Recent Advances in Fiber-Shaped Electronic Devices for Wearable Applications

Round 1

Reviewer 1 Report

In this review paper, the authors have done a good job summarizing recent research in e-fibers/textiles and the practical challenges involved. Other than minor updates to the English language, this paper can be published as-is.

The authors may consider citing the following work, as they deem appropriate.
- Vasandani, Paresh, et al. "Triboelectric nanogenerator using microdome‐patterned PDMS as a wearable respiratory energy harvester." Advanced Materials Technologies 2.6 (2017): 1700014.

Author Response

Reviewer #1 (Remarks to the Author):

In this review paper, the authors have done a good job summarizing recent research in e-fibers/textiles and the practical challenges involved. Other than minor updates to the English language, this paper can be published as-is.

Response: Thank you for the reviewer’s positive comment. We revised several wordings in the manuscript accordingly. This paper was revised by a professional English editing service. (eWorldEditing, https://eworldediting.com).

The authors may consider citing the following work, as they deem appropriate.
- Vasandani, Paresh, et al. "Triboelectric nanogenerator using microdome‐patterned PDMS as a wearable respiratory energy harvester." Advanced Materials Technologies 2.6 (2017): 1700014.

Response: Thank you for the reviewer’s comment. We cited the following references (ref. 72).

Reviewer 2 Report

This review article summarizes recent research in fiber-shaped electronic devices including fiber-shaped transistors, sensors, memory unit, energy harvesting & storage, LEDs, and their integrated systems. The authors firstly introduce the structures of electronic fibers, followed by discussing the approaches and applications of fiber-shaped devices and integrated system. Challenges associated with the development of electronic fibers have also been discussed. This review provides a comprehensive and detailed discussion on fiber-shaped electronic devices and applications, and is considered to be published in Applied Sciences after addressing the following concerns:

1. A definition of fiber-shaped can be given at the beginning of the article. Besides, are there any differences among “fiber-shaped” and “fiber-based”? My understanding is that “fiber-shaped” highlights the 1D configuration of the devices, while “fiber-based” indicates the material fabrication approach, i.e., the device is built upon fiber materials. In terms of the topic of this review, these two terms are suggested to unify.

2. The integration of 1D electronic fibers is not just weaving. Knitting, embroidery, braiding, etc. are also the approaches for integrating electronic fibers into 2D textiles (J Mater. Chem. A 2014, 2, 10776; Adv. Energy Mater. 2016, 6, 1600783). Figure 1 is a bit misleading. 1(a)-1(c) are the ways to fabricate fiber-shaped devices, while 1(d) is just one method to integrating fiber devices among many ways. More detailed illustrations can be provided.

3. 3D layer-by-layer structure is similar to the coaxial structure. It needs more explanation/schematic illustrations to distinguish them.

4. “Automatic processing technologies that can produce well-aligned arrays and robust interconnections between electronic fibers and electrodes have been developed to construct scalable e-textiles.” Are there some examples to support this statement?

5. More representative work needs to be discussed/cited. For example, very representative works on TENGs from Zhong Lin Wang’s group, Zinc-ion fiber battery from Chunyi Zhi‘s group, conductive textiles, and fiber-based supercapacitors from Zijian Zheng’s group…

6. For the challenges and outlook part, encapsulation is also a challenging issue for electronic fibers. The author could elaborate more about it.

Author Response

Reviewer #2 (Remarks to the Author):

This review article summarizes recent research in fiber-shaped electronic devices including fiber-shaped transistors, sensors, memory unit, energy harvesting & storage, LEDs, and their integrated systems. The authors firstly introduce the structures of electronic fibers, followed by discussing the approaches and applications of fiber-shaped devices and integrated system. Challenges associated with the development of electronic fibers have also been discussed. This review provides a comprehensive and detailed discussion on fiber-shaped electronic devices and applications, and is considered to be published in Applied Sciences after addressing the following concerns:

Thank you for the reviewer’s valuable comments. To address the reviewer’s concerns pertaining to this review and improve the quality of the present state in the manuscript, we sought to answer all the questions by including additional explanations.

1. A definition of fiber-shaped can be given at the beginning of the article. Besides, are there any differences among “fiber-shaped” and “fiber-based”? My understanding is that “fiber-shaped” highlights the 1D configuration of the devices, while “fiber-based” indicates the material fabrication approach, i.e., the device is built upon fiber materials. In terms of the topic of this review, these two terms are suggested to unify.

Response: We agree with this comment. We have made the change as per suggested. We have revised the text from ‘fiber-based’ to ‘fiber-shaped’ for clarity.

2. The integration of 1D electronic fibers is not just weaving. Knitting, embroidery, braiding, etc. are also the approaches for integrating electronic fibers into 2D textiles (J Mater. Chem. A 2014, 2, 10776; Adv. Energy Mater. 2016, 6, 1600783). Figure 1 is a bit misleading. 1(a)-1(c) are the ways to fabricate fiber-shaped devices, while 1(d) is just one method to integrating fiber devices among many ways. More detailed illustrations can be provided.

Response: Thank you for the reviewer’s comment. Textiles are mainly divided into 1D, 2D, and more complex 3D structures. While from the viewpoint of manufacturing techniques, textiles can be fabricated by weaving, knitting, braiding, and nonwoven methods. By assembling/interlocking thousands of fibers with various techniques (e.g., twisting, twining, or blending) along their axial directions, 1D yarn or thread can be formed. 1D yarns can be further integrated into 2D or 3D fabrics. (Adv. Mater. 2020, 32, 1902549) Although various textile forming processes (knitting, embroidery, stitching, braiding, and felting, etc.) have been used to integrate functional fibers into fabrics, the 2D woven structure is the most widely used to integrate electronic fiber devices. The diverse manufacturing techniques have been employed to fabricate energy harvesting/storage textiles rather than electronic textiles. In this review, we focus on the significant advances, related challenges, and future perspectives of e-fibers/textiles because many researchers have already made in-depth comments and reviews on energy harvesting and storage fibers in recent years. (Adv. Mater. 2020, 32, 1902549; Adv. Energy Mater. 2016, 6, 1600783; Appl. Sci. 2021, 11, 531; Nat. Rev. 2017, 2, 17023; EcoMat. 2020, 2, e12054; Sensors 2020, 20, 5938) For this reason, we mainly present representative device structures of 1D electronic fibers and 2D e-textiles such as transistors, memories, computing units, light-emitting fibers, and circuitry. However, we know we have made some misleading narratives thus have modified those in the revised manuscript. Regarding the reviewer’s comment, we revised the following caption of figure 1 (Page 5) and paragraph (Page 4-5). We believe that it is now clearly mentioned in the revised manuscript.

• Figure 1. Schematics of representative device structures of (a-c) 1D electronic fibers and (d) 2D electronic textiles.
• Fiber-shaped devices have mainly been fabricated into four representative structures: coaxial, twisted, three-dimensional layer-by-layer (3D LBL), and woven (Figure 1).
• A representative device structure of 2D e-textiles is shown in Figure 1d.

3. 3D layer-by-layer structure is similar to the coaxial structure. It needs more explanation/schematic illustrations to distinguish them.

 Response: Thank you for the reviewer’s comment. We are aware of the similarity of 3D LBL and coaxial structures. We believe that it is worth to add a brief explanation in the revised manuscript in terms of presenting the distinction of 3D LBL structures. For this reason, we revised the following paragraph in the revised manuscript (page 5).

• The geometry and architecture of 3D LBL devices are tunable within a single fiber, moreover, discrete device units can be embedded into the preform. In this regard, monolithic integration of multiple functionalities in a 3D LBL electronic fiber can be demonstrated with increasing the density of devices [18].

4. “Automatic processing technologies that can produce well-aligned arrays and robust interconnections between electronic fibers and electrodes have been developed to construct scalable e-textiles.” Are there some examples to support this statement?

Response: Thank you for the important comment. We should have cited references to support the statement. Shi et al. demonstrated large-area display textile that withstands repeated machine-washing. They optimized the dip-coating method and have developed the device structure and fibers that are suitable for the weaving process. Thermal drawing process, additive functionalization, and embroidery manufacturing have demonstrated new paradigm for the integration of highly sophisticated functionalities into fibers and textiles. Regarding the reviewer’s comment, we cited the following references in the revised manuscript (Page 5).

• Shi, X.; Zuo, Y.; Zhai, P.; Shen, J.; Yang, Y.; Gao, Z.; Liao, M.; Wu, J.; Wang, J.; Xu, X. Large-area display textiles integrated with functional systems. Nature 2021, 591, 240-245.
• Yan, W.; Dong, C.; Xiang, Y.; Jiang, S.; Leber, A.; Loke, G.; Xu, W.; Hou, C.; Zhou, S.; Chen, M.; Hu, R. Thermally drawn advanced functional fibers: New frontier of flexible electronics. Materials Today 2020, 35, 168-194.

5. More representative work needs to be discussed/cited. For example, very representative works on TENGs from Zhong Lin Wang’s group, Zinc-ion fiber battery from Chunyi Zhi‘s group, conductive textiles, and fiber-based supercapacitors from Zijian Zheng’s group…

Response: Thank you for your suggestion. We have summarized recent research in e-fibers/textiles and the practical challenges involved. We already introduced a representative work on TENGs from Zong Lin Wang’s group (Page 20, ref. 74). The recent work shows the demonstration of highly advanced multifunctional energy fiber.

• To integrate various functions in a single fiber and realize versatile energy fibers, Han et al. fabricated a multifunctional coaxial energy fiber for energy generation, storage, and use [74]. The energy fiber comprises a fiber-shaped TENG, supercapacitor, and pressure sensor in a coaxial geometry [74]. Each energy unit showed a length-specific capacitance density of 13.42 mF cm-1, stable charging/discharging cycling (~96.6% loss), maximum power generation of 2.5 μW, and good tactile sensitivity of 1.003 V kPa-1 (below 23 kPa) [74]. The demonstration of a soft and multifunctional energy fiber makes it an attractive option for human-machine interactive systems, intelligent robots, and smart tactile-sensing clothes [74].

In response to the reviewer's comment, the representative works on Zinc-ion fiber battery from Chunyi Zhi’s group and fiber-shaped supercapacitors from Zijian Zheng’s group were cited in the revised manuscript (Page 20).

We have added the following paragraph in the manuscript (Page 20).  

• Li et al. developed a washable zin ion battery (ZIB) using double-helix yarn electrodes and a polyacrylamide electrolyte [70]. The yarn ZIB exhibits a high specific capacity (302 mAh g^-1) and volumetric energy density (54 mWh cm^-1) as well as excellent knittability and stretchability (up to 300% strain) [70]. Owing to its tailorable nature, long yarn ZIB was woven into a textile that was used to power a flexible LED belt [70].
• Among promising energy storage devices for future wearable applications, fiber-shaped supercapacitors have attracted significant attention in recent years due to their good electrochemical stability under mechanical deformation. They can be easily assembled into 3D fabric structures and integrate into cloth by traditional textile forming processes [75]. Yu et al. fabricated textile-based supercapacitors (TSCs) on different types of textile fabrics using additive functionalization and embroidery manufacturing (AFEM) [75]. High areal energy storage and power capabilities of TSCs were demonstrated with various electrode materials, device structures, pattern designs, and array connections during the AFEM process [75]. The AFEM-fabricated TSCs show high potential for mass production in the near future [75].

6. For the challenges and outlook part, encapsulation is also a challenging issue for electronic fibers. The author could elaborate more about it.

Response: Thank you for your suggestion. In response to the reviewer's comment, the corresponding explanation has also been added in the revised manuscript (Page 24).

• Additionally, 1D devices should be protected by encapsulation because of the high sensitivity of many active and electrode materials to oxygen and moisture atmosphere, which could accelerate device degradation [2].

Author Response File: Author Response.docx

Reviewer 3 Report

The paper is presented in a professional way with no need (at least to my impression) to change anything. Only the figures are a little overwhelming and could be seperated into more less complex figures.

Author Response

Reviewer #3 (Remarks to the Author):

The paper is presented in a professional way with no need (at least to my impression) to change anything. Only the figures are a little overwhelming and could be seperated into more less complex figures.

Response: Thank you for your suggestion. We have separated the figures into partitions to make it easier for readers to understand.

Reviewer 4 Report

This article presents a state of the art on electronic fibers. The authors first present the type of fiber that exists in electronics, then they present the different types of electronic fibers and their roles. The state of the art is very rich and well explained.

The article itself is well structured, understandable and makes you want to go to the end. The end of the article presents the pros and cons of electronic fibers.

Some points need to be corrected:

- It is a shame to see the figures at the end of the article. You have to move around in the article each time, which makes it difficult to read.

- Figure 8 is missing. I think to write figure 7 instead of figure 8.

Author Response

Reviewer #4 (Remarks to the Author):

This article presents a state of the art on electronic fibers. The authors first present the type of fiber that exists in electronics, then they present the different types of electronic fibers and their roles. The state of the art is very rich and well explained.

The article itself is well structured, understandable and makes you want to go to the end. The end of the article presents the pros and cons of electronic fibers.

Some points need to be corrected:

- It is a shame to see the figures at the end of the article. You have to move around in the article each time, which makes it difficult to read.

Response: We appreciate the reviewer’s comment. We have inserted figures in the manuscript to make it easier for the readers to follow.  

- Figure 8 is missing. I think to write figure 7 instead of figure 8.

Response: Thank you for helping us catch this mistake. We have made the correction accordingly.

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

In the revised version, the author well addressed all my concerns and suggestions. I don't have further comments.