Any engineered tissue depends on its microvasculature for nutrients needed to survive.  In the past, scientists have attempted to create networks of small vessels either by introducing a growth factor between existing vessels or by implanting vascular cells programmed to self-organize.  Both of these techniques are slow, so researchers in the laboratory of Joe Tien, PhD, are seeking a faster method of fabricating systems of micro-vessels. 

Their idea is to make a collagen gel filled with micro-channels and to then line the micro-channels with endothelial cells.  The simplest method that they have explored is pouring a collagen gel around a thin object such as a needle and then removing the needle, forming a tube that can subsequently be lined with endothelial cells.  Another subtractive method that they have tried involves lithography.  In this case, the researchers create two-dimensional gelatin molds in the shape of the desired vasculature, pour collagen around the gelatin mold, and then melt away the gelatin.  Finally, Tien’s team has tried using an additive method in which they create a collagen gel with channels on its surface and then fuse another collagen gel on top.  They have found that collagen gels can be bonded together using guanidine hydrochloride, a compound that seems to partially depolymerize the gels so that two gels can repolymerize as one.  The researchers in Tien’s group have found that the permeability of their engineered microvasculature is significantly affected by a number of factors including the pressure, the flow rate, and the concentration of certain second messenger molecules such as cAMP.  

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