A hand‐targeted auxiliary personal protective equipment for intervention of fomite transmission of viruses

Abstract In COVID‐19, fomite transmission has been shown to be a major route for the spreading of the SARS‐CoV‐2 virus due to its ability to remain on surfaces for extended durations. Although glove wearing can mitigate the risk of viral transmission especially on high touch points, it is not prevalent due to concerns on diversion of frontline medical resources, cross‐contamination, social stigma, as well as discomfort and skin reactions derived from prolonged wearing. In this study, we developed FlexiPalm, a hand‐targeted auxiliary personal protective equipment (PPE) against fomite transmission of viruses. FlexiPalm is a unique palmar‐side hand protector designed to be skin‐conforming and transparent, fabricated from medical‐grade polyurethane transparent film material as a base substrate. It serves primarily as a barrier to microbial contamination like conventional gloves, but with augmented comfort and inconspicuousness to encourage a higher public adoption rate. Compared to conventional glove materials, FlexiPalm demonstrated enhanced mechanical durability and breathability, comparable hydrophobicity, and displayed a minimal adsorption of SARS‐CoV‐2 spike protein and virus‐like particles (VLP). Importantly, FlexiPalm was found to bind significantly less viral protein and VLP than artificial human skin, confirming its ability to reduce viral contamination. A pilot study involving participants completing activities of daily living showed a high level of comfort and task completion, illustrating the usability and functionality of FlexiPalm. Moreover, we have demonstrated that surface modification of FlexiPalm with microtextures enables further reduction in viral adsorption, thereby enhancing its functionality. An effective implementation of FlexiPalm will bolster PPE sustainability and lead to a paradigm shift in the global management of COVID‐19 and other infectious diseases in general.


| INTRODUCTION
COVID-19 is a pandemic that has affected more than 550 million people worldwide and caused more than 6 million deaths across the world. 1 Despite diligent measures to control the spread of the SARS-CoV-2 virus, the test positivity rate remains high in the community. While the main route of SARS-CoV-2 transmission is via close contact and aerosols, 2 the extent of fomite transmission through inanimate surfaces also plays an important role. 3 SARS-CoV-2 virus particles have been shown to remain viable for 2 to 3 days on smooth surfaces such as stainless steel, plastic, glass, as well as at lower temperature and humidity. 4,5 The SARS-CoV-2 virion has also been shown to remain stable and contagious for up to 9 hours on human skin. 6 Furthermore, SARS-CoV-2 virus particles can easily be detected on high touch points such as shopping carts and baskets. 7 Hospital wards, both intensive care and general, have also been found to harbor extensive viral contamination, with 56.7% of rooms having at least one environmental surface contaminated with SARS-CoV-2 viruses. 8 High touch surface contamination was found in 66.7% of rooms occupied by patients in the first week of illness, and in 20% for patients beyond the first week of illness. 8 These studies indicate that there is a high possibility of viral transmission and infection through surface contact.
Recent studies have proposed that personal protective equipment (PPE) appropriate for protection against SARS-CoV-2 should not only consist of protective masks but also gloves, to significantly reduce the risk of infection. 9,10 However, glove usage has not been widely practiced in countries across the world, with only a few countries adopting the use of gloves, such as the United States of America (USA), 11 Hong Kong, 12 and Malaysia 13 ; even in these countries the adoption rate is modest. For some, glove usage is discouraged due to the diversion of medical resources from the frontline, as well as complacency and contamination due to improper glove removal. 14 Other reasons that can lead to low adoption rate of gloves include social stigma associated with excessive protection 15 as well as discomfort and skin reactions derived from prolonged wearing of tight-fitting gloves. 16 We also conducted a survey which confirmed that a substantial proportion of participants indeed have these concerns. Hence, this necessitates an alternative form of hand protection, which circumvents these concerns.
Here, we designed FlexiPalms, the first palm-directed hand PPE to protect against fomite transmission of viruses. Previous studies have demonstrated the predominance of palmar hand-to-face and hand-to-mouth contacts as opposed to the dorsal side. 17,18 Separately, the palmar side of the hand has been observed to make more F I G U R E 1 Overview of FlexiPalm properties and design criteria. FlexiPalm (center) is a hand-targeted auxiliary PPE with a unique palmar-side hand protection against fomite transmission of viruses. FlexiPalm is designed to satisfy the following criteria: (1) durable, (2) conformable, (3) waterproof, (4) breathable, (5) comfortable, (6) multiple sizes, (7) ease of application, (8) ease of removal, and (9) low contamination (properties surrounding the FlexiPalm). PPE, personal protective equipment frequent contact with surfaces than the back of the hand. 19 Furthermore, other studies have alluded to the lower usage of the dorsal surface of gloves. 20,21 In view of this, the FlexiPalms are intended to protect the palmar side of the hands, which also reduces material usage and boosts hand PPE sustainability. However, by removing the dorsal side of support, this necessitates an adhesive layer to stick the FlexiPalms to the users' palms directly. Furthermore, there is a need for the following design criteria: (1) good mechanical properties with high elasticity and durability for prolonged usage, (2) hydrophobic surface that is waterproof to reduce aerosol contact with virus particles, (3) high permeability for improved breathability resulting in enhanced comfort, (4) user-friendly design that allows for ease of wearing and removal, and (5) low viral adsorption with minimal chances of contamination ( Figure 1).
To achieve these design criteria, the FlexiPalms were fabricated from a medical-grade polyurethane (PU) transparent film material as a base substrate. 22 This material boasts high water vapor permeability, which prevents moisture buildup and bacterial infections on the skin surface. 23 In addition, the acrylate adhesive minimizes skin damage and can stick to the skin for long durations. 24,25 We benchmarked the PU material used to fabricate the FlexiPalms against other conventional glove materials, including nitrile, latex, and low-density polyethylene (LDPE) to ascertain its suitability to be used for hand protection.
The PU material demonstrated enhanced mechanical durability, superior breathability, and minimal adsorption of SARS-CoV-2 spike protein and virus-like particles (VLP). Importantly, we confirmed Flexi-Palm's ability to reduce viral contamination by showing that it binds significantly less VLP and viral protein than artificial human skin. We also conducted a pilot study to collect user feedback from the execution of tasks while donning the FlexiPalms. Results from our pilot study showed that FlexiPalms display good functionality and attain a high level of receptiveness from the participants as a new form of PPE for hand protection. Furthermore, we conducted a proof-of-concept demonstration of the surface modifiability of FlexiPalm with microtextures, which enabled additional reduction in the adsorption of viral protein and VLP, thereby enhancing its functionality.

| Market survey to gather public perception on hand protection
A survey was conducted to obtain feedback from the general population regarding their view on hand protection during COVID-19 pandemic. A total of 130 participants from 10 different countries including Singapore, USA, China, United Kingdom, Malaysia, India, Indonesia, Sweden, South Korea, and Israel, participated in the survey.
Briefly, we gathered participants' views towards the COVID-19 situation, including their attitude towards the pandemic, how the pandemic has affected their lives, as well as their risks and potential exposure to the SARS-CoV-2 virus. From there, we followed to ask the participants about their frequency of masks and gloves usage, as well as other hygiene routines such as hand washing and usage of sanitizers and disinfectants. We then specifically asked about the participants' perception of glove wearing as a form of protection during the pandemic, including their awareness of the SARS-CoV-2 virus remaining on surfaces for prolonged durations and possible fomite transmission, attitude towards using gloves, concerns with glove usage, as well as receptiveness to adopting a new form of hand PPE (FlexiPalm). This study was conducted following the study protocol approved by the Institutional Review Board of National University of Singapore (NUS-IRB-2020-816). (v) Biomedia latex glove (Biomedia, Singapore), and (vi) LDPE transparent film (The Glad Products Company, USA). The six materials are hereafter referred to as "TGM PU," "OPS PU," "CXG PU," "Nitrile," "Latex,"

| Polymeric materials for benchmarking studies
and "LDPE," respectively. The surface modification of the FlexiPalm was performed by casting TGM PU onto aluminum oxide sandpapers of varying grit sizes (800, 360, and 60 grit) to create the microtextured surface.

| Fabrication and usage of applicator
For ease of donning of the FlexiPalms, we further designed an applicator prototype to allow fast alignment and contouring of FlexiPalms to the users' hands ( Figure S1). The lid with a palm-shaped cut-out as well as the base to contain a memory foam block were 3D-printed by fused deposition modeling (UP BOX, Tiertime, China) using acrylonitrile butadiene styrene as the primary material ( Figure S1A). To don the FlexiPalms, the perforated peelable backing material was removed and pasted onto the lid with careful alignment with the palm-shaped cut-out ( Figure S1B), with the adhesive layer exposed for application ( Figure S1C). The FlexiPalm was pressed through the palm-shaped opening along the perforated line by the user ( Figure S1D). Pressure was exerted onto the FlexiPalm against the memory foam block, which conformed to the user's palm contours. The user's hand was withdrawn from the applicator upon the donning of the FlexiPalm ( Figure S1E).

| Mechanical characterization
Uniaxial tensile tests were conducted to determine the mechanical properties of the materials. The testing protocol was adapted from ASTM D638. The materials were cut into a 6 mm by 115 mm Dog-Bone shape and mounted onto the grippers of a tensile tester (Instron 3345, Instron, MA, USA). The extension rate was set at 300 mm/min and the initial load and displacement were zeroed prior to each measurement. The mechanical parameters of tensile strength, Young's modulus, and elongation at break were derived from the generated stress-strain curves.

| Adhesive strength test
Adhesive strength tests were conducted to measure the amount of force required to peel the three different PU transparent film samples from porcine skin. Porcine skin was purchased from a local abattoir and prepared with reference to the preparation guidelines in ASTM F2256. These were subsequently mounted onto an acrylic block, which was secured by the bottom gripper of the Instron tensile tester.
The test materials were cut into 24 mm by 300 mm rectangular strips, with the adhesive surfaces at either end anchored to the top gripper and adhered to the porcine skin respectively at an angle of 180 . The extension rate for the machine was set at 300 mm/min and the initial load and displacement were zeroed prior to measurements. The adhesive strength of the characterized materials was derived from the generated load-extension curve.

| Wettability measurements
The wettability of the samples was characterized by the water contact angle (WCA). WCA was measured using the sessile drop method with a 10 μL drop of deionized (DI) water. All WCA data was averaged over measurements at three different locations on the samples. The samples were mounted on the stage of a micro-manipulator (M3301R, Prime Bioscience, Singapore) and images were captured with a highdefinition camera (XCAM1080PHA, ToupTek, China), and subsequently analyzed using an image analysis software (ImageJ, National Institutes of Health, USA).

| Moisture vapor transmission test
where T is the duration in the oven, A is area of the mouth of the centrifuge tubes, and W 0 and W 24 refer to the weight of the tubes before and after the 24-hour period.

| Pilot study to assess the functionality and performance of FlexiPalms
To assess the durability and comfort of the FlexiPalms, a pilot study was conducted on 41 individuals. The inclusion criteria were healthy individuals between the ages of 21 to 65 years. Individuals who are unable to move their upper limb, with preexisting dermatological conditions or with injuries that would render them unable to carry out the tasks in the pilot study were excluded from the study. Written informed consent was obtained from all participants prior to the start of the study. The amount of damage sustained by the FlexiPalms was assessed based on the number of peel-off areas and classified as "major" (>2 peel-off areas), "minor" (≤2 peel-off areas), or "no peeloff." The comfort level was determined by users' discretion based on how they felt while performing the tasks. This study was conducted following the study protocol approved by the Institutional Review Board of the National University of Singapore (NUS-IRB-2021-22).
Participants of the pilot study were instructed to perform a total of 11 activities of daily living adapted from the Graded Repetitive Arm Supplementary Program (GRASP) rehabilitation program for stroke patients (Task 1A to 7B, Figure S2). 27 To ascertain if mechanical loading associated with the pilot study activities resulted in attenuated mechanical integrity, used FlexiPalms were removed from participants' hands, from which 50 Â 10 mm rectangular strips were cut for postloading mechanical characterization.

| Skin irritation assay
We performed a skin irritation assay according to the OECD 439 in vitro skin irritation test to check the cytotoxicity on human epidermal tissue induced by the FlexiPalm material for up to 72 hours.
Reconstructed human epidermal tissue samples (MatTek, MA, USA) were preincubated with 0.9 mL of assay media in a 6-well plate for 1 hour, followed by a media change and incubation at 37 C in a 5%

| Measurement of static coefficient of friction (CoF)
The static CoF of the smooth and microtextured TGM PU samples was measured by the inclined plane testing method ASTM-G219.
40 Â 40 mm sample pairs were cut and mounted onto the platform of a micromanipulator and the base of a 160 g stainless steel sled, respectively. The platform was tilted gradually until the sled first moved. The static CoF was calculated based on the tangent of the tilt angle.

| Statistical analysis
Data visualization and statistical analysis were analyzed using  (Figure 3a), only 22% of them wear gloves as a hand PPE to protect themselves against contracting viruses (Figure 3b). This lack of gloves wearing to prevent fomite transmission suggests that people have concerns with using the currently available hand PPE.
Hence, it is important to understand the concerns that people have and the factors that may encourage people to adopt the use of hand PPE to protect themselves. Concerns highlighted in the previous studies 15,16 were presented to respondents to collect quantitative information on the relative importance of each concern or consideration to understand the general sentiment underscoring the lack of glove usage. We identified that the respondents' main concerns and considerations with using conventional gloves include hand conformability and comfort (54%), ease and convenience of removal (51%), diversion of frontline medical resources (39%), and social stigma associated with glove wearing (32%) (Figure 3c). These highlight the limitations of existing gloves, which necessitates a new form of hand PPE with a novel design to encompass these features. We then presented the respondents with our novel FlexiPalm concept, which was designed to address the aforementioned concerns. Remarkably, 80% of the participants responded that they will likely adopt the use of FlexiPalms First, there were no significant differences observed between the three PU materials in terms of their tensile strength, Young's modulus, and elongation (Figure 4b- (Figure 5c), illustrating its superior breathability and suitability as a hand PPE as compared to other conventional glove materials.

| Participants favored FlexiPalms over conventional gloves in pilot study
Having completed the materials and biological testing for the Flexi-Palms, we went on to find out more about the usability and functionality of our FlexiPalm prototype by conducting a pilot study on 41 participants. We asked them to perform a series of activities of daily living adapted from the GRASP rehabilitation program for stroke patients (Task 1A to 7B, Figure S2A). We first asked the participants about the comfort level and conspicuousness of the FlexiPalms. All participants rated these two aspects as "comfortable/inconspicuous" and "neutral," with 90.2% and 87.8% of the participants commenting that the initial wearing of FlexiPalms was comfortable and inconspicuous to the eye respectively, and none of them rated "uncomfortable/ conspicuous" (Figure 7a). To determine the ease of removal of the FlexiPalms, we asked participants to rate how they felt as they peeled off the FlexiPalms. The majority of the participants (90.2%) felt that the process of FlexiPalms removal was "easy," whereas 7.3% felt "neutral" and 2.5% felt "difficult" (Figure 7a). High ease of removal, together with the demonstrated water repellency and minimized viral adsorption, will alleviate cross-contamination with the usage of FlexiPalms. 30 We also assessed the participants' perception of FlexiPalms by evaluating both their degree of completion of task activities and their comfort level while performing each task. Among the 11 different tasks ( Figure S2B), almost all the users were able to complete the tasks with no peel-off or some minor peel-off (Figure 7b). Of note, no rupture and breakage of FlexiPalms were observed during the user study. Users faced the most challenge in completing tasks 7A and 7B, which correspond to wringing a dry towel or wet towel, respectively, where about 30% to 35% of the participants completed the task with minor peel-off, with 2% to 5% of major peel-off (Figure 7b). From the user feedback, we established that this was mainly due to the loose unadhered edges of the FlexiPalms entangling with the towel, resulting in peel-off during the wringing motion. Interestingly, when the FlexiPalms were adhered snugly to the hand, no peel-off was observed upon the completion of these tasks. This suggests that the peel-off was associated with improper donning of FlexiPalms which results in imperfect adherence. This limitation may be averted with refinement to the application procedure.
For the comfort level, more than 90% of the participants felt that task completion was "comfortable" and "neutral," indicating no impediment with hand motion and dexterity. The majority of the participants further commented that the FlexiPalms felt comfortable and breathable. However, in Tasks 1 and 5A which require a high level of dexterity and maneuverability (eg, writing and fiddling with small items), 20% to 30% and 2% to 10% of participants rated "neutral" and "uncomfortable" respectively, compared to other tasks (Figure 7c). In addition, 7% to 12% of the participants rated Tasks 7A and 7B as "neutral" (Figure 7c), which may be attributed to their elevated incidence of peel-off.
Notably, in the context of wearing the FlexiPalms for daily activities for protection against fomite transmission of viruses, 70.7% of participants preferred the FlexiPalms due to better comfort, higher tactile sensitivity, increased breathability, and conforming like a F I G U R E 6 Adsorption assays to quantify the binding propensity of SARS-CoV-2 spike protein and VLP onto artificial human skin and tested materials.

| Surface modification of FlexiPalms for enhanced functionality
While the TGM PU has been demonstrated to be suitable for use as the substrate material for FlexiPalms, we sought to ascertain its surface modifiability to enhance its functionality. To this end, we adopted a facile process to produce microtextures on the FlexiPalms surface by casting the TGM PU onto sandpaper. This increases the surface roughness which has been linked to augmented surface hydrophobicity and imparting of superhydrophobicity. 34,35 We cast the TGM PU on sandpaper with three levels of roughness-low (800 grit), medium  35 As such, we proceeded to further evaluate the medium roughness surface, henceforth referred to as "TGM PU (textured)," while the raw TGM PU will subsequently be annotated as "TGM PU (smooth)." We characterized the surface topology of the samples by laser scanning microscopy which revealed an increase in the surface roughness from 9.45 ± 0.33 μm for TGM PU (smooth) to 13.75 ± 1.91 μm for TGM PU (textured) (Figure 8b,c).
This increased roughness is also postulated to reduce the contact between the virus and the material surface, hence reducing viral adsorption. 36,37 To confirm this, we conducted the protein adsorption

| DISCUSSION
The use of PPE has been a stalwart addition to the fight against COVID-19 in managing community transmission. To this end, tremendous effort has gone into sourcing for PPE, 39 developing alternative PPEs, [40][41][42][43] addressing environmental sustainability, 44 and understanding the role of PPE donning and doffing on cross-contamination. 30 We acknowledge that there is mixed opinion on the relevance of gloves usage for protection against the SARS-CoV-2 virus. 45 to a variety of activities. We also collected astute feedback and additional design considerations for future refinement of the prototype. In the next phase of our study to assess the basic functionality of Flexi-Palms, we will recruit a larger number of participants from a variety of demographics, which will also serve to reduce biases of the data. Furthermore, our current tasks in the pilot study are based on the GRASP rehabilitation exercises which only target activities of daily living that are more static in nature. We will expand the activities to include Subsequently, we tested the surface modifiability of the TGM PU by creating microtextures on the TGM PU surfaces which remarkably yielded a significant improvement in the functionality of the Flexi-Palms. We found an increase in wettability which may be attributed to the textured surface topology producing discrete three-phase (solid-air-liquid) contact points that have been shown to display extremely low surface adhesion due to the trapping of an air plastron which reduces the liquid-solid contact area. 63 Concomitantly, the reduced contact between the virus and the microtextured surface resulted in a reduction in viral adsorption. 36,37 We also observed a reduction in adhesive friction post modification as increasing the surface roughness reduces the adhesion between elastic solids. 64,65 Our recommendation is to adopt the existing practice of regular handwashing and the use of sanitizer and disinfectant in tandem with the wearing of FlexiPalms. While usage of ethanol-based disinfectant can swiftly inactivate the virion, 6 a surge in the prevalence of hand dermatitis due to prolonged and frequent hand washing was observed. 66 FlexiPalms can serve as a physical barrier against harsh disinfectants during the washing of hands, enabling users to maintain good hand hygiene practices with reduced risks of dermatitis, while reducing the occurrence of cross-contamination. Furthermore, the suitability for use of FlexiPalms in the clinical setting, especially in surgical procedures involving the need for whole hand protection, remains to be evaluated. Nonetheless, general usage in wards and public areas by nurses, doctors, and auxiliary personnel can be considered for an added level of protection. FlexiPalms may also be adopted for use in other industries such as food handling, retail, and automotive, with facile modifications where necessary.

| CONCLUSION
In summary, we developed FlexiPalms, a unique palmar-side hand PPE for protection against fomite transmission of viruses. We showed that compared to conventional glove materials, the FlexiPalms demonstrated enhanced mechanical durability and breathability, comparable hydrophobicity, and displayed minimal adsorption of SARS-CoV-2 spike protein and VLP. Importantly, from the pilot study conducted,