VO-Notches Subjected to Tension-Torsion Loading: Experimental and Theoretical Fracture Study on Polymeric Samples.

In this research, the fracture behavior of brittle specimens weakened by V-shaped notches with end holes (VO-notches) is studied. First, an experimental investigation is conducted to evaluate the effect of VO-notches on fracture behavior. To this end, VO-notched samples of PMMA are made and exposed to pure opening mode loading, pure tearing mode loading, and some combinations of these two loading types. As part of this study, samples with end-hole radii of 1, 2, and 4 mm are prepared to determine the effect of the notch end-hole size on the fracture resistance. Second, two well-known stress-based criteria, namely the maximum tangential stress (MTS) criterion and the mean stress (MS) criterion, are developed for VO-shaped notches subjected to mixed-mode I/III loading, also determining the associated fracture limit curves. A comparison between the theoretical and the experimental critical conditions indicates that the resulting VO-MTS and VO-MS criteria predict the fracture resistance of VO-notched samples with about 92% and 90% accuracy, respectively, confirming their capacity to estimate fracture conditions.

4D printing: a cutting-edge platform for biomedical applications.

Nature's materials have evolved over time to be able to respond to environmental stimuli by generating complex structures that can change their functions in response to distance, time, and direction of stimuli. A number of technical efforts are currently being made to improve printing resolution, shape fidelity, and printing speed to mimic the structural design of natural materials with three-dimensional printing. Unfortunately, this technology is limited by the fact that printed objects are static and cannot be reshaped dynamically in response to stimuli. In recent years, several smart materials have been developed that can undergo dynamic morphing in response to a stimulus, thus resolving this issue. Four-dimensional (4D) printing refers to a manufacturing process involving additive manufacturing, smart materials, and specific geometries. It has become an essential technology for biomedical engineering and has the potential to create a wide range of useful biomedical products. This paper will discuss the concept of 4D bioprinting and the recent developments in smart materials, which can be actuated by different stimuli and be exploited to develop biomimetic materials and structures, with significant implications for pharmaceutics and biomedical research, as well as prospects for the future.

Recent progress in extrusion 3D bioprinting of hydrogel biomaterials for tissue regeneration: a comprehensive review with focus on advanced fabrication techniques.

Over the last decade, 3D bioprinting has received immense attention from research communities for developing functional tissues. Thanks to the complexity of tissues, various bioprinting methods have been exploited to figure out the challenges of tissue fabrication, in which hydrogels are widely adopted as a bioink in cell printing technologies based on the extrusion principle. Thus far, there is a wealth of literature proposing the crucial parameters of extrusion-based bioprinting of hydrogel biomaterials (e.g., hydrogel properties, printing conditions, and tissue scaffold design) toward enhancing performance. Despite the growing research in this field, numerous challenges that hinder advanced applications still exist. Herein, the most recently reported hydrogel-based bioprinted scaffolds, i.e., skin, bone, cartilage, vascular, neural, and muscular (including skeletal, cardiac, and smooth) scaffolds, are systematically discussed with an emphasis on the advanced fabrication techniques from the tissue engineering perspective. The methods covered include multiple-dispenser, coaxial, and hybrid 3D bioprinting. The present work is a unique study to figure out the opportunities of the novel techniques to fabricate complicated constructs with structural and functional heterogeneity. Finally, the principal challenges of current studies and a vision of future research are presented.

Synthesis of a novel nitrogen-doped carbon dot by microwave-assisted carbonization method and its applications as selective probes for optical pH (acidity) sensing in aqueous/nonaqueous media, determination of nitrate/nitrite, and optical recognition of NOX gas.

A novel nitrogen-doped carbon dot (N-CD) was synthesized via carbonization of citric acid in the presence of triethylenetetramine as a nitrogen source. The average size of the N-doped CDs and also the quantum yield of the synthesized N-doped CDs were both estimated to be 9 ± 2 nm and 39.5%, respectively. The applications of the synthesized carbon nanostructure as a high quantum yield fluorescence probe were initially adopted in the fabrication of a novel optical pH (acidity) sensor in both aqueous and nonaqueous environments. Two optimum dynamic intervals were obtained with the ranges of1.5-5.0 and 7.0-10.0. for the fabricated pH sensor with a standard deviation of 0.09 pH (n = 4). The quantity of HClO4 inside acetic acid was determined as the degree of acidity with a linear range between 1.0 and 4.0%. Determination of nitrate (NO3-) and nitrite (NO2-) based on the fluorescence quenching of N-CDs was also evaluated in detail. The linear ranges for NO2- and NO3- species were estimated to be from 1 × 10-7to 7.5 × 10-5 and from 2.5 × 10-6 to 7.5 × 10-4 mol L-1, respectively with RSD of 3.69% (n = 5) for NO2- and 3.54% (n = 5) for NO3-. The LODs (X+3Sb) for both NO2- and NO3- were estimated to be 2.5 × 10-8 and 7.5 × 10-7 mol L-1, respectively. The synthesized N-CDs were also applicable for NOX recognition in the gaseous form at part per thousand (ppt) levels with linear ranges of 3.77-36.51 and 27.67-43.77 ppt, LOD (X+3Sb) of 1.41 ppt (n = 4) and RSD of 4.37% (n = 5). The reliability of these methods was also evaluated via the analyses of different forms of gaseous, water and rumen samples.