"Toward the objective of creating stronger BVS materials by combining nanofillers with poly(Llactide) (PLLA), experiments at Caltech with ENEA staff evaluated biocompatibility in vitro with two types of cells relevant to vasculature (endothelial cells that line blood vessel walls and smooth muscle cells). When tungsten disulfide nanotubes are incorporated into PLLA, the material remains well tolerated. This is true in ""direct contact"" experiments and in experiments that expose cells to medium that has leached constituents of the nanocomposite. These represent significant steps in the preclinical evaluation of biocompatibility. Also toward the objective of creating stronger BVS, ENEA and Warwick collaboration with Caltech through reciprocal secondments showed that the addition of WS2 nanotubes does accelerate nucleation of crystallization in PLLA and the resulting interactions make the material stronger and more ductile.
Progress toward the objective of understanding the processing-structure-property relationships of new BVS materials has focused on developing methods, initially using PLLA alone as our foundation and later PLLA-WS2 nanocomposites. All four institutions have contributed significantly. The ENEA-Caltech collaboration created an apparatus that imposes elongation in ""tube expansion,"" corresponding to an essential step in producing BVS. The instrument is the first of its kind and brings innovative measurement capabilities to see structure development in situ during stretch blow moulding. Exciting results were obtained when the instrument was used for the first time for real-time synchrotron X-ray measurements: deformation proceeds in distinct steps, first dominated by the glassy character of the pre-formed tube and the later stage that is marked by a sudden appearance of oriented crystals. Successively, an upgraded version of the instrument enabled data acquisition with optimized measurement conditions, easier sample interchange and enhanced stretching modalities.
Warwick established the ability to extrude samples in the form of sheets that were used at Queens in biaxial extensional measurements revealing strong effects of temperature and elongation rate. With these input parameters, we developed computational tools to predict the macroscopic mechanical properties of PLLA-WS2 (constitutive models developed by Queens) from the molecular and nanoscopic scale (multiscale modelling by Warwick). Both constitutive and multiscale modelling started from the PLLA-based model and then the nanofillers were incorporated: constitutive modelling firstly captured the behaviour of PLLA during stretch blow moulding and then incorporated the features due to WS2; similarly, the multiscale modelling studied the composite system as interaction of the nanotubes with the PLLA polymer previously modelled alone. Finally, the two models linked: the underlying molecular and nanoscopic mechanisms (validated by in situ x-ray measurements) provided the parameters for a predictive constitutive model (validated by biaxial elongation measurements).
Multiple dissemination activities were directed both to expert academic audiences and to the general public. Dissemination resulted from presentations in international webinars, academic seminars, lectures, and through publications on peer-reviewed journals and conference communications. Additional forms of promotion took place through publishing in each institution webpages, newsletters, periodic journals and national newspapers.
The dissemination activities fostered the development of a consolidated networking that became a launch pad for collaborations with academic and industrial companies mainly involved in biomedical. Exploitation of the acquired knowledge throughout the conducted research also targeted new R&D projects by monitoring open calls especially focusing on bilateral cooperative actions (see UK-US and IT-US)."
