HaptEx: Investigating Haptic Notification Channels for Exoskeletons Across Different Levels of ActuationExoskeletons are increasingly deployed in real-world contexts, where communicating critical system states or unexpected events is important for effective interaction. Haptic feedback offers a direct communication channel, integrating naturally with the actuated body region. Yet, it remains unclear how well haptic feedback is perceived while the body is being actuated. In a controlled study (N=24) with a shoulder exoskeleton, we compare four common haptic notification channels (poking, proprioceptive, thermal, vibrotactile) under different levels of actuation. Results show that poking was detected fastest, while thermal and proprioceptive notifications were most accurate and noticeable. Actuation levels affected error rates and noticeability, but not response times. Participants reported that thermal notifications aligned best with the actuation levels, producing a distinct sensation that blended naturally with movement. In contrast, proprioceptive notifications conveyed the strongest sense of urgency. We discuss design implications for leveraging haptic notifications to support embodied communication with exoskeletons.2026MMMarie Muehlhaus et al.Saarland Informatics CampusVibrotactile Feedback & Skin StimulationForce Feedback & Pseudo-Haptic WeightHaptic WearablesCHI
Forefeel the Move: Investigating Proprioceptive Feedback for Communicating Imminent Motions of Body-actuating SystemsSystems actuating the body can proactively assist users in diverse tasks. However, unexpected body actuation may pose safety risks. We propose proprioceptive feedback to inform users about an imminent actuation before the system takes control. In a user study, we compare different proprioceptive cues that either interrupt or augment user motion to convey (1) solely that a body actuation is imminent, (2) its direction, or (3) its target. To enable a controlled investigation, we confined the cues to one degree-of-freedom joints and implemented them in an elbow exoskeleton. The results show that all cues are highly noticeable, offering an integrated feedback channel; yet, their effectiveness in communicating direction and target differed: While cues that augmented user motion were more accurate and preferred, disruptive cues enabled faster but less accurate interpretations. Furthermore, our analysis revealed that proprioceptive feedback enhanced the expressiveness of the conveyed information and user's aspirations for adaptive feedback.2026MMMarie Muehlhaus et al.Saarland Informatics CampusForce Feedback & Pseudo-Haptic WeightHaptic WearablesVibrotactile Feedback & Skin StimulationCHI
EmbroForm: Digital Fabrication of Soft Freeform Objects with Machine Embroidered Pull-up StringsPull-up objects form 3D shapes by pulling a string routed through a 2D material, offering low-cost 2D fabrication and reversible transformation. However, existing approaches rely on origamic folding, which creates faceted, oftentimes rigid surfaces and requires manual pull-up string routing. We introduce EmbroForm, a digital fabrication pipeline for fully soft pull-up objects with organic, higher-fidelity shapes. Instead of folding, EmbroForm forms 3D shapes by seaming the boundaries of a flexible 2D patch unwrapped from the target. To enable this, we contribute a fabrication technique that automates the routing of sliding strings on flexible sheet materials with machine embroidery, which we extend on to design zig-zag lacings for seaming the boundaries. Then we introduce an end-to-end pipeline that, given a 3D mesh, creates an optimized 2D unwrapped patch and generates pull-up string routing paths for fabrication. We provide a design tool for customization and validate our approach with technical experiments and implemented application cases.2026YJYu Jiang et al.Saarland University, Saarland Informatics CampusShape-Changing Interfaces & Soft Robotic MaterialsCircuit Making & Hardware PrototypingCustomizable & Personalized ObjectsCHI
Privacy & Safety Challenges of On-Body Interaction TechniquesOn-body computing systems offer new forms of interaction, but while they are increasingly integrated into everyday contexts, their unique privacy and safety challenges remain understudied. This paper examines these challenges through a two-round interview study with $N = 15$ experts in human-computer interaction, and privacy and safety, using speculative scenarios and adversarial roleplaying to elicit insights. Our findings reveal risks specific to on-body interactions, including over-collection of sensitive data, unwanted inferences, harm to bystanders, and threats to bodily autonomy and psychological well-being. Importantly, in the on-body context, privacy and safety concerns are deeply interconnected and cannot be addressed in isolation. We contribute an empirically grounded characterization of these entangled challenges and derive eight actionable design guidelines to support safer, more privacy-aware, on-body systems. This work informs future research and design in ubiquitous computing by highlighting the need for proactive and integrated approaches to privacy and safety in trustworthy on-body computing.2026DGDañiel Gerhardt et al.CISPA Helmholtz Center for Information SecurityContext-Aware ComputingPrivacy by Design & User ControlPrivacy Perception & Decision-MakingCHI
Efficient Human-in-the-Loop Optimization via Priors Learned from User ModelsHuman-in-the-loop optimization identifies optimal interface designs by iteratively observing user performance. However, it often requires numerous iterations due to the lack of prior information. While recent approaches have accelerated this process by leveraging previous optimization data, collecting user data remains costly and often impractical. We present a conceptual framework, Human-in-the-Loop Optimization with Model-Informed Priors (HOMI), which augments human-in-the-loop optimization with a training phase where the optimizer learns adaptation strategies from diverse, synthetic user data generated with predictive models before deployment. To realize HOMI, we introduce Neural Acquisition Function+ (NAF+), a Bayesian optimization method featuring a neural acquisition function trained with reinforcement learning. NAF+ learns optimization strategies from large-scale synthetic data, improving efficiency in real-time optimization with users. We evaluate HOMI and NAF+ with mid-air keyboard optimization, a representative VR input task. Our work presents a new approach for more efficient interface adaptation by bridging in situ and in silico optimization processes.2026YLYi-Chi Liao et al.ETH ZürichMid-Air Haptics (Ultrasonic)Hand Gesture RecognitionImmersion & Presence ResearchCHI
User-reconfigured Haptics: Combining User-Reconfiguration and Visual Manipulations to Enhance Dynamic Passive Haptic Experiences for VRVirtual Reality (VR) depends on haptic feedback to create immersive experiences. Traditional passive proxies align physical props with their virtual counterparts but remain limited in scalability and expressiveness, or require bulky actuators to support reconfiguration. We introduce User-reconfigured Haptics, an approach that utilizes implicit user actions to reconfigure haptic interfaces to extend the gamut of VR haptic experiences. Modular 3D-printed cells are assembled into dynamic interfaces that express diverse haptic properties such as softness and weight. By masking physical reconfigurations with visual (re)mapping, user actions unnoticeably change haptic properties, resulting in user-driven, dynamic haptic experiences. User studies show that our design can provide distinguishable haptic experiences and is perceived as realistic and enjoyable in a VR task. We further showcase four applications: a fishing rod that changes weight and flexibility, a dynamic desktop of pressable buttons, a glove with adjustable squeezing, and a crossbow with variable pulling resistance.2026XWXinrong Wang et al.Saarland Informatics Campus (DFKI)Haptic WearablesImmersion & Presence ResearchShape-Changing Interfaces & Soft Robotic MaterialsCHI
Scene2Hap: Generating Scene-Wide Haptics for VR from Scene Context with Multimodal LLMsHaptic feedback contributes to immersive virtual reality (VR) experiences. However, designing such feedback at scale for all objects within a VR scene remains time-consuming. We present Scene2Hap, an LLM-centered system that automatically designs object-level vibrotactile feedback for entire VR scenes based on the objects' semantic attributes and physical context. Scene2Hap employs a multimodal large language model to estimate each object’s semantics and physical context, including its material properties and vibration behavior, from multimodal information in the VR scene. These estimated attributes are then used to generate or retrieve audio signals, subsequently converted into plausible vibrotactile signals. For more realistic spatial haptic rendering, Scene2Hap estimates vibration propagation and attenuation from vibration sources to neighboring objects, considering the estimated material properties and spatial relationships of virtual objects in the scene. Three user studies confirm that Scene2Hap successfully estimates the vibration-related semantics and physical context of VR scenes and produces realistic vibrotactile signals.2026AJArata Jingu et al.Saarland Informatics CampusMid-Air Haptics (Ultrasonic)Social & Collaborative VRImmersion & Presence ResearchCHI
Move with Style! Enhancing Avatar Embodiment in Virtual Reality through Proprioceptive Motion FeedbackIn virtual reality (VR), users slip into a variety of roles, represented by a rich diversity of avatars that each exhibit specific visual attributes and motion styles. While users can see their avatar's motion in VR, they usually cannot feel it. To enhance avatar embodiment, we propose active proprioceptive feedback that aligns users' physical movements with the expected motion style of their avatar, for instance, by mimicking the avatar's weight, typical motion speed or motion range. We introduce a conceptual space of relevant motion properties which enable designers to create expressive proprioceptive motion styles for avatars. We instantiate this concept with MotionStyler: a system for designing customized motion styles and rendering them in real-time with an arm-based exoskeleton that is synchronized with the VR avatar. Results from a survey confirmed the expressiveness of the proposed conceptual space. A user study demonstrated the system's capability to create diverse proprioceptive motion styles which enhance user's self-identification with their avatar and thereby positively contribute to avatar embodiment in VR.2025DWDavid Wagmann et al.Force Feedback & Pseudo-Haptic WeightIdentity & Avatars in XRUIST
Imaginary Joint: Proprioceptive Feedback for Virtual Body Extensions via Skin StretchVirtual body extensions such as a wing or tail have the potential to offer users new bodily experiences and capabilities in virtual and augmented reality. To use these extensions as naturally as one’s own body—particularly for body parts that are normally hard to see, such as a tail—it is essential to provide proprioceptive feedback that allows users to perceive the position, orientation, and force exerted by these parts, rather than relying solely on visual cues. In this study, we propose a novel approach by introducing an "Imaginary Joint" at the interface between the user's actual body and the virtual extension, delivering information about joint flexion and force through skin-stretch feedback. We present a wearable device for skin-stretch feedback and explore informing mappings that convey the bending rotation and torque of the Imaginary Joint. The final system presents both types of information simultaneously by superimposing these skin deformations. Results from a controlled experiment with users demonstrate that users could identify tail position and force without relying on visual cues, and do so more effectively than in the vibrotactile condition. Furthermore, the tail was perceived as more embodied than in a vibrotactile condition, resulting in a more naturalistic and intuitive sensation. Finally, we introduce several application scenarios, including Perception of Extended Bodies, Enhanced Bodily Expression, and Body-Mediated Communication, and discuss the potential for future extensions of this system.2025STShuto Takashita et al.Haptic WearablesShape-Changing Interfaces & Soft Robotic MaterialsDance & Body Movement ComputingUIST
eTactileKit: A Toolkit for Design Exploration and Rapid Prototyping of Electro-Tactile InterfacesElectro-tactile interfaces are becoming increasingly popular due to their unique advantages, such as delivering fast and localised tactile response, thin and flexible form factors, and the potential to create novel tactile experiences. However, insights from a formative study with typical designers highlighted the lack of resources, limited access to information and complexity of software and hardware tools. This establishes a high barrier to entry and limits the ability to rapidly prototype and experiment with electro-tactile interfaces. To address these challenges, we propose eTactileKit, a scalable and accessible toolkit providing end-to-end support for designing and prototyping electro-tactile interfaces. eTactileKit comprises a hardware platform and a software framework for designing, simulating and exploring electro-tactile stimuli. We evaluated the impact and usability of eTactileKit through a three-week long take-home study, which demonstrated increased accessibility, ease of use, and the toolkit's positive impact on design workflow. Additionally, we implemented a set of use cases to demonstrate the toolkit's practicality and effectiveness across various applications.2025PPPraneeth Bimsara Perera et al.Electrical Muscle Stimulation (EMS)Prototyping & User TestingUIST
Texergy: Textile-based Harvesting, Storing, and Releasing of Mechanical Energy for Passive On-Body ActuationHumans instinctively manipulate and "actuate" their clothing, for instance, to adapt to the environment or to modify aesthetics. However, such manual actuation remains inflexible and directly tied to user action. We introduce Texergy, a textile-based technical framework that decouples user input and actuated output to make passive on-body actuation interactive and programmable. Texergy achieves this by harvesting energy from user interactions with a set of input modules, storing it mechanically on the body in elastic materials, later releasing the energy on demand, and finally connecting to output end-effectors that realize the actuation. We present a fabrication approach based on almost entirely textile materials using laser-cutting and simple manual assembly to enable integration into clothing and easy prototyping. We report the results of technical experiments and provide a design tool to support customizing the actuation’s force and distance, type of harvesting, and deployment of Texergy mechanisms. We practically demonstrate the capabilities of Texergy with four applications, including a quick-release belt, a passive exosuit with dynamic assistance, a haptic feedback top powered by implicit user actions in VR, and a dance-driven shape-changing costume.2025YJYu Jiang et al.Force Feedback & Pseudo-Haptic WeightHaptic WearablesShape-Changing Interfaces & Soft Robotic MaterialsUIST
GestureCoach: Rehearsing for Engaging Talks with LLM-Driven Gesture RecommendationsThis paper introduces GestureCoach, a system designed to help speakers deliver more engaging talks by guiding them to gesture effectively during rehearsal. GestureCoach combines an LLM-driven gesture recommendation model with a rehearsal interface that proactively cues speakers to gesture appropriately. Trained on experts’ gesturing patterns from TED talks, the model consists of two modules: an emphasis proposal module, which predicts when to gesture by identifying gesture-worthy text segments in the presenter notes, and a gesture identification module, which determines what gesture to use by retrieving semantically appropriate gestures from a curated gesture database. Results of a model performance evaluation and user study (N=30) show that the emphasis proposal module outperforms off-the-shelf LLMs in identifying suitable gesture regions, and that participants rated the majority of these predicted regions and their corresponding gestures as highly appropriate. A subsequent user study (N=10) showed that rehearsing with GestureCoach encouraged speakers to gesture and significantly increased gesture diversity, resulting in more engaging talks. We conclude with design implications for future AI-driven rehearsal systems.2025ARAshwin Ram et al.Hand Gesture RecognitionHuman-LLM CollaborationCreative Collaboration & Feedback SystemsUIST
ExoKit: A Toolkit for Rapid Prototyping of Interactions for Arm-based ExoskeletonsExoskeletons open up a unique interaction space that seamlessly integrates users' body movements with robotic actuation. Despite its potential, human-exoskeleton interaction remains an underexplored area in HCI, largely due to the lack of accessible prototyping tools that enable designers to easily develop exoskeleton designs and customized interactive behaviors. We present ExoKit, a do-it-yourself toolkit for rapid prototyping of low-fidelity, functional exoskeletons targeted at novice roboticists. ExoKit includes modular hardware components for sensing and actuating shoulder and elbow joints, which are easy to fabricate and (re)configure for customized functionality and wearability. To simplify the programming of interactive behaviors, we propose functional abstractions that encapsulate high-level human-exoskeleton interactions. These can be readily accessed either through ExoKit's command-line or graphical user interface, a Processing library, or microcontroller firmware, each targeted at different experience levels. Findings from implemented application cases and two usage studies demonstrate the versatility and accessibility of ExoKit for early-stage interaction design.2025MMMarie Muehlhaus et al.Saarland Informatics Campus, Saarland UniversityForce Feedback & Pseudo-Haptic WeightShape-Changing Interfaces & Soft Robotic MaterialsCircuit Making & Hardware PrototypingCHI
3HANDS Dataset: Learning from Humans for Generating Naturalistic Handovers with Supernumerary Robotic LimbsSupernumerary robotic limbs are robotic structures integrated closely with the user's body, which augment human physical capabilities and necessitate seamless, naturalistic human-machine interaction. For effective assistance in physical tasks, enabling SRLs to hand over objects to humans is crucial. Yet, designing heuristic-based policies for robots is time-consuming, difficult to generalize across tasks, and results in less human-like motion. When trained with proper datasets, generative models are powerful alternatives for creating naturalistic handover motions. We introduce 3HANDS, a novel dataset of object handover interactions between a participant performing a daily activity and another participant enacting a hip-mounted SRL in a naturalistic manner. 3HANDS captures the unique characteristics of SRL interactions: operating in intimate personal space with asymmetric object origins, implicit motion synchronization, and the user’s engagement in a primary task during the handover. To demonstrate the effectiveness of our dataset, we present three models: one that generates naturalistic handover trajectories, another that determines the appropriate handover endpoints, and a third that predicts the moment to initiate a handover. In a user study (N=10), we compare the handover interaction performed with our method compared to a baseline. The findings show that our method was perceived as significantly more natural, less physically demanding, and more comfortable.2025AAArtin Saberpour Abadian et al.Saarland University, Saarland Informatics CampusTeleoperated DrivingHuman-Robot Collaboration (HRC)CHI
Embrogami: Shape-Changing Textiles with Machine EmbroideryMachine embroidery is a versatile technique for creating custom and entirely fabric-based patterns on thin and conformable textile surfaces. However, existing machine-embroidered surfaces remain static, limiting the interactions they can support. We introduce Embrogami, an approach for fabricating textile structures with versatile shape-changing behaviors. Inspired by origami, we leverage machine embroidery to form finger-tip-scale mountain-and-valley structures on textiles with customized shapes, bistable or elastic behaviors, and modular composition. The structures can be actuated by the user or the system to modify the local textile surface topology, creating interactive elements like toggles and sliders or textile shape displays with an ultra-thin, flexible, and integrated form factor. We provide a dedicated software tool and report results of technical experiments to allow users to flexibly design, fabricate, and deploy customized Embrogami structures. With four application cases, we showcase Embrogami’s potential to create functional and flexible shape-changing textiles with diverse visuo-tactile feedback.2024YJYu Jiang et al.Haptic WearablesShape-Changing Interfaces & Soft Robotic MaterialsUIST
SoftBioMorph: Fabricating Sustainable Shape-changing Interfaces using Soft BiopolymersBio-based and bio-degradable materials have shown promising results for sustainable Human-Computer Interaction (HCI) applications, including shape-changing interfaces. However, the diversity of shape-changing behaviors achievable with these materials remains unclear as the fabrication knowledge is scattered across multiple research fields. This paper introduces SoftBioMorph, a fabrication framework that aims to integrate the fabrication know-how of sustainable soft shape-changing interfaces with biopolymers. Based on the example of Sodium Alginate, the framework contributes (1) a set of material synthesis processes that modify the biopolymer's properties to fulfill different functions; (2) a set of DIY crafting-based assembling techniques that functionalize the material and assembling properties to achieve three primitive types of change in shape; and (3) a series of application cases that demonstrate the versatility of the framework. We further discuss limitations, research questions, and fabrication challenges, presenting a comprehensive approach to sustainable prototyping in HCI.2024MNMadalina Nicolae et al.Shape-Changing Interfaces & Soft Robotic MaterialsShape-Changing Materials & 4D PrintingSustainable HCIDIS
Flextiles: Designing Customisable Shape-Change in Textiles with SMA-Actuated Smocking PatternsShape Memory Alloys (SMAs) afford the seamless integration of shape-changing behaviour into textiles, enabling designers to augment apparel with dynamic shaping and styling. However, existing works fall short of providing versatile methods adaptable to varying scales, materials, and applications, curtailing designers’ capacity to prototype customised solutions. To address this, we introduce Flextiles, parameterised SMA design schema that leverage the traditional craft of smocking to integrate planar shape-change seamlessly into diverse textile projects. The conception of Flextiles stems from material experimentation and consultative dialogues with designers, whose insights inspired strategies for customising scale, elasticity, geometry, and actuation of Flextiles. To support the practical implementation of Flextiles, we provide a design tool and experimentally characterise their material properties. Lastly, through a design case study with practitioners, we explore the multifaceted applications and perspectives surrounding Flextiles, and subsequently realise four scenarios that illustrate the creative potential of these modular, customisable patterns.2024AHAlice C Haynes et al.Saarland Informatics CampusHaptic WearablesShape-Changing Interfaces & Soft Robotic MaterialsShape-Changing Materials & 4D PrintingCHI
Shaping Compliance: Inducing Haptic Illusion of Compliance in Different Shapes with Electrotactile GrainsCompliance, the degree of displacement under applied force, is pivotal in determining the material perception when touching an object. Vibrotactile actuators can be used for creating grain-based virtual compliance, but they have poor spatial resolution and a limiting rigid form factor. We propose a novel electrotactile compliance illusion that renders grains of electrical pulses on an electrode array in response to finger force changes. We demonstrate its ability to render compliance in distinct shapes through a thin, lightweight, and flexible finger-worn interface. Detailed technical parameters and the implementation of our device are provided. A controlled experiment confirms the technique can (1) create virtual compliance; (2) adjust the compliance magnitude with grain and electrode parameters; and (3) render compliance with specific shapes. In three example applications, we present how this illusion can enhance physical objects, elements in graphical user interfaces, and virtual reality experiences.2024AJArata Jingu et al.Saarland Informatics CampusVibrotactile Feedback & Skin StimulationHaptic WearablesShape-Changing Interfaces & Soft Robotic MaterialsCHI
Biohybrid Devices: Prototyping Interactive Devices with Growable MaterialsLiving bio-materials are increasingly used in HCI for fabricating objects by growing. However, how to integrate electronics to make these objects interactive still needs to be clarified. This paper presents an exploration of the fabrication design space of Biohybrid Interactive Devices, a class of interactive devices fabricated by merging electronic components and living organisms. From the exploration of this space using bacterial cellulose, we outline a fabrication framework centered on the biomaterials‘ life cycle phases. We introduce a set of novel fabrication techniques for embedding conductive elements, sensors, and output components through biological (e.g. bio-fabrication and bio-assembling) and digital processes. We demonstrate the combinatory aspect of the framework by realizing three tangible, wearable, and shape-changing interfaces. Finally, we discuss the sustainability of our approach, its limitations, and the implications for bio-hybrid systems in HCI.2023MNMadalina Nicolae et al.Automated Driving Interface & Takeover DesignShape-Changing Interfaces & Soft Robotic MaterialsUIST
WRLKit: Computational Design of Personalized Wearable Robotic LimbsWearable robotic limbs (WRLs) augment human capabilities through robotic structures that attach to the user’s body. While WRLs are intensely researched and various device designs have been presented, it remains difficult for non-roboticists to engage with this exciting field. We aim to empower interaction designers and application domain experts to explore novel designs and applications by rapidly prototyping personalized WRLs that are customized for different tasks, different body locations, or different users. In this paper, we present WRLKit, an interactive computational design approach that enables designers to rapidly prototype a personalized WRL without requiring extensive robotics and ergonomics expertise. The body-aware optimization approach starts by capturing the user’s body dimensions and dynamic body poses. Then, an optimized fabricable structure of the WRL is generated for a desired mounting location and workspace of the WRL, to fit the user’s body and intended task. The results of a user study and several implemented prototypes demonstrate the practical feasibility and versatility of WRLKit.2023AAArtin Saberpour Abadian et al.Shape-Changing Interfaces & Soft Robotic MaterialsHuman-Robot Collaboration (HRC)UIST