Mechanical writing of electrical polarization in poly (L-lactic) acid.

Stimuli responsive materials are found in a broad range of applications, from energy harvesters to biomolecular sensors. Here, we report the production of poly (L-lactic acid) (PLLA) thin films that exhibit a mechanical stress responsive behaviour. By simply applying a mechanical stress through an AFM tip, a local electrical polarization was generated and measured by Kelvin Probe Force Microscopy. We showed that the magnitude of the stress generated electrical polarization can be manipulated by varying the thickness or crystallization state of the PLLA thin films. Besides exhibiting a mechanical stress-response behaviour with potential for energy harvesting and sensor applications, we show by AFM that these platforms react to mechanical forces with physiological relevance: interaction forces as low as a cell sheet migrating over a substrate or larger ones as the fluid induced stresses in bone tissue. In living tissues, as most mechanical stimuli are transduced as strain gradients for the anatomical structures, these mechanically responsive substrates can be used as ex vivo platforms to study the protein and cells response over a large range of electrical stimuli amplitude. As a proof of concept, selective adsorption of a human fibronectin was demonstrated by local patterning of the stimuli responsive PLLA films. STATEMENT OF SIGNIFICANCE: Bioelectricity is inherent to the formation and repair of living tissues and electrical stimulation has been recognized for promoting regeneration. Given the proven beneficial effects of electric fields and the absence of a suitable method of stimulation, there is a clinical need for smart substrates, which can generate a polarization (charges) to promote tissue regeneration without the need of external devices. In this work, we report the fabrication of poly(L-lactic) acid platforms that exhibit a mechanical stress responsive behaviour when subjected to physiologically relevant forces. This behaviour can be tailored by varying the thickness or crystallization state of the PLLA films. We further demonstrate the biofunctionality of such platforms by exploiting the mechanically-induced charge for adhesion protein adsorption.

Ash from a pulp mill boiler--characterisation and vitrification.

The physical, chemical and mineralogical characterisation of the ash resulting from a pulp mill boiler was performed in order to investigate the valorisation of this waste material through the production of added-value glassy materials. The ash had a particle size distribution in the range 0.06-53 microm, and a high amount of SiO(2) (approximately 82 wt%), which was present as quartz. To favour the vitrification of the ash and to obtain a melt with an adequate viscosity to cast into a mould, different amounts of Na(2)O were added to act as fluxing agent. A batch with 80 wt% waste load melted at 1350 degrees C resulting in a homogeneous transparent green-coloured glass with good workability. The characterisation of the produced glass by differential thermal analysis and dilatometry showed that this glass presents a stable thermal behaviour. Standard leaching tests revealed that the concentration of heavy metals in the leaching solution was lower than those allowed by the Normative. As a conclusion, by vitrification of batch compositions with adequate waste load and additive content it is possible to produce an ash-based glass that may be used in similar applications as a conventional silicate glass inclusively as a building ecomaterial.