Tissue processing and characterization. Storage and compressive modulus of samples of porcine brain, lung, liver, and heart were obtained as described above. Fresh tissues kindly donated from a local butcher (J. Waldron Butchers, Hamilton, ON, Canada) were sliced, cut into 8 mm pucklike samples, and soaked in cell culture media for 1 h before the characterization. Similar data was also acquired without submerging the tissue in cell culture media. At least ten replicate samples were prepared and measured per tissue type.