Nanoscale friction and wear of a polymer coated with graphene.

Friction and wear of polymers at the nanoscale is a challenging problem due to the complex viscoelastic properties and structure. Using molecular dynamics simulations, we investigate how a graphene sheet on top of the semicrystalline polymer polyvinyl alcohol affects the friction and wear. Our setup is meant to resemble an AFM experiment with a silicon tip. We have used two different graphene sheets, namely an unstrained, flat sheet, and one that has been crumpled before being deposited on the polymer. The graphene protects the top layer of the polymer from wear and reduces the friction. The unstrained flat graphene is stiffer, and we find that it constrains the polymer chains and reduces the indentation depth.

Molecular-Dynamics Simulations of the Emergence of Surface Roughness in a Polymer under Compression.

Roughness of surfaces is both surprisingly ubiquitous on all length scales and extremely relevant practically. The appearance of multi-scale roughness has been linked to avalanches and plastic deformation in metals. However, other, more-complex materials have mechanisms of plasticity that are significantly different from those of metals. We investigated the emergence of roughness in a polymer under compression. We performed molecular-dynamics simulations of a slab of solid polyvinyl alcohol that was compressed bi-axially, and we characterised the evolution of the surface roughness. We found significantly different behaviour than what was previously observed in similar simulations of metals. We investigated the differences and argue that the visco-elasticity of the material plays a crucial role.

Drug interactions related to self-medication: a French pharmacovigilance database study.

Self-medication (SM) is a common practice perceived by patients as harmless which can, however, entail health risks. The aim of the study was to identify drug-drug interactions (DDIs) involving SM drugs leading to adverse drug reactions (ADRs) in the National French Pharmacovigilance Database. All ADR reports from 1 January 1985 to 31 July 312018, coded as 'interaction' and 'self-medication', were selected and studied. Patient characteristics, the level and type of interaction, and the therapeutic classes of the drugs were examined. Adverse drug reactions were analysed and classified according to the system organ classes of the Medical Dictionary for Regulatory Activities. One hundred and three reports totalling 158 ADRs (71% severe cases) were included; 153 DDIs (59.5% pharmacodynamic) involving 234 drugs were identified. The latter included 119 SM drugs (51% available on prescription), mainly analgaesics, anti-inflammatory drugs, dietary supplements and antibiotics. Haemostasis disorders and renal failure were the most frequently reported ADRs. The analysis of reference documents raised concerns on the lack of information provided by package leaflets. In conclusion, the present study highlights the risks of medically unapproved re-use of prescription drugs or the consumption of dietary supplements without monitoring possible interactions and ADRs. Patient awareness could be improved by more regular updates of medication package inserts.