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The behavior of a cell is strongly influenced by the physical properties and stimuli in its microenvironment. Furthermore, the activation and modulation of mechanotransduction pathways are involved in tissue development and homeostasis and even pathological processes. Thus, when developing materials aimed at mimicking the extracellular matrixes of healthy or pathological tissues, their mechanical features should be closely considered. In this context, nanoindentation represents a powerful technique for mechanically characterizing biological tissues and hydrogels at the cell-length scale. However, standardized experimental protocols and data analysis techniques are lacking. Here, we proposed a methodological approach based on the nanoindentation technique for quantitatively analyzing and comparing the time-dependent load relaxation responses of soft biological tissues and hydrogels. As this was an explanatory study, stress-relaxation nanoindentation tests were performed on samples of pig and human lung tissues and of a specific gelatin-methacryloyl (GelMA) hydrogel to quantify and compare their viscoelastic properties. The proposed method allowed for identifying the characteristic parameters needed for describing the behavior of each sample, permitting us to quantitatively compare their mechanical behaviors. All samples showed load relaxation at a defined indentation depth because of their intrinsic viscoelastic behaviors, and the GelMA samples showed the highest relaxation capabilities. The distribution of the characterization parameters showed that the biological samples presented similar time-dependent responses, while differences were observed in the GelMA samples. Overall, the proposed methodological approach allows for providing key insights into the time-dependent behaviors of soft biological tissues and hydrogels at the cell-length scale in view of supporting tissue engineering and pathophysiological investigations. [ABSTRACT FROM AUTHOR]

Purpose: The aim of this in vitro study was to evaluate the effect of curing time on the mechanical properties of fiberpost luting cement. The null hypothesis was that curing time does not affect hardness and Young's modulus. Materials and Methods: 24 premolars were endodontically treated and a class II cavity with 1.5 mm residual wall thickness and an 8-mm-deep post space was prepared. Fiber posts were luted trough a standardized procedure: etch for 20 s; rinse for 20 s; rinse with ethanol for 30 s; universal adhesive application (UBQ, Kuraray); fiber post insertion (Rabilda, Voco) after luting cement (DC Core, Kuraray) placement in the post space. Samples were divided into 3 groups according to the curing time (n = 8 each): G1, no light; G2, 20 s; G3, 120 s. Light curing was performed with an LED lamp (Celalux 2, Voco) at 1000 mW/s with the tip placed in contact with the fiber post. The occlusal cavity was restored with a nanofilled resin composite (Filtek Supreme XTE, 3M). After 7 days, half of each group's samples were submitted to cyclic fatigue testing with a chewing simulator for 500,000 cycles at 50 N load, 2 mm excursion, under water (CS 4.4, SD Mechatronik). Samples were sectioned into 1-mm-thick slices perpendicularly to the long axis of the fiber post. Samples were tested with a Nanoindenter XP, equipped with a diamond Berkovich indenter and characterized by a theoretical force resolution of 50 nN and a theoretical displacement resolution lower than 0.01 nm. The loading displacement (P-h) curves were analyzed using the Oliver-Pharr method to obtain the Young's modulus and hardness. The data were analyzed with ANOVA (α < 0.05). Results: Young's modulus and hardness were not correlated with the curing time (p = 0.0623). Cyclic fatigue significantly reduced the luting cement's mechanical properties (p = 0.0001) except when 120 s curing time was performed. Conclusion: The null hypothesis was partially rejected since curing time significantly affect the mechanical behavior of luting cement. [ABSTRACT FROM AUTHOR]

In recent years, bioactive glasses gained increasing scientific interest in bone tissue engineering due to their capability to chemically bond with the host tissue and to induce osteogenesis. As a result, several efforts have been addressed to use bioactive glasses in the production of three-dimensional (3D) porous scaffolds for bone regeneration. In this work, we creatively combine typical concepts of porous glass processing with those of waste management and propose, for the first time, the use of bread as a new sacrificial template for the fabrication of bioactive scaffolds. Preliminary SEM investigations performed on stale bread from industrial wastes revealed a suitable morphology characterized by an open-cell 3D architecture, which is potentially able to allow tissue ingrowth and vascularization. Morphological features, mechanical performances and in vitro bioactivity tests were performed in order to evaluate the properties of these new "sustainable" scaffolds for bone replacement and regeneration. Scaffolds with total porosity ranging from 70 to 85 vol% and mechanical strength comparable to cancellous bone were obtained. Globular hydroxyapatite was observed to form on the surface of the scaffolds after just 48-h immersion in simulated body fluid. The results show great promise and suggest the possibility to use bread as an innovative and inexpensive template for the development of highly-sustainable bone tissue engineering approaches. [ABSTRACT FROM AUTHOR]