The Lubricating Properties of Human Whole Saliva

We demonstrate the efficient boundary lubricating properties of human whole saliva (HWS) in a soft hydrophobic rubbing contact, consisting of a poly(dimethylsiloxane) (PDMS) ball and a PDMS disk. The influence of applied load, entrainment speed and surface roughness was investigated for mechanically stimulated HWS. Lubrication by HWS results in a boundary friction coefficient of μ ≈ 0.02, two orders of magnitude lower than that obtained for water. Dried saliva on the other hand results in μ ≈ 2–3, illustrating the importance of hydration for efficient salivary lubrication. Increasing the surface roughness increases the friction coefficient for HWS, while it decreases that for water. The boundary lubricating properties of HWS are less sensitive to saliva treatment than are its bulk viscoelastic properties. Centrifugation and ageing of HWS almost completely removes the shear thinning and elastic nature observed for fresh HWS. In contrast, the boundary friction coefficients are hardly affected, which indicates that the high-M _w (supra-)molecular structures in saliva, which are expected to be responsible for its rheology, are not responsible for its boundary lubricating properties. The saliva-coated PDMS surfaces form an ideal model system for ex-vivo investigations into oral lubrication and how the lubricating properties of saliva are influenced by other components like food, beverages, oral care products and pharmaceuticals.     

Synthesis and characterization of a plant cutin mimetic polymer

A mimetic polymer of plant cutin have been synthesized from 9,10,16-trihydroxyhexadecanoic (aleuritic) acid through a low temperature polycondensation reaction. Reaction conditions (solvent, catalyst, temperature, etc…) were studied and modified to optimize yield and product characteristics. The resulting polyaleurate polymer was characterized by Attenuated Total Reflection-Fourier Transform Infrared Spectroscopy (ATR-FTIR), Differential Scanning Calorimetry (DSC), X-ray Diffraction (XRD) and solid state ¹³C-Cross Polarization/Magic Angle Spinning Nuclear Magnetic Resonance (¹³C-CP/MAS NMR). Mechanical and hydrodynamic properties were also investigated. In the average, the product obtained is physically and chemically very similar to plant cutin (a hydrophobic polyester). However, a more detailed analysis of results reveals that polyaleurate framework is more rigid than natural cutin and with additional larger short-range ordered domains. Also, the synthetic polymer displays slightly different mechanical properties with respect to natural cutin. Additional hydrogen bonding within the framework of polyaleurate is considered to be responsible for such experimental observations.     

Biomimetic micro-textures,mechanical behaviors and intermittent turning performance of textured Al2O3/TiC micro-composite and micro-nano-composite ceramics

This work was conducted to investigate biomimetic micro-textures, mechanical behaviors and intermittent turning performance of textured Al₂O₃/TiC micro-composite and micro-nano-composite ceramics. Chip characteristics and the geometry features of the structures on the cuticle of Procambarus clarkia were considered in the preparation of the laser-induced biomimetic micro-textures on the composite ceramic surfaces. Characteristics of the biomimetic micro-textures were revealed in terms of geometry, morphology and chemical composition. The connection between the thermal stress resulting from laser pulse and the fractal dimension of the micro-crack on the micro-textures was analyzed and identified. The correlation between the mechanical behaviors (damage and fracture toughness) of the textured composite ceramics and the fractal dimension of the micro-crack was fitted and revealed quantitatively. The performance of the textured composite ceramic tools was pre-evaluated by means of a proposed indicator. Damage, fracture toughness and tool stress were incorporated in the indicator. The indicator and the experimental tool wear were compared for validating the effectiveness of the proposed indicator. It was found that the micro-composite ceramic exhibited greater sensitivity to laser than the micro-nano-composite ceramic did. The damage of the textured micro-composite ceramic was larger than that of the textured micro-nano-composite ceramic when the same laser parameters were utilized in the micro-texture preparation. On the contrary, the fracture toughness of the textured micro-composite ceramic was found to be smaller. There was a negative correlation between the damage of the textured composite ceramic and the fractal dimension of the micro-crack. Conversely, there was a positive correlation between the fracture toughness and the fractal dimension. The performance of the textured micro-nano-composite ceramic tool was better than that of the textured micro-composite ceramic tool. The proposed indicator can be used to predict the combination of laser parameters that resulted in the optimum performance of the textured composite ceramic tool.     

Direction-dependent adhesion of micro-walls based biomimetic adhesives

The adhesive properties of a biomimetic anisotropic micro-structured surface are investigated. The system is constituted by parallel elastic wall-like structures topped with a thin film. The micro-walls are assumed in perfect contact with a rigid substrate and the adhesive interaction is modeled by considering full contact conditions. Because of its crack trapping behavior, this geometry, when loaded with an external moment acting perpendicularly to the walls direction, shows enhanced adhesive properties compared to the simple flat surface.In the present paper, we study how the adhesive properties depend on the direction of crack propagation. In particular, we determine how the applied moment needed to detach the adhesive depends on the angle that the crack propagation direction makes with the micro-walls one. We find that crack trapping occurs only when crack propagates perpendicularly to the walls. In all the other cases, the system compliance linearly increases with the crack length, causing the energy release rate at the crack to be constant during the crack propagation: crack trapping cannot occur in such conditions.We also propose a simplified analytical model, based on the Euler–Bernoulli beam theory, to calculate the adhesion strength of the system. Analytical solution and numerical calculations show perfect agreement for all directions of crack propagation and values of geometrical parameters.     

Adhesion and interfacial characterization of biomimetically texturized lithium disilicate

Lithium disilicate glass-ceramic (LS2) can be biomimetically textured by crystal orientation, mimicking the microstructure of dental enamel and inducing anisotropic mechanical responses to crack growth. The deliberate texturization of LS2 plays to the clinical advantage of reinforcing weak sites of typical fracture initiation in dental prosthetic constructs. Similar to enamel, adhesion of biomimetically textured LS2 could also show anisotropic behavior. Therefore, tensile bond strength (TBS) before and after thermocycling (TC) and interfacial characterization of biomimetically textured LS2 (parallel (PAR) or perpendicular (PER) crystal orientation) after different pre-treatment modes (hydrofluoric acid etching (HFE), grit blasting (GBL) and self-etching glass-ceramic primer (SGP)) were investigated. TC reduced significantly TBS for all specimens except for GBL. Biomimetic textured LS2 after HFE showed anisotropic behavior regarding adhesion. Crystal orientation reduced TBS for the PER HFE specimens after TC significantly. In general, the TBS of HFE specimens was still higher or not significantly lower compared to other pre-treatment modes like GBL or SGP. For the GBL and SGP specimens, crystal orientation had no influence on TBS and interfacial characteristics. In contrast HFE specimens showed different interfacial characteristics depending if they were PAR or PER texturized. Based on these findings, HFE of biomimetic textured LS2 can be recommended. For bonding, the PAR orientation is recommended as its adhesion potential is less prone to degrade.     

Design of untethered soft material micromachine for life-like locomotion

Living organisms composed of composite materials with complex structures support autonomous and intelligent behaviors, such as motility, perception and response to changes of the environment. By studying the biological structures and their environmental interactions, researchers are now using these natural systems as models for building soft material machines. In this review, we discuss materials and machine engineering principles to achieve life-like locomotion and functionalities in untethered soft micromachines. Through the various mechanochemical or physical mechanisms, we show how molecular motion can be collectively amplified into versatile macroscopic deformation by materials engineering across multiple length scales. In controlled ways, mobile micromachines are made to crawl, roll or jump and adaptive to various terrains, typically inspired by the terrestrial animals while propulsion of swimming micromachines are guided by aquatic organisms. Besides, out-of-equilibrium behaviors of living systems, such as cell cycling, have stimulated the design of autonomous movement. Furthermore, we review the recent efforts on robotic locomotion intelligence to achieve adaptive, functional locomotion and navigation in complex environment. We finally provide a critical perspective for the field of soft micromachines, and highlight the key challenges of different material systems that need to be overcome to realize practical use.     

绳驱动纱筒抓取仿生机械手设计

针对纱筒上下料对人力过度依赖的问题,在研究仿生学手指基础上,构建面向智能制造的纱筒抓取仿生机械手。首先,采取模块化设计思想,设计适合纱筒抓取的仿生机械手结构模型,并选择绳索传动作为驱动方式;其次,详细分析仿生机械手的组成及其抓取原理,运用D-H坐标法,实现机械手指坐标系和手指基座坐标系之间变换,推导机械手末端位置方程,得到最优抓取姿态;最后,利用有限元软件,建立三维欠驱动仿生机械手模型并对其进行虚拟装配与运动仿真分析,以验证机械手抓取纱筒的可行性和稳定性,形成机器人智能抓取仿生机械手的关键技术。     

仿生魟鱼环形胸鳍波动推进的流场仿真

针对自主设计的仿生魟鱼水下机器人环形胸鳍波动推进过程进行了流场仿真研究。基于魟鱼前进运动时的胸鳍波动特征,建立了仿生环形胸鳍三维波动运动模型。利用CFD对胸鳍波动推进过程进行数值计算,分析了波动胸鳍产生的拉力以及前向运动的速度等推进性能。研究了周期波动过程中鳍面的周向压力分布,进行鳍面附近核心涡以及切面二维涡分量的计算,分析了涡的产生、发展以及尾迹涡的相关特性。结果表明,稳定后的拉力系数以近似正弦波形式进行波动,鳍面波动前后缘分布的高压和低压区域随波动沿周向从前往后传播,环形波动长鳍最终在尾迹处形成卡门涡,流场分析为仿生魟鱼水下机器人的运动控制及性能优化提供理论基础。     

火山岩型铀矿中基性岩与铀成矿作用研究

传统地球化学理论认为火山岩型铀矿的热液铀矿床中的铀都是通过氧化溶液搬运的,并由六价还原成四价而沉淀成矿;或者是是碱交代作用形成的。但大量的文献表明,铀的成矿不仅与火山岩和次火山岩有关,还与深源的中基性岩有关。     

Biomimetic chitosan-hydroxyapatite hybrid biocoatings for enamel remineralization

Development of biomimetic ceramic-based materials is currently a challenge in dental tissue engineering. Synthetic hybrid chitosan (CS)-hydroxyapatite (HAP) layers are regarded as candidates for teeth remineralization, protection against further demineralization ensuring also antibacterial activity. Thus, the aim of this work was to obtain new biomimetic CS-HAP layers for restoration of damaged mature enamels and to pursue morphological, compositional, structural and hardness modifications of the grown layers by immersion for 4, 7 and 10 days into artificial saliva (AS) under CS-Emdogain (EMD) hydrogel action. SEM-EDX, HRTEM-SAED, FTIR and micro-Raman findings indicated formation of carbonate-substituted HAP, B-type, with c-axis orientation in the newly formed CS-HAP coatings. Prolonged immersion span of 10 days caused increasing CS content in the superficial grown layer while carbonate content diminished. Optimum Ca/P ratio (1.85 at%) and hardness of 2.48 GPa were recorded for seven days growth using CS-EMD hydrogel. Subtle changes in HAP lattice parameters were recorded for 10-day grown layer while c-axis orientation of HAP crystals at mesoscale was preserved. Mechanism of CS interaction during in situ biomimetic synthesis and self-assembly of HAP crystals under CS-EMD hydrogel presence is also discussed.