FULL PAPER © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1 wileyonlinelibrary.com A Compressible Scaffold for Minimally Invasive Delivery Of Large Intact Neuronal Networks Amélie Béduer,* Thomas Braschler, Oliver Peric, Georg E. Fantner, Sébastien Mosser, Patrick C. Fraering, Sidi Benchérif, David J. Mooney, and Philippe Renaud DOI: 10.1002/adhm.201400250 Dr. A. Béduer, Dr. T. Braschler, Prof. P. Renaud STI-IMT-LMIS4, Station 17, EPFL 1015, Lausanne, Switzerland E-mail: amelie.beduer@epfl.ch Dr. T. Braschler, Dr. S. Benchérif, Prof. D. J. Mooney School of Engineering and Applied Sciences Harvard University, 02138, Cambridge, MA, USA O. Peric, Prof. G. E. Fantner STI-IBI-LBNI, Station 17, EPFL 1015, Lausanne, Switzerland S. Mosser, Prof. P. C. Fraering SV-BMI-CMSN, Station 15, EPFL 1015, Lausanne, Switzerland Millimeter to centimeter-sized injectable neural scaffolds based on macropo- rous cryogels are presented. The polymer-scaffolds are made from alginate and carboxymethyl-cellulose by a novel simple one-pot cryosynthesis. They allow surgical sterility by means of autoclaving, and present native laminin as an attachment motive for neural adhesion and neurite development. They are designed to protect an extended, living neuronal network during compression to a small fraction of the original volume in order to enable minimally inva- sive delivery. The scaffolds behave as a mechanical meta-material: they are soft at the macroscopic scale, enabling injection through narrow-bore tubing and potentially good cellular scaffold integration in soft target tissues such as the brain. At the same time, the scaffold material has a high local Young modulus, allowing protection of the neuronal network during injection. Based on macroscopic and nanomechanical characterization, the generic geometri- cal and mechanical design rules are presented, enabling macroporous cellular scaffold injectability. procedures involved in implanting com- plex and large solid grafts into the brain are very invasive and can easily lead to further tissue damage rather than the desired reconstruction outcome. [4] A number of minimally invasive delivery methods have been proposed, allowing to apply in situ gelling formulations, micro- particulate scaffold suspensions, partially dissociated tissue, or neural stem cell suspensions through narrow-bore nee- dles. [5–15] Unfortunately, without the guid- ance of a large-scale organized scaffold, the cells typically build chaotic structures rather than repairing the native tissue architecture as desired. [14] As a result, the associated functional recovery is never complete and data from successful human clinical studies are extremely scarce. [15] We propose here to address this current major bottleneck of neural tissue engi- neering by the use of a smart cellular scaffold system, which is highly and reversibly compressible, allowing for minimally invasive implantation of large, potentially preorganized con- structs. To achieve this goal, several requirements must be met: The scaffold material must be highly compressible, such that mL-scale volumes can be delivered through narrow-bore tubing or needles, yet it should recover its original shape, volume and organization after the injection process. It should protect dif- ferentiated neurons with their extended neurites during the compression associated with the delivery process, but neverthe- less behave as a globally soft material to minimize glial scarring reactions in the brain. [16] For the long-term culture necessary to develop differentiated neuronal networks, and in light of potential clinical translation, the scaffolds need to be reliably sterilized, preferentially by autoclaving. Last but not least, it is desirable to be able to provide native extracellular matrix (ECM) proteins to guide cell adhesion and differentiation. Macropo- rous scaffolds with shape memory amenable to injection through narrow-bore tubing can be fabricated by different tech- niques, such as emulsion polymerization, lyophilization, and cryogelation. [17–19] We base our scaffolds on the process of cryo- gelation, involving polymerization of a hydrogel precursor at subzero temperature, since this has been observed to produce particularly robust gels, and since the possibility of neuronal tissue engineering with cryogels has been reported. [19–21] We provide a novel cryogel fabrication paradigm, consisting of a 1. Introduction It is a clinical observation that the adult human brain typically fails to repair large-scale tissue damage. [1] This contrasts with the observation that neurons are continuously generated in the subventricular zone and dentate gyrus, [2,3] and it is indeed the hope and aim of cell-based therapies to extend the brain’s regeneration capacity to large-scale lesions. A major limitation on the path to successful neural tissue engineering and deep brain transplantation is the development of minimally inva- sive surgical techniques and scaffolds. Indeed, the surgical Adv. Healthcare Mater. 2014, DOI: 10.1002/adhm.201400250 www.advhealthmat.de www.MaterialsViews.com