Medical Patch for Haptics-enabled Mechanotherapy

Medical Patch for Haptics-enabled Mechanotherapy Niccol` o Petrilli DIISM University of Siena, Siena, Italy [email protected] Alberto Villani DIISM University of Siena, Siena, Italy [email protected] Domenico Prattichizzo DIISM University of Siena, Siena, Italy [email protected] Abstract—Wearable haptic technologies are emerging as promising tools for home-based therapy. We present a robotic patch capable of delivering controlled mechanical stimulation to human skin through compact actuation, compliant design, and integrated sensing. Experimental tests confirmed its ability to reproduce clinically relevant indentation and pressure levels, while morphological analysis demonstrated broad applicability across body regions. These findings suggest that wearable mechanotherapy can provide a safe and adaptable approach to support rehabilitation. Index Terms—wearable haptics, mechanotherapy, medical robotics I. INTRODUCTION In recent years, growing attention has been devoted to telemedicine and home-based care, as these approaches reduce healthcare costs, patient travel, and hospital burden. While telerehabilitation and remote physiotherapy are well-studied, less effort has been directed toward enabling skin manipulation for therapeutic purposes in domestic environments. Haptic technologies, originally developed for gaming and robotics, are now widely applied in rehabilitation with exoskeletons [1], but wearable haptic interfaces for therapeutic touch and analgesia remain underexplored. Evidence shows that tactile stimulation can replicate manual therapy effects, activating natural pain-inhibition mechanisms and reducing inflammation [2], while thermal stimulation is a well-established modality for musculoskeletal pain relief [3]. Moreover, recent studies identify rhythmic pressure stimulation as a medium to control cancer growth and duplication [4]. Exploiting mechanical stimulation by wearable devices could therefore provide localized, non-invasive treatments for conditions such as CRPSI, osteoarthritis, or derma-related pathologies, including skin cancers like melanoma. Building on this perspective, the proposed work aims to develop and test a highly wearable haptic device that can be applied to a wide range of human body parts for providing local tactile stimulation at the lower layer of human epidermis and dermis, offering a novel, patientcentered approach to home-based therapy. II. MECHANOTHERAPY PATCH The proposed haptic device is primarily designed for oncological purposes. It must meet both common medical requirements as biocompatibility, adaptability to different sites of human body, including arms, neck, and chest; delivering of long-term, reliable stimulation, both oncological needs as reaching 5 mm skin penetration to achieve dermis layer where Fig. 1. Rendered CAD models of proposed therapeutic haptic patch. tumor recurrence are common localized. Moreover the device should be usable (safe, wearable, ergonomic). Guided by the design requirements, the proposed device, visually rendered in Fig. 1, consists of a robotic patch powered by two DC motors with a two-phase reduction system that converts rotary motion into linear displacement. A lead screw generates a horizontal translation, which is then transformed into a vertical displacement through a custom wedge mechanism, enabling a mobile platform to indent the user’s skin. The actuators and transmission were selected based on the average stiffness of human skin, ensuring sufficient force to fully indent the epidermis and reach the dermis. The actuation phase is monitored by a time-of-flight sensor with a precision of 1 mm, while the applied mechanical stimulation is controlled by a force sensor placed on the end-effector. All components are mounted on a soft-rigid platform, 3D-printed using layered rigid and soft materials, providing both structural support and bending capability to ensure the adaptability to different body regions. In detail, the base platform is formed by a PTFE rigid layer of 1.5 mm and a soft part of 0.5 mm realized in TPU, both at 100% infill. The entire device is encapsulated within a silicone shell, ensuring safety, wearability, and biocompatibility with human skin, thereby making it suitable for prolonged use in daily life. The adhesion layer is achieved through a Dermatac treatment, which provides a stable yet removable interface: it keeps the device securely in place during therapy while allowing painless detachment without causing discomfort or skin irritation. In addition, the silicon shell is easily removable and washable ensuring the 2025 I-RIM Conference October 17-19, Rome, Italy ISBN: 9788894580570 10.5281/zenodo.17629720 95 re-usability and sterility of the device. Data Samples Mean Subcutaneous Tissues Dermis Epidermis 0.1 0.2 0.25 0.33 0.5 0.67 1 Frequency [Hz] Indentation [mm] Force [N] 6 5 4 3 2 1 0 2 4 6 8 10 12 Fig. 2. Indentation test results conducted at different frequencies of end effector penetration and corresponding force. III. TESTING The proposed device was prototyped and tested to evaluate its ability to reach deeper regions of the dermis and adapt to body curvatures. In the first phase, we tracked the end-effector indentation on a standard skin phantom for surgical training using an OptiTrack Trio motion capture system. In the second phase, employing the same optoelectronic tracking setup, we assessed the bending behavior of the support platform by measuring the vertical displacement of edge markers relative to central ones during manual deformation of the patch. The collected results were then compared with average models of human skin and anthropometric geometries. Results: We repeated the indentation tests at different endeffector frequencies. The results (Fig. 2) demonstrated that, in the frequency range [0.2−0.7] Hz, the device was able to penetrate up to the base of the dermis, reaching an indentation depth of 4.1±0.11 mm with a peak applied pressure of 99 ±3.96 kPa at 0.2 Hz. In general, under low-frequency stimulation, the device achieved 100% penetration of the epidermis and more than 50% of the dermis. Conversely, at higher stimulation frequencies, the current design allowed a complete stimulation of the epidermis (2.19 ±0.14 mm of indentation with an applied pressure of 37±1.83 kPa), without reaching the dermis. Regarding the banding tests, the device exhibited a maximum deflection of 4.25 mm without compromising its integrity. The bent shape was approximated with a paraboloid, characterized by maximum admissible curvature kmax = 10.51 m−1and footprint (60 mm ×60 mm), and compared with body morphology from the SMPL model [5]. For each mesh vertex, a local neighborhood was analyzed: a geodesic disk and PCA based frame reconstruction enabled curvature estimation via quadratic fitting. Applicability was verified by checking (i) that the curvature along the long axis is below kmax and the orthogonal curvature under a relaxed threshold, and (ii) that the projected footprint exceeds (W, L). Fig. 3. Feasible and unfeasible pad placement regions on the SMPL body models respectively in light and dark areas. A face was considered valid if at least two of its vertices met these conditions. As illustrated in Fig. 3, valid regions cover about 68.9% of the female body and 68.7% of the male body. It should be emphasized that the locations excluded from this validation could still be addressed by leveraging the compliance and adaptability of the silicone patch embedded in the shell. IV. CONCLUSIONS This study has introduced a novel device designed for mechanotherapy treatments of dermis in different areas of human body. Future work will focus on developing a control system, using the sensors already incorporated, capable of delivering periodic and efficient mechanical stimulation that follows a desired trend while ensuring user safety and therapeutic consistency. In parallel, efforts will be directed toward designing a user interface that enhances both usability and controllability of the device. Finally, the adhesion strategy adopted in this study will be extended to include additional methods, such as elastic bands, to ensure applicability across a wider range of human body regions. REFERENCES [1] M. Dragusanu et al., “Design and prototyping of an underactuated hand exoskeleton with fingers coupled by a gear-based differential,” Frontiers in Robotics and AI, vol. 9, p. 862340, Mar. 2022. [2] A. S. I. Salgado et al., “Manual therapy reduces pain behavior and oxidative stress in a murine model of complex regional pain syndrome type I,” Brain Sciences, vol. 9, no. 8, p. 197, Aug. 2019. [3] A. Ariana et al, “The effect of local heat therapy versus cold rub gel on pain and joint functions in patients with knee osteoarthritis,” Clinical Nursing Research, vol. 31, no. 6, pp. 1014–1022, Jul. 2022. [4] A. Villani et al., “RobHeart: Soft robot for heart-like volumetric stress on seeded cardiac cells,” in Proc. 9th IEEE RAS/EMBS Int. Conf. Biomed. Robot. Biomechatronics (BioRob), Seoul, South Korea, 2022, pp. 1–8. [5] M. Loper, N. Mahmood, J. Romero, G. Pons-Moll, and M. J. Black, “SMPL: A skinned multi-person linear model,” in Seminal Graphics Papers: Pushing the Boundaries, Volume 2, pp. 851–866, 2023. 96