ASTM_F_2952_-_14.pdf

Designation:F295214Standard Guide forDetermining the Mean Darcy Permeability Coefficient for aPorous Tissue Scaffold1This standard is issued under the fixed designation F2952;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.1.Scope1.1 This guide describes test methods suitable for determin-ing the mean Darcy permeability coefficient for a porous tissuescaffold,which is a measure of the rate at which a fluid,typically air or water,flows through it in response to an appliedpressure gradient.This information can be used to optimize thestructure of tissue scaffolds,to develop a consistent manufac-turing process,and for quality assurance purposes.1.2 The method is generally non-destructive and non-contaminating.1.3 The method is not suitable for structures that are easilydeformed or damaged.Some experimentation is usually re-quired to assess the suitability of permeability testing for aparticular material/structure and to optimize the experimentalconditions.1.4 Measures of permeability should not be considered asdefinitive metrics of the structure of porous tissue scaffolds andshould complement measures obtained by other investigativetechniques e.g.,scanning electron microscopy,gas flow porom-etry and micro-computer x-ray tomography(ASTM F2450).1.5 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2.Referenced Documents2.1 ASTM Standards:2D4525 Test Method for Permeability of Rocks by FlowingAirF2450 Guide for Assessing Microstructure of PolymericScaffolds for Use in Tissue-Engineered Medical ProductsF2603 Guide for Interpreting Images of Polymeric TissueScaffolds2.2 American Petroleum Institute(API)Document:3RP-27 Recommended Practice for Determining Permeabilityof Porous Media3.Terminology3.1 Definitions:3.1.1 tortuosity,nthe ratio of the actual path lengththrough connected pores to the Euclidean distance(shortestlinear distance).4.Significance and Use4.1 This document describes the basic principles that needto be followed to obtain a mean value of the Darcy permeabil-ity coefficient for structures that consist of a series of intercon-nected voids or pores.The coefficient is a measure of thepermeability of the structure to fluid flowing through it that isdriven by a pressure gradient created across it.4.2 The technique is not sensitive to the presence of closedor blind-end pores(Fig.1).4.3 Values of the permeability coefficient can be used tocompare the consistency of manufactured samples or to deter-mine what the effect of changing one or more manufacturingsettings has on permeability.They can also be used to assessthe homogeneity and anisotropy of tissue scaffolds.Variabilityin the permeability coefficient can be also be indicative of:4.3.1 Internal damage within the sample e.g.,cracking orpermanent deformation.4.3.2 The presence of large voids,including trapped airbubbles,within the structure.4.3.3 Surface effects such as a skin formed during manu-facture.4.3.4 Variable sample geometry.4.4 This test method is based on the assumption that theflow rate through a given sample subjected to an appliedpressure gradient is constant with time.NOTE1If a steady state flow condition isnt reached,then this could1This test method is under the jurisdiction ofASTM Committee F04 on Medicaland Surgical Materials and Devices and is the direct responsibility of SubcommitteeF04.42 on Biomaterials and Biomolecules for TEMPs.Current edition approved March 1,2014.Published April 2014.DOI:10.1520/F2952-14.2For referenced ASTM standards,visit the ASTM website,www.astm.org,orcontact ASTM Customer Service at serviceastm.org.For Annual Book of ASTMStandards volume information,refer to the standards Document Summary page onthe ASTM website.3Available from American Petroleum Institute(API),1220 L.St.,NW,Washington,DC 20005-4070,http:/www.api.org.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 be due to structural damage(i.e.,crack formation or the porous structuredeformed as a result of the force being placed upon it by the fluid flowingthrough it).Sample deformation in the form of stretching(bowing)canalso occur for less resilient structures as a result of high fluid flow rates.This topic is discussed in more detail in Section 7.4.5 Care should be taken to ensure that hydrophobic mate-rials are fully wetted out when using water or other aqueous-based liquids as permeants.4.6 Conventionally,the pressure differential created across asample is measured as a function of both increasing anddecreasing flow rates.An al