压电材料课件

单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,*,单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,*,单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,*,单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,*,单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,*,压电材料,（,P,iezoelectric,M,aterial）,Speaker：Zhangquan,Team members:,Sihewei and Fengtiantian,压电材料,1,、压电现象,压电现象是100多年前居里兄弟研究石英时发现的。压电现象主要发现在晶体分子排列不对称的材料上。,2,、压电效应,如果对压电材料施加压力，它便会产生电位差（称之为正压电效应），反之施加电压,则产生机械应力（称为逆压电效应）。如果压力是一种高频震动，则产生的就是高频电流。而高频电信号加在压电陶瓷上时，则产生高频声信号（机械震动），这就是我们平常所说的超声波信号。也就是说，压电陶瓷具有机械能与电能之间的转换和逆转换的功能。,3,、压电材料的分类,第一类是无机压电材料，分为压电晶体和压电陶瓷，压电晶体一般是指压电单晶体；压电陶瓷则泛指压电多晶体。压电晶体一般指压电单晶体，是指按晶体空间点阵长程有序生长而成的晶体。这种晶体结构无对称中心，因此具有压电性。压电陶瓷是指用必要成份的原料进行混合、成型、高温烧结，由粉粒之间的固相反应和烧结过程而获得的微细晶粒无规则集合而成的多晶体。这类材料的研制成功，促进了声换能器，压电传感器的各种压电器件性能的改善和提高。,第二类是有机压电材料，又称压电聚合物，如偏聚氟乙烯（PVDF）（薄膜）及其它为代表的其他有机压电（薄膜）材料。这类材料及其材质柔韧，低密度，低阻抗和高压电电压常数(g)等优点为世人瞩目，且发展十分迅速，现在水声超声测量，压力传感，引燃引爆等方面获得应用。,第三类是复合压电材料，这类材料是在有机聚合物基底材料中嵌入片状、棒状、杆状、或粉末状压电材料构成的。至今已在水声、电声、超声、医学等领域得到广泛的应用。,Piezoelectric materials for tissue regeneration:A review,1.Introduction,Piezoelectric materials are smart materials that can generate electrical activity in response to minute deformations.First discovered by Pierre and Jacques Curie in 1880,deformation results in the asymmetric shift of ions or charges in piezoelectric materials,which induces a change in the electric polarization,and thus electricity is generated.,Piezoelectric materials are widely used in various electronic applications such as transducers,sensors and actuators.,For biomedical applications,piezoelectric materials allow for the delivery of an electrical stimulus without the need for an external power source.As a scaffold for tissue engineering,there is growing interest in piezoelectric materials due to their potential of providing electrical stimulation to cells to promote tissue formation.,In this review,the author cover the discovery of piezoelectricity in biological tissues,and summarizes their potential as a promising scaffold in the tissue engineering field.,-Helix is a right handed coil,stabilized by the hydrogen bonds,between the hydrogen of one,amine group with the oxygen of,a consecutive carbonyl group.As,demonstrated in Fig.1,the helical,structure repeatedly aligns the,dipoles of thebackbone amino,acids and causes a significant,permanent polarization.,Fig.1.Schematic illustration of permanent polarization in a-helix.Red arrows demonstrate,the direction of the dipole moment.,Yasuda reported the piezoelectricity of bone in 1954.Later,Yasuda and Fukada observed piezoelectricity in boiled bone and consequently concluded that living cells were not responsible for the piezoelectric response.They attributed the piezoelectric behavior of bone to the application of shear on collagen.Bone is a composite of densely packed aligned collagen fibrils containing hydroxyapatite particles.,Fig.2 shows the topography of a single collagen fibril imaged by AFM,and its,corresponding shear piezoelectricity,imaged by lateral PFM,demonstrating,the periodicity of the piezoforce,amplitude attributed to the gaps and,overlaps in the quarter-staggered,structure of collagen.,Fig.2.Topography of a single collagen fibril imaged by atomic force microscopy(a),and the amplitude of its corresponding shear piezoelectricity acquired by piezoforce microscopy in the lateral mode(b,),3.Piezoelectricity and streaming potential,In 1892,Julius Wolff suggested that bone remodels its architecture in response to stress.Wolffs Law manifests itself in the denser bone in tennis players racket-holding arms or bone loss in astronauts.After the discovery of piezoresponse in dry bone,the proposed mechanism to describe bone growth and resorption in response to stress was piezoelectricity.,Bassett observed that unlike undeformed samples,periodically deformed cultivated chick embryonic tibiae produced large periosteal chondroid masses after 7 days,and described Wolff s law as a negative feedback loop:applied load on bone causes strain in less dense regions;while denser and consequently stiffer regions remain unstrained.The strain is transformed into an lectric field that aggregates and aligns macromolecules and ions in the extracellular matrix,which stimulates cells to remodel the bone architecture until the signal is switched off.,The attention in neural regeneration has been drawn to repairing peripheral nerve injuries through improved neural differentiation and directional outgrowth of neurites.However,promising results are not limited to neurons;an early study on the effect of electrical stimulation on bone formation showed that implanting insulated batteries in the medullary canal of canine femora caused substantial formation of endosteum near the cathode in a 1421 day period.Even in the absence of external electrical stimulation,implanting poled sintered hydroxyapatite disks in canine cortical bone resulted in the lling of a 0.2 mm gap between the negatively charged hydroxyapatite surface and the cortical bone in 14 days,while no bon