For applications where extreme needle flexibility is required nitinol is an available choice. This shape memory material can be used as a solid stylet or in tubing form. Nitinol can be made to hold a new shape if the material is held tightly in a fixture and then heat treated. The amount of cold working nitinol tube or wire prior to its shape set anneal will determine the strength of the material. Different surface finishes can be achieved. An oxide surface can vary in color due to preparation in controlled environment from black to amber. An oxide surface is very smooth.
If you plan to coat with Teflon or other material a rougher surface is achieved with pickling in an acid bath. Various needle point styles can be ground to make your product superior.