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Frictional drag from the submerged hull surface of a ship is a major component of the resistance experienced when moving through water. Techniques for measuring frictional drag on test surfaces include towing tanks, flow tunnels and rotating discs. These large-scale methods present practical difficulties that hinder their widespread adoption and they are not conducive to rapid throughput. In this study a miniaturized benchtop rotating disc method is described that uses test discs 25 mm in diameter. A highly sensitive analytical rheometer is used to measure the torque acting on the discs rotating in water. Frictional resistance changes are estimated by comparing momentum coefficients. Model rough surfaces were prepared by attaching different grades of sandpaper to the disc surface. Discs with experimental antifouling coatings applied were exposed in the marine environment for the accumulation of microbial fouling, and the rotor was capable of detecting the increased drag due to biofilm formation. The drag due to biofilm was related to an equivalent sand roughness.

Structural characterization of porous tissue scaffolds is challenging due to their complexity. Most investigators report the porosity of the material together with an estimate of the mean pore size and the pore size distribution. The usefulness of these measures is limited, especially in predicting the time-dependent permeation characteristics of a biodegradable, cell-seeded scaffold. A potential solution to this problem is to measure the permeability of the matrix and determine the Darcy permeability coefficient. Darcy permeability coefficients of 3.1 x 10(-14) and 6.3 x 10(-14) m(2) were measured for air and water, respectively, in microporous polycaprolactone scaffolds by monitoring fluid flow in response to a range of pressure differentials. Permeability coefficients for phosphate-buffered saline (5.3 x 10(-14) m(2)), glucose (5.7 x 10(-14) m(2)), and bovine serum albumin (1.8 x 10(-14) m(2)) were obtained by monitoring the change in concentration of molecular probes. This approach revealed the efficiency of transport of glucose molecules through the porous material and the existence of protein-scaffold interactions that resulted in protein retention and a reduction in fluid permeation rate. Darcy permeability measurements can provide valuable insights concerning the transport properties of nutrients, metabolites, and polypeptide growth factors in porous tissue engineering scaffolds and a method of quality assurance in scaffold processing.