Epidermal haptic interfaces: Physiological foundations, actuation technologies, and biocompatible materials

Epidermal haptic interfaces that laminate directly onto the skin have drawn attention as a promising strategy to overcome the limitations of rigid, irritative haptic hardware in current virtual and augmented reality (VR/AR) systems and broader bioelectronic applications. This article reviews the physiological foundations, actuation technologies, and material strategies that underpin these next-generation skin-integrated systems, with a focus on achieving mechanical and sensory compatibility with human tissue. First, the anatomy of the skin and the functional roles of four primary mechanoreceptors are summarized to understand the fundamentals of sensations, which will be basis for designing parameters of the system such as optimal vibration frequency ranges, spatial resolution, and actuator placement informed by regional variations in touch sensitivity and two-point discrimination thresholds. Next, major haptic actuation modalities including electromagnetic, pneumatic/hydraulic, shape memory alloy, electrostatic (dielectric elastomer), thermal, and electrical (TENS and electrotactile) approaches are compared in terms of bandwidth, force output, form factor, and suitability for soft, wearable vibrohaptic systems. Then we will review the soft substrates conductive elements, and encapsulation strategies that enable mechanical matching to skin, stable electrical performance under large strain, and long-term skin contact. Finally, the article outlines remaining challenges including robust adhesion, high-density actuation, power and wireless communication, durability, and user comfort and highlights future directions such as self-healing and two-dimensional materials, AI-driven personalized haptics, multimodal sensory integration, and system-on-patch architectures for applications in VR/AR, prosthetics, human–robot interaction, telemedicine, and continuous health monitoring.