Charged nanoscale filaments are well-known in natural systems such as filamentous viruses and the cellular cytoskeleton. The unique properties of these structures have inspired the design of self-assembled nanofibers for applications in regenerative medicine, drug delivery, and catalysis, among others. We report here on an amphiphile of completely different chemistry based on azobenzene and a quaternary ammonium bromide headgroup that self-assembles into highly charged nanofibers in water and orders into two-dimensional crystals. Interestingly small-angle X-ray scattering (SAXS) shows that these fibers of 5.6 nm cross-sectional diameter order into crystalline arrays with remarkably large interfiber spacings of up to 130 nm. Solution concentration and temperature can be adjusted to control the interfiber spacings, and addition of salt destroyed the crystal packing indicating the electrostatic repulsions are necessary for the observed ordering. Our findings here demonstrate the universal nature of this phenomenon in systems of highly charged nanoscale filaments.

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Introduction: Pacemaker implantation in infants typically consists of surgical epicardial lead placement with an abdominal generator. Here, we describe the chronic performance of our minimally invasive prototype miniature pacemaker implanted under direct visualization in an immature porcine model. Methods:Twelve piglets underwent miniature pacemaker implantation. A self-anchoring twochannel access port was inserted into a 1 cm incision in the subxiphoid space, and a thoracoscope was inserted into the main channel to visualize the thoracic cavity under insufflation. The pacemaker leadlet was inserted through a sheath via secondary channel and affixed against the epicardium using a helical side-biting electrode. The miniature pacemaker was tucked into the incision, which was sutured closed. Ventricular sensing, leadlet impedance, and capture thresholds were measured biweekly. A limited necropsy was performed after euthanasia.Results: Nine piglets were followed for a median of 78 (IQR 52-82) days and gained 6.6 ± 3.2 kg.Three animals were censored from the analysis due to complications unrelated to the procedure. Capture thresholds rose above maximal output after a median of 67 (IQR 40-69) days. At termination, there was a significant decrease in R-wave amplitude (P = .03) and rise in capture thresholds at 0.4 ms (P = .01) and 1.0 ms pulse widths (P = .02). There was no significant change in leadlet impedance (P = .74). There were no wound infections.Conclusions: There were no infections following minimally invasive implantation of our prototype miniature pacemaker. Improvements to epicardial fixation are necessary to address diminished leadlet efficacy over time. K E Y W O R D S epicardial, miniature pacemaker, minimally invasive, pediatric, porcine 1 Pacing Clin Electrophysiol. 2020;43:93-99. c

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