Three-dimensional electron microscopy imaging of medical materials

许多与医疗材料行业相关的样品都很复杂，样品中含有混合相和界面。例如，人们可以考虑将假体装置植入动物/人类体内时会发生什么。细胞必须附着在设备上，并健康地传播和生长。因此，研究这种界面的性质是至关重要的，而且重要的是要找到方法来成像其附近的三维结构。另一个例子是药丸和药片，作为运送药物的一种手段。对于这些，片剂的孔隙率(这将取决于片剂的加工方式)以及药物在多孔结构中的分布方式是关键变量。因此，能够以相当高的放大倍数成像这些结构，从而使结构的细节清晰，是至关重要的。由于分辨率有限，光学显微镜不能总是提供所需的详细程度。然而，传统的电子显微镜通常需要使用高倍率，要么可以进行超薄样品(透射式电子显微镜)，要么只能进行表面成像(扫描电子显微镜)。在这项建议中，我们描述了一种新的电子显微镜，它克服了这些问题，并开辟了建立这些复杂医学材料的三维图像的途径。这项技术使用了一种所谓的双束仪，它既包括传统的电子束，也包括可以穿透材料的聚焦离子束。离子束穿过材料，暴露出埋藏的界面。电子束使用所谓的环境扫描电子显微镜(ESEM)柱，允许以高分辨率对这些暴露的界面进行成像。由于ESEM成像是在低水平气体存在的情况下进行的，而不是像大多数扫描电子显微镜那样是在超高真空中进行的，因此绝缘体不会在电子束下充电。因此，分辨率不会因为充电或需要在样品上涂上某种导电材料而降低。这种方法将被开发用于医疗材料，既为这一相当新的方法开发适当的方案，也为了解决与片剂的孔隙度以及扩散细胞和无机底物之间的界面的性质有关的具体问题。

Many samples of relevance to the medical materials industry are complex, containing mixed phases and interfaces buried within the sample. As an example one can consider what happens when a prosthetic device is implanted in an animal/human. The cells must stick to the device and spread and grow healthily. Studying the nature of this interface is therefore crucial, and it is important to find ways to image the three dimensional structure in its vicinity. Pills and tablets, as a means of delivering medicines, are another example. For these, the porosity of the tablet (which will depend on how the tablet was processed) and how the drug is distributed within the porous structure are key variables. The ability to image these structures at rather high magnifications, so that the detail of the structure is clear, is therefore crucial. Optical microscopy cannot always provide the level of detail required because of its limited resolution. However, conventional electron microscopy usually requires the use of high magnification and either ultra-thin samples (transmission electron microscopy) or only surface imaging can be performed (scanning electron microscopy). In this proposal we describe a new kind of electron microscopy which overcomes these problems, and opens up the way to build up three dimensional images of these complex medical materials. The technique uses a so-called Dual beam instrument, comprising both a conventional electron beam and also a focussed ion beam which can mill through materials. The ion beam cuts down through the material to expose buried interfaces. The electron beam, using a so-called environmental scanning electron microscope (ESEM) column, allows imaging of these exposed interfaces at high resolution. Because ESEM imagaing occurs in the presence of a low level of gas - and not an ultra high vacuum as in most scanning electron microscopes - insulators do not charge up under the electron beam. Thus the resolution is not degraded due to charging or the necessity of coating a sample with some conductive material. This approach will be developed for medical materials, both to develop appropriate protocols for this rather new approach, and also to solve specific problems to do with the porosity of tablets, and the nature of interfaces between spreading cells and an inorganic substrate.