Health care is no longer a hospital patent, and it is increasingly closely related to people's daily lives. Medical devices are gradually evolving from portable devices to wearable devices, which means that devices should be able to be used continuously for long periods of time. These new devices present many new challenges for designers. This article will explore some of these challenges and provide solutions.
Drug perfusion therapy The human wearable medical device is not new. Many people are familiar with wearable products such as nicotine patches and motion sickness patches. They lay the foundation for a new generation of electronic products. The iontophoresis patch is one of the new generations of this product.
Electron iontophoresis uses an electrical current to complete the injection of the drug through the skin. The transdermal drug is ionized, dissolved in an aqueous solution, and applied to the electrode in the patch. This specially formulated ionized mixture can then be transmitted through the skin under the action of a direct current, as shown in Figure 1. Most patches currently in use can be worn anywhere from minutes to hours, depending on the drug and the condition being treated.
Figure 1: Typical iontophoresis process Electron iontophoresis has several advantages. First, the drug can reach a very high dose level locally, rather than distributing the drug throughout the body like a syringe injection. This topical treatment improves efficacy and reduces side effects.
With the development of electronic technologies such as switching power supply design and cost-effective high-performance MCUs, it has become possible to produce low-cost disposable drug dispensers. Many consumers have been using self-service iontophoresis products for a variety of conditions including headache, cold sores and wrinkles.
Designers face numerous challenges in designing devices such as iontophoresis patches. The biggest challenge is that the critical electronic components are located in the wearable portion of the device, and that portion is discarded after being used once. This situation forces the patch electronics to be small and inexpensive. At the same time, because this is a small disposable product, battery cost and capacity have further limited the design. Moreover, the design should also be easily modified to perform other functions, such as changing the dose of the drug and the duration of the perfusion.
In order for the drug to be injected through the skin, the device must generate sufficient voltage to provide the current required to maintain a particular implant dose rate for a specified period of time. Designing a cost-sensitive, small-ion iontophoresis device can be as simple as a DC/DC boost converter that drives controlled current through the skin and uses a microcontroller (MCU) to control the converter.
A boost regulator is used to raise the low voltage of the battery to a high enough level to pass the required current through the skin. The chip electronic components can be powered using inexpensive coin-cell lithium batteries or alkaline batteries.
To meet both cost and functional requirements, a small, highly integrated MCU.Microchip 8-pin 8-bit PIC12F1822 MCU is required for this device with an internal 10-bit ADC, fixed reference voltage, comparator, PWM, hardware Timers and EEPROMs meet the design integration requirements. The fixed reference voltage eliminates the need for a voltage regulator or an external voltage reference and keeps the design within the 8-pin MCU range to reduce cost and board size.
Innovations in long-term monitoring of electronic technologies are driving the development of wearable medical devices, where patients can wear equipment for long periods of time, thereby improving quality of life and quality of care. Continuous blood glucose monitors and wearable heart monitors are two well-known examples of such devices.
The ovulation prediction system is a special case of this type of equipment, bringing the long-term use of the equipment to a whole new level. The device has been widely used by women who want to get the most out of pregnancy. The DuoFerTIlity brand of birth monitor is such a wearable device, as shown in Figure 2. Manufactured by Cambridge Temperature Concepts, this device integrates many of the features normally essential for long-term monitoring systems.
Figure 2: The monitor and sensor of the birth monitor The ovulation process in the female body is associated with small changes in basal body temperature. Accurate measurement of changes in body temperature over multiple menstrual cycles can help estimate ovulation days.
The continuous blood glucose monitor can be designed to work up to one week in a row, while the sensors on the fertility monitoring device continuously measure the basal body temperature for up to six months. The device uses this information to make predictions and predicts ovulation activity up to six days in advance. Continuous monitoring of small changes in body temperature can eliminate many of the variables that women may have when manually measuring body temperature.
One of the challenges faced by designers of such devices is to design physical shapes that can be worn for months. In this case, the solution is to make a system consisting of two parts. The coin-sized sensor unit is attached to the user's body by a biocompatible adhesive patch. The handheld reader unit is used to analyze the data and allows the user to pass the data to a medical professional for in-depth analysis. This functional division allows the sensor worn by the human body to be as small and light as possible. The sensor and reader block diagram of the monitor is shown in Figure 3.
Figure 3: Block diagram of the sensor and reader Another challenge is to anticipate all the environments in which the user is located and the activities that the user may be involved in. Because of the useful life of several months, wearable devices must adapt to a variety of situations, including sleeping, exercising, showering, and even skiing. In this case, the design of the sensor and its packaging must enable accurate temperature measurement, whether the sensor is open to the outside or covered by the user's arm. Designers use a pair of matched thermistors to solve this problem. These two thermistors measure the temperature and heat flow from one side of the sensor to the other, making the sensor accurate to a few thousandths of a degree. In addition, an accelerometer is integrated into the sensor design to allow for user motion.
The electronic components worn by the human body must be very small, which means that the space available for installing the battery is very limited. Therefore, another challenge in sensor design is to maintain very low power consumption. The sensor designer used an 8-bit PIC16F886 MCU to minimize sensor current consumption. They use the MCU's ultra-low-power wake-up feature to achieve minimum current consumption.
When a reading is required, the sensor is powered up and measured, then returns to sleep mode; all operations are completed within 1 ms. This short wake-up time allows device designers to achieve an average power consumption of less than 1μA, so a small button-type CR1216 lithium battery can be used to meet the six-month continuous operation of the device.
Another challenge is to transmit measurement data. This sensor module uses an improved RFID protocol to send data to the reader, holding the reader close to the sensor to initiate communication. Data transfer requires higher power consumption than data measurement, so designers save sensor temperature readings in 16 megabytes of independent flash memory to minimize current consumption. This reader data will be uploaded every few days. Since data collected by long-term sensors may need to be analyzed by trained personnel, creating a direct and cost-effective way to transfer measurement data to and communicate over the Internet is another important design consideration. The second part of the device, the handheld reader, is used for this purpose.
The reader transfers data to the PC via an on-chip USB peripheral inside the Microchip 16-bit PIC24FJ256GB106 MCU with nanoWatt technology. Users can enter additional data via the front panel buttons via the MCU's internal charge time measurement unit (CTMU) and mTouch capacitors. Touch technology implementation.
Device manufacturers can communicate with readers to improve the accuracy of ovulation predictions. This feature also allows remote reconfiguration of the MCU. With its flexibility, manufacturers can run diagnostics and send software updates to the monitoring system.
With continuous innovation in the fields of biology, physiology, chemistry and electronics, wearable medical devices designed for long-term use will offer new diagnostic and therapeutic options to deal with more diseases and conditions.
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