Macroscopic structures that can undergo rapid and reversible stiffness transitions can serve as functional polymeric materials for many applications in robotics and medical devices. Thermomechanical phase transitions can provide a suitable mechanism for transient control of mechanical properties. However, the characteristic time scale for actuation is large and dictated by the dimensions of the structure. Embedding vascular networks within bulk polymers can reduce the characteristic length scale of the material and permit rapid and reversible thermomechanical transitions. Here, perfusable bulk materials with embedded microvascular networks are reported that can undergo rapid and reversible stiffness transitions. Acrylate-based thermoplastic structures exhibit storage moduli with a dynamic range between E′ = 1.02 ± 0.07 GPa and E′ = 13.5 ± 0.7 MPa over time scales as small as 2.4 ± 0.5 s using an aqueous thermal perfusate. The spatiotemporal evolutions of temperature profiles are accurately predicted using finite element simulations and compared to experimental values. Rigid-compliant transitions are leveraged in a demonstration in which a microvascularized device is used to grasp an external object without the aid of moving parts.

Materials with embedded vascular networks afford rapid and enhanced control over bulk material properties including thermoregulation and distribution of active compounds such as healing agents or stimuli. Vascularized materials have a wide range of potential applications in self-healing systems and tissue engineering constructs. Here, the application of vascularized materials for accelerated phase transitions in stimuli-responsive microfluidic networks is reported. Poly(ester amide) elastomers are hygroscopic and exhibit thermo-mechanical properties (T_g ≈ 37 °C) that enable heating or hydration to be used as stimuli to induce glassy-rubbery transitions. Hydration-dependent elasticity serves as the basis for stimuli-responsive shape-memory microfluidic networks. Recovery kinetics in shape-memory microfluidics are measured under several operating modes. Perfusion-assisted delivery of stimulus to the bulk volume of shape-memory microfluidics dramatically accelerates shape recovery kinetics compared to devices that are not perfused. The recovery times are 4.2 ± 0.1 h and 8.0 ± 0.3 h in the perfused and non-perfused cases, respectively. The recovery kinetics of the shape-memory microfluidic devices operating in various modes of stimuli delivery can be accurately predicted through finite element simulations. This work demonstrates the utility of vascularized materials as a strategy to reduce the characteristic length scale for diffusion, thereby accelerating the actuation of stimuli-responsive bulk materials.

Advanced polymeric biomaterials continue to serve as a cornerstone for new medical technologies and therapies. The vast majority of these materials, both natural and synthetic, interact with biological matter in the absence of direct electronic communication. However, biological systems have evolved to synthesize and utilize naturally-derived materials for the generation and modulation of electrical potentials, voltage gradients, and ion flows. Bioelectric phenomena can be translated into potent signaling cues for intra- and inter-cellular communication. These cues can serve as a gateway to link synthetic devices with biological systems. This progress report will provide an update on advances in the application of electronically active biomaterials for use in organic electronics and bio-interfaces. Specific focus will be granted to covering technologies where natural and synthetic biological materials serve as integral components such as thin film electronics, in vitro cell culture models, and implantable medical devices. Future perspectives and emerging challenges will also be highlighted.