Elaboration and characterization of the electrodeposited phosphates masses doped with various ions on stainless steel

The present paper is focused on elaboration of phosphate masses with good molar ratios on SS 316L, with fluoride, Zn2+ and Cu2+ as dopant ions, using an electrochemical procedure and also the attempt to select the best conditions for stainless steel. The surface was characterized using X-ray difraction, AFM and contact angle measurements. X-ray has evidenced crystaline phases, contact angle measurements has established the balance hydrophyl-hydrophob and AFM established roughness values. The inductively coupled spectrometry (ICP-MS) has quantified the amount of cooper and zinc ions released. In order to be used in biomedical applications hemolysis and antibacterial tests have been performed.Fil: Totea, G.. Faculty of Applied Chemistry and Materials Science; RumaniaFil: Ionita, D.. Faculty of Applied Chemistry and Materials Science; RumaniaFil: Katunar, Maria Rosa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigación En Ciencia y Tecnología de Materiales (i); Argentina. Universidad Nacional de Mar del Plata. Facultad de Ingeniería; ArgentinaFil: Cere, Silvia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigación En Ciencia y Tecnología de Materiales (i); Argentina. Universidad Nacional de Mar del Plata. Facultad de Ingeniería; ArgentinaFil: Demetrescu, I.. Faculty of Applied Chemistry and Materials Science; Rumani

Thermodynamics of clay – Drug complex dispersions: Isothermal titration calorimetry and high-performance liquid chromatography

An understanding of the thermodynamics of the complexation process utilized in sustaining drug release in clay matrices is of great importance. Several characterisation techniques as well as isothermal calorimetry were utilized in investigating the adsorption process of a model cationic drug (diltiazem hydrochloride, DIL) onto a pharmaceutical clay system (magnesium aluminium silicate, MAS). X-ray powder diffraction (XRPD), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and optical microscopy confirmed the successful formation of the DIL-MAS complexes. Drug quantification from the complexes demonstrated variable behaviour in the differing media used with DIL degrading to desacetyl diltiazem hydrochloride (DC-DIL) in the 2 M HCl media. Here also, the authors report for the first time two binding processes that occurred for DIL and MAS. A competitor binding model was thus proposed and the thermodynamics obtained suggested their binding processes to be enthalpy driven and entropically unfavourable. This information is of great importance for a formulator as care and consideration should be given with appropriate media selection as well as the nature of binding in complexes

Real time calorimetric characterisation of clay – drug complex dispersions and particles

Isothermal titration calorimetry (ITC) along with attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDX) and high-performance liquid chromatography (HPLC) were employed to investigate the process of adsorption of propranolol hydrochloride (PPN) onto magnesium aluminium silicate (MAS) and to characterise the MAS-PPN particles formed upon complexation. The composition of MAS was confirmed by infrared (IR) spectroscopy and a calcimeter. The calorimetric results confirmed the binding between PPN and MAS at various pHs and temperatures. The overall change in enthalpy was found to be exothermic with a comparatively small entropic contribution to the total change in Gibbs free energy. These findings suggest that the binding process was enthalpically driven and entropically unfavourable (lower affinity) suggesting hydrogen bonding and electrostatic interactions dominating the interaction. The variation of pH and temperature did not have a great impact on the thermodynamics of the binding process, as observed from the similarity in enthalpy (ΔH), entropy (ΔS) or Gibbs free energy (ΔG). A slight reduction in the binding affinity (Ka) with varing pH and temperature was however observed. SEM/EDX studies showed the occurrence of changes in the microstructural properties of MAS following complexation which may explain the potential of MAS-PPN complexes for controlled drug release promoting pharmaceutical innovation

Corrosion behaviour of new quaternary ZrNbTiAl alloys in simulated physiological solution using electrochemical techniques and surface analysis methods

The potential biomedical application of three new quaternary Zr alloys, namely Zr6Ti15Nb4Al, Zr32Ti15Nb4Al, and Zr49Ti15Nb4Al, was evaluated in vitro using electrochemical methods complemented with surface analysis of corrosion resistance. Cyclic potentiodynamic polarization (CCP) and electrochemical impedance spectroscopy (EIS) tests were performed in Ringer’s solution at 37 ºC. The electrochemical behavior of the ZrTiNbAl quaternary alloys was consistent with the formation of passivating oxide films on the surfaces of these materials. Localized breakdown of the oxide layer occurred on Zr6Ti15Nb4Al and Zr32Ti15Nb4Al alloys subjected to positive anodic polarization, a feature confirmed by scanning electron microscopy (SEM) on retrieved samples. The Zr49Ti15Nb4Al alloy, which had the highest titanium (49 wt.%) content, exhibited a larger passive range in the polarization curve and was immune to localized corrosion breakdown in a simulated physiological solution for the range of polarizations that can occur in the human bod

Characterisation of smectite clay-drug complexes in polymer matrices using isothermal titration calorimetry and evaluation of drug release

This thesis investigated the process of adsorption of three cationic drugs having different molecular weights and therapeutic effects (propranolol hydrochloride (PPN), diltiazem hydrochloride (DIL) and metformin hydrochloride (MET)) onto a smectite clay (magnesium aluminium silicate (MAS)) and the effects of this process on extending the release of such drugs. Furthermore, two different polymers (xanthan gum (XG) and polyethylene oxide (PEO)) were used in the study in combination with the formulated clay-drug complexes. The process of adsorption of the three drugs onto MAS was explored using isothermal titration calorimetry (ITC) along with attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDX), high-performance liquid chromatography (HPLC), microscopy and small angle X-ray scattering (SAXS). The calorimetric results confirmed the binding between MAS and the drugs at various pHs and temperatures. In all cases, an overall change in enthalpy was found to be exothermic with a comparatively small entropic contribution to the total change in Gibbs free energy. However, the binding profiles were different, one binding event being observed upon binding of PPN and MET onto MAS. The binding of DIL onto MAS exhibited two binding events and were attributed to DIL binding to montmorillonite and saponite. The findings suggest that the binding process was enthalpically driven and entropically unfavourable (lower affinity) suggesting hydrogen bonding and electrostatic interactions dominate the interaction. The latter part of this thesis aimed to investigate the capacity of the formed MAS-PPN complexes combined with XG and PEO, compared to MAS-PPN physical mix combined with the same polymers to control the release of PPN. Bulk compaction behaviour was studied for the formulations prepared as plots of relative density vs. upper punch pressure measured during loading to 130 MPa (10 kN) and unloading. The compaction curves of all the samples tested followed roughly similar trends: the compaction behaviour was dominated by plastic recovery during the loading stage following non-reversible deformation, movement and fragmentation of the particles. Compacts were further tested for their dissolution properties in pH 1.2 hydrochloric acid and pH 6.8 buffer. Results showed that PEO was able to provide controlled PPN release in both acid and buffer at very low polymer concentrations in tablets (5% w/w), whereas burst effects were observed upon dissolution of compacts containing the same amount of XG which may be as a result of it anionic nature. Overall, a more controlled PPN release rate from the tablets containing MAS-PPN complexes compared to those containing MAS-PPN physical mixture was observed which is a result of the MAS-PPN binding and adds important benefits to drug release. This information therefore provides a better understanding of the mechanisms of adsorption of PPN, DIL and MET onto MAS, and demonstrates the promising potential of MAS-cationic drug (drugs with short half-life) complexes as drug reservoirs in polymeric matrices to modulate drug release