# Polydimethylsiloxane (PDMS)-Based Flexible Resistive Strain Sensors for Wearable Applications
## 5 Conclusions and Outlook  
We have presented a comprehensive review of the recent technological advances of PDMS-based flexible resistive strain sensors. We introduced substrate and active materials, several fabrication methods, performance parameters, and their applications. It leads us to believe that flexible strain sensors can potentially function in many applications, such as virtual reality and entertainment technology, human-machine interfaces, personal healthcare, and sports performance monitoring. Wearable intelligent electronic systems will play an increasingly critical role in our daily life. Nevertheless, the wearable sensors in practical applications are still facing huge challenges. At present, most of the strain sensors have sole functions and can only monitor deformation in one direction because they are not capable of decoupling more than one type of stimuli at a time. Strain sensors measuring decoupled strains in multi-direction or multi-plane deformations have not been successfully fabricated yet, even though many strain- and pressure-sensitive sensors have been reported. Besides, strain sensors with relatively high modulus materials and weak adhesion structures make them wearing uncomfortable and lead them to easily slide off their particular position. Therefore, they cannot be reliably integrated with the human body for real-time effective deformation measurements. Moreover, packaging flexible sensors with other components has received less attention. There are still some problems including the followings: the electronic circuit is rigid and the size is not small, making it impractical to integrate with soft sensors; the communication module electricity consumption is huge even using low-power miniaturized Bluetooth technologies; the current thin-film batteries lack sufficient capacity and recharging is complex and time-consuming, etc. To solve these problems, in addition to selecting or developing functional materials, more efficient methods and optimization of devices are needed to be explored for improving the sensing performance.  
This research was partially supported by Shenzhen Fundamental Research Project (JCYJ20170307165039508), the National Natural Science Foundation of China (NSFC: U1713219), Key Deployment Project of Chinese Academy of Sciences (Grant No. KFZD-SW-214), and SIAT Innovation Program for Excellent Young Researchers. (Grant No. 2016053).  
Figure 5: **(a)** The graphene woven fabric (GWF)/PDMS-type sensor’s relative change of resistance of the respiratory in the rest and exercise states, respectively. Reprinted with permission from [72], Copyright John Wiley and Sons, 2014; **(b)** The nanoscale crack sensor attached to skin recording human speech and pulse measurement. Reprinted by permission from [78], Copyright Springer Nature, 2014; **(c)** Data glove with five implanted sensors detected finger moving. Reprinted with permission from [63], Copyright John Wiley and Sons, 2013; **(d)** A wearable carbon nanotube strain sensor integrated into a stocking to detect knee motion. Reprinted with permission from [46], Copyright Springer Nature, 2011.  
**Author Contributions:** [PERSON] and [PERSON] proposed the idea; [PERSON] and [PERSON] conceived and designed the structure of this review; [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], and [PERSON] contributed the materials, figures, and tables for this review; [PERSON] and [PERSON] wrote the paper.  
**Conflicts of Interest:** The authors declare no conflict of interest.