Evolution of a Polydisperse Ensemble of Ellipsoidal Crystals with Fluctuating Growth Rates in Supercooled Melts

In this paper, an analytical solution to the model of the evolution of ellipsoidal crystals with fluctuating growth rates at the intermediate step of bulk phase transition is presented. A complete system of integrodifferential equations describing the problem was derived and analytically solved using the Laplace integral method. The kinetics of supercooling removal in melts has been found. The particle-volume distribution function represents a pike-shaped curve decreasing its maximum with time. It is demonstrated the differences in the distribution function for ellipsoidal and spherical crystals.

Environmentally benevolent synthesis and characterization of silver nanoparticles using Olea ferruginea Royle for antibacterial and antioxidant activities

In this study, we reported an easy, rapid, cost-effective and environmentally benign method for the fabrication of silver nanoparticles (Ag-NPs) using Olea ferruginea as reducing, capping and stabilizing agent. For this, an aqueous extract of leaf and bark of O. ferruginea was treated with 1 mM AgNO3, which reduces Ag ions to Ag-NPs by establishing reddish brown color. The synthesized Ag-NPs were spherical crystals, with a mean size of 23 and 17 nm for leaf- and bark-mediated Ag-NPs, respectively. Fourier transform infrared spectroscopy affirmed the role of leaf and bark extracts of O. ferruginea as reducing, capping and stabilizing agent. These biosynthesized Ag-NPs showed profound antibacterial activity against Gram-negative (Pseudomonas aeruginosa and Escherichia coli) and Gram-positive (Streptococcus pneumonia and Staphylococcus aureus) bacteria. The highest antibacterial activity was shown by bark Ag-NPs against S. aureus (14.00 mm), while leaf Ag-NPs showed higher activity against S. pneumonia (13.00 mm). Additionally, they produced effective antioxidant activity against 2,2-diphenyl-1-picrylhydrazyl (DPPH) as compared to plant extracts and positive control. It was observed that the bark-mediated Ag-NPs had higher percentage (90%) of scavenging potential than the leaf-mediated Ag-NPs (78%). The significance of the current study is the synthesis of eco-friendly, easy and cost-effective Ag-NPs as biomedical products.

Hollow and Solid Spherical Azithromycin Particles Prepared by Different Spherical Crystallization Technologies for Direct Tableting

Many drugs have a propensity for agglomeration, resulting in poor flowability. Spherical crystallization can be used to improve product properties including flowability and particle size. In this work, two methods were developed and utilized to successfully make two kinds of azithromycin spherical particles, namely solid and hollow spheres. The resultant product exhibited regular spherical shape, large particle size, narrow particle size distribution and excellent flowability. The formation mechanism of these different spherical crystals was investigated with the help of a particle vision microscope (PVM). The immersion mechanism and the counter diffusion mechanism were proposed as the formation mechanisms for solid and hollow spheres, respectively. The effects of crystallization parameters on the spherical crystallization processes were investigated systematically. Furthermore, the tablet properties were evaluated to verify that the spherical particles obtained in this work can be directly used for tableting, thus avoiding granulation processes and reducing cost.

On the theory of the unsteady-state growth of spherical crystals in metastable liquids

Motivated by a large number of applications, we consider the process of non-stationary growth of spherical crystals in a supercooled binary melt. The moving-boundary problem describing the unsteady-state distributions of temperature and impurity concentration around the growing crystal as well as the dynamics of its radius and growth rate is solved by means of the methods of small-parameter expansion and Laplace–Carson integral transform. We show that the growth rate of crystals contains the main contribution (which is proportional to the supercooling degree Δ) and the first correction (which is proportional to Δ 2 t , where t is time). The second correction is also found. The non-stationary temperature and concentration fields are determined as power functions of Δ and t . We demonstrate that the first corrections to the dynamics of crystal radius R ( t ) and its growth rate V ( t ) play an important role. It is shown that R ( t ) and V ( t ) can change more than twice in comparison with the previously known steady-state solution with the course of time. Such a behaviour will significantly modify the dynamics of a polydisperse ensemble of crystals evolving in a metastable liquid. This article is part of the theme issue ‘Heterogeneous materials: metastable and non-ergodic internal structures’.

Spherical Crystallization: An Overview

Introduction: In 1986, Kawashima developed the spherical crystallization technique for size enlargement of drugs in the field of pharmacy. Spherical crystallization is defined as “An agglomeration process that transforms crystalline drug directly into compact spherical forms for improving the flowability, solubility and compactability”. Methods: General methods for preparing spherical crystallization are spherical agglomeration, emulsion solvent diffusion method, ammonia diffusion method and neutralization method. Factors controlling the process of agglomeration include solubility profile, mode and intensity of agitation, temperature of the system and residence time. Results: Spherical crystals can be characterized by Optical microscopy, X-ray powder diffraction, Electron scanning microscopy, Fourier Transform Infrared spectrometer (FTIR) and differential scanning calorimeter (DSC).Spherical crystallization has wide applications in pharmaceuticals like improvement of flowability and compressibility of poorly compressible drugs, masking bitter taste of drugs and improving the solubility and dissolution rate of poorly soluble drugs. Conclusion: Spherically agglomerated crystals can be directly converted into a tablet thus saving time and reducing cost.