ASTM F2603-06(R2020) pdf free download

ASTM F2603-06(R2020) pdf free download.Standard Guide for Interpreting Images of Polymeric Tissue Scaffolds
1. Scope
1.1 This guide covers the factors that need to be considered in obtaining and interpreting images of tissue scaffolds includ- ing technique selection, instrument resolution and image quality, quantification and sample preparation. 1.2 The information in this guide is intended to be appli- cable to porous polymer-based tissue scaffolds, including naturally derived materials such as collagen. However, some materials (both synthetic and natural) may require unique or varied sample preparation methods that are not specifically covered in this guide. 1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard. 1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appro- priate safety, health, and environmental practices and deter- mine the applicability ofregulatory limitations prior to use. 1.5 This international standard was developed in accor- dance with internationally recognized principles on standard- ization established in the Decision on Principles for the Development of International Standards, Guides and Recom- mendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
5. Measurement Objectives
5.1 Much of the research activity in tissue engineering is focused on the development ofsuitable materials and structures for optimal growth of a range of tissue types including cartilage, bone, and nerve. This requires a quantitative assess- ment of the scaffold structure. The key parameters that need to be determined are (1) the overall level of porosity, (2) the pore size distribution, which can range from tens of nanometers to several hundred micrometres, and (3) the degree of interconnectivity and tortuosity of the pores.
6. Imaging Methods and Conditions
6.1 There are many experimental ways of obtaining key scaffold physical parameters as described in Guide F2450. When imaging and subsequent quantitative analysis is chosen as the method for determining these parameters, it is critical that any image under consideration be a true representation of the scaffold of interest. Some imaging methods require sample preparation. Some do not. When sample preparation is required prior to imaging, care must be taken that the procedures do not significantly alter the morphology of the scaffold. See Appen- dix X1 for further information on sample preparation. 6.2 Images obtained using techniques such as light microscopy, electron microscopy, and magnetic resonance imaging are two-dimensional (2-D) representations of a three- dimensional (3-D) structure. These can be a planar or cross- sectional view with a relatively large depth of field or a series of physical or virtual 2-D slices, each with a small depth of field, that can be reassembled in a virtual environment to produce a 3-D mesostructure.6.3 There are limits to the extent an image (2-D or 3-D) can faithfully represent the physical artifacts that are influenced by factors germane to the imaging method, such as spatial resolution and dynamic range, image contrast, and the signal- to-noise ratio. Table 1 lists some ofthe techniques available for producing images of porous structures, along with their con- trast source, maximum demonstrated spatial resolution, and typical dynamic range. Proper technique selection depends both on the material properties of the scaffold (that is, optical methods cannot be used with opaque materials) the contrast available, and the target pore size range. 6.4 The images generated by the techniques shown in Table 1 cannot reproduce features smaller than the spatial resolution of the method. Features that are faint, that is, those that do not have significant contrast, or signal significantly above background, will be resolved at length scales larger than the maximum resolution. Excessive contrast can also limit the penetration depth due to scattering effects. This is particularly true of optical microscopies using differences in refractive index as the contrast mechanism. An appropriate level of contrast that can be established by experimentation is therefore critical to high quality imaging. 6.5 Contrast can be enhanced by using exogenous agents, such as florescence tags in optical microscopy and stains containing heavy metal complexes in electron microscopies. Excessive contrast can be ameliorated in optical microscopies by imbibing the structure with a fluid that has an index of refraction similar to that of the solid making up the structure (this is termed “index-matching”). There are many excellent resources describing factors influencing widefield and confocal optical microscopy (1-3), 4 optical coherence microscopy (4), MRI (5), and electron microscopies (6).