Formation Of Porous Surface Research Articles

TUNING SURFACE ROUGHNESS OF ELECTROSPUN POLY CAPROLACTONE FIBRES BY SINGLE SOLVENT ELECTROSPINNING SYSTEM

Secondary surface texture or surface roughness is having a powerful impact on morphological variety and magnifies the application areas of electrospun fibres. This paper for the first time assesses the formation of varying degrees of surface pores on electrospun poly caprolactone (PCL) fibres by using a single solvent system. PCL solutions were prepared by dissolving PCL granules in dichloromethane (DCM) at the concentration of 5, 10, 15 and 20% (w/v), before being subjected to the electrospinning process at lower kV values of 5, 10 and 15, respectively. The morphology of electrospun fibres was characterised by field emission scanning electron microscope (FESEM). The resultant PCL fibres showed a highly porous surface was formed at lower PCL concentration. The surface roughness of PCL fibres was increased gradually with the increment of PCL concentration. The formation of porous surface was mainly due to the fast phase separation process while pore size and pore size distribution was found to depend on the blend composition.

Crosslinked Chitosan/Casein Polyelectrolyte Multilayers for Drug Delivery

Polyelectrolyte multilayers (PEMs) are widely used as drug delivery systems, but still remain challenging for their small drug immobilizing capacity. One way to increase the immobilized drug amount may be crosslinking of the PEMs, which stabilize them and increase their porosity. The aim of the present study is fabrication and characterization of chitosan/casein PEMs, which are crosslinked with different crosslinking agents – glutaraldehyde, sodium tripolyphosphate, CaCl2 and combinations of two of them. XPS method was used to prove the PEMs crosslinking. SEM was used to observe film morphology and its variation due to cross­linking. Water capacity of PEMs in 100 % relative humidity was investigated. Release of model drug Benzydamine Hydrochloride was monitored spectrophotometrically at 306 nm. The crosslinking improves the PEMs stability and causes formation of porous surface. After crosslinking the amount of the immobilized drug increased several times.

Microstructure development of HfOx thin films

ABSTRACTMorphological and crystallographic characteristics of HfOx with different oxygen concentrations (0 ≤ x ≤ 2.5) and thicknesses (18 nm ≤ t ≤ 310 nm) were analyzed in this work before and after thermal annealing at 700°C in N2 atmosphere for 1h. The morphology of the as-deposited, low oxygen concentration films (t = 100 nm) is formed by a well-defined granular structure with grains around 20 nm in diameter. For higher oxygen concentration, the roughness increases, as a consequence of a very porous surface morphology. At the same time, the crystallographic structure changes from HCP with a {0002} preferred orientation to an amorphous structure as oxygen concentration increases. As the thickness of the HfO2 films increases, we also observed the formation of a high surface porosity, with pore diameter ranging from 80 nm to 120 nm. The changes observed in morphology and crystallinity of the films, as we increase the concentration of contaminants, occurs because of the lowering of the adatoms surface diffusion, which prevents them from reaching lower energy points during the formation of the microstructure of the films. Furthermore, this lowered surface diffusion favors the process of grain renucleation, which leads to roughness increasing, and to an enhancement of the formation of porous surfaces. After annealing, all films exhibit the monoclinic crystallographic phase associated with HfO2. Surface morphology of the films is consistent with a polycrystalline structure with grain diameters varying between 10 nm and 200 nm. As their size increases, the grains become very faceted, a finding consistent with the improvement in film crystallinity. Our results suggest that long-time annealing promotes the diffusion of oxygen from the SiO2-Hf interface to the film, compensating any O2 deficit in the film. Formation of the monoclinic phase is also favored by the improvement in the film stoichiometry promoted by thermal treatment. Also, the critical size of the nuclei, associated with a grain growth in a particular crystallographic orientation, decreases as a consequence of the high temperature during thermal annealing. Therefore, formation of faceted grains and increasing of surface roughness are favored in thicker films.

Effects of Chemical and Heat Treatments on Surface Characteristics and Biocompatibility of Titanium-Niobium Alloys

Alkali solution- and heat-treatments were employed to modify the surfaces of Ti-6Al-4V, Ti-40Nb-1Hf and Ti-30Nb-1Fe-1Hf alloys, and then the surface characteristics and the biocompatibility of the treated alloys were analyzed. The formation of porous surfaces that contain numerous nano-pores and irregular cracks, together with the increase in hydroxyl, TiO2 and Nb2O5 contents in the surface layer of the treated Ti40Nb-1Hf and Ti-30Nb-1Fe-1Hf alloys, have been found to enhance biocompatibility which was evaluated by the osteoblast cell culture in vitro. In addition, the biocompatibility of both Ti-40Nb-1Hf and Ti-30Nb-1Fe-1Hf alloys are comparable to that of Ti-6Al-4V alloy. Alkali solutionand heat-treatments are believed to enhance bone-bonding ability of both Ti-40Nb-1Hf and Ti-30Nb-1Fe-1Hf alloys, and therefore are useful for surface modification practice. [doi:10.2320/matertrans.MER2007083]

Preparation of macroporous chitosan layer coated on silica gel and its application to affinity chromatography for trypsin inhibitor purification

Macroporous chitosan layer coated on silica gel (CTS-SiO 2) was prepared by phase inversion and polyethylene glycol (PEG) molecular imprinting methods. Effects of chitosan and PEG content on the formation of porous surface were investigated by scanning electron microscopy (SEM). Trypsin could be covalently coupled as an affinity ligand on the macroporous chitosan layer activated with epoxy groups. The activity of the immobilized enzymes in the optimum conditions was 594 ± 8 U per gram CTS-SiO 2 bead, which account for 47.5 ± 0.6% of original trypsin activity in the incubation solution. In comparison with the free enzyme, the immobilized enzyme showed high stability at room temperature with less than 10% activity loss in 7 days storage. Moreover, non-specific adsorption was not observed on this kind of affinity chromatographic matrix. The immobilized trypsin bead was packed into column to separate the trypsin inhibitors (TIs) from egg white. The recovery rate of the trypsin inhibitor activity was 54.5 ± 1.2% and purification folds could reach 9.1 after one step of chromatographic process.

Development of EBC for Silicon Nitride

Various coating methods of EBC layer for silicon nitride were discussed. High density EBC layer was successfully coated by different techniques such as sputtering, sol-gel and reaction sintering methods. Water vapor corrosion and recession mechanisms of Lu2Si2O7 which is a potential material for EBC were discussed. The problems in the development of EBC revealed by corrosion tests were summarized. The most important problem addressed here was the corrosion of silica at grain boundary. Due to corrosion of silica at the boundary, formation of porous surface is inevitable, then the silicon nitride substrate gets easily oxidized and/or corroded by water vapor. To resolve this issue, we propose a new EBC material without boundary silica and the corrosion mechanism of this improved EBC material is discussed.