Table 3.
Research wearables and sensors for health monitoring.
| Target | Device Type (Year of Publication) | Functioning | Sensors Used | Real-Time Monitoring | Elderly User Ready |
|---|---|---|---|---|---|
| Glucose Monitoring | Non-invasive intravascular glucose measuring sensor (2017) | It consists of ultra-thin skin-like biosensors on a flexible biocompatible paper battery. The battery generates subcutaneous electrochemical channels (ETC) by binding to the skin; the sensors act through the penetration of hyaluronic acid into the anode channel, the refiltration of intravascular blood glucose from the vessels, and the reverse iontophoresis of glucose to the skin surface [92]. | Ultrathin skin-like biosensors | No | Yes |
| Glucose Monitoring | Wearable-band type visible-near infrared optical biosensor (2019) | It is a highly portable blood glucose sensor with a data acquisition time window that enables long-term, non-invasive continuous blood glucose monitoring (CGM). The biosensor exploits information from the pulsatile components that continuously measure the arterial blood volume in the wrist tissue during the change in blood glucose concentration [93]. | Multi-chip sensor package of SFH7060 (OSRAM Semiconductor Inc., Regensburg, Germany) | Yes | Yes |
| Glucose Monitoring | Contact Lens (2018) | The human eye is read using a photon microstructure with a periodicity of 1.6 µm on a selective glucose hydrogel film functionalized with phenylboronic acid [94]. | A photonic structure glucose sensor | Yes | No |
| Glucose Monitoring | Patch (2020) | It is a non-invasive, continuous, portable system, inspired by the anatomy of the vasculature, based on electro-magnetism (EM) for glycemic measurements. The structure of the sensor mimics the vasculature anatomy. The multiple detection system, depending on the patient’s characteristics, provides personalized monitoring [95]. | EM sensors | Yes | No |
| Glucose Monitoring | Wearable-band type (2017) | It is an autonomous and minimally invasive portable microsystem for pseudo-continuous monitoring of blood glucose. With a shape memory alloy (SMA) microactuator, the microsystem pierces a slight wound in the skin and draws a whole blood sample from the skin [96]. | Shape memory alloy (SMA)-based microactuator | Pseudo | Yes |
| Glucose Monitoring | Patch (2017) | It is a disposable patch-type device that measures glucose levels in sweat and automatically applies metformin, thanks to a transdermal drug delivery device [97]. | Extendable sensors (humidity, glucose, pH, and temperature) are integrated in a monolithic way. | Yes | Yes |
| Glucose Monitoring | Band (2017) | The system induces sweat with different excretion rates at periodic intervals employing wirelessly programmable iontophoresis. The induced sweat can be immediately analyzed for glucose monitoring by integrating sensor iontophoresis electrodes on the same substrate [98]. | Iontophoresis and sweat sensing electrodes for detection of Na + and Cl− | Yes | yes |
| Glucose Monitoring | Patch and Smart Band (2018) | It is a multifunctional wearable health management system that analyzes sweat glucose levels using a disposable sweat-based glucose detector strip and a wearable smart band [99]. It also continuously monitors vital signs (i.e., heart rate, blood oxygen saturation level, and activity). | Sensors for light-based photoplethysmography, accelerometer-based activity monitoring, and sweat-based electrochemical analysis | Yes | No |
| HR Monitoring | Bracelet (2020) | It is an IoT-based wearable HR monitoring smart sports bracelet. IoT technology enables real-time monitoring, storage, and analysis of data transmitted to a PC or mobile phone. After data processing and analysis, abnormal data will receive an alarm in time to track the health status [100]. | heart rate sensor son7015 and step acceleration sensor mma9555lr1 | Yes | Yes |
| HR Monitoring | Belt (2018) | It is a multifunctional portable electrical impedance tomography (EIT) system based on a high-performance application-specific integrated circuit (ASIC) active electrode that can record heart rate signals and measure humidity and ambient temperature [101]. | ECG, accelerometers | Yes | No |
| HRV | Leg belt (2017) | It is a portable ECG sensor system that captures vital patient skin data from amplified signals detected by patched electrodes. These modules are capable of collecting 6 ECG lead signals [102]. | ECG, accelerometers | Yes | yes |
| HR Monitoring | Bracelet (2019) | It integrates an HR measurement device using an optics-based pulse sensor and a Bluetooth-based communication module. In addition, an Android-based smartphone application receives and processes the sensor data [103]. | Optical based pulse sensor | Yes | Yes |
| HR Monitoring | Finger case (2017) | A portable heart rate monitoring system that uses photoplethysmography (PPG). Based on the detection of the cardiovascular pulse, this method presents the analysis of light variations in biological tissues [104]. | Pulse sensors | Yes | Yes |
| HR Monitoring | Smartwatch (2018) | It is a prototype that allows monitoring of the heart rate and the intervals between beats for some subjects. This prototype was made using the Samsung Gear S3 Smartwatch, with WebSocket library, nodejs, and JavaScript [105]. | Samsung Gear S3 sensors | Yes | No |
| HRV | Armband (2019) | The device consists of a cuff designed to fit on the upper left arm that provides 3 ECG channels based on three pairs of dry electrodes (without hydrogel) [106]. | ECG | Yes | Yes |
| HRV | Ear wear (2019) | It is a lightweight, portable device that continuously monitors stress in daily life by measuring electrocardiograms (ECG) and EEG. The system can be easily worn by hanging it from both ears [107]. | ECG | No | No |
| PRV | (2019) | It is a portable device that collects PRV values in real-time. The device includes an amplifier and filter for signal accuracy. An accelerometer is used to eliminate noise due to motion. This device can transmit the acquired PPG signal wirelessly with the use of Wi-Fi technology [108]. | Pulse sensors | Yes | |
| PRV | Wristband (2017) | A small portable device worn on the wrist detects and records gestures, arm movements, and biometric information such as skin temperature and pulse rate during sports activities using an inertial measurement unit [109]. | 6DOF motion sensor, temperature sensor, pulse rate sensor | Yes | No |
| PRV | Wristband (2018) | A portable sensing device capable of continuously monitoring cardiac movements and parameters on the wrist by using impedance plethysmography (IPG) technology. The sensor’s design consistently allows getting high-resolution measurements for up to 48 h [110]. | - | Yes | Yes |
| PRV | Wristband (2018) | A handheld cuffless integrated system utilizes a piezoresistive tunneling sensor, achieving ultra-high sensitivity to detect slight wrist artery pressure. After the read, a circuit amplifies and converts the pulse pressure-induced signal to be wirelessly transmitted to the cloud for its storage [111]. | Tunneling piezoresistive sensor | Yes | No |
| Respiratory Rate | Fabric (2018) | It is a smart textile based on a piezoresistive sensor element for respiratory monitoring [112]. | Silver-plated nylon knitted fabric | Yes | No |
| Respiratory Rate | Stretchable sensor (2019) | It is an easy-to-use, low-cost, stretchable, and portable RR sensor that measures respiratory volumetric changes. The sensor is manufactured using polydimethylsiloxane substrates (PDMS) and a soft lithography technique for the stretchable sensor body. An inkjet printing technology creates the conductive circuit by depositing silver nanoparticles on top of PDMS substrates that detect inductance fluctuations [113]. | RR sensor | Yes | No |
| Respiratory Rate | Armband (2018) | Respiratory rate is estimated from a cuff ECG using a method based on variations in the slopes of the QRS and the angle of the R wave. The estimates are compared with those obtained from the respiration signal. The cuff includes a pair of dry electrodes that record the ECG and is designed for long-term monitoring. [114]. | ECG | Yes | No |
| Oxygen saturation of blood | Finger case (2018) | The device connects to a cloud gateway to support IoT applications using an MCU node as a data processor. The data sent to the cloud can be later accessed online for detailed analysis [115]. | Photodetector | Yes | No |
| Oxygen saturation of blood | In-ear device (2020) | It is a device entered into the ear canal for real-time oxygen saturation measurement in the blood using a photoplethysmography sensor. It consists of green (537 nm), red (660 nm), and infrared (880 nm) emitting diodes, as well as a photodiode to measure reflected light [116]. | Photoplethysmography sensor | Yes | No |
| Oxygen saturation of blood | Patch (2018) | It is a patch-type device that uses green light emitters to calculate oxygen saturation levels in the blood [117]. | Photoplethysmography sensor | Yes | No |
| Oxygen saturation of blood | Neck device (2021) | An integrated PPG sensor (MAX30102 by MAXIM integrated) housed in a PCB emits red light (650–670 nm) and IR (870–900 nm). Then, the PPG sensor coupled to a photodiode quantifies light absorption. A three-axis linear accelerometer (LIS2DH12 by ST Electronics) assesses activity and eliminates motion artifacts as necessary [118]. | PPG sensor, accelerometers | Yes | No |
| Oxygen saturation of blood | Finger case (2019) | It is a portable optical biosensor system that continuously measures pulse oximetry and heart rate using a reflectance-based probe [119]. | Photodetector | Yes | No |
| Blood pressure | Wrist-watch (2017) | It is a wristwatch blood pressure monitor to measure blood pressure by holding the watch against the sternum wall to detect micro-vibrations of the chest related to the heartbeat. As the pulse wave travels from the heart to the wrist, an optical sensor and an accelerometer in the watch allow estimating the travel time (pulse transit time (PTT) to estimate BP [120]. | Optical based pulse sensor | Yes | Yes |
| Blood pressure | In-ear device (2019) | A device called eBP measures BP from inside the ear, minimizing interference with the user’s everyday activities while maximizing their comfort level. Three key components provide this functionality: (1) a light-based pulse sensor connected to an inflatable tube placed into the ear, (2) a digital air pump with a controller, and (3) a BP calculation algorithm [121]. | Optical based pulse sensor | Yes | No |
| Blood pressure and HR | Ear wear (2017) | ECG and PPG-based HR and BP monitor attachable to the ear for greater usability. It is suggested to place the ECG and PPG sensors at the back of the ears with the possibility of integrating them into glasses or headphones [122]. | ECG and PPG | Yes | No |
| Blood pressure and HR | Glasses (2017) | It is a portable device that monitors the HR at three points on the user’s head. The lens prototype incorporates optical sensors, processing, storage, and communication components. The device continuously records the flow of reflected light intensities from the bloodstream and the inertial measurements of the wearer’s head [123]. | Optical based pulse sensor | Yes | Yes |