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. In this article we introduce the PlastoLock concept, which uses thermoplastics that are reversibly switched from rigid to compliant by changing their temperature from 5°C to 43°C. These materials are used to make a shaft that can be rendered flexible to follow the flexible endoscope and rigid to guide it. To find polymers that are suitable for the PlastoLock concept an extensive database and internet search was performed. The results suggest that many suitable materials are available or can be custom synthesized to meet the requirements. The thermoplastic polymer Purasorb® PLC 7015 was obtained and a dynamic mechanical analysis showed that it is suitable for the PlastoLock concept. A simple production test indicated that this material is suitable for prototyping by molding. Overall, the results in this article show that the PlastoLock concept can offer simple, scalable solutions for medical situations that desire stiffness at one instance and flexibility at another.