Chronic neural probe for simultaneous recording of single-unit, multi-unit, and local field potential activity from multiple brain sites

Drug resistant focal epilepsy can be treated by resecting the epileptic focus requiring a precise focus localization using stereoelectroencephalography (SEEG) probes. As commercial SEEG probes offer only a limited spatial resolution, probes of higher channel count and design freedom enabling the incorporation of macro and microelectrodes would help increasing spatial resolution and thus open new perspectives for investigating mechanisms underlying focal epilepsy and its treatment. This work describes a new fabrication process for SEEG probes with materials and dimensions similar to clinical probes enabling recording single neuron activity at high spatial resolution. Polyimide is used as a biocompatible flexible substrate into which platinum electrodes and leads are... The resulting probe features match those of clinically approved devices. Tests in saline solution confirmed the probe stability and functionality. Probes were implanted into the brain of one monkey (Macaca mulatta), trained to perform different motor tasks. Suitable configurations including up to 128 electrode sites allow the recording of task-related neuronal signals. Probes with 32 and 64 electrode sites were implanted in the posterior parietal cortex. Local field potentials and multi-unit activity were recorded as early as one hour after implantation. Stable single-unit activity was achieved for up to 26 days after implantation of a 64-channel probe. All recorded signals showed modulation during task execution. With the novel probes it is possible to record stable biologically relevant data over a time span exceeding the usual time needed for epileptic focus localization in human patients. This is the first time that single units are recorded along cylindrical polyimide probes chronically implanted 22 mm deep into the brain of a monkey, which suggests the potential usefulness of this probe for human applications

Hybrid multisite silicon neural probe with integrated flexible connector for interchangeable packaging

Multisite neural probes are a fundamental tool to study brain function. Hybrid silicon/polymer neural probes combine rigid silicon and flexible polymer parts into one single device and allow, for example, the precise integration of complex probe geometries, such as multishank designs, with flexible biocompatible cabling. Despite these advantages and benefiting from highly reproducible fabrication methods on both silicon and polymer substrates, they have not been widely available. This paper presents the development, fabrication, characterization, and in vivo electrophysiological assessment of a hybrid multisite multishank silicon probe with a monolithically integrated polyimide flexible interconnect cable. The fabrication process was optimized at wafer level, and several neural probes with 64 gold electrode sites equally distributed along 8 shanks with an integrated 8 µm thick highly flexible polyimide interconnect cable were produced. The monolithic integration of the polyimide cable in the same fabrication process removed the necessity of the postfabrication bonding of the cable to the probe. This is the highest electrode site density and thinnest flexible cable ever reported for a hybrid silicon/polymer probe. Additionally, to avoid the time-consuming bonding of the probe to definitive packaging, the flexible cable was designed to terminate in a connector pad that can mate with commercial zero-insertion force (ZIF) connectors for electronics interfacing. This allows great experimental flexibility because interchangeable packaging can be used according to experimental demands. High-density distributed in vivo electrophysiological recordings were obtained from the hybrid neural probes with low intrinsic noise and high signal-to-noise ratio (SNR).This work has been funded by: national funds through the Foundation for Science and Technology (FCT)—projects UIDB/50026/2020 and UIDP/50026/2020; the projects NORTE-01-0145- FEDER-000013 (“PersonalizedNOS—New avenues for the development of personalized medical interventions for neurological, oncologic and surgical disorders”) and NORTE-01-0145-FEDER-000023 (“FROnTHERA—Frontiers of technology for theranostics of cancer, metabolic and neurodegenerative diseases”), supported by Norte Portugal Regional Operational Programme (NORTE 2020), under the PORTUGAL 2020 Partnership Agreement, through the European Regional Development Fund (ERDF); ICVS Scientific Microscopy Platform, member of the national infrastructure PPBI— Portuguese Platform of Bioimaging (PPBI-POCI-01-0145-FEDER-022122); FCT project PTDC/MEDNEU/ 28073/2017 (POCI-01-0145-FEDER-028073); and The Branco Weiss fellowship—Society in Science, (ETH Zurich)

Fabrication and characterization of transparent conductive oxide surface sensors for electrocorticography – TrECoG

Understanding how the brain works has been one of the greatest goals of mankind. This desire fuels the scientific community to pursue novel techniques able to acquire the complex information produced by the brain at any given moment. The Electrocorticography (ECoG) is one of those techniques. By placing conductive electrodes over the dura, or directly over the cortex, and measuring the electric potential variation, one can acquire information regarding the activation of those areas. In this work, transparent ECoGs, (TrECoGs) are fabricated through thin film deposition of the Transparent Conductive Oxides (TCOs) Indium-Zinc-Oxide (IZO) and Gallium-Zinc-Oxide (GZO). Five distinct devices have been fabricated via shadow masking and photolithography. The data acquired and presented in this work validates the TrECoGs fabricated as efficient devices for recording brain activity. The best results were obtained for the GZO- based TrECoG, which presented an average impedance of 36 kΩ at 1 kHz for 500 μm diameter electrodes, a transmittance close to 90% for the visible spectrum and a clear capability to detect brain signal variations. The IZO based devices also presented high transmittance levels (90%), but with higher impedances, which ranged from 40 kΩ to 100 kΩ

Stretchable and Skin-Conformable Conductors Based on Polyurethane/Laser-Induced Graphene

The conversion of various polymer substrates into laser-induced graphene (LIG) with a CO2 laser in ambient condition is recently emerging as a simple method for obtaining patterned porous graphene conductors, with a myriad of applications in sensing, actuation, and energy. In this paper, a method is presented for embedding porous LIG (LIG-P) or LIG fibers (LIG-F) into a thin (about 50 μm) and soft medical grade polyurethane (MPU) providing excellent conformal adhesion on skin, stretchability, and maximum breathability to boost the development of various unperceivable monitoring systems on skin. The effect of varying laser fluence and geometry of the laser scribing on the LIG micro-nanostructure morphology and on the electrical and electromechanical properties of LIG/MPU composites is investigated. A peculiar and distinct behavior is observed for either LIG-P or LIG-F. Excellent stretchability without permanent impairment of conductive properties is revealed up to 100% strain and retained after hundreds of cycles of stretching tests. A distinct piezoresistive behavior, with an average gauge factor of 40, opens the way to various potential strain/pressure sensing applications. A novel method based on laser scribing is then introduced for providing vertical interconnect access (VIA) into LIG/MPU conformable epidermal sensors. Such VIA enables stable connections to an external measurement device, as this represents a typical weakness of many epidermal devices so far. Three examples of minimally invasive LIG/MPU epidermal sensing proof of concepts are presented: as electrodes for electromyographic recording on limb and as piezoresistive sensors for touch and respiration detection on skin. Long-term wearability and functioning up to several days and under repeated stretching tests is demonstrated

Flexible sensors technology for Point-Of-Care diagnostics with integrated micro fluidics on paper

Nowadays the hospitals and the medical centres face a huge challenge finding solutions to improve the efficiency of medical diagnosis. The scope of this project was to develop a “Point-of-Care Diagnostic” (POCD) device, that can give a better alternative for genetic analysis, instead of the usual methods of PCR (polymerase chain reaction). This device is composed by three layers. The first layer which works as a transporter and filter was built on paper. The second layer is the substitute of the regular thermocycling phase in the PCR technique and the third layer incorporates an interdigital capacitor that works as a DNA (deoxyribonucleic acid) sensor with high sensitivity to detect DNA hybridisation. These last two layers were made in kapton film. The devices were produced with microfabrication methods using inkjet printing, lithographic and deposition processes. The device’s characterisation was based on impedance spectroscopy methods. With the purpose of testing the device, the capacitor was functionalised with the YWHAZ gene. However, this process can be performed with any other gene. Due to its characteristics, the device under study was designed to run RT-qPCR (Real time quantitative polymerase chain reaction) and presents itself as an effective way to substitute the traditional PCR techniques. Even more, as the transport of samples to a laboratory and the recruitment of specialised personnel are not necessary, costs and response time are reduced

OPTIMIZATION OF TIME-RESPONSE AND AMPLIFICATION FEATURES OF EGOTs FOR NEUROPHYSIOLOGICAL APPLICATIONS

In device engineering, basic neuron-to-neuron communication has recently inspired the development of increasingly structured and efficient brain-mimicking setups in which the information flow can be processed with strategies resembling physiological ones. This is possible thanks to the use of organic neuromorphic devices, which can share the same electrolytic medium and adjust reciprocal connection weights according to temporal features of the input signals. In a parallel - although conceptually deeply interconnected - fashion, device engineers are directing their efforts towards novel tools to interface the brain and to decipher its signalling strategies. This led to several technological advances which allow scientists to transduce brain activity and, piece by piece, to create a detailed map of its functions. This effort extends over a wide spectrum of length-scales, zooming out from neuron-to-neuron communication up to global activity of neural populations. Both these scientific endeavours, namely mimicking neural communication and transducing brain activity, can benefit from the technology of Electrolyte-Gated Organic Transistors (EGOTs). Electrolyte-Gated Organic Transistors (EGOTs) are low-power electronic devices that functionally integrate the electrolytic environment through the exploitation of organic mixed ionic-electronic conductors. This enables the conversion of ionic signals into electronic ones, making such architectures ideal building blocks for neuroelectronics. This has driven extensive scientific and technological investigation on EGOTs. Such devices have been successfully demonstrated both as transducers and amplifiers of electrophysiological activity and as neuromorphic units. These promising results arise from the fact that EGOTs are active devices, which widely extend their applicability window over the capabilities of passive electronics (i.e. electrodes) but pose major integration hurdles. Being transistors, EGOTs need two driving voltages to be operated. If, on the one hand, the presence of two voltages becomes an advantage for the modulation of the device response (e.g. for devising EGOT-based neuromorphic circuitry), on the other hand it can become detrimental in brain interfaces, since it may result in a non-null bias directly applied on the brain. If such voltage exceeds the electrochemical stability window of water, undesired faradic reactions may lead to critical tissue and/or device damage. This work addresses EGOTs applications in neuroelectronics from the above-described dual perspective, spanning from neuromorphic device engineering to in vivo brain-device interfaces implementation. The advantages of using three-terminal architectures for neuromorphic devices, achieving reversible fine-tuning of their response plasticity, are highlighted. Jointly, the possibility of obtaining a multilevel memory unit by acting on the gate potential is discussed. Additionally, a novel mode of operation for EGOTs is introduced, enabling full retention of amplification capability while, at the same time, avoiding the application of a bias in the brain. Starting on these premises, a novel set of ultra-conformable active micro-epicortical arrays is presented, which fully integrate in situ fabricated EGOT recording sites onto medical-grade polyimide substrates. Finally, a whole organic circuitry for signal processing is presented, exploiting ad-hoc designed organic passive components coupled with EGOT devices. This unprecedented approach provides the possibility to sort complex signals into their constitutive frequency components in real time, thereby delineating innovative strategies to devise organic-based functional building-blocks for brain-machine interfaces.Nell’ingegneria elettronica, la comunicazione di base tra neuroni ha recentemente ispirato lo sviluppo di configurazioni sempre più articolate ed efficienti che imitano il cervello, in cui il flusso di informazioni può essere elaborato con strategie simili a quelle fisiologiche. Ciò è reso possibile grazie all'uso di dispositivi neuromorfici organici, che possono condividere lo stesso mezzo elettrolitico e regolare i pesi delle connessioni reciproche in base alle caratteristiche temporali dei segnali in ingresso. In modo parallelo, gli ingegneri elettronici stanno dirigendo i loro sforzi verso nuovi strumenti per interfacciare il cervello e decifrare le sue strategie di comunicazione. Si è giunti così a diversi progressi tecnologici che consentono agli scienziati di trasdurre l'attività cerebrale e, pezzo per pezzo, di creare una mappa dettagliata delle sue funzioni. Entrambi questi ambiti scientifici, ovvero imitare la comunicazione neurale e trasdurre l'attività cerebrale, possono trarre vantaggio dalla tecnologia dei transistor organici a base elettrolitica (EGOT). I transistor organici a base elettrolitica (EGOT) sono dispositivi elettronici a bassa potenza che integrano funzionalmente l'ambiente elettrolitico attraverso lo sfruttamento di conduttori organici misti ionici-elettronici, i quali consentono di convertire i segnali ionici in segnali elettronici, rendendo tali dispositivi ideali per la neuroelettronica. Gli EGOT sono stati dimostrati con successo sia come trasduttori e amplificatori dell'attività elettrofisiologica e sia come unità neuromorfiche. Tali risultati derivano dal fatto che gli EGOT sono dispositivi attivi, al contrario dell'elettronica passiva (ad esempio gli elettrodi), ma pongono comunque qualche ostacolo alla loro integrazione in ambiente biologico. In quanto transistor, gli EGOT necessitano l'applicazione di due tensioni tra i suoi terminali. Se, da un lato, la presenza di due tensioni diventa un vantaggio per la modulazione della risposta del dispositivo (ad esempio, per l'ideazione di circuiti neuromorfici basati su EGOT), dall'altro può diventare dannosa quando gli EGOT vengono adoperati come sito di registrazione nelle interfacce cerebrali, poiché una tensione non nulla può essere applicata direttamente al cervello. Se tale tensione supera la finestra di stabilità elettrochimica dell'acqua, reazioni faradiche indesiderate possono manifestarsi, le quali potrebbero danneggiare i tessuti e/o il dispositivo. Questo lavoro affronta le applicazioni degli EGOT nella neuroelettronica dalla duplice prospettiva sopra descritta: ingegnerizzazione neuromorfica ed implementazione come interfacce neurali in applicazioni in vivo. Vengono evidenziati i vantaggi dell'utilizzo di architetture a tre terminali per i dispositivi neuromorfici, ottenendo una regolazione reversibile della loro plasticità di risposta. Si discute inoltre la possibilità di ottenere un'unità di memoria multilivello agendo sul potenziale di gate. Viene introdotta una nuova modalità di funzionamento per gli EGOT, che consente di mantenere la capacità di amplificazione e, allo stesso tempo, di evitare l'applicazione di una tensione all’interfaccia cervello-dispositivo. Partendo da queste premesse, viene presentata una nuova serie di array micro-epicorticali ultra-conformabili, che integrano completamente i siti di registrazione EGOT fabbricati in situ su substrati di poliimmide. Infine, viene proposto un circuito organico per l'elaborazione del segnale, sfruttando componenti passivi organici progettati ad hoc e accoppiati a dispositivi EGOT. Questo approccio senza precedenti offre la possibilità di filtrare e scomporre segnali complessi nelle loro componenti di frequenza costitutive in tempo reale, delineando così strategie innovative per concepire blocchi funzionali a base organica per le interfacce cervello-macchina

Fabrication of Flexible Hybrid Circuits in Parylene

In recent years, with the increasing research interest in personalized medicine, new and disruptive technologies such as the Internet of Things (IoT) and flexible wearable electronics have emerged and have become trending topics in the scientific community. Despite consistent progress in the area of fully flexible electronics, these continue to reveal some restrictions, which can be overcome by traditional silicon integrated circuits (ICs). The combination between these technologies generated the new concept of flexible hybrid electronics (FHE) igniting a new generation of wearable health monitoring systems. This thesis reports a new way to the use parylene C as substrate, dielectric and encap- sulation layers to accommodate silicon ICs, surface mounted devices (SMDs) and thin metal layers, in order to create flexible and conformable double layered hybrid sensing membranes for body temperature monitoring, one of the most relevant physiological pa- rameters upon a medical diagnosis, since it’s among the main indicators for inflammation and infection. To achieve the thin metal and parylene C layers, thin-film microfabrica- tion techniques were employed and corroborated by superficial, electrical and structural characterization techniques. In addition the establishment of an electrical connection by the integration of silicon ICs and SMDs onto the thin metal layer was successfully tested using a low-temperature solder paste and a reflow oven, which reproduced a previously inputted time-temperature profile. Furthermore, this thesis analyses the repercussions of this integration procedure on the peel off process. Throughout this work, commercial body temperature measuring circuits were used as inspiration for the temperature sensing circuits developed. The interface between the produced membranes and their respective microcontrollers was also tested, although no temperature measurements were obtained due to parylene’s performance as a dielectric. The successful production of a fully functional flexible and conformable double layered hybrid sensing membrane could propel the adaptation of other rigid health monitoring electronics to FHE membranes, further engraving this technology into people’s daily lives.Com o crescente interesse na pesquisa em medicina personalizada, novas tecnologias como a Internet of Things (IoT) e a eletrónica flexível, surgiram e tornaram-se tópicos de tendência na comunidade científica. Apesar dos progressos na área da eletrónica totalmente flexível, continuam a existir algumas restrições, que podem ser superadas pelos circuitos integrados de silício (ICs) tradicionais. A junção entre estas tecnologias gerou um novo conceito de eletrónica híbrida flexível (FHE) dando início a uma nova geração de sistemas de monitorização de saúde. Esta tese aborda uma forma inovadora de usar parileno C como substrato, dielétrico e camada de encapsulamento para acomodar ICs de silício, surface mounted devices (SMDs) e camadas metálicas finas, a fim de criar circuitos em membranas híbridas de dupla camada flexíveis e conformáveis para monitorização da temperatura corporal, um dos parâmetros fisiológicos com maior relevância aquando do diagnóstico, uma vez que é um dos principais indicadores de infeções e inflamações. Para obter as camadas finas de metal e parileno C, foram empregues técnicas de microfabricação de filmes finos, corroboradas por caracterizações superficiais, elétricas e estruturais. Utilizando uma pasta de solda de baixa temperatura e um forno de refluxo, reproduzindo um perfil de tempo-temperatura, foi desenvolvido um protocolo para a conexão e integração de ICs na fina camada de metal. São ainda apresentados resultados relativos às implicações deste processo no método do peel off. Os circuitos desenvolvidos durante esta tese tiveram por base circuitos comerciais que medem a temperamtura corporal. Apesar da interface entre as membranas produzidas e os seus respetivos microcontroladores ter sido testada, não foi possível medir a temperatura com os circuitos desenvolvidos devido à performance do parileno como dielétrico. A produção bem-sucedida de uma membrana híbrida de dupla camada, flexível e conformável, totalmente funcional pode impulsionar a adaptação de outros equipamentos rígidos de monitorização de saúde para membranas híbridas flexíveis, inserindo ainda mais esta tecnologia na vida quotidiana

LTCC packaging for Lab-on-a-chip application

LTCC -pakkaus Lab-on-a-chip -sovellukseen. Tiivistelmä. Tässä työssä suunniteltiin, valmistettiin ja testattiin uusi pakkaustekniikka ”Lab-on-a-chip” (LOC) -sovellukseen. Pakkaus tehtiin pii-mikrosirulle, jolla voidaan mitata solujen kiinnittymistä sirun pintaan solujen elinkelpoisuuden indikaattorina. Luotettavuustestaukset tehtiin daisy-chain -resistanssimittauksilla solunkasvatusolosuhteissa. Lisäksi työssä selvitettiin LTCC- ja ”Lab-on-a-chip” -teknologioiden perusteet teoreettiselta pohjalta. Mikrosirun pakkauksessa käytettiin joustavaa LTCC-teknologiaa. Sähköisiin kontakteihin ja niiden suojauksiin käytettiin sekä johtavia että eristäviä epoksi-liimoja. LOC-sovelluksiin on tärkeää kehittää uusia pakkausmenetelmiä jotta näiden laitteiden kaikki ominaisuudet saadaan toimimaan luotettavasti. Pakkaus testattiin samoissa olosuhteissa missä sitä tullaan käyttämään ja pakkaus kesti kaikki nämä haasteet. Lisäksi esitetty valmistusprosessi on sellainen, että sitä voidaan käyttää myös muihin ”Lab-on-a-chip” -sovelluksiin.Abstract. This work presents design, manufacturing and testing of new packaging method for Lab-on-a-chip (LOC) application. Packaging was made for silicon microchip which can measure cell adhesion on chips surface as indication of cell viability. Reliability testing was done with daisy-chain resistance measurement in real conditions. Moreover basic theory of LTCC and Lab-on-a-chip technology is presented. Resilient LTCC technology was used for packaging material and conductive/insulating epoxies were applied for electrical contacts and barriers against the environment. It is fundamentally important to develop new packaging methods for LOC applications, so all the properties can be utilized reliably. Packaging was tested under the cell growth conditions and the package showed to withstand all these challenges. Moreover the presented packaging method is possible to use also in other Lab-on-a-chip applications

Manipulation of Microenvironment with a Built-in Electrochemical Actuator in Proximity of a Dissolved Oxygen Microsensor

Biochemical sensors for continuous monitoring require dependable periodic self diagnosis with acceptable simplicity to check its functionality during operation. An in-situ self-diagnostic technique for a dissolved oxygen microsensor is proposed in an effort to devise an intelligent microsensor system with an integrated electrochemical actuation electrode. With a built-in platinum microelectrode that surrounds the microsensor, two kinds of microenvironments, called the oxygen-saturated or oxygen-depleted phases, can be created by water electrolysis, depending on the polarity. The functionality of the microsensor can be checked during these microenvironment phases. The polarographic oxygen microsensor is fabricated on a flexible polyimide substrate (Kapton) and the feasibility of the proposed concept is demonstrated in a physiological solution. The sensor responds properly during the oxygen-generating and oxygen-depleting phases. The use of these microenvironments for in-situ self-calibration is discussed to achieve functional integration, as well as structural integration, of the microsensor system