Springy or Crumbly: Depends on crosslinking protocol when we make porous colloid/polymer hybrids

Recently, we demonstrated¹ that macroporous scaffolds can be produced by ice-templating a dispersion of colloids, polymer and crosslinker and, by crosslinking this hybrid in the frozen state. Such scaffolds show elastic recovery even after 90% compression, despite being comprised predominantly of inorganic (> 90% w/w). We have demonstrated the formation of elastic sponges using different particles, polymers and crosslinking chemistries. In my talk, I will contrast these elastic sponges with those crosslinked after lyophilization to remove the ice. Both these scaffolds appear chemically and structurally identical. However, monoliths prepared in absence of ice are brittle and fail catastrophically at low compressive strains. We use rheology, SAXS, NMR and AFM to understand how the difference between elastic sponges and plastic monoliths (made by crosslinking after removal of ice crystals ). We show that crosslinking in the presence of ice results in spatially homogeneous crosslinking, while crosslinking after lyophilization renders the spatial distribution of crosslinks highly heterogeneous. Thus, remarkably, the presence (or absence) of macroscopic ice crystals influence the microscopic spatial localization of chemistry in these scaffolds².