The design of polymeric microneedles for the delivery of sensors for real-time physiological monitoring

Ce mémoire de maîtrise porte sur le développement d’un système d’administration de microaiguilles pour livrer des sondes et des capteurs fluorescents dans le contexte du diagnostic et de la surveillance des soins de santé. Bien que parfois négligés en faveur des soins de santé axés sur le traitement, le diagnostic précoce de la maladie et la surveillance préventive des paramètres biologiques peuvent considérablement améliorer les résultats des soins de santé et joueront probablement un rôle plus important dans les années à venir. Cependant, il reste des obstacles importants à cette approche, à savoir le caractère relativement invasif et perturbateur des analyses biologiques. La nécessité de se rendre dans une clinique et de subir un prélèvement de sang (ou de liquide biologique) invasif présente des inconvénients importants par rapport aux traitements classiques, qui consistent souvent de médicaments pouvant être pris à domicile sans douleur. Une solution à ces problèmes réside dans la mise au point de systèmes minimalement invasifs de diagnostic et de suivi médical, idéalement ceux qui peuvent être utilisés à domicile sans nécessiter de personnel qualifié. À cet égard, les microaiguilles sont une technologie au potentiel énorme, car leur petite taille les rend peu invasives et pratiquement indolores, et leur nature simple à usage unique permet potentiellement une administration à domicile par le patient. Particulièrement prometteuses pour les applications de diagnostic et de surveillance sont les microaiguilles en polymère soluble; fabriquées à partir de polymères synthétiques ou biologiques injectables, ces microaiguilles sont solubilisées après la perforation de la peau, libérant ainsi les composés qu’elles contiennent. Bien que prévu initialement pour la livraison d'agents thérapeutiques, en utilisant ces microaiguilles pour livrer des molécules fluorescentes spécifiquement conçues, il est possible de créer un tatouage médical de diagnostic affichant un signal fluorescent précis. En associant cette technologie à un détecteur de fluorescence portable, la surveillance en temps réel d’un large éventail de paramètres biologiques pourrait devenir accessible en dehors du contexte clinique. Afin de fournir un contexte pour le développement de cette technologie, cette mémoire commence par une revue des principes et des avancées majeures récentes dans le domaine des applications diagnostiques des microaiguilles (Chapitre 1). Par la suite, un tatouage par microaiguille est présenté sous la forme d'un capteur de ROS délivré sur la peau, avec des implications diagnostiques pour le vieillissement et la carcinogenèse de la peau liés aux UV, ainsi que pour des affections inflammatoires telles que le psoriasis, comme validation de concept (Chapitre 2). En outre, un autre tatouage par microaiguille est introduit, consistant d’un capteur spécialement adapté ciblant le système lymphatique, permettant la quantification en temps réel du drainage lymphatique, avec des implications pour la détection précoce de plusieurs affections, notamment le lymphœdème (Chapitre 3).This Master’s thesis concerns the development of a microneedle (MN) delivery system for fluorescent dyes and sensors in the context of diagnostics and healthcare monitoring. While sometimes overlooked in favor of treatment-focused healthcare, early disease diagnosis and preventative monitoring of biological parameters can meaningfully improve healthcare outcomes and will likely play a greater role in coming years. However, significant obstacles to this approach remain, namely the relatively invasive and disruptive nature of biological analyses. The need to travel to a clinic and undergo invasive blood (or biological fluid) sampling presents significant inconveniences relative to common treatments, often consisting of medications that can be taken painlessly at home. A solution to these problems lies in the development of minimally invasive systems for diagnostics and healthcare monitoring, ideally ones which can be used at home without the need for trained personnel. In this regard, MNs are a technology with tremendous potential, as their small size renders them minimally invasive and virtually painless, and their simple, single-use nature potentially allows for at-home administration by the patient. Showing particular promise for diagnostic and monitoring applications are dissolving polymeric MNs; made from injectable synthetic or biological polymers, these MNs are solubilized after breaching the skin, releasing any compound contained within. Though initially envisioned for the delivery of therapeutic agents, by using these MNs to deliver specifically designed fluorescent molecules, it is possible to create a diagnostic medical tattoo displaying a precise fluorescent signal. By pairing this technology with a portable fluorescence detector, real-time monitoring of a wide range of biological parameters could become accessible outside of a clinical setting. To provide context for the development of this technology, this thesis begins with a review of the principles and major recent advances in the field of diagnostic applications of MNs (Chapter 1). Subsequently, a proof-of-concept MN tattoo is introduced in the form of a ROS-sensor delivered to the skin, with diagnostic implications for UV-related skin aging and carcinogenesis, as well as inflammatory conditions such as psoriasis (Chapter 2). Further, another MN tattoo is introduced, consisting of a specifically tailored sensor targeting the lymphatic system, allowing the real-time quantification of lymphatic drainage, with implications in the early detection of several conditions, including lymphedema (Chapter 3)

CLINICAL EVALUATION OF NOVEL METHODS FOR EXTENDING MICRONEEDLE PORE LIFETIME

Microneedles are a minimally invasive method for delivering drugs through the impermeable skin layers, and have been used to deliver a variety of compounds including macromolecules, vaccines, and naltrexone. Microneedles can be applied to the skin once, creating micropores that allow for drug delivery into the underlying circulation from a drug formulation. The utility of this technique, however, is blunted by rapid micropore closure. This research project sought to: 1) characterize micropore lifetime and re-sealing kinetics, and 2) prolong micropore lifetime via inhibition of the skin’s barrier restoration processes. Impedance spectroscopy was used as a surrogate technique in animals and humans to measure micropore formation and lifetime. A proof of concept study in humans, using impedance spectroscopy, demonstrated that diclofenac (a topical anti-inflammatory) applied to microporated skin resulted in slower re-sealing kinetics compared to placebo, in agreement with previous animal studies. The clinical feasibility of prolonging micropore lifetime with diclofenac was confirmed via 7-day delivery of naltrexone through microneedle treated skin in humans (compared to 72 hour delivery with placebo). Lastly, naltrexone gels with calcium salts were applied to microneedle treated skin (hairless guinea pigs) to restore the altered epidermal calcium gradient; this method did not significantly extend micropore lifetime

Minimally invasive clinical monitoring and data transference in cardiac patients

'Wet' electrodes used in electrocardiography (ECG), are applied to the surface of the skin to record cardiac activity. Over time, water-based electrolytic gels between the electrodes and skin dehydrate, reducing signal quality. Microneedle-electrodes negate the need for conductive gels and potentially improve signal fidelity by circumventing the stratum corneum and contacting the underlying conductive epidermal layers. This thesis aimed to assess the wearability and functionality of microneedle-electrodes in cardiac signal acquisition. Epoxy, 500μm-length microneedles were applied to excised skin models to assess insertion performance. Increasing downward application force increased microneedle penetration efficiency from 79%±8.20 (5N) to 87%±13.32 (15N). The microneedle application technique also had an impact on penetration efficiency, with impact insertion (93%±5.75) proving more effective than manual downward force (71%±22.01). Metallised versions of the epoxy microneedles were integrated into a commercial electrode and compared to conventional wet electrodes in human volunteers. Wet electrodes recorded higher quality signals than microneedle-electrodes in healthy human participants (1.6dB difference between the electrode types). This clinical data informed the development of an in vitro laboratory skin model to assess the influence of microneedle-electrode parameters on a simulated ECG signal. Increasing microneedle length from 500μm (25.2dB±3.25) to 600μm (24.3dB±2.31) did not result in a sustained improvement in signal quality (p>0.05). Bespoke second-generation microneedle-electrodes were manufactured allowing an improved signal quality to be maintained over the recording period (17.3dB±2.11 compared to 15.0dB±1.97 for wet electrodes; p>0.05) in the laboratory model. Human participant studies assessed their wearability and functionality. At rest, the metallised epoxy (23.2dB±5.79) and bespoke (22.5dB±7.57) microneedle-electrode performance was comparable to wet electrodes (24.9dB±6.44) (p>0.05). Under active conditions, the signal-to-noise ratio declined for all electrodes and ECG traces highlighted increased motion artifacts. Participants preferred wet electrodes and highlighted seven key wearability themes. Further optimisation of microneedle-electrodes for ECG monitoring is therefore, warranted

Microneedle based electrochemical (bio)sensing: towards decentralized and continuous health status monitoring

Microneedle (MN) based electrochemical (bio)sensing has become a growing field within the discipline of analytical chemistry as a result of its unique capacity for continuous, decentralized health status monitoring. There are two significant advantages to this exclusive feature: i) the ability to directly analyze interstitial fluid (ISF), a body fluid with a similar enough composition to plasma (and blood) to be considered a plentiful source of information related to biologically relevant molecules and biomarkers; and ii) the capacity to overcome some of the major limitations of blood analysis including painful extraction, high interferant concentrations, and incompatibility with diagnosis of infants (and especially newborns). Recent publications have demonstrated important advancements in electrochemical MN sensor technology, among which are included new MN fabrication methods and various modification strategies, providing different architectures and allowing for the integration of electronics. This versatility highlights the undeniable need for interdisciplinary efforts towards tangible progress in the field. In a context evidently dominated by glucose sensing, which is slowly being expanded towards other analytes, the following crucial questions arise: to what extent are electrochemical MN (bio)sensors a reliable analytical tool for continuous ISF monitoring? Which is the best calibration protocol to be followed for in vivo assays? Which strategies can be employed to protect the sensing element during skin penetration? Is there an appropriate validation methodology to assess the accuracy of electrochemical MN (bio)sensors? How significant is the distinction between successful achievements in the laboratory and the real commercial feasibility of products? This paper aims to reflect on those previous questions while reviewing the progress of electrochemical MN (bio)sensors in the last decade with a focus on the analytical aspects. Overall, we describe the current state of electrochemical MN (bio)sensors, the benefits and challenges associated to ISF monitoring, as well as key features (and bottlenecks) regarding its implementation for in vivo assays

Micromachined three-dimensional electrode arrays for in-vitro and in-vivo electrogenic cellular networks

This dissertation presents an investigation of micromachined three-dimensional microelectrode arrays (3-D MEAs) targeted toward in-vitro and in-vivo biomedical applications. Current 3-D MEAs are predominantly silicon-based, fabricated in a planar fashion, and are assembled to achieve a true 3-D form: a technique that cannot be extended to micro-manufacturing. The integrated 3-D MEAs developed in this work are polymer-based and thus offer potential for large-scale, high volume manufacturing. Two different techniques are developed for microfabrication of these MEAs - laser micromachining of a conformally deposited polymer on a non-planar surface to create 3-D molds for metal electrodeposition; and metal transfer micromolding, where functional metal layers are transferred from one polymer to another during the process of micromolding thus eliminating the need for complex and non-repeatable 3-D lithography processes. In-vitro and in-vivo 3-D MEAs are microfabricated using these techniques and are packaged utilizing Printed Circuit Boards (PCB) or other low-cost manufacturing techniques. To demonstrate in-vitro applications, growth of 3-D co-cultures of neurons/astrocytes and tissue-slice electrophysiology with brain tissue of rat pups were implemented. To demonstrate in-vivo application, measurements of nerve conduction were implemented. Microelectrode impedance models, noise models and various process models were evaluated. The results confirmed biocompatibility of the polymers involved, acceptable impedance range and noise of the microelectrodes, and potential to improve upon an archaic clinical diagnostic application utilizing these 3-D MEAs.Ph.D.Committee Chair: Mark G. Allen; Committee Member: Elliot L. Chaikof; Committee Member: Ionnis (John) Papapolymerou; Committee Member: Maysam Ghovanloo; Committee Member: Oliver Bran

Fabrication of microdevices for biomedical applications based on lithographic approach

Well established integrated circuits technologies, traditionally used in production of microprocessors, are more and more exploited in different fields, very distant from classic electronics, such as medicine and biology. However, transferring these technologies from the integrated circuit industry to other scientific fields is not trivial, since it requires large efforts to adapt traditional materials and processes to these areas or in some cases to develop and use alternative materials and processes with respect to traditional ones. The research activity presented in this PhD thesis is placed in this contest with the aim to define new fabrication procedures, combining lithographic processes of both hard and soft materials, for the realization of three innovative microdevices for biomedical applications. In particular, microneedles based devices for drug delivery and biosensing, and device for microfluidic filtration have been explored