This paper systematically elaborates on the physical basis, design methods, and medical applications of Principle 1 of the Stiffness-Switching paradigm—"Stitch but Not Tighten." This principle utilizes the superelastic plateau of shape memory alloys to replace traditional rigid or elastic connections, achieving "connection without locking." In the static state, a preset separation gap is maintained; during dynamic motion, relative movement is accommodated with constant, low force; and after motion ceases, automatic reset occurs via self-recovery. This paper first establishes the mechanical model of SMA flexible connections, comparing their essential differences in force-displacement characteristics from rigid and linearly elastic connections. Subsequently, four cross-disciplinary medical case studies—a passive adaptive snoring stopper, a three-ring decoupling device for parkinsonian wrist tremor, an adaptive nasal stent, and an SMA constant-force sleep monitoring chest band—demonstrate the universality of this principle in intracavitary support, movement disorder intervention, otorhinolaryngology instruments, and wearable medical devices. The paper further discusses the synergistic mechanisms between SMA flexible connections and wavy anchor safety redundancy (Principle 7) and function-stroke decoupling (Principle 10), as well as the expansive prospects of this principle in orthopedics, rehabilitation medicine, and wearable devices.
hanbin zhao (Mon,) studied this question.