Polyvinyl alcohol hydrogel (PVA-H) is increasingly used as vascular modeling material due to its low friction and high transparency. Since mechanical, fluid dynamic and implant performance tests are commonly performed in aqueous environments, a thorough understanding of time-dependent changes in geometrical, mechanical and optical properties of PVA-H in water is imperative. In this study, a comprehensive analysis of the short- and long-term behavior of PVA-H in water for vascular modelling applications has been performed. PVA-H properties were investigated for six weeks, with the swelling behavior characterized by mass and area change. Young's modulus was assessed, as well as compliance for medium-sized (Ø 6.8mm) and large artery models (Ø 30mm). Friction coefficients were determined via planar sliding test and UV-Vis spectroscopy served to assess optical transparency of PVA-H. Geometric analysis revealed initial slight swelling of the PVA-H, followed by shrinkage up to -33.3±0.5 % after six weeks. Compliance increased considerably within the first hours of water exposure, followed by an increase in Young's modulus and a decrease in compliance over days to weeks. Furthermore, friction coefficients increased considerably from 0.110±0.001 after half an hour up to 1.142±0.038 after five weeks. Optical transparency initially fluctuated and subsequently stabilized above 90 % up to six weeks. In conclusion, this study provides a comprehensive understanding of short- and long-term changes in geometrical, mechanical, and optical properties of PVA-H in water, demonstrating that precise timing is required when used as models for vascular research and implant testing.

To evaluate the biomechanical behavior of bilayer crowns with traditional and modified core designs using fatigue survival testing and finite element analysis (FEA), aiming a suitable rehabilitation for the anterior teeth area. Forty-five crowns were manufactured, according to the following groups: CC (conventional core), MCS (modified core/stratified veneer) and MCM (modified core/machined veneer). Cores were machined (lithium disilicate); veneers of CC and MCS groups were made through stratification (fluorapatite), and veneers of MCM group were also machined (leucite). Next, the crowns were cemented using resin cement (Variolink Esthetic LC) over full crown preparations made of epoxy resin and then subjected to cyclic fatigue test. After mechanical testing two events were considered: the presence of crack and/or chipping (event 1) and catastrophic failure of the crown (event 2). The average load to failure and number of cycles to failure in which events 1 and 2 occurred were used to perform the survival analysis according to Kaplan-Meier and Log-Rank (Mantel-Cox; 95%). Fracture marks and failure mode of the crowns were evaluated and classified by optical stereomicroscope and scanning electron microscope. Finally, FEA was performed to evaluate the stress distribution on the crowns. Fatigue test results showed that considering event 1 the groups with modified cores (MCS: 1020N and MCM: 913N) presented higher average loads and number of cycles to failure than the group CC (773N). Considering event 2 all groups showed similar fatigue performance (∼1028N). FEA results evidenced higher stress concentration at the load application area, with a slight stress at the cervical margin of the crowns regardless the group. Modified core designs improved resistance to initial veneer damage without compromising catastrophic failure performance. Stress distribution patterns supported the mechanical findings, indicating favorable biomechanical behavior.

The mechanical integrity and failure mechanisms of human hair fibers are critically dependent on the hierarchical structure of the cuticle, which serves as a durable record of biological and environmental history. In this study, we employed a multi-parametric approach to quantify the nanomechanical evolution of hair degradation, establishing a correlation between surface physicochemistry and local tribological properties. We combined Atomic Force Microscopy in Quantitative Nanomechanical Mapping (QNM) mode with Power Spectral Density (PSD) analysis, Scanning Electron Microscopy (SEM), and Energy-Dispersive X-ray Spectroscopy (EDS). QNM revealed distinct nanomechanical signatures: bleached fibers exhibited elevated adhesion domains and markedly increased heterogeneity compared to virgin counterparts. These tribological behaviors were consistent with trends observed in EDS analysis regarding chemically adsorbed sodium and oxidative residues, although morphological changes remained the primary indicator of damage. While natural aging in distal regions induced surface deterioration, the magnitude of damage was significantly more pronounced in fibers subjected to combined bleaching and UV irradiation. This suggests a synergistic degradation pathway where chemical pre-treatment amplifies the susceptibility to UV-induced defects. This study demonstrates that chemical adsorption and weathering can co-occur, yet manifest along statistically distinct chemical and structural dimensions that jointly compromise the cuticle barrier function. These findings highlight the potential utility of nanoscale multiparametric mapping not only for assessing cosmetic treatments, but also for informing forensic and clinical contexts, where such tribological descriptors may support diagnostic profiling of structural and chemical anomalies.

The high hardness and low fracture toughness of zirconia-containing lithium silicate glass ceramics (ZLS) leads to dominant brittle fracture behaviour, which prompts extensive surface and subsurface cracking during machining, reducing long-term stability of dental restorations. This study evaluated the in-situ nanoindentation behaviour of this material class aiming to describe the real-time deformation response and nanomechanical mechanisms of cracking in ZLS according to their crystallized state. The in-situ nanoindentation tests on polished pre-crystallized and crystallized ZLS (Vita Suprinity PC, Vita Zahnfabrik, Germany) were performed inside a scanning electron microscopy (SEM) at 500mN peak load and 2mN/s loading rate. SEM images were taken at different stages of loading-unloading cycles to correlate morphological responses to force-displacement events in real-time. Pop-in events in force displacement curves were matched to edge chipping in pre-crystallized state and to radial cracking in crystallized ZLS. Although both pre-crystallized and crystallized ZLS materials exhibited brittle fracture behavior under indentation, their microstructural responses revealed distinct fracture mechanisms. In the pre-crystallized ZLS, the brittle fracture was accompanied by edge chipping, rupture and radial cracks. In contrast, crystallized ZLS had shear-band, pile up, and radial cracks. Pre-crystallized ZLS had significantly lower hardness, Young's modulus, resistance to machining-induced cracking, and maximum shear stress compared with the crystallized state. Further, the larger indentation imprint volume observed in the pre-crystallized ZLS suggests higher material removal efficiency during machining. This study highlights the microstructure-property dependence of ZLS materials, providing valuable insights into their micromechanics upon abrasive machining.