Core-shell Polymer Microspheres Research Articles

Biocide-encapsulated core–shell polymer microspheres: A novel approach for preparing long-lasting antimicrobial coatings

Antimicrobial coatings play a crucial role in combating pathogenic microorganisms. However, developing long-lasting antimicrobial coatings presents substantial challenges. In this study, we developed a robust method for fabricating durable antimicrobial coatings using crosslinked, biocide-encapsulated core–shell polymer microspheres. These microspheres were prepared by emulsion polymerization, facilitating simultaneous synthesis and biocide loading. Designed with a hydrophilic shell and a hydrophobic core, the microspheres predominantly stored the hydrophobic biocides within the core, thus reducing the biocide concentration at the shell. This design, which is governed by Fickian diffusion, substantially slowed the rate of biocide migration from the shell to the external environment, thereby enhancing the coating's antimicrobial longevity. The synthetic process for these biocide-encapsulated microspheres was optimized to encapsulate biocides with a Log P range of 1–3, achieving an encapsulation efficiency exceeding 85 % for all tested biocides. Specifically, microspheres containing N-butyl-1,2-benzisothiazolin-3-one (BBIT) were used to develop an antimicrobial coating. The coating can be applied to various substrates, including glass, metal, wood, ceramics, and plastics. It exhibits excellent hardness, adhesion, mechanical strength, and solvent resistance on these surfaces. Antimicrobial tests and release analyses demonstrated that the coating maintains high biological activity for at least 10 months, effectively inhibiting bacterial and fungal growth. The release behavior of the coating adhered to the Peppas–Sahlin model, with diffusion as the predominant mechanism. The model predicted an antimicrobial retention rate of over 66 % after 1 year, confirming its sustained antimicrobial effectiveness.

Experimental Study on Injection and Plugging Effect of Core-Shell Polymer Microspheres: Take Bohai Oil Reservoir as an Example.

To meet the technical requirements of deep fluid diversion in Bohai oilfield, the swelling property, plugging effect, transport characteristics of polymer microspheres, and fluid diversion effect in heterogeneous cores are studied in this paper. There are two kinds of polymer microspheres including core–shell microspheres and traditional microspheres. The instruments used in this study include a biomicroscope, a metallurgical microscope, a scanning electron microscope, and core displacement experimental devices. The results of microscopes indicated that the core–shell microspheres were successfully synthesized, and the microspheres had good hydration expansion effect. The expanded microspheres could attract each other through the electrostatic force of anions and cations to achieve the purpose of coalescence. Compared with traditional microspheres (initial particle size is 3.8 μm), the initial particle size of the synthesized core–shell microspheres is close to 3.3 μm, but the particle size distribution is more concentrated, so the injection performance is close to that of traditional microspheres (initial particle size is 3.8 μm). After 8 days of hydration expansion, although the expansion multiple is small, it can coalesce and enhance the plugging effect, which can adapt to a wider range of permeability, ranging from 200 × 10–3 to 3000 × 10–3 μm2 (200 × 10–3–1500 × 10–3 μm2 for traditional microspheres). Under the same conditions (heterogeneous core), compared with the traditional microspheres, the core–shell microspheres have the characteristics of coalescence. Therefore, its fluid diversion effect is better, and the oil recovery is increased by 5.5%. Nevertheless, there is the “end effect” during the injection process, which weakens the steering effect of deep liquid flow. The results show that the “end effect” can be effectively reduced by alternate injection of microspheres and water. Meanwhile, the effect of deep fluid diversion is improved, and the increase of oil recovery is increased by 2.06%.

Preparation and properties of soil conditioner microspheres based on self-assembled potassium alginate and chitosan

Fulvic acid (FA), as one type of soil conditioner, can enhance drought tolerance, improve nutrient ingestion, stabilize pH values of soil, and reduce fertilizer extracting behaviors. Moreover, it shows a good effect on increasing the permissiveness of plants to various environments, and the stress of salinity and drought is included. Therefore, it can be used as an ideal soil conditioner. In order to extend its effect, it may be loaded into the core-shell polymer microspheres. In this study, FA was added to calcium carbonate (CaCO3) microspheres, potassium alginate (PAL) and chitosan (CS) were assembled outside. Thus, PAL/CS/FA-CaCO3 microspheres were prepared using layer-by-layer self-assembly methods. The surface morphology, encapsulation efficiency and in vitro drug release characteristics were investigated. It was revealed that PAL/CS/FA-CaCO3 microspheres were formed with a particle size distribution between 2 and 6 μm due to self-assembly between PAL and CS. Drug release behavior analysis exhibited the sustained release processes were delayed to varying degrees due to different degradation degrees of CaCO3 microspheres at different pH values. Results also illustrated that these microspheres had a high loading capacity for FA, and possessed good biodegradability. Thus, PAL/CS/FA-CaCO3 microspheres exhibited promise for future applications compared with that of traditional soil conditioners.

Tough, stretchable chemically cross-linked hydrogel using core–shell polymer microspheres as cross-linking junctions

A series of chemically cross-linked microgel composite hydrogels (MCH gels) with excellent toughness and stretchability were prepared using core–shell polymer microspheres as cross-linking junctions. In our strategy, MCH gels are obtained by connecting microspheres with polyacrylamide (PAAm) chains chemically grafted onto their surfaces, where an organic cross-linking agent is completely unnecessary. The mechanical behavior of the MCH gels was analyzed, and superresolution fluorescence microscopy and scanning electron microscopy were used to investigate their toughening mechanism. The results indicated that the homogeneous network structure resulting from the good compatibility between the core–shell microspheres and matrix was an important reason for the excellent toughness of the MCH gels. In addition to interactions among H bonds in the grafted PAAm chains, reversible deformation of the core–shell microspheres acting as cross-linking junctions, which arises from the flexibility of the microspheres, and the effect of cavitation between the microspheres and matrix could also effectively dissipate energy during deformation of the MCH gels.

Rapid and efficient enantioseparation of (S)-amlodipine by surface-imprinted core-shell polymer microspheres.

We present a protocol for the preparation of surface-imprinted polymer microspheres by core-shell precipitation polymerization for the enantioseparation of (S)-amlodipine. In this work, submicron mesoporous silica microspheres were prepared with gemini cationic surfactant as soft template. Molecularly imprinted polymers were coated on the silica supports with a low level of crosslinking, and the thickness of the thin-walled imprinted shell was about 45 nm. The material showed fast binding kinetics for (S)-amlodipine (within only 20 min for complete equilibrium), and the saturation adsorption capacity reached 309.2 mg/g, indicating the good accessibility of binding sites and improved mass transfer for target molecule. The imprinted microspheres exhibited an appreciable enantiomeric excess of (S)-amlodipine of 11.3% when used as a glass chromatography column for the enantioseparation of (S)-amlodipine from amlodipine besylate without extra chiral additives. The surface-imprinted materials display potentially amplification for industrial enantioseparation of (S)-amlodipine.

Long-Term Subconjunctival Delivery of Brimonidine Tartrate for Glaucoma Treatment Using a Microspheres/Carrier System.

Core-shell polymer microspheres with poly(d,l-lactic-co-glycolic acid) core and poly(l-lactic acid) (PLLA) shell are developed for the long-term subconjunctival release of brimonidine tartrate (BT) in order to reduce intraocular pressure (IOP) in the treatment of glaucoma. The PLLA-rich shell acts as a diffusion barrier, enabling linear release of BT over an extended period of 40 d. The microspheres are encased in a porous non-degradable methacrylate-based carrier for ease of subconjunctival implantation in a glaucoma-induced rabbit model. In vivo release of BT from the microspheres/carrier system has enabled a significant, immediate IOP reduction of 20 mmHg, which is sustained for 55 d. Long-term IOP reduction may be maintained by periodic replacement of the microspheres/carrier system.

Synthesis and Characterization of Dual-Functionalized Core-Shell Fluorescent Microspheres for Bioconjugation and Cellular Delivery

The efficient transport of micron-sized beads into cells, via a non-endocytosis mediated mechanism, has only recently been described. As such there is considerable scope for optimization and exploitation of this procedure to enable imaging and sensing applications to be realized. Herein, we report the design, synthesis and characterization of fluorescent microsphere-based cellular delivery agents that can also carry biological cargoes. These core-shell polymer microspheres possess two distinct chemical environments; the core is hydrophobic and can be labeled with fluorescent dye, to permit visual tracking of the microsphere during and after cellular delivery, whilst the outer shell renders the external surfaces of the microspheres hydrophilic, thus facilitating both bioconjugation and cellular compatibility. Cross-linked core particles were prepared in a dispersion polymerization reaction employing styrene, divinylbenzene and a thiol-functionalized co-monomer. These core particles were then shelled in a seeded emulsion polymerization reaction, employing styrene, divinylbenzene and methacrylic acid, to generate orthogonally functionalized core-shell microspheres which were internally labeled via the core thiol moieties through reaction with a thiol reactive dye (DY630-maleimide). Following internal labeling, bioconjugation of green fluorescent protein (GFP) to their carboxyl-functionalized surfaces was successfully accomplished using standard coupling protocols. The resultant dual-labeled microspheres were visualized by both of the fully resolvable fluorescence emissions of their cores (DY630) and shells (GFP). In vitro cellular uptake of these microspheres by HeLa cells was demonstrated conventionally by fluorescence-based flow cytometry, whilst MTT assays demonstrated that 92% of HeLa cells remained viable after uptake. Due to their size and surface functionalities, these far-red-labeled microspheres are ideal candidates for in vitro, cellular delivery of proteins.

Preparation of monodisperse fluorescent core–shell polymer microspheres with functional groups in the shell layer by two‐stage distillation–precipitation polymerization

AbstractMonodisperse crosslinked core–shell micrometer‐sized microspheres bearing a brightly blue fluorescent dye, carbazole, and containing various functional groups in the shell layers were prepared by a two‐stage distillation–precipitation polymerization in acetonitrile in the absence of any stabilizer. Commercial divinylbenzene (DVB), containing 80 vol.% of DVB, was polymerized by distillation–precipitation in acetonitrile without any stabilizer using 2,2′‐azobisisobutyronitrile (AIBN) as the initiator for the first stage of polymerization which resulted in monodisperse polyDVB microspheres used as the core. Several functional monomers, including 2‐hydroxyethyl methacrylate and acrylonitrile together with N‐vinylcarbazole blue fluorescent comonomer, were incorporated into the shell layers with AIBN as initiator during the second stage of polymerization. The resultant core–shell polymer microspheres were characterized using scanning electron microscopy, Fourier transform infrared spectroscopy, UV‐visible spectroscopy and fluorescence spectroscopy. Copyright © 2006 Society of Chemical Industry

Synthesis of core-shell polymer microspheres by two-stage distillation–precipitation polymerization

Narrow- or monodisperse core-shell polymer microspheres with a dense core and a lightly crosslinked shell with different functional groups, such as ester, hydroxyl, cyano, were prepared by two-stage distillation–precipitation polymerization without any stabilizer. Commercial divinylbenzene (DVB), containing 80% of DVB was polymerized by distillation–precipitation polymerization with 2,2′-azobis(2-methyl propionitrile) (AIBN) as initiator in neat acetonitrile in the absence of any stabilizer as the first stage polymerization and used as the core. When the conversion of DVB was about 35% in the first stage, the second-comonomers with different functional groups, such as methyl methacrylate (MMA), ethyl methacrylate (EMA), butyl methacrylate (BMA), 2-hydroxyethyl methacrylate (HEMA), i-octyl acrylate ( i-OA), dodecyl acrylate (DA), methyl acrylate (MA), ethyl acrylate (EA), ethylene glycol dimethacrylate (EGDMA), triethyleneglycol dimethacrylate (TEGDMA), trimethylolpropane trimethacrylate (Trim), and acrylnitrile (AN) together with AIBN were introduced, respectively, into the reaction system and copolymerized with unreacted DVB on the core surface to form a lightly crosslinked functional shell. The resulting core-shell polymer particles were characterized with scanning electron microscopy (SEM) and FT-IR spectra.

Carbon Nanotubes Prepared by Spinning and Carbonizing Fine Core-Shell Polymer Microspheres

Carbon nanotubes prepared from core–shell polymer particles are reported. As depicted in the Figure, polymethylmethacrylate (PMMA) core/polyacrylonitrile (PAN) shell microspheres are blended with a PMMA matrix, spun, and elongated. Then the shell is stabilized and finally carbonized to produce contaminant-free carbon nanotubes.

Architecture of Polymeric Superstructures: Self-Color Tone Films Constructed by Mesoscopically Ordered Cubic Lattices

Graft polymerization of photofunctional core–shell polymer microspheres of polystyrene-block-poly(4-vinylpyridine) in methyl methacrylate locks the microspheres in a body-centered cubic arrangement and yields a polymeric superstructure that exhibits a blue color tone (see picture). Similar optical properties are also observed in a diblock polymer with a lamellar morphology.

Architecture of polymeric superstructures: Locking of cubic lattices by graft polymerization from photofunctional core-shell polymer microspheres

It is well known that submicron-size colloidal spheres form a body-centered cubic (BCC) or face-centered cubic (FCC) lattice in an aqueous solution [1–5]. More recently, Asher et al. [6] have developed an approach to permanently lock in the crystalline colloidal array ordering in a hydrogel matrix. We have also constructed polymeric superstructures by free radical polymerization of N-vinylpyrrolidone (VP) monomer as a matrix, after polypyrrole microspheres were arranged on a BCC lattice in VP monomer solution [7]. More recently, we demonstrated that the core-shell polymer microspheres [8] and highly armed star polymers [9] led to hierarchical structure transformation of the cubic lattices. That is to say, these radial branched polymers formed a lattice with a BCC structure near the overlap threshold (C∗). In the bulk of the film, this structure changed to a FCC lattice. After such branched polymers formed a cubic lattice in polymerizable vinyl monomer, the polymeric superstructures were locked permanently into an ordered lattice in a solid matrix by means of free-radical polymerization [10, 11]. This technique is one of the best methods for creating nanoscopic polymeric superstructures composed of three or two phase-separated microdomains. However, the microspheres exhibiting relatively large particle diameter were packed with irregular arrangement in places due to polymerization-induced phase separation. In this communication, we report the architecture of polymeric superstructure films formed by locking of polymer matrix by means of graft polymerization from photofunctional core-shell polymer microspheres. The well-defined polystyrene-block-poly(4-vinylpyridine) (PS-block-P4VP) diblock copolymer (SV: Mn = 7.27× 104, P4VP block 26.7 mol%) was prepared by the sequential anionic polymerization technique. The details concerning the synthesis, purification and characterization of diblock copolymers have been given elsewhere [12]. Fig. 1a shows the transmission electron microscopy (TEM) photograph of SV specimen cast from toluene. The dark portions are the P4VP phases selectively stained with OsO4. The morphological structure showed the dispersed P4VP spheres in a PS matrix. Core-shell polymer microspheres (SV-M) were synthesized by crosslinking the segregated chains in P4VP spherical microdomains with 1,4-dibromobutane (DBB) vapor at room temperature. The details concerning the synthesis and the characterization of such microspheres have been given previously [13]. Characteristics of the SV-M microsphere are listed in Table I. The crosslink density of P4VP cores was 30.3 mol%. Fig. 1b shows a TEM photograph of SV-M cast from 1.0 wt% toluene solution. This specimen corresponds to the restructural film from the core-shell microspheres. It is found from this photograph that dark crosslinked P4VP cores (average diameter Dc = 30.2 nm) with a narrow size distribution are dispersed in a PS matrix. It was also mentioned previously from small-angle Xray scattering (SAXS) measurements that P4VP cores were packed with a FCC arrangement in a bulk film [8]. The hydrodynamic diameter (DH = 96.9 nm) of microspheres was determined by means of dynamic light scattering (DLS). The C∗ [14] of the SV-M in benzene was calculated to be 11.9 wt% from the DH and total molecular weight of the microsphere. Photofunctional core-shell microspheres (SV-MP) were prepared as follows. The PS shell of parent

Synthesis and structural ordering of core–shell polymer microspheres

Synthesis and structural ordering of core–shell polymer microspheres

Architecture of polymeric superstructures formed by locking cubic lattices of core-shell polymer microspheres

Poly (4-vinylpyridine) (P4VP) core-policy (α-methylstyrene) shell polymer microspheres have been synthesized by cross-linking the P4VP spherical microdomains of poly (α-methylstyrene-b-4-vinyl-pyridine) diblock copolymer films with 1,4-dibromobutane. These microspheres formed a lattice with a body-centred cubic structure near the overlap concentration. In the bulk of as-cast film of microspheres, this structure changed to a face-centred cubic lattice. After these microspheres formed a cubic lattice in methyl methacrylate (MMA) monomer, the polymeric superstructures were constructed by locking permanently ordered lattice in a solid matrix by means of free radical polymerization of MMA monomer. This technique is one of the best methods for creating nanoscopic polymeric superstructures composed of three phase-separated microdomains. © 1997 Elsevier Science Ltd.