10.3.5　Drug delivery skin device

Compared with traditional drug treatment，personalized treatment for different patients has more advantages.Personalized treatment requires of monitoring the patient' s various physiological indicators during the treatment process and tracking the patient's recovery.With these information，doctors can adjust the treatment plan，such as the choice and dosage of drugs.Recently，researchers integrated electrophysiological signal sensors，chemical sensors，and drug controlled release devices into the flexible e-skin.Through the changes in electrophysiological signals and the chemical composition of body fluid，the device can feed back to the drug controlled release device，to control the release speed and the amount of the drug.The drug controlled release device can be integrated with a variety of devices according to the patient's treatment needs.At present，this method has become a new generation of transdermal drug delivery technology with very good application prospects.

For example，Kim et al.designed an e-skin device that integrated strain sensing，information storage，and controlled drug release（Figure 10-9）.They used a silicon film to prepare a strain sensor that could detect movement disorders caused by Parkinson's disease.The collected information could be stored in the device.By analyzing the vital signs information of the human body，the information was sent to the drug controlled release module.When the drug controlled release module received the drug release signal，the heating component started to work to promote the release of the drug，and enhanced the diffusion and transdermal abilities of the drug.

In addition，the electrophysiological signal sensors can be integrated with the drug controlled release module to form a multifunctional e-skin device.When an abnormal electrophysiological signal is detected，the drug controlled release module starts to work to achieve transdermal drug delivery.Iontophoresis electrodes can also be integrated in the device to promote the penetration of drugs through iontophoresis，so that the drugs can penetrate deeper into the skin more efficiently，thereby achieving higher drug utilization and better therapeutic effects.(https://www.daowen.com)

The e-skin can detect the chemical composition of human body fluid through chemical sensors to monitor the health of the human body.Researchers combine chemical sensors with drug controlled release devices to integrate the diagnosis and treatment of diseases.As shown in Figure 10-10，the glucose sensor，temperature sensor，humidity sensor，and pH sensor are integrated.Then the human blood sugar level can be obtained by detecting the glucose level in sweat.Furthermore，the heating module and the microneedle patch loaded with the metformin are integrated with the above-mentioned sensor device.The microneedle patch is made of temperature-responsive materials.At low temperatures，the microneedles remain intact，which can avoid the denaturation of the drugs in them；at high temperatures，the microneedles quickly dissolve in body fluid and release the drugs.In addition，the microneedles can penetrate the dermis to increase the transdermal absorption rate of the drugs.When the glucose sensor detects that the human blood glucose level exceeds the normal value，the heating module heats the microneedle patch，so that metformin is released from the microneedles and absorbed through the skin into the circulatory system，thereby achieving the control of blood glucose levels.

The emergence of transdermal drug delivery e-skin devices overcomes the problems of poor penetration and low efficiency in skin drug delivery，and realizes real-time monitoring of patient health status and intelligent control of drug release，which greatly promotes transdermal drug delivery technology（see extended reading 4）.However，there are still some difficulties and challenges in this field.For example，the stability and reliability of transdermal drug delivery e-skin devices need to be further improved.At present，the diseases that can be detected and treated by transdermal drug delivery e-skin devices are still limited.Some macromolecular drugs（e.g.，peptides，nucleic acids，and proteins）are still difficult to achieve transdermal drug delivery through e-skin devices.The solution to the above problems depends on the in-depth development of device structures，materials，drugs，etc.，so that the various modules of the device can have a synergistic effect，improving its sensing accuracy and drug delivery efficiency.