Monitoring with In Vivo Electrochemical Sensors: Navigating the Complexities of Blood and Tissue Reactivity

The disruptive action of an acute or critical illness is frequently manifest through rapid biochemical changes that may require continuous monitoring. Within these changes, resides trend information of predictive value, including responsiveness to therapy. In contrast to physical variables, biochemical parameters monitored on a continuous basis are a largely untapped resource because of the lack of clinically usable monitoring systems. This is despite the huge testing repertoire opening up in recent years in relation to discrete biochemical measurements. Electrochemical sensors offer one of the few routes to obtaining continuous readout and, moreover, as implantable devices information referable to specific tissue locations. This review focuses on new biological insights that have been secured through in vivo electrochemical sensors. In addition, the challenges of operating in a reactive, biological, sample matrix are highlighted. Specific attention is given to the choreographed host rejection response, as evidenced in blood and tissue, and how this limits both sensor life time and reliability of operation. Examples will be based around ion, O2, glucose, and lactate sensors, because of the fundamental importance of this group to acute health care

In Vivo Analytical Performance Assessment of Nitric Oxide-Releasing Glucose Biosensors

The utility of implantable glucose biosensors as continuous glucose monitoring technologies is limited by poor in vivo accuracy, resulting primarily from the foreign body response (FBR). Polymeric membranes capable of releasing nitric oxide (NO)—an endogenous gas and key mediator of inflammation and angiogenesis—have been shown to mitigate the FBR and thus hold promise for improving in vivo glucose sensor function. Herein, the effect of a reduced FBR on in vivo glucose sensor function was studied using NO-releasing membranes. To address the low NO storage of silica nanoparticles, a new particle system (mesoporous silica) was synthesized for use in glucose sensor membranes. Briefly, an interfacial ion exchange reaction was developed and used to chemically modify mesoporous silica nanoparticles with NO donors. The resulting materials were capable of large NO storage (0.8–2.4 µmol mg-1) and tunable NO-release kinetics (NO-release durations 2–40 h). The NO-releasing nanoparticles were employed as dopants within polyurethane materials and adapted as coatings for amperometric glucose biosensors. The in vivo analytical performance of the NO-releasing glucose biosensors was evaluated in a pre-clinical swine model. Two separate NO-releasing sensors were designed to release similar amounts of NO (~3.1 µmol cm-2) for 16.0 h (short) or 3.1 d (extended) durations. Relative to controls, both NO-releasing sensors exhibited improved accuracy during the acute (3 d) implantation period. Sensors capable of ~3 d NO release were also characterized by a shorter response time (5.8 min) at 3, 7, and 10 d. The NO-releasing sensor membranes were also used to study the FBR in a streptozotocin-induced diabetic swine model. Histopathological evaluation of tissue surrounding control (i.e., non-NO-releasing) materials revealed a more severe inflammatory response, reduced collagen deposition, and inhibited angiogenesis associated with diabetes. Materials capable of ~7–14 d NO release were uniquely capable of mitigating inflammation and increasing blood vessel formation at the implant-tissue interface (relative to 2–3 d NO release). The ~7–14 d NO-releasing membranes also reduced collagen deposition in healthy pigs, but did not produce an effect in the diabetic animal model.Doctor of Philosoph

Low power CMOS IC, biosensor and wireless power transfer techniques for wireless sensor network application

The emerging field of wireless sensor network (WSN) is receiving great attention due to the interest in healthcare. Traditional battery-powered devices suffer from large size, weight and secondary replacement surgery after the battery life-time which is often not desired, especially for an implantable application. Thus an energy harvesting method needs to be investigated. In addition to energy harvesting, the sensor network needs to be low power to extend the wireless power transfer distance and meet the regulation on RF power exposed to human tissue (specific absorption ratio). Also, miniature sensor integration is another challenge since most of the commercial sensors have rigid form or have a bulky size. The objective of this thesis is to provide solutions to the aforementioned challenges

Mechanoresponsive drug delivery: harnessing forces for controlled release

Mechanically-activated delivery systems harness existing physiological and/or externally-applied forces to provide spatiotemporal control over the release of active agents. The presence and necessity of these forces in the human body and in the increasing use of mechanically-driven medical devices (e.g., stents, balloon catheters, gastric bands, tissue expanders) can serve as functional dynamic triggers. Therefore, this dissertation investigates the use of applied tensile strain and cyclic loading to control release of entrapped agents, and further translates the concept towards clinical applications by integrating the system with commercial medical devices that provide precise forces to trigger release. As an initial proof-of-concept, mechanoresponsive composites, consisting of highly-textured superhydrophobic barrier coatings over a hydrophilic substrate, are fabricated. The release of entrapped agents, controlled by the magnitude of applied strain, results in a graded response due to water infiltration through propagating patterned cracks in the coating. The strain-dependent delivery of anticancer agents with in vitro efficacy as well as the ex vivo delivery to esophageal tissue with an integrated stent system are demonstrated. Release is further modulated by barrier coating properties. Thicker coatings afford slower release rates with preserved in vitro activity for both a chemotherapeutic and an enzyme. Localizing coating crack patterns based on different geometric stress concentration factors further controls the selective sequential release of multiple agents. Finally, the development of a reversible mechanoresponsive system is investigated to provide cycle-mediated pulsatile release. Optimization of mechanical parameters results in delivery of multiple doses. To translate this concept towards the clinic, the system is integrated with commercial balloon catheters to provide multidose delivery of small molecules to ex vivo vessels. Using the inherent inflation and deflation of the catheter to trigger release, the system enhances existing capabilities to treat cardiovascular and peripheral artery diseases. In summary, the development of mechanoresponsive systems that respond to tensile strain and cycle number are described for the delivery of a wide-range of active agents (hydrophilic and hydrophobic small molecules as well as an enzyme), and their integration with existing medical devices. Furthermore, the comprehensive range of specific kinetic profiles, including triggered release, pulsatile delivery, and the sequential delivery of multiple agents, showcases the capabilities and versatility of these dynamic mechanoresponsive systems to modulate release for the treatment of various clinical diseases.2019-02-20T00:00:00

Advances in Bioengineering

The technological approach and the high level of innovation make bioengineering extremely dynamic and this forces researchers to continuous updating. It involves the publication of the results of the latest scientific research. This book covers a wide range of aspects and issues related to advances in bioengineering research with a particular focus on innovative technologies and applications. The book consists of 13 scientific contributions divided in four sections: Materials Science; Biosensors. Electronics and Telemetry; Light Therapy; Computing and Analysis Techniques

Tissue Integration and Antimicrobial Effects of Surface-derived Nitric Oxide Release

The analytical performance of glucose sensors is inhibited by the host’s foreign body response (FBR) and risk of bacterial infection. To date, no one strategy has circumvented the physiological reactions to implanted materials. Nitric oxide (NO) is an endogenously produced free radical that acts to initiate events in the FBR and fight bacterial infection. Herein, the potential of NO-releasing surfaces to both mitigate the FBR and bacterial invasion is described. Evaluation of the performance of NO-releasing surfaces to improve glucose sensor performance in vivo was carried out through imparting NO release to microdialysis probes. Perfusion of saturated NO solutions through implanted probes delivered a constant flux of 162 pmol cm-2 s-1 delivering 4.6 μmol cm-2 NO each day. The NO-releasing probes recovered significantly greater concentrations of glucose after 7 d of implantation versus controls. Histological analysis revealed a thinner collagen capsule and decreased inflammation adjacent to NO-releasing probes. To investigate the necessary NO-release properties to achieve the observed histological benefits, NO-releasing polyurethane-coated wires were implanted into a porcine model for up to 6 weeks. Polyurethanes were doped with small molecules or nanoparticles to alter the NO release kinetics, fluxes, and total payloads. Materials with a NO-release duration of 14 d and large NO payload (9.3 μmol cm-2) were most effective at decreasing the collagen encapsulation and inflammation adjacent to the implants. Inflammation was only modulated during active NO release from the implant. While modulation of the FBR is essential for the development of glucose sensors, infection by bacteria is a constant threat. Biomaterial-associated infections most commonly begin through adhesion to the implanted material. Therefore, evaluation of the anti-adhesive properties of NO-releasing surfaces was undertaken by examining the adhesion of six bacterial strains to a wide range of NO fluxes (0.5–50 pmol cm-2 s-1). An average NO flux between 50 pmol cm-2 s-1 reduced surface coverage of all strains by >80% over 1 h. Further, after incubation of adhered bacteria in bacteriostatic conditions for 24 h, large surfacederived NO payloads (1.7 μmol cm-2) decreased viability of adhered bacteria by ≥85%.Doctor of Philosoph

Semiconducting Polymers for Electronic Biosensors and Biological Interfaces

Bioeletronics aims at the direct coupling of biomolecular function units with standard electronic devices. The main limitations of this field are the material needed to interface soft living entities with hard inorganic devices. Conducting polymers enabled the bridging between these two separate worlds, owing to their biocompatibility, soft nature and the ability to be tailored according to the required application. In particular, the intrinsically conductive poly(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid) (PEDOT:PSS) is one of the most promising polymers, having an excellent chemical and thermal stability, reversible doping state and high conductivity. This thesis relies on the use of PEDOT:PSS as semiconducting material for biological interfaces and biosensors. In detail, OECTs were demonstrated to be able to real-time monitor growth and detachment of both strong-barrier and no-barrier cells, according to the patterning of the device active area and the selected geometry. Thus, these devices were employed to assess silver nanoparticles (AgNPs) toxicity effects on cell lines, allowing further insights on citrate-coated AgNPs uptake by the cells and their toxic action, while demonstrating no cytotoxic activity of EG6OH-coated AgNPs. Moreover, PEDOT:PSS OECTs were proved to be capable of detecting oxygen dissolved in KCl or even cell culture medium, in the oxygen partial pressure range of 0-5%. Furthermore, PEDOT:PSS OECTs were biofunctionalized to impart specificity on the device sensing capabilities, through a biochemical functionalization strategy, electrically characterized. The resulting devices showed a proof of concept detection of a fundamental cytokine for cells undergoing osteogenic differentiation. Finally, PEDOT:PSS thickness-controlled films were employed as biocompatible, low-impedance and soft interfaces between the animal nerve and a gold electrode. The introduction of the plasticizer polyethylene glycol (PEG) enhanced the elasticity of the polymer, while keeping good conductivity and low-impedance properties. An in-vivo, chronic recording of the renal sympathetic nerve activity in rats demonstrated the efficiency of the device

DEVELOPMENT OF FUNCTIONAL NANOCOMPOSITE MATERIALS TOWARDS BIODEGRADABLE SOFT ROBOTICS AND FLEXIBLE ELECTRONICS

World population is continuously growing, as well as the influence we have on the ecosystem\u2019s natural equilibrium. Moreover, such growth is not homogeneous and it results in an overall increase of older people. Humanity\u2019s activity, growth and aging leads to many challenging issues to address: among them, there are the spread of suddenly and/or chronic diseases, malnutrition, resource pressure and environmental pollution. Research in the novel field of biodegradable soft robotics and electronics can help dealing with these issues. In fact, to face the aging of the population, it is necessary an improvement in rehabilitation technologies, physiological and continuous monitoring, as well as personalized care and therapy. Also in the agricultural sector, an accurate and efficient direct measure of the plants health conditions would be of help especially in the less-developed countries. But since living beings, such as humans and plants, are constituted by soft tissues that continuously change their size and shapes, today\u2019s traditional technologies, based on rigid materials, may not be able to provide an efficient interaction necessary to satisfy these needs: the mechanical mismatch is too prohibitive. Instead, soft robotic systems and devices can be designed to combine active functionalities with soft mechanical properties that can allow them to efficiently and safely interact with soft living tissues. Soft implantable biomedical devices, smart rehabilitation devices and compliant sensors for plants are all applications that can be achieved with soft technologies. The development of sophisticated autonomous soft systems needs the integration on a unique soft body or platform of many functionalities (such as mechanical actuation, energy harvesting, storage and delivery, sensing capabilities). A great research interest is recently arising on this topic, but yet not so many groups are focusing their efforts in the use of natural-derived and biodegradable raw materials. In fact, resource pressure and environmental pollution are becoming more and more critical problems. It should be completely avoided the use of in exhaustion, pollutant, toxic and non-degradable resources, such as lithium, petroleum derivatives, halogenated compounds and organic solvents. So-obtained biodegradable soft systems and devices could then be manufactured in high number and deployed in the environment to fulfil their duties without the need to recover them, since they can safely degrade in the environment. The aim of the current Ph.D. project is the use of natural-derived and biodegradable polymers and substances as building blocks for the development of smart composite materials that could operate as functional elements in a soft robotic system or device. Soft mechanical properties and electronic/ionic conductive properties are here combined together within smart nanocomposite materials. The use of supersonic cluster beam deposition (SCBD) technique enabled the fabrication of cluster-assembled Au electrodes that can partially penetrate into the surface of soft materials, providing an efficient solution to the challenge of coupling conductive metallic layers and soft deformable polymeric substrates. In this work, cellulose derivatives and poly(3-hydroxybutyrate) bioplastic are used as building blocks for the development of both underwater and in-air soft electromechanical actuators that are characterized and tested. A cellulosic matrix is blended with natural-derived ionic liquids to design and manufacture completely biodegradable supercapacitors, extremely interesting energy storage devices. Lastly, ultrathin Au electrodes are here deposited on biodegradable cellulose acetate sheets, in order to develop transparent flexible electronics as well as bidirectional resistive-type strain sensors. The results obtained in this work can be regarded as a preliminary study towards the realization of full natural-derived and biodegradable soft robotic and electronic systems and devices

Electrically conductive bacterial cellulose for tissue-engineered neural interfaces

Bacterial cellulose (BC) with its high crystallinity, tensile strength, degree of polymerisation, and water holding capacity (98%) becomes increasingly attractive as 3D nanofibrillar material for biomedical applications. Such multi-scale fibrillary BC networks can be potentially functionalised with electrically conductive moieties to facilitate the conductive properties required for various smart biomedical devices, in particular, in the construction of bioelectronic neural interfaces. In this thesis, BC fibres are chemically modified with poly(4-vinylaniline) (PVAN) interlayer for further enhancement of electrical conductivity and cell viability of subsequent polyaniline (PANI) coatings as a bilayer grafted BC nanocomposite. This functional poly(4-vinylaniline)/polyaniline (PVAN/PANI) bilayer can be efficiently anchored onto BC fibrils through successive surface-initiated atom transfer radical polymerisation and in situ chemical oxidative polymerisation. PVAN is found to have promoted the formation of a uniform PANI layer with 1D nanofiber- and nanorod-like supramolecular structures, with an overall augmentation of PANI yield, hence further improved electrical performance. Compositional and microstructural analysis reveals such a PVAN/PANI bilayer with a thickness up to ~2 µm on BC formed through a significant growth of PANI with rough surface morphology due to the insertion of PVAN, which has improved the functional properties of the BC nanocomposites. Successful impregnation of both layers onto BC fibrils was corroborated with systematic microstructural and chemical analysis. The solid-state electrical conductivity of such synthesised BC nanocomposites with PVAN interlayer reaches as high as (4.5±2.8)×10-2 S.cm-1 subject to the amounts of PVAN chemically embraced. Electrochemical examination evinces the switching in the electrochemical behaviour of BC/PVAN/PANI nanocomposites at -0.70/0.74 V (at 100 mV.s-1 scan rate) due to the existence of PANI, where the maximal electrical performance can be achieved at charge transfer resistance of as low as 21 Ω and capacitance of as high as 39 μF. Both electrochemical and mechanical properties can be tailored onto an incomplete BC dehydration, where a mathematical model is herein developed to predict BC water loss accordingly. BC/PVAN/PANI nanocomposites are thermally stable up to 200 ºC. Furthermore, further improvement of the electrical conductivity has been achieved through grafting Carbon Nano Tubes (CNTs) into the BC/PVAN/PANI nanocomposites, where the interactions between PANI and CNTs present new electrochemical characteristics with enhanced capacity. PANI/CNTs coatings with a nanorod-like morphology can promote the efficient ions diffusion and charge transfer, resulting in the increased electrical conductivity up to (1.0±0.3)×10-1 S.cm-1. An escalating amplification of the double charge capacity to ~54 mF of the CNTs grafted BC nanocomposites was also detected through electrochemical analysis. In addition, the thermal stability of CNTs grafted BC/PVAN/PANI nanocomposites are improved, and they become stable up to 234 ºC. Cytocompatibility tests conducted using two neuronal cell linages show non-cytotoxic effects for PC-12 Adh cells and SVZ neural stem cells, confirming cell viability that can be over 80 % and neuronal differentiation capability of the electrically functionalised BC-based nanocomposite membranes, which can induce neurites outgrowth up to 115±24 μm long. These voltage-sensible nanocomposites can hence interact with neural cells, thereby significantly stimulate specialised response. These findings pave the path to the new tissue engineered neural interfaces which embraces electronic functions into the tissue regeneration, to enable full functional neural tissue recovery