Journal of Biomechanics 34 (2001) 1197–1202 Technical note Direct perfusion measurements of cancellous bone anisotropic permeability $ Sean S. Kohles a, *, Julie B. Roberts a,1 , Maureen L. Upton a,2 , Christopher G. Wilson a , Lawrence J. Bonassar b , Alyssa L. Schlichting a,3 a Department of Biomedical Engineering, Worcester Polytechnic Institute, 100 Institute Road, Worcester, MA 01609, USA b Center for Tissue Engineering, University of Massachusetts, Worcester, MA, USA Accepted 30 April 2001 Abstract More extensive characterization of trabecular connectivity and intertrabecular space will be instrumental in understanding disease states and designing engineered bone. This project presents an experimental protocol to define the directional dependence of transport properties as measured from healthy cancellous bone when considered as a biologic, porous medium. In the initial design phases, mature bovine bone was harvested from the femoral neck (n=6 cylinders) and distal condyle (n=4 cubes) regions and used for ‘proof of concept’ experimentation. A power study on those results led to the presented work on 20 cubic samples (mean volume=4.09cm 3 ) harvested from a single bovine distal femur. Anisotropic intrinsic permeabilities (k i ) were quantified along the orthogonal anatomic axes (i=medial–lateral, anterior–posterior, and superior–inferior) from each individual cubic bone sample. Using direct perfusion measurements, permeability was calculated based upon Darcy’s Law describing flow through porous media. The maximum mean value was associated with the superior–inferior orientation (4.65  10 10 m 2 ) in comparison with the mean anterior–posterior (4.52  10 10 m 2 ) and medial–lateral (2.33  10 10 m 2 ) direction values. The results demonstrate the anisotropic ( p ¼ 0:0143) and heterogeneous ( p ¼ 0:0002) nature of the tissue and encourage the ongoing quantification of parameters within the established poroelastic models. r 2001 Elsevier Science Ltd. All rights reserved. Keywords: Cancellous bone; Transport; Permeability; Anisotropy; Fluid flow 1. Introduction Cancellous bone is a biphasic structure consisting of a continuous three-dimensional network of intercon- nected rods and plates (trabecular solid) and a pore space filled by a viscous fluid phase. The hydraulic nature of this fluid–solid interaction enhances the tissue’s load bearing capacity (Downey et al., 1988; Ochoa et al., 1997). Several investigations into the structure–function relationship of the tissue have indicated that the mechanical and transport properties are highly dependent upon tissue orientation and anatomic location (Ashman et al., 1989; Grimm and Williams, 1997; Nauman et al., 1999). In addition, bone structural anisotropies have been defined using fluid movement via streaming potentials, tracers, and flow visualization (Pollack et al., 1984; Wehrli et al., 1993; Schemitsch et al., 1994; MacGinitie et al., 1997; Wang et al., 2000). The objectives of this study were to demonstrate a methodology to isolate the trabecular void space and then to quantify this space using a direct perfusion process. The resulting technique measures anisotropic permeability from single cancellous samples. This effort is intended to contribute to the development of anisotropic indices (Kohles, 2000) and poroelastic models (Cowin, 1999), and to provide design criteria for engineered bone substitutes (Vacanti and Bonassar, 1999). $ Presented in part at the Annual Fall Meeting of the Biomedical Engineering Society, Seattle, WA, October 2000, and the 47th Annual Meeting of the Orthopaedic Research Society, San Francisco, CA, February 2001. *Corresponding author. Tel.:+1-508-831-5384; fax:+1-508-831- 5541. E-mail address: kohles@wpi.edu (S.S. Kohles). 1 Currently with TEI Biosciences Inc., Boston, MA, USA. 2 Currently with Department of Biomedical Engineering, Duke University, Durham, NC, USA. 3 Currently with Boston Scientific, Corp., Natick, MA, USA. 0021-9290/01/$-see front matter r 2001 Elsevier Science Ltd. All rights reserved. PII:S0021-9290(01)00082-3