The potential of electron beam irradiation for simultaneous surface modification and bioresorption control of PLLA for medical device applications

Bioresorbable polymers have been widely investigated as materials exhibiting significant potential for successful application in the medical fields of bone fixation devices and drug delivery. Further to the ability to control degradation, surface engineering of polymers has been highlighted as a key method central to their development. Previous work has demonstrated the ability of electron beam (e-beam) technology to control the degradation profiles and bioresorption of a number of commercially relevant bioresorbable polymers (poly-l-lactic acid (PLLA), L-lactide/ DL-lactide co-polymer (PLDL) and poly(lactic-co-glycolic acid) (PLGA). This work investigates the further potential of e-beam technology to impart added biofunctionality through the manipulation of polymer (PLLA) surface properties. A Dynamatron Continuous DC e-beam unit (Synergy Health, UK), with beam energies of 0.5, 0.75, and 1.5 MeV, was used for the irradiation of PLLA samples with delivered surface doses of 150 or 500 kGy at each energy level. The chosen conditions reflect the need to achieve a specific surface modification for the control of surface degradation as demonstrated in previous work. Surface characterization was then performed using contact angle analysis, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and atomic force microscopy.
Results demonstrated a significant increase in surface wettability post e-beam treatment. In correlation with this, XPS data showed the introduction of oxygen-containing functional groups to the surface of PLLA. Raman spectroscopy indicated chain scission in the near surface region of PLLA. E-beam irradiation did not seem to affect the surface roughness of PLLA as a direct consequence of the treatment. In conclusion electron beam surface modification has been found to modify both the surface-to-bulk bioresorption profile and the surface hydrophilicity. Both could provide benefits in relation to the performance of implantable medical devices.

The effect of heating temperature on the properties of vermiculites from Tanzania with respect to potential agronomic applications

This study was carried out to assess the properties of vermiculites from Tanzania with respect to the temperature used to expand them. Vermiculites from five locations in the Mozambique Belt of Tanzania were sampled and heated at 15, 200, 400, 600 and 800 °C in a muffle furnace. Palabora Europe Ltd provided one sample for comparison from their South Africa deposit which provides vermiculite used worldwide as a soil amendment. Water release characteristic, cation exchange capacity, pH, mass loss, and bulk density were among the properties assessed. All six vermiculites responded differently on heating, and had a significant variation in their agronomic properties. Water release characteristic varied with the degree of exfoliation and phase composition. Although vermiculites from Tanzania expanded on heating, their capacity to retain plant available water was relatively low as compared to vermiculite from Palabora. Disintegration on heating and the presence of a high amount of iron could be among the factors affecting their water release characteristic. Loss of hydroxyl water was higher in vermiculites than in hydrobiotites. Dehydroxylation enhanced the availability of exchangeable K⁺ and reduced significantly the cation exchange capacity of vermiculites. The optimum exchangeable K⁺ was obtained on heating at a temperature of 600 °C. The pH was unaffected by heating to a temperature of less than 600 °C. At higher temperature, the pH increased in some samples and was accompanied by substantial amounts of exchangeable Mg²⁺. Thus, it was concluded that initial characterization of vermiculites is essential prior to potential agricultural applications in order to optimize their agronomic potential. © 2008 Elsevier B.V. All rights reserved.

Mechanisms of plant resistance to metal and metalloid ions and potential biotechnological applications

Metal and metalloid resistances in plant species and genotypes/accessions are becoming increasingly better understood at the molecular and physiological level. Much of the recent focus into metal resistances has been on hyperaccumulators as these are excellent systems to study resistances due to their very abnormal metal(loid) physiology and because of their biotechnological potential. Advances into the mechanistic basis of metal(loid) resistances have been made through the investigation of metal(loid) transporters, the construction of mutants with altered metal(loid) transport and metabolism, a better understanding of the genetic basis of resistance and hyperaccumulation and investigations into the role of metal(loid) ion chelators. This review highlights these recent advances. © Springer 2005.

Synthesis and Thermophysical Properties of Ether Functionalized Sulfonium Ionic Liquids as Potential Electrolytes for Electrochemical Applications

During this work, a novel series of hydrophobic room temperature ionic liquids (ILs) based on five ether functionalized sulfonium cations bearing the bis(trifluoromethyl)sulfonylimide, [NTf2]- anion were synthesized and characterized. Their physicochemical properties, such as density, viscosity and ionic conductivity, electrochemical window along with thermal properties including phase transition behavior and decomposition temperature, have been measured. All of these ILs showed large liquid range temperature, low viscosity and good conductivity. Additionally, by combining DFT calculations along with electrochemical characterization it appears that these novel ILs show good electrochemical stability windows, suitable for the potential application as electrolyte materials in electrochemical energy storage devices.