PCSs) with a high specific surface area (1769 m2 g−1) and in situ self-doped multiple heteroatoms (N, P, and O) were skillfully fabricated via one-step direct pyrolysis of cross-linked poly(cyclotriphosphazene-co-phloroglucinol) microspheres. The doping carbon structure of NPO-PCSs with intrinsic microporosity promises the potential for the adsorption of cationic and anionic dyes (Methyl Blue and Methyl Orange). Moreover, there is a π-π interaction between the ordered graphite units of NPO-PCSs and the aromatic rings of dye molecules, which promotes the dye adsorption capacity of NPO-PCSs. Meanwhile, these in situ self-doped heteroatoms (N, P, and O) can play as Lewis base and the formed Lewis acid-base interaction improves the adsorption performance of the NPO-PCSs. Additionally, for the large containing oxygen groups of the NPO-PCSs adsorbent, there could be the electrostatic attraction between the NPO-PCSs adsorbent and the dye molecules. As results, the absorptivity of the NPO-PCSs for MB and MO could reach 356 and 281 mg g−1 at 25 °C and pH = 7, respectively. Thus, the high-performance NPO-PCSs versatile adsorbent might have a great potential for practical application in wastewater purification.

Temperature-controlled fabrication of hydrophilic manganese oxide microspheres as high-performance electrode materials for supercapacitors

The supercapacitive properties of manganese oxides (MnOx) are strongly affected by their crystal structure. Nevertheless, the relationship between the crystal structure and supercapacitive performance of MnOx is elusive. Herein, a temperature-controlled fabrication method was developed to achieve MnO2, Mn3O4, MnO and Mn2O3 microspheres with various crystal structure as electrode materials tunable for supercapacitors. The detailed material and electrochemical characterizations revealed the structure-activity relationship of MnOx microspheres by systematically investigating the effect of valence state, specific surface area, conductivity and morphology on supercapacitive performance. Among these MnOx materials, nanoneedle-like MnO2 delivered a relatively high specific capacitance of 274.1 F/g at 1 A/g due to a high Mn valence state of +4, a large specific surface area of 113.4 m2/g and a desirable electronic conductivity of 1.73 × 10–5 S/cm. Furthermore, MnO2 presented a remarkable cycle stability with 115% capacitance retention after 10,000 cycles owing to the enhancement of wettability. This work not only provides a facile strategy to modulate MnOx crystal structure, but also offers a deep understanding of structure-dependent supercapacitive performance of MnOx.

Fabrication of self-reinforced polymorphic cellulose nanofiber composite microspheres for highly efficient adsorption of proteins

Fabrication of self-reinforced polymorphic cellulose nanofiber composite microspheres for highly efficient adsorption of proteins

Lysozyme microspheres incorporated with anisotropic gold nanorods for ultrasound activated drug delivery

We report on the fabrication of lysozyme microspheres (LyMs) incorporated with gold nanorods (NRs) as a distinctive approach for the encapsulation and release of an anticancer drug, 5-Fluorouracil (5-FU). LyMs with an average size of 4.0 ± 1.0 µm were prepared by a sonochemical method and characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier-transform infrared spectroscopy (FTIR). The LyMs were examined using hydrophobic (nile red) as well as hydrophilic (trypan blue) dyes under confocal laser scanning microscopy (CLSM) to obtain information about the preferential distribution of fluorescent molecules. Notably, the fluorescent molecules were accumulated in the inner lining of LyMs as the core was occupied with air. The encapsulation efficiency of 5-FU for LyMs-NR was found to be ∼64%. The drug release from control LyMs as well as LyMs incorporated with NRs was investigated under the influence of ultrasound (US) at 200 kHz. The total release for control LyMs and LyMs incorporated with gold NRs was found to be ∼70 and 95% after 1 h, respectively. The density difference caused by NR incorporation on the shell played a key role in rupturing the LyMs-NR under US irradiation. Furthermore, 5-FU loaded LyMs-NR exhibited excellent anti-cancer activity against the THP-1 cell line (∼90% cell death) when irradiated with US of 200 kHz. The enhanced anti-cancer activity of LyMs-NR was caused by the transfer of released 5-FU molecules from bulk to the interior of the cell via temporary pores formed on the surface of cancer cells, i.e., sonoporation. Thus, LyMs-NR demonstrated here has a high potential for use as carriers in the field of drug delivery, bio-imaging and therapy.

Fabrication of monodisperse polyacrylonitrile hollow microspheres containing transition metals and low-temperature catalytic graphitization

Fabrication of monodisperse polyacrylonitrile hollow microspheres containing transition metals and low-temperature catalytic graphitization

Rational design and fabrication of monophasic bioceramic microspheres with enhanced mechanical and biological performances in reconstruction of segmental bone defect.

Over the past decades, there has been extensive study on the design of porous bioceramic scaffolds with controlled bioactivity and biodegradation in bone tissue repair. A variety of suggestive models and concepts have been proposed with regard to the role of microstructure and composition of biomaterials which affect new bone tissue growth. However, it is a challenge to fabricate functional scaffolds with the desired physiological properties and osteogenic potentials that is comparable to the bone's natural healing time scale. We demonstrate a one-step versatile fabrication of a single-phase and homogenously mixed bioactive load-bearing scaffolds (Sr-CS, CaSiO3/Ca2SiO4, and CaP) with superior biological properties in a critical size bone defect (Ø ~ 6.0 × 8.0mm). In vivo study revealed the CaSiO3/Ca2SiO4 scaffold had the best amount of new bone growth and osteogenic repair. The Sr-CS exhibited an adequate pore network for rapid inorganic exchange and moderate mechanical stability; however, the CaSiO3/Ca2SiO4 saw over-fast resorption and mass loss compared to the Sr-CS and CaP. On the other hand, the CaP scaffold saw mechanically outstanding elastroplastine and stability but had limited biodegradation of its constructs which retarded new cancellous bone growth. The CaSiO3/Ca2SiO4 group saw superior acceleration and formation of mineralized new bone tissues in the defect. Moreover, the CaSiO3/Ca2SiO4 showed appreciable decay of the biomaterials beneficial for osteogenic cell activity. The dramatic stimulation of bone repair and angiogenesis with the CaSiO3/Ca2SiO4 suggests a promising application of this novel bioactive scaffold in the repair of skeletal defects. Systemic representation of the fabricated microspheres with in vivo and in vitro study analysis.

Generating porous polymer microspheres with cellular surface via a gas-diffusion confined scCO2 foaming technology to endow the super-hydrophobic coating with hierarchical roughness

Porous polymer microspheres have been applied in various fields due to their hierarchical morphology and extensive surface area. However, it is difficult to create porous microspheres, especially porous microspheres without solid skin layer, via conventional supercritical carbon dioxide (scCO2) foaming technology due to the fast diffusion of gas. In order to prevent gas diffusing from microspheres, a continuous polymethyl methacrylate (PMMA) phase is employed as a gas-diffusion confinement in this work. When pressure quenched, CO2 is retained in/on the polystyrene (PS) microspheres for the cell nucleation and development. Therefore, a porous PS microsphere is fabricated by a diffusion-confined scCO2 foaming technology for the first time. The prepared microsphere displays an open cellular surface and a closed cellular core. The cell structure of porous microspheres is tunable depending on the foaming parameters. This method with the advantages of simple, versatile and controllable provides a novel perspective for fabrication of porous polymer microspheres. Furthermore, a super-hydrophobic coating is constructed using polymer microspheres as fillers and beeswax as a hydrophobic agent. Compared to the arrays composed of solid microspheres, the arrays composed of porous polymer microspheres show a super-hydrophobicity, low water-adhesion, outstanding antifouling and self-cleaning property.

Fabrication of astaxanthin-enriched colon-targeted alginate microspheres and its beneficial effect on dextran sulfate sodium-induced ulcerative colitis in mice.

Astaxanthin (Ax) with a strong antioxidant activity is beneficial to human health, but its application is limited by its highly unsaturated structure and poor water-solubility. Ax-enriched colon targeted alginate particles (Ax-Alg) was prepared by high-pressure spraying and ionic gelation, and most of particles was in the range of 0.5-3.2μm in a diameter. The in vitro models showed that Ax-Alg can maintain the structural integrity in the different conditions (pH, heat and ion). In addition, Ax-Alg can well tolerate the conditions in the mouth, stomach and small intestine and reach the colon where Ax was released due to fermentation of gut microbiota. Mice experiment showed that Ax-Alg reduced dextran sulfate sodium-induced colitis, involving weight loss, disease activity index, colonic mucosal integrity and inflammation, and oxidative damage. On the other hand, Ax-Alg regulated the gut microbiota composition and reduced the abundances of Bacteroidetes members that had positive correlation with ulcerative colitis. Ax-Alg had better effect on the treatment of ulcerative colitis than oil-in-water emulsion, which can be attributed to the synergistic effect of Ax and alginate. This study can be helpful for the application of colon-targeted delivery system in the foods and treatment of colon diseases.

Polyvinylpyrrolidone-regulated synthesis of hollow manganese vanadium oxide microspheres as a high-performance anode for lithium-ion batteries

We report the fabrication of well-defined phase-pure Mn2V2O7 hollow microspheres (h-MVO), assembled from the porous plate-like building blocks, via a facile solvothermal method followed by annealing, with the assistance of polyvinylpyrrolidone (PVP) as the structure-regulating agent. The microstructure dependent electrochemical properties of h-MVO as anode materials for lithium ion batteries (LIBs) are investigated, and excellent lithium storage performance is obtained with a reversible capacity of 1707 mAh g−1 after 700 cycles at 0.5 A g−1, revealing that the unique hierarchical framework of the h-MVO microspheres with hollow interiors and porous building blocks could not only accelerate the transport of Li+ ions and electrolyte, but also efficiently suppress the electrode pulverization upon cycling. More importantly, we demonstrate that PVP can be an effective agent to tune the microstructures, which would be promising for the development of high-performance energy storage devices.

Porous ZnO Microspheres Grafted with Poly‐(N‐isopropylacrylamide) via SI‐ATRP: Reversible Temperature‐Controlled Switching of Photocatalysis**

AbstractWe report on the fabrication of porous ZnO microspheres (pZnO MSs) grafted with thermo‐responsive polymers of poly(N‐isopropylacrylamide) (PNIPAM) via surface‐initiated atom transfer radical polymerization (SI‐ATRP) for photocatalysis applications. Photodegradation of Rhodamine B (Rh‐B) is used to evaluate the photocatalysis performance of pZnO MSs grafted with PNIPAM (pZnO MSs‐PNIPAM). The results show that pZnO MSs‐PNIPAM exhibits a reversible temperature‐controlled photocatalysis activity and good recycling performance. By adjusting the environmental temperature, the photocatalysis property of pZnO MSs‐PNIPAM can be turned on/off, resulting in a temperature‐controlled switching function of the obvious/unobvious photocatalysis performance below/upon the lower critical solution temperature (LCST) of PNIPAM. Additionally, the dispersion property of pZnO MSs‐PNIPAM in water can also be regulated by changing the environment temperature, demonstrating the potential applications in that of photocatalysis‐related fields for the graft systems.

One-pot synthesis strategy of sea urchin-like hollow microspheres comprising MoOx nanorods attached via N-doped C as anodes for lithium-ion batteries

A one-pot synthetic strategy that takes only 2.3 s was developed for the fabrication of sea urchin-like hollow microspheres comprising MoOx nanorods attached via N-doped C for the first time. The inclusion of diethylenetriamine as a starting material played a key role in the formation of MoOx nanorods constituting the hollow shell. Additionally, the MoOx nanorods were coated and entangled with N-doped C, which established a rapid pathway for electrons and Li ions during the charge–discharge process when used as anodes for Li-ion batteries. Besides, numerous MoOx nanorods grafted in the shell provided efficient one-dimensional electron transport along the longitudinal direction, enabling more efficient interaction with the Li-ions. Therefore, superior cycling performance was achieved: the nanostructure produced a discharge capacity of 794 mA h g−1 after 400 cycles at 0.2 A g−1 with a low decay rate of 0.074% per cycle. Discharge capacities of 891, 589, 358, 250, and 193 mA h g−1 were obtained at current densities of 0.5, 1.5, 3.0, 5.0, and 7.0 A g−1, respectively. The facile synthetic strategy to prepare hollow microspheres using spray pyrolysis has important potential for the mass production of hierarchically hollow nanostructures in a wide range of fields, including energy storage.