  Short DNA linkers are increasingly being exploited for driving specific
self-assembly of Brownian objects. DNA-functionalised colloids can assemble
into ordered or amorphous materials with tailored morphology. Recently, the
same approach has been applied to compliant units, including emulsion droplets
and lipid vesicles. The liquid structure of these substrates introduces new
degrees of freedom: the tethers can diffuse and rearrange, radically changing
the physics of the interactions. Unlike droplets, vesicles are extremely
deformable and DNA-mediated adhesion causes significant shape adjustments. We
investigate experimentally the thermal response of pairs and networks of
DNA-tethered liposomes and observe two intriguing and possibly useful
collective properties: negative thermal expansion and tuneable porosity of the
liposome networks. A model providing a thorough understanding of this
unexpected phenomenon is developed, explaining the emergent properties out of
the interplay between the temperature-dependent deformability of the vesicles
and the DNA-mediated adhesive forces.
