Biomimetic-Hydrogel-Based Electronic Skin: An Overview Based on Patenting Activities and the Market ^†

Abstract

Electronic skin (e-skin) is an innovative technology characterized by its flexibility, stretchability, and self-healing properties, designed to biomimic the functionalities of human or animal skin. This technology is well-suited for applications in robotics, prosthetics, and health monitoring since it can sense a wide range of tactile signals, such as humidity, pressure, temperature, and stress. Developing e-skin for wearable devices faces several challenges. One major challenge is the need for soft and stretchable electronic materials, as conventional materials are brittle. Furthermore, the development of skin-like hydrogel devices for wearable electronics faces challenges such as limited functionality, low ambient stability, poor surface adhesion, and relatively high power consumption. Innovation in this area has the potential to pay off. Organizations that invest in and develop innovative e-skin technologies based on biomimetic hydrogels can secure intellectual property rights through patents. This study is dedicated to reviewing the state of the art by presenting what has been patented concerning biomimetic-hydrogel-based e-skin. At the end, a section presents relevant patents to demonstrate the innovation and formulation of such hydrogels as biomimetic materials for e-skin applications. A market overview of e-skins is also presented. This contextualizes the significance of research in biomimetic-hydrogel-based e-skins within the broader commercial landscape.

1. Introduction

Recent advancements in electronic skin (e-skin) have revolutionized the field by enabling the development of monolithic versions that integrate nerve-like electronics, allowing for comprehensive sensory perception using only skin-like materials [1]. These e-skins mimic natural skin properties, providing feedback on pressure and touch, thus enhancing prosthetics and offering users a more natural and interactive experience [2]. The progress in e-skins has also focused on achieving multimodal sensing capabilities, combining different sensory inputs to improve perceptual accuracy and sensitivity [3].

The development of e-skins with high flexibility and stretchability is essential for conforming to different surfaces, particularly the human body, enabling comfortable wear and robust signal acquisition [4,5]. Integrating self-healing properties into e-skin technologies enhances their durability and longevity by allowing the material to repair itself when damaged [6]. Research has focused on creating e-skins with tissue-like softness, stretchability, and self-protection against adverse loading events, showcasing the potential for long-term use and reliability [7].

One major challenge is the need for soft and stretchable electronic materials, as conventional materials present limited functionality, low surface adhesion, and relatively high power consumption [8,9]. Among the various materials explored for e-skins, biomimetic hydrogels have emerged as a promising candidate due to their flexibility, stretchability, and ability to mimic the mechanical and sensory properties of natural skin [10].

Biomimetic-hydrogel-based e-skins are innovative materials designed to replicate the properties and functionalities of natural skin. Originating from the concept of biomimetics, these hydrogels are engineered to mimic the elasticity, flexibility, and self-healing capabilities of biological tissues [11]. Hydrogels are superior to other materials in e-skin applications due to their unique combination of softness, stretchability, and high water content, which closely resemble the mechanical properties of natural skin. Additionally, hydrogels can be easily modified to incorporate various sensory functions, such as pressure and temperature sensing, making them ideal candidates for creating electronic skins that can closely replicate the sensory feedback of natural skin [12]. This intrinsic flexibility and biocompatibility make hydrogels highly promising for next-generation e-skin technologies. However, the development of skin-like hydrogel devices introduces additional challenges, such as low ambient stability, due to their sensitivity to environmental conditions [11].

Investing in the development of innovative e-skin technologies based on biomimetic hydrogels can indeed lead to significant payoffs for organizations, potentially securing intellectual property rights through patents. Research has shown advancements in creating e-skins with desirable properties like stretchability, self-healing, antibacterial activities, and stimulus responsiveness [13,14,15].

Research and development are making progress in addressing these challenges, and there have been notable advancements in the field of biomimetic-hydrogel-based e-skin [16]. Despite the growing interest in this area, there has been a lack of comprehensive analysis focusing on the patent landscape surrounding biomimetic-hydrogel-based e-skin technologies [12,17].

This study addresses this gap by conducting a detailed patent analysis to review the state of the art in this field. By analyzing patent data, this research aims to uncover patterns in patenting activities, including when patents are filed, who the key players are, what specific innovations are being protected, and where these patents are being filed [18]. The insights gained from this analysis not only provide a clearer picture of the current technological landscape but also help identify emerging trends and areas of potential innovation in biomimetic-hydrogel-based e-skins. Finally, key parts of this work at the end concern the relevant patents to demonstrate the innovation and formulation of such hydrogels as biomimetic materials for e-skin applications, as well as market statistics in this area. This addition should provide a comprehensive overview of the market, contextualizing the significance of research in biomimetic-hydrogel-based e-skins within the broader commercial landscape.

2. Methodology

Different patent databases, such as the Espacenet, Lens, Patentscope, Google Patents, and USPTO databases, were employed, utilizing diverse sets of keywords and associated terms [19,20,21,22,23]. Searches were carried out based on patent titles, abstracts, and claims to ensure comprehensive coverage and retrieval of relevant information. The searches were filtered regarding patent applications and granted patents (Figure 1). The results concerning biomimetic-hydrogel-based e-skins were then presented with data on publication year, patent applicants, patent classifications, and patent jurisdictions.

In addition to providing control data, the patent search strategy was designed to comprehensively cover all patents in the relevant technical fields. By including broader categories such as “e-skins based on other materials” and “biomimetic hydrogels”, the search captured a wide range of patents that intersect with the specific area of “biomimetic-hydrogel-based e-skins”. This thorough approach ensures that the analysis is representative of the entire technical field, offering a more complete picture of the innovation landscape.

3. Results and Discussion

3.1. Control Data

To better understand the significance and level of interest in the specific area of biomimetic-hydrogel-based e-skins, a comparative analysis using control data from related fields was conducted. This comparison provides a broader context and helps to position biomimetic-hydrogel-based e-skins within the landscape of current research and development activities.

Table 1. Statistics about number of patent documents on different topics.

Topics	Patent Applications	Granted Patents
E-skins	1350	517
Biomimetic hydrogels	320	70
Biomimetic-hydrogel-based e-skins	54	6

resumes statistics about number of patent documents on more general topics (control data) such as “biomimetic hydrogels” and “electronic skins based on other materials” for the sake of comparison.

E-skins are a broader category that includes various materials and technologies that aim to mimic the properties of human skin. The data collected on patent applications and granted patents in this category have 1350 and 517 data points, respectively. Biomimetic hydrogels represent another related field, focused on creating materials that mimic the properties of natural hydrogels found in biological tissues. The data collected on patent applications and granted patents in this field have 320 and 70 data points, respectively. Biomimetic-hydrogel-based e-skins combine the properties of both biomimetic hydrogels and e-skins. This specific area, though narrower, reflects a growing interest, as shown by the following data: 54 patent applications and 6 granted patents.

The data presented above highlight the relative level of interest in biomimetic-hydrogel-based e-skins compared to the more established fields of e-skins and biomimetic hydrogels. While the number of patents in biomimetic-hydrogel-based e-skins is lower, this is consistent with the emerging nature of this interdisciplinary area. The comparative figures provide valuable insight into the current patent landscape and help contextualize the importance and potential of biomimetic-hydrogel-based e-skins.

3.2. Publication Year

In total, 60 patent documents related to biomimetic-hydrogel-based e-skin have been published between 1990 and 2024 (until 7 May). In detail, there are about 54 patent applications and six granted patents. Notably, the zeniths of patent document activity occurred in 2013 and 2021 (Figure 2). The inception of biomimetic-hydrogel-based e-skin patenting can be precisely traced back to the earliest priority date, pinpointing 1988 as the commencement year. This concerns a patent application published in July 1990 related to stabilized microporous materials and hydrogel materials. Through this invention, the inventor Anderson claims a bioelectronic device composed of a skin-like material, such as a soft tissue substitute comprising a stabilized hydrogel material [24].

To confirm how much this area is of interest, the number of journal articles published per year related to biomimetic-hydrogel-based e-skin are displayed in Figure 3. The figure shows a clear trend of increasing interest in this topic, particularly from 2017 onward. This rapid growth in publications suggests that the field of biomimetic-hydrogel-based e-skin has gained significant attention, likely due to advancements in technology and the growing potential applications of e-skin in various fields, such as healthcare, robotics, and wearable devices [17,25]. The sharp rise in publications from 2017 to 2023 indicates a strong and increasing research focus on this topic.

3.3. Patent Applicants

The top three patent applicants in the field of biomimetic-hydrogel-based e-skins were identified, and they can be considered to be organizations: two companies and one university. The company Wearoptimo Pty Ltd. (West End, Queensland, Australia), as a legal entity, is ranked as the first applicant who has recorded seven patent documents. On the other hand, Momentive Performance Materials Inc. (Niskayuna, NY, USA) and Northwestern University (Evanston, IL, USA) are ranked as the co-second applicants, having recorded four patent documents each.

3.4. Patent Classifications

The patent classifications are part of the International Patent Classification (IPC) system, which is used to categorize patents and patent applications based on the technical features of the invention [26]. This system is developed and maintained by the World Intellectual Property Organization (WIPO). It is used to classify patent applications and granted patents based on the technical features of the inventions, facilitating the retrieval and examination of patent documents according to specific technical fields [27].

In this study, each code segment represents a specific aspect or technology within the broader field of medical instruments and methods.

Table 2. Top 5 IPC codes in the field of biomimetic-hydrogel-based e-skin as a function of the patent record.

IPC Code	Field *	Patented Application *	Patent Records
A61B5/00	Medical instruments, devices, or methods for diagnostic purposes.	Includes a wide range of technologies used in medical diagnostics, such as imaging devices, diagnostic testing equipment, and patient monitoring systems.	10
A61B5/145	Measurement of blood characteristics in vivo (inside the body).	Specifically, it focuses on devices and methods for measuring various parameters of blood while it is within a living organism, such as gas concentration and pH levels.	7
A61B5/296	Measurement of pressure in the heart or blood vessels.	Covers instruments and techniques used for measuring pressures within the cardiovascular system, including catheters with pressure sensors and other invasive or non-invasive methods.	6
A61M37/00	Apparatus for introducing media into the body and percutaneous methods.	Encompasses medical devices used to introduce substances into the body, including, but not limited to, infusion devices, injection devices, and devices for percutaneous administration of medications or fluids.	6
A61N1/30	Apparatus for iontophoresis or cataphoresis.	Refers to devices and methods used to introduce ions into body tissues using electric currents (iontophoresis) or passive diffusion (cataphoresis), commonly employed in therapeutic treatments or drug delivery systems.	5

* Fields and patented applications are based on the WIPO IPC Portal [30].

provides patent records in the field of biomimetic-hydrogel-based e-skin as a function of the top 5 IPC codes. These definitions provide a clearer understanding of how each patent classification code relates to specific fields within the field of medical technology and their applications in healthcare and biomedical sciences [28,29].

3.5. Patent Jurisdictions

Figure 4 presents the leading jurisdictions in the field of biomimetic-hydrogel-based e-skin. In summary, the results illustrate the distribution of patents across different patent systems and jurisdictions in this field. Each patent record (%) represents an application or granted patent within its respective jurisdiction or system, reflecting the global and regional strategies of patent protection adopted by inventors and companies [31,32].

As a result, there are 31 international patents filed through the Patent Cooperation Treaty (PCT) system, indicating that these inventions are seeking protection across multiple countries that are signatories to the PCT. It should be noted that the PCT allows applicants to seek patent protection simultaneously in multiple countries by filing a single international patent application. Moreover, the WIPO administers the PCT system, providing a unified procedure for filing and processing international patent applications. Second, there are 26 patents filed in the United States, showing a focus on obtaining exclusive rights to these inventions in the US market or territory. Third, there are two patents filed in China, indicating a smaller number of inventions focused on the Chinese market or seeking protection solely within China. Finally, there is one regional patent filed in Europe, indicating an invention seeking protection across European countries that are signatories to the European Patent Convention (EPC). The EPC system is administered by the European Patent Office (EPO) and allows applicants to obtain patent protection simultaneously in multiple European countries through a single regional patent application.

4. Relevant Patents on Hydrogels as Biomimetic Materials for e-Skin Applications

This section is dedicated to the three relevant patents to demonstrate the innovation and formulation of such hydrogels as biomimetic materials for e-skin applications.

In 2022, two patents concerning e-skins were filed in China. The first invention introduces a high-strength, self-recoverable conductive hydrogel exhibiting dual temperature–pH responsiveness. It was synthesized through a method involving the dissolution and polymerization of two comonomers, an anionic biological macromolecular salt, and cross-linking agents in water. The hydrogel’s formulation supports robust mechanical properties, elasticity, and self-recovery, coupled with adjustable conductivity sensitive to temperature, stretching, and pH variations, offering versatile adhesion properties. These attributes position a hydrogel that is suitable for diverse biomedical applications, including biosensors, wearable e-skins, soft tissue engineering, and controlled drug release systems, underscoring its potential in advanced biomedical technologies [33].

The second invention presents a method for preparing a tendon-imitating double-physical crosslinking conductive hydrogel with exceptional stretchability, toughness, and resistance to swelling. Initially, a single physical crosslinked hydrogel (P-hydrogel) is formulated by mixing sodium chloride, sodium dodecyl sulfate, and acrylamide in water, followed by the addition of functional adenine, acrylic acid, and potassium persulfate, and curing at 60 °C. Subsequently, P-hydrogel is immersed in varying concentrations of ferric cation (Fe³⁺) to form a coordination hydrogel, which is then treated with deionized water to remove excess Fe³⁺, yielding the tendon-imitating double-physical-crosslinking conductive hydrogel (E-hydrogel). This hydrogel’s network structure incorporates hydrophobic association interactions of functionalized adenine and coordination interactions of carboxylic acid with iron ions, endowing it with superior mechanical properties and swelling resistance. The presence of free ions enables high-sensitivity deformation responsiveness, facilitating applications in deformation sensing and information encryption. This novel hydrogel design exhibits outstanding performance in comparison to conventional counterparts, making it promising for applications in motion monitoring, flexible e-skin, wearable equipment, and beyond [34].

One year later, an international patent application describes a multimodal robotic sensing system integrating two printed flexible e-skins. The inventors proposed an e-skin fabrication method comprising coating chemical sensors with flexible gelatin hydrogel. The first skin is applied to a robotic interface, featuring a substrate, electrodes, sensors, and encapsulation. The second skin is applied to a human subject with similar components. These skins communicate wirelessly via a module. Additional claims detail specific applications: the first skin is on a robotic hand and arm; the second is on a human forearm controlling a corresponding robotic arm. Both skins incorporate advanced sensor arrays, such as physicochemical and surface electromyography (sEMG) sensors, which enhance tactile, temperature, and analyte detection capabilities. Machine learning algorithms improve robotic movement by analyzing sensor data. The first skin’s sEMG sensors are used for remote control, decoding human movements to control a robotic arm. The second skin’s physicochemical sensors are employed for threat detection, assessing object properties and activating human subject stimulation if a threat is identified. Additionally, an e-skin fabrication method details the processes for printing and assembling these skins with precise sensor and electrode configurations, including nanoengineered and kirigami structures, thereby enhancing functionality for various applications [35].

5. Market Overview of e-Skins

The global e-skin market has witnessed substantial growth in recent years, indicating rising interest and innovation in wearable technology, healthcare, and robotics. As of 2023, the market was valued at approximately USD 7.14 billion and is projected to reach around USD 22.3 billion by 2030, with a compound annual growth rate of 22.9% during the forecast period [36,37]. This rapid growth is fueled by several factors, including the increasing demand for advanced healthcare monitoring devices, the rise in robotics requiring sophisticated sensory feedback mechanisms, and the expanding consumer electronics market focused on wearable devices [38].

Healthcare is a primary sector driving the demand for e-skins, particularly for applications such as wearable health monitors that track vital signs like heart rate, temperature, and blood pressure. The ability of e-skins to conform to the human body and provide real-time, non-invasive monitoring makes them highly attractive for medical applications [36,39]. Additionally, the robotics industry is experiencing a surge in the use of e-skin technology, which is essential for developing robots with advanced tactile sensing capabilities, enabling them to interact more naturally with their environment and humans [37,40].

North America and the Asia Pacific region are currently leading the e-skin market. These regions benefit from a strong presence of key industry players, substantial research and development investments, and a high adoption rate of new technologies [39,40]. Major companies like 3M (Saint Paul, MN, USA), MC10 (Cambridge, MA, USA), and Xsensio (Lausanne, Switzerland) are at the forefront of e-skin development, focusing on innovations applicable in various fields, including smart wearables, prosthetics, and human–machine interfaces [37,39].

6. Conclusions

The inception of biomimetic-hydrogel-based e-skin patenting can be precisely traced back to the earliest priority date, pinpointing 1988 as the commencement year. Notably, the zenith of patent document activity occurred in 2013 and 2021. Analyses reveal that the United States and China stand out as the most prolific nations in patenting biomimetic-hydrogel-based e-skin. As of the latest data, there have been a total of 54 patent applications and 6 granted patents in this specific area. This reflects a growing interest in biomimetic-hydrogel-based e-skins, which combine the properties of biomimetic hydrogels and electronic skins. These inventions are predominantly designed for use in prostheses, coatings, or chemical sensors and are distinguished by their functional attributes and physical properties. The classification of these patents includes a wide range of technologies used in medical diagnostics, such as imaging devices, diagnostic testing equipment, and patient monitoring systems. Internationally, 31 patents have been filed through the PCT system, indicating that these inventions are seeking protection across multiple countries that are signatories to the PCT. Additionally, 26 patents have been filed in the United States, showing a focus on obtaining exclusive rights in the US market. In China, two patents have been filed, indicating a smaller but notable interest in seeking protection within the Chinese market. The burgeoning market for e-skins underscores the increasing relevance of this technology across multiple industries. As research continues to advance, particularly in areas like biomimetic-hydrogel-based e-skins, the commercial potential of these technologies is expected to grow further, paving the way for new applications and improved integration with everyday technologies. This work, which offers a competitive analysis spanning trends in biomimetic-hydrogel-based e-skin, provides several recommendations aimed at guiding the formulation of innovative research strategies.