Engineering extracellular matrix structure in 3D multiphase tissues.

In native tissues, microscale variations in the extracellular matrix (ECM) structure can drive different cellular behaviors. Although control over ECM structure could prove useful in tissue engineering and in studies of cellular behavior, isotropic 3D matrices poorly replicate variations in local microenvironments. In this paper, we demonstrate a method to engineer local variations in the density and size of collagen fibers throughout 3D tissues. The results showed that, in engineered multiphase tissues, the structures of collagen fibers in both the bulk ECM phases (as measured by mesh size and width of fibers) as well as at tissue interfaces (as measured by density of fibers and thickness of tissue interfaces) could be modulated by varying the collagen concentrations and gelling temperatures. As the method makes use of a previously published technique for tissue bonding, we also confirmed that significant adhesion strength at tissue interfaces was achieved under all conditions tested. Hence, this study demonstrates how collagen fiber structures can be engineered within all regions of a multiphase tissue scaffold by exploiting knowledge of collagen assembly, and presents an approach to engineer local collagen structure that complements methods such as flow alignment and electrospinning.

The effect of paraformaldehyde fixation on the delayed gadolinium-enhanced MRI of cartilage (dGEMRIC) measurement.

The delayed Gadolinium-Enhanced Magnetic Resonance Imaging of Cartilage (dGEMRIC) method allows for both qualitative and quantitative measurement of the spatial distribution of glycosaminoglycan [GAG] in excised cartilage. The objective of this study was to determine the effect of paraformaldehyde fixation on dGEMRIC measurements. Five bovine and seven human cartilage pieces were punched into 5-mm plugs, fixed for 18 h in 4% paraformaldehyde solution, and washed. The magnetic resonance imaging (MRI) parameter T1 was measured prior and post fixation in cartilage without (T1(0)) and with (T1(Gd)), the ionically charged MRI contrast agent Gd(DTPA)(2-). Images of tissue before and after fixation were qualitatively very similar. The ratios of T1(0), T1(Gd), and calculated [GAG] after fixation, relative to before fixation, were near or slightly higher than 1 for both bovine cartilage (1.01 +/- 0.01, 1.04 +/- 0.02, 1.05 +/- 0.03, respectively) and for human cartilage (0.96 +/- 0.11, 1.03 +/- 0.05, 1.09 +/- 0.13). Thus, these data suggest that dGEMRIC can be used on previously fixed samples to assess the three dimensional spatial distribution of GAG.