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Trabajo presentado en la 32nd Annual Conference of the European Society for Biomaterials, celebrada en Burdeos (Francia), del 4 al 8 de septiembre de 2022, Electrical stimulation (ES) has been employed in nume-rous biomedical applications such as neural stimulation, neural interfacing and tissue regeneration. The biological complexity of in vivo conditions encouraged many researchers to evaluate the role of ES via in vitro devices1. Among the several ES delivery methods, direct coupling is the one that fairly mimics implantable devices. The electrochemical properties of in vitro ES devices and the characteristics of the delivered electrical field remain broadly understudied. Electrode materials have a critical role in determining the impedance (Z) and charge injection capacity (CIC) of the system. A small CIC and high Z require larger potentials to inject a significant amount of charge, which may corrode the electrode or hydrolyse the electrolyte. In addition, electrochemical reactions result in by-products such as reactive oxygen species (ROS) or changes in the pH, which are harmful for the cells2. Nano-structuration is shown to improve the electrochemical properties of bioelectrodes. In this study, we defined biologically safe limits of ES delivered by both Pt thin films (TF) and nanostructured (NC) electrodes incorporated in an in vitro ES device. To this end, we performed comprehensive electrochemi-cal characterization in biologically relevant conditions., Funding from Comunidad de Madrid (Atracción de Talento Programme, Modalidad-1 Ref. 2019-T1/IND1335, project S2018/NMT-4291 TEC2SPACE and YEI contract PEJ-2019-AI/IND-14451 with support from FSE) and CSIC (ILINK+2020 Ref. LINKA20342).

Trabajo presentado en el XVI Congreso Nacional de Materiales CNMAT 2022, celebrado en Ciudad Real (España), del 28 de junio al 1 de julio de 2022, La técnica de pulverización catódica operada en geometría de ángulo oblicuo es bien conocida por permitir el crecimiento de películas delgadas nanocolumnares sobre sustratos planos. En otro tipo de sustratos, e.g. rugosos o litografiados, la casuística es variada, apareciendo estructuras complejas y diversas, incluso para espesores del orden de la micra. Estos resultados sugieren la existencia de una fuerte conexión entre el crecimiento de la película y la topografía del sustrato, que podría utilizarse para obtener un mayor control nanoestructural. En esta presentación se analiza teórica y experimentalmente la relación entre ambos aspectos al utilizar la técnica de pulverización catódica a ángulo oblicuo. Se demuestra la posibilidad de crecer estructuras singulares como, por ejemplo, cruces nanopilares o incluso de huecos dentro de una matriz compacta, ordenados de acuerdo a un patrón regular con distancias típicas del orden de cientos de nanómetros (ver Figura 1). Se describe, por lo tanto, el marco conceptual que permitiría que las técnicas actuales de litografía superficial se puedan utilizar como técnicas efectivas de control nanoestructural de películas delgadas. Como resultado, se demuestran varios principios que definen los diferentes estadios de la deposición que servirían como guías para el diseño inteligente del sustrato e inducir crecimientos a la carta. Estos principios se han validado experimentalmente al crecer diferentes películas delgadas sobre un total de 16 sustratos litografiados con diferentes topografías, patrones y escalas típicas por debajo de la micra, así como en otros sustratos con rugosidad intrínseca sometidos a diferentes tipos de pulido.

It is demonstrated that, besides classical nanocolumnar arrays, the oblique angle geometry induces the growth of singular structures in the nanoscale when using wisely designed patterned substrates. Well-ordered array of crosses, cylindrical nanorods or hole structures arranged in square or hexagonal regular geometries are reported as examples, among others. The fundamental framework connecting substrate topography and film growth at oblique angles is presented, allowing the use of substrate patterning as a feasible thin film nanostructuring technique. A systematic analysis of the growth of TiO2 thin films on 4 different lithographic patterned substrates in 4 different scale lengths is also presented. A first conclusion is the existence of a height-based selective growth in the initial stages of the deposition, by which the film preferentially develops on top of the tallest substrate features. This behavior is maintained until the film reaches a critical thickness, the so-called Oblivion Thickness, above which the film topography becomes gradually independent of the substrate features. A general formula relating the spatial features of the pattern, the coarsening exponent and the Oblivion Thickness has been deduced., The authors thank the financial support from MCIN/AEI/10.13039/ 501100011033 projects PID2019-110430GB-C21, PID2020-112620GBI00, PID2020-114270RA-I00 and RTI2018-098117-B-C21 (also financed by FEDER Una manera de hacer europa), the Junta de Andalucía (PAIDI- 2020 through projects P18-RT-3480 and P18-RT-6079, and through its 2019 PhD Researcher Hiring Program), the CSIC (2019AEP161 and 201860E050), the Regional Government of Madrid (project IND2017/ IND-7668 and YEI contract PEJ-2019-AI/IND-14451 with support from FSE), the H2020-EU.1.2.1-FET OPEN program (grant 899352, project SOUNDofICE, and the EFRE Infra-Pro project ChAMP), and the University of Seville (VI PPIT-US). The work is supported by the Deutsche Forschungsgemeinschaft (DFG, grant Scha 632/24, “Tailored Disorder” and Scha 632/27, “DFGGer ¨atezentrum”). This work is also supported by the free state of Thuringia under grants 2015 FGI 0025 305 (FastμXRD) and B715-10009 (BioMacroNano2020), all co-financed by the European Union within the framework of the European Regional Development Fund (ERDF). The service from the MiNa Laboratory at IMN-CNM (CSIC), funded from CM (project S2018/NMT-4291 TEC2SPACE), MINECO (project CSIC13-4E- 1794) and EU (FEDER, FSE), is also acknowledged.

Resumen del trabajo presentado en la 31st Annual Conference of the European Society for Biomaterials, celebrada virtualmente del 5 al 9 de septiembre de 2021, Neural implants are increasingly investigated to assist patients with defects or pathologies in nervous system. There is a growing research about developing new biomaterials to improve the effectiveness and biocompatibility of neural implants. For example, inflammatory responses to implantation of these devices, also called foreign body reactions (FBR), are still a challenge for their performance. During FBR, immune cells such as monocytes and macrophages are recruited and activated, leading to several consequences. One of those is the increased amount of reactive oxygen species (ROS) due to differentiation and phagocytosis of macrophages. ROS affects the performance of neural implants in the long-term by increasing corrosion and delamination. Reactive accelerated aging tests (RAAT) are used as a tool to test the durability of bioelectrodes and neural implants, mimicking the presence of ROS in vivo. In RAAT, an H2O2 solution with high temperature can mimic several years of implantation during a few weeks due to the increased reaction rate provided by temperature. A RAAT protocol for testing neural implants has been recently approved by FDA. In this work, we have built a RAAT setup based on this protocol. We have studied different parameters that affect the stability of the system and we have employed RAAT to analyse the durability of different flat and nanostructured metallic layers.