Stiffness memory nanohybrid scaffolds generated by indirect 3D printing for biologically responsive soft implants

Abstract

© 2018 The Authors. Cell and tissue stiffness is an important biomechanical signalling parameter for dynamic biological pro-cesses; responsive polymeric materials conferring responsive functionality are therefore appealing forin vivoimplants. We have developed thermoresponsive poly(urea-urethane) nanohybrid scaffolds with‘stiffness memory’ through a versatile 3D printing-guided thermally induced phase separation (3D-TIPS) technique. 3D-TIPS, a combination of 3D printing with phase separation, allows uniform phase-separation and phase transition of the polymer solution at a large interface of network within the printedsacrificial preform, leading to the creation of full-scale scaffolds with bespoke anatomical complex geom-etry. A wide range of hyperelastic mechanical properties of the soft elastomer scaffolds with intercon-nected pores at multi-scale, controlled porosity and crystallinity have been manufactured, notpreviously achievable via direct printing techniques or phase-separation alone. Semi-crystalline poly-meric reverse self-assembly to a ground-stated quasi-random nanophase structure, throughout a hierar-chical structure of internal pores, contributes to gradual stiffness relaxation duringin vitrocell culturewith minimal changes to shape. This ‘stiffness memory’ provides initial mechanical support to surround-ing tissues before gradually softening to a better mechanical match, raising hopes for personalized andbiologically responsive soft tissue implants which promote human fibroblast cells growth as modeland potential scaffold tissue integration.