FULL PAPER © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 4561 wileyonlinelibrary.com promise to improve safety and extend the lifetime of components in a variety of applications ranging from aerospace to microelectronics. [1–5] Most prior work in this field focuses on recovering mechanical or fracture properties for materials con- taining cracks of width less than 100 μm; however, catastrophic damage events that remove mass or create millimeter-scale crack separations require new self-healing strategies. [6] Blaiszik et al. [7] identified three major categories of self-healing materials: intrinsic, capsule-based, and vascular. Intrinsic self-healing materials possess reversible chemical functionalities (i.e., ionic or hydrogen bonding) which break during a damage event and reform to facilitate healing. Intrinsic self-healing materials are unable to repair large crack separations because healing occurs on the molecular level and requires intimate contact. [8,9] In contrast, capsule-based approaches may tolerate small crack separa- tions. Fluid-filled spheres are embedded into a material and the encapsulated liquids, or healing agents, consist of monomers or other reactive chemical species. When a fracture event occurs, the crack will traverse the material and intersect the embedded capsules to release a liquid payload. The healing agents fill the damage zone and polymerize to rebond the crack planes and arrest further crack propagation. Restrictions on capsule size and concentration limit the total volume of healing agents avail- able for delivery, and thus, limit the maximum crack separation that can be repaired. [10,11] Vascular self-healing systems are synthetic materials with embedded biomimetic microvascular networks that circulate a continuous supply of liquid healing agents. [11–20] As a damage event occurs, cracks intersect the vascular network to release healing agents. Despite occupying a very a low proportion of the total material volume (≈0.50 vol% for a pervasive network), [20] vasculature can supply a virtually limitless quantity of healing agents from a reservoir external to the material system. There- fore, microvascular self-healing materials are capable of the mass transport necessary to address large damage volumes, but new materials are required to regenerate functional structures (i.e., achieve volumetric recovery) rather than simply rebond crack planes or repair surfaces. [21] For example, Yong et al. report on computational analysis of a gel matrix that regrows after a significant portion is severed [22] and Zavada et al. dem- onstrate repair of ballistic impact on resin-filled panels using Strategies for Volumetric Recovery of Large Scale Damage in Polymers Brett P. Krull, Ryan C. R. Gergely, Windy A. Santa Cruz, Yelizaveta I. Fedonina, Jason F. Patrick, Scott R. White, and Nancy R. Sottos* The maximum volume that can be restored after catastrophic damage in a newly developed regenerative polymer system is explored for various mixing, surface wetting, specimen configuration, and microvascular delivery condi- tions. A two-stage healing agent is implemented to overcome limitations imposed by surface tension and gravity on liquid retention within a damage volume. The healing agent is formulated as a two-part system in which the two reagent solutions are delivered to a through-thickness, cylindrical defect geom- etry by parallel microvascular channels in thin epoxy sheets. Mixing occurs as the solutions enter the damage region, inducing gelation to initiate an accretive deposition process that enables large damage volume regeneration. The pro- gression of the damage recovery process is tracked using optical and fluores- cent imaging, and the mixing efficiency is analyzed. Complete recovery of gaps spanning 11.2 mm in diameter (98 mm 2 ) is achieved under optimal conditions. DOI: 10.1002/adfm.201600486 Dr. B. P. Krull, Y. I. Fedonina, Prof. N. R. Sottos Department of Materials Science and Engineering Beckman Institute for Advanced Science and Technology University of Illinois at Urbana-Champaign Urbana, IL 61801, USA E-mail: n-sottos@illinois.edu R. C. R. Gergely Department of Mechanical Science and Engineering Beckman Institute for Advanced Science and Technology University of Illinois at Urbana-Champaign Urbana, IL 61801, USA Dr. W. A. Santa Cruz Department of Chemistry Beckman Institute for Advanced Science and Technology University of Illinois at Urbana-Champaign Urbana, IL 61801, USA Dr. J. F. Patrick Beckman Institute for Advanced Science and Technology University of Illinois at Urbana-Champaign Urbana, IL 61801, USA Prof. S. R. White Department of Aerospace Engineering Beckman Institute for Advanced Science and Technology University of Illinois at Urbana-Champaign Urbana, IL 61801, USA 1. Introduction Although autonomous repair of injured tissue is commonplace in biological systems, synthetic materials remain susceptible to damage. Recent advances in self-healing material systems Adv. Funct. Mater. 2016, 26, 4561–4569 www.afm-journal.de www.MaterialsViews.com