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1、压电材料 （Piezoelectric Material）,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
2、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
3、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,CONTENTS,1. Introduction2. Piezoelectricity in biological tissues3. Piezoelectricity and streaming potential4. Cellular response to electrical stimulation5. Piezoelectric mat
4、erials in tissue regeneration applications6. Conclusion,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 c
5、harges 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
6、 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 a
7、uthor cover the discovery of piezoelectricity in biological tissues,and summarizes their potential as a promising scaffold in the tissue engineering field.,2. Piezoelectricity in biological tissues,In 1940, Martin noticed the first demonstration of biological piezoelectricity, when he detected elect
8、ric potentials from a bundle of wool encapsulated in shellac while compressed by two brass plates. The main constituent of mammalian hair, wool, horn and hoof is -keratin, which has a spiral -helix structure.The piezoelectricity of such tissues is attributed to the compact alignment of these highly
9、ordered -helices and their inherent polarization.,-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 amin
10、o 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
11、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.,Piezo
12、force microscopy (PFM) is a modification of atomic force microscopy (AFM), which has been recently used to study the piezoelectricity of nanomaterials. An AC bias between the conductive AFM tip and the substrate beneath the sample applies an electric field through the sample, causing a deformation i
13、n the piezoelectric material. The ontacting AFM tip detects the deformation, which is subsequently translated to the amplitude of the piezoresponse. PFM can be performed in vertical or lateral modes; vertical deflection of the AFM tip manifests normal deformation of the material. In lateral mode, to
14、rsion of the AFM tip reveals shear deformation of the domain.,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 th
15、e 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),For years, it was believed that since hydroxyapatite
16、 crystalizes in a centrosymmetric space group in the hexagonal system, it could not be piezoelectric. However, computational studies reported a lack of an inversion center in hydroxyapatite that could theoretically suggest possible piezoelectricity of this crystal. Tofail et al. have demonstrated th
17、e piezoelectricity of sintered hydroxyapatite using PFM, which suggests that alongside collagen,hydroxyapatite may also contribute to the piezoelectricity of bone. Piezoelectricity of other collagenous tissues such as tendon, dentin, cementum and cartilage have also been reported. Polysaccharides such as wood and chitin as well as polynucleotides such as deoxyribonucleic acid (DNA) have also revealed piezoelectric response.,
