Assessing the biocompatibility of silver nanoparticles with Schmidtea mediterranea, a stem cell model organism

Because of their antibacterial and anti-inflammatory properties, silver nanoparticles (AgNPs) are among the nanomaterials most often incorporated in nanofunctionalised consumer products such as paints, food containers, clothing and surgical instruments, and are considered beneficial for tissue regeneration and wound repair. Despite their industrial and medical advantages, AgNPs have a cyto- and genotoxic potential and can affect different tissues and cell types, including stem cells, which are a relevant target of nanoparticles. This makes an in-depth knowledge on stem cell toxicology essential in understanding the heterogeneity of toxic responses, especially in developmental and carcinogenic tissues. We assessed the biocompatibility of non-coated (NC) and polyvinylpyrrolidone (PVP) coated spherical AgNPs using the stem cell model organism, Schmidtea mediterranea. This free-living freshwater triclad (planarian) allows uncomplicated set-ups and high-throughput screening and is uniquely positioned because of its easily accessible population of adult somatic stem cells. As such, it is possible to study underlying mechanisms of nanoparticle toxicity on stem cells in vivo, and link them to physiological parameters like regeneration and development. After a physicochemical AgNP characterisation and cellular uptake and localization study, a sensitivity screen revealed a higher susceptibility for regenerating compared to fully developed organisms. An in-depth assessment of molecular, cellular and physiological effects showed a delayed neurodevelopment at all levels, which was stronger for PVP-AgNP. AgNPs also decreased the motility of regenerating S. mediterranea and changed the type of motility behavior in a concentration-dependent way. Underlying to the behavioral effects, a significant inhibition of brain and eye regeneration was observed. This is probably caused by altered stem cell dynamics, as an exposure to different concentrations of AgNPs induced a significant decrease in stem cell proliferation. The reduced stem cell proliferation also induced an overall delay in tissue development resulting in a smaller blastema. The results of this ongoing research project indicate that effects of AgNPs on development processes in S. mediterranea are factual and should be considered in future risk analysis

Toronto stentless aortic valve replacement in elderly patients

From July 1992 to October 1994, we inserted new Toronto SPV stentless aortic heterografts (SJM Med, Inc., St Paul, Minneapolis, USA) in 40 of a series of 50 consecutive patients older than 70 years. The mean age was 75.7 years (range 70 - 86 years). All, except 4 patients, were pre-operatively in NYHA functional class III or higher. The aortic clamp time was significantly higher in the stentless group (75 v. 53 minutes, P < 0.001). The average 255 mm size of the implanted valves stands in stark contrast to the low body surface area (1.69 m(2)) of this patient group. The surgeon's (in)experience was the major reason for the drawbacks (5/50) associated with a stentless procedure. The follow-up period ranged from 2 to 27 months and was complete in 100% of cases. We encountered 1 hospital death and no late deaths (97.5% actuarial survival). The mean NYHA class at follow-up was 1.5, and without exception patients were in class I or II. We noted one transient ischaemic attack immediately postoperatively and another later incident in a patient with a previous severe vascular history. With a low-intensity anticoagulation regimen for the first 3 months, there were two incidents of haemorrhaging necessitating premature anticoagulation withdrawal. Echocardiographic transthoracic valvular gradients compared favourably with the reported gradients of other biological valves, especially the smaller ones and significantly better haemodynamics were noted in most cases 6 months after implantation. Comparison of data with stented valves implanted during the same period indicates that the average size of the stentless valves was significantly higher (223 v. 255 mm, P < 0.001) in an equivalent population

The pretarsus of the honeybee

Although the honeybee (Apis mellifera L.) is a well-studied species, the functional morphology of its pretarsal structure is still not fully understood. We conducted an in-depth scanning electron microscopic study on these complex structures to contribute to the comprehension of the pretarsal structure-function relationships. As a result, this study has provided valuable information on the ultrastructure of the pretarsus, and in particular on the spines of the unguitractor surface and the small spines and scalloped surface of the claws with longitudinal grooves. Special attention was given to the adhesive contact zone of the arolium with its highly specialized fibrillary cuticle texture. Remarkably, several of the observed pretarsal structures, such as the pyramidal structures on the unguitractor and the thin hairs on both the grooved claws, and the hairs of the manubrium have not been previously described. All observed structures in this study were characterized with respect to their possible physiological and mechanical roles.</jats:p