Flexible endoscopes are used for diagnostic and therapeutic interventions in the human body for their ability to be advanced through tortuous trajectories. However, this very same property causes difficulties as well. For example, during surgery a rigid shaft would be more beneficial since it provides more stability and allows for better surgical accuracy. In order to keep the flexibility and obtain rigidity when needed, a shaft guide with controllable rigidity could be used. On this page we introduce the PlastoLock shaft-guide concept, which uses thermoplastics (Purasorb PLC 7015) that are reversibly switched from rigid to compliant by changing their temperature from 5 to 43 degrees Celcius. These materials were used to make a shaft that can be rendered flexible to follow the flexible endoscope and rigid to guide it.  A feasibility study shows the great potential of this concept in terms of achievable flexural rigidity, miniaturization, and simplicity.