  Hydrogels engineered for medical use within the human body need to be
delivered in a minimally invasive fashion without altering their biochemical
and mechanical properties to maximize their therapeutic outcomes. In this
regard, key strategies applied for creating such medical hydrogels include
formulating precursor solutions that can be crosslinked in situ with physical
or chemical cues following their delivery or forming macroporous hydrogels at
sub-zero temperatures via cryogelation prior to their delivery. Here, we
present a new class of injectable composite materials with shape recovery
ability. The shape recovery is derived from the physical properties of red
blood cells (RBCs) that are first modified via hypotonic swelling and then
integrated into the hydrogel scaffolds before polymerization. The RBCs'
hypotonic swelling induces the formation of nanometer-sized pores on their cell
membranes, which enable fast liquid release under compression. The resulting
biocomposite hydrogel scaffolds display high deformability and shape-recovery
ability. The scaffolds can repeatedly compress up to ~87% of their original
volumes during injection and subsequent retraction through syringe needles of
different sizes; this cycle of injection and retraction can be repeated up to
ten times without causing any substantial mechanical damage to the scaffolds.
Our biocomposite material system and fabrication approach for injectable
materials will be foundational for the minimally invasive delivery of
drug-loaded scaffolds, tissue-engineered constructs, and personalized medical
platforms that could be administered to the human body with conventional
needle-syringe systems.
