Casting of microstructured shark skin surfaces and possible applications on aluminum casting parts

Within the project "Functional Surfaces via Micro-and Nanoscaled Structures" which is part of the Cluster of Excellence "Integrative Production Technology" established and financed by the German Research Foundation (DFG),an investment casting process to produce 3-dimensional functional surfaces down to a structural size of 1μm on near-net-shape-casting parts has been developed.The common way to realize functional microstructures on metallic surfaces is to use laser ablation,electro discharge machining or micro milling.The handicap of these processes is their limited productivity.The approach of this project to raise the efficiency is to use the investment casting process to replicate microstructured surfaces by moulding from a laser-microstructured grand master pattern.The main research objective deals with the investigation of the single process steps of the investment casting process with regard to the moulding accuracy.Actual results concerning making of the wax pattern,suitability of ceramic mould and core materials for casting of an AlSi7Mg0.3 alloy as well as the knock-out behavior of the shells are presented.By using of the example of an intake manifold of a gasoline race car engine,a technical shark skin surface has been realized to reduce the drag of the intake air.The intake manifold consists of an air-restrictor with a defined inner diameter which is microstructured with technical shark skin riblets.For this reason the inner diameter cannot be drilled after casting and demands a very high accuracy of the casting part.A technology for the fabrication and demoulding of accurate microstructured castings are shown.Shrinkage factors of different moulding steps of the macroscopic casting part as well as the microscopic riblet structure have been examined as well.

NUMERICAL SIMULATION AND EXPERIMENTAL STUDY OF DRAGREDUCING SURFACE OF A REAL SHARK SKIN

It is well known that shark skin surface can effectively inhabit the occurrence of turbulence and reduce the wall friction, but in order to understand the mechanism of drag reduction, one has to solve the problem of the turbulent flow on grooved-scale surface, and in that respect, the direct numerical simulation is an important tool. In this article, based on the real biological shark skin, the model of real shark skin is built through high-accurate scanning and data processing. The turbulent flow on a real shark skin is comprehensively simulated, and based on the simulation, the drag reduction mechanism is discussed. In addition, in order to validate the drag-reducing effect of shark skin surface, actual experiments were carried out in water tunnel, and the experimental results are approximately consistent with the numerical simulation.

An Application of the Shark Skin Denticle Geometry for Windbreak Fence Design and Fabrication

Windbreak fences in open and urban areas can be used to effectively reduce the wind velocity. In this paper we examine how the geometrical shape of the windbreak fence can optimally mitigate wind velocity. We propose an approach for windbreak fence design based on a bionic parametric model of the shark skin denticle geometry, which improves the reduction of the wind velocity around and behind the windbreak fences. The generative model was used to estimate improvements by variations in the parameters of the fence panel＇s geometrical shape, inspired by shark skin denticles. The results of the Computational Fluid Dynamics （CFD） analysis indicates that the fence surface inspired by shark skin performs much better than both flat and cor- rugated surfaces. Taking into account the complex geometry of the surface inspired by shark skin denticles, we propose a fab- rication process using an expanded polystyrene foam （EPS） material, created using an industrial robot arm with a hot-wire tool. Creating EPS moulds for the shark skin denticle panels allows for a richer variety material to be used in the final design, leading both to higher efficiency and a more attractive design.

Study on the micro-replication of shark skin

Direct replication of creatural scarfskins to form biomimetic surfaces with relatively vivid morphology is a new attempt of the bio-replicated forming technology at animal body. Taking shark skins as the replication templates, and the micro-embossing and micro-molding as the material forming methods, the micro-replicating technology of the outward morphology on shark skins was demonstrated. The preliminary analysis on replication precision indicates that the bio-replicated forming technology can replicate the outward morphology of the shark scales with good precision, which validates the application of the bio-replicated forming technology in the direct morphology replication of the firm creatural scarfskins.

High-precision bio-replication of synthetic drag reduction shark skin

Nano-long chains were grafted over the replicated micro-grooves of shark skin in a novel attempt to replicate bio-synthetic drag reduction structure with high precision through synthetic bio-replication. Pre-treated shark skin was used as casting template to prepare a flexible female die of silicone rubber by soft die formation. A waterborne epoxy resin was then used to graft long-chains of drag reduction agent and prepare a synthetic drag reduction shark skin with nano-long chain drag reduction interface and lifelike micro-grooves. Replication precision analysis shows that this technology could replicate the complicated three-dimensional morphology of a biological drag reduction surface with high precision. Drag reduction experiments show that the material had an excellent synthetic drag reduction effect, with a maximal drag reduction rate of up to 24.6% over the velocities tested.

Bio-replicated forming of the biomimetic drag-reducing surfaces in large area based on shark skin

On the investigation of biomimetic drag-reducing surface, direct replication of the firm scarfskins on low-resistance creatures to form biomimetic drag-reducing surfaces with relatively vivid morphology relative to the living prototype is a new attempt of the bio-replicated forming technology.Taking shark skin as the bio-replication template, the hot embossing method was applied to the microreplication of its outward morphology. Furthermore, the skins were jointed together to form the drag-reducing surface in large area. The results of the resistance measurements in a water tunnel according to the flat-plate sample pieces have shown that the biomimetic shark-skin coating fabricated by the bio-replicated forming method has significant drag reduction effect, and that the drag reduction efficiency reached 8.25% in the test conditions.

Beneficial effects of a novel shark-skin collagen dressing for the promotion of seawater immersion wound healing

Background: Wounded personnel who work at sea often encounter a plethora of difficulties. The most important of these difficulties is seawater immersion. Common medical dressings have little effect when the affected area is immersed in seawater, and only rarely dressings have been reported for the treatment of seawater-immersed wounds. The objective of this study is to develop a new dressing which should be suitable to prevent the wound from seawater immersion and to promote the wound healing.Methods: Shark skin collagen(SSC) was purified via ethanol de-sugaring and de-pigmentation and adjusted for p H. A shark skin collagen sponge(SSCS) was prepared by freeze-drying. SSCS was attached to an anti-seawater immersion polyurethane(PU) film(SSCS+PU) to compose a new dressing. The biochemical properties of SSC and physicochemical properties of SSCS were assessed by standard methods. The effects of SSCS and SSCS+PU on the healing of seawaterimmersed wounds were studied using a seawater immersion rat model. For the detection of SSCS effects on seawaterimmersed wounds, 12 SD rats, with four wounds created in each rat, were divided into four groups: the 3 rd day group, 5 th day group, 7 th day group and 12 th day group. In each group, six wounds were treated with SSCS, three wounds treated with chitosan served as the positive control, and three wounds treated with gauze served as the negative control. For the detection of the SSCS+PU effects on seawater-immersed wounds, 36 SD rats were divided into three groups: the gauze(GZ)+PU group, chitosan(CS)+PU group and SSCS+PU group, with 12 rats in each group, and two wounds in each rat. The wound sizes were measured to calculate the healing rate, and histomorphology and the immunohistochemistry of the CD31 and TGF-β expression levels in the wounded tissues were measured by standard methods.Results: The results of Ultraviolet-visible(UV-vis) spectrum, Fourier-transform infrared(FTIR) spectrum, circular dichroism(CD) spectra, sodium dodecyl sulfate polyacrylamide gel electrophoresis(SDS-PAGE), and amino acid composition analyses of SSC demonstrated that SSC is type I collagen. SSCS had a homogeneous porous structure of approximately 200μm, porosity rate of 83.57%±2.64%, water vapor transmission ratio(WVTR) of 4500 g/m2, tensile strength of 1.79±0.41 N/mm, and elongation at break of 4.52%±0.01%. SSCS had significant beneficial effects on seawater-immersed wound healing. On the 3 rd day, the healing rates in the GZ negative control, CS positive control and SSCS rats were 13.94%±5.50%, 29.40%±1.10% and 47.24%±8.40%, respectively. SSCS also enhanced TGF-in the initial stage of the healing period. The SSCS+PU dressing effectively protected woundsβ and CD31 expression from seawater immersion for at least 4 h, and accelerated re-epithelialization, vascularization and granulation formation of seawater-immersed wounds in the earlier stages of wound healing, and as well as significantly promoted wound healing. The SSCS+PU dressing also enhanced expression of TGF-n and gauze dressings.β and CD31. The effects of SSCS and SSCS+PU were superior to those of both the chitosaConclusion: SSCS has significant positive effects on the promotion of seawater-immersed wound healing, and a SSCS+PU dressing effectively prevents seawater immersion, and significantly promotes seawater-immersed wound healing.

胃肠微环境下吻合钉仿生表面对细菌黏附的微流场仿真

目的模拟在吻合钉植入人体以后,吻合钉表面与肠壁组织之间的微流场环境,研究其仿生疏水化表面对细胞外液流速和壁面处流体剪切力的影响,进而通过流场的变化调控细菌的黏附。方法观察鲨鱼皮肤微结构,建立细菌在微流场环境中的简化二维运动模型。通过计算流体动力学数值仿真,模拟静态流场和动态流场中,细菌分别在光滑表面和微织构表面的运动,比较两种表面环境下细菌周围的流场特征和流体剪切力,分析流体剪切力影响细菌黏附的内在机制。结果仿生微织构的加入增强了微流场内细胞外液的流速,在静态流场中流体对细菌的黏滞作用较小;动态流场中流体对细菌的推动作用更强;一定范围内的微坑宽度使微织构壁面所受流体剪切力更大。结论吻合钉的仿生微织构表面,加快了细胞外液的流速,提高了微织构壁面和细菌所受流体剪切力,对细菌的附着有一定影响。研究结果为吻合钉抑菌表面的研究提供了理论依据。

仿生鲨鱼皮复合微纳减风阻结构的仿真与制备

仿生学与减阻技术的结合,为减阻开辟了重要的研究方向,在航空航天领域有着潜在的发展与应用前景。为提高降低风阻效果,本文对复合微纳减风阻结构进行了研究,基于仿生学原理,采用CFD仿真及激光微纳制造技术,建立了减阻结构组合模型,并在飞行器的大气传感器半球头体模型表面制造仿生鲨鱼皮复合微纳结构,即在仿生鲨鱼皮鳞片结构的基础上,通过激光干涉扫描二级微沟槽,以进一步提升减阻效果。采用CFD仿真与风洞实验相结合的方式,对减阻机理进行理论分析,完成了复合结构的微纳制造,减阻率最高可达10.3%。

空气炸鲨鱼皮工艺条件的优化

为开发鲨鱼皮即食休闲食品,本文对鲨鱼皮进行空气炸工艺条件的优化。采用鲨鱼皮为原料,以质构特性和色泽变化为指标,通过预干燥控制鲨鱼皮水分含量,确定最佳预干燥条件;并在单因素试验的基础上进行正交实验优化,研究碱液浓度、泡碱时间、空气炸温度和空气炸时间对鲨鱼皮品质的影响。结果表明,当预干燥控制水分含量在30%~60%时,鱼皮具有膨化作用,确定空气炸鲨鱼皮最佳工艺条件为预干燥温度80℃、干燥时间90 min、碱液浓度15 g·L^(-1)、泡碱时间10 min、空气炸温度150℃、空气炸时间14 min。该条件下制备的鲨鱼皮膨化效果最佳、色泽均匀、脆度和酥度较好。本研究旨在为空气炸鲨鱼皮即食产品工艺提供一定的理论基础。

混合流态下鲨鱼皮织构滑动轴承静特性分析

轴瓦表面的织构会导致油膜厚度分布不均匀,整个流场中雷诺数差异较大,形成紊流和层流并存的混合流态。另外在高速运转工况下润滑油温度会大幅升高,从而影响其黏度及轴承承载能力等性能。鉴于鲨鱼皮结构在减阻、防污方面的成功应用,根据鲨鱼的盾鳞结构抽象建立了类鲨鱼皮二维织构的数学模型;同时考虑紊流以及油膜温度的作用,将类鲨鱼皮织构用于滑动轴承轴瓦形面的设计上,从鲨鱼皮织构的周向和轴向分布位置、织构深度、转速4个方面,对比分析了鲨鱼皮织构与球坑以及圆柱坑织构对滑动轴承静特性的影响。结果表明:1)织构位置分布对径向滑动轴承的性能影响非常大;2)不同织构深度下,鲨鱼皮织构始终表现出良好的减摩效果;3)高速紊流状态下的鲨鱼皮织构滑动轴承相比其他轴承减阻效果更加明显。

鲨鱼盾鳞肋条结构的减阻仿生研究进展

鲨鱼体表覆有一层细小的盾鳞(Placoid scale),盾鳞上的脊状突起称为肋条(Riblet),肋条之间构成具圆弧底的沟槽。这种沟槽形态的鲨鱼盾鳞肋条结构(Riblet surfaces)具有良好的减阻作用。从盾鳞的结构、形态和功能出发,详细介绍了鲨鱼盾鳞肋条结构减阻相关的流体动力学机理及其仿生材料模型的设计与测试方法,概括了目前肋条结构仿生材料的减阻应用情况,并展望了其未来的发展方向。

仿鲨鱼皮表面微结构材料制备的研究

以具有极佳减阻能力的鲨鱼皮为模板,采用模板技术对鲨鱼皮表面微观拓扑结构进行大面积的仿生复制。通过扫描电子显微镜对鲨鱼皮以及其复制品的表面形貌进行表征,结果表明,复制的鲨鱼皮具有和模板结构一致的表面微观拓扑结构。该复制方法具有工艺简便、成本低廉、适合大面积复制等优点。

不同鲨鱼皮胶原蛋白的分离及其特性研究

目的探讨不同鲨鱼皮胶原蛋白的分离方法，并对分离胶原蛋白的部分生化特性进行研究。方法用稀碱溶胀酶解法和缓冲液溶胀分离法分别从水鲨头皮和马鲛鲨皮中分离胶原蛋白，利用聚丙烯酰胺凝胶电泳法（SDS-PAGE）、差示扫描量热仪法（DSC）、园二色谱仪法（CD）对分离胶原蛋白进行纯度及分子大小、变性温度和二级结构的测定。结果鲨鱼皮胶原蛋白回收率为鲜重的2．9％～4．1％；分离胶原蛋白在SDS-PAGE上呈现清晰的3条谱带。相对分子质量分别为205，134，118 KDa；水鲨头皮和马鲛鲨皮胶原蛋白的热变性温度分别为69℃、47℃；两种分离胶原蛋白的二级结构均主要是伊折叠和无规卷曲。不存在α-螺旋。结论采用稀碱溶胀酶解法和缓冲液溶胀分离法均能制备高纯度的胶原蛋白，从水鲨头皮和马鲛鲨皮分离的胶原蛋白相对分子质量和分子构成一致。但提取条件的不同能影响胶原蛋白的热变性温度和二级结构。

鲨鱼皮仿生防污研究

介绍了海洋生物污损对船舶的影响,大型海洋生物鲨鱼皮的结构及其防污机理,重点概述了目前关于鲨鱼皮仿生防污研究的进展。

鲨鱼皮胶原蛋白肽的成分分析及对血管紧张素转化酶活力的影响

以鲨鱼皮为原料,采用现代生物化学技术制备胶原蛋白肽水解液,经过喷雾干燥,获得鲨鱼皮胶原蛋白肽干粉.对获得的胶原蛋白肽样品进行成分分析,测定了粗蛋白、粗脂肪、水分、灰分以及K、Na、Ca、Fe、Cu、Zn、Pb等金属元素的含量,应用氨基酸自动分析仪测定样品的氨基酸组成,并用化学分析法测定羟脯氨酸含量为7.08%,应用MALDI-TOF分析胶原蛋白肽分子量的分布,表明我们得到的鲨鱼皮胶原蛋白的水解产物——胶原蛋白肽的分子量主要分布在2～3ku,为水溶性多肽混合物.研究鲨鱼皮胶原蛋白肽对血管紧张素转化酶(ACE)的抑制效应,表明该样品对ACE有较强的抑制作用,其IC50为4.8 mg/mL.本文还探讨了鲨鱼皮胶原蛋白的吸湿性和保湿性.

LLDPE/LDPE共混熔体不稳定流动性的研究

采用恒速型双毛细管流变仪对比研究了LDPE/LLDPE不同组分含量共混物在较宽速率范围内的流变行为,通过研究共混物的黏度、弹性、挤出压力振荡、流动曲线、挤出畸变的差异,分析讨论了共混组成对黏弹性,进而对挤出压力振荡、鲨鱼皮等不稳定流动现象的影响。结果表明,共混使熔体的非线性黏性、弹性均增加,挤出畸变现象加重;少量LDPE的混入可消除LLDPE的挤出压力振荡现象,但鲨鱼皮畸变加重;而少量LLDPE的混入却不能消除LDPE熔体在毛细管入口处的压力振荡现象。

鲨鱼皮仿生结构应用及制造技术综述

鲨鱼体表的盾鳞沟槽结构具有显著的减阻效果。鲨鱼仿生沟槽结构的应用涉及航空、舰艇、汽车、管路运输、风力发电等领域。鲨鱼皮沟槽结构的仿生制造主要有两个途径,即沟槽结构形式与鲨鱼盾鳞仿真结构形式。文章针对沟槽结构的微槽滚压、金刚石多轮廓磨削、飞秒激光烧蚀等制造技术,及鲨鱼盾鳞仿真结构的微压印法、固化法、微电铸法、微纳米滚压法、软刻技术等进行了综述,并对鲨鱼皮仿生结构制造技术进行了展望。

鲨鱼皮微沟槽结构复制技术研究

表面具有大量微沟槽结构的鲨鱼皮具有良好的减阻效果,因此鲨鱼皮复制技术成为国内外减阻技术研究的热点之一.以鲨鱼表面微小盾鳞结构为复制模板,采用热压成型法和真空浇注法,分别在有机玻璃和不饱和树脂表面进行微结构复制,同时利用触针式轮廓仪和体视显微镜对不同材料和复制方法制备的仿生鲨鱼皮进行了对比分析.结果表明:相对于热压成型法,不饱和树脂作为复制模具材料,采用真空浇注法复制的液态硅橡胶仿鲨鱼皮,具有清晰完整的鲨鱼皮微沟槽结构,是一种较为可行的大面积高精度复制鲨鱼皮微沟槽的方法.

鲨鱼皮微电铸复制工艺研究

采用微电铸技术对生物表面形貌进行直接复制以成形出与生物原型形貌相接近的仿生表面,是生物复制成形技术由高聚物成形向金属沉积成形扩展的新途径。以鲨鱼皮为生物模板,针对其表皮微形貌结构特征,通过倾斜溅射方式先在其鳞片表面沉积导电层,进而采用正负间断脉冲电流对鲨鱼皮生物模板进行微电铸复制,成形出鲨鱼皮微电铸模板及仿鲨鱼表面。复制精度分析结果表明,采用微电铸生物复制成形工艺可以实现对鲨鱼皮外端沟槽微形貌的高逼真复制,证明该工艺可以应用于微尺度、复杂生物表面形貌的直接复制。