A study of tensile and bending properties of 3D-printed biocompatible materials used in dental appliances

In the last years, a large number of new biocompatible materials for 3D printers have emerged. Due to their recent appearance and rapid growth, there is little information about their mechanical properties. The design and manufacturing of oral appliances made with 3D printing technologies require knowledge of the mechanical properties of the biocompatible material used to achieve optimal performance for each application. This paper focuses on analysing the mechanical behaviour of a wide range of biocompatible materials using different additive manufacturing technologies. To this end, tensile and bending tests on different types of recent biocompatible materials used with 3D printers were conducted to evaluate the influence of the material, 3D printing technology, and printing orientation on the fragile/ductile behaviour of the manufactured devices. A test bench was used to perform tensile tests according to ASTM D638 and bending tests according to ISO 178. The specimens were manufactured with nine different materials and five manufacturing technologies. Furthermore, specimens were created with different printing technologies, biocompatible materials, and printing orientations. The maximum allowable stress, rupture stress, flexural modulus, and deformation in each of the tested specimens were recorded. Results suggest that specimens manufactured with Stereolithography (SLA) and milling (polymethyl methacrylate PMMA) achieved high maximum allowable and rupture stress values. It was also observed that Polyjet printing and Selective Laser Sintering technologies led to load–displacement curves with low maximum stress and high deformation values. Specimens manufactured with Digital Light Processing technology showed intermediate and homogeneous performance. Finally, it was observed that the printing direction significantly influences the mechanical properties of the manufactured specimens in some cases.

Biomolecules Orchestrating Cardiovascular Calcification

Vascular calcification, once considered a degenerative, end-stage, and inevitable condition, is now recognized as a complex process regulated in a manner similar to skeletal bone at the molecular and cellular levels. Since the initial discovery of bone morphogenetic protein in calcified human atherosclerotic lesions, decades of research have now led to the recognition that the regulatory mechanisms and the biomolecules that control cardiovascular calcification overlap with those controlling skeletal mineralization. In this review, we focus on key biomolecules driving the ectopic calcification in the circulation and their regulation by metabolic, hormonal, and inflammatory stimuli. Although calcium deposits in the vessel wall introduce rupture stress at their edges facing applied tensile stress, they simultaneously reduce rupture stress at the orthogonal edges, leaving the net risk of plaque rupture and consequent cardiac events depending on local material strength. A clinically important consequence of the shared mechanisms between the vascular and bone tissues is that therapeutic agents designed to inhibit vascular calcification may adversely affect skeletal mineralization and vice versa. Thus, it is essential to consider both systems when developing therapeutic strategies.

Avaliação das propriedades mecânicas de filmes biodegradáveis e sua aplicação em embalagens para acondicionamento de plantas

Neste trabalho empregou-se a técnica de casting para a produção de filmes. Utilizou-se quantidades distintas de amido de milho, glicerina e extrato de própolis-verde, sendo avaliadas as propriedades mecânicas (módulo de Young, elasticidade e tensão à ruptura) dos materiais obtidos. Verificou-se o efeito das variáveis e de suas interações pelo gráfico de Pareto. Superfícies de resposta foram construídas em testes conduzidos com 95% de confiança. A análise dos resultados indicou que o amido de milho foi o que mais influenciou na determinação do módulo de Young. Por outro lado, para a elongação, a glicerina, utilizada como agente plastificante, foi o fator mais relevante. Na análise da tensão à ruptura, observou-se que a interação entre a glicerina e o extrato de própolis-verde foi a mais significativa. Foi então selecionado o filme que apresentou as características mais adequadas no acondicionamento de mudas de alface. Os resultados indicaram que a amostra produzida a partir de 4 g de amido de milho, 1 g de glicerina e 0,12 g de extrato de própolis-verde foi a mais apropriada. Com relação ao acondicionamento da muda de alface, foi feita uma análise visual e macroscópica com a finalidade de verificar a resistência do filme biodegradável quando o substrato e a muda foram adicionados na embalagem. Foi observado que o material sintetizado e escolhido teve uma capacidade adequada para a sua retenção, o que favorece e ratifica o seu emprego, uma vez que, ao ser biodegradável, pode se tornar substituto de plásticos convencionais. Palavras-chave: Técnica casting. Módulo de Young. Elasticidade. Tensão à ruptura. Evaluation of the mechanical properties of biodegradable films and their application in packaging for packaging plants Abstract In this work the technique of casting was used for the production of films. Different quantities of corn starch, glycerin and propolis-green extract were used, and the mechanical properties (Young's modulus, elasticity and tensile strength) of the materials obtained were evaluated. The effect of the variables and their interactions on the Pareto graph was verified. Response surfaces were constructed in tests conducted with 95% confidence. The analysis of the results indicated that the corn starch was the most influential in determining the Young's modulus. On the other hand, for elongation, glycerin, used as a plasticizing agent, was the most relevant factor. In analyzing the rupture stress, it was observed that the interaction between glycerin and the propolis-green extract was the most significant. It wasthenselectedthefilmthatpresentedthemost suitable characteristics in the packaging of lettuce seedlings. The results indicated that the sample produced from 4 g of cornstarch, 1 g of glycerin and 0.12 g of propolis-green extract was the most appropriate. Regarding the conditioning of the lettuce change, a visual and macroscopic analysis was performed to verify the resistance of the biodegradable film when the substrate and the change were added to the packaging. It hás been observed that the synthesized and selected material hás the proper capacity for its retention, which favors and ratifies its use, since, being biodegradable, it can be come a substitute for conventional plastics. Keywords:Casting technique. Young's module. Elasticity. Tensionto break.

Evaluation of Hardness, Sliding Wear and Strength of a Hypoeutectic White Iron with 25%Cr after Heat Treatments

Hypoeutectic white cast irons with a high chrome content are commonly used in the industrial mining sector where there is a demand for both high resistance to adhesive wear and an acceptable toughness for the absorption of impacts and falls of diverse materials. Through the application of a design of experiment (DoE) technique, factors related to thermal treatment are analyzed with respect to resistance to sliding wear, maximum rupture stress and toughness. The results show that, in order to increase resistance to adhesive wear, it is convenient to use destabilization temperatures of 1050 °C and tempering of two hours at 400 °C. This foments a very hard martensite and a high proportion of highly alloyed retained austenite, which, with low tempering, achieves a precipitation of carbides from this austenite with hardly any loss of hardness of the martensite. In order to increase the energy which this material is capable of absorbing until breakage, furnace cooling set at 150 °C followed by tempering at 550 °C would be favorable. Slower cooling implies a greater quantity of conditioned retained austenite, so that, following this, it may be transformed into lower bainite with a high density of finely dispersed precipitated carbides. Furthermore, this tempering also allows the transformation of martensite into ferrite with finely dispersed carbides.

Rupture stress of liquid metal nanoparticles and their applications in stretchable conductors and dielectrics

Few works had systematically investigated the relationship between the rupture stress of the oxide shell and the diameter of liquid metal nanoparticles (LMNPs). Here, we fabricated a series of elastomer/LMNPs composites, which were based on various polyurethanes with different shore hardness and LMNPs with different diameters, to systematically study the rupture stress of LMNPs. We established a reliable and guidable relationship between the stress–strain curves of elastomers with different shore hardness and rupture stress of LMNPs with various diameters by both experiments and numerical calculations. Based on this guidance, we can facilely prepare stretchable conductors with remarkable stretchability and conductivity (i.e., 24,130 S · cm−1 at 500% strain) and stretchable dielectrics with excellent stretchability and permittivity (i.e., dielectric constant of 76.8 with 580% strain) through controlling the shore hardness of elastomers and diameter of LMNPs. This work will facilitate the systematic study of LMNPs and expand their use in stretchable electronics.

Tubular chitosan device for use as prosthesis coating in vascular surgery

Chitosan is a natural, biodegradable, non-toxic and biocompatible polymer, with characteristics such as a healing, hemostatic, antimicrobial agent, among others. Therefore, the aim of this study is to develop a tubular chitosan device for use as a prosthetic coating application in vascular surgery. The chitosan wires were obtained by the spinning method in a 2M sodium hydroxide coagulant solution (NaOH) and used in the form of wires and screens as a reinforcement structure to obtain the tubes. In order to characterize the tubes, optical microscopy, contact angle, degree of swelling, in vitro biodegradation, cytotoxicity and tensile strength were used. The results indicated that the tubes have uniformity over the entire length and as for the resistance to the trace, the tube reinforced with mesh presented greater deformation, while the tube reinforced with wire presented a higher value of rupture stress. The degree of swelling was higher in chitosan tubes with mesh. As for the biodegradation test, it was observed that the lysozyme samples showed greater loss of mass and the cytotoxicity test confirmed the cell viability of the material, concluding that the tubes reinforced with chitosan wires are promising for use in vascular surgeries.

Self-Healing Thermoplastic Polyurethane Linked via Host-Guest Interactions

High toughness with self-healing ability has become the ultimate goal in materials research. Herein, thermoplastic polyurethane (TPU) was linked via host-guest (HG) interactions to increase its mechanical properties and self-healing ability. TPU linked via HG interactions was prepared by the step-growth bulk polymerization of hexamethylene diisocyanate (HDI), tetraethylene glycol (TEG), and HG interactions between permethylated amino βCD (PMeAmβCD) and adamantane amine (AdAm). TPU linked with 10 mol% of HG interactions (HG(10)) showed the highest rupture stress and fracture energy (GF) of 11 MPa and 25 MJ·m−3, which are almost 40-fold and 1500-fold, respectively, higher than those of non-functionalized TEG-based TPU (PU). Additionally, damaged HG(10) shows 87% recovery after heated for 7 min at 80 °C, and completely cut HG(10) shows 80% recovery after 60 min of reattachment at same temperature. The HG interactions in TPU are an important factor in stress dispersion, increasing both its mechanical and self-healing properties. The TPU linked via HG interactions has great promise for use in industrial materials in the near future.