Spherical CaCO3 Research Articles

Synthesis of High-Precision Sub-Micron CaCO3 Anticancer Drug Carriers from Coral Remains

Calcium carbonate (CaCO3) particles have attracted increasing attention as a promising material for drug delivery systems. In this study, coral remains were utilized as a raw material for a novel drug carrier. A series of pre-treatment and parameter experiments were conducted to synthesize sub-micron spherical CaCO3 particles. The CaCO3 particles exhibited uniform size distribution, with the minimum mean size being only 344 nm. The effects on the CaCO3 crystal phases and particle sizes were also discussed in this study. Drug loading experiments were also conducted to assess the feasibility of the CaCO3 drug carrier. We loaded TRITC-Dextran into CaCO3 particles for the simulation experiments. The loading capacity reached up to 9.6 wt.%, which was as high as common drug carriers such as liposomes. In this study, we aimed not only to tackle the local environmental issues caused by coral remains, but also to synthesize a suitable drug carrier for cancer therapy using the outstanding properties and low cost of CaCO3.

Tailoring microstructure of superabsorbent film for active food packaging using carboxy methyl cellulose and biogenic vaterite CaCO3–Ag hybrid microspheres

Eliminating microbial growth and preventing food degradation from excess moisture is an important technological advance in packaging. This article describes the development of a novel antimicrobial superabsorbent pad for food packaging, which uses carboxy methyl cellulose (CMC) as a polymer matrix and biogenic vaterite calcium carbonate microspheres loaded with AgNPs (CaCO3–Ag). The spherical vaterite CaCO3–Ag hybrid was obtained by precipitating CaCO3 from discarded eggshells in silver colloid. The vaterite CaCO3–Ag microspheres were incorporated into the CMC matrix, which underwent physical cross-linking initially and was further chemically cross-linked during film surface treatment. The resulting three-layer film exhibits improved hardness and modulus of 0.09 and 3.30 GPa, respectively. The crystallinity was enhanced, and water absorption capacity attained was 13.87 times of film weight. The antimicrobial activity with inhibition zones of 6 and 14 mm against Escherichia coli and minced pork bacteria, makes it suitable for use as an antimicrobial superabsorbent pad in meat packaging applications.

Polyelectrolyte Microcapsules as a Tool to Enhance Photosensitizing Effect of Chlorin E6

Introduction: Photodynamic therapy is a promising method of tumors treatment using photosensitizers and light of a certain wavelength. PS modification improves and enhances the phototoxic effect with decreased dark cytotoxicity. Materials and Methods: We compared the photosensitizing effect of polyelectrolyte microcapsules with chlorin E6 (ClE6) and free ClE6 at equivalent concentrations on murine fibroblast culture L929 using in vitro tests. Microcapsules were prepared layer by layer, sequentially depositing oppositely charged polyelectrolytes onto spherical CaCO3 particles. Cellular uptake of capsules was assessed using confocal microscopy. MTT test was used for a study of cell viability, and the relative amount of ROS was determined by the fluorescent method. Results: Microcapsules with ClE6 (in all tested concentrations) after exposure to red light (660 nm) reduced cell viability from 20% to 5%, while these capsules did not have dark cytotoxicity. Free ClE6 at the same concentrations as in the capsules after irradiation reduced viability from 65% to 35%. The level of ROS in the group of cells with capsules was 2 times higher compared to the group with CLE6. Discussion: The most probable mechanism of toxicity increase is creation of a higher ROS concentration and effect localization in the area of microcapsule interaction with the cell membrane. ROS production activation may stem from capsules providing a higher local PS concentration in the cell or nearby than the drug’s free form. Conclusion: The inclusion of chlorin E6 in polymer capsules reduced dark toxicity and increased the photosensitizing effect compared to the free form of ClE6.

Spherical CaCO3: Synthesis, Characterization, Surface Modification and Efficacy as a Reinforcing Filler in Natural Rubber Composites

Natural rubber (NR), an important natural polymer derived from the Hevea brasiliensis tree, has been widely used in the rubber industry owing to its excellent elastic properties. However, it requires reinforcing fillers to improve its mechanical properties for the manufacturing of rubber products. Generally, calcium carbonate (CaCO3) is employed as a non-reinforcing filler. This work aimed to synthesize spherical-shaped CaCO3 at a submicrometric scale without and with surface treatment and explore its utilization as a reinforcing filler in NR composites. The morphological shape and polymorphic phase of CaCO3 were investigated using SEM, TEM, XRD, ATR-FTIR and Raman techniques. The mechanical properties of various amounts (0 to 60 phr) of CaCO3-filled NR composites were explored. As a result, the NR/treated CaCO3 composites provided higher tensile strength than the NR/untreated CaCO3 composites and pure NR at all filler loadings. This may have been due to the improved interfacial interaction between NR and CaCO3 with the improved hydrophobicity of CaCO3 after treatment with olive soap. The optimal filler loading was 20 phr for the highest tensile strength of the rubber composites. In addition, the elongation at break of the NR/treated CaCO3 was slightly decreased. Evidence from SEM and FTIR revealed the vaterite polymorph and shape stability of CaCO3 particles in the NR matrix. The results demonstrate that the particle size and surface treatment of the filler have essential effects on the mechanical property enhancement of the rubber composites. Synthesized spherical CaCO3 could be a potential reinforcing filler with broader application in polymer composites.

Preparation and Characterization of Thermal-Insulating Microporous Breathable Al/LLDPE/CaCO3 Composite Films.

Breathable films were prepared based on linear low-density polyethylene (LLDPE), calcium carbonate (CaCO3), and aluminum (Al; 0, 2, 4, and 8 wt.%) using extrusion molding at a pilot scale. These films must generally be able to transmit moist vapor through pores (breathability) while maintaining a barrier to liquids; this was accomplished using properly formulated composites containing spherical CaCO3 fillers. The presence of LLDPE and CaCO3 was confirmed by X-ray diffraction characterization. Fourier-transform infrared spectroscopy results revealed the formation of Al/LLDPE/CaCO3 composite films. The melting and crystallization behaviors of the Al/LLDPE/CaCO3 composite films were investigated using differential scanning calorimetry. Thermogravimetric analysis results show that the prepared composites exhibited high thermal stability up to 350 °C. Moreover, the results demonstrate that surface morphology and breathability were both influenced by the presence of various Al contents, and their mechanical properties improved with increasing Al concentration. In addition, the results show that the thermal insulation capacity of the films increased after the addition of Al. The composite with 8 wt.% Al showed the highest thermal insulation capacity (34.6%), indicating a new approach to transform composite films into novel advanced materials for use in the fields of wooden house wrapping, electronics, and packaging.

Hollow spherical vaterite calcium carbonate prepared by spray-bubble template method for immobilization of papain

Calcium carbonate (CaCO3) possesses unique advantages as a carrier , however, some critical issues need to be addressed, such as low productivity, irregular structures, and weak adsorption ability. Herein, hollow spherical vaterite CaCO3 (HSVC) was synthesized in an improved spray apparatus with high mass transfer using carbon dioxide (CO2) as a template and was in turn applied for papain immobilization. Results revealed that HSVC can be prepared cleanly and efficiently with a regular spherical morphology having a surface area of 17.03 m2·g−1 and immobilization amount of 1068 mg·g−1 for papain. Interestingly, the pH stability, temperature stability and reusability of papain were dramatically improved after immobilization by HSVC. Molecular dynamics simulation (MDS) disclosed that the formation of CO32– and Ca2+ ion pairs was the key factor for the preparation of HSVC and the binding energy (BE) between amino acid molecules and vaterite (110) facilitated the ultra-high adsorption of papain. The decrease in BE of system after immobilization facilitated high catalytic capacity of the immobilized papain. The prepared HSVC exhibits promising prospects in enzymes immobilization based applications.

Synthesis of hollow fibroin using calcium carbonate as a template

AbstractSilk fibroin is a unique biomaterial and has gained much attention in biomedical applications. In this study, we have demonstrated the formation of hollow fibroin using the selective etching method. Initially, spherical CaCO3 was synthesized in the presence of polyelectrolyte, poly(4‐styrenesulfonate). CaCO3 particles were treated with aqueous silk fibroin solution, followed by methanol treatment. The sequential deposition of silk fibroin was achieved through a layer‐by‐layer (LbL) strategy to obtain fibroin‐encapsulated CaCO3. Finally, the fibroin‐ encapsulated CaCO3 was treated with an acid solution to form hollow fibroin. The crystalline phase of as‐prepared products was measured using powder X‐ray diffraction, and vibrational modes of products were characterized using Fourier transform infrared spectroscopy. The hollow fibroin morphology was examined using electron microscopy. The resultant hollow fibroin has good stability and can be explored in various applications.

Preparation of high-purity vaterite CaCO3 from lead-zinc tailings

This study introduced a green scheme for high value treatment of lead-zinc tailings, which produced high-purity vaterite from lead-zinc tailings. The effects of different experimental parameters on the leaching and carbonization of Ca2+ in lead-zinc tailings were discussed. It was found that the optimum leaching ratio of Ca2+ in NH4Cl solution was 74.87% and the optimum carbonization ratio of Ca2+ in the leaching solution was 96.96%. The spherical CaCO3 with d50 < 10 μm, 99.41% purity, and 98.70% whiteness was prepared under suitable carbonization conditions. The XRD results showed that the CaCO3 product was high purity vaterite. The presence of NH4+ and Zn2+ in the leaching solution hindered the transformation of vaterite into calcite, leading to the formation of high-purity vaterite CaCO3. The SEM results indicated that the dispersants STP or PEG-6000 could improve the dispersion of vaterite, and STP contributed to the formation of fine particle vaterite. This method proposed an approach for the production of vaterite from lead-zinc tailings, broad application prospects.

A promising strategy for the large-scale preparation of spherical calcium carbonate by efficiently using carbon dioxide

Spherical calcium carbonate (CaCO3) is widely used in industries. However, its large-scale synthesis still remains a challenging issue. Herein, we report the preparation of spherical CaCO3 at a high calcium hydroxide (Ca(OH)2) concentration (1.08 M) using CO2 highly efficiently in methanol (CH3OH)-water mixed solvent with polyethyleneimine (PEI) as a crystal modifier by carbonation method. Experimental results revealed that the introduction of CH3OH in the reaction systems decreased the saturation Ca2+ concentration in the solvent, and then formed spherical CaCO3 under the controlled action of PEI. Besides, spherical CaCO3 with a particle size of about 1 µm can be obtained at concentration of Ca(OH)2 of 1.08 M, PEI of 5 g/L, and CH3OH volume content of 30%, stirring rate of 450 rpm, and CO2 flow rate of 1.4 m3/h. The formation mechanism of spherical CaCO3 indicated that the particles converted from an initial amorphous precursor, to needle-like, bundle-like, block-like and hemispherical shaped aggregates, and finally to a complete spherical CaCO3 morphology. This research provides an effective method for the preparation of high yield spherical CaCO3 by industrial carbonation method.

N-(2-hydroxyl)-propyl-3-trimethylammonium chitosan chloride/carboxymethyl cellulose films filled with in-situ crystallized calcium carbonate

The research and development of substitutes for petroleum-based plastics has become a hot topic. The N-(2-hydroxyl)-propyl-3-trimethylammonium chitosan chloride (HTCC, 10 wt%)/sodium carboxymethyl cellulose (CMC) films have showed enhanced mechanical properties, which also provide a potential substitute to petroleum-based plastics. In this paper, calcium carbonate was crystallized (cry-CaCO3) in HTCC/CMC film-forming solutions, and the effects of the cry-CaCO3 particles on HTCC/CMC film properties including microstructures, mechanical properties, thermal stability, whiteness, and wettability were characterized. An HTCC/CMC film with commercially available CaCO3 (com-CaCO3) was used as a control. The results showed that the cry-CaCO3 promoted the homogeneous distribution of the HTCC/CMC matrix and significantly improved mechanical properties, but showed little effect on the thermal stability, whiteness and wettability of the films. To reveal the affecting mechanism of cry-CaCO3 on HTCC/CMC film properties, the cry-CaCO3 particles were isolated from film-forming solutions and characterized by scanning electron microscope (SEM), powder X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), thermogravimetric analysis (TGA) methods. The results showed that the HTCC/CMC matrix modulated spherical CaCO3 particles, and the macromolecules were encapsulated in cry-CaCO3 particles, decreasing their adhesion to the HTCC/CMC matrix while increasing their distribution in the HTCC/CMC matrix. The strong electrostatic, hydrogen bonding and flexible interaction between CMC and cry-CaCO3 particles played a key role in improving the mechanical properties of HTCC/CMC films.

Calcium Carbonate@silica Composite with Superhydrophobic Properties.

In this paper, spherical calcium carbonate particles were prepared by using CaCl2 aqueous solution + NH3·H2O + polyoxyethylene octyl phenol ether-10 (OP-10) + n-butyl alcohol + cyclohexane inverse micro emulsion system. Then, nanoscale spherical silica was deposited on the surface of micron calcium carbonate by Stöber method to form the composite material. Scanning electron microscope (SEM), X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS) were used to characterize the morphology and structure of the composite material. It is found that the surface of the composite material has a micro-nano complex structure similar to the surface of a “lotus leaf”, making the composite material show hydrophobicity. The contact angle of the cubic calcium carbonate, spherical calcium carbonate and CaCO3@SiO2 composite material were measured. They were 51.6°, 73.5°, and 76.8°, respectively. After modification with stearic acid, the contact angle of cubic and spherical CaCO3 were 127.1° and 136.1°, respectively, while the contact angle of CaCO3@SiO2 composite was 151.3°. These results showed that CaCO3@SiO2 composite had good superhydrophobicity, and the influence of material roughness on its hydrophobicity was investigated using the Cassie model theory.

Characterization of a Novel CaCO3-Forming Alkali-Tolerant Rhodococcus erythreus S26 as a Filling Agent for Repairing Concrete Cracks.

Biomineralization, a well-known natural phenomenon associated with various microbial species, is being studied to protect and strengthen building materials such as concrete. We characterized Rhodococcus erythreus S26, a novel urease-producing bacterium exhibiting CaCO3-forming activity, and investigated its ability in repairing concrete cracks for the development of environment-friendly sealants. Strain S26 grown in solid medium formed spherical and polygonal CaCO3 crystals. The S26 cells grown in a urea-containing liquid medium caused culture fluid alkalinization and increased CaCO3 levels, indicating that ureolysis was responsible for CaCO3 formation. Urease activity and CaCO3 formation increased with incubation time, reaching a maximum of 2054 U/min/mL and 3.83 g/L, respectively, at day four. The maximum CaCO3 formation was achieved when calcium lactate was used as the calcium source, followed by calcium gluconate. Although cell growth was observed after the induction period at pH 10.5, strain S26 could grow at a wide range of pH 4–10.5, showing its high alkali tolerance. FESEM showed rhombohedral crystals of 20–60 µm in size. EDX analysis indicated the presence of calcium, carbon, and oxygen in the crystals. XRD confirmed these crystals as CaCO3 containing calcite and vaterite. Furthermore, R. erythreus S26 successfully repaired the artificially induced large cracks of 0.4–0.6 mm width.

Synthesis and Characterization of Spherical Calcium Carbonate Nanoparticles Derived from Cockle Shells

Cockle shells are a natural reservoir of calcium carbonate (CaCO3), which is widely used in bone repair, tissue scaffolds, and the development of advanced drug delivery systems. Although many studies report on the preparation of CaCO3, the development of a nanosized spherical CaCO3 precursor for calcium oxide (CaO) that is suitable to be incorporated in dental material was scarce. Therefore, this study aimed to synthesize a nanosized spherical CaCO3 precursor for CaO derived from cockle shells using a sol–gel method. Cockle shells were crushed to powder form and mixed with hydrochloric acid, forming calcium chloride (CaCl2). Potassium carbonate (K2CO3) was then fed to the diluted CaCl2 to obtain CaCO3. The effect of experimental parameters on the morphology of CaCO3, such as volume of water, type of solvents, feeding rate of K2CO3, and drying method, were investigated using field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffractometry (XRD), Brunauer–Emmett–Teller surface area analysis, and thermogravimetric analysis. Optimized CaCO3 was then calcined to form CaO. XRD analysis of CaCO3 nanoparticles was indicative of the formation of a calcite phase. The well-structured spherical shape of CaCO3 was obtained by the optimum condition of the addition of 50 mL of water into CaCl2 in ethanolic solution with a 1 h feeding rate of K2CO3. Less agglomeration of CaCO3 was obtained using a freeze-drying technique with the surface area of 26 m2/g and average particle size of 39 nm. Spherical shaped nanosized CaO (22–70 nm) was also synthesized. The reproducibility, low cost, and simplicity of the method suggest its potential applications in the large-scale synthesis of the nanoparticles, with spherical morphology in an industrial setting.

DRY SLIDING FRICTION and WEAR PROPERTIES of CACO3 NANOPARTICLE FILLED EPOXY/CARBON FIBER COMPOSITES

Metal/Fiber reinforced polymer (FRP) composite joints with lower friction coefficients are increasingly replacing metal-metal couples in a variety of fields. The wear performance of metal / FRP tribo-contacts becomes a key design parameter for their service life and the improvement in the wear performance of metal-FRP friction pairs is needed to extend their applications. In this paper, sliding friction and wear characteristics of carbon fiber reinforced epoxy composites against metallic counterparts were investigated. Tests were performed on a ball-on-disk tester at a constant normal load and velocity against chromium steel under dry ambient. Moreover, CaCO3 nano reinforcements were introduced into carbon/epoxy composites to improve their wear performance. The coefficient of friction (65%) and the specific wear rate (75%) were drastically reduced with the addition of CaCO3 nano reinforcements. Worn surfaces were analyzed by scanning electron microscopy (SEM) to evaluate the wear mechanisms. It was concluded that the abrasion dominated wear mechanism of the bare carbon/epoxy composites transformed into adhesion for the multi-scale composites which are responsible for the increased wear performance. This impact was most likely attributed to two main factors: spherical CaCO3 particles facilitate sliding and act as a solid lubricant.

Spherical vaterite microspheres of calcium carbonate synthesized with poly (acrylic acid) and sodium dodecyl benzene sulfonate

Calcium carbonate (CaCO3) microspheres of vaterite polymorph were successfully obtained by combining calcium chloride (CaCl2) and sodium carbonate (Na2CO3) in the presence of poly (acrylic acid) (PAA) and sodium dodecyl benzene sulfonate (SDBS). The experimental results suggested that increasing the SDBS concentration could inhibit the growth of calcite and promote the formation of vaterite. Meanwhile, the molar content of vaterite was also influenced by reaction temperature and PAA concentration. It was proposed that vaterite CaCO3 was obtained via calcium ions adsorbed on the PAA-SDBS complexes by electrostatic interaction, and studies on the formation mechanism showed that PAA-SDBS complexes could provide the templates for vaterite CaCO3 and prevent the metastable vaterite CaCO3 transforming to calcite CaCO3 through dissolution-recrystallization process. This research provides a way for industrial preparation of spherical vaterite CaCO3.

A new route to synthesize calcium carbonate microspheres from phosphogypsum

In this work, monodisperse spherical vaterite calcium carbonate (CaCO3) was synthesized at room temperature and atmospheric pressure through a simple and efficient ‘phase transfer-precipitation’ route using phosphogypsum (PG) as raw material, sodium gluconate(SG) as phase transfer agent and CO2 as precipitator. CaCO3 samples were characterized by Field-emission scanning electron microscopy (FE-SEM), x-ray diffraction (XRD), and Dynamic light scattering (DLS). The composition of the as-obtained sample was almost monodisperse spherical vaterite CaCO3 by adjusting the concentration of SG and other operational conditions. The effects of SG and STP on the formation of CaCO3 microspheres were investigated. The results indicated that the existence of SG inhibited the nucleation and growth of calcite but promoted the formation of vaterite. The effects between SG and Ca2+ played a key role in the formation process of monodisperse spherical vaterite CaCO3. The existence of STP can effectively control the further growth and enhance the uniformity of the particle size of CaCO3 microspheres. These studies are promising for the industrial preparation and further commercial applications of monodisperse spherical vaterite CaCO3.

A study by response surface methodology (RSM) on optimization of phosphorus adsorption with nano spherical calcium carbonate derived from waste.

A nano spherical CaCO3 (NSC) derived from solid waste (precipitated from tris(α-chloropropyl) phosphate and triethyl phosphate mixed wastewater) was prepared as adsorbent for phosphorus removal from aqueous solution. Response surface methodology (RSM) was used to develop an approach for the evaluation of phosphorus adsorption process, and Box-Behnken design was performed to investigate the effects of various experimental parameters (temperature, contact time, initial pH and dosage of absorbent) on phosphorus adsorption. The model results of experimental data gave a high correlation coefficient (R2 = 0.9658), and a predictive model of quadratic polynomial regression equation and optimum level values were established successfully. It was found that the adsorption efficiency and adsorption capacity reached 97.05% and 123.79 mg/g, respectively, under conditions of temperature of 45 °C, initial pH 5.3, contact time of 11 h, and absorbent amount of 392 mg/L. X-ray diffraction (XRD) analysis testified new phase, Ca10(PO4)6CO3, was produced in the adsorption process. Apart from that, adsorption behavior fitted well with the Langmuir isotherm model and logistic growth model. The thermodynamic study indicated that phosphorus removal by NSC as adsorbent was a spontaneous, endothermic, and mainly chemical adsorption process.

Effect of particle morphology on mechanical properties of liquid marbles

In order to better understand the influence of the shape of solid particles on the stability of liquid marbles, we investigated liquid marbles stabilized by hydrophobized calcium carbonate particles with spherical and rod-shaped morphologies. Static properties, such as the effective surface tension, and the dynamic behavior i.e. the compression-decompression features for several cycles of the liquid marbles were investigated. Liquid marbles stabilized with spherical CaCO3 particles show an elastic response to mechanical deformation almost up to collapse. In contrast, liquid marbles prepared with rod-like particles exhibit a more plastic response to compression. It is concluded that the main differences in behavior of the prepared liquid marbles arise from how the solid particles can arrange/orient at the air/water interface.

Preparation and characterization of calcium carbonate microspheres and their potential application as drug carriers.

The influence of lecithin from egg yolk (LE) on calcium carbonate (CaCO3) biomineralization was investigated. In the present study, spherical CaCO3 particles were synthesized via coprecipitation in the presence of LE. LE multilamellar liposomes were first tuned by sonication to provide better control over the nucleation of CaCO3. Subsequently, monodisperse microspheres ~2µm in size were generated by controlling the aggregation and growth of CaCO3 under appropriate concentrations of LE. In contrast to unstable vaterite, the microspheres generated in aqueous solution remained stable for at least 10days without transforming into calcite, due to the strong interaction between the LE and calcium ions. The microspheres as drug carriers of doxorubicin (DOX) were assessed and were observed to have a good encapsulation efficiency, sustained drug release without a burst release and notable pH sensitivity. In addition, invivo tumor inhibition examination demonstrated that DOX‑loaded CaCO3 microspheres formulation had more superior efficacy to significantly restrain tumor growth. These novel LE/CaCO3 hybrids may provide novel options for various biomedical applications.

Facile fabrication of varisized calcium carbonate microspheres as vaccine adjuvants.

Functional calcium carbonate (CaCO3) particles of micron and submicron sizes used in catalysis and biomedicine have attracted considerable attention for decades. In this paper, the process parameters for CaCO3 crystallization were systematically investigated. Our experimental results demonstrated the significance of temperature during fabrication. Under the optimized conditions, various uniform-sized and spherical CaCO3 microparticles (MPs) with average diameters from 0.8 μm to 5 μm were facilely and rapidly fabricated via different mixing strategies including mechanical stirring, homogenization, and ultrasonication. The physicochemical characteristics of the CaCO3 microspheres were evaluated. And, the hepatitis B surface antigen (HBsAg) used as a model antigen was encapsulated into the particles (1 μm and 4 μm) for investigating the immune responses elicited after vaccination. In vitro, dendritic cells (DCs) were significantly activated by the MP-based vaccine formulations with up-regulated co-stimulatory molecules expression of CD40 and CD83. After immunization, CaCO3 MPs loaded with HBsAg induced greater lymphocyte activation, more cytokine secretion, higher antigen-specific IgG titers and more memory T cell generation to protect against reinfection. Therefore, the CaCO3 MPs, especially the 1 μm particles, could induce strong cellular and humoral immune responses, probably because of easier uptake and more efficient antigen-presentation by DCs. With the advantages of good biocompatibility, high loading capacity and easy preparation, they could be potentially useful as vaccine adjuvants. These results might provide further design principles for potent inorganic particulate adjuvant and delivery systems.