Over the last several decades, human-machine interactions have been limited to vision and audio channels. The introduction of haptics technologies has enabled users to receive mechanical feedbacks in the form of virtual touch. While the rapidly advancing haptics technologies in wearable devices and surface haptic devices have enabled many exciting applications in virtual reality (VR), augmented reality (AR), telecommunication, and teleoperation, they still suffer from issues in bulkiness, comfortability, and consistency. The solutions to these issues lie in the fundamental understanding of the multi-physics interactions in the human-machine interface, which include contact deformation, capillary formation, electric field, heat transfer, material non-linearity, and their complicated coupling effects. In this talk, Dr. Ma will discuss models on the multi-physics interactions in human-machine interface, with a special emphasis on modeling the finger friction variation on textured surfaces. This talk will also include how the multi-physics models have been applied in developing new wearable sensors, actuators, and surface haptics devices. The discussed models lay the foundation to develop haptics artificial materials (metamaterials) that can deliver any desired haptics performances for the next generation of human-machine mechanical interfaces.