Technology wearable or wearables are increasingly becoming part of everyday clothing. From smart bracelets, which have practically redefined the name watch, to rings, electronic skins, biosensors and implantable technology, these devices are the new invisible companions of our lives. All of these devices are more than just an accessory, they are on a mission to whisper to us at all times how we are doing. The wearables are able to detect our position and movement, measure cardiovascular health, and some can even analyse our mood and stress through sweat. As a result, their integration into everyday life has had a huge impact on health. Thanks to the wearables, In other words, they have democratised access to health data and are thereby promoting a culture of prevention and self-care. In other words, they have democratised access to health data and are thereby fostering a culture of prevention and self-care.
In addition, constantly measuring health parameters is another advantage, since the more data we have in a normal situation, the easier it is to detect alterations that may pose a risk. Thus, the massive collection of information, together with advances in artificial intelligence, have resulted in the development of algorithms capable of interpreting the huge amount of data and predicting situations that could endanger people, such as falls or cardiac alterations.
This is why a good implementation of the technology wearable has the potential to revolutionise the healthcare system. However, its ubiquity also raises ethical and privacy challenges that must be at the centre of future research, as responsible management of the data it generates is essential to ensure the trust and security of users.
INSIDE. Monitoring health with consumer devices and nanotechnology
In every wardrobe there are shoes, shirts, skirts and trousers. Pieces of clothing with which we go out in the street, which transmit our personality, or which show (or not) our affinity with current fashion. But in this last decade we are no longer just wearing clothes. Wearable technologies or wearables have gained enormous popularity, offering us not only a new garment with which to show the world who we are, but also control over the data our bodies produce. The wearables The devices contain decades of research and scientific advances that allow them, from triangulating our position, to measuring our heartbeat. These parameters, together with a mobile phone in almost anyone's handbag or pocket, allow us to constantly monitor our health. Data that, if correctly analysed, can detect in time and warn autonomously in the event that a person suffers a fall, is about to have a heart attack or has low glucose levels. In short, these new accessories and garments are not only purely aesthetic, but also combine very interesting functionalities.
Looking back, the watch, both in its pocket version (from around the 15th century) and its wristwatch (attributed to the virtuoso watchmaker Abraham-Louis Breguet for Caroline Murat, Napoleon Bonaparte's younger sister in 1812), is still in use today.[i]), could be considered one of the earliest forms of wearable technology. The watches did their job well and informed their wearer of the time whenever they wanted to, without having to go to a room with a grandfather clock or, if outdoors, without relying on other more rudimentary and less accurate forms of timekeeping.
While important for the time, this progress may not seem like much today, and so to see a significant evolution in technology, we have to move forward to the beginning of the 21st century, when there was a fantastic combination of the miniaturisation of computers and a widespread enthusiasm for technology. This was the time of the popularisation of mobile phones, the beginning of personal laptops and an internet that was constantly expanding its roots. Computers moved out of their usual home, the office, and into the world, and with the digital age, ubiquitous computing began. There would always be a computer ready to collect and analyse data close to the user. With this change in everyday reality also came new opportunities and possibilities for companies that saw the enormous potential.
The development of miniaturised sensors, long-lasting batteries and wireless communication systems has created a communion between smart devices and the human body. A communion that is revolutionising personal wellness and healthcare, and enabling elite athletes and professionals in a variety of industries to reach their full potential. Today, we find ourselves in an environment where technology becomes an extension of the individual, a data age that defines contemporary society.
Today, the variety of wearable technologies continues to grow. The most common are those accessories, such as bracelets or rings, that have been popularised by the tech giants. These wearables also act as complements and are subject to fashions or trends. They usually have a high number of functions and generally sacrifice accuracy in their functionalities for this reason. Except in rare cases, they are not medical grade devices, but they do help to give an idea of overall health status, or whether a particular sport plan is being adhered to.
In the specific case of sports, the use of smart bands, patches and T-shirts is becoming increasingly common. They offer a dual function: on the one hand, they help to adapt an athlete's training to his or her condition in real time; and, on the other hand, they make it possible to detect irregularities in the body's functioning resulting from the demanding physical work it has to endure. In this way, both athletes and their coaches can know for sure that they are making the most of the athlete's capabilities.
Finally, there are also portable or implantable biosensors. These tend to be more specialised in performing a specific task, such as measuring blood glucose. Users may wear them because they have a known medical condition, such as diabetes. Both sensors and devices differ according to the parameter they are intended to detect and the function they are intended to perform.[ii].
To communicate with the receiving device, which will analyse the data, wearables use Bluetooth transmitters, certain radio frequencies, or NFC technology, similar to that used by credit cards. contactless. In this way, they do not need to store and analyse the information they collect, but the computational effort falls on the nearest mobile device, tablet or computer. Today, this information is typically sent to the cloud via the internet, where it is analysed on each company's central servers.
They are the most common devices and have gradually taken over from the wristwatches of yesteryear because of their design and versatility. In addition to telling the time, many of these smartwatches include an optical technology called photoplethysmography that can detect the amount of blood flowing under the skin. The mechanism behind this technique is simple, yet ingenious. Curious people will have noticed that when the watch starts measuring heart rate, it turns on a green light directed at the skin. This light hits a region on the back of the hand called the dorsal radiocarpal anastomosis, which joins the blood vessels of the radial artery and the dorsal interosseous artery. The large number of ducts translates into a large volume of blood flowing through the area and thus an opportunity to measure health-related parameters such as heart rate or the amount of oxygen in the blood.
This technology is possible because blood is red, because it absorbs all wavelengths of light except red. Therefore, if we focus a green light on the blood, it will absorb it, and the more blood, the more green light it absorbs. Accompanying the LEDs, photodiodes are able to detect the amount of light returning to the watch and thus the volume of blood under the skin at that moment. The light, flashing hundreds of times per second, takes hundreds of measurements, revealing the subtle variations that occur during the heartbeat and displaying them live on the screen. For oxygen concentration in the blood, photoplethysmography also detects variations in the colour intensity of the blood. Blood tends to have a more intense red colour depending on its oxygenation level.[iii].
In addition to these sensors, some smartwatches of well-known companies also include electrodes capable of performing an electrocardiogram. These sensors are FDA-approved and therefore medically valid, and are very useful for monitoring people with a history of heart disease. They can detect irregular heartbeats (atrial fibrillation) or even pre-infarction situations. They are not as sensitive as conventional electrocardiograms, since the latter take simultaneous measurements of 12 or more areas of the heart and the watch only analyses one. But the clinical trials conducted by the two companies gave results very similar to those of health care professionals. The advantage is that this device can be worn comfortably and does not require electrodes.
Finally, smartwatches also include other functions such as a pedometer, thermometer and a GPS position and movement log. Some of them have this technology built into the wristband itself, while others delegate the function to the mobile phone. With all this data, plus blood data, they can estimate the number of steps and distance travelled, stress level, calories burned, sleep quality, or detect falls and alert the health system. The reliability of the data depends, to a large extent, on the fine-tuning of the analysis software and the algorithms of each application used for the device.
Along the same lines as watches and bracelets, smart rings offer a miniaturised version with virtually the same functionality. In this case, the ring only contains the detectors and a Bluetooth system to communicate with the mobile device, which provides all the computing power to analyse the data from the detectors. One of the major differences is that the rings do not have a screen and are therefore completely dependent on the mobile phone. They also offer, in a limited way, the same functions as the wristbands, although their minimalist design may attract more people to the technology. wearable, The wearer may find it more comfortable to rely on a ring than on a bracelet or watch.
Recently, due to the amount of data handled by these technologies, a number of companies are employing machine learning and other types of artificial intelligence to be able to sort and make sense of information, or to improve the user experience. In this way, they can offer personalised health and lifestyle recommendations and communicate them in natural language. The implementation of AI is still partial and offers a world of opportunities for even more benefits to be derived from sensors.
Washington St. Louise University and Texas University respectively offer a window into this world, as they are currently pursuing two projects that could benefit thousands of people. In the first, a team bringing together engineering, data science and gynaecology is creating a system to track the risk of early pregnancy based on changes in a mother-to-be's sleep patterns.[iv]. In Texas, on the other hand, they use the same data to warn of the subtle differences between a sick person who has not yet begun to show symptoms. In this way, they could more effectively prevent the possible transmission of epidemics.[v]. These are two clear examples of the link between AI and device data. wearables, and they are not the only ones. Other universities are also finding correlations between subtle changes in posture and walking pace with neurodegenerative diseases such as Alzheimer's and Parkinson's disease.[vi], This offers the possibility of early diagnosis and treatment.
However, there is also some risk with these systems, because it can sometimes be difficult to differentiate between a user suffering a crisis and a user who is in a normal state. Due to the potential for false positive wearables without a medical degree, hospitals may waste medical resources on fake emergencies. The data collected by these devices is highly sensitive, as it collects important medical information, so it is vital that it is properly encrypted and anonymised so that it is not exposed and sold on portals.
In addition to the wearables In addition to the most popular devices, a whole world of electronic devices focused on the constant monitoring of medical data has also recently arrived on the market. These devices, designed for patients requiring monitoring over a period of time or for people with chronic diseases, have to meet three conditions: comfort and discretion for the user, and accuracy in data collection for the healthcare staff. Figure 1 reviews the main properties sought in the materials from which they are made and Figure 2 lists some examples of biosensors in medicine. The most common option is patches, which attach sensors to the skin and provide real-time data on certain useful parameters, such as those mentioned above. More advanced systems are also being developed, such as electronic skins or tattoos, where flexible sensors can better adapt to the imperfections of the human body and cover areas where high stresses are generated, such as joints.
So far, we have discussed optical (such as photoplethysmography) or mechanical (such as motion sensors) detection methods, but many of the health-focused devices are based on biomarker analysis, i.e. chemical or biological analysis of substances excreted by the body. These include the analysis of solutes present in sweat as it contains metabolites, such as lactate or urea, and minerals, which provide a non-invasive view of the body's physiological state of health.[vii]. However, there is still a great deal of uncertainty in data analysis, as the composition and quantity of sweat depends on a large number of variables and therefore the information analysed may not be conclusive. Therefore, experts still urge caution when trying to derive sports or medical data from this fluid.
Possible solutions to these problems include the development of sensors that are capable of simultaneously measuring sweat solutes and other physical parameters, such as skin impedance. Research is also investigating the use of microfluidics to monitor various markers present in sweat in real time, while collecting fluid quickly and continuously. This would circumvent the problems of inaccuracy and reliability that occur in traditional methods.
Biosensors can not only measure substances or physical parameters, but can also collect data on the skin's own composition. Recently, it has been demonstrated that a bandage-type biosensor can detect tyrosinase, an enzyme necessary for the production of the pigment melatonin on the skin surface. To do this, the product of the enzymatic reaction, benzoquinone, is detected, making it possible to find out the activity of the reaction.[viii]. This type of sensor can be very useful in distinguishing the early stages of melanoma, where there is a large increase in enzyme activity. In this (and virtually any) type of cancer, early detection is vital for treatments to be effective, so being able to constantly monitor a suspicious area could help the patient's treatment and recovery.
In addition to patches, smart textiles are also emerging as one of the most promising platforms in the field of sports and health. Due to their adaptable manufacturing methods and wide application potential, they are devices with high flexibility in both properties and design. In smart textiles, the fibres themselves can include electronic devices and integrated circuits that detect medical parameters throughout the body, from temperature in different areas of the body to hormones such as cortisol, and so on.[ix].
Another type of technology is the wearables Implantable devices, which are devices that are inserted inside the body. They require major surgery and are nowadays a last resort to treat an ailment or disease. A clear example is the pacemaker, with millions of users around the world, which controls the heart rhythm. Neural implants, which detect brain currents and, via a brain-computer interface, connect the biological and computational worlds, are also being developed. In this way, people who have lost a limb have regained some of their functionality, or people who have lost their voice due to ALS can communicate with the outside world again.
This is the case of Casey Harrel, who lost the ability to speak due to ALS at the age of 42. As he told the UC Davis news website in an interview, not being able to communicate was frustrating and demoralising. «It's like being trapped,» he said. So he signed up for a pioneering study to test a neuroimplant capable of transforming his thoughts into words.[x]. Similarly, Noland Arbaugh, who was left completely paralysed after a problem during a dive, described his experience. Arbaugh was the first person to receive a neural implant from Neuralink, the transhumanist company founded by Elon Musk. Both can now communicate via brain-computer interface. Unfortunately, in Arbaugh's case, a series of problems related to scarring of the brain tissue around the implant have put the system at risk, and the surgery may need to be repeated in the coming months.
These technologies face major hurdles. On the one hand, the materials must be strong and biocompatible in order to adhere to the tissue without causing damage. But at the same time they have to avoid biofouling, The problems are not only technical, but also raise ethical questions about the processing of the data provided by the device. Moreover, the problems are not only technical, but also raise ethical questions about the processing of the data provided by the device.
The future of personal monitoring, in short, seems to be moving towards an increasing integration of technology into everyday life. Wristbands, rings, and more specialised devices are entering the healthcare system and offering users a novel insight into their health status. At the same time, collaboration between engineering and biomedical sciences is fertile ground for the emergence of new technologies and the improvement of existing ones. These advances augur a promising future in the detection of diseases, personalised medicine and, in short, the improvement of quality of life.
IN ACTION. Large-scale collaboration to boost biosensors
Interactions between all physiological systems, in particular between the neuroendocrine system and the hypothalamus, control physiological variables such as growth and development, vitamins, thermoregulation, energy balance, oxygenation, detoxification, acid-base balance and osmoregulation. Biosensors for disease diagnosis[xi] seek to detect and monitor changes in these factors, but they have yet to overcome a number of challenges. In the US, the FDA (Food and Drug Administration) had cleared only 96 fully implantable sensor devices between 1982 and 2023.[xii]. The European Parliament has addressed possible measures to improve the lives of the up to 36 million people in the EU living with a rare disease, according to the European Medicines Agency. In more than 90% of cases, they lack sufficient diagnostic and treatment tools, due to the high cost of research and development (R&D) and the low success rate, which creates market failures known as “unmet medical needs”.”[xiii].
Most of the existing vital signs monitoring systems worldwide only provide global information and fail to monitor deep tissues or work in real time. Also, it is not easy to obtain a sufficient number of test targets and environmental contamination can affect the results, so it is essential to study the correlations between the tests and the intended detection targets.
Its role can be key, however, in the monitoring and treatment of diseases that have a critical impact on the wellbeing of the population. Around 1.5 million people die each year directly from diabetes, half of them before the age of 70. Diabetes also causes complications such as kidney and cardiovascular disease and hypoglycaemia, which can lead to acute brain and heart damage. Chronic kidney disease (CKD) has been identified as a global epidemic disease over the past three decades.[xiv]. It affects more than 800 million people, approximately 10% of the world's population, and by 2040 it could have risen from the 16th leading cause of death to the 5th.
Cardiovascular diseases remain the leading cause of death worldwide, 85% of the time due to strokes and heart attacks.[xv], and hypertension affects approximately 30%-45% of the world's adult population, according to the WHO. Current treatments, in the first case, are still based on stents and synthetic implantable grafts to treat blood vessels when they become blocked. The economic benefits can be enormous if alternative solutions can be found, because the market for stents is estimated at USD 12.73 billion and grafting at USD 5.4 billion.[xvi].
The innovation race proposes, as an alternative route, in both cases, the introduction of biosensors for real-time vascular monitoring, capable of simulating the functions of an electrocardiogram in the home.[xvii]. It should not be forgotten that, thanks to advances in microfabrication, for example, a modern pacemaker can measure as little as 2.5 cm and weigh less than 15 grams. However, the only device that had been cleared by the FDA to monitor heart failure patients until 2023 was the CardioMEMS intra-arterial[xviii].
In the neurological field, between 150,000 and 200,000 people worldwide have deep brain stimulation (DBS) implants to treat various neurological conditions, such as Parkinson's disease, essential tremor, dystonia and obsessive-compulsive disorder (OCD). Work is underway on ingestible smart pills for precise drug monitoring, and even implantable tools designed to restore damaged nerves.
It is not only intrinsic factors that mobilise innovation in this field. External factors such as rising temperatures, one of the extreme phenomena associated with climate change, must be considered. Constant monitoring technology can help prevent heat stress, both for the general public and for high-intensity workers such as construction workers and firefighters.[xix].
By identifying a patient's genetic predisposition to a particular health condition and combining it with real-time data from wearable biosensors, health systems can predict, prevent or monitor disease with unprecedented accuracy.[xx]. In this sense, Health 5.0 incorporates monitoring and detection and is reinforced by virtual care and intelligent health management.[xxi]. What is now known as ubiquitous computing (pervasive computing) could enhance the application and performance of biosensors.[xxii], in a context of personalised medical care.
Advances in artificial intelligence (AI) and the internet of medical things (IoMT) are driving a paradigm shift. With large amounts of data becoming increasingly affordable, healthcare services are gradually moving away from traditional centralised systems. Integrated healthcare platforms will combine data from wearable and implantable biosensors with information from electronic medical records to provide healthcare professionals with a holistic view of a patient's health.
In doing so, they could be helped by machine learning algorithms designed to identify patterns, predict disease progression and optimise treatment plans. As technology evolves, the potential to empower people and encourage them to actively participate in their healthcare, promoting health literacy and self-management, will increase. In addition, interactions of new drugs and treatments can be better understood and monitored through the use of these devices, both in human and animal clinical trials, leading to improvements in current testing procedures.
The path to developing these new solutions is, however, complex and fraught with difficulties, beyond the already intricate innovation process, which involves multiple steps such as research, prototyping, testing and validation. One of the starting problems is that implantable sensors are often not widely used in clinical practice, mainly due to their limited availability. Many medical centres lack the infrastructure, resources and expertise to offer these devices to their patients. As a result, the prevalence of implantable sensors is not homogeneous, and still varies between countries.[xxiii].
This inevitably translates into the cost of implantable sensors, which can make them unaffordable for many patients and healthcare systems. R&D, regulatory, manufacturing, manufacturing, marketing and sales, legal and patent costs are estimated to exceed $100 million in some cases. In fact, the expected average capitalised development cost per complex therapeutic medical device in the US is $522 million.[xxiv], The majority of these are at the non-clinical development stage. As can be seen in Figure 3, this country leads in medical publications that include the terms implantation and sensor.
In addition to their limited market, these biosensors tend to be more expensive also due to the invasive nature of their implantation in some cases. And for patients with chronic diseases, who require long-term monitoring, the cost disadvantage continues to accumulate over time. Only large medical device companies with considerable financial resources are usually able to commercialise these technologies. The evidence is that implantable sensor technology is not yet widely available in developing countries, despite the fact that, paradoxically, they end up being more cost-effective in the long run.
Another category of problems for implantable sensors, whose applications can be seen in Figure 4, relates to ethical and legal issues, which are addressed in many countries by applying the Declaration of Helsinki for medical research on human subjects. In some cases, physicians are reluctant to use these devices because they favour a healthcare system that encourages «device-free» patients and avoids unnecessary prescriptions. More and more voices are calling for a strict regulatory framework to ensure the safety of biosensors, as well as their proper functioning and use.
Reality shows that the latter is not proving easy for legislators. The EU, which has 24 reference networks (RERs) to strengthen R&D coordination, regulates biosensors generally as medical devices (stand-alone biosensors and biosensors in combination with medical devices).[xxv], although they are also mentioned in laws not strictly aimed at them.[xxvi]. The US FDA has established classifications for approximately 1,700 different generic types of medical devices, grouped into 16 medical specialties, and has divided them into three regulatory classes. Class I devices represent the lowest risk, and Class III devices, which include implantable biosensors, are attributed the highest risk.
In both cases, the review and approval process for these devices prior to their use in clinical settings is lengthy and costly, as in other areas of healthcare, and becomes an obstacle for small companies and researchers. In addition, guidelines for these devices change frequently, making it difficult for companies to adapt to the regulatory process. Some modern medical technologies are, in fact, trying to circumvent this convoluted legal environment with open source or DIY solutions.do it yourself), with the support of communities online.
One of the effects of the above is that there is a lack of real-world data on the application of implantable sensors in medicine, and this in itself is another serious obstacle to their proliferation. For example, smart orthopaedic implants with sensing properties have been used exclusively as research tools. This can make it difficult for clinicians and healthcare organisations to make informed decisions, and ultimately makes it difficult to obtain funding for these devices, limiting their application in the clinical setting. It is the problem of the fish that bites its own tail.
Data must also be integrated as part of a normal clinical workflow to be effective. The EU is working on a European Health Data Space (EHDS) to support public health and for use in medicines regulation.[xxvii]. It is aware that, without action in this area, it could become an unattractive region for the global life sciences industry, and innovative therapies and technologies would not reach European patients as quickly as in other regions. But the field is relatively new and rapidly evolving, there are no established standards for the implantation, calibration or monitoring of the most sophisticated monitoring devices, so clinical practice can vary significantly, making it difficult to compare results between different studies or institutions.
Moreover, the lack of useful materials also limits the development of high-performance devices for implantable biodegradable biosensors. The components and format of traditional biosensors are incompatible with implantable biodegradable biosensors. The former are heavy and bulky, the latter must be small and lightweight for seamless integration into the body. Conventional sensors designed for rigid surfaces are not suitable for soft, curvilinear human tissues. Soft and elastic sensor materials are required, with mechanical properties identical to those of tissues and capable of adapting to the non-flat shape of the human anatomy without triggering any somatosensory response.[xxviii].
The fact is that the rise of biosensors has sparked an exciting race to discover the personalised health materials of the future. The chemical structure of silk, for example, makes it interesting as a basis for transistors and a wide range of photonic devices, and indeed scientists around the world are creating a wide range of wearable sensor patterns on flexible substrates and textiles.[xxix]. Similarly, gelatine and shellac have been applied in various fields related to implantable biosensors, such as the creation of coaxial fibres and electrode coatings, a particularly sensitive area because of the risk of infection due to a phenomenon known as «biofouling».»[xxx]. To prevent this, a variety of alternative coatings and antimicrobials have been studied, including silver ions, nitric oxide, bioactive antibodies and other bactericidal compounds.[xxxi].
Synthetic polymers are also gaining importance to create electronic platforms compatible with living organisms and as a substrate or coating for implantable devices, photodetectors, transistors, light-emitting diodes and sensors. In the same vein, innovation has turned to organic semiconductors. They are used as active layers to replace traditional devices, although silicon transistors remain essential in applications such as pressure sensors to amplify changes in physiological signals.[xxxii].
Advances in DNA sequencing are helping in the development of optoelectronic modulators, capable of manipulating the properties of light. Interesting new candidates for dielectric materials, which function as insulators thanks to their low electrical conductivity, are also emerging. One notable option for the latter is albumin, found in chicken egg whites, useful in the process of building microlasers. Finally, melanin can be used effectively as an active layer for pH sensing. It is considered advantageous for bioelectronic applications due to its biocompatibility, including electronic devices that interact with biological systems, such as brain neurons.
Finding the right materials, however, will not solve all the challenges associated with driving biosensors. Conventional microfabrication techniques are also not applicable to most biodegradable materials due to their solubility and sensitivity to high temperatures. Progress has been made in fields such as soft lithography, screen printing and transfer printing. However, lithography-based techniques cannot produce fine microstructures and complex interconnections in sensors, and print-based methods are costly and time-consuming to manufacture. Improvements in 3D and 4D printing techniques are therefore needed to facilitate low-cost, scalable, reliable and reproducible manufacturing in the future. This will pave the way for the commercialisation of biodegradable sensors.
Inkjet printing, with an optimised nanoparticle ink formulation, now enables the mass production of robust and flexible biosensors that have been proven to monitor the impact of therapeutic drugs on cancer patients.[xxxiii]. In the field of biosensor printing, screen printing is relatively low cost and easier to use than more advanced deposition methods, making it a much more scalable and commercially viable option for use in health monitoring devices.[xxxiv]. A novel approach, in this sense, proposes the creation of a sensor network produced by nano-functional inkjet printing on a semi-permeable substrate, with wireless and battery-less near field communication (NFC) technology, for reading data through smartphones. The sensors can be integrated into a mussel-inspired bio-inspired membrane with natural adhesive that is easily attached to the skin, ensuring reliable and continuous data collection.
On the patient side, innovation must take into consideration how patients perceive and adapt to the use of implanted sensors, an area that has been the focus of a growing body of psychological research. For example, it has been shown that patients may experience different levels of anxiety and discomfort before and after implantation, and that their acceptance may be influenced by the perceived benefits and control they have over its use. Aspects related to the patient's subjective view include the continuous calibration of implantable biodegradable sensors to provide reliable information, a complex task.[xxxv]. Infection, inflammation and post-implant contamination are a risk to watch out for, and sensor performance decreases due to material ageing, mechanical wear and tissue encapsulation.
Connectivity is another key area for innovation in the field of biosensors. In some cases, they use Bluetooth technology as a wireless data transmission system linked to smartphone applications. Bluetooth communication uses long-term keys, connection signature resolution keys and identity resolution keys during the pairing process, but not all hardware is capable of reading and decoding them, so progress is needed in this area.
The development of high-speed data communication is also crucial for new medical devices, but security and privacy must be ensured in wireless body area networks (WBANs), with special attention to secure data storage and precise access control. The company WiTricity is exploring wireless power transfer and communication for biomedical sensors and implants. All information exchanged between the biosensor and the outside world must be encrypted to make the implants secure for everyday use. If this is ensured, the versatility and transformative potential of implantable sensors will be enormous and will lay the foundation for a new era in personalised and proactive healthcare.[xxxvi].
Another key challenge concerns the electrical charging of these devices. Battery-free implantable biosensors will play an important role in the future of healthcare and biomedical research, but for those that still need it, radiofrequency energy harvesting (RFEH) is a promising avenue of innovation due to its non-invasive nature and use of ambient energy. Questions remain about its efficiency and device integration.
Techniques such as harnessing magnetic fields near power lines and thermoelectric generators (TEGs), which can convert body heat into electricity, are also emerging.[xxxvii]. However, as in other cases, the scenario of implantable biodegradable devices, which require bioresorbable power sources such as batteries, energy harvesters or flexible circuits, must also be considered here.
A notable advance in this regard is the use of sweat or sweat-equivalent solutions as electrolytes.[xxxviii]. Both in this case and in the case of electrical generators based on the mechanical movement of the body.[xxxix], The disadvantages are that they are bulky compared to the sensor itself, they lose their functionality quickly when placed in biofluids and they lack the necessary flexibility. Other lines of research are aimed at creating flexible energy harvesting and storage systems, such as epidermal biofuel cells, tattoo-based batteries, supercapacitors, textile-based energy microgrids and multimodal hybrid energy systems.
The convergence of multidisciplinary lines of scientific and technological research in the field of implantable biosensors is currently sensational. From material sciences to wireless communication, wireless energy transfer, biomedical engineering, electronics and healthcare, the development of wireless implantable electronic systems is accelerating.[xl]. Dermal biosensors for tattoos are benefiting from this wave of transformation.
These are promising platforms for real-time biomarker monitoring. They are an evolution of traditional solutions based on the use of small molecules as biosensors and eliminate the need to extract body fluids for measurement. Tattoos are typically present 0.4 to 2.2 mm deep in the dermis, a layer of skin containing a variety of cells, blood vessels and nerves surrounded by interstitial fluid (ISF). The rise of synthetic biology now allows the use of genetically modified bacteria as live analytical tools.[xli]. Genetically modified bacteria are encapsulated in micrometre-scale hydrogel microspheres prepared by scalable microfluidics. These biosensors can detect both biochemical (model biomarkers) and biophysical signals (temperature changes using RNA thermometers), with fluorescent readings.[xlii].
The tattoo is naturally degradable because it incorporates hydrogel-degrading enzymes, and altering the biosensors for further customisation requires changing the genetic circuitry of the bacteria, incorporating new logic gates and more advanced biocomputational elements, as well as systems that allow tighter control of gene expression. A skin-mounted microfluidic device, developed at UC San Diego and commercialised by Innovosens, allows the measurement of sweat metabolites for sports and fitness. Fingertips are one of the most sweaty spots on the body and rapid detection of cortisol concentration in natural sweat is now possible at this point on the body.[xliii].
The «inks» are biocompatible and can detect a wider range of stimuli over longer periods of time compared to small molecule-based biosensors.[xliv]. By incorporating hydrogel-degrading enzymes into microgels, a naturally degradable tattoo is obtained. All of these methods allow for further customisation of the tattoo platform, which is vital for creating a widely used biosensor system.
IN SPAIN. A country of components and advanced research
Spain is home to companies that produce key components for the manufacture of biosensors. The Madrid plant of Sigma-Aldrich, part of the Merck group, works on biosensors and bioimaging technologies to detect pathogens, toxins and biomarkers in different biomedical and environmental contexts at the molecular level. It has provided reagents for collaborative R&D projects such as the one to produce biosensors to prevent heat stress in construction workers. The same project used solvents from the Scharlab plant, also in Madrid.
In the field of research, the ELECTROBIONET thematic network, specialising in electrochemical sensors and biosensors, has been operating since 2015. It is made up of Spanish research groups ranging from fundamental research to the design and development of applications in devices. In this regard, for example, the PKU OTM Foundation, together with the Hereditary Metabolic Diseases laboratory of the Hospital Sant Joan de Déu and the Universitat Autonòma de Barcelona, are working on an ammonium biosensor to improve home care for patients by detecting episodes of hyperammonaemia and hyperphenylalaninaemia more quickly.
A multidisciplinary team from four European countries, including Spain through the Tecnalia technology centre, has developed a highly sensitive biosensor platform within the framework of the DeDNAed project.[xlv]. It will be used to detect biomolecules and is expected to detect food toxins and disease biomarkers with increased sensitivity, versatility and ultra-fast optical focusing. The structure of the DeDNAed sensor features several components that are assembled with nanometre precision thanks to DNA origami, foldable like that of paper, but composed of a single strand of DNA and arranged in 2D or 3D. DeDNAed precisely attaches a biorecognition element to its “sticky ends”, such as the antibodies with atomic nanoclusters developed by Tecnalia, making it a highly sensitive sensor capable of detecting very low concentrations of the analyte.
The EU-funded H2Train project focuses on enabling digital technologies for health, lifestyle, motivation and monitoring assistance, supported by AI networks.[xlvi]. It is coordinated by Spain through the University Institute of Applied Microelectronics (IUMA) of the University of Las Palmas de Gran Canaria. Thirty-five public and private institutions participate in the consortium, including SMEs and large companies from six EU Member States (Austria, Germany, Spain, Finland, France, Italy, Poland).
Among the main objectives of H2TRAIN, the largest project of its kind funded by the EU's Chips Act, is the development of new prototypes of smart biosensors made of graphene that can be attached, like a sticker, to the skin or form part of the fabric of clothing. They will be used for continuous monitoring of athletes, as well as chronic patients or people undergoing rehabilitation. The aim is to measure, among other things, physiological signals from their body, as well as stress-related biomarkers (through sweat, monitoring cortisol, lactate and C-reactive protein). The electrodes attached to the garments will capture electrical parameters specific to human physiology, and should be capable of energy recovery through thermoelectricity and piezoelectricity. Where appropriate, they will be used to monitor the elderly population in need of regular medical care. Finally, CIC biomaGUNE, the Complutense University of Madrid, BCMaterials, the University of the Basque Country, and the NanoSelf group of the CICA University of A Coruña are participating in the international ECLectic project.[xlvii]. One of the lines of work is the detection of biomarkers of sepsis by electrochemiluminescence (ECL) measurements. For this purpose, carbon-based nanoparticles (carbon-dots) will be developed at the San Sebastian centre, while at the UDC different chemically modified graphene materials will be evaluated for the construction of the electrodes. ECLectic addresses the global problem of sepsis and bacterial infection from completely new diagnostic paradigms. According to its promoters, it will bridge the gap between innovative research in the field of nanostructured materials and their application in nanostructured biosensor technology.
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