Pores Of Microspheres Research Articles

Transport properties of hydrophilic compounds in PLGA microspheres

Biodegradable polyesters, such as the poly(lactic-co-glycolic acid) (PLGA), have been extensively used as a polymer matrix for entrapping a variety of active compounds. In this study, the physicochemical phenomena that control the mass transport mechanism of hydrophilic compounds released from PLGA microspheres were identified. This study aims to produce and characterize PLGA microspheres loaded with metformin hydrochloride (MH) and perform a case study using the literature data of PLGA microspheres loaded with fluorescein isothiocyanate-dextran (FITC-dextran). The MH is a low molecular weight compound that was easily and rapidly transported by diffusion mechanism through the microsphere pores. The FITC-dextran, as a high molecular weight compound, depended on the mechanism of polymer erosion and mesopore formation, with 18 days of duration, before its release by diffusion mass transfer. Values of the effective diffusion coefficient of MH and FITC-dextran, both in PLGA, were 2.4 x 10-13 and 5.3 x 10-18 m2 s-1, respectively, with a difference of five orders of magnitude attributed to the molecular weight of these hydrophilic compounds and the main mass transport that governed their release. This study provides important insights into the mechanisms of mass transfer and their correlation with the physicochemical properties of both hydrophilic compounds and the PLGA matrix, contributing to the development of biodegradable controlled delivery systems for a variety of applications in chemical, biotechnological, and pharmaceutical industries.

Effects of Chitosan on Loading and Releasing for Doxorubicin Loaded Porous Hydroxyapatite-Gelatin Composite Microspheres.

Porous hydroxyapatite–gelatin (Hap–Gel) composite microspheres derived by wet chemical methods were used as carriers of doxorubicin (DOX) coupled with chitosan (Chi) for treating cancers. Through X-ray diffraction, specific surface area porosimetry, chemisorption analysis and inductively coupled plasma mass spectrometry, the crystalline phase, composition, morphology, and pore distribution of HAp–Gel microspheres were all characterized. HAp nanosized crystals and Gel polymers form porous microspheres after blending and exhibit a specific surface area of 158.64 m2/g, pore sizes from 3 to 150 nm, and pore volumes of 0.4915 cm3/g. These characteristics are suitable for carriers of DOX. Furthermore, by the addition of chitosan during drug loading, its drug-entrapment efficiency increases from 70% to 99% and the release duration increases from a 100% burst within a day to only 45% over half a year since the pores in the composite microspheres provide a shielding effect throughout the degradation period of the chitosan. According to the MTT tests, cell viability of DOX–Chi/HAp–Gel is 57.64% on day 5, similar to the result treated with DOX only. It is concluded that under the protection of pores in the microspheres, the chitosan abundant of hydroxyls combining HAp–Gel and DOX by forming hydrogen bonds indeed enhances the entrapment efficiency, prolongs the releasing period and maintains DOX’s ability to perform medicine functions unaffected after loading.

Luminescence properties of rare earth complexes bonded to novel mesoporous spherical hybrid materials

YVO4:Eu3+ phosphors have been widely used in optoelectronic integration fields of its chemical and thermal stability. However, the excitation spectrum band of VO43− is too narrow for high-efficiency luminescence, restricting its further development. Herein, flower-like and linear-like YVO4:Eu3+ hollow mesoporous spheres were synthesized and connected with Eu organic ligand, to obtain a new hybrid luminescent material. The characterization shows that the pores of microspheres are in size of about 2–50 nm, sticked with regular morphology, well crystallized, and in uniform distribution. The emission intensity of hybrid luminescent material is higher than that of single YVO4:Eu3+ and single Eu complexes realizing the purpose of mutually reinforcing luminescence. This paper provides a new idea to connect rare earth complexes for a new non-silicon-based mesoporous spherical matrix.

The effect of washing process on the cracking of ZrO2 microspheres by internal gelation

AbstractZrO2 microspheres are widely used as a simulant of UO2 in the development of nuclear fuel. However, the cracking of ZrO2 microspheres prepared by internal gelation is still a challenge during drying and sintering processes. To address this issue, we designed and optimized the washing process for obtaining crack‐free ZrO2 microspheres. Through thermogravimetric, infrared, Raman, BET, and SEM analysis, it is shown that the cracking of the microspheres is mainly related to the pores in microspheres. The washing solvent with low surface tension is used to reduce the effect of capillary force on pore shrinkage. Therefore, the optimal washing process was designed as trichloroethylene (TCE)—0.5 M NH3.H2O—Propylene glycol methyl ether (PM) and gel microspheres with a high specific surface area of 315.3 m2/g and pore volume of 0.4125 cm3/g were obtained. The characterizations also further showed that when the microspheres were dried and sintered, the water vapor and the decomposition gas of organic matter were completely released from the pores in the microspheres. Our new washing process could be directly extended for preparing crack‐free ceramic microspheres by internal gelation.

Interface Chemical Modification between All-Inorganic Perovskite Nanocrystals and Porous Silica Microspheres for Composite Materials with Improved Emission.

In recent years, there has been rapid progress in the development of photonic devices based on lead halide perovskite nanocrystals since they possess a set of unique optical and charge transport properties. However, the main limiting factor for their subsequent application is poor stability against exposure to adverse environmental conditions. In this work, a study of a composite material based on perovskite CsPbBr3 nanocrystals embedded in porous silica microspheres is presented. We developed two different approaches to change the interface between nanocrystals and the surface of the microsphere pores: surface treatment of (i) nanocrystals or (ii) microspheres. The surface modification with tetraethylorthosilicate molecules not only increased stability but also improved the optical responses of the composite material. The position of the emission band remained almost unchanged, but its lifetime increased significantly compared to the initial value. The improvement of the optical performance via surface modification with tetraethylorthosilicate molecules also works for the lead-free Bi-doped Cs2AgInCl6 double perovskite nanocrystals leading to increased stability of their optical responses at ambient conditions. These results clearly demonstrate the advantage of a composite material that can be used in novel photonic devices with improved performance.

Manipulation of pore structure during manufacture of agarose microspheres for bioseparation.

Agarose microspheres with a controllable pore structure were manufactured by varying agarose types and crosslinking degrees. Various agarose could tailor the gel formation of microspheres matrix and thus affect the final pore structures. Small pores in microspheres could be fabricated by agarose with a higher molecular weight, which was demonstrated by the packed column with lower distribution coefficient (Kav) values measured by gel filtration chromatography. Further, higher Kav values also demonstrated that more and larger pores were formed with increasing the crosslinking degree of agarose microspheres. Either using agarose with a high molecular weight or increasing the crosslinking degree would finally lead to the enhancement of the flow rate during flow performance of packed column as necessary for improving separation efficiency. This provides a foundation for high‐resolution chromatography with a controllable separation range as beneficial for downstream process.

In situ pocket-type microcarrier (PMc) as a therapeutic composite: Regeneration of cartilage with stem cells, genes, and drugs

We prepared pocket-type micro-carriers (PMc) with pores larger than 30 μm for use in cell delivery by adding 40 mg pluronic F-127 copolymers (F-127) to biodegradable PLGA dissolved in dichloromethane solution. The controlling the size of the pockets in this way facilitates the adhesion of cells by regulating the size of the pockets according to the cells having various sizes. The size of PMc pores could be controlled within a range of 2 to 30 μm by varying the F-127 content. The ratio of F-127 to DOPA-bPEI was most appropriate at 1: 1, and the pocket size at 10 mg/ml of F-127 was appropriate for adhering 20–30 μm stem cells. F-127 containing SOX9 pDNA, in combination with DOPA-polyethylene–coated gold nanoparticles and dexamethasone loaded in PMcs, promoted cartilage differentiation. Gold nanoparticles complex and dexamethasone (DEX) loaded in PMcs were identified by micro-CT imaging and fluorescence imaging, respectively. By captured in pore generated on/in microspheres, the stem cells were safe and stable for use in delivery, both in vitro and in an animal model. Thus, microsphere pores can safely capture stem cells, and at the same time provide a microenvironment in which the captured stem cells can differentiate into chondrocytes.

Newly Designed Copolymers for Fabricating Particles with Highly Porous Architectures

A new type of designed copolymers has been synthesized for the formation of porous polymeric microspheres. The copolymers contain hydrophobic (styrene, methyl methacrylate, vinylbenzyl chloride, or vinylbenzyl ethyl ether) and hydrophilic (vinylbenzyl alcohol) repeating units. Since the specially designed copolymers have unique chemical and physical properties, the porous structure can be easily accomplished by a facile single-step process. The resulting porous microspheres exhibit good morphological quality, showing open pore structure with a pore size ranging from submicrometer to micrometer, by neither use of porogens nor the requirement of complicated multistep emulsifications. The discovery for the exceptional performance of pores in microspheres is exciting and groundbreaking. The chemical features of the proposed copolymers for the availability in the formation of porous architecture provide important insights into the design principle of high quality porous structures.

Raft polymerization ofN,N-dimethylacrylamide from magnetic poly(2-hydroxyethyl methacrylate) microspheres to suppress nonspecific protein adsorption

Nonspecific interaction is a key parameter affecting the efficiency of proteins, nucleic acids or cell separation. Currently, many approaches to introduce antifouling properties to materials have been developed. Among these, surface modification with polymer brushes plays a prominent role. The aim of this study was to synthesize new magnetic microspheres grafted with poly(N,N-dimethylacrylamide) (PDMA) that resist nonspecific protein adsorption. Monodisperse macroporous poly(2-hydroxyethyl methacrylate) (PHEMA) microspheres, 4 μm in size, were synthesized by a multiple swelling polymerization method. To render the microspheres magnetic, iron oxide was precipitated inside the microsphere pores. Functional carboxyl groups, introduced by the hydrolysis of the 2-(methacryloyl)oxyethyl acetate (HEMA-Ac) comonomer, were used to react with propargylamine, followed by coupling of a chain transfer agent via an azide-alkyne click reaction. PDMA was grafted from the PHEMA microspheres using reversible addition-fragmentation chain transfer polymerization (RAFT), resulting in surfaces with more than 81 wt % PDMA attached. The successful modification of the microspheres was confirmed by XPS. The magnetic microspheres grafted with PDMA showed excellent antifouling properties as tested in bovine serum protein solutions. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 1036–1043

Synthesis of polyethylenimine-functionalized poly(glycidyl methacrylate) magnetic microspheres and their excellent Cr(VI) ion removal properties

Micron-sized polyethylenimine-functionalized poly(glycidyl methacrylate) superparamagnetic microspheres (m-PGMA-PEI) were prepared by a process involving: (1) synthesis of PGMA microspheres using the dispersion polymerization method; (2) ring-opening reaction of epoxy groups on PGMA microspheres with ethylenediamine (EDA) to yield amino groups; (3) in situ coprecipitation of Fe3O4 nanoparticles into the pores of microspheres; (4) Michael addition of amino groups with methyl acrylate (MA) to yield ester groups; and (5) amidation of the terminal ester groups with polyethylenimine (PEI). Once generated, the resulting m-PGMA-PEI microspheres were tested for their ability to remove Cr(VI) from an aqueous solution in batch experiments. The results demonstrated that Cr(VI) adsorption was significantly pH dependent. The optimized pH value was 2.0. The adsorption isotherm of the adsorbent fit the Langmuir model, with the maximum adsorption capacity of 492.61mg/g. The Cr(VI) adsorption rate was rapid, and the adsorption reached equilibrium within 15min. The thermodynamic parameters (ΔG0, ΔH0, ΔS0) demonstrated that the adsorption process was endothermic and spontaneous in nature. The presence of the coexisting anions involving Cl−, NO3-, H2PO4- and HPO42- had no remarkable influence on Cr(VI) adsorption except SO42-. The regeneration study proved that the m-PGMA-PEI microspheres could be repeatedly utilized with no significant loss of adsorption efficiency.

Immunomagnetic sulfonated hypercrosslinked polystyrene microspheres for electrochemical detection of proteins

Poly(styrene-co-divinylbenzene) microspheres of narrow size distribution were prepared by (2-hydroxypropyl)cellulose-stabilized dispersion copolymerization of styrene and divinylbenzene in a 2-methoxyethanol/ethanol mixture under continuous addition of divinylbenzene. The copolymerization was initiated with dibenzoyl peroxide. The obtained microspheres were chloromethylated using several chloromethylation agents and then hypercrosslinked. Their porous structure was analyzed by nitrogen adsorption and mercury porosimetry. Superparamagnetic iron oxide nanoparticles were precipitated within the pores of microspheres from Fe(II) and Fe(III) chloride solution. The Fe content in the microspheres was determined by carbon analysis, atomic absorption spectroscopy and thermogravimetric analysis. Magnetic properties of the microspheres were characterized by magnetization curves and the temperature dependence of magnetic susceptibility. Finally, sulfo groups were introduced into the microspheres to prepare an immunomagnetic electrochemical biosensor for protein detection with ovalbumin as a model substance.

Adipose-Derived Stem Cell Delivery into Collagen Gels Using Chitosan Microspheres

Integration of stem cells to injured tissues requires an appropriate delivery device and scaffolding system. In the present study we have developed an in vitro strategy to load and release adipose-derived mesenchymal stem cells (ASC) from chitosan microspheres (CSM) into a collagen gel scaffold. Porous CSM of uniform size and composition were prepared and used as a stem cell carrier. ASC were allowed to attach to the microspheres and infiltrate through the microsphere pores. The number of viable cells was counted in vitro, using MTT and Calcein acetoxymethyl ester (AM) assays, and it showed a proportional increase with seeding density and reached a maximum cell number by 24 h. The cells inside the microspheres remained metabolically active and viable, could be retrieved from the spheres, and maintained expression of stem-cell-specific markers. Electron microscopic evaluation of the cell-microsphere complex showed that the CSM were able to support cell attachment and that the cells had infiltrated into the pores of the microspheres. The ability of the cells to proliferate and differentiate into adipogenic- and osteogenic-like precursors indicates that the cells have maintained their multipotency after migration out of the microspheres. To mimic cell delivery into a tissue, ASC-loaded CSM were embedded in type-1 collagen scaffold by mixing them with type-1 collagen solution while inducing gelation. By 14 days the cells released into the collagen gel and were able to populate the entire scaffold. When observed through transmission electron microscopy, the cells align along the collagen fibrils with a characteristic fibroblast-like morphology. This study provides a model to capture pluripotent stem cells, expand their cell number within a biomaterial scaffold in vitro, and deliver within an appropriate matrix to repair damaged tissue.

Composite tectocapsules via the self-assembly of functionalized poly(divinylbenzene) microspheres

Abstract Poly(divinylbenzene-55)[poly(DVB-55] microspheres were used as building blocks to form polymer capsule walls consisting of interconnected microspheres. The microspheres had to be surface-functionalized with maleic acid to facilitate their interfacial assembly. In addition, porous and functionalized poly(DVB-55) microspheres were embedded across interfacial polyurea capsule membranes to form composite tectocapsules where release of core materials is designed to occur through the microsphere pores, rather than by conventional wall diffusion. Electron microscopy and X-ray spectromicroscopy were used to characterize the wall compositions, and release data are presented to illustrate the role of microspheres acting as release portals.