The Impact of COVID on Lower-Limb Exoskeleton Robotic System Patents—A Review

Abstract

In recent decades, the field of physical rehabilitation, with the help of robotic systems that aid the population of any age with locomotor difficulties, has been evolving rapidly. Several robotic exoskeleton systems of the lower limbs have been proposed in the patent literature and some are even commercially available. Given the above, we are asking ourselves at the end of the COVID-19 pandemic: how much has this pandemic affected both the publication of patents and the application of new ones? How has new patents’ publication volume or application in robotic exoskeleton systems changed? We hypothesize that this pandemic has caused a reduction in the volume of new applications and possibly publications. We compare pandemic analysis and the last decade’s analysis to answer these questions. In this study, we used a set of statistical tests to see if there were any statistically significant changes. Our results show that the pandemic had at least one effect on applying for new patents based on the information analyzed from the three databases examined.

1. Introduction

According to the literature, exoskeleton systems can be classified into two broad categories: medical and non-medical systems, depending on the field of applicability. Medical ones include the exoskeleton systems used for rehabilitation, compensation, paraplegics, and amputees. In contrast, the type of non-medical ones consists of those used in the army (help soldiers transport heavy equipment on rough roads, improving mobility), rescue operations (rescuers can use it to transport supplies or firefighters can use it to transport firefighting equipment), construction (workers can use it to transport construction materials), and support (for healthy older adults). Although the study of the exoskeleton of the lower limbs came from the military, in recent years, the medical field has become a priority. In the following, we will focus on the systems of the exoskeletons of the lower limbs mainly, and only the patents of the exoskeletons that treat the whole leg or certain parts of the lower limb are considered. Exoskeletal patents involving the upper body, although vital in themselves, do not significantly contribute to mobility and are therefore omitted from this study.

The oldest exoskeleton patent was probably registered by Nicholas Yagn from Russia in 1890 [1] under the name “Apparatus for facilitating walking, running and jumping” (Figure 1a). As it stands in the original request, this patent aims to increase the efficiency of walking, running, and jumping, thus reducing the inherent fatigue that arises as a result of these actions. Such a “device”, which acts parallel with the human body to aid human locomotion, is now called the exoskeleton and can be considered a starting point for modern exoskeleton systems [2,3].

Exoskeleton lower-limb rehabilitation robots constitute a significant class of robotic rehabilitation systems. Rehabilitation of the lower limbs with the help of robotic exoskeletons appeared over 40 years ago as an alternative to conventional manual gait training [4,5]. These exoskeletal systems connect to the human body in a portable way. Compared to traditional therapy, walking rehabilitation using a robotic exoskeletal system can provide highly controlled training (being able to control the movement of all joints in the training and recovery process), repetitive and intensive [6], and can reduce the physical load on the therapist and provide accurate and fast progress of patients [7,8]. Among the latest patents applied for and published in 2021 (according to the Google Patents platform), it is registered in South Korea. It is entitled “Lower extremity exoskeleton robotic device” (Figure 1b). The patent application states that the present invention relates to a robot device with a lower exoskeleton used for rehabilitation exercises. The exoskeleton robotic system is a device mainly used for rehabilitation by supporting the muscular strength of the wearer when the lower extremities are paralyzed by accident or when the muscular strength of the lower extremities is insufficient due to old age. This device can also be used for industrial or military purposes, such as running [9].

Figure 1. (a) US420179—Apparatus for facilitating walking, running and jumping (see the reference [1]); (b) KR102292983B1—Lower extremity exoskeleton robotic device (see the reference [9]).

Several revisions have emerged over the last decade that address various aspects of lower extremity rehabilitation and support devices. For example, in 2013, Chen et al. [4] focused on robotic lower extremity care exoskeletons used in rehabilitation therapy. In 2015, Yan et al. [10] presented a comprehensive analysis of all lower-limb exoskeletons developed after the 1990s; all devices analyzed were classified based on four criteria: mechanical structure, robot control system, user validation, and sensory devices used. Moreover, in 2015, Meng et al. [11] analyzed the recent evolution of control mechanisms and strategies for robotic lower-limb rehabilitation devices. Then, in 2016, Rupal et al. [12] conducted a review of exoskeleton robots’ construction and technological features for existing lower extremities, classifying them based on amplifying and rehabilitating human power into commercial or prototype versions. Moreover, in 2016, Chen et al. [13] described the evolution of the exoskeletons of the lower limbs in terms of their structure, the control algorithms used, the detection technology to determine the wearer’s intention to move, and the detection technology, the remaining challenges in this area. The walking rehabilitation exoskeletons presented in this review were classified as treadmill and ground training/assistance exoskeletons. Then, Shi et al. [14] published a comprehensive study in 2019 summarising the current state of exoskeleton robots for lower limbs, focusing on human gait analysis and the design of the drive system and control of these devices. Moreover, in 2019, Sanchez-Villamañan et al. [15] analyzed 52 wearable exoskeletons of the lower limbs in their review, focusing on three main aspects of compliance: drive, structure, and interface attachment components. The authors highlighted the disadvantages and advantages of different solutions and suggested several promising lines of research. In 2021, Koch and Font-Llagunes [16] conducted a review in which the primary purpose was to provide a comprehensive overview of the technological status of exosuits and the clinical results obtained when applied to users with reduced mobility based on 19 studies identified by the authors as relevant. Finally, in March 2022, Kian et al. [17] published a study that provides a comprehensive review of how portable sensor technology has contributed to the activation and control of motorized ankle exoskeletons developed over the past two decades. The authors also investigated the control schemes and operating principles used in the revised motorised ankle exoskeletons and their interaction with the integrated sensor systems. Other reviews have focused on reviewing the technological aspects of exoskeletons from a general perspective [2], while others have concentrated on bipedal locomotion [18,19] or designing specific joints [20]. This review provides an overview of robotic lower-limb exoskeletal systems for rehabilitation that are intended primarily for use by people with gait disorders.

Compared to other studies, we set out to analyze the effect of the COVID-19 pandemic on the publication and application of new patents. According to the World Health Organization, the year 2020 began with the extremely rapid spread of the COVID-19 pandemic and, by 2022, has already reached multiple peaks. This pandemic has affected almost every aspect of life, from industry, economics, and tourism to politics, arts, sports, and in particular health, and yet there has been a global union and effort, especially from the scientific research community, to find ways to deal with it. As such, the patterns of innovative research have also been severely affected by this crisis. Therefore, this systematic review was conducted to answer the following questions: (1) how much has this pandemic affected the publication of patents and the application of new ones? (2) how has new patents’ publication volume or application in robotic exoskeleton systems changed? According to our literature analysis, scientometric analysis has not been performed on research involving robotic exoskeleton patents for lower limbs. Thus, our study is the first evaluation analysis of this field of research using this method. We aim to provide an objective picture of the development of science and the productivity of researchers, as well as to evaluate the topicality of this field of research on the following aspects: (1) a historical map of the subject; (2) a ranking of countries in terms of patent application/publication; (3) the distribution between exoskeletons dealing with the whole of the respective lower system, which deals in part with segments; (4) the time elapsed between the filing and publication of the patent; (5) type of exoskeleton structure: rigid or suit, and mode of wearing: portable or non-portable; (6) patents applied/published during the COVID-19 pandemic. We hope that this study could provide a guide for researchers when they want to file a new patent on robotic exoskeleton rehabilitation for lower limbs, and, at the same time, encourage them in the sense that whenever a situation arises—a crisis (even worldwide) or any impediment of any kind—solutions will be found to help continue their research work. Although work information (patents) collected from public platforms are known and can be accessed by the general public, this paper seeks to generate debate focused on improving current systems and also on how to cover the shortcomings of other identifiable solutions.

2. Review Methodology

2.1. Search Strategy

2.1.1. Inclusion Criteria

All patterns must be:

• Filter 1: published in or translated to English and directly related to rehabilitation of lower-limb exoskeletons robot systems.
• Filter 2: related to the International Patent Classification (IPC) A61H3/00—appliances for aiding patients or disabled persons to walk about; A61F 5/0102—orthopedic devices for correcting deformities of, or supporting, limbs; A61F 5/0106—for the knees, A61F 5/0111—for the feet or ankles.
• Filter 3: describing the design, manufacturing method, and control of an exoskeleton.
• Filter 4: able to be registered in any patent office in any country.
• Filter 5: granted.
• Filter 6: in the COVID-19 pandemic period 12 March 2020–12 March 2022.

2.1.2. Exclusion Criteria

All patterns must not be:

• Filter 7: patent application or limited patent.
• Filter 8: inactive, discontinued or pending legal status.
• Filter 9: related to upper rehabilitation limb (hand or arm) exoskeletons robot systems.
• Filter 10: published in a non-English language and those whose translations to English were very inadequate.
• Filter 11: with an application date before 2012.

2.1.3. Information Databases and Search Methodology

We considered that portable exoskeletons are all those that have a rigid external structure, but also soft exoskeletons or exosuits were included in the present study. Exoskeletons that have used bodyweight support or a treadmill have been excluded to focus only on patents with the effect of wearable technology.

We searched for pattern publications in three online databases: Google Patents, PatentScope, and Lens, from 1 March 2012 until 31 March 2022, using the following search terms: (exoskeleton) AND (robot) AND (walk OR gait) AND ((leg OR lower) AND (limb OR extremity)) AND (rehabilitation).

With the above keywords and filters: 1, 2, 4, and 9, we initially retrieved 1021 patents on Google Patents, 128 patents on PatentScope and 161 patents on Lens. After applying filters 5, 7, and 8, we get the following: 281 patents on Google Patents, 128 patents on PatentScope, and 74 patents on Lens.

An example of the application of the search methodology presented above can be seen in Figure 2 for the Lens platform. Initially, we obtained 161 patents that fulfilled the respective filters: of which 84 appear as patent applications, and the remaining 77 are published patents. Moreover, out of the 161 patents, 120 complied with the requirement of filter 8. After applying filters 5 and 7, we obtained a number of 74 patents. Further, using filters 6 and 12, we get 74 patents. The numerical distribution of these patents by year of publication and by inventors can be seen in Figure 2.

Figure 2. (a) Publications in COVID-19 pandemic period—highlight a selection to filter 6; (b) Inventors—patents count.

2.2. Data Collection

The data obtained from the queries of the three patent platforms are presented in the tables in Appendix A (Table A1, Table A2 and Table A3). Moreover, in the tables in Appendix A, a classification of the exoskeletons was made according to the area of the lower limb that treats it (in whole or part), the type of rigid or suit structure and the portability mode: portable, portable with wheels (which also contain a set of auxiliary wheels for locomotion) and non-portable (which are fixed and can only be used in the spaces where they were placed).

2.3. Analysis Method

We used both a short-term analysis technique, focusing on the pandemic period 13 March 2020–13 March 2022, and an analysis technique in the longer term by which we compared the publication patterns of the last decade (2012–2022). Our study used a set of statistical tests to find statistically significant changes. These tests were performed both short-term and longitudinally on each of the three platforms, Google Patents, PatentScope, and Lens. At the short-term level, these tests indicate whether there are statistically significant differences when comparing the number of patents applied with those published. At the longitudinal level, these tests show whether there are statistically significant differences when comparing patents published before the pandemic with those published during the pandemic.

3. Results

To answer the two questions that were the main objectives (Section 1), we used the method of analysis presented in Section 2.3. Following these tests, we obtained the following results presented in the subsections below.

3.1. Google Patents Platform

In the first analysis of the data collected, one can see a particular concern for the development of exoskeletons of Asian researchers. We studied the applications for granting patents worldwide aimed at exoskeletons. We observed that out of 281 published patents (for the period 2012–2022), researchers from Asia applied for a percentage of 70% of them. We can see these data in Table 1 and Figure 3, respectively.

Table 1. The number of application patents by region.

Regions	Number of Application Patents
Europe	27
Asia	197
SUA+Canada	57
Total	281

Figure 3. Percentage distribution by region after applying filters 5, 7 and 8.

The distribution of these requests, divided by country, reveals, and reinforces the fact that there is a concern in finding the best and most refined solutions to the problems that exoskeletons can solve. Furthermore, Chinese researchers are very active, and an extraordinary number of applications support this. Our statements are reinforced by the data in Table 2 and the graphs in Figure 3.

Table 2. The number of application patents by country.

Country Code	Number of Application Patents
CA	3
CN	129
DE	1
ES	16
EP	10
JP	13
KR	50
RU	4
TW	1
US	54

Once we have established the areas of interest, we can move on to data analysis. An important aspect is the date on which the patent applications were filed. The period analyzed in this study is from the year beginning 2005. It seems a timid beginning for what this field can offer today. Still, the researchers of a US team started with gait rehabilitation methods and apparatuses, the essential operation for the development of new techniques and technologies. It was a timid start because the patent was validated after nine years. From Table 3, it can be easily seen that when new roads are opened, a period of adaptation and understanding of the proposed new techniques and technologies is needed. From here, a series of waiting for the results appears. From our study, the period in which nothing was published is quite long (applications submitted in the period 2005–2011 began to be approved only in 2012), strengthening the abovementioned beliefs.

Table 3. The number of patent applications and publications distributed per year.

Year	Application Date	Publication Date
2005	1	0
2006	1	0
2007	1	0
2008	2	0
2009	9	0
2010	2	0
2011	2	0
2012	6	3
2013	17	5
2014	16	10
2015	23	9
2016	59	9
2017	42	22
2018	51	40
2019	34	48
2020	12	65
2021	4	58
2022	0	13

What we found earlier entitles us to refine our study further, and we will take for analysis the last decade, i.e., the period 2012–2022. In 2012, there were more patent applications in North America and Asia.

We now consider only patent applications. At the beginning of the analyzed period, a typical trajectory of things can be observed in Table 3. We can say that the ascending trend was set in terms of research in exoskeletons and filing patent applications. However, we see that starting in 2020, the presence of the pandemic is starting to make itself felt. For example, if in 2018, 51 applications were submitted, and in 2019 they decreased to 34 (i.e., the applications decreased by more than 30%), then in 2020 and 2021 they were likely to be drastically reduced. One of the ideas that emerges from the analysis of the above data would be the one that affected entire areas during the pandemic, namely the limitation of the interaction between the members of the research teams.

The analyzed phenomenon has two components (the patent filing component and the one for their approval); the second one must be investigated. If we examine the above, we can conclude that the pandemic was a disaster on all levels, but there is still a positive aspect. Analyzing Table 3 and the data collected on granting patents, we can observe an increasing trend even during the pandemic. We can say that we tried to help put into practice as many scientific ideas as possible used by all humanity during this period.

Another interesting issue is the problem that these exoskeletons deal with of exoskeletons. Here are two approaches:

• − Treatment of the entire lower system
• − Partial treatment of the lower system (its different subsystems).

During the analysis period (2012–2022), out of the 264 patents applied in the Google Patents platform, 82% treated the entire lower system, and another part focused on different subsystems. This aspect can also be seen in Figure 4.

Figure 4. Distribution of patents by design (Complete Exoskeleton versus Exoskeleton Subsystems).

Another aspect can be observed by analyzing Table 4 and Table 5, namely that the pandemic, in a way, prevented the development of things. Until 2018, we follow an increasing trend in the analysis and implementation of complete exoskeletons and the performance and improvement of research in subsystems. From 2019 we can see, unfortunately, a downward trend. This trend is seen to have affected subsystem research more strongly. From the analyzed patents, the research teams focused on updating entire exoskeleton structures to help patients move in conditions where they could no longer move to specialized centers.

Table 4. Distribution by year of the number of patents according to the time elapsed between application and publication conforms with the Google Patents platform.

Application Date	The Time Elapsed between the Application and Publication of the Patent		Number of PExo_t	Number of PExo_p
	Minimum Period	Maximum Period
2012	1 year	5 years	5	1
2013	1 year	7 years	15	2
2014	1 year	7 years	11	5
2015	2 years	7 years	20	3
2016	1 year	5 years	50	9
2017	1 year	5 years	32	10
2018	1 year	4 years	41	8
2019	1 year	3 years	29	4
2020	4 months	2 years	9	5
2021	7 months	1 year	4	1

Table 5. Distribution of patents by year of publication.

Year	PExo_c.t	PExo_c.p
2012	3	0
2013	2	3
2014	9	1
2015	9	0
2016	5	4
2017	19	2
2018	34	6
2019	37	10
2020	55	11
2021	48	11
2022	11	2

Regarding publishing patents, we can say that an increasing trend is observed, as shown in Table 4. The data analysis makes us say that this trend was ensured by the conditions imposed by the appearance of the COVID-19 pandemic.

Furthermore, we will resume a previously mentioned aspect, namely that the research, during the pandemic, was directed towards ensuring the movement of patients and, therefore, this research was focused on the entire lower system and not only on its subsystems. It is also easy to see that more patents deal with the total lower exoskeleton than those dealing with the exoskeleton that treats the same leg parts.

The subject of interest is the time interval between the date of application of a patent and the date of its publication. The patents analyzed by us in this platform reveal a fascinating fact. During the pandemic, the time elapsed between the moment of application for a patent and the date when it was published was reduced. Therefore, we can say that more attention has been paid to these patents to implement the obtained results faster.

Further, in Figure 5, you can see the numerical distribution of patent types based on the year of publication. Figure 5 shows two peaks of a substantial increase in the number of patents published on PExoRP in 2018 (32 patents) and 2020 (48 patents). The number of patents published on PExoRNP follows a growth curve with the maximum growth peak in 2021 (12 patents). Patents published on PExoPR have gained more interest since 2019. There has also been an interest in PEoxS since 2013 (one patent) continuing to grow timidly in 2021 (three patents). We can say that patents published on PEoxRP, compared to other types, predominate throughout the period.

Figure 5. Distribution by year of the number of published patents according to the type of structure and portable mode.

3.2. PatentScope Platform

As we did in the previous case, we analyzed the number of applications and the number of patent publications on this platform. The distribution by region according to the year of application of the patent after the use of the filters 5 and 7 can be seen in Figure 6. The highest percentage of patent applications is registered in South America.

Figure 6. Distribution of patent applications by region after applying filters 5 and 7.

As can be seen from Table 6, the period in which we find information is longer. It includes requests since the early 2000s. As in the case of the analysis in the previous subsection, due to the minimal number of applications/publications, we can conclude that the valuable research period can be considered as starting with the year 2012. Hence, in this case, the data distribution confirms that the period in which we did the analysis is correct and fair.

Table 6. The number of patent applications and publications distributed per year.

Year	Application Date	Publication Date
2000	3	0
2001	0	2
2002	0	0
2003	1	1
2004	0	1
2005	1	0
2006	2	3
2007	0	0
2008	6	3
2009	4	1
2010	0	3
2011	0	2
2012	4	1
2013	16	7
2014	12	6
2015	15	13
2016	14	21
2017	20	10
2018	10	15
2019	7	14
2020	5	9
2021	6	16
2022	0	0

Going further with the data analysis, for the period considered in our study to be the reference period, we find some ideas previously stated in Section 3.1. In Figure 7, we can see the direction of declining patent applications as the pandemic begins. In terms of patent approval, an upward trend can be seen. Following these findings, we maintain the idea stated at the beginning of the study, namely that the pandemic negatively affected the research teams and their results. However, we can also say that the publishing process has shown an upward trend.

Figure 7. Distribution of patents in the period 2012–2022.

From 2012 to 2022, 74% treated the total lower system, and 26% focused on different subsystems of the lower limb. This aspect can also be seen in Figure 8.

Figure 8. Distribution of patents in the period 2012–2022.

Next, for a more in-depth study, we looked at the problem that these exoskeletons treat. We found that most research that debates and applies issues of the entire lower patient system has been preserved, as shown in Figure 9 and Figure 10.

Figure 9. Distribution of patents by year of application and the problem that these exoskeletons deal with.

Figure 10. Distribution of patents by year of publication and the problem that these exoskeletons deal with.

As we did in the case of the analysis of the Google Patents Platform, we also determined for this platform the time intervals between the date of filing the patent and the date of its publication. The results obtained can be seen in Table 7 It is also observed that during the COVID-19 pandemic, the maximum interval decreased.

Table 7. Distribution by year of the number of patents according to the time elapsed between application and publication conforms with the PatentScope platform.

Application Date	The Time Elapsed between the Application and Publication of the Patent		Number of PExo_t	Number of PExo_p
	Minimum Period	Maximum Period
2012	1 year	2 years	4	0
2013	7 months	8 years	15	1
2014	7 months	7 years	12	0
2015	8 months	3 years	9	5
2016	6 months	5 years	7	8
2017	6 months	4 years	11	9
2018	4 months	2 years	9	1
2019	6 months	2 years	6	1
2020	6 months	1 year	3	2
2021	7 months	10 months	5	1

Figure 11 shows the following: a fluctuation in the number of patents published on PExoRP, in the sense that their number increased significantly in 2016, decreased in 2017, increased in 2018, and then fell and increased again in 2021. As for the number of patents published on PExoRNP, it seems to keep the same trend of increase and decrease every 2 years (+/− 1) until 2018, and then there will be a more considerable difference in the period 2019–2020 (+3), and 2021–2022 (−2). Patents published on PExoPR gain interest only in 2019 and then decrease. There is also an interest in PEoxS since 2015, continuing with growth peaks in 2019 and 2021. Overall, we can say that patents published on PEoxRP predominate throughout the period compared to other types.

Figure 11. Distribution by year of the number of published patents according to the type of structure and portable mode.

3.3. Lens Platform

Our analysis on this platform is presented in Section 2.1.3 and presented in Figure 12. However, due to the small number of patents obtained because of the consequences of filter use, we consider it unnecessary to detail further. Here, it should be mentioned that no patents have been found on this platform with the application date being 2020–2022 and complying with the filtering criteria considered.

Figure 12. Distribution of patents by year of publication and the problem that these exoskeletons deal with.

According to Figure 12, most published patents dealt with the total foot.

In Figure 13, you can see the numerical distribution of patent types based on the year of publication. For example, according to Figure 13, there is a decrease in published patents. Their distribution by structure and applicability is as follows: in 2020, eight PExoRP, two PExoRP and one PExoS; in 2021, five PExoRP and one PExoRP, and in 2022 it is completely absent.

Figure 13. Distribution of patents by year of publication, the type of structure, and portable mode.

4. Discussion

Lower-limb exoskeletal robotic systems integrate advanced mechanical structures, materials, electronics, bionics, control, and even artificial intelligence. In the last decade, the progress in their development has been remarkable. Significant improvements have been made in performance and design. This thing is also clear from the reviews that have been written on this topic. Over time, several studies have looked at the exoskeletons of the lower limbs for rehabilitation. Some of these reviews have focused on reviewing general aspects of exoskeleton technology [2,20,21,22,23]; others have focused on more specific issues, such as control strategies [19,24] or joint design [25]. In [20], Meda-Gutiérrez and the team aim to identify state of the art medical device designs, based on an analysis of patents and literature. Although they encountered some difficulties in processing records due to a lack of filters and standardization of names (discrepancies appearing between search engines), the conclusion obtained from the study reflects a tendency to use the mechanical design of exoskeletons based on rigid structures, joints, and elements that provide strength for the movement of the system.

Based on our research in the literature at the time of this study, there have been no reviews of the COVID-19 pandemic patent study results. The only review [26] found in the literature studied the influence of the COVID-19 pandemic on publishing research articles. In this paper, Aviv-Reuven and Rosenfeld analyzed changes in biomedical publication patterns due to the pandemic.

4.1. The Context of the Main Objective Analysis

The COVID-19 pandemic posed an unprecedented challenge to humanity and science. As a result of the new outbreaks of Coronavirus, a state of emergency was declared in almost all countries on 13 March 2020. At the same time, all national institutions closed their activities with the public, with employees being forced to work from home through video conferencing, telephone, or online platforms. This has also happened with national and international patent or trademark registration offices. Moreover, starting on 13 March, these offices announced some different forms of exemption available to patent and trademark applicants. These exemption forms can be divided into two broad categories: term extensions and tax exemptions. For example, in the US, extensions were not granted automatically but were conditional on the actual existence of the COVID-19 outbreak. In addition, for an extension to be valid, the party requesting the exemption had to submit a statement that the delay in filing or payment was due to the COVID-19 outbreak. The applicant also had to be a micro or small institution that was in the process of processing or paying pre-examination maintenance fees.

4.2. General Discussion on the Results of the Analysis of the Patent Platforms

A pertinent observation, we would say, would be that the pre-pandemic period was a perfect time for researchers/research teams. They have been able to develop different relationships and have been able to carry out their activity without limitations. Therefore, the results obtained have led to many patent applications. However, this large volume of applications probably hindered the approval process and hence the time differences between the application and approval periods (a statement from our study). With the onset of the COVID-19 pandemic, research teams have been limited in their interactions physically (at least) and hence there have been fewer patent applications. However, this was a “plus” (if we can say so) for the patent application evaluation teams having, on the one hand, a small number of applications to analyze and sufficiently thorough time. Another aspect that we noticed was that during the pandemic, the difference between the date of the filing of the patent application and its publication decreased a lot. Despite introducing tax exemptions, the number of patents granted is not high due to the introduction of term extensions for regions with a COVID-19 outbreak.

If we analyze the data in Table 7 versus the data in Table 6 that deal with the same issue, we can see the effects of processing a large volume of data. The publication period on the PatentScope platform is significantly shorter in most cases; this may be due to prioritizing patent applications.

Another predominant general idea that emerged from the analysis of the mentioned platforms is that the number of patents published during the entire analyzed period (as well as during the pandemic) on rigid and portable structured exoskeletons is much higher than the rest of the types. This fact is essential and beneficial in gaining the independence of users from hospital spaces in particular and the physical presence of specialists specialized in recovery, especially during the pandemic.

Another interesting aspect that emerges from the Google Patents platform is that although the COVID-19 pandemic had as its starting point in China, the most patent applications have been filed in this country. On the other hand, according to data extracted from the PatentScope platform, the country with the most patent applications during the pandemic was the US. According to Lens platform, no patent application has been filed during this period.

Over the last decade, research on real-life exoskeletons has grown significantly; this can be estimated from the number of patents reported in Section 3. The main reason would be that the lifestyle of modern society is constantly growing and developing rapidly, and people always want to stay active, independent, and live a quality life. Portable exoskeleton technology (whether rigid or suitable) is the key to providing individualized mobility recovery solutions for millions of people immobilized from various causes (injuries, trauma, disabilities, or ageing) to continue their desired activities. Despite the above, the technology is in its infancy. There are still factors that are not/are less addressed about obtaining a fully efficient exoskeleton, in terms of performance and cost.

To see the chronological evolution of the development of this technology, we arbitrarily analyzed some of the patents on the PatentScope platform, selecting the patents published at the beginning, middle, and end of the analyzed period.

The first patents published since 2013, as presented, are designed to reinforce joints. After that, the patents designed for this specific domain gradually became more complex and complementary. From this point forward, several improvements regarding gait rehabilitation have been made, focusing on enhancing previous studies and patents. For example, suppose the first patent focused on knee joint reinforcement. In that case, the following patent is designed to adjust pelvic movement with the same objective: gait training to help people have a more natural walk movement.

The first patent focuses on knee joint reinforcement, followed by concepts designed to adjust pelvic movement with the same objective: gait training to help people have a more natural walk movement.

The Active Knee Rehabilitation Orthotic System (ANdROS) [27] is intended to assist everyday tasks rather than gait retraining. The invention describes wearable and portable assistive equipment for gait neuro-rehabilitation that addresses primary gait abnormalities by reinforcing around the knee joint a preferred gait pattern via correcting torque fields applied. The patent is a wearable assistive device for gait rehabilitation in patients who have lost motor control due to a neurological condition, such as a stroke.

A motorized footplate with force feedback and an exoskeleton to regulate pelvic movement during gait training [28] makes this innovation perfect for implementing ecologically sound procedures that accurately simulate real-life settings and maximize motor improvements in stroke patients. In addition, to optimize rehabilitation effects, an active pelvic prosthesis with a non-treadmill pedal system is necessary.

The following published patents were born from ideas intended to improve mobility further. Therefore, exosuit-based systems with actuators were developed to provide active support for the ankle. Fixed in three points on the leg and created from a lightweight material, it shows comfort for the user and improves torque.

This patent [29] discusses three-point contact with the leg and a series of elastic elements for improved torque control. Apart from their small size (0.88 kg), these devices can monitor joint angle and torque. A combination of proportional feedback and suspension injection is employed during walking trials to modulate torque. The closed-loop torque control of the exoskeleton devices was evaluated by controlling 50 N-m and 20 N-m linear chirps in intended torque while using exoskeletons and measuring bandwidths more significant than 16 Hz and 21 Hz, respectively. There was a maximum torque of 120 N-m and a tracking error of 2.0 N-m. These testbeds demonstrate how exoskeletons may be employed to study a variety of control and support paradigms rapidly. The document provides an exoskeleton system that comprises a cable, a lever attached to the cable, a frame having a strut directing the cable to the lever, and a motor coupled to the cable and adapted to cause the cable to deliver torque around the rotating joint.

In addition to previous innovations, it was considered the proper time to introduce smart materials that will block or even actuate joints to expand the possibilities of implementation for wearable robotic devices. However, smart material-based exoskeleton publications are found in a minimal number and provide a substantial implementation complexity; therefore, such a type of patent is to be considered.

The work [30] aims to offer an exoskeletal device with semi-active joints that can lower articular tensions caused by limb weight, reduce physical labor load, and promote physical workouts for motor ability rehabilitation following cerebral or orthopedic accidents. In addition, other objectives are realized via a mechanism, namely, an exoskeleton with at minimum two links joined by an electro- or magneto-rheological fluid joint.

Further improvements of the exoskeletons are being developed concerning the user’s biological skeleton and flexible materials to deliver improved customized mobility according to the user’s needs.

With a soft exosuit system and an actuator system, the concept [31] provides active support for natural actions, such as normal leg movement. The soft exosuit uses flexible materials and actuators and depends on the user’s biological skeleton to aid in applying forces and transferring loads, unlike previous art-rigid exoskeletons.

It has lower mechanical impedance and kinematic constraints than rigid exoskeletons and does not considerably limit or restrict the user’s flexibility. Furthermore, by adding regulated energy impulses rather than the direct command of limb position(s), this system can help improve locomotion and minimize the metabolic cost of movement without limiting mobility.

Other powered devices and control methods [32] can greatly aid ambulation, especially in youngsters with cerebral palsy (CP). Less complex knee extension help was tested in the stance and late swing phase. Compared to the baseline condition, the tested gadget reduced crouching. Moreover, it considerably changed lower extremity kinematics, increasing maximal knee extension in both the left and right legs during the stance phase.

4.3. Limitations of This Study

The main limitation of this study is that these platforms do not declare patent applications unless they have been approved and published. Thus, for the period of the COVID-19 pandemic, the analysis of the number of patent applications was performed only on the data extracted from these platforms. However, the primary purpose of this review was to provide a comprehensive overview of the effort to innovate the lower-limb exoskeletons even during this pandemic.

5. Conclusions

This study looked at how the COVID-19 pandemic affected the publication and application of new patents based on data extracted from three platforms: Google Patents, PatentScope and Lens. We used two types of analysis to address our research questions: short-term analysis (pandemic period 2020–2022) and longer-term analysis (2012–2022). Following the analysis made, the hypothesis issued by us at the beginning of the study that the pandemic has caused a reduction in the volume of new applications and, possibly, the publications, is valid. However, only on the data extracted from these platforms did the number of new patent applications drop dramatically. The number of published patents has been much higher than the number of applications. Therefore, we can say that the COVID-19 pandemic has negatively affected the number of applications for new patents in the field of exoskeletal robotic systems of the lower limbs and in a positive sense (at least kept the trend of recent years) affected the number of patents published (granted).

The main challenge of the paper was to conduct an in-depth analysis of the systems and current patents to summarize their need for development in terms of the benefits of exoskeletal rehabilitation technology. In addition, through its scientometric analysis of patents, this paper wanted to be state of the art and offer/act as a reference point for scientists and researchers. Who wants to develop systems to meet the needs of millions of people with locomotor problems?

In the future, we want to carry out new analysis in which we will use delimiters related to the materials of the components and the actuation and control systems of the exoskeleton robots. Moreover, following the research conducted in the literature, there is a need to perform a qualitative comparative study on the ease of using these robotic exoskeleton systems by patients. The lack of such a study could lead to some biases, especially related to the clinical efficacy of lower-limb exoskeletons for rehabilitation.

Another interesting study that we would like to do is analysis, such as the one made in this review, but post-pandemic.