A Pharmacokinetic Model of a Tissue Implantable Cortisol Sensor

Cortisol Monitoring Devices toward Implementation for Clinically Relevant Biosensing In Vivo

Cortisol is a steroid hormone that regulates energy metabolism, stress reactions, and immune response. Cortisol is produced in the kidneys' adrenal cortex. Its levels in the circulatory system are regulated by the neuroendocrine system with a negative feedback loop of the hypothalamic-pituitary-adrenal axis (HPA-axis) following circadian rhythm. Conditions associated with HPA-axis disruption cause deteriorative effects on human life quality in numerous ways. Psychiatric, cardiovascular, and metabolic disorders as well as a variety of inflammatory processes accompanying age-related, orphan, and many other conditions are associated with altered cortisol secretion rates and inadequate responses. Laboratory measurements of cortisol are well-developed and based mainly on the enzyme linked immunosorbent assay (ELISA). There is a great demand for a continuous real-time cortisol sensor that is yet to be developed. Recent advances in approaches that will eventually culminate in such sensors have been summarized in several reviews. This review compares different platforms for direct cortisol measurements in biological fluids. The ways to achieve continuous cortisol measurements are discussed. A cortisol monitoring device will be essential for personified pharmacological correction of the HPA-axis toward normal cortisol levels through a 24-h cycle.

Single-Walled Carbon Nanotubes as Fluorescent Probes for Monitoring the Self-Assembly and Morphology of Peptide/Polymer Hybrid Hydrogels

Hydrogels formed via supramolecular self-assembly of fluorenylmethyloxycarbonyl (Fmoc)-conjugated amino acids provide excellent scaffolds for 3D cell culture, tissue engineering, and tissue recovery matrices. Such hydrogels are usually characterized by rheology or electron microscopy, which are invasive and cannot provide real-time information. Here, we incorporate near-infrared fluorescent single-walled carbon nanotubes (SWCNTs) into Fmoc-diphenylalanine hydrogels as fluorescent probes, reporting in real-time on the morphology and time-dependent structural changes of the self-assembled hydrogels in the transparency window of biological tissue. We further demonstrate that the gelation process and structural changes upon the addition of cross-linking ions are transduced into spectral modulations of the SWCNT-fluorescence. Moreover, morphological differences of the hydrogels induced by polymer additives are manifested in unique features in fluorescence images of the incorporated SWCNTs. SWCNTs can thus serve as optical probes for noninvasive, long-term monitoring of the self-assembly gelation process and the fate of the resulting peptide hydrogel during long-term usage.

Blubber and serum cortisol concentrations as indicators of the stress response and overall health status in striped dolphins

The impacts of environmental changes and anthropogenic threats in marine mammals are a growing concern for their conservation. In recent years, efforts have been directed to understand how marine mammals cope with stressors and to assess and validate stress biomarkers, mainly levels of glucocorticoid hormones (e.g. cortisol) in certain body tissues. The aims of this study were to assess the impact of different causes of stranding (chronically affected and bycaught striped dolphins) on cortisol concentrations in serum and in blubber; and to evaluate the association between cortisol levels in these tissues. Blubber and blood samples were collected from striped dolphins (n = 42) stranded on the Mediterranean coast between 2012 and 2018. Cortisol concentrations were measured by using enzyme immunoassay. A high correlation was found between circulating and blubber cortisol concentrations (R² = 0.85, p < 0.01). Necropsies and pathological studies concluded that a third of the dolphins were bycaught in fishing nets and released by fishermen (Bycaught animals group), while the other two thirds were euthanized, or died, due to a disease or chronic condition (e.g. calves separated from the mother or animals infected with dolphin morbillivirus or Brucella ceti) that impeded survival (Chronically affected animals group). Cortisol concentrations (mean ± SD) were six times higher in chronically affected animals (35.3 ± 23 ng cortisol/g blubber and 6.63 ± 3.22 μg cortisol/dl serum) compared to those bycaught in fishing nets (6.2 ± 4.3 ng cortisol/g blubber and 1.15 ± 1.51 μg cortisol/dl serum). Results suggests that serum and blubber cortisol concentrations can contribute in inferring the overall health and welfare of free-ranging cetaceans. However, further research is required to understand better the kinetics of blubber cortisol incorporation and removal, the factors involved in these processes, and the local conversion of cortisol in the blubber.

In vivo imaging of fluorescent single-walled carbon nanotubes within C. elegans nematodes in the near-infrared window

Caenorhabditis elegans (C. elegans) nematodes serve as a model organism for eukaryotes, especially due to their genetic similarity. Although they have many advantages like their small size and transparency, their autofluorescence in the entire visible wavelength range poses a challenge for imaging and tracking fluorescent proteins or dyes using standard fluorescence microscopy. Herein, near-infrared (NIR) fluorescent single-walled carbon nanotubes (SWCNTs) are utilized for in vivo imaging within the gastrointestinal track of C. elegans. The SWCNTs are biocompatible, and do not affect the worms' viability nor their reproduction ability. The worms do not show any autofluorescence in the NIR range, thus enabling the spectral separation between the SWCNT NIR fluorescence and the strong autofluorescence of the worm gut granules. The worms are fed with ssDNA-SWCNT which are visualized mainly in the intestine lumen. The NIR fluorescence is used in vivo to track the contraction and relaxation in the area of the pharyngeal valve at the anterior of the terminal bulb. These biocompatible, non-photobleaching, NIR fluorescent nanoparticles can advance in vivo imaging and tracking within C. elegans and other small model organisms by overcoming the signal-to-noise challenge stemming from the wide-range visible autofluorescence.

Closed-Loop Fuzzy Energy Regulation in Patients With Hypercortisolism via Inhibitory and Excitatory Intermittent Actuation

Hypercortisolism or Cushing's disease, which corresponds to the excessive levels of cortisol hormone, is associated with tiredness and fatigue during the day and disturbed sleep at night. Our goal is to employ a wearable brain machine interface architecture to regulate one's energy levels in hypercortisolism. In the present simulation study, we generate multi-day cortisol profile data for ten subjects both in healthy and disease conditions. To relate an internal hidden cognitive energy state to one's cortisol secretion patterns, we employ a state-space model. Particularly, we consider circadian upper and lower bound envelopes on cortisol levels, and timings of hypothalamic pulsatile activity underlying cortisol secretions as continuous and binary observations, respectively. To estimate the hidden cognitive energy-related state, we use Bayesian filtering. In our proposed architecture, we infer one's cognitive energy-related state using wearable devices rather than monitoring the brain activity directly and close the loop utilizing fuzzy control. To model actuation in the real-time closed-loop architecture, we simulate two types of medications that result in increasing and decreasing the energy levels in the body. Finally, we close the loop using a knowledge-based control approach. The results on ten simulated profiles verify how the proposed architecture is able to track the energy state and regulate it using hypothetical medications. In a simulation study based on experimental data, we illustrate the feasibility of designing a wearable brain machine interface architecture for energy regulation in hypercortisolism. This simulation study is a first step toward the ultimate goal of managing hypercortisolism in real-world situations.

Surface-specific washing-free immunosensor for time-resolved cortisol monitoring

Cortisol is a steroid hormone that regulates a wide range of vital processes. Its level changes with diurnal rhythm and reacts to stress. Measurement of cortisol levels is still a complex multi-step process. A reversible washing-free registration method is required. Here we describe metal-enhanced fluorescence assay based on a displacement of a dye labeled BSA-cortisol conjugate from the immune complex immobilized on the golden islands by free cortisol. This competitive approach allows time-resolved monitoring of the fluorescent signal, surface-enhanced by the gold film, and provides the possibility of continuous real-time cortisol monitoring based on the implantable surface-enhanced immunosensor, which was not demonstrated so far even in vitro.

Implantable Nanosensors for Human Steroid Hormone Sensing In Vivo Using a Self-Templating Corona Phase Molecular Recognition

Dynamic measurements of steroid hormones in vivo are critical, but steroid sensing is currently limited by the availability of specific molecular recognition elements due to the chemical similarity of these hormones. In this work, a new, self-templating synthetic approach is applied using corona phase molecular recognition (CoPhMoRe) targeting the steroid family of molecules to produce near infrared fluorescent, implantable sensors. A key limitation of CoPhMoRe has been its reliance on library generation for sensor screening. This problem is addressed with a self-templating strategy of polymer design, using the examples of progesterone and cortisol sensing based on a styrene and acrylic acid copolymer library augmented with an acrylated steroid. The pendant steroid attached to the corona backbone is shown to self-template the phase, providing a unique CoPhMoRE design strategy with high efficacy. The resulting sensors exhibit excellent stability and reversibility upon repeated analyte cycling. It is shown that molecular recognition using such constructs is viable even in vivo after sensor implantation into a murine model by employing a poly (ethylene glycol) diacrylate (PEGDA) hydrogel and porous cellulose interface to limit nonspecific absorption. The results demonstrate that CoPhMoRe templating is sufficiently robust to enable a new class of continuous, in vivo biosensors.

Observing the unwatchable: Integrating automated sensing, naturalistic observations and animal social network analysis in the age of big data

In the 4.5 decades since Altmann (1974) published her seminal paper on the methods for the observational study of behaviour, automated detection and analysis of social interaction networks have fundamentally transformed the ways that ecologists study social behaviour. Methodological developments for collecting data remotely on social behaviour involve indirect inference of associations, direct recordings of interactions and machine vision. These recent technological advances are improving the scale and resolution with which we can dissect interactions among animals. They are also revealing new intricacies of animal social interactions at spatial and temporal resolutions as well as in ecological contexts that have been hidden from humans, making the unwatchable seeable. We first outline how these technological applications are permitting researchers to collect exquisitely detailed information with little observer bias. We further recognize new emerging challenges from these new reality-mining approaches. While technological advances in automating data collection and its analysis are moving at an unprecedented rate, we urge ecologists to thoughtfully combine these new tools with classic behavioural and ecological monitoring methods to place our understanding of animal social networks within fundamental biological contexts.

Anthropogenic Change Alters Ecological Relationships via Interactive Changes in Stress Physiology and Behavior within and among Organisms

Anthropogenic change has well-documented impacts on stress physiology and behavior across diverse taxonomic groups. Within individual organisms, physiological and behavioral traits often covary at proximate and ultimate timescales. In the context of global change, this means that impacts on physiology can have downstream impacts on behavior, and vice versa. Because all organisms interact with members of their own species and other species within their communities, the effects of humans on one organism can impose indirect effects on one or more other organisms, resulting in cascading effects across interaction networks. Human-induced changes in the stress physiology of one species and the downstream impacts on behavior can therefore interact with the physiological and behavioral responses of other organisms to alter emergent ecological phenomena. Here, we highlight three scenarios in which the stress physiology and behavior of individuals on different sides of an ecological relationship are interactively impacted by anthropogenic change. We discuss host-parasite/pathogen dynamics, predator-prey relationships, and beneficial partnerships (mutualisms and cooperation) in this framework, considering cases in which the effect of stressors on each type of network may be attenuated or enhanced by interactive changes in behavior and physiology. These examples shed light on the ways that stressors imposed at the level of one individual can impact ecological relationships to trigger downstream consequences for behavioral and ecological dynamics. Ultimately, changes in stress physiology on one or both sides of an ecological interaction can mediate higher-level population and community changes due in part to their cascading impacts on behavior. This framework may prove useful for anticipating and potentially mitigating previously underappreciated ecological responses to anthropogenic perturbations in a rapidly changing world.

A Cortisol-Based Energy Decoder for Investigation of Fatigue in Hypercortisolism

Hormones play a fundamental role in homeostasis. We develop a state-space model relating the body's internal energy to cortisol hormone secretions. Cortisol is secreted in pulses and follows a 24 h circadian rhythm. Secretory event timings carry important information regarding internal feedback signaling taking place, as do the upper and lower serum cortisol levels. We relate an internal energy state variable to cortisol pulse timings and to the upper and lower serum cortisol envelopes. We derive Bayesian filter equations for state estimation and use the Expectation-Maximization algorithm for model parameter recovery. Results on multi-day simulated data show circadian energy variations in healthy subjects and non-circadian fluctuations throughout 24 h periods in patient models suffering from hypercortisolism. The results shed new light on why patients diagnosed with excess cortisol disorders frequently experience symptoms of daytime fatigue and sleep disturbances at night. The state-space model is also an important first step towards the design of closed-loop controllers for treating hormone-related disorders in a manner that closely emulates the body's own pulsatile feedback mechanisms.

Fluorescent Single-Walled Carbon Nanotubes for Protein Detection

Nanosensors have a central role in recent approaches to molecular recognition in applications like imaging, drug delivery systems, and phototherapy. Fluorescent nanoparticles are particularly attractive for such tasks owing to their emission signal that can serve as optical reporter for location or environmental properties. Single-walled carbon nanotubes (SWCNTs) fluoresce in the near-infrared part of the spectrum, where biological samples are relatively transparent, and they do not photobleach or blink. These unique optical properties and their biocompatibility make SWCNTs attractive for a variety of biomedical applications. Here, we review recent advancements in protein recognition using SWCNTs functionalized with either natural recognition moieties or synthetic heteropolymers. We emphasize the benefits of the versatile applicability of the SWCNT sensors in different systems ranging from single-molecule level to in-vivo sensing in whole animal models. Finally, we discuss challenges, opportunities, and future perspectives.

Optimizing the use of biologgers for movement ecology research

The paradigm-changing opportunities of biologging sensors for ecological research, especially movement ecology, are vast, but the crucial questions of how best to match the most appropriate sensors and sensor combinations to specific biological questions and how to analyse complex biologging data, are mostly ignored. Here, we fill this gap by reviewing how to optimize the use of biologging techniques to answer questions in movement ecology and synthesize this into an Integrated Biologging Framework (IBF). We highlight that multisensor approaches are a new frontier in biologging, while identifying current limitations and avenues for future development in sensor technology. We focus on the importance of efficient data exploration, and more advanced multidimensional visualization methods, combined with appropriate archiving and sharing approaches, to tackle the big data issues presented by biologging. We also discuss the challenges and opportunities in matching the peculiarities of specific sensor data to the statistical models used, highlighting at the same time the large advances which will be required in the latter to properly analyse biologging data. Taking advantage of the biologging revolution will require a large improvement in the theoretical and mathematical foundations of movement ecology, to include the rich set of high-frequency multivariate data, which greatly expand the fundamentally limited and coarse data that could be collected using location-only technology such as GPS. Equally important will be the establishment of multidisciplinary collaborations to catalyse the opportunities offered by current and future biologging technology. If this is achieved, clear potential exists for developing a vastly improved mechanistic understanding of animal movements and their roles in ecological processes and for building realistic predictive models.

Estimates for energy expenditure in free-living animals using acceleration proxies: A reappraisal

It is fundamentally important for many animal ecologists to quantify the costs of animal activities, although it is not straightforward to do so. The recording of triaxial acceleration by animal-attached devices has been proposed as a way forward for this, with the specific suggestion that dynamic body acceleration (DBA) be used as a proxy for movement-based power. Dynamic body acceleration has now been validated frequently, both in the laboratory and in the field, although the literature still shows that some aspects of DBA theory and practice are misunderstood. Here, we examine the theory behind DBA and employ modelling approaches to assess factors that affect the link between DBA and energy expenditure, from the deployment of the tag, through to the calibration of DBA with energy use in laboratory and field settings. Using data from a range of species and movement modes, we illustrate that vectorial and additive DBA metrics are proportional to each other. Either can be used as a proxy for energy and summed to estimate total energy expended over a given period, or divided by time to give a proxy for movement-related metabolic power. Nonetheless, we highlight how the ability of DBA to predict metabolic rate declines as the contribution of non-movement-related factors, such as heat production, increases. Overall, DBA seems to be a substantive proxy for movement-based power but consideration of other movement-related metrics, such as the static body acceleration and the rate of change of body pitch and roll, may enable researchers to refine movement-based metabolic costs, particularly in animals where movement is not characterized by marked changes in body acceleration.

Implanted Nanosensors in Marine Organisms for Physiological Biologging: Design, Feasibility, and Species Variability

In recent decades, biologists have sought to tag animals with various sensors to study aspects of their behavior otherwise inaccessible from controlled laboratory experiments. Despite this, chemical information, both environmental and physiological, remains challenging to collect despite its tremendous potential to elucidate a wide range of animal behaviors. In this work, we explore the design, feasibility, and data collection constraints of implantable, near-infrared fluorescent nanosensors based on DNA-wrapped single-wall carbon nanotubes (SWNT) embedded within a biocompatible poly(ethylene glycol) diacrylate (PEGDA) hydrogel. These sensors are enabled by Corona Phase Molecular Recognition (CoPhMoRe) to provide selective chemical detection for marine organism biologging. Riboflavin, a key nutrient in oxidative phosphorylation, is utilized as a model analyte in in vitro and ex vivo tissue measurements. Nine species of bony fish, sharks, eels, and turtles were utilized on site at Oceanogràfic in Valencia, Spain to investigate sensor design parameters, including implantation depth, sensor imaging and detection limits, fluence, and stability, as well as acute and long-term biocompatibility. Hydrogels were implanted subcutaneously and imaged using a customized, field-portable Raspberry Pi camera system. Hydrogels could be detected up to depths of 7 mm in the skin and muscle tissue of deceased teleost fish ( Sparus aurata and Stenotomus chrysops) and a deceased catshark ( Galeus melastomus). The effects of tissue heterogeneity on hydrogel delivery and fluorescence visibility were explored, with darker tissues masking hydrogel fluorescence. Hydrogels were implanted into a living eastern river cooter ( Pseudemys concinna), a European eel ( Anguilla anguilla), and a second species of catshark ( Scyliorhinus stellaris). The animals displayed no observable changes in movement and feeding patterns. Imaging by high-resolution ultrasound indicated no changes in tissue structure in the eel and catshark. In the turtle, some tissue reaction was detected upon dissection and histopathology. Analysis of movement patterns in sarasa comet goldfish ( Carassius auratus) indicated that the hydrogel implants did not affect swimming patterns. Taken together, these results indicate that this implantable form factor is a promising technique for biologging using aquatic vertebrates with further development. Future work will tune the sensor detection range to the physiological range of riboflavin, develop strategies to normalize sensor signal to account for the optical heterogeneity of animal tissues, and design a flexible, wearable device incorporating optoelectronic components that will enable sensor measurements in moving animals. This work advances the application of nanosensors to organisms beyond the commonly used rodent and zebrafish models and is an important step toward the physiological biologging of aquatic organisms.

Chronic and acute stress monitoring by electrophysiological signals from adrenal gland

We present electrophysiological (EP) signals correlated with cellular cell activities in the adrenal cortex and medulla using an adrenal gland implantable flexible EP probe. With such a probe, we could observe the EP signals from the adrenal cortex and medulla in response to various stress stimuli, such as enhanced hormone activity with adrenocorticotropic hormone, a biomarker for chronic stress response, and an actual stress environment, like a forced swimming test. This technique could be useful to continuously monitor the elevation of cortisol level, a useful indicator of chronic stress that potentially causes various diseases.

Insulin Detection Using a Corona Phase Molecular Recognition Site on Single-Walled Carbon Nanotubes

Corona phase molecular recognition (CoPhMoRe) is a technique whereby an external, adsorbed phase around a colloidal nanoparticle is selected such that its molecular conformation or interaction recognizes a specific target analyte. In this work, we employ a high-throughput screening of a library of poly(ethylene glycol) (PEG)-conjugated lipids adsorbed onto near-infrared fluorescent single-walled carbon nanotubes to discover a corona phase selective for insulin. We find that a C₁₆-PEG(2000 Da)-ceramide causes a 62% fluorescent intensity decrease of the (10,2) chirality nanotube in the presence of 20 μg/mL insulin. The insulin protein has no prior affinity toward the C₁₆-PEG(2000 Da)-ceramide molecules in free solution, verified by isothermal titration calorimetry, and the interaction occurs only upon their adsorption onto the single-walled carbon nanotube scaffolds. Testing a panel of proteins originating from human blood as well as short 7 amino acid fragments of the insulin peptide rules out nonselective recognition mechanisms such as molecular weight, isoelectric point, and hydrophobicity-based detection. Interestingly, longer fragments of isolated α- and β-peptide chains of insulin are detected by the construct, albeit with lower affinity compared to that of the intact insulin protein, suggesting that the construct recognizes insulin in its native form and conformation. Finally, the insulin recognition and the quantification of its solution concentration were demonstrated both in buffer and in blood serum, showing that the CoPhMoRe construct works in this complex environment despite the presence of potential nonspecific adsorption. Our results further motivate the search for nonbiological synthetic recognition sites and open up a new path for continuous insulin monitoring in vivo with the hope of improving glycemic control in closed-loop artificial pancreas systems.

Emerging Trends in Micro- and Nanoscale Technologies in Medicine: From Basic Discoveries to Translation

We discuss the state of the art and innovative micro- and nanoscale technologies that are finding niches and opening up new opportunities in medicine, particularly in diagnostic and therapeutic applications. We take the design of point-of-care applications and the capture of circulating tumor cells as illustrative examples of the integration of micro- and nanotechnologies into solutions of diagnostic challenges. We describe several novel nanotechnologies that enable imaging cellular structures and molecular events. In therapeutics, we describe the utilization of micro- and nanotechnologies in applications including drug delivery, tissue engineering, and pharmaceutical development/testing. In addition, we discuss relevant challenges that micro- and nanotechnologies face in achieving cost-effective and widespread clinical implementation as well as forecasted applications of micro- and nanotechnologies in medicine.