Sonochemical reactions: mass transfer and kinetic studies of a solid-liquid system

Ultrasound has been shown to have desirable effects on both homogeneous and heterogeneous reactions, such as increasing the conversion, enhancing the selectivity, and improving the yield. Enhancements due to ultrasound may be attributed to chemical effects or mechanical effects, or to both simultaneously. The chemical effects of ultrasound are attributed to the implosion of microbubbles, generating free-radicals with a great propensity for reaction. Mechanical effects are caused by shock waves formed during symmetric cavitation, or by microjets formed when the bubble implodes asymmetrically. Research emphasis in this area attempts to discern the mechanisms behind ultrasound\u27s mechanical effects by selecting a model solid-liquid noncatalytic reacting system in which the chemical effects of ultrasound are negligible. A rigorous kinetic modeling approach is used which allows for reaction in both the liquid and solid phases. After an extensive analysis of the experimental data obtained from the system, it is concluded that the reaction occurs on the solid phase, and that the liquid phase reaction is negligible;Using several investigative techniques, the expected effects of ultrasound were observed, such as the degradative effects on particle size leading to increased surface area. More importantly, some novel findings of the effects of ultrasound on mass transfer parameters are reported. Results clearly show that ultrasound enhances the intrinsic mass transfer coefficient as well as the effective diffusivity of an organic reactant through the ionic lattice of the product layer. In addition, ultrasound also induces supersaturation of solid sodium sulfide in the solvent acetonitrile, increasing the solubility by a factor of 1.4 over the equilibrium saturation concentration. This enhanced solubility is attributed to cavitation which creates localized hot spots containing solvent in a supercritical state. The normally sparingly soluble solid is highly soluble in the solvent when it exists as a supercritical fluid. The increased solubility in these localized area has memory and is retained, even after the hot-spot dissipates into the bulk liquid. The use of ultrasound to induce supersaturation has significant applications in the areas of chemical kinetics when the reaction occurs in the liquid film or the bulk liquid phase

NANOSUSPENSION TECHNOLOGY: A INNOVATIVE SLANT FOR DRUG DELIVERY SYSTEM AND PERMEABILITY ENHANCER FOR POORLY WATER SOLUBLE DRUGS

Nanosuspension contains submicron colloidal dispersion of pharmaceutical active ingredient particles in a liquid phase stabilized by surfactants. The poor water solubility of drugs is major problem for drug formulation. The reduction of drug particles into the sub-micron range leads to a significant increase in the dissolution rate, bioavailability as well as improve stability. Nanosuspension consists of the pure poorly water-soluble drug without any matrix material suspended in dispersion. Nanosuspension many attempts have been made to deliver poorly water soluble drugs as a nanosuspension prepared by adopting various methods. Techniques such as media milling and high pressure homogenization have been used commercially for producing nanosuspension. Recently, the engineering of nanosuspension employing emulsions and microemulsion as templates. The unique features of nanosuspension have enabled their use in various dosage forms, including specialized delivery systems such as mucoadhesive hydrogels, parenteral, peroral, ocular and pulmonary routes. Keywords: Nanosuspension, Solubility enhancement, Saturation solubility, Homogenization

Small volume drug release testing using ultrasonic agitation: development, characterization, and applications

The first standardized methods for in vitro drug release testing of solid dosage forms were first introduced in the 1960s. Drug release testing has since become an important analytical measure along all stages of the drug development process. Despite the expanded role of dissolution testing and innovations in the types of dosage forms reaching the market, the fundamental methods and approaches to dissolution testing have not changed from their original introduction. This lack of innovation and one-size-fits-all approach to drug release testing has led to inefficiencies in testing and limited the scope of applications where this type of information could have an impact. In order to meet this need, we have designed, characterized, and implemented a small volume drug release test using ultrasonic agitation to screen for differences in dosage form composition. Our approach aims to supplement official methods for use during multiple stages of the drug development process. The hydro-acoustic environment in the system was characterized as a function of input power and position of the acoustic source. Drug release behavior from tablets was also studied over these system parameters, and a preliminary mechanistic explanation is made linking the two. The interplay between fragmentation and diffusion on solid dissolution processes was then explored through a deterministic partial differential equation model. This model provides the first instance of time-evolving particle size distributions in a dissolution model. In the final sections of this dissertation, uses of the ultrasonic agitation mediated drug screening method are demonstrated at two different parts of the drug development process – during early formulation development for the study of composite microparticle matrix structure on drug release behavior and post market surveillance for the screening of substandard tablets.2020-02-28T00:00:00

Fabrication of Porous Particulate Scaffolds Using Electrohydrodynamics and Thermally Induced Phase Separation for Biomedical Engineering Applications

Abstract The availability of forming technologies able to mass produce porous polymeric microspheres with diameters ranging from 150 to 300 µm is significant for some biomedical applications where tissue augmentation is required. Moreover, appropriate assembly of microspheres into scaffold is an important challenge to enable direct usage of the scaffolds in chronic wound treatments. In this thesis, the feasibility of the electrohydrodynamic (EHD) atomization forming combined with thermally induced phase separation (TIPS) for production of such drug delivery carriers, using biodegradable polymers (poly (lactic-co-glycolic acid) and poly (ε-caprolactone)) was explored. To achieve this goal, the first part of the thesis describes comprehensive parametric mode mappings of the diameter distribution profiles of the microspheres obtained over a broad range of key processing parameters and correlating this with the material parameters of five different polymer solutions of various concentrations. Based on the mode mapping studies, combination of poly (lactic-co-glycolic acid) (PLGA) and dimethyl carbonate (DMC) was found to be ideal for generating the microspheres within the targeted diameter range (150-300 µm). Surface porosity was achieved by electrospraying the PLGA/DMC solution and collecting the required size of the polymer particles in liquid nitrogen followed by lyophilisation. The second aim of this thesis was the in vitro release studies. In order to conduct this part of the study, the single needle and co-axial needle EHD/TIPS methods were used to generate the dye loaded microspheres of the required size. Three different dyes (Erythrosin B, Pyronin B and Reichardt’s) were selected as model drugs to be encapsulated separately in the produced microspheres. The purpose of selecting three different dyes was to have a prediction on the release profile of immunosuppressants with high toxicity used for treatment of chronic wounds such as perianal fistulae. The in vitro release studies showed that the dyes were released with the high initial burst release phase in 3.5-5.5 hours followed by a long and sustained release phase (in 30-360 hours). Systematic investigations using different external stimuli such as temperature, fresh media and sonication exposure was also carried out to observe their effects on the release rate of the encapsulated materials from the produced microspheres. The results acquired from the in vitro release studies showed that the temperature variations and the sonication with different frequencies have significant effects on the release rates of the incorporated materials from the polymeric microspheres. Moreover, the results demonstrated that the products collected by the single needle EHD/TIPS method is more capable of releasing the payload in a longer period of time with more sustained manner compared to their counterparts obtained from the co-axial needle method

Electrodeposition of Ni-W & Ni-Mo under ultrasonication

AbstractThe advancement of science demands materials with superior properties. Surface coating technology can be used to impart required wear or corrosion resistance on surfaces. The current research relates to the development of a deposition method for coating nanostructured Ni-W alloy and Ni-Mo alloy onto contoured external and internal surfaces of metallic components for improved corrosion and erosion resistant applications. The coatings should have a high alloy content with reproducible concentration, and should not have through thickness cracks. Electrodeposition of pure tungsten or molybdenum from an aqueous solution is not possible. However, these metals can be co-deposited along with iron group metals as an alloy. These deposits are the result of an induced co-deposition mechanism that gives an anomalous amount of W or Mo in the deposit. Ultrasonic assisted electrodeposition has been developed to give reproducible results of the chemical composition of the coating. Ultrasonication results in higher current densities during cyclic voltammetry. Increasing the deposition current density increases the tungsten content of the deposit under ultrasonicated conditions. The coatings obtained with ultrasonication show a uniform chemical composition across the thickness of the coating. Ultrasonication also minimizes hydrogen incorporation in the coatings, distributes the defect concentration more uniformly in the deposit, and promotes finer crystallite nucleation. Furthermore, ultrasonication doubles the nucleation kinetics under otherwise similar electrochemical conditions. The TEM and XRD analyses also support the nano crystallite morphology of the Ni-W deposits. The newly developed deposition method is capable of producing crack-free coatings that are nanocrystalline with high hardness, which can be used for both corrosion and wear resistant applications