Engineering a Stable Synaptogenic Extracellular Matrix Laila Al-Alwan 1 , Markus Hellmund 2 , Rainer Haag 2 and Timothy Kennedy 1 1 Montreal Neurological Institute, McGill University, 3801 Univerity Street, Montreal, Canada 2 Chemistry and Biochemistry Institute, Freie University Berlin, Berlin, Germany Keywords: Neural Biocompatibility, Synthetic Synapse, Neural Prosthetic, Biomimetic Functionalised Surfaces, Polymer Chemistry, Synaptogenic Protein. Abstract: Synapses are specialized sites of asymmetric cell – cell contact that mediate information transfer between neurons and their targets. Many proteins involved in the recruitment, organization and maintenance of synapses have been identified. Surprisingly, synaptic differentiation does not require a biological membrane surface. Instead, synaptic specializations can form quickly at sites of neurite adhesion to microspheres (beads) coated with synaptogenic proteins or even poly-lysine, a synthetic cationic polypeptide, raising the possibility that functional hemi-synaptic connections could be formed onto designer engineered surfaces. Previous studies examining the stability of synapses formed in brain onto poly-lysine coated beads found they were unstable, degraded, and ultimately replaced by a glial scar. Here, we address the capacity of an extreme biomimetic of poly-lysine, PGB50, a dendritic polyglycerol (dPG)-amine soft matter nanoparticle, to enhance synapse formation in long-term cultures of rat cortical neurons. Microbeads coated with PGB50 exhibit substantially enhanced synaptogenesis and synapse stability compared to poly-lysine. We propose that synaptogenic extracellular matrices could be used to engineer synaptogenic electrodes with enhanced neural-compatibility, reducing glial scaring and inflammation, and allowing for bi-directional communication with neurons through the formation of stable of synaptic specializations. 1 INTRODUCTION Deficits due to neurodegeneration or injury-induced brain diseases are, ultimately, a direct reflection of the loss of functional synapses. Synapses are specialized sites of asymmetric cell – cell contact that mediate information transfer between neurons and their targets. Many proteins involved in the recruitment, organization, and maintenance of synapses have been identified and the molecular biology of synaptic adhesion is increasingly well understood. Furthermore, neural activity can now be read out to activate muscles or control the movement of robotic limbs (Hochberg et al., 2012; van den Brand et al., 2012). In spite of these advances, contemporary microelectrodes, made of metal or glass, present fundamentally invasive surfaces that neural cells isolate by enclosing in a glial scar. Synaptic specializations can assemble rapidly following axon – dendrite contact. Surprisingly, the formation of an active pre-synaptic terminal does not require a biological post-synaptic membrane surface. Instead, pre-synaptic specializations can form quickly at sites of axonal adhesion to microspheres (beads) coated with specific lipids or proteins, including the synthetic poly-cationic polypeptide poly-lysine (PLL) (Burry, 1982; Lucido et al., 2009; Gopalakrishnan et al., 2010; Goldman et al., 2013; Suarez et al., 2013). PLL is a naturally occurring polymer that is susceptible to degradation by several common secreted proteases, including trypsin and cathepsins. Consistent with this, presynaptic specializations formed onto PLL coated beads in vivo were not stable but completely degraded within two weeks, replaced by an astrocytic glial scar that isolated the bead (Burry, 1983, 1985). PDL, a protein biomimetic enantiomer of PLL, was developed to resist protease degradation, and thereby enhance its utility as a cell culture substrate. Here, using long- term cultures of embryonic rat cortical neurons we address the capacity of an extreme biomimetic of PLL, PGB50, an ~75 kDa dendritic polyglycerol (dPG)-amine soft matter nanoparticle based on a highly stable and biocompatible polyglycerol scaffold (Hellmund et al., 2015), to enhance synapse formation. We propose that synaptogenic extracellular matrices may be engineered to enhance biocompati- Al-Alwan, L., Hellmund, M., Haag, R. and Kennedy, T. Engineering a Stable Synaptogenic Extracellular Matrix. In Extended Abstracts (NEUROTECHNIX 2016), pages 11-13 Copyright c  2016 by SCITEPRESS – Science and Technology Publications, Lda. All rights reserved 11