A shear stress threshold for angiogenesis

In vitro experiments using microfabricated microfluidic devices have revealed a threshold of shear stress from fluid flow above which endothelial cell monolayers sprout new blood vessels.  The shear stress also sustained the sprout and prevented vessel retraction.  Further experiments revealed that matrix metalloproteinase 1 expression increased dramatically at the shear threshold.  These findings offer a basic mechanism for regulating vessel densities in tissue modulated by other mechanical, geometric,and biochemical factors.

Fluid shear stress threshold regulates angiogenic sprouting; P.A.Galie et al; PNAS; doi:10.1073/pnas.1310842111

http://www.pnas.org/content/early/2014/05/16/1310842111.abstract

Delivering siRNAs to endothelial cells

Scientists have synthesised nanoparticles which efficiently delivered siRNAs to endothelial cells in vivo and facilitated silencing of up to five different endothelial genes concurrently.  Gene expression in several other cell types was not significantly affected by the presence of the delivery agent.  The nanoparticles, made of low-molecular-weight polyamines and lipids, reduced target gene expression in multiple animal models.  In lung cancer models, primary tumour growth and metastases were both reduced. 

In vivo endothelial siRNA delivery using polymeric nanoparticles with low molecular weight; J.E. Dahlman et al, Nature Nanotechnology, DOI: 10.1038/NNANO.2014.84.

http://www.nature.com/nnano/journal/vaop/ncurrent/abs/nnano.2014.84.html

Vascularised hydrogels

Researchers have created networks of microchannels in a variety of hydrogels using a micromolding strategy.   Networks of channels enhanced osteogenic cell viability and differentiation in cell-laden micromolded gels.  The channels could be lined with a confluent layer of endothelial cells to create an engineered vasculature.  The hydrogels remained fully perfused. 

Hydrogel Bioprinted Microchannel Networks for Vascularization of Tissue Engineering Constructs; L.E.Bertassoni et al, Lab on a Chip, DOI: 10.1039/C4LC00030G

http://pubs.rsc.org/en/content/articlelanding/2014/lc/c4lc00030g#!divAbstract